In-Situ Testing of a Carbon/Epoxy IsoTruss Reinforced Concrete Foundation Pile

Brigham Young University BYU ScholarsArchive All Theses and Dissertations 26-4-14 In-Situ Testing of a Carbon/Epoxy IsoTruss Reinforced Concrete Foundation Pile Sarah Richardson Brigham Young University - Provo Follow this and additional works at: http://scholarsarchive.byu.edu/etd Part of the Civil and Environmental Engineering Commons Recommended Citation Richardson, Sarah, "In-Situ Testing of a Carbon/Epoxy IsoTruss Reinforced Concrete Foundation Pile" (26). All Theses and Dissertations. Paper 417. This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in All Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact scholarsarchive@byu.edu.

IN-SITU TESTING OF A CARBON/EPOXY ISOTRUSS REINFORCED CONCRETE FOUNDATION PILE by Sarah Richardson A thesis submitted to the faculty of Brigham Young University in partial fulfillment of the requirements for the degree of Master of Science Department of Civil and Environmental Engineering Brigham Young University April 26

BRIGHAM YOUNG UNIVERSITY GRADUATE COMMITTEE APPROVAL of a thesis submitted by Sarah Richardson This thesis has been read by each member of the following graduate committee and by majority vote has been found to be satisfactory. Date David W. Jensen, Chair Date Kyle M. Rollins Date Fernando S. Fonseca

BRIGHAM YOUNG UNIVERSITY As chair of the candidate s graduate committee, I have read the thesis of Sarah Richardson in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date David W. Jensen Chair, Graduate Committee Accepted for the Department E. James Nelson Graduate Coordinator Accepted for the College Alan R. Parkinson Dean, Ira A. Fulton College of Engineering and Technology

ABSTRACT IN-SITU TESTING OF A CARBON/EPOXY ISOTRUSS REINFORCED CONCRETE FOUNDATION PILE Sarah Richardson Department of Civil and Environmental Engineering Master of Science This thesis focuses on the field performance of IsoTruss R -reinforced concrete beam columns for use in driven piles. Experimental investigation included one instrumented carbon/epoxy IsoTruss R -reinforced concrete pile (IRC pile) and one instrumented steel-reinforced concrete pile (SRC pile) which were driven into a clay profile at a test site. These two piles, each 3 ft (9 m) in length and 14 in (36 cm) in diameter, were quasi-statically loaded laterally until failure. Behavior was predicted using three different methods: 1) a commercial finite difference-based computer program called Lpile; 2) a Winkler foundation model; and, 3) a simple analysis based on fundamental mechanics of materials principles.

Both Lpile and Winkler foundation model predictions concluded that the IRC pile should hold approximately twice the load of the SRC pile. Applying mechanics of materials principles found the predicted stiffness of the piles to be consistent with the laboratory results. Due to unresolveable errors, experimental field test data for the SRC pile is inconclusive. However, analysis predictions in conjunction with field test data for the IRC pile show that the IRC pile should perform similar to predictions and laboratory test results. Therefore, IsoTruss R grid-structures are a suitable alternative to steel as reinforcement in driven piles.

Table of Contents List of Tables List of Figures x xi 1 Introduction 1 1.1 Brief History of Reinforced-Concrete.................. 2 1.2 Driven Piles................................ 4 1.3 Introduction to the IsoTruss R..................... 4 1.3.1 IsoTruss R Geometry....................... 5 1.3.2 Benefits of the IsoTruss R In Deep Foundation Piles...... 6 1.4 Description of Research.......................... 7 2 Summary of Pile Design and Fabrication 9 2.1 Design of the Pile Reinforcement.................... 9 2.2 Fabrication of Reinforced Concrete Piles................ 12 2.3 Pile Properties.............................. 15 3 Summary of Pile Lab Tests 19 3.1 Lab Test Description........................... 19 3.2 Pile Stiffness................................ 21 3.3 Pile Strength............................... 23 3.4 Pile Failure Mode............................. 25 vi

3.5 Pile Toughness.............................. 25 3.6 Review of Results............................. 26 3.7 Recommendations and Conclusions................... 26 4 Field Test Set-Up 29 4.1 Test Site.................................. 29 4.2 Pile Driving................................ 3 4.2.1 Accelerometer Installation.................... 31 4.2.2 Pile Cushions........................... 31 4.2.3 Pile Orientation.......................... 32 4.3 Data Acquisition Equipment....................... 33 4.3.1 Strain Gages........................... 34 4.3.2 String Potentiometers...................... 34 4.3.3 Inclinometer............................ 35 4.3.4 Load Cell............................. 37 4.4 Test Preparation............................. 38 4.4.1 Hydraulic Jack and Extensions................. 38 4.4.2 Hydraulic Jack Placement.................... 4 4.4.3 Equipment Check......................... 4 5 Experimental Procedure 43 5.1 IsoTruss R Reinforced Concrete Pile Test................ 43 5.2 Steel Reinforced Concrete Pile Test................... 45 5.3 Inclinometer Data Reduction....................... 45 5.3.1 Strain and String Potentiometer Data Reduction....... 5 vii

5.3.1.1 Data Consolidation................... 5 5.3.2 Data Reversal Correction..................... 52 6 Experimental Results 55 6.1 Loading Rate............................... 55 6.2 Deflection................................. 55 6.2.1 String Potentiometer....................... 56 6.2.2 Inclinometer............................ 57 6.2.3 Strain............................... 62 7 Analytical Procedure 65 7.1 Lpile Program Analysis.......................... 65 7.1.1 Soil Properties Input....................... 65 7.1.2 Pile Properties Input....................... 66 7.2 Winkler Foundation Model Analysis................... 73 7.3 Application of Mechanics of Materials.................. 8 7.3.1 Cracked Moment of Inertia.................... 8 7.3.2 Pile Moment Capacity...................... 86 8 Analytical Results 89 8.1 Lpile Deflection Predictions....................... 89 8.2 Winkler Foundation Model Deflection Predictions........... 92 9 Discussion of Results 97 9.1 Pile Stiffness................................ 98 9.1.1 Comparison to Lab Stiffness Results.............. 98 9.1.2 Verification of Lab Stiffness Results............... 99 viii

9.2 Deflection................................. 1 9.3 Loading Rate............................... 11 9.4 Energy................................... 13 9.5 Energy-Modified Results......................... 14 9.6 Lpile Adjusted Soil Predictions..................... 17 9.7 Lpile SRC Pile Adjusted Reinforcement Predictions.......... 112 9.8 Error Evaluation............................. 113 9.9 Summary................................. 115 1 Conclusions and Recommendations 117 1.1 Conclusions................................ 118 1.2 Recommendations............................. 118 References 121 ix

List of Tables 2.1 Pile Lengths [1].............................. 16 2.2 Pile Geometric Properties........................ 17 2.3 Reinforcement Weights [1]........................ 17 3.1 Summary of Lab Pile Strength Results for Lab Tests [2]....... 24 3.2 Comparison of Stiffness, Moment, Curvature, Ductility and Toughness of the Lab Piles [2]............................ 26 5.1 Inclinometer Readings Taken During Field Testing.......... 46 5.2 Example of Inclinometer Data...................... 47 7.1 Material Properties............................ 85 7.2 Mechanics of Materials Analysis Results................ 87 7.3 Pile Failure Loads............................. 87 8.1 Lpile Prediction Notation........................ 9 9.1 Comparison of Laboratory Test and Predicted Stiffness Values.... 1 9.2 Original and Adjusted Soil Properties for the Top Two Layers in the Soil Profile................................. 18 x

List of Figures 1.1 Applications for Deep Foundation Piles................. 5 1.2 Schematic of an 8-Node IsoTruss R Grid-Structure........... 6 2.1 IsoTruss R End Views: (a) Standard IsoTruss R ; and,(b) IsoTruss R with Rounded Nodes [1]......................... 11 2.2 Cutting of First IsoTruss R Structure: (a) As Manufactured; and, (b) As Tested [1]............................... 13 2.3 Cutting of Second IsoTruss R Structure: (a) As Manufactured; and, (b) As Tested [1]............................. 13 2.4 Steel Extension to IsoTruss R Reinforcement [1]............ 14 2.5 Steel Reinforcement Splice [1]...................... 15 2.6 Pile Cross Section............................. 16 3.1 Lab Test Pile with Strain Gage Locations Marked [2]......... 2 3.2 SRC Pile Ready to Be Tested in the Laboratory [2].......... 2 3.3 Lab Results for Average Deflections of All Piles [2].......... 21 3.4 Lab Results for Moments vs. Curvature of All Piles [2]........ 23 3.5 Lab Results for Average Moment vs. EI for the IRC and SRC Piles in the Center Region (gages 4-8) [2].................... 24 4.1 Plan View of the Pile Testing Site [2].................. 3 4.2 Pile Cushions Attached with Pieces of the Cardboard Concrete Forms [2]..................................... 32 xi

4.3 Strain Gage Offset to Intended Line of Force [2]............ 33 4.4 Drawing Showing a Plan View of the Beam, Loads, and Resisting Forces [2]................................. 34 4.5 Inclinometer Casing........................... 35 4.6 Photo of an Inclinometer Probe..................... 36 4.7 Hydraulic Jack, Load Cell, Swivel Head, and Pile Cradle....... 37 4.8 Gap Between Piles and Reaction Load Points............. 39 4.9 Jack Extension Layout.......................... 41 5.1 Taking Inclinometer Readings for the IRC Pile............ 44 5.2 Diagram of the Angle of Inclination and Related Lateral Deviation. 48 5.3 Slice of the Top of the Pile Showing the Angle Offset from Line of Load to Inclinometer Readings........................ 49 5.4 Comparison of Data: (a) Raw; (b) Consolidated Using the Consolidation Macro; and, (c) Both........................ 52 5.5 Comparison of Data: (a) Raw; (b) Adjusted Using the Reversal Macro, and; (c) Both............................... 53 6.1 Load vs. Time from Field Tests..................... 56 6.2 String Potentiometer Deflection from Field Tests............ 57 6.3 Deflection at point of Load Application based on Inclinometer Readings from Field Tests.............................. 58 6.4 Deflected Shape of the IRC Pile based on Inclinometer Readings from Field Tests................................. 59 6.5 Deflected Shape of the SRC Pile based on Inclinometer Readings from Field Tests................................. 6 6.6 Deflected Shape of the IRC and SRC Piles based on Inclinometer Readings from Field Tests........................... 61 6.7 Strain vs. Load of the IRC Pile from Field Tests............ 62 xii

6.8 Strain vs. Load of the SRC Pile from Field Tests........... 63 6.9 Strain vs. Load of the IRC and SRC Piles from Field Tests...... 63 7.1 Soil Properties at the Test Site [3]................... 67 7.2 Moment-Stiffness Generated by Lpile given SRC Pile Properties... 68 7.3 Lab Test Moment vs. Curvature Data................. 69 7.4 Chauvenet s Criterion Envelope for Lab Test SRC Pile 2 Gage 8... 7 7.5 Moment vs Stiffness from Laboratory Testing............. 71 7.6 Moment vs. Stiffness curve from Laboratory Testing with Simplified Curve for Lpile Input........................... 72 7.7 Elastic Foundation Model: (a) As Loaded; and, (b) Statically Adjusted Load for Winkler Foundation Model................... 74 7.8 Three Displacement Components for Pile................ 76 7.9 Deflection of the Beam due to Rotation at the Ground Surface.... 78 7.1 Shifted Neutral Axis of Cracked Concrete Pile............. 81 7.11 Area of a Circular Segment [4]...................... 83 7.12 Stress Distribution in Concrete Compression Region.......... 84 8.1 Lpile Prediction 1: Load vs. Deflection of the SRC Pile from the Field Tests.................................... 9 8.2 Lpile Prediction 2: Load vs. Deflection of the IRC and SRC Piles from Field Tests................................. 91 8.3 Lpile Prediction 1 and 2: Load vs. Deflection of the IRC and SRC Piles from Field Tests........................... 92 8.4 Winkler Foundation Model Predicted Deflection at Point of Load Application of the IRC Pile from Field Tests................ 93 8.5 Winkler Foundation Model Predicted Deflection at Point of Load Application of the SRC Pile from Field Tests............... 94 xiii

9.1 Deflections of All Piles in Lab Tests................... 98 9.2 Load vs. Deflection based on String Potentiometer Readings from Field Tests.................................... 99 9.3 String Potentiometer and Inclinometer Tip Deflection Results from Field Tests................................. 11 9.4 Load vs. Time from Field Tests..................... 12 9.5 Adjusted Load vs. Time from Field Tests................ 12 9.6 Soil Compaction Energy of the IRC and SRC Piles.......... 15 9.7 Energy-Modified Load vs. Deflection Data from Field Tests...... 16 9.8 Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the IRC Pile in the Field...... 17 9.9 Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the SRC Pile in the Field..... 18 9.1 Lpile Deflection Prediction for the SRC Pile Compared to Adjusted String Potentiometer Deflection Results for the SRC Pile in the Field 19 9.11 Actual Load vs. Deflection Behavior Compared to Lpile Predictions based on Adjusted Soil Properties.................... 11 9.12 Actual Deflected Shape of the SRC Pile Compared to Lpile Predictions Based on Original and Adjusted Soil Properties............ 111 9.13 SRC Pile Adjusted Reinforcement Predictions............. 113 9.14 Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the IRC Pile in the Field...... 115 xiv

Chapter 1 Introduction This thesis focuses on the field performance of IsoTruss R grid-reinforced concrete beam columns for use in driven piles. Experimental investigation included one instrumented carbon/epoxy IsoTruss R grid-reinforced concrete (IRC) pile and one instrumented steel-reinforced concrete (SRC) pile which were driven into a clay profile at a test site. These two piles were quasi-statically loaded laterally until failure. Behavior was predicted using three different methods: 1) a commercial finite difference-based computer program called Lpile; 2) a Winkler foundation model; and, 3) a simple analysis based on fundamental mechanics of materials principles. This thesis is the concluding section of a three-part investigation of the suitability of IsoTruss R grid-reinforced concrete columns for use as driven piles. Part one, performed by David McCune [1], included the design and fabrication of the test piles. Part two, performed by Monica Ferrell [2], assessed the strength and stiffness of IsoTruss R grid-reinforced concrete piles through laboratory testing and preliminary field test design. Due to the significance of this research to the 1

investigation performed in this thesis, McCune s and Ferrell s work is summarized in Chapters 2 and 3, respectively with some of Ferrell s field test design in Chapter 4. This chapter includes a brief history of reinforced concrete which introduces the reader to previous research and the reasons for conducting further investigation in the area of reinforced concrete. An introduction to driven piles as well as a description of the IsoTruss R grid-structure used as reinforcement is also provided. A description of the research performed for this thesis concludes the chapter. 1.1 Brief History of Reinforced-Concrete In the mid seventeen hundreds, pebbles were added to a cement paste introducing the world to what would become a great power in structural materials, concrete. Concrete underwent another improvement when French gardener, Joseph Monier, added steel wire to his concrete pots. The use of steel in concrete was expanded to rail ties, pipes, floors, arches, and bridges [5]. Today this steel and concrete mixture, known as reinforced concrete, is used in almost every modern structure. Reinforced concrete has allowed engineers to design with the compressive strength of concrete combined with the tensile strength of steel thus making a strong, economic building material. Unfortunately, the addition of steel to concrete was not without flaws. Steel tends to corrode when exposed to water and chemical agents. As a result of this corrosion, the steel reinforcement looses strength and de-bonds from the concrete. 2

