Rapid Short and Medium Span Bridge Construction Using Innovative. Precast Structural Systems

Transcription

1 Rapid Short and Medium Span Bridge Construction Using Innovative Precast Structural Systems By: Derek M. Scullion A thesis in partial fulfillment of the requirements for the degree of Master of Science (Civil Engineering) UNIVERSITY OF WISCONSIN MADISON 2010

2 Rapid Short and Medium Span Bridge Construction Using Innovative Precast Structural Systems APPROVED BY: Dr. Michael G. Oliva Date: Major Advisor Professor of Civil and Environmental Engineering University of Wisconsin Madison 2

3 Table of Contents: List of Figures:... 6 List of Tables:... 9 Acknowledgements Abstract Chapter 1: Introduction and Definition of Problem Objectives: Scope: Process for achieving objectives: development of a short span bridge system: Chapter 2: Literature Review Precast construction in Bridges: Wisconsin Bridge Manual The State of the Art of Precast/Prestressed Adjacent Member Bridges Rapid bridge construction technology: precast elements for substructures Precast deck panels The NEXT Beam: A Robust Double Tee Prestressed Beam Super T Beams Precast Channel Beam Use in Bridges: Chapter 3: Preliminary System Investigation: Double Ts Section Description: Failure Limits: Live Load Moments: Dead Load Moments: Stress Calculations: Preliminary Investigation results: Second Analysis Prestressing effect: Third Analysis Negative Moment: Conclusions of Preliminary Calculations: Refined Analysis: Double Ts Computer Program construction: Distribution Factors:

4 3.13 Losses in prestressing: Live load moment generation: Span code: Stress calculation: Refined Analysis: First Refined Analysis Moment Similarity Comparison: Second Analysis Varying Slab thickness Refined Analysis 2a: Dead Loads Only Refined Analysis 2b: Live Loads Only Refined Analysis 2c: Service Loads Conclusions: Chapter 4: Development of More Efficient Bridges with Channel Sections Background research on Channel girders: Maintenance issues: Transverse Connections Between Girders: Shear Keys: Mechanical connections: Post tensioning: Reinforced concrete deck: New Section Design: Goals for new section: Design of section: Preliminary Analysis: Eccentricity equations: Analysis of Channel Section: Channel Analysis 1: Draping effect Channel Analysis 2: One and Two span comparison Chapter 5: Conclusions Chapter 6: Recommendations Lab testing on the newly designed Channel beam: Construction of a pilot bridge: Develop Design Guidance:

5 Works Cited: Appendix A: Equations used for Analysis Appendix B: Example problems Problem 1: 1 span Problem 2: 2 span symmetric Problem 3: Non symmetric 3 span, with draped design Appendix C: Buffalo County Bridge Construction Study Appendix D: Plan set for Buffalo County bridge

6 List of Figures: Figure 1 1, Formwork for a haunched cast in place slab, note the large steel girders and cross beams (Photo courtesy of WisDOT, 2004) Figure 1 2, Stay in place precast forming members with cast in place slab Figure 2 1, Economical span ranges for different bridge types (WisDOT, 2010) Figure 2 2, Precast panel being placed, note that the bridge is still open for traffic on the right side (Oliva et al., 2007) Figure 2 3, NEXT beam on a trailer (photo courtesy of Dailey Precast) Figure 2 4, Closed (Left), and Open (Right) Super T beams, (Connal, 2010) Figure 3 1, Plot of change in the number of usable sections (2 span bridge) versus a change from nonsimilar bridge with span length difference (Δ) to a bridge with all equal spans Figure 3 2, Plot of change in the number of usable sections (3 span, 1 st equal to 3 rd ) versus a change from non similar bridge with span length difference (Δ) to a bridge with all equal spans Figure 3 3, Plot of change in the number of usable sections (3 span, 2 nd equal to 3rd) versus a change from non similar bridge with span length difference (Δ) to a bridge with all equal spans Figure 3 4, Plot of the average change in the number of usable sections for all slab thicknesses, versus a change from non similar bridge with span length difference (Δ) to a bridge with all equal spans for the 3 span configurations Figure 3 5, Plot of Usable Double T sections vs. Span Length, Dead Loads only Figure 3 6, Plot of Usable Double T sections vs. Span Length, Live Loads only, single span Figure 3 7, Plot of Usable Double T sections vs. Span Length, Live Loads only, two spans Figure 3 9, Plot of usable Double T sections vs. Span length, Service Loads, 2 spans Figure 4 1, Sealed reflective cracks in the asphalt overlay of a precast channel bridge. (Photo courtesy of Scot Becker, and Travis McDaniel, WisDOT, 2009 ) Figure 4 2, Corrosion and spalling of reinforcement at the bottoms of webs (Wipf et al., 2006) Figure 4 3, Grouted, diamond hexagonal shaped shear key Figure 4 4, Mechanical connection on a precast channel beam (Wipf et al., 2006) Figure 4 5, 4C S, precast channel beam, 20 inches tall, 4 feet wide at the base

