MAGNUM HELIX FOUNDATION TECHNICAL REFERENCE GUIDE PRODUCT TESTING REPORT August 30, 2001 by Howard A. Perko, P.E. Consulting Engineer for Magnum Piering, Inc.
TABLE OF CONTENTS INTRODUCTION... -2- SECTION 1. Helix Blade Compressive Strength... -3- SECTION 2. Coupling Tensile Strength... -6- SECTION 3. Coupling Torsional Strength... -9- SECTION 4. Bracket Mechanical Capacity... -12- SECTION 5. Bracket Concrete Anchor Capacity... -15- SECTION 6. Full-Scale Field Capacity... -18- INTRODUCTION This document contains an overview of the types of testing used by Magnum Piering, Inc. to determine capacities of its helix foundation products. Procedures and results of various field and laboratory tests are presented. Tests include helix blade compressive strength, coupling tensile strength, coupling torsional strength, bracket mechanical capacity, bracket concrete anchor capacity, and full-scale field capacity. Only a sample of the results from the first round of testing are provided. For quality assurance, Magnum Piering, Inc. periodically tests various components of its product line. For Magnum Piering, Inc., product testing and quality assurance is an ongoing effort. Contact Magnum Piering, Inc. headquarters for additional information and test results on any product. -2-
Theoretical Helix Blade Capacity SECTION 1. Helix Blade Compressive Strength Weld: Shaft Diameter, d = 3 in Shaft Circumference, % d = 9.42 in Minimum Weld Thickness, t w = 0.25 in x 2 (both sides) Minimum Steel Yield Strength, ) y = 36 ksi Approximate Steel Shear Strength, ) s = 0.7 x ) y Weld Strength = % d t w ) s = (9.42)(0.5)(36)(0.7) = 120 kips Blade Folding: Blade Diameter, D = 8 to 14 in Minimum Blade Thickness, t p = 3/8 in Blade Moment of Inertia, I = 1/12 L t p 3 Centroid of Half-Circle: 2D/3% Length of Fold*, L = ½ D + ½ d *accounts for opening in helix blade Distance from Fold to Centroid, = 2D/3% - ½ d Area of Half-Circle, A = 1/8 % D 2 Assume Uniform Folding Pressure, P Applied Bending Moment per Fold = P A Resisting Moment per Fold = ) y (½ t p ) / I Find Folding Pressure by M, j P = ) y (½ t p ) / I A Maximum Blade Folding Capacity, Q = 2 A P Results D L I A P Q 8 in 5.5 in 0.024 in 4 0.20 in 25 in 2 56 ksi 2,800 kips 10 in 6.5 in 0.029 in 4 0.62 in 39 in 2 10 ksi 780 kips 12 in 7.5 in 0.033 in 4 1.05 in 57 in 2 3.4 ksi 390 kips 14 in 8.5 in 0.037 in 4 1.47 in 77 in 2 1.6 ksi 250 kips Maximum Capacity is Theoretically Governed by Weld Shear and is = 120 kips -3-
Helix Blade Capacity Test Materials: Test Specimen helix blade welded to 1' long tubular shaft with blunt ends Load Fixture thick wall tube with diameter equal to 2/3 blade diameter, cut to receive helix blade, and fitted with center positioning rod Test Equipment: Test Location: 100+ kip Capacity Load Frame Cooperheat - MQS, Inc., Woodlawn, OH Test Procedures: 1. Using a caliper, measure, verify, and record helix plate and weld thicknesses 2. Position test specimen on load fixture 3. Place test specimen and load fixture in load frame 4. Photograph specimen and load frame prior to start of test 5. Mount displacement gage and record initial reading 6. Apply compressive load in 10 kip increments 7. Record displacement for each increment 8. Periodically photograph test specimen condition 9. Continue test until failure 10. Record maximum load applied 11. Plot load vs. displacement and establish yield point -4-