To increase the life of steel-reinforced concrete structures, fiber-reinforced polymer (FRP) wraps have been researched and implemented in many situations. Research indicates that FRP wraps increase the flexural and shear strength of existing steel-reinforced structures [6, 7]. These FRP wraps have also been found to increase the fatigue life of steel-reinforced concrete structures, which is important in cases of frequent freeze-thaw [8]. Not only are FRP being used for repair, they are also entering the concrete field as a primary reinforcement material that is lighter and more corrosion-resistant than steel with increased stiffness and tensile capacity [9]. However, with these advantages, FRP reinforcement generally has a lower bonding quality than steel and tends to be brittle [1]. Different shapes of FRP-reinforcement have proven to increase the strength and bond characteristics [1, 11]. An improvement to the one-dimensional FRP bars are FRP grids. FRP grids have shown to be both predictable and reliable [12]. The grid allows for a good transfer of load from the concrete to the reinforcement thus making a great alternative to steel as reinforcement in concrete [13, 12]. The IsoTruss R, which is discussed in further detail later in this chapter, is a superior type of FRP grid structure which could prove to be the most innovative improvement concrete has undergone since its invention over a century ago. 3

1.2 Driven Piles Pile foundations are long, slender structural elements driven into the soil profile to develop sufficient bearing resistance to support high-rise buildings and bridges. Piles typically consist of timber, steel pipe, or reinforced concrete columns. Piles are becoming more advantageous as America s infrastructure increases in size and diversity. Soils once considered unsuitable for building can be developed with the addition of piles. New buildings are taller and new bridges span greater distances than before and therefore require greater strength from the subsurface materials. Piles can play a key role in providing this strength. Figure 1.1 shows several applications for foundation piles. One application is to transfer loads from weak or active upper layers of soil to stronger, more stable layers of soil and rock found deep in the earth. Piles are also used to resist horizontal loads introduced by earthquakes or strong winds. They can reduce uplift or provide more bearing strength in cases of erosion. Piles therefore resist primarily high bending and compression forces [14]. 1.3 Introduction to the IsoTruss R The IsoTruss R is a composite structural grid built of strong fibers held together by polymer resin. The efficient shape and innovative material of the IsoTruss R make it a strong structure with several benefits for deep foundations. 4

Figure 1.1: Applications for Deep Foundation Piles 1.3.1 IsoTruss R Geometry The unique geometry of the IsoTruss R gives it incredible strength at very low weights. Loads are carried in the IsoTruss R through two different sets of members. Longitudinal members run parallel to the length of the IsoTruss R and carry most of the compression and tension forces, as well as the bending forces in the structure. A second set of members wraps around the core of the IsoTruss R, crossing the longitudinal members at regular intervals between 3 and 6 degrees relative to the longitudinal axis of the IsoTruss R. These members, called helicals, resist the torsional and shear loads. When not placed in concrete, the helical members also play a critical role by bracing the longitudinal members to decrease their effective length and consequently reduce the onset of buckling. Load is transferred from one member to another through interweaving of the fibers at the intersections. Figure 1-2 shows these two types of members and how they form the 5

Figure 1.2: Schematic of an 8-Node IsoTruss R Grid-Structure IsoTruss R grid-structure. The longitudinal members are represented in black and the helical members are represented in gray. 1.3.2 Benefits of the IsoTruss R In Deep Foundation Piles Traditional foundation piles have been constructed of steel, concrete, and timber. Steel and concrete piles can be very strong but are limited to land applications due to their corrosive nature in water. Timber fares better in water but provides significantly less strength than concrete or steel piles. Even on land, the deterioration of steel reinforcement is a significant problem that has plagued the reinforced concrete industry for decades. This deterioration is becoming an even greater concern as our world s infrastructure is getting older. In 6

Corrosion of Steel in Concrete, the author states that: The economic loss and damage caused by the corrosion of steel in concrete makes it arguably the largest single infrastructure problem facing industrialized countries [15]. The IsoTruss R provides a nice solution to the corrosion problem encountered by foundation piles without sacrificing strength. Because of its non-metallic material, the IsoTruss R resists the chemical agents and water that rusts and weakens steel reinforcement. In addition to being non-corrosive, the IsoTruss R is significantly lighter than other building materials. Steel rebar is heavy and therefore more labor is required for its transport and installation. 1.4 Description of Research Research performed for this thesis focused on the field performance of an IsoTruss R reinforced concrete pile. Because the IsoTruss R is an alternative to steel reinforcement, the strength of an IsoTruss R reinforced concrete (IRC) pile was compared to that of a similar steel reinforced concrete (SRC) pile. Both experimental procedure as well as analysis were performed to understand the pile behavior. Experimental testing was performed on two reinforced concrete foundation piles: one with composite reinforcement and the other with similar steel reinforcement. Each pile was 3 ft (9.14m) long and 14 in (35.56 cm) in diameter. After the piles had been driven at the test site, a static lateral load test was 7

performed on each pile. The results of these tests were analyzed to compare the flexural strength and stiffness of the piles. Three different methods were used to predict the flexural strength and stiffness of the driven piles. The first method used a commercial software program called Lpile and the second method applied a Winkler elastic foundation model. These approaches were used to predict the flexural strength of the piles. The third method was based on mechanics of materials principles. The third approach included calculations to predict the cracked moment of inertia, stiffness, and bending strength of the pile. Both laboratory test data and material properties were used as input for these analyses. 8

Chapter 2 Summary of Pile Design and Fabrication This chapter provides an overview of the design and fabrication process McCune followed to construct the piles studied in this thesis. A more detailed description of the design and manufacturing process is provided in Reference 1. 2.1 Design of the Pile Reinforcement The process followed to design the IRC and SRC piles focused on creating two separate types of piles which would be comparable in application. Each pile was designed to have the same pile diameter, length, and stiffness. The IRC pile was designed such that it: (1) efficiently held the desired pile loading; (2) met typical pile form dimensions; and, (3) could be easily compared to the steel reinforcing cage. In order to meet these requirements, slight changes were made to the usual IsoTruss R geometry and corresponding equations that describe the modified geometry were developed. 9

The overall diameter of the IRC pile was determined by the size of a typical concrete form, 14 in (37 cm). Because composite materials are very corrosion resistant, a 1. in (2.5 cm) cover was used and therefore a 13 in (33 cm) outer diameter was chosen for the IsoTruss R reinforcement. The longitudinal members were designed to match the bending stiffness of the #4 grade 6 steel rebar used in the steel reinforced pile. The number of fibers in the longitudinal members determines the size and stiffness of the longitudinal members. Therefore the fiber number was adjusted until the longitudinal stiffness matched the rebar stiffness. The size of the longitudinal IsoTruss R members is expressed in tows, or bundles of 12, fibers. The final design was determined to be 8 longitudinal members consisting of 133 tows each, for a total member cross-sectional area of.15 in 2 (.97 cm 2 ). The helical IsoTruss R members were designed with respect to the longitudinal IsoTruss R members. Typically, a ratio of the longitudinal members to the helical members for an IsoTruss R of 1 to 2 has 2 3 been used. A ratio of 2 3 was chosen for the piles resulting in a helical design of 89 tows with a cross-sectional area of.1 in 2 (.65 cm 2 ). The most novel change made to the IsoTruss R geometry was the rounding of the usually pointed nodes of the helical members. The change in the IsoTruss R nodes was motivated by a desire to maximize the bending strength of the IsoTruss R reinforcement in the confined geometry. Bending strength is a function of the material properties and moment of inertia. To maximize the moment of inertia, the 1

longitudinal members were positioned as far away as possible from the center of the IsoTruss R within the constraints of the pile and IsoTruss R. This was achieved in a volume-constrained application by rounding the nodes of the helical members. Figure 2.1 shows a cross-section of a typical IsoTruss R and the comparative position of the longitudinal members with the new rounded nodes. By moving the longitudinal members further out, the moment of inertia was increased 7%, resulting in a corresponding increase in the bending strength of the IsoTruss R. (a) (b) Figure 2.1: IsoTruss R End Views: (a) Standard IsoTruss R ; and,(b) IsoTruss R with Rounded Nodes [1] Careful design of the steel reinforcement was important to ensure the SRC piles were comparable to the IRC piles. Eight #4 grade 6 steel bars were chosen for the longitudinal steel reinforcement for two reasons. First, eight bars is consistent with the 8-node design of the IsoTruss R structure. Second, #4 bars 11

permit testing with reasonable loads. The final step was to design the transverse reinforcement in the steel pile to be equivalent to the helical members of the IsoTruss R grid-reinforcement. The helical members spiral around the IsoTruss R. Therefore, comparing the composite helicals to the transverse steel reinforcement required estimation of the strength of the helical members in the direction of the transverse steel reinforcement based on the angles that the helical members form with a cross-section of the pile. 2.2 Fabrication of Reinforced Concrete Piles The two piles were fabricated using different processes. The IsoTruss R reinforcement was manufactured from T3C 2NT 12K tow carbon fiber pre-impregnated with TCR UF3325-95 epoxy resin. Fabrication of the IsoTruss R reinforcement required three main steps. First, the pre-impregnated carbon fiber tows were wrapped around a collapsible form, called a mandrel. Layer upon layer of carbon fiber was wound onto the mandrel in bundles of 4 to 6 tows alternating between helical and longitudinal members in a predetermined pattern. This process formed interwoven joints and continued until the required amount of fiber was placed in each member. Second, the members were consolidated by wrapping Dunston Hi-shrink tape tightly around each member. Finally, the IsoTruss R was cured in a rudimentary plywood oven according to the curing instructions for Thiokol UF 3325-95 resin. 12

Figure 2.2: Cutting of First IsoTruss R Structure: (a) As Manufactured; and, (b) As Tested [1] Figure 2.3: Cutting of Second IsoTruss R Structure: (a) As Manufactured; and, (b) As Tested [1] Two 3 ft (9 m) long IsoTruss R structures were manufactured for testing purposes. The first IsoTruss R is shown in Figure 2.2. A short section measuring 32.75 in (83 cm) was cut from each pile to be used in compression testing for quality control purposes. A longer section measuring 26.9 ft (8.2 m) was cut for the in-situ testing. The second IsoTruss R is shown in Figure 2.3. Two sections measuring 13.38 ft (8.2 m) were cut for lab bending tests. In addition, small pieces from the second IsoTruss R were tested to assess the local member strength. 13

Figure 2.4: Steel Extension to IsoTruss R Reinforcement [1] The IRC pile to be tested in the field was designed to be 3 ft (9 m) long; however, Figure 2.2 shows that 32.75 in (83 cm) was removed from the end of the pile for compression testing. To compensate for the lost length, a short section of steel cage reinforcement was attached to the end of the pile. Figure 2.4 shows the splice between the IsoTruss R and the steel rebar. The steel reinforcement was constructed according to industry methods. The longitudinal bars were attached to the transverse hoops in an 8-bar pattern. The #4 bars used for the longitudinal reinforcement came in lengths of 2 ft (6 m) and therefore splices were only necessary for the 3 ft (9 m) long in-situ SRC pile reinforcement. Figure 2.5 shows how the splices were alternated each bar so four of the splices were at one end of the pile and the other four were at the other end. Texas Measurements FLA-3-11-3LT strain gages were placed in several locations on the longitudinal members of the IsoTruss R and on the longitudinal 14

Figure 2.5: Steel Reinforcement Splice [1] steel reinforcement. A special pipe was inserted in each of the piles in order to take inclinometer readings. The pipe has an outer diameter of 2.75 in. (6.99 cm), and an inner diameter of 2.32 in (5.89 cm). To complete the pile construction, the reinforcements were placed in 14 in (36 cm) diameter Kolumn Forms forms purchased from Caraustar TM. The concrete was placed by Eagle Precast Company. 2.3 Pile Properties Four of the piles were for laboratory testing, two piles with IsoTruss R reinforcement and two with steel reinforcement. Each of the laboratory piles was 13 ft (4 m) in length. Two of the piles, 3 ft (9m) in length, were for field testing. Table 2.1 reports the lengths of each of the piles fabricated. A cross section of the pile is shown in Figure 2.6 and the specific measurements for each pile is shown in Table 2.2. 15

SRC1 SRC2 Pile [ft(m)] IRC1 6.58(2.1) Table 2.1: Pile Lengths 6.67(2.3) [1] IRC2 6.65(2.3) R p Center Line d 2 d 1 Figure 2.6: Pile Cross Section Something interesting to note is the difference in weight between the IsoTruss R and steel reinforcements, as shown in Table 2.3. For approximately the same length and diameter, the IsoTruss R reinforcement is only about 37% as heavy as the steel reinforcement. 16

Table 2.2: Pile Geometric Properties Property IRC Pile SRC Pile Radius of the Pile, R p [in (cm)] Radius of the Reinforcement, r r [in (cm)] Cross Sectional Area of the Reinforcement, A r [in 2 (cm 2 )] Distance from Center to Bottom Layer of Reinforcement, d 1 [in (cm)] Distance from Center to Second Layer of Reinforcement, d 2 [in (cm)] Moment of Inertia of the Longitudinal Reinforcement, I m [in 4 (cm 4 )] 7 (17.8) 7 (17.8).22 (.56).25 (.64).15 (.38).2 (.51) 5.69 (14.5) 4.25 (1.8) 4.2 (1.2) 3.1 (7.6).184 (.77).31 (.12) Table 2.3: Reinforcement Weights [1] Sample Type Reinforcement Pile Lab Field Weight [lb (kg)] Steel 1 97 (44) 2 97 (44) 1 37 (17) IsoTruss 2 37 (17) Steel 1 232 (14) IsoTruss w/o steel piece 1 76 (34) IsoTruss w/ steel piece 1 11 (5) 17