7 Figure 4 6, 4C S, precast channel beam, 24 inches tall, 4 feet wide at the base Figure 4 7, 4C S, precast channel beam, 28 inches tall, 4 feet wide at the base Figure 4 8, 4C S, precast channel beam, 32 inches tall, 4 feet wide at the base Figure 4 9, Comparison of Double T beams to Channel Beams, % Usable Sections vs. Span Length Figure 4 11, Plot of percentage of usable sections vs. span length, service loads, 8 inch deck, (LW = lightweight concrete in channel beams) Figure 4 12, Plot of percentage of usable sections vs. span length, service loads, 12 inch deck, (LW = lightweight concrete in channel beams) Figure 4 14, Plot of number of percentage of usable sections versus span length for draped and undraped, 1 span and 2 span, with 8 inch deck thickness Figure 4 15, Plot of number of percentage of usable sections versus span length for draped and undraped, 1 span and 2 span, with 12 inch deck thickness Figure 0 1, Location of precast bent cap project Figure 0 2, B before replacement. Looking North (HSIS, 2010) Figure 0 3, Partially filled formwork Figure 0 4, PVC pipes for the grouted dowels in the ship lap joint which forms the connection between pieces Figure 0 5, Cross section of Pile pocket, note the hour glass shape which prevents vertical displacement Figure 0 6, Styrofoam cutouts used to create the pile pockets Figure 0 7, A 3 yard bucket is used to transport the concrete to the formwork Figure 0 8, Bent cap being lifted from the forms, note the pile pocket forms Figure 0 9, Removal of the pile pocket forms Figure 0 10, Elevation of the B bridge pile bent pier Figure 0 11, Pier pile template, supported at the corners. Note the cut pile shells spaced across the deck Figure 0 12, Lunda vibrated the pile shells to a depth of 35 feet prior to driving them Figure 0 13, Delmag D 30 hammer, lifted by a Terex HC 110 crane

8 Figure 0 14, To save time two welders worked on the same pile, each doing half the job Figure 0 15, A completed open pile bent Figure 0 16, Template used to align piles for the abutments Figure 0 17, Completed piling for an abutment, piles shown before being cut off to proper height Figure 0 18, Friction collars installed on an open pile bent Figure 0 19, Completed working surface Figure 0 20, Piling being filled with concrete Figure 0 21, Wooden seat (or radial sled), used to seal the connection between socket and pile Figure 0 22, Half of a bent cap being delivered Figure 0 23, One half of the precast bent cap being placed Figure 0 24, Second half of bent cap being placed, note the poly styrene in the joint Figure 0 25, Sealed ship lap joint Figure 0 26, Abutment bent cap being placed, note the piles that will be embedded in the cap (Photo courtesy of Kathy Currie, WisDOT, 2010) Figure 0 27, two palettes of grout, delivered off camera and moved into place by crane Figure 0 28, Combination 2 bucket mixer and pump, used to mix the grout on site and pump it to the caps Figure 0 29, Topping off a pile pocket with grout Figure 0 30, Completed pile bent, four girders have been placed, note the built in beam steps Figure 0 31, Completed abutment bent cap, note the built in beam steps Figure 0 32, Option 1 for the pile bent caps. Single piece with 30, 0.5 φ full length prestressing strands Figure 0 33, Option 2 for the pile bent caps. Two pieces with ship lap joint connected by 4 dowels Figure 0 34, Approximate mid point of the bridge, looking Southwest (Photo courtesy of Kathy Currie, WisDOT, 2010) Figure 0 35, Approximate mid point of the bridge, looking Northwest (Photo courtesy Kathy Currie, WisDOT, 2010)

9 List of Tables: Table 3 1, Initial selection of Double T sections for analysis Table 3 2, List of dead, and live load moments used in the preliminary analysis Table 3 3, Stress limits per AASHTO Service 3 loading, for initial analysis Table 3 4, Summary of first stress analysis on Double T beams, at top and bottom of beam Table 3 5, Double T sections used in second analysis Table 3 6, Summary of second stress analysis on Double T beams Table 3 7, Double T sections used in third analysis Table 3 8, Summary of results for the third analysis on Double T beams Table 4 1, Table of all custom sections designed and analyzed Table 0 1, Direct dollar cost comparison between the precast, and the cast in place bent cap Table 0 2, Total estimated time for the two substructure alternatives