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Chapter 3 Summary of Pile Lab Tests This chapter summarizes the basic testing procedure Ferrell followed with a summary of results obtained from the four pile sections tested in the laboratory. A more detailed description can be found in Reference 2. 3.1 Lab Test Description Four-point bending tests were performed in the laboratory on two instrumented carbon/epoxy IsoTruss R reinforced concrete piles (IRC piles) and two instrumented steel-reinforced concrete piles (SRC piles). The piles were were loaded to failure while monitoring load, deflection, and strain data. As shown in Figure 3.1, strain gages were located on opposite sides of the reinforcement at nine different locations on the test piles. Figure 3.2 shows one of the SRC piles in the test fixture, ready to be tested. Each of the four piles was tested to failure in the same manner. Lab testing revealed much about the stiffness, load capacity, failure mode, toughness, and ductility of the two piles. Each of these properties is addressed individually in the following sections. 19

9 14.5in(36.8cm) 87654321 14.5in(36.8cm) 15.1in(38.3cm) 7.44in(18.9cm) 15.in(38.1cm) 7.44in(18.9cm) 29.1in(73.8cm) 14.8in(37.6cm) Pile Figure 3.1: Lab Test Pile with Strain Gage Locations Marked [2] Figure 3.2: SRC Pile Ready to Be Tested in the Laboratory [2] 2

Deflection [cm] 5 1 15 2 25 Total Transverse Load [kips] 7 6 5 4 3 2 1 S1-SRC L4-SRC L3-SRC L2-SRC L1-SRC C-SRC R1-SRC R2-SRC R3-SRC R4-SRC S2-SRC S1 Load Cell 1 Load Cell 2 S1-IRC L4-IRC L3-IRC L2-IRC L1-IRC C-IRC R1-IRC R2-IRC R3-IRC R4-IRC S2-IRC S2 3 25 2 15 1 5 Total Transverse Load [kn] L4 L3 L2 L1 C R1 R2 R3 R4 1 2 3 4 5 6 Deflection [in] Figure 3.3: Lab Results for Average Deflections of All Piles [2] 3.2 Pile Stiffness The steel and IsoTruss R reinforcement were designed to have the same stiffness. Lab testing was useful in verifying the equality of stiffness in the two differently-reinforced piles. The stiffness is represented by the slope of the load vs. deflection curves, shown in Figure 3.3. Both types of piles exhibit similar displacements for the same load level until the steel in the SRC pile begins to yield, leading to eventual failure. Another verification of the pile stiffness was obtained from the strain data gathered. Stiffness can be related to moment, M, and curvature, κ, through the 21

following relationship: M = EIκ (3.1) where the product of E (modulus of elasticity) and I (moment of inertia) is stiffness. The moment was easily obtained from statics by multiplying the applied load by the distance to the strain gage locations marked in Figure 3.1. Assuming a linear strain distribution through the thickness (diameter) of the pile, the curvature is a function of the longitudinal strain: κ = ɛ l ɛ u h (3.2) where ɛ u and ɛ l are the strains on the upper and lower reinforcements, respectively, and h is the distance between the two strain gages. This distance was 9. in (23 cm) for the SRC piles and 12. in (31 cm) for the IRC piles. Moment curvature plots were developed for each of the nine locations on both piles. Two specimens of each pile type were tested and therefore averaged plots were made from the two moment vs. curvature plots. These plots are shown in Figure 3.4. As given in Equation 3.1, stiffness is the moment divided by the curvature, or the slope of the moment vs. curvature plot in Figure 3.4. These stiffness values are plotted as a function of moment in Figure 3.5. 22

2 Curvature [microstrain/cm] 5 1 15 2 25 3 35 Moment [kip-in] 15 1 1-SRC 2-SRC 3-SRC 4-SRC 5-SRC 6-SRC 7-SRC 8-SRC 9-SRC 1-IRC 2-IRC 3-IRC 4-IRC 5-IRC 6-IRC 7-IRC 8-IRC 9-IRC 2 15 1 Moment [kn-m] 5 S1 Load Cell 1 Load Cell 2 S2 5 9 8 7 6 5 4 3 2 1 2 4 6 8 1 Curvature [microstrain/in] Figure 3.4: Lab Results for Moments vs. Curvature of All Piles [2] Using a linear regression function in Excel, the average slope of the curves was calculated. The region between curvatures of 1 and 14 micro strain were chosen for these calculations because it is a region just after the initial noise and before yielding of the piles. These slope values were 3.8 kip-in 2 (19 kn-cm 2 ) for the SRC piles and 3.4 kip-in 2 (98 kn-cm 2 ) for the IRC piles. The closeness of the two stiffness values verifies the design objective of similar stiffness values for the two different reinforcement materials. 3.3 Pile Strength Laboratory testing of the IRC and SRC piles showed that the IRC piles held nearly twice the bending moment as the SRC piles at failure. The IRC piles failed 23

Moment [kn-cm] 1 2 3 4 5 6 7 3 25 S1 Load Cell 1 Load Cell 2 S2 9 8 7 6 5 4 3 2 1 SRC IRC 4 EI x 1 6 [kip-in 2 ] 2 15 1 5 3 2 1 EI x 1 6 [kn-cm 2 ] 2 4 6 8 1 Moment [kip-in] Figure 3.5: Lab Results for Average Moment vs. SRC Piles in the Center Region (gages 4-8) [2] EI for the IRC and at an average moment of 1,719 kip-in (194 kn-m) while the SRC piles failed at an average moment of 895 kip-in (11 kn-m). Table 3.3 summarizes the ultimate load held by each of the four piles. Table 3.1: Summary of Lab Pile Strength Results for Lab Tests [2] Specimen SRC Piles Ultimate Load [kips (kn)] IRC Piles 1 36.2 (161) 63 (28) 2 37.9 (169) 65.4 (291) Average 37.1 (165) 64.2 (286) Standard Deviation 1.2 (5.66) 1.7 (7.78) 24

3.4 Pile Failure Mode The failure modes for the two different types of piles were very different. The failures of the SRC piles were ductile, as expected, while the failures of the IRC piles lacked ductility. Figure 3.3 shows that the deflection of the IRC pile increases linearly until failure while the SRC pile yields significantly prior to failure. statement: Ferrell explains the observed physical failure of the piles in the following From the very beginning of load application the IRC piles behaved differently than the SRC piles. At loads where the SRC piles had yielded and were heavily cracked throughout the region between load points, the IRC pile had much smaller deflections, and hence, much smaller hair-line cracks. The IRC pile seemed to be able to take the load much better and maintain its shape until loads much higher than the total capacity of the SRC piles [2]. 3.5 Pile Toughness The energy required to fracture a material is known as the toughness. Toughness is calculated by determining the area under the load vs. deflection curves. As a result of the brittle fracture of the IRC piles, the SRC piles absorbed approximately twice as much total energy as the IRC piles before failure. However, if toughness is calculated at the maximum loads rather than the maximum 25

Table 3.2: Comparison of Stiffness, Moment, Curvature, Ductility and Toughness of the Lab Piles [2] Property SRC IRC Flexural Stiffness [kip-in 2 (kn-cm 2 )] 3.8 (19) 3.4 (98) Maximum Moment [kip-in (kn-m)] 895 (11) 1719 (194) Maximum Curvature from Strain Gage [ E/in ( E/cm)] 149 (413) 55 (199) Maximum Curvature from Deflections [ E/in ( E/cm)] 12 (472) 12 (472) Maximum Strain in Reinforcement [ E] 54 (54) 72 (72) Toughness at Maximum Displacement [kip-in (kn-m)] 168 (19) 83 (94) Toughness at Maximum Loads [kip-in (kn-m)] 74 (836) 83 (94) deflections, the toughness of the IRC piles is 83 kip-in (94 kn-cm) while the toughness of the SRC piles is only 74 kip-in (836 kn-cm). This comparison seems more indicative of the pile capacity when considering that piles are designed for a specific load rather than a specific deflection. 3.6 Review of Results toughness. Table 3.6 displays the results for stiffness, moment, curvature, and 3.7 Recommendations and Conclusions Despite the lack of ductility observed in these tests, the IRC piles are nevertheless still suitable for use as pile foundations, due to their substantially greater strength than SRC piles. However, further investigations are recommended 26

to improve the ductility of the IRC piles, since ductility has been observed in other IsoTruss R grid-reinforced concrete piles. 27

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Chapter 4 Field Test Set-Up Field test set-up, initiated by Ferrell [2] and completed as part of this thesis, included choosing a testing site, driving the piles, ensuring the data acquisition instruments were functioning properly and getting the load from the jack to the pile. Data acquisition tests were conducted before the field tests were performed and pile cradles and jack extensions were fabricated to ensure the load was distributed to the piles effectively. 4.1 Test Site The site chosen for testing the piles had a predominatly clay profile and was located near South Temple in Salt Lake City, Utah. Two freeways pass over the site and a railroad track is located several meters away from the test piles. The site was partially excavated in order to expose an old freeway concrete footing. This footing provided a surface against which the actuator could push to load the IRC pile. A pile made completely of steel was driven and provided a surface against which the actuator could push to test the SRC pile. Careful consideration was taken to ensure 29

1 1 7'(2m) 24'(7m) 15'(5m) 23SteelPile Legend IRCPile SRCPile 8'(2.5m) 4'(1m) 7'(2m) 27'11"(2.4m) 2'11"(.1m) 37'4"(2.2m) D14"(36cm) 28'(9m) 6'(2m) 17'(5m) Figure 4.1: Plan View of the Pile Testing Site [2] that the testing of one pile did not disturb the soil surrounding the other piles. Figure 4.1 shows a plan view of the test site with the piles in place. 4.2 Pile Driving The piles were driven using an A IHC S-7 pile hammer on July 19, 24. The top 2. ft (.6 m) of both piles was left exposed above ground. Two concerns needed to be considered in the pile driving. First, the tops of the piles required protection from the force of the pile driver to avoid chipping the concrete. Second, 3

the strain gages in the piles needed to be oriented parallel to the actuator so that proper strain measurements could be recorded. 4.2.1 Accelerometer Installation An accelerometer and strain gage was attached to measure the acceleration and strain in the piles during driving. The data gathered from the accelerometer and strain gage can be used to estimate the axial capacity of the pile at the end of driving for the piles. Personnel from the Utah Department of Public Transportation performed the installation. The first attempt to install the accelerometer in the steel reinforced pile began at the same location as the strain gages. When this was discovered, the drilling was stopped, the column was rotated 9 degrees, and the installation resumed. Because the initial drilling was not deep, the wires and gages were not likely damaged. 4.2.2 Pile Cushions Cushions were made out of wooden disks to protect the ends of the piles from the driving hammer. Wedges were attached to hold the disks in place while the piles were being driven. This method proved to be ineffective when the disks shifted, exposing the concrete to the pile hammer. A portion of concrete was chipped from the top of the steel reinforced pile; however, this damage was not sufficient to influence the testing. The disks were better attached using pieces of the concrete forms as shown in Figure 4.2. This method proved to be effective. 31

Figure 4.2: Pile Cushions Attached with Pieces of the Cardboard Concrete Forms [2] 4.2.3 Pile Orientation The orientation of the piles was critical in ensuring a direct line of action from the load point on the pile to the plane of the strain gages. The driving of the SRC pile was successful in orienting the pile parallel to the actuator s load. However, complications arose when the IRC pile rotated during the driving process leaving the strain gages 16.5 o out of alignment from the desired orientation. This rotation of the pile was large enough that the concrete foundation intended for use as a surface, on which the actuator could push, was no longer in the projected line of the strain gages. Figure 4.3 shows this offset from the projected line of the strain gages to the line of force intended. In order to solve the problem presented when the IRC pile rotated, a beam was connected to the existing concrete foundation thus providing an alternate 32

(.89m) 2' 11" 16.5 13"(33cm) Figure 4.3: Strain Gage Offset to Intended Line of Force [2] surface for the hydraulic jack to push against. The new surface needed to be oriented at the same angle as the strain gages, 16.5 o. The beam also needed to hold the large moment that would be created by the offset. The beam and connecting bolts were designed to hold the required loading and a small ramp was attached to the beam to provide the necessary angle. Figure 4.4 shows the beam and ramp that was installed at the test site. 4.3 Data Acquisition Equipment This section describes the instrumentation used during the field tests to acquire strain, deflection and load measurements. 33

Fsp Fb Fsf Pw Py P Px Figure 4.4: Drawing Showing a Plan View of the Beam, Loads, and Resisting Forces [2] 4.3.1 Strain Gages Ten TML WFLA-6-11 strain gages were installed on the tension and compression sides of the pile reinforcement. Wires were run from the actual gages, along the reinforcement, and up through the top of the concrete. These bundles of wire were protected in a thick plastic wrapping after fabrication and were not exposed until the day of testing. 4.3.2 String Potentiometers String potentiometers were placed 6. in (15 cm) from the top of each pile to record tip deflection. The potentiometers were attached to an independent reference frame consisting of a wood beam which was supported outside of the heavily disturbed soil region. 34

4.3.3 Inclinometer A Slope Indicator Digitilt R Inclinometer Probe was used to take slope readings throughout the length of the pile. This inclinometer system is composed of four main components: Inclinometer Casing Inclinometer Probe Control Cable Inclinometer Readout Unit The inclinometer casing provides a shaft through which the probe may pass to take slope measurements. An inclinometer casing, shown in Figure 4.5, was placed in the center of both piles. Figure 4.5: Inclinometer Casing 35

The inclinometer probe was composed of an aluminum shaft with wheel assemblies at the top and bottom of the shaft. Figure 4.6 shows a photo of the probe. The upper and lower wheel assemblies are tilted to facilitate passage through the casing and to differentiate between positive and negative slope readings. Tilt is measured in the inclinometer probe by two force-balanced servo-accelerometers. One of the accelerometers measures tilt in the plane containing the wheels, the A axis. The other accelerometer measures tilt in the plane perpendicular to the wheels, the B axis. Figure 4.6: Photo of an Inclinometer Probe The control cable is connected to the top of the inclinometer probe to transmit readings to the inclinometer readout unit. Readings were taken at 2 ft (.6 m) intervals in each pile starting at 2 ft (.6 m) down from the top of the pile and ending 2 ft (.6 m) up from the bottom of the pile. Seven and nine sets of readings were taken for the SRC and IRC piles, respectively. Each set of readings includes two slope data readouts for each 2 ft (.6 m) interval. One of the readouts comes 36

from the first pass the inclinometer makes down the inclinometer casing. This process was repeated with the inclinometer rotated 18 degrees. In theory, the two passes should yield the same data, although the second data set will have the opposite sign. This practice provides redundancy in the data and eliminates bias in the probe. 4.3.4 Load Cell An RST Instruments model SG3 3-kip (13 kn) capacity load cell with a tolerance of +/-.1% was used to monitor the load applied to the pile. The load cell can be viewed in Figure 4.7. The center of the applied load was 18 in (46 cm) above the ground surface. Figure 4.7: Hydraulic Jack, Load Cell, Swivel Head, and Pile Cradle 37

4.4 Test Preparation Final test preparations included installation of pile cradles and jack extensions to effectively transfer the load to the piles. The data acquisition equipment also underwent final checks before beginning the field tests. In order to test the piles, a flat surface that the hydraulic jack could push against needed to be attached to the pile faces. As shown in Figure 4.7, a cradle was built using 3 4 in (1.9 cm) A36 steel to provide this flat surface for the IRC and SRC piles. An 8 in (2 cm) channel was tack welded onto the solid steel pile to provide its flat surface. 4.4.1 Hydraulic Jack and Extensions A Power Team 15-ton (13 kn) hydraulic jack, shown in Figure 4.7, was used to apply the load. However, the jack was not capable of extending the entire gap between the piles and their respective reaction load points, extensions were designed to shorten these gaps. The distances between the IRC pile and the SRC pile with their reaction load points measured 68 in (17 cm) and 82 in (21 cm), respectively. The jack itself is 22 in (56 cm) long with an additional 5 in (13 cm) attached load cell. Two extensions were constructed to shorten the rest of the distance shown in Figure 4.8 and provide a reaction for the compressive load. The material available to construct these extensions was 35 ksi (24 kn/cm 2 ), 6 in (15 cm) diameter standard steel pipe. Because the pipe was to be used in 38

(a) (b) Figure 4.8: Gap Between Piles and Reaction Load Points compression, it was analyzed as a column. The compressive strength was calculated for the pipe using a conservative K value of 1 and effective lengths of 29 in (74 cm) and 42 in (11 cm) for the extensions. Table 4-8 of the AISC Manuel of Steel Construction lists a factored compressive strength of 158 kips (73 kn) for the pipe at effective lengths under 6 ft (1.5 m). This capacity was well beyond the anticipated testing load of 5 kips (22 kn) to 6 kips (27 kn) [16]. The next step was to determine the required thickness for the end plates on the jack extensions. The AISC Manual of Steel Construction gives the following 39

equation for the minimum base plate thickness, t min : 2Pu t min = l.9f y BN (4.1) where F y is the yield strength; B and N represent the length and the width of the plate, respectively; P u is the ultimate required load; and l is the length of the pipe. A conservative value of 8 kips (936 kn) for P u and a 12 in (31 cm) x 12 in (31 cm) plate yielded a minimum thickness of.66 in (1.68 cm) for the 42 in (11 cm) pipe and.45 in (1.1 cm) for the 29 in (74 in) pipe. In order to accommodate both extensions, a.75 in (1.9 cm) base plate thickness was selected. Figure 4.9 shows the finished layout for the extensions. 4.4.2 Hydraulic Jack Placement The hydraulic jack could was carefully positioned to ensure a precise load was directed from the jack, through the extension and pile cradle, and onto the pile. The center line of the jack, extension, and cradle was aligned and held in place as the jack was extended enough to wedge all pieces between the pile and the reaction load points. This procedure was followed for each pile before testing began. 4.4.3 Equipment Check Equipment checks were performed on the strain gages, string potentiometers, and load cells. After the strain gages were connected to the computer input, several of the gages were either dysfunctional (showing very large strain without loading) or nonfunctional (no data entering the computer). To ensure the connection was not to 4

(a) (b) Figure 4.9: Jack Extension Layout blame for the output, each gage connection that did not function properly was rechecked several times and channels were changed until either the gage gave a reasonable readout or the gage was determined to be faulty. 41

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Chapter 5 Experimental Procedure Experimenal procedure involved testing one IRC pile and one SRC pile in the field. This chapter includes a description of the field tests as well as the procedure followed for reducing data recorded during these tests. 5.1 IsoTruss R Reinforced Concrete Pile Test Testing of the IRC pile was performed October 4, 24, 77 days after pile driving. Once the loading devices were properly aligned and the strain gages and string potentiometer connected to the computer input, a lateral load was applied. The test was perfomed by applying a load sufficiant to achieve a given deflection target after which this load was held constant for five minutes. Target deflection levels were.5 in (1.3 cm). Inclinometer readings were taken at each target deflection. Figure 5.1 shows the inclinometer readings being taken with one operator lowering the probe and one operator at the readout unit. 43

Figure 5.1: Taking Inclinometer Readings for the IRC Pile The process of holding the load constant led to a gradual increase in deflection with time. Therefore, during the time that inclinometer readings were made the load was allowed to decrease somewhat although the pile head deflection remained essentially the same. Because the failure of the IRC pile was abrupt in the laboratory, inclinometer readings were discontinued after the load reached 21 kips (93 kn). This was done to avoid injury to those people right next to the pile taking inclinometer readings in case of sudden failure of the pile. 44

The IRC pile failed abruptly at 32 kips (14 kn) of load. A pop was heard as the pile apparently fractured at approximately 6 ft (2 m) below the ground surface. 5.2 Steel Reinforced Concrete Pile Test The SRC pile underwent testing the day following the IRC pile test. Loading of the pile was performed in the same manor as that of the IRC pile and the same adjustments were made during the inclinometer reading pauses. The failure of the SRC pile differed from the IRC pile in that early yielding was followed by a slow ductile failure. At a load of 28 kips (12 kn), the SRC pile continued to deflect without any increase in load. 5.3 Inclinometer Data Reduction An inclinometer was used to measure the slope at 2 ft (.6 m) intervals along the depth of the piles. Readings were intended to be taken after every.5 in (1.3 cm) of deflection as measured by the string potentiometer, which was placed 6. in (15.2 cm) down from the top of the pile. Once the piles experienced significant pile head deflection, however, inclinometer readings were discontinued for safety reasons. Table 5.1 shows the number of readings taken and the load on the pile at the time of the reading [17]. An Excel file was created to convert the inclinometer readings to deflection values. An example of the inclinometer data is shown in Table 5.2. 45

Table 5.1: Inclinometer Readings Taken During Field Testing Deflection Pile Type Load [kips (kn)] Before Inclinometer Reading [in(cm)] After Inclinometer Reading [in(cm)] Reading IRC SRC Initial 7.5 (33.4).5 (1.3).65 (1.7) 1 1.7 (47.6) 1. (2.5) 1.2 (3.1) 2 12.7 (56.5) 1.5 (3.8) 1.73 (4.4) 3 14.9 (66.3) 2. (5.1) 2.25 (5.8) 4 17. (75.6) 2.5 (6.4) 2.77 (7.) 5 19.1 (85.) 3. (7.6) 3.29 (8.4) 6 21.2 (94.3) 3.5 (8.9) 3.93 (1.) 7 24.4 (18) 4.5 (11.4) 5.3 (12.8) After Failure Initial 14.8 (65.8).5 (1.3).68 (1.7) 1 19.2 (85.4) 1. (2.5) 1.14 (2.9) 2 22.4 (98.8) 1.5 (3.9) 1.75 (4.5) 3 24.5 (19) 2. (5.1) 2.31 (5.9) 4 26.2 (117) 2.5 (6.4) 2.86 (7.3) 5 28. (125) 3. (7.6) 3.78 (9.6) 6 29. (129) 4. (1.2) 5.5 (12.8) After Failure The data has seven columns. The first column, the pointer, identifies the pile number. The IRC pile test was recorded as pointer number 4 and the SRC pile is marked as pointer number 5. The second column marks the ridge set or the reading set number for that pile. The third column indicates the depth of the reading relative to the top of the pile. The last four columns are the angle of inclination readings on the A and B axis, respectively, for the o and 18 o passes, respectively. Once the data file was retrieved with the inclinometer readings, a spreadsheet was created to convert these angle of inclination readings to slope in radians and deflection along the pile. An average of the o and 18 o readings was calculated for 46

Table 5.2: Example of Inclinometer Data Pointer Rdg_Set Depth A_ A_18 B_ B_18 4 1 2-177 19-511 521 4 1 4-135 15-328 338 4 1 6-117 134-198 215 4 1 8-145 16-262 278 4 1 1-158 173-298 31 4 1 12-135 151-37 326 4 1 14-143 159-325 341 4 1 16-143 161-342 348 4 1 18-165 18-437 45 4 1 2-183 199-389 43 4 1 22-14 156-244 259 4 1 24-148 165-268 28 4 1 26-186 25-433 435 4 1 28-244 259-79 794 each depth on each data set. The initial data set readings were considered the zero load point and were therefore subtracted from all of the following data set readings at higher loads. Readings were converted to slopes using the following equation: Reading = sin θ Instrument Constant (5.1) The instrument constant for English units is 2, for our inclinometer and therefore Equation 5-1 becomes: sin θ = Reading (English Units) 2, (5.2) Knowing the angle of inclination makes it possible to find the deflected shape of the pile, using simple geometry. The hypotenuse is the length of the pile between measurements and the side opposite the angle of inclination is the lateral deviation. Figure 5.2 displays this concept. 47

Lateral Deviation (L Sinθ) Angle of Inclination θ (θ) Measurement Interval (L) Inclinometer Casing Figure 5.2: Deviation Diagram of the Angle of Inclination and Related Lateral Because the measurement interval and angle of inclination is known, the deviation can be calculated as: Deviation = L sin θ (5.3) where L is the measurement interval [24 in (61 cm)] and θ is the angle of inclination. The deflected shape of the pile is achieved by summing the deviations from the bottom to the top of the pile. The calculations for slope and deflection from inclinometer angle of inclination readings assume a two-dimensional deflection. Ideally, our inclinometer readings were in-plane with the load. However, the load was in-line with the strain gages which were slightly out of the plane containing the grove in the inclinometer casing. This angle, marked φ in Figure 5.3, was measured 11 o and 11.5 o for the IRC and SRC piles respectively. 48

Load φ Orientation of Inclinometer Readings Figure 5.3: Slice of the Top of the Pile Showing the Angle Offset from Line of Load to Inclinometer Readings To account for this offset, two correction methods were employed and compared. The first method calculated the resultant slope from the average A and B axis readings using the following equation: Corrected Reading = Reading A 2 + Reading B 2 (5.4) This corrected reading represents the maximum slope, which should coincide with the direction of load application. The deviations were found using this resultant reading value. The second method used the A axis reading and the measured angle offset between the inclinometer and the loading plane shown in Figure 5.3. The deviations 49

were derived from the A axis readings and adjusted using the equation, Corrected Displacement = DisplacementfromReading A, (5.5) cos φ where φ equals 11 o and 11.5 o for the SRC and IRC piles, repectively. Results obtained using these processes show excellent correlation. However, corrected angle results were used in subsequent calculations and results. 5.3.1 Strain and String Potentiometer Data Reduction Over 1, data points were taken for each field test and therefore a process of consolidation was necessary to reduce the data to workable numbers. Each set of data was unique and two different processes were used for consolidation. These two processes are explained in the following sections. 5.3.1.1 Data Consolidation A program developed by CASC personnel, was the primary method applied to reduce data. This program uses the process of least-squares to reduce a curve with many data points to a curve with data points at regular intervals. The process uses a straight line: y = a + bx (5.6) to approximate a data set with many points, (x 1, y 1 ), (x 2, y 2 ),...,(x n, y n ). The least-square error, L.S.E., is found by squaring the difference between the data 5

points and the function evaluated at those points. Or, stated mathematically: n n LSE = [y i f(x i )] 2 = [y i (a + bx i )] 2 (5.7) i=1 i=1 This error can be minimized by taking the derivative of this function, setting it equal to zero, and solving for the unknown variables a and b. Once a and b are known, x can be determined at any point. The data consolidation program allows the user to specify the step between the x values of the data points and the number of data points used to derive the equation of the line for a specific region. A load-time curve for the IRC pile is shown in Figure 5.4. Both the raw data curve and the curve made with the data consolidated by the data consolidation macro are displayed to show the accuracy of the macro. One limitation of the data consolidation macro is that it cannot process data sets that do not pass the vertical line test. Or, in other words, the macro can only consolidate curves with consistently increasing x values. Reversal of the x values in the data curves can be traced to two main causes. One cause is due to the pauses taken during the loading process when inclinometer readings were taken. As explained previously, due to continued deflection of the piles during inclinometer readings, the load dropped slightly, causing reversal both in load and strain. Another reason is that some strain gages did not experience high strains from the tests and were highly affected by physical or electrical interference outside of the testing process. In these instances the data seamed to fall around a general curve 51

35 35 3 7 3 7 Load [kips] 25 2 15 6 5 4 3 Load [kn] Load [kips] 25 2 15 6 5 4 3 Load [kn] 1 2 1 2 5 1 5 1 2 4 6 8 1 12 14 Time [min] (a) 2 4 6 8 1 12 14 Time [min] (b) 35 Load [kips] 3 25 2 15 1 5 Raw IRC Pile Data Consolidated IRC Pile Data 7 6 5 4 3 2 1 Load [kn] 2 4 6 8 1 12 14 Time [min] (c) Figure 5.4: Comparison of Data: (a) Raw; (b) Consolidated Using the Consolidation Macro; and, (c) Both causing decreasing x-values in the data sets. Therefore, to consolidate these data sets, a slight adjustment to the procedure was implemented. 5.3.2 Data Reversal Correction A macro was developed to delete points with diminishing x values. This Excel macro simply stepped through the data list, checked the x-value, compared this value to the preceding x value, and deleted the data point if the x-value was less than the previous x value. The new curve made from the adjusted data set is plotted with the original raw data in Figure 5.5 to show the deleted reversal regions. 52

Load [kips] 35 3 25 2 15 Deflection [cm] 5 1 15 2 14 12 1 8 6 Load [kn] Load [kips] 35 3 25 2 15 Deflection [cm] 5 1 15 2 14 12 1 8 6 Load [kn] 1 4 1 4 5 2 5 2 1 2 3 4 5 6 7 8 9 Deflection [in] (a) 1 2 3 4 5 6 7 8 9 Deflection [in] (b) 35 Deflection [cm] 5 1 15 2 Load [kips] 3 25 2 15 1 14 12 1 8 6 4 Load [kn] 5 Raw SRC Pile Data 2 Data Regression Corrected SRC Pile Data 1 2 3 4 5 6 7 8 9 Deflection [in] (c) Figure 5.5: Comparison of Data: (a) Raw; (b) Adjusted Using the Reversal Macro, and; (c) Both Once the reversal macro was completed for a particular data set, the data was further consolidated using the data consolidation macro. It is important to note that the deleted reversal points did not affect the results of this test analysis. The relaxation of the strain gages during the inclinometer readings is irrelevant in determining the strength and stiffness of the piles. 53