10 Acknowledgements The author would first like to thank his major advisor, Professor Michael Oliva, for all of his guidance, support, insight, and most of all patience. The author is truly grateful for everything that he has learned while working with Professor Oliva, and knows the lessons learned will serve him well in the future. The author would also like to thank the Wisconsin Department of Transportation, especially Scot Becker, Travis McDaniel, Dave Genson, Mike Williams, Dave Koepp, Paul Conlin, and Kathy Currie for the support, and advice throughout the research process. Gratitude is also extended to Professors Steven Cramer, and James Schneider for serving on the defense committee. The author would like to acknowledge the financial support provided by the University of Wisconsin Madison, Wisconsin Department of Transportation, and the Federal Highway Administration, without their support none of this would be possible. Finally, the author extends gratitude to his family, friends, co workers, colleagues, fellow gradstudents. And most especially his girlfriend Kyle, for her loving support, patience, and levity, the author hopes she will forgive him for all of the late nights working. 10

11 Abstract The direct costs of bridge construction, such as materials, labor, and equipment are all well known. Recently however the indirect costs such as the cost of traffic disruptions, and construction safety are beginning to be factored into design decisions. These new considerations have led the Federal Highway Administration (FHWA) to explore Accelerated Bridge Construction (ABC), which is also known as a get in, get out, stay out approach to bridge construction and replacement. Accelerated Bridge Construction is defined as replacement, or new bridge construction that uses design and construction methods to minimize impacts to the traveling public, river traffic, railroads, and the environment all while maintaining high levels of quality and safety. In other words, make bridge construction faster, and safer, while also making bridges last longer by using modern technology. This project focuses on one approach to ABC construction, using more precast elements, in an attempt to move towards an all precast bridge. Precast elements are fabricated offsite, in a controlled environment, and shipped to the project, where a crane is used to place them. Systems being examined in this project include precast stay inplace forms for short to medium span bridges, and precast pile bent caps. Both of these systems can be used to dramatically reduce the amount of cast in place concrete on a typical bridge project. For the precast stay in place formwork system, this report first examines current practices of using precast concrete and bridges, and then identifies possible precast sections for further study in the proposed system. Double T beam sections are identified for further study, next a series of analyses are run to identify a group of characteristics that would make a newly designed section more efficient. Using these characteristics, a new Channel section is designed, and analyzed against the Double T section, the new section is found to offer a broader span range, and is designed to reduce several key 11

12 maintenance issues prevalent in adjacent member bridges. A list of recommendations for further study and discussion on this topic is included. Also included in this report is a construction study done on a bridge near Reynolds Wisconsin which used precast pile bent caps. The report follows the project from the precasting of the pile caps at County Materials in Roberts Wisconsin, to the placement and connection of caps to the piles, in Reynolds Wisconsin. Several problems were experienced with the construction process, and from these a list of recommendations for improvement was generated, and is included with the report. 12

13 Chapter 1: Introduction and Definition of Problem Short span cast in place slab bridges are used commonly in the Midwest for stream crossings with spans of 50 feet or less. This is because slabs are generally perceived to be the most economical choice for the given span range. In the five years starting from 2005 and ending in 2009, slab type bridges have represented on average 69% (WisDOT, 2010) of the bridge construction projects for stream crossings in Wisconsin. These bridges are generally shorter spans, so the total cost per bridge is generally much lower than other alternatives. Unfortunately, slab bridges have several drawbacks that offset their economy. The first problem noted with cast in place concrete slab bridges is that they are relatively slow to construct. Significant amounts of time and labor are needed for the construction, and removal of formwork, and tying and placing large reinforcing steel cages. The formwork and temporary shoring for cast in place slabs cannot be removed without allowing the poured concrete to cure to an adequate strength to resist deflections; this generally takes at least seven days. This added construction time not only affects the direct cost of the bridge, but also influences secondary costs such as traffic delays and wear on alternative routes. Another drawback of traditional slab bridge construction is that some aspects of the construction are inherently dangerous, specifically the removal of the temporary shoring and formwork. This process is made dangerous by the heavy form components, often constructed from large lumber and plywood pieces as well as steel cross beams for support. Removal is made dangerous because of the precarious positions that workers must put themselves in to remove the forms from under the completed bridge, which is generally over water, an example of this can be seen in Figure 1 1. The removal also has to be done with limited crane support, because the newly constructed bridge gets in the way of the lift. 13

14 Figure 1 1, Formwork for a haunched cast in place slab, note the large steel girders and cross beams (Photo courtesy of WisDOT, 2004) Finally, some construction activities for cast in place slab bridges can be sensitive to scheduling issues and weather. The deck pour for a slab type bridge can take a significant amount of time, depending on the span length and thickness it is not uncommon for them to last 12 hours or longer. Often these activities are done at night because it is cooler, and they are scheduled weeks in advance. But poor weather can cause deck pours to have to be rescheduled, which can lead to delays, and additional direct costs. 14