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Chapter 6 Experimental Results 6.1 Loading Rate As mentioned in the procedure section, the loading was paused in order to take inclinometer readings. During these pauses, the pile continued to deform, resulting in a loss of pressure on the pile face. Because the hydraulic jack was not capable of applying very small levels of pressure, the adjustments made by the jack to compensate for the displacement resulted in high pressure variance during the pauses. The effects of the pauses in both the SRC and IRC pile testing are evident when the loading rate is plotted as shown in Figure 6.1. 6.2 Deflection Both string potentiometers and the inclinometer were used to retrieve displacement data for the two piles during the loading process. Although the displacement was measured in each case, the results produced two primary differences: 55

Load [kips] 35 3 25 2 15 14 12 1 8 6 Load [kn] 1 5 IRC Pile SRC Pile 4 2 2 4 6 8 1 12 14 Time [min] Figure 6.1: Load vs. Time from Field Tests 1. Measurements by the string potentiometers were recorded every.5 seconds throughout the testing, while only five or six inclinometer measurements were taken during the testing process. 2. One single string potentiometer for each pile took measurements at the load point while the inclinometer recorded displacements every 2 ft (.6 m) along the depth of the pile. 6.2.1 String Potentiometer A single string potentiometer was used for each pile to measure lateral deflection at the pile head. This deflection is shown in Figure 6.2. The string potentiometer was not placed exactly at the pile head but rather at the point of 56

35 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 3 25 2 15 1 14 12 1 8 6 4 Load [kn] 5 IRC Pile from String Potentiometer Data SRC Pile from String Potentiometer Data 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 6.2: String Potentiometer Deflection from Field Tests load application located 6 in (15.24 cm) from the top of the pile. However, for simplicity, any deflection measurement taken at this point will be referred to as tip deflection. 6.2.2 Inclinometer Inclinometer readings were used to produce a deflected shape of the pile as described in Chapter 5. The deflection data is plotted in two different ways. In order to compare inclinometer deflection data to the deflection data recorded by the string potentiometers, Figure 6.3 plots the pile head deflections. Figures 6.4 and 6.5 57

35 Deflection at Point of Load Application [cm] 5 1 15 2 3 14 25 12 1 Load [kips] 2 15 8 6 Load [kn] 1 4 5 IRC Pile from Inclinometer Data SRC Pile from Inclinometer Data 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 6.3: Deflection at point of Load Application based on Inclinometer Readings from Field Tests plot the deflected shape of the piles at each inclinometer reading set for the IRC and SRC piles, respectively. The deflections are essentially zero below depths of 8 ft (2.4 m) and 5 ft (1.5 m)for the IRC and SRC piles, respectively. A comparison of the deflection vs. depth curves for both the IRC and SRC piles is provided in Figure 6.6. The deflected shape is considerably more shallow for the SRC than the IRC pile. 58

-5 Displacement Based on Inclinometer Readings [in].5 1 1.5 2 2.5 3 3.5 4-1.5.5 5 Depth Below Ground Surface [ft] 1 15 2.5 4.5 Depth Below Ground Surface [m] 2 25 IRC Pile Load [kips(kn)] 7.5 (33.4) 1.7 (47.6) 12.7 (56.5) 14.9 (66.3) 17. (75.6) 19.1 (85.) 21.2 (94.3) 6.5 8.5 3 1 2 3 4 5 6 7 8 9 1 Displacement Based on Inclinometer Readings [cm] Figure 6.4: Deflected Shape of the IRC Pile based on Inclinometer Readings from Field Tests 59

-5 Displacement Based on Inclinometer Readings [in].5 1 1.5 2 2.5 3 3.5 4-1.5.5 5 Depth Below Ground Surface [ft] 1 15 2.5 4.5 Depth Below Ground Surface [m] 2 25 3 SRC Pile Load [kips (kn)] 14.8 (65.8) 19.2 (85.4) 22.2 (98.8) 24.5 (19) 26.2 (117) 28. (125) 1 2 3 4 5 6 7 8 9 1 Displacement Based On Inclinometer Readings [cm] 6.5 8.5 Figure 6.5: Deflected Shape of the SRC Pile based on Inclinometer Readings from Field Tests 6

-5 Displacement [in].5 1 1.5 2 2.5 3 3.5 4-1.5.5 5 Depth below Ground Surface [ft] 1 15 2.5 4.5 Depth [m] 2 25 3 Pile Load [kips (kn)] 7.5 (33.4)-IRC 14.8 (65.8)-SRC 1.7 (47.6)-IRC 19.2 (85.4)-SRC 12.7 (56.5)-IRC 22.2 (98.8)-SRC 14.9 (66.3)-IRC 24.5 (19)-SRC 17. (75.6)-IRC 26.2 (117)-SRC 19.1 (85.)-IRC 28. (125)-SRC 21.2 (94.3)-IRC 1 2 3 4 5 6 7 8 9 1 Displacement Based On Inclinometer Readings [cm] 6.5 8.5 Figure 6.6: Deflected Shape of the IRC and SRC Piles based on Inclinometer Readings from Field Tests 61

6.2.3 Strain Strain gage readings were taken during each test and the results are shown in Figures 6.7, 6.8, and 6.9. Not all of the strain gages functioned properly and so the malfunctioning strain data was not included. Strain gage depths are noted in the legend. It is interesting to note that almost no strain was measured below the 1 ft (3. m) depth which is consistent with the low deflection values observed with the inclinometer tests. 35 Load [kips] 3 25 2 15 1 5 IRC Pile Depth of Strain Gage [ft (m)] IRC N-4.1 (1.2) IRC N-6.1 (1.9) IRC N-1. (3.) IRC N-14.5 (4.3) IRC N-21.8 (6.6) IRC S-2.1 (.6) IRC S-4.1 (1.2) IRC S-7.85 (2.4) IRC S-1. (3.) IRC S-14.5 (4.3) IRC S-18.1 (5.5) IRC S-21.8 (6.6) IRC S-25.8 (7.9) -5-3 -1 1 3 5 7 9 microstrain 14 12 1 8 6 4 2 Load [kn] Figure 6.7: Strain vs. Load of the IRC Pile from Field Tests 62

35 3 14 Load [kips] 25 2 15 SRC Pile Depth of Strain Gage [ft (m)] 12 1 8 6 Load [kn] 1 5 SRC N-2.1 (.6) SRC N-4.1 (1.2) SRC N-6.1 (1.9) SRC N-7.85 (2.4) SRC N-1. (3.) SRC N-14.5 (4.3) SRC S-2.1 (.6) SRC S-4.1 (1.2) SRC S-6.1 (1.9) SRC S-1. (3.) SRC S-14.5 (4.3) SRC S-21.8 (6.6) -5-3 -1 1 3 5 7 9 microstrain 4 2 Figure 6.8: Strain vs. Load of the SRC Pile from Field Tests 35 3 14 12 25 1 Load [kips] 2 15 1 5 Depth of Strain Gage [ft (m)] IRC N-4.1 (1.2) SRC N-2.1 (.6) IRC N-6.1 (1.9) SRC N-4.1 (1.2) IRC N-1. (3.) SRC N-6.1 (1.9) IRC N-14. 5 (4.3) SRC N-7.85 (2.4) IRC N-21.8 (6.6) SRC N-1. (3.) IRC S-2.1 (.6) SRC N-14. 5 (4.3) IRC S-4.1 (1.2) SRC S-2.1 (.6) IRC S-7.85 (2.4) SRC S-4.1 (1.2) IRC S-1. (3. ) SRC S-6.1 (1.9) IRC S-14.5 (4.3 ) SRC S-1. (3.) IRC S-18.1(5.5) SRC S-14.5 (4.3 ) IRC S-21.8 (6.6 ) SRC S-21.8 (6.6) IRC S-25.8 (7.9 ) 8 6 4 2 Load [kn] -5-3 -1 1 3 5 7 9 microstrain Figure 6.9: Strain vs. Load of the IRC and SRC Piles from Field Tests 63

64

Chapter 7 Analytical Procedure Three different analyses were performed: 1) a commercial finite difference-based computer program called Lpile; 2) a Winkler foundation model; and, 3) a simple analysis based on fundamental mechanics of materials principles. Procedures followed for these analyses comprise this chapter. 7.1 Lpile Program Analysis Computer analysis of the pile testing was performed using Lpile version 4M. This program models the behavior of a pile driven into specific soil strata using finite difference equations. Therefore, by inputting our test pile properties, soil properties, and boundary conditions, several predictions could be developed [18]. 7.1.1 Soil Properties Input The site used for these pile tests had been analyzed previously to determine the soil properties of the area. Lpile allows the user to choose from nine different types of soil from which Lpile automatically generates a soil-resistance (p-y) curve, 65

based on basic soil properties. A p-y curve can also be manually input if this information is available. Because we did not have a p-y curve for the test site, soil properties from the site were input into the Lpile program. Figure 7.1 shows the soil properties used for the field test analysis in the Lpile program. Included are several properties such as unit weight, stiffness, and undrained shear strength. 7.1.2 Pile Properties Input Lpile offers two options for pile stiffness input. The first option requires the user to input the properties of the pile including diameter, size and placement of reinforcement, rebar strength, and concrete strength. From this information Lpile generates a moment-stiffness curve for the pile. This approach works for the SRC pile but not the IRC pile because Lpile only offers steel as a reinforcement option. The moment-stiffness curve generated by Lpile given the SRC reinforcement properties is shown in Figure 7.2. The second option for pile stiffness is to input a moment-stiffness curve for the pile. The moment-curvature graphs from the laboratory test data were used to create moment-stiffness curves for both the SRC and IRC piles. Stiffness data was taken from the five strain gages (gages 4-8) located between the two center point loads in the lab bending test. The creation of the moment-stiffness curves used in Lpile predictions included three steps: 66

Depth [in] Depth [cm] Soil Type 1 γ =.54976852 pci k = 5 pci c = 1 e5 =.7 Soil Type 1 Stiff Clay without Free Water γ = Effective Unit Weight k = p-y Modulus c = Cohesive Strength e5 = Soil Strain 43 53.8 65.8 Soil Type 1 Soil Type 2 Soil Type 1 γ =.18865741 pci k = 5 pci γ =.18865741 pci k = 225 pci γ =.18865741 pci k = 1 pci c = 15.5 e5 =.5 19.22 c = 1 e5 =.7 136.7 φ = 36 Soil Type 2 167.1 Sand (Reese) γ = Effective Unit Weight k = p-y Modulus φ = Friction Angle 119.8 137.8 161.8 Soil Type 2 Soil Type 1 γ =.18865741 pci k = 225 pci φ = 36 γ =.18865741 pci k = 1 pci c = 15.5 e5 =.5 34.3 35 411 Soil Type 2 γ =.18865741 pci k = 225 pci φ = 38 23.8 Soil Type 1 γ =.54976852 pci k = 1 pci c = 5 e5 =.1 517.7 Figure 7.1: Soil Properties at the Test Site [3] 67

3 25 Moment [N*m x 1 6 ] 5 1 15 2 18 16 EI [lb*in 2 x 1 9 ] 2 15 1 14 12 1 8 6 EI [N*m2 x 1 6 ] 5 SRC Pile Input for Lpile Prediction 1 2 4 6 8 1 12 14 16 18 2 Moment [in*lb x 1 3 ] Figure 7.2: Moment-Stiffness Generated by Lpile given SRC Pile Properties 4 2 1. Check moment vs. curvature graphs from the lab tests for consistency using Chauvenet s Criterion [19]; 2. Change the moment vs. curvature graphs from the lab tests to one average moment-stiffness curve for each pile; and, 3. Develop a simplified moment vs curvature curve that can be used in Lpile for each pile. Test data for the lab tests included two bending tests each for both the SRC and IRC piles. Five strain gages were located between the two load cells and 68

2 Curvature [microstrain/cm] 5 1 15 2 25 3 35 Moment [kip-in] 15 1 1-SRC 2-SRC 3-SRC 4-SRC 5-SRC 6-SRC 7-SRC 8-SRC 9-SRC 1-IRC 2-IRC 3-IRC 4-IRC 5-IRC 6-IRC 7-IRC 8-IRC 9-IRC 2 15 1 Moment [kn-m] 5 S1 Load Cell 1 Load Cell 2 S2 5 9 8 7 6 5 4 3 2 1 2 4 6 8 1 Curvature [microstrain/in] Figure 7.3: Lab Test Moment vs. Curvature Data therefore a total of 1 gage readings for each pile were used to develop stiffness data. Figure 7.3 shows moment vs curvature data from one of the SRC pile lab tests. From this figure, one can see that the data from gage 8 of the SRC pile deviated from the rest of the test data [19]. Chauvenet s Criterion was used to determine if the slightly outlying data could be deleted from the data set. Chauvenet proposed that a data point could be deleted from a data set with n number of readings if the probability of that point deviating from the mean was less than 1. Using this criteria, an acceptable 2n envelope was plotted for gage 8 and is shown in Figure 7.4. 69

Curvature [microstrain/cm] 12 5 1 15 2 25 3 35 Moment [kip-in] 1 8 6 4 12 1 8 6 4 Moment [kn-m] 2 SRC Pile Gage 8 Data Chauvenet Envelope 2 1 2 3 4 5 6 7 8 9 1 Curvature [microstrain/in] Figure 7.4: Chauvenet s Criterion Envelope for Lab Test SRC Pile 2 Gage 8 The envelope showed that 22% of the curve did not pass Chauvenet s Criterion. However, the failing region is barely outside of the envelope. Because more than three-fourths of the curve fit Chauvenet s Criterion and the failing portion did not fall far from the envelope, the data was determined to be legitimate and therefore kept in the data set. Because the moment-curvature data had been consolidated at equal intervals, creating an average curve for each pile was straight forward. The data progressed in curvature increments of.5 microstrain/in (.197 microstrain/cm); 7

3 Moment [N*m x 1 6 ] 5 1 15 2 18 25 16 14 EI [lb*in 2 x 1 9 ] 2 15 1 IRC Pile Lab Test 12 1 8 6 EI [N*m2 x 1 6 ] 5 SRC Pile Lab Test 4 2 2 4 6 8 1 12 14 16 18 2 Moment [in*lb x 1 3 ] Figure 7.5: Moment vs Stiffness from Laboratory Testing therefore an average moment was taken at these curvature increments using the 1 moment values. With the moment plotted on the y-axis and the curvature on the x-axis, the stiffness is the slope of the moment vs. curvature lab tests. A slope calculating function in Excel was used to find the slope using 3-point data sets. For example, the average slope of data points one through three yields the corresponding slope value for the moment at data point two, etc. The average moment-stiffness curves for the IRC and SRC piles are shown in Figure 7.5. 71

To allow lpile to apply the moment-stiffness curve to the analysis, the curve needed to be further simplified. This is a fairly new application in the Lpile program and the processes required to simplifiy the data to a form that Lpile could use was not explained in the user or technical manuals. Therefore, the stiffness was averaged over moment sections of 1 in*lb x 1 3 (17 N*m x 1 6 ) to form the simplified curve shown in Figure 7.6. Moment [N*m x 1 6 ] 5 1 15 2 3 18 25 16 EI [lb*in 2 x 1 9 ] 2 15 1 5 IRC Pile Lab Test SRC Pile Lab Test IRC Pile Input for Lpile Prediction 2 SRC Pile Input for Lpile Prediction 2 14 12 1 8 6 4 EI [N*m2 x 1 6 ] 2 2 4 6 8 1 12 14 16 18 2 Moment [in*lb x 1 3 ] Figure 7.6: Moment vs. Stiffness curve from Laboratory Testing with Simplified Curve for Lpile Input 72

7.2 Winkler Foundation Model Analysis A Winkler foundation model was applied to the test piles in order to predict the slope, deflection, and moment along the length of the pile. This analysis is similar to the Lpile ananlysis in that it requires input of soil properties and pile properties. The difference is that while the Lpile program uses non-linear soil and pile stiffness values, the Winkler foundation mondel used linear soil and pile stiffness values. The three values of soil stiffness applied were the maximum, minimum, and weighted average soil stiffness in the soil profile. The average soil siffness was weighted by the depth of soil in the profile it extended. Pile stiffness was taken as the average stiffness of the piles from laboratory tests. Using the Winkler foundation model required two assumptions that were not exactly indicative of our test situation. The first assumption was that the soil behaves elastically. The soil, in fact, has some plastic behavior. The second assumption was that the beam is semi-infinite and therefore fixed on one end. The pile is not semi-infinite, although it is long enough to exhibit cantilever behavior. One simplification was applied to utilize a simpler form of the Winkler equations. The point load was shifted down to the ground surface by adding a corresponding moment. As a result of this adjustment, the equations derived from the Winkler analysis are only valid below the ground surface. These concepts are shown in Figure 7.7. 73

Z,w P h Ground Surface Z,w M P Ground Surface x (a) x (b) Figure 7.7: Elastic Foundation Model: (a) As Loaded; and, (b) Statically Adjusted Load for Winkler Foundation Model The moment, M, in the pile at the ground surface is given by: M = P h (7.1) where h is the distance from the ground surface to the load application point. The governing equation for a uniform beam on a Winkler foundation is [Elastic Foundations]: EI d4 w + kw = q (7.2) dx4 where x is the depth below ground surface [L], w is the deflection of the beam [L], k is the soil stiffness [F/L 2 ], E is the modulus of elasticity of the beam [F/l 2 ], I is the moment of inertia of the beam [L 4 ], and q is the distributed load on the beam [F/L]. In the case of the pile, there is no distributed load and therefore q is zero [2]. 74

When the differential equation is solved, the following Equations 7.3, 7.4, and 7.5 are obtained for the deflection, w[l]; slope, θ[rad]; and, moment, M[F L] respectively: w(x) = 2βP k θ(x) = 2β2 P k D βx 2β2 M C βx (7.3) k A βx + 4β3 M D βx (7.4) k M(x) = P β B βx + MA βx (7.5) where and β = ( k ) 1 4 4EI (7.6) A βx = e βx (cos βx + sin βx) = D βx + B βx (7.7) B βx = e βx sin βx (7.8) C βx = e βx (cos βx sin βx) = D βx B βx (7.9) D βx = e βx cos βx (7.1) Equations 7.3, 7.4, and 7.5 can be further simplified with the substitution of Equation 7.1. This substitution yields the following Equations 7.11, 7.12, and 7.13 for w, θ, and M respectively: w(x) = 2βP k (D βx + βhc βx ) (7.11) θ(x) = 2β2 P k (A βx 2βhD βx ) (7.12) ) M(x) = P ( Bβx 75 β + ha βx (7.13)

w PH w c w θ w gs h Ground Surface Figure 7.8: Three Displacement Components for Pile Equations 7.11, 7.12, and 7.13 were used to describe the behavior of the IRC and SRC piles below ground surface, as a function of P, x, EI, and k. Equation 7.11 provides a relationship between displacement, w, and load, P. However, in order to compare these results to those obtained by the string potentiometer, these deflections must continue above the ground surface. Additional displacement occurs at the load point which is 18 in (.46 m) above the ground. Therefore, there are three components to the pile displacement above the ground surface, as shown in Figure 7.8. 76

The total deflection of the pile at the point of load application, w P H is equal to the sum of these three components: w P H = w gs + w θ + w c (7.14) where w gs, w θ, and w c are as shown in Figure 7.8. The first displacement is the deflection at the ground surface, w gs. Equation 7.11 defined this displacement for a Winkler foundation. At the ground surface, x is zero and consequently both D x and C x equal 1, simplifying the deflection equation to: w gs = 2P k (β + β2 h) (7.15) The second displacement, w θ, component is from the rotation of the pile at the ground surface. This concept can be seen in Figure 7.9. Using geometry, the relationship among deflection (w), distance above ground surface (h), and the angle of the pile at the ground surface (θ) is as follows: tan θ = w θ h (7.16) Because θ is small, the small angle assumption (tan θ θ ) can be used, therefore: w θ = θ h (7.17) where θ = θ(x = ) as defined in Equation 7.12. The slope is desired at the ground surface and so, similar to displacement, x is zero and the two variables A x and B x equal 1, simplifying the slope equation to: θ = 2P k (β2 2β 3 h) (7.18) 77

w θ θ h Ground Surface Figure 7.9: Deflection of the Beam due to Rotation at the Ground Surface Substituting Equation 7.18 into Equation 7.17 yields the equation: w θ = 2P h k (β2 2β 3 h) (7.19) The third component is from cantilever bending of the pile, which basic beam theory defines as: w c = P h3 3EI (7.2) where h is the distance from the ground surface to the point of load application, 18 in (.46 m). Once all components are defined, the total deflection can be obtained by substituting Equations 7.15, 7.19, and 7.2 into Equation 7.14 to yeild: ( ) ( ) 2P 2P w P H = k (β + β2 h) + h k (β2 2β 3 h) + P h3 3EI (7.21) 78

Pile Head deflection can be plotted for load values up to theoretical failure. Beam theory in combination with the Winkler equations can be used to find the theoretical failure point. Beam theory states that: σ f = Mc I (7.22) where M is the maximum moment, σ f is the failure stress of the reinforcement material, I is the moment of inertia of the pile and c is the distance from the centroid of the reinforcement to the outermost fiber of reinforcement. By substituting Equation 7.13 into Equation 7.22, the stress at failure is: σ f = P c I ( Bβx β + ha βx ) (7.23) Substituting the necessary equations from Equations 7.8 and 7.7 into Equation 7.23 gives: σ f (x) = P c I [ e βx ] sin βx + he βx (cos βx + sin βx) β (7.24) When Equation 7.24 is differentiated with respect to the position (x), the following equation results: σ f = dσ f dx = P c [ e βx ( sin βx + cos βx 2hβ sin βx) ] (7.25) I Equation 7.25 can be equated to zero in order to solve for the position on the pile where the greatest stress occurs in the reinforcement: = P c I [ e βx ( sin βx + cos βx 2hβ sin βx) ] (7.26) 79

7.3 Application of Mechanics of Materials Mechanics of materials equations were used to determine the location of the neutral axis and moment of inertia of the cracked pile. Using these properties, the moment capacity of the piles was calculated. 7.3.1 Cracked Moment of Inertia After the load is applied to the pile, the portion of the concrete in tension begins to crack and therefore changes the effective moment of inertia of the pile. The cracked moment of inertia was determined by finding the neutral axis of the cracked cross-section and applying the parallel axis theorem to adjust the moment of inertia. The neutral axis is located a distance y from the center of the pile where the compressive strength of the concrete above this axis is equal to the tensile strength of the reinforcement below the axis. A linear stress distribution was assumed for the concrete and the reinforcement. This concept is portrayed in Figure 7.1 where C represents the compression strength of the concrete and T i represents the tensile stress on the reinforcement. The location of the neutral axis, y, is unknown but can be determined. For equilibrium to occur in the pile cross section, the following relationship must exist: C = i T i (7.27) where C and T are both functions of y. 8

f c C Neutral Axis y Center Line T 3 y T 2 d 2 d 1 T 1 f y Figure 7.1: Shifted Neutral Axis of Cracked Concrete Pile The magnitude of the tensile strength T of the reinforcement is the product of the reinforcement area and the tensile stress. As shown in Figure 7.1, the bottom reinforcing bar is fully stressed and therefore the magnitude of T 1 is: T 1 = A r f y (7.28) where A r is the area of the reinforcement and f y is the tensile (yield) strength of the reinforcement. Using similar triangles, T 2 and T 3 are, respectively: where: T 2 = T 1L 2 L 1 (7.29) T 3 = T 1L 3 L 1 (7.3) L 1 = y + d 1 (7.31) L 2 = y + d 2 (7.32) L 3 = y (7.33) 81

calculated: Using the stress distribution shown in Figure 7.1, the total tension force is T = T 1 + 2T 2 + 2T 3 (7.34) It is important to note that if the value of y was greater than d 1 or d 2, additional reinforcing bars would be added to the total tension force using similar triangles as was used to determine T 2 and T 3. Like the reinforcement, the strength of the concrete section, C, is the product of the stress on the concrete compression section and the area over which it is applied. However, unlike the reinforcement which could be approximated as a localized force, the area and stress of the concrete section is distributed and requires integration. Therefore, an integral was applied to determine the strength of the concrete section. For practical purposes a numerical integration was used instead of an analytical integration. As shown in Figure 7.11, the area of the concrete compression section was divided into slices defined by angle α. The relationship between the area of the circle above the point of interest, A c, and the angle representing the point of interest, α, is given by: A c (α) = R 2 p(α sin α cos α) (7.35) where: α = cos 1 ( h R p ) (7.36) 82

A c (α) A c (α+dα) y h α dα 9 α ΝΑ R p Neutral Axis Center Line Figure 7.11: Area of a Circular Segment [4] Therefore the area of the i th slice is: A i = A c (α i + dα) A c (α i ) (7.37) As shown in Figure 7.12, the top most fiber of the compression section experiences a stress of f c at failure. is: Using similar triangles, the stress in the slice at a distance h from the center f ch = With the stress and the area of each slice defined, C is: (h y) (R p y) f c (7.38) C = N (h y) i = 1 R p y f ca i (7.39) 83

f c f c h y h R p Neutral Axis Center Line Figure 7.12: Stress Distribution in Concrete Compression Region An Excel spreadsheet was created to determine the neutral axis distance y that resulted in an equal value for the compression, C, and the tension, T. Using this value for y, the cracked moment of inertia is the sum of the moment of inertia of the section of concrete that is not cracked and the effective moment of inertia of the reinforcing bars outside of the uncracked section of concrete. The moment of inertia of the concrete section about the neutral axis is [4]: I c = R4 p 4 (α NA sin α NA cos α NA + 2 sin 3 α NA cos α NA ) (7.4) where α NA is as shown in Figure 7.11. The moment of inertia of the i th steel bar is given by: I i = I r + A r d 2 i (7.41) 84

Table 7.1: Material Properties Property IRC Pile From Lab Tension Tests [Toray] SRC Pile From Lab Tension Tests [McCune] Compressive Strength of the Concrete, f' c [ksi (N/m 2 ] Yield Strength of the Reinforcement, f y [ksi (N/m2] 7.22 (2.7) 7.22 (2.7) 262 (75) 67.8 (195) Ultimate Strength of the Reinforcement, f u 262 (75) 16 (34) [ksi (N/m 2 ] Modulus of Elasticity of the Concrete, E c [psi (N/m 2 )] x 1 3 4.8 (13.8) 4.8 (13.8) Modulus of Elasticity of the Reinforcement, E r [psi (N/m 2 )] x 1 3 17.1 (49.2) 29. (83.2) Moment of Inertia of the Reinforcement, I r [in 4 (cm 4 )] Moment of Inertia of the Concrete, I c [in 4 (cm 4 )] Moment of Inertia of the Pile, I p [in 4 (cm 4 )] 27.1 (113) 46.4 (193) 599 (249) 23 (845) 695 (289) 481 (2) where A r is the area of the reinforcement member, d i is the distance to the neutral axis, and: I r = πd4 r 64 (7.42) where d r is the diameter of the reinforcement. The total cracked moment of inertia of the pile section can be stated: 5 I pile = I c = I i (7.43) i=1 The pile properties used to calculate the tension and compression forces and the neutral axis are shown in Table 7.1. 85

7.3.2 Pile Moment Capacity The moment capacity of the pile is found by summing the moments resisted by the concrete and the steel about any axis in the pile. Using the cracked neutral axis found previously, the magnitude of the tension forces of the steel, T, and compression force of the concrete, C, the moment capacity can be determined. For simplicity, the moment arms were measured from the central line of the pile. These values are d 1 and d 2 for the steel and values between y and R p for the concrete slices. As in the moment of inertia calculations, the concrete is represented as a summation of slices. The moment capacity of each slice is determined by multiplying the compressive force found previously by its distance to the center line of the pile. The total moment capacity is determined by summing the slices. The resulting moment equation is: M = i C i h i + i T i d i (7.44) The results obtained for the location of the neutral axis, cracked moment of inertia and moment capacity are shown in Table 7.2. The moment capacity can be used to determine the ultimate load by using Equation 7.13 and the position of maximum stress derivation, expressed in Equation 7.26. The ultimate load is shown for different soil stiffness values in Table 7.3. These soil stiffness values correspond to the minimum, average, and maximum soil stiffness, respectively, at the test site. 86