15 1.1 Objectives: The general objective of this study was to investigate the possibility of using an all precast bridge system, and determine its usefulness in increasing the speed of bridge construction, while also increasing the quality of the constructed facility and worker safety at the construction site. Increased construction speeds would result in lower costs to the traveling public in the form of reduced delays and alternative routing. Increasing the quality of workmanship would reduce the costs of maintenance over the life of a built structure. Finally, improved worker safety could reduce the cost to the contractors and state agencies, in the form of lower labor costs and possibly insurance claim reductions. Both substructure, and superstructure systems are considered for precast applications in bridge projects, substructure design analysis is being done by a concurrent study. The primary objective of this study was to prove that a system of precast stay in place forms acting compositely with a concrete deck could replace the current standard of a cast in place slab for bridges with spans in the 20 to 60 foot range. Long span bridges are not being focused on because the use of precast beams in spans over 60 feet is common practice. Another objective was to ensure that the proposed stay in place formwork system could achieve all of the general objectives of the study, while also maintaining a relatively low cost. 15

16 1.2 Scope: The scope of this report is limited to the design and application of precast superstructure elements to replace the current practice of cast in place slab bridges. It is further limited by the range of precast alternatives that precasters in Wisconsin would consider to be practical or readily achievable. This report will focus on reducing the amount of cast in place concrete in bridge construction in an effort to reduce the time it takes to construct short to medium span bridges. Another focus will be on developing an efficient, lightweight section shape that can be standardized for multiple bridge span configurations, and can be used repetitively enough by WisDOT to justify purchase of reusable forms by the precast industry. Only precast, prestressed concrete sections were considered in this report. The results from this study will be relevant to stream crossing structures in the State of Wisconsin with span ranges between 20 and 60 feet. A typical solution process for a scientific, or an engineering problem such as this is initiated by a literature review to define the state of knowledge. The next step is to define a hypothesis, in this case, the hypothesis was that an existing standard precast section could be used as a stay in place form to replace cast in place slab bridges in Wisconsin. To test a hypothesis, preliminary calculations are done first. The intention of the preliminary calculations is to check the viability of the concept without investing a lot of resources. Once a preliminary analysis is done, and assuming that the hypothesis is still valid, a more refined analysis can be undertaken. The goal of the refined analysis is to provide more generalized, and higher quality results than the preliminary analysis, and should provide sufficient evidence to either prove, or deny the hypothesis. If necessary, adjustments are made to the hypothesis until sufficient evidence is obtained to prove it. Finally, conclusions are drawn from the evidence compiled, and a list of recommendations for future work is generated. 16

17 In addition to the precast superstructure design and analysis, a side study will be performed on a construction project that will utilize precast structural elements. The purpose of this side study will be to assess the strengths, and weaknesses of using precast elements in bridge construction, and to apply this knowledge in the design of the precast superstructure element. 17

18 1.3 Process for achieving objectives: development of a short span bridge system: The new system is intended to replace the use of cast in place slab type superstructures for short span bridges, with a system of precast, stay in place forms made composite with a thin concrete deck. The sections examined for the stay in place forms should have wide top flanges, such that when the sections are placed next to each other they would form a working surface, this working surface would double as the bottom of the deck form. The stay in place forms would be made composite with the cast in place concrete deck with the use of a roughened top surface combined with either studs, or rebar hoops, protruding from the top flange and lined up with the webs of the stay in place section to ensure adequate anchorage. Prior to the concrete deck being poured, the entire stay in place form system would be tied together using one or more of the following methods to ensure adequate vertical load transfer and sharing between adjacent members, and thus prevent relative displacement of the beams and reflective cracking in the concrete deck: 1. Grouted shear keys If it is possible for the section used for the stay in place form, a shear key would be created on both sides of every section. When placed next to each other, the section s shear keys would align, and be open at the tops to allow grouting. The shear keys need to be of sufficient depth and width to transfer the vertical forces between members. 2. Mechanically connected Mechanical connection ducts could be created in the webs of the section by the precaster. Once on site, the contractor would need to add either steel or cast inplace concrete between the sections, similar to the diaphragms on prestressed and steel girder bridges. The connections could also consist of large bolts that tie the webs of adjacent sections together. Again, the spacing and amount of mechanical connections would vary, depending on the bridge geometry and the vertical force transfer needed between members. 18

19 3. Post Tensioning During fabrication of the sections to be used as stay in place forms, transverse post tensioning ducts would be created in the section or the webs of each of the sections. If it is a webbed section, once the section is cast, it would need to be flipped over, and have a transverse post tensioning duct and concrete strut placed between the webs. The section is then shipped to the construction site, each section is placed, and then post tensioned together transversely. The spacing and amount of post tensioning required would vary greatly, and is dependent on the specific bridge geometry and vertical force transfer needed between members. Once the precast members acting as forms are tied together, the reinforcing for the slab can be placed directly above. Railings, or the reinforcing for parapets, can be embedded where the slab will be cast or attached directly to the stay in place forms at this time. A small amount of forming is still needed on the sides, and at the ends of the precast beams to prevent the concrete from flowing over. The edge forms will also likely be used to support rails for striking off the slab surface after casting. The edge forms will likely be supported by the precast edge member. These small forms will be easily accessible and removable and should not have a significant impact on construction duration. Once the edge forms are in place, the last step would be to pour the concrete deck (see figure 1 2). 19