Table 7.2: Mechanics of Materials Analysis Results Property IRC Pile Based on Properties From Lab Tension Tests [Toray] SRC Pile Based on Properties From Lab Tension Tests [McCune] Distance from Center to Cracked Neutral Axis, x [in (cm] Cracked Moment of Inertia, I [in 4 (cm 4 ] Moment Capacity, M max [kip-in (kn-m)] 2.53 (6.4) 4.47 (11.4) 695 (28) 481 (2) 1131 (127) 439 (49.6) Table 7.3: Pile Failure Loads Soil Stiffness, k IRC Pile Failure Load SRC Pile Failure Load [pci (kn/cm 3 )] [kip (kn)] [kip (kn)] 1 (7.3) 36 (16) 13.9 (61) 5 (36.4) 43.6 (194) 16.9 (75) 1 (72.9) 46.6 (27) 18.1 (81) 87

88

Chapter 8 Analytical Results Results for the the Lpile analysis and Winkler foundation model are presented in this chapter. 8.1 Lpile Deflection Predictions Using the computer program, Lpile, pile head deflections were computed for various load levels. Predictions were made with two different types of pile input. The first prediction, Lpile prediction 1, uses the Lpile generated moment-stiffness for the pile given the SRC pile properties. This prediciton is only made for the SRC pile. The second prediction, Lpile prediction 2, uses the laboratory moment-stiffness data for the pile stiffness input. This prediction is made for the both the IRC and SRC piles. Table 8.1 summarizes the Lpile prediction notation. and 8.2. Pile head deflection from the two Lpile predictions are shown in Figures 8.1 89

Table 8.1: Lpile Prediction Notation Soil Input Pile Input Lpile Prediction 1 Lpile Prediction 2 As Measured at the Test Site Lpile-Generated Pile Stiffness Given Pile Properties As Measured at the Test Site Laboratory Test Pile Stiffness 4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 1 16 14 12 1 8 6 4 Load [kn] 5 SRC Pile from Lpile Prediction 1 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] 2 Figure 8.1: Lpile Prediction 1: Load vs. Deflection of the SRC Pile from the Field Tests When the two predictions for the SRC pile are shown together as in Figure 8.3, the difference in the predictions is apparent. Lpile prediction 1 assumes field conditions. The second Lpile prediction was made with lab pile stiffness properties. As was mentioned in the previous chapter, adequate information about 9

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 16 14 12 1 8 6 Load [kn] 1 5 IRC Pile from Lpile Prediction 2 SRC Pile from Lpile Prediction 2 4 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 8.2: Lpile Prediction 2: Load vs. Deflection of the IRC and SRC Piles from Field Tests Lpile prediction 2 using nonlinear pile stiffness is not available in the Lpile manuals. Also, significant error could have been induced through the manipulation of the stiffness data required to apply it as input for Lpile. Therefore, because the SRC pile Lpile prediction 2 is significantly different than Lpile prediction 1, Lpile prediction 2 may not be the best representation of the field test and will not be used to compare to the field test results. However, because the same process and data was used for the the IRC and SRC pile input in Lpile prediction 2, they may be compared to one another. This comparison reveals that the IRC pile should have a much higher load capacity than the SRC pile. 91

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 1 5 SRC Pile from Lpile Prediction 1 IRC Pile from Lpile Prediction 2 SRC Pile from Lpile Prediction 2 16 14 12 1 8 6 4 2 Load [kn] 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 8.3: Lpile Prediction 1 and 2: Load vs. Deflection of the IRC and SRC Piles from Field Tests 8.2 Winkler Foundation Model Deflection Predictions Using the Winkler foundation model equations from Chapter 7, pile head deflection was predicted and plotted at different load levels. Figures 8.4 and 8.5 plot the deflection at the load point, located 6 in (15.2 cm) below the pile head, for the IRC and SRC piles, respectively. Three curves are plotted for each pile. The three curves correspond to three different soil stiffness values used for the calculations. The three stiffness values are the minimum, weighted average, and maximum soil stiffness for all of the soil layers found at the test site. The average was weighted by summing the soil stiffness multiplied by the depth over which it covered and then 92

5 Deflection at Point of Load Application [cm] 1 2 3 4 5 6 7 8 45 2 Load [kips] 4 35 3 25 2 15 1 5 IRC Pile Winkler Model Deflection Predictions with Soil Stiffness k [pci (kn/cm 3 )] k = 1 (7.3) k = 5 (36.4) k = 1 (72.9).5 1 1.5 2 2.5 3 3.5 Deflection at Point of Load Application [in] 15 1 5 Load [kn] Figure 8.4: Winkler Foundation Model Predicted Deflection at Point of Load Application of the IRC Pile from Field Tests deviding by the total depth. The curves end at the predicted failure value found using the Winkler foundation model in conjuction with the moment capacity of the piles. For these values, please refer to Table 7.3. The Winkler foundation predictions differ from the Lpile predictions and actual field results because the pile stiffness is assumed to be linear. Because the pile stiffness is similar for the IRC and SRC piles, the slope of the corresponding soil stiffness load-deflection curves are nearly the same. The only difference in the two figures is the predicted failure. Winkler equations predict the failure of the SRC pile to be between 13.9 kips (61 kn) and 18.1 kips (81 kn) and the IRC pile to be 93

5 Deflection at Point of Load Application [cm] 1 2 3 4 5 6 7 8 45 2 Load [kips] 4 35 3 25 2 15 1 5 SRC Pile Winkler Model Deflection Predictions with Soil Stiffness k [pci (kn/cm 3 )] k = 1 (7.3) k = 5 (36.4) k = 1 (72.9).5 1 1.5 2 2.5 3 3.5 Deflection at Point of Load Application [in] Figure 8.5: Winkler Foundation Model Predicted Deflection at Point of Load Application of the SRC Pile from Field Tests 15 1 5 Load [kn] between 36 kips (16kN) and 46.6 kips (27 kn). The deflection at failure is significantly altered by the linear pile stiffness assumption. In reality the piles would decrease in stiffness as they neared failure. The Winker foundation prediction shows that the SRC pile only deflects between 1 in (2.5 cm) and 1.2 in (3. cm) before failure when the actual results show almost 5 in (12.7 cm) of deflection before failure. Similarly, the Winker foundation model predicts between 2.5 in (6.35 cm) and 3.2 in (8.1 cm) of deflection before failure of the IRC pile while field results show nearly 8 in (2.3 cm) of deflection. In general, what the Winkler foundation 94

model shows is that the IRC pile is expected have a higher load capacity and deflect more at failure than the SRC pile. 95

96

Chapter 9 Discussion of Results The data gathered during the field testing of the SRC and IRC piles is suspicious and contradictory and therefore likely erroneous. In an attempt to extract as much information as possible, the data has been examined in both conventional and non-conventional ways. Through study of the results and comparisons of the results to laboratory tests, Winkler foundation model predictions, and Lpile predictions, four potential sources of error were determined: 1. SRC pile load data; 2. Soil properties; 3. Steel reinforcement splice location; or 4. Damage to the IRC pile before testing. The following sections describe the reasons for doubting the field test data and evaluate the possible sources of error. 97

Deflection [cm] 5 1 15 2 25 Total Transverse Load [kips] 7 6 5 4 3 2 1 S1-SRC L4-SRC L3-SRC L2-SRC L1-SRC C-SRC R1-SRC R2-SRC R3-SRC R4-SRC S2-SRC S1 Load Cell 1 Load Cell 2 S1-IRC L4-IRC L3-IRC L2-IRC L1-IRC C-IRC R1-IRC R2-IRC R3-IRC R4-IRC S2-IRC S2 3 25 2 15 1 5 Total Transverse Load [kn] L4 L3 L2 L1 C R1 R2 R3 R4 1 2 3 4 5 6 Deflection [in] Figure 9.1: Deflections of All Piles in Lab Tests 9.1 Pile Stiffness 9.1.1 Comparison to Lab Stiffness Results The piles tested in the laboratory were constructed not only with similar construction and materials but at the same time as the piles tested in the field. Consequently, similar results in strength and stiffness should be expected. Surprisingly, data retrieved from field testing did not concur with that from the lab testing. The most obvious difference is the stiffness. Figure 9.1 (repeated from Figure 3.3) and Figure 9.2 plot the load vs. deflection curves for the lab and field tests respectively. The laboratory tests show that the two piles have similar stiffness 98

35 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 3 25 2 15 1 14 12 1 8 6 4 Load [kn] 5 IRC Pile from String Potentiometer Data SRC Pile from String Potentiometer Data 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.2: Load vs. Deflection based on String Potentiometer Readings from Field Tests until the SRC pile begins to yield. However, the field test shows that the SRC pile has a significantly higher initial stiffness than the IRC pile. 9.1.2 Verification of Lab Stiffness Results Three test specimens of each pile type were tested in the laboratory, one in axial compression and two in four-point bending tests. All three tests gave consistent stiffness values for each pile type. In addition, stiffness values can be calculated from the material properties. The composite stiffness is simply the sum of the stiffness of the reinforcement and the concrete. Results for the pile stiffness 99

Table 9.1: Comparison of Laboratory Test and Predicted Stiffness Values Source Stiffness [lb-in 2 x 1 9 (N-cm 2 x 1 9 )] SRC Pile IRC Pile Lab Compression Tests 4.3 (123) 3.8 (19) Lab Bending Tests 3.8 (19) 3.4 (98) Predicted 3.7 (16) 3.8 (11) Average 3.9 (113) 3.7 (16) Standard Deviation.33 (9.5).24 (6.9) calculations are shown in Table 9.1.2 with the laboratory stiffness results to show the consistency among the stiffness values. 9.2 Deflection Two independent sources were used to gather deflection information during the field testing. One source was the string potentiometers which gathered tip deflection readings. The second source was the inclinometer which took slope measurements along the length of the pile from which tip deflection was derived. Figure 9.3 plots the tip deflection from each source on the same plot. The agreement between the two sources is very strong; especially considering the inclinometer deflection was derived from slope readings. The closeness of the two independent results verifies the accuracy of the deflection data. Although the deflection data appears accurate, the load-deflection curves are suspicious, as indicated earlier, thus inferring that the load data is probably not correct. 1

35 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 3 25 2 15 1 5 IRC Pile from Inclinometer Data SRC Pile from Inclinometer Data IRC Pile from String Potentiometer Data SRC Pile from String Potentiometer Data 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] 14 12 1 8 6 4 2 Load [kn] Figure 9.3: String Potentiometer and Inclinometer Tip Deflection Results from Field Tests 9.3 Loading Rate The oddity of the load data is also apparent when loading rate is considered. According to the data shown in Figure 9.4, the SRC pile took over twice as much load as the IRC pile within the first three minutes of testing. However, after the first few minutes of testing, the rate of load change with time is very similar for both piles. This is shown in Figure 9.5 where the SRC and IRC curves have been collapsed so that the origin is located at the point just after the first inclinometer reading break (as marked in Figure 9.4). The first inclinometer reading was taken for both piles when the pile reached.5 in (1.3 cm) of displacement. Because the 11

Load [kips] 35 3 25 2 15 14 12 1 8 6 Load [kn] 1 IRC Pile SRC Pile 4 5 IRC Pile Adjustment Point 2 SRC Pile Adjustment Point 2 4 6 8 1 12 14 Time [min] Figure 9.4: Load vs. Time from Field Tests 35 Load [kips] 3 25 2 15 14 12 1 8 6 Load [kn] 1 5 IRC Pile SRC Pile 4 2 2 4 6 8 1 12 14 Time [min] Figure 9.5: Adjusted Load vs. Time from Field Tests 12

stiffness of the IRC and SRC piles is so similar, at such a small deflection this load would be expected to be very similar. The load difference between the first inclinometer readings is 6.5 kips (28.9 kn). 9.4 Energy Further suspicion of the load data can be validated by energy considerations. Conservation of energy states that the energy put into the pile through the hydraulic jack should be equal to the energy absorbed by the pile and surrounding soil. Because the piles have the same stiffness, the energy absorbed by the piles should be equal until failure or at least until yielding begins. Therefore, at equivalent load levels, the SRC and IRC piles should apply equal amounts of energy on the surrounding soil. To determine the energy absorbed by the surrounding soil, the soil was modeled as a spring with stiffness equal to the soil stiffness. This required an assumption that the soil behaved perfectly elastic when in reality the soil experienced some plastic deformation. Although the elastic assumption may not be numerically accurate, the plastic differences will be the same for both piles making this a viable way to compare the soil compaction energies. The equation for the energy of a spring is given by: U s = 1 2 kx2 (9.1) 13

where U s is the energy of the spring, k is the spring stiffness, and x is the spring displacement. To apply this theory to the soil, x was defined as the displacement of the pile and k was defined as the stiffness of the soil. To convert the soil stiffness to spring stiffness, the soil stiffness was multiplied by the pile diameter, D. To determine the deflection, x, of the pile, a sixth-order polynomial equation was fit to the deflected shape of the pile as recorded by the inclinometer data. Deflection, w, is a function of the position, x, along the pile. The total soil energy was obtained by integrating the soil energy over the length of the pile. The modified soil compaction energy is given by: U s = L D 2 kw(x)2 dx (9.2) Figure 9.6 shows the results for the SRC and IRC pile soil compaction energy as calculated using Equation 9.2. The figure makes it clear that for a particular load level, the soil compaction energies are not the same. In fact, the calculated average difference in load at a particular load level is 7.1 kips (31.6 kn). This value is very similar to the 6.5 kip (28.9 kn) difference between the first inclinometer reading loads on the load vs. time charts. 9.5 Energy-Modified Results To account for the energy difference shown in Figure 9.6, the SRC pile load was decreased the average difference in energy, 7.1 kips (31.6 kn). Modifying the SRC pile test data revealed an accord with the laboratory findings, material 14

Soil Displacement Energy [kip*ft]) 8 7 6 5 4 3 2 1 Load [kn] 2 4 6 8 1 12 14 IRC Pile SRC Pile Difference Average Difference 1 8 6 4 2 Soil Displacement Energy [kj] 5 1 15 2 25 3 35 Load [kips] Figure 9.6: Soil Compaction Energy of the IRC and SRC Piles properties, and predictions. The modified load vs. deflection results are shown in Figure 9.7. The modified load vs. deflection curve shows similar behavior to lab test results. The initial slope of the SRC pile is slightly steeper than the IRC pile, indicating a slightly higher stiffness in the SRC pile. This difference in stiffness is also apparent in the lab test results where the stiffness of the SRC pile was 12% greater than the stiffness of the IRC pile. The calculated stiffness of the piles also suggested a slightly greater stiffness for the the SRC pile. 15