20 Figure 1 2, Stay in place precast forming members with cast in place slab The proposed system of precast stay in place formwork members with a composite slab will address all three of the concerns of traditional slab construction. In order they are: Speed of Construction Because there is no temporary formwork to put up or take down, significant time savings can be achieved by using this system. The precast formwork sections can be set the same day that they are delivered to the site, the shear keys could be grouted, and the end diaphragm and side forms might be set the same day. The concrete deck could be poured within days. Railings and other finishing work could be done within a few days. The slab concrete will need minimal strength to support the weight of people and machines working because of the contribution of the composite precast form member. Safety Worker safety is immediately increased substantially by the elimination of the need to build and subsequently remove the formwork from beneath the finished bridge. The surface 20

21 provided by the top flange of the formwork system provides workers with a stable and level working surface to place the reinforcing steel, without worrying about balancing on beams and twisting their ankle, or possibly falling into the water. Scheduling The system of stay in place forms does not eliminate the need for a concrete deck pour, it does however reduce the time that it will take. With the system, a significantly thinner deck is used, between 6 and 12 inches, with an average of 8 inches. Pouring an 8 inch deck takes significantly less time than a comparable 24 inch thick cast in place deck. Because the deck pour takes less time it becomes easier to schedule, and thus less susceptible to weather, or unforeseen events. Subsequent detailing work on the bridge can take place shortly after the pour because the slab concrete will need only minimal strength. The first step in developing this system will be to identify a precast section type that could be used to prove the concept, and run some preliminary calculations to determine if this concept is possible. Once this has been accomplished, a method would need to be created to generalize the findings to ensure that the system had no glaring flaws. Finally, based on what was found in the refined study, a new, improved section could be designed, if necessary, and verified through a similar process. This report covers the preliminary, and the refined development and analysis of a stay in place precast formwork system using standard PCI precast Double T sections. The goal of these analyses was to define a set of criteria for developing a new section to be used in a precast stay in place formwork system. This analysis required the development of a program in Excel to assist in the calculations, the development of this program is covered in the refined analysis section of this report. Once one set of criteria were found for the development of a new precast section in terms of limiting the stresses due to load in the section, this report shifts its focus to limiting the maintenance issues in the newly designed section. Additional criteria were defined to be used in a refined 21

22 development of the system. A new concrete section can then be designed to efficiently meet the criteria. The program developed for analyzing the Double T beams can be reconfigured for the new section. After developing a bridge solution, an analysis tool (computer program) for engineers to use in designing the system will be prepared for WisDOT. To make the information used in the research analysis program more accessible, to have the program function more as a design aid rather than a research tool, and to have in general a more user friendly functionality, modification will be made to the initial analysis program. The next chapter, Literature review, will summarize the sources used in this report, give a brief description of findings of the review, as well as its relevance to this report. Chapter 3 will outline the preliminary analysis that was done on precast Double T beams to obtain proof of concept. Also in Chapter 3, the analysis on Double T beams is refined by including more in depth calculations, and expanded to include more bridge configurations and deck thicknesses. Chapter 4 lists the specific problems found in adjacent Channel beam bridges, and then discusses a new design for Channel beams that addresses those issues. Chapter 5 offers conclusions to the report. Chapter 6 is a list of recommendations, based on the first part of the report, on topics for further discussion and research. 22

23 Chapter 2: Literature Review The use of precast materials in bridge construction is relatively common. The beams in many long span bridges are precast, prestressed, concrete I girders, and can support spans of more than 160 feet. To determine a baseline for where to begin our research, a review was performed that focused on two areas: the current use of precast structural elements in bridges, and the use of precast channel beams in bridges. Several relevant sources were found, and the results are summarized below. 2.1 Precast construction in Bridges: The current use of precast structural elements in bridges refers to any use of precast elements in a structural manor on a bridge, which could be as beams, driving surfaces, and substructure units. Two types of sources were found in this section, those that only referred to well established methods and section types, such as the Wisconsin Bridge Manual (WisDOT, 2010), and those that referred to more experimental sections such as the IBRC3 (Oliva et al., 2007) that studied precast concrete deck panels Wisconsin Bridge Manual The Wisconsin Bridge Manual has been developed by the Wisconsin Department of Transportation (WisDOT), Bureau of Structures, for the purpose of assisting design engineers and construction personnel in the design, plan preparation, and construction of bridges in the State of Wisconsin. The manual is intended to encourage the reader to conform to the standard methods developed by the Bureau of Structures, to perform design calculations, and layout their plan sets, which would reduce confusion between the consultants, and state engineers charged with approving a design. The Wisconsin Bridge Manual also offers recommendations for the economical use of materials, specifically the type of bridge most suitable for a given span range, see Figure

24 Figure 2 1, Economical span ranges for different bridge types (WisDOT, 2010) In addition to the recommended span ranges, and design calculations, the manual provides a complete list of the standardized precast sections available for use in Wisconsin bridges, along with their section properties, for use in design calculations. The Wisconsin Bridge Manual is a good source to find information on the current common design, and construction practices used in the State of Wisconsin. The Wisconsin Bridge Manual only deals with well understood, standardized construction methods, which makes its usefulness in developing new methods somewhat limited beyond a basic understanding of current practices The State of the Art of Precast/Prestressed Adjacent Member Bridges A report on adjacent member bridges (PCI, 2007) addresses the state of the art in design and construction of precast/prestressed adjacent member bridges, and particularly presents a discussion of current practices regarding box beam bridges. PCI sent surveys to the departments of transportation for the 50 states in the U.S., as well as the 13 territories and provinces of Canada. The objective of the survey was to discover who was using box beams, how they were using them, what issues they have had with them, and to offer the respondents an opportunity to share their experiences, good and bad with 24

25 box beams. Approximately two thirds of the respondents reported still using box beams in highway bridges. From the survey responses PCI compiled the report outlining the general characteristics of box beams, and adjacent member bridges, including their uses in railroad bridges, and composite versus non composite construction. This report attempted to summarize the practices of the respondents in as concise a manner as possible, and outline the current state of adjacent member bridges in the U.S. and Canada. Based on the survey responses a list of design recommendations was compiled, such as the use of non shrink, non metallic grout in shear keys, sandblasting shear keys prior to grouting, and the use of bearing pads to prevent rocking of the beams during construction. This report also serves as a good reference for general information on the current use of precast materials in bridge construction, but doesn t offer much in terms of recommendations for developing a new section or method Rapid bridge construction technology: precast elements for substructures A new report currently in a draft stage (Oliva et al., 2010) elaborates on the ongoing efforts of the University of Wisconsin Madison and WIsDOT to utilize precast technology for bridge substructures in Wisconsin as a rapid construction technique. The report cites two construction projects in Wisconsin, that used precast substructure units, one near Baldwin, in St. Croix county on USH 63, a second near Reynolds, in Buffalo county on WIS 25. The University was involved in the design of the substructures for both of the bridge projects, and monitored the construction of both the bridges. Based on the results of the two construction studies, a list of recommendations was compiled, and improvements to the design of the substructures were studied. This report makes several additional recommendations based on industry and agency feedback, as well as design analysis. The report also begins the process of designing standardized 25

26 precast substructure elements for use in bridge construction, and offers several examples that could be standardized, and used in most bridge applications. The process of standardizing the precast sections is the most important in terms of making the section cost effective, and this paper takes several steps towards accomplishing that task for precast substructure units. The report also serves as a good example of how an experimental application can gain acceptance, and lead to a better understanding by contractors, and lead to lower construction costs Precast deck panels Traditionally the WisDOT has used cast in place methods for the repair and replacement of highway bridge decks. A recent project, however, focused on the alternative of using precast full depth deck panels connected to the bridge girders with shear studs, and joined transversely using posttensioning (Oliva et al., 2007). The testing, and construction of a bridge using the panels is summarized in this report. The deck panels were tested to ensure adequate strength could be developed in the transverse connections to prevent the displacement of the panels relative to each other, in addition to testing the edges to ensure that cracking would not develop if a wheel load were applied directly to a panel edge. With the construction of a scale model bridge, the researchers were able to prove that the maximum spacing for shear studs allowed by AASHTO could be violated for a bridge using these panels, without reducing the performance of the supporting girders. To maintain traffic, the bridge that was selected was rehabilitated in stages, leaving half of it open for traffic as shown in Figure 2 2. Each precast panel was half the width of the bridge, creating a longitudinal joint for the full length of the bridge. Since traffic would be open on one half of the bridge 26

27 but not the other, the researchers tested the longitudinal joint to ensure it would perform if the panels shifted during the grouting, or while the grout was curing. Figure 2 2, Precast panel being placed, note that the bridge is still open for traffic on the right side (Oliva et al., 2007). This system could easily be adapted for use in an all precast bridge system, or could possibly be adapted for use in a stay in place formwork system The NEXT Beam: A Robust Double Tee Prestressed Beam The Precast/Prestressed Concrete Institute Northeast (PCINE) developed a new bridge girder called a NEXT beam, which stands for Northeast Extreme Tee (Baur et al., 2010). This beam was developed to replace more traditional adjacent member bridge sections such as box beams, for span ranges of 30 to 90 feet. Two variants of this beam have been developed. The Type F, or form NEXT beam has a 4 inch top flange and is intended to be used with a cast in place concrete deck. The Type D or deck NEXT beam has an 8 inch top flange which is intended to be used as the driving surface. The F type beams rely on the concrete deck to transfer load between beams, whereas the D type 27