Load (SRC Pile Load Adjusted) [kips] 35 3 25 2 15 1 5 Deflection at Point of Load Application [cm] 5 1 15 2 IRC Pile from String Potentiometer Data SRC Pile from String Potentiometer Data 14 12 1 8 6 4 2 Load (SRC Pile Load Adjusted) [kn] 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.7: Energy-Modified Load vs. Deflection Data from Field Tests When Lpile prediction 1 is plotted with the IRC pile deflectin as recorded by the string potentiometers in the field, the prediction matches the initial slope and therefore stiffness of the IRC pile. This comparison, shown in Figure 9.14, validates the load-deflection data for the IRC pile. In addition, when SRC pile Lpile prediction 1 is plotted with the SRC pile results from the field tests, as shown in Figure 9.9, the results are not equivalent. However, if the load of the SRC piles in the field is decreased by 7.1 kips as suggested by the energy calculations, Figure 9.1 shows that the adjusted field results are similar to the Lpile prediction. 16

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 1 5 IRC Pile from String Potentiometer Data SRC Pile from Lpile Prediction 1 16 14 12 1 8 6 4 2 Load [kn] 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.8: Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the IRC Pile in the Field 9.6 Lpile Adjusted Soil Predictions Variability of soil stiffness surrounding the test piles could explain the difference in energy. If the soil surrounding the SRC pile was stiffer than the soil data gathered at the test site, this would produce a higher load capacity for the SRC pile. To see the difference soil properties can make, alterations were made to the top two layers of the soil in Lpile prediction 1. Only the top two layers were altered because inclinometer data did not show significant deflection in deeper soil layers. These two layers were increased in strength until the resulting load-deflection 17

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 16 14 12 1 8 6 Load [kn] 1 5 SRC Pile from String Potentiometer Data SRC Pile from Lpile Prediction 1 4 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.9: Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the SRC Pile in the Field Table 9.2: Original and Adjusted Soil Properties for the Top Two Layers in the Soil Profile Soil Property As Measured at the Test Site Adjusted to Match SRC Pile Field Results Soil Strain.7.5 Cohesive Strength 1 12 data matched the load-deflection data gathered in the field. The altered soil properties are shown in Figure 9.6. 18

Load (SRC Pile Load Adjusted) [kips] 35 3 25 2 15 1 5 Deflection at Point of Load Application [cm] 5 1 15 2 SRC Pile from String Potentiometer Data SRC Pile Lpile Prediction 1 14 12 1 8 6 4 2 Load [kn] 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.1: Lpile Deflection Prediction for the SRC Pile Compared to Adjusted String Potentiometer Deflection Results for the SRC Pile in the Field If the soil surrounding the SRC pile was different than the field-tested soil properties, the resulting load-deflection curve, shown in Figure 9.11, could match the actual field test behavior. However, the soil properties required to produce the actual field data are unlikely if not impossible. A different subsurface material such as an existing foundation is a more probable source of the increased load capacity of the SRC pile. This would also be a more reasonable cause because it would produce a very localized increase in subsurface strength where a change in soil properties in a distance of about 15 ft (4.6 m) would be unlikely. 19

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 1 5 SRC Pile from String Potentiometer Data SRC Pile from Lpile Prediction 1 with Soil Adjustment 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] 16 14 12 1 8 6 4 2 Load [kn] Figure 9.11: Actual Load vs. Deflection Behavior Compared to Lpile Predictions based on Adjusted Soil Properties The oddity of the SRC pile results is also apparent when the Lpile-predicted deflected shape is plotted with the actual test results. Figure 9.12 shows actual deflected shapes of the SRC Pile from inclinometer readings with Lpile prediction 1 based on original and adjusted soil properties. All Lpile predictions represent deflected shapes at the same load levels as the inclinometer readings. Only the deflected shapes before failure are shown. For the original soil, Lpile prediction 1, only one deflected shape is shown because Lpile predicted failure before the second inclinometer reading. Two deflected shapes are shown for the adjusted soil properties. According to Lpile, at the field test recorded loads, the SRC pile should 11

-5 Displacement [in].5 1 1.5 2 2.5 3 3.5 4-1.5.5 5 Depth Below Ground Surface [ft] 1 15 2.5 4.5 Depth [m] 2 25 3 SRC Pile Load [kips (kn)] 14.8 (65.8) Inclinometer Data 19.2 (85.4) Inclinometer Data 19.2 (98.8) Inclinometer Data 24.5 (19) Inclinometer Data 26.2 (117) Inclinometer Data 28. (125) Inclinometer Data 14.8 (65.8) Lpile Prediction 1 14.8 (65.8) Lpile Prediction 1 with Soil Adjustment 19.2 (98.8) Lpile Prediction 1 with Soil Adjustment 1 2 3 4 5 6 7 8 9 1 Displacement [cm] 6.5 8.5 Figure 9.12: Actual Deflected Shape of the SRC Pile Compared to Lpile Predictions Based on Original and Adjusted Soil Properties 111

have already yielded and failed much sooner. Even increaseing the soil strength could not reach the high failure load of the SRC pile in the field. Notice the shapes of the three data types. A 14.8 kip (66 kn) curve is provided for the inclinometer data, Lpile prediction 1, and Lpile prediction 1 with adjusted soil. The shape of Lpile prediction 1 infers a much softer soil profile with deflection reaching greater depths. The inclinometer data and the stiffer soil Lpile prediction have similar shapes showing that the pile does not deflect much lower than 4 ft (1.2 m) and not at all below 6 ft (1.8 m). This comparision suggests something stiff reacted against the SRC pile below the ground surface. 9.7 Lpile SRC Pile Adjusted Reinforcement Predictions The SRC pile was 3 ft (9 m) long, however the steel reinforcement came in 2 ft (6 m) lengths. Splices were required to construct the pile. These splices were alternated, every other bar, between the top and the bottom of the pile. Because the SRC pile field data recorded that the pile withstood a significantly greater load than was predicted, these splices became suspect. To determine the significance of these splices, an analysis was performed using Lpile. The analysis increased the reinforcement to see what the effect would be on the load-deflection data. The pile tested in the field had 8 # 4 bars. One test analysis increased the reinforcement to 8 #5 bars, or, 5% greater area in each bar. Another test analysis increased the reinforcement to 8 #6 bars, or 12% greater area in each bar. These analyses were performed using Lpile prediction 1 input (with the exception of the adjusted 112

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 1 5 SRC Pile from String Potentiometer Data SRC Pile from Lpile Prediction 1; 8 #4 bars (.2 in 2 ) SRC Pile from Lpile Prediction 1; 8 #5 bars (.31 in 2 ) SRC Pile from Lpile Prediction 1; 8 #6 bars (.44 in 2 ) 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] 16 14 12 1 8 6 4 2 Load [kn] Figure 9.13: SRC Pile Adjusted Reinforcement Predictions reinforcement). The results for these analyses, shown in Figure 9.13, make it apparent that while the increased reinforcement does alter the load capacity of the pile, even a gross overestimation of the splice does not produce a load capacity as high as the SRC pile field results. 9.8 Error Evaluation An error in the load data for the SRC pile seems likely when considering the loading rate and the energy balance. Each method of analysis suggests an approximate 7 kip (31 kn) adjustment in load. When this adjustment is made, the SRC results concur with both the Lpile predictions and laboratory test results. 113

The difference in energy transfered to the soil could also be explained by a difference in the soil surrounding the piles. Lpile predictions show that a change in the top layers of soil can significantly alter the load-deflection data. However, the changes in the soil necessary to match the IRC pile field data are not likely for the test site. However, an unknown subsurface material such as an existing foundation could cause the subsurface material to absorb energy resulting in an artificial increase in the pile load capacity. The splice in the SRC Pile reinforcement increased the area of the reinforcing members; however, Lpile predictions show that even with over double the area in each bar (a huge overestimate for the splice) the load-deflection curves are still significantly lower than the SRC field test results. Therefore, the splice may have altered the results, but it could not have been the single reason for the error in the data. The last possible error considered is damage to the IRC pile prior to the field tests. The IRC pile stiffness is consistent with the Lpile predictions for the SRC pile. Both laboratory testing and material property analysis showed similar stiffness between the SRC and IRC piles. Taking the agreement of the IRC pile with analysis in conjunction with the considerable doubt in the SRC pile field data, the IRC pile data is most likely not the source of error. 114

4 Deflection at Point of Load Application [cm] 5 1 15 2 Load [kips] 35 3 25 2 15 16 14 12 1 8 6 Load [kn] 1 5 IRC Pile from String Potentiometer Data SRC Pile from Lpile Prediction 1 4 2 1 2 3 4 5 6 7 8 9 Deflection at Point of Load Application [in] Figure 9.14: Lpile Deflection Prediction for the SRC Pile Compared to String Potentiometer Deflection Results for the IRC Pile in the Field 9.9 Summary No evidence suggests that the IRC pile data is in error. However, substantial evidence concludes that the SRC pile field data is flawed and therefore not useful for comparison to the IRC pile field results. Lpile prediction 1 is a viable alternative to experimental data for the SRC pile. To understand the comparative behavior of the IRC pile to a similar SRC pile, the IRC pile field deflection data is shown with Lpile prediction 1 for the SRC pile in Figure 9.14. 115

Figure 9.14 reveals that for two piles of similar stiffness, one reinforced with an IsoTruss R grid-structure and one with steel re-bar, the IRC pile is approximately twice as strong. This result concurs with the laboratory tests which also showed that the IRC pile was approximately twice as strong as the SRC pile [2]. 116

Chapter 1 Conclusions and Recommendations This thesis focused on the field performance of IsoTruss R grid-reinforced concrete beam columns for use in driven piles. Experimental investigation included one instrumented carbon/epoxy IsoTruss R grid-reinforced concrete pile (IRC pile) and one instrumented steel-reinforced concrete pile (SRC pile) which were driven at a clay profile test site. These two piles, each 3 ft (9 m) in length and 14 in (36 cm) in diameter, were quasi-statically loaded laterally until failure. Behavior was predicted using three different methods: 1) a commercial finite difference-based computer program called Lpile; 2) a Winkler foundation model; and, 3) a simple analysis based on fundamental mechanics of materials principles. Due to unresolveable errors, experimental field test data for the SRC pile is inconclusive. However, analysis predictions in conjunction with field test data for the IRC pile show that the IRC pile should perform similar to laboratory test results. Therefore, IsoTruss R grid-structures are a suitable alternative to steel as 117

reinforcement in driven piles. This chapter includes the conclusions drawn from the field research and recommendations to improve further research. 1.1 Conclusions 1. Both Lpile and Winkler foundation model predictions agree with the laboratory results that the IRC pile is almost twice as strong as the SRC pile. 2. Experimental results were not consistent with those obtained in the laboratory and are inconclusive due to unresolveable errors. Conservation of energy principles also suggest that the SRC pile data was in error. Modifying the SRC pile field test data to account for a more realistic energy balance revealed an accord with laboratory findings and Lpile predictions. 3. Soil stiffness contributes significantly to the field performance of driven piles. 4. Applying mechanics of materials principles found the predicted stiffness of the piles to be consistent with laboratory results. 1.2 Recommendations 1. At least two of each pile type should be tested to increase result dependability. 2. The test site should be carefully chosen and studied to ensure the soil is undisturbed and consistent among test piles. 3. The piles need not be greater than 2 ft (6m) for field bending test. 4. Carefully protect strain gages to avoid corrupt data. 118

5. Additional field tests are required to ensure field performance of IsoTruss R grid-reinforced concrete piles. 119

12

References [1] D. T. McCune, Manufacturing quality of carbon/epoxy isotruss reinforced concrete structures, Master s thesis, Brigham Young University, 25. [2] M. J. Ferrell, Flexural behavior of carbon-epoxy isotruss-reinforced concrete beam-columns, Master s thesis, Brigham Young University, 25. [3] K. Rollins, R. Olsen, J. Egbert, K. Olsen, D. Jensen, and B. Garrett, Response, analysis, and design of pile groups subject to static and dynamic lateral loads, Tech. Rep. UT-3.3, Research Div., Utah Departement of Transportation, Salt Lake City, Utah, 23. [4] J. M. Gere, Mechanics of Materials. Brooks/Cole, 5 ed., 21. [5] M. Bellis, The history of concrete and cement, http://inventors.about.com/library/inventors/blconcrete.htm. [6] C. Deniaud and J. R. Cheng, Review of shear design methods for reinforced concrete beams strengthened with fibre reinforced plolymer sheets, Canadian Journal of Civil Engineering, vol. 28, pp. 271 281, 21. [7] S. F. Brena, S. L. Wood, and M. E. Kreger, Using carbon fiber composites to increase the felxural capacity of reinforced concrete bridges, tech. rep., Center for Transportation Research, The Unversity of Texas at Austin, September 21. [8] D. D. D. Chung, Carbon fiber reinforced concrete, tech. rep., National Research Council, 1992. [9] Material selection guide: Reinforcement, Concrete Construction, March 25. [1] D. Brand, Undergrads salute sagan, technology by building bridge with new materials, Cornell Chronicle, vol. 31, November 1999. [11] A. Ferreira, P. Camanho, A. Marques, and A. Fernandes, Modelling of concrete beams reinforced with frp re-bars, Composite Structures, vol. 53, pp. 17 116, 21. 121

[12] C. W. Smart, Flexure of concrete beams reinforced with advanced composite orthogrids, Master s thesis, Brigham Young University, Provo, UT, 1997. [13] F. A. Tavarez, L. C. Bank, and M. E. Plesha, Analysis of fiber-reinforced polymer composite grid reinforced doncrete beams, ACI Structural Journal, vol. 1-S27, pp. 25 258, March-April 23. [14] B. M. Das, Principles of Foundation Engineering. Brooks/Cole, 5 ed., 24. [15] J. P. Broomfield, Corrosion of Steel in Concrete; Understanding, Investigation and Repair. E & FN Spon, 1997. [16] AISC Manual of Steel Construction Load and Resistance Factor Design, 3 ed. [17] Digitilt Inclinometer Manual, 25. [18] Lpile Plus 4. for Windows, Technical Manual. [19] J. Holman and J. W.J. Gajda, Experimental Methods for Engineers. McGraw-Hill Book Company, 5 ed., 1989. [2] Hetenyi, Beams on Elastic Foundation. The University of Michigan, 1946. [21] J. G. MacGregor and J. K. Wight, Reinforced Concrete Mechanica and Design. Person Prentice Hall, Inc., 4 ed., 25. [22] Salas and Hille, Calculus One and Several Variables. John Wiley & Sons, Inc, 7 ed., 1995. 122