28 beams have a reinforced longitudinal joint that is filled with non shrink grout that will transfer loads transversely. Published standards have been developed for this beam that address section properties, beam reinforcing, strand arrangements, diaphragm details, and sample parapet sections, as well as other design information. This beam has been used with success on one project in Maine, the York County Bridge over York River and is shown in Figure 2 3. NEXT beams were used to replace a 17 span, 510 foot bridge with a 7 span bridge of the same length. Figure 2 3, NEXT beam on a trailer (photo courtesy of Dailey Precast) The York River bridge included options for the contractors to use a standard Bulb Tee beam or to use the NEXT beam, 4 out of the 5 bidding contractors, including the winner, chose to use the NEXT beam because the construction cost was estimated to be lower. The NEXT beam is an example of a 28

29 practical precast bridge superstructure that is used in conjunction with a cast in place concrete deck, a very similar system to the one this study is focusing on. Tuckman et al. (2010) summarize the selection process that led to the use of the NEXT beam, for a project in New York State. The project that this beam was selected for the Queens Boulevard Bridge, over the Van Wyck Expressway. The design of this bridge calls for 114 NEXT beams to be placed side by side, and an 8 inch fully reinforced deck will be poured over them using lightweight concrete. There is no post tensioning called for in the design, nor are there any diaphragms, so the engineers are relying on the concrete deck to transfer loads between the beams. Construction is scheduled to begin in the Summer of Designers determined that the most economical construction process involved using a precast superstructure with a composite cast in place deck. Designers compared this option to several other traditional options, but ultimately chose to use the NEXT beam. This project, as designed is intending to use a precast girder system as formwork for a cast in place concrete deck, which when cured would act compositely with the girders. The shape of the section being used for this project is similar to the Double Tee beams that were explored in the early stages of this project. NEXT beams have one issue that make them impractical for the span ranges that this report is focusing on, they are heavy. With the smallest NEXT beam section weighing more than 1200 plf, their weight makes them impractical for all but the largest of bridge construction projects because a large crane would be required to lift the sections into place. 29

30 2.1.6 Super T Beams Connal (2010) describes the Super T Beam, a commonly used beam section in Australia. The Super T Beam is a hybrid design, combining elements of a U beam, and Double Tee beams. The beam is intended to be used for medium span bridges with lengths of approximately 80 to 130 feet. The beam is relatively large, with widths up to 10 feet, and depths up to 6 feet; but the beam itself is relatively light because of its minimized cross section as shown in Figure 2 4. Figure 2 4, Closed (Left), and Open (Right) Super T beams, (Connal, 2010) To increase manufacturer efficiency, reduce weight, and speed up quality assurance processes, the top flange between the two webs was removed. To form the deck, sacrificial formwork is placed in the spaces between webs which adds considerably to the dead weight during service. This beam can be shaped for cross slopes, by varying the thicknesses of the top flanges, and shows excellent torsional rigidity. The Super T Beam has been used extensively in Australia, as well as other nearby countries. This beam has been used successfully on several bridge projects in Australia, over the last ten years, and could be used on bridges in the United States. The beam allows for accelerated bridge construction and uses a similar method of construction to the stay in place formwork system being explored. Though an interesting section, this beam has a higher cost, and its unique shape make it 30

31 difficult to inspect tolerances. Super T beams are typically used for spans of 100 feet or longer, thus this beam does not appear appropriate for the short span ranges addressed in this project. 2.2 Precast Channel Beam Use in Bridges: Precast channel beams were used commonly from the mid 1950s through the mid 1970s, but fell out of use for several reasons, most notably maintenance issues. The following three references address these issues, comment on them individually, offer insight into each of the problems severity, and finally they offer recommendations to improve the design and use of precast channel beams. A first report attempted to draw a link between the load carrying capacity and deteriorated condition for precast channel beams in the State of Arkansas (Durham et al., 2003). The precast channels used for this study were all from a previously standardized plan for channel bridges, and were 19 ft. long, not prestressed, and contained no shear reinforcing. Samples for testing were drawn from bridges in Arkansas that had been scheduled for repair or replacement. The bridges that the samples were taken from had all been constructed between 1952 and The samples were subsequently categorized as being in good, average, poor, or poorrepaired condition, based on deterioration, cracking, and overall condition of the beam. The samples were then tested to determine their ultimate strengths in flexure using a four point loading test. Finally standardized tests were performed to determine the samples material strengths and properties. It was concluded that in general, the failure mode of the beams was not a function of the perceived condition of the beams, but similarities in load capacity were observed between bridges that were in similar conditions. The authors concluded that the lack of shear reinforcement controlled the ultimate strength for 90% of the beams tested. Authors noted that the most common form of deterioration present in these precast channels was spalled concrete and corrosion of the primary reinforcing in the webs. 31

32 Following on research from the paper by Durham above, a second paper attempted to correlate the level of deterioration observed in a standardized precast, non prestressed channel beam with no shear reinforcing, with its load capacity (Heymsfield et al., 2007). The authors research team conducted visual inspections of roughly 75% of the bridges that were built using the afore mentioned standard, and that were categorized as being in either poor or average condition by AASHTO standards. This was done to develop a current, bias free report on the current state of these bridges in Arkansas. The Authors then collected sample precast non prestressed beams with no shear reinforcing from replaced bridges in Arkansas State. The samples were again separated into one of four categories, being, good, average, poor, and poor repaired. These samples were subjected to four point bending tests to determine their ultimate load capacity. As in the previously mentioned paper, nearly all of the beams failed in shear after exhibiting ductile behavior. After the samples had failed standard testing methods were used to determine their reinforcing and concrete compressive strengths. As before, the authors were unable to draw a link between the perceived condition of the beam and its load capacity. They were however able to generate rating factors that when used with the as tested concrete compressive strength of the bridge, gives a conservative strength estimate. All the beams tested, regardless of the deterioration present, had higher load capacities than they were originally designed for. The load capacity of deteriorated precast channel bridges (PCB) in the State of Iowa were examined in another report (Wipf et al., 2006). The authors used a combination of field and laboratory tests to collect their data. 32

33 The authors first determined the bridges that would be field tested, the criteria were based on the extent of deterioration, whether the bridge was scheduled for replacement, and geographic location. Non destructive testing was used in the field using a loaded tandem axle dump truck along with a tractor semitrailer combination was used to apply Iowa legal limit loads. Strain gauges were applied at the midspans of each bridge and the data was collected with the trucks at various locations and speeds crossing the bridges. Second the authors took several panels from bridges that had been replaced and performed destructive laboratory testing on them. The panels were all tested in a four point bending test, and the failure mode for all panels was a compression failure in the top flange of the channel, preceded by excessive deflections. Finally the authors constructed a full scale laboratory test using four 25 foot long PCB panels from a bridge that had recently been replaced. Load tests were run on this section with three configurations of transverse connection, loose bolts, tight bolts, and tight bolts with grouted keyways. The bolts were 7/8 inch diameter, and connected the sections together through the webs. Load was applied at four different discrete locations on the sections, incrementally until failure occurred. The failure mode was observed as a longitudinal crack forming in the grouted keyways. Wipf et al. concluded that deterioration of the primary reinforcing and the associated spalling of the webs had little impact on the overall strength of the sections. The less common form of deterioration, deck delamination, had a large effect on load capacity. The hooked ends observed in the primary reinforcing reduced the need for bonding along the length of the span. The largest effect on load capacity observed in this report was the presence or absence of keyway connectors, which have a relatively large effect on the load fractions observed in any individual PCB panel. 33

34 The calculated load capacity of the laboratory constructed PCB bridge, with tight bolts and grouted keyways was nearly equal to the dead load weight of 3 HS20 44 trucks, this configuration was concluded to be the best for transverse load distribution. Additional capacity was observed in all bridges that had properly installed transverse connectors. Similarly the maximum observed load fractions in these bridge s panels was substantially lower than those without the connectors. Shear failure was never observed with the PCBs in this study, showing that when shear reinforcement is properly designed the sections will fail in flexure as intended. Deflections for all tested bridges were well within the AASHTO recommend limit of L/800. Wipf et al. do not recommend specific values for the number, size, or torque values of the mechanical connections. Additionally, they do not discuss the specific values associated with the grouted shear keys found on the Channel beams tested, only that in general they increase the capacity of the bridge. 34

35 Chapter 3: Preliminary System Investigation: Double Ts Initially, several section shapes were looked at for use in a system of stay in place forms for a new short span bridge system. These sections included: Box shapes: Box sections are commonly used throughout the U.S., including Wisconsin. These sections have already been standardized, and their construction use, and maintenance needs are well understood. Unfortunately, they are heavy in the span ranges that we looked at for this application, the prestressing can be fit easily into the webs, which makes the bottom flange in a box section essentially extra weight. At this stage minimizing the weight of the section was a priority. They are also difficult to form and cast according to Wisconsin precasters. After construction, inspection on the interior is very difficult. Inverted T beam: These sections have been used with some success in Minnesota and are being produced by a Wisconsin precaster, but were ruled out for further study for two reasons. The first reason is that the system is very heavy, and results in a bridge cross section that is very thick. Surveys of other states conducted as part of an ongoing NCHRP project (10 71) showed that an overall opinion was that box systems are more efficient. Secondly, bridges using inverted t beams have not yet been built for spans longer than 40 feet, thus the system was ruled out, as it was our intention to replace slab systems of up to 60 feet in length. U Beams: These systems are used in a number of states in the U.S.. The U beam system is essentially a box beam that has the top flange removed, the sections are placed, small sacrificial forms are placed across the webs, and the slab is poured, tying all of the sections together to form a composite box beam. Similar to the precast box beams, the U beam s bottom flange will not be necessary in the span ranges to be studied, and thus these sections were ruled out for further study. 35