Helix Blade Capacity Test Results Blade at 50 kips Blade at 70 kips Blade at 90 kips Magnum Blade Test 120 100 Ultimate Strength of Blade = 103 kips 80 Yield Strength of Blade = 80 Load (kips) 60 40 20 Note: Deflection Measurements Include Deformation of Test Fixture 0 0 0.2 0.4 0.6 0.8 1 1.2 Deflection (in) Example Graphical Test Results Summary of Test Results Magnum Helix Foundation Type Yield Capacity Ultimate Cap. Standard and Heavy Duty 80 kips 103 kips Light Duty 40 kips 59 kips -5-
Theoretical Coupling Tensile Capacity SECTION 2. Coupling Tensile Strength Weld: Shaft Diameter, d = 3 in Shaft Circumference = %d = 9.42 in Minimum Weld Thickness, t w = 1/4 in Minimum Steel Yield Strength, ) y = 46 ksi Approximate Steel Shear Strength, ) s = 0.7 x ) y Weld Strength = %d t w ) s = (9.42)(1/4)(0.7)(46) = 76 kips Sleeve Shear: Length of Shear Path, l = 2 in x 2 paths x 2 sides of sleeve = 8 in Thickness of Sleeve*, t s = 0.25 in *(inner shaft has same thickness and same strength) Sleeve Strength = l t s ) s = (8)(0.25)(0.7)(46) = 64 kips Bolt Shear: Bolt Diameter, d b = 7/8 in Bolt Grade = SAE 5 Minimum Bolt Yield Strength, ) y = 92 ksi Approximate Bolt Shear Strength, ) s = 0.7 x ) y Bolt Area = 1/4 % d b 2 x 2 sides = 1.20 in 2 Bolt Strength = 1/4 % d b 2 )s = (1.20)(0.7)(92) = 77 kips Shaft Tension: Shaft Thickness, t = 0.25 in Minimum Steel Tensile Strength, ) t = 62 ksi Bolt Hole Diameter = 1 in Shaft Tension Strength = %d t ) t = 134 kips Reduction due to Bolt Holes = (1 in)(2 holes)/(9.42) = 21% Modified Shaft Tension = 105 kips Maximum coupling tensile strength is theoretically governed by sleeve shear and is = 64 kips -6-
Coupling Tensile Strength Test Materials: Test Specimen sections of helix shaft connected with external sleeve coupling and bolt Load Fixture solid bar stock welded to opposing ends of helix shaft sections and fitted with bolted connection Test Equipment: Test Location: 100+ kip Capacity Load Frame Cooperheat - MQS, Inc., Woodlawn, OH Test Procedures: 1. Using a caliper, measure, verify, and record thicknesses of coupling sleeve, bolt holes, and shaft diameter 2. Draw axial and circumferential grid lines on test specimen 3. Place test specimen with load fixtures in load frame 4. Photograph test specimen and load frame prior to start of test 5. Mount displacement gage and record initial reading 6. Apply tensile load in 10 kip increments 7. Record displacement for each increment 8. Periodically photograph condition of test specimen 9. Continue test until failure 10. Record maximum load applied 11. Plot load vs. displacement and establish yield point -7-
Coupling Tensile Test Results Coupling Failure Close Up #1 Coupling Failure Close Up #2 Magnum Connector Tension Test 70 60 Ultimate Strength of Connector =64 Kips Yield Strength of Connector =60 Kips 50 Load (kips) 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 1.2 Displacement (in) Example Graphical Test Results Magnum Helix Foundation Type Yield Capacity Ultimate Cap. Standard and Heavy Duty 60 kips 64 kips Light Duty 50 kips 59 kips -8-
Theoretical Coupling Torsional Capacity SECTION 3. Coupling Torsional Strength Light & Standard Duty Single-Sleeve Connectors Inner Shaft Torsional Shear: Shaft Outside Radius, b = 1.50 in Shaft Inside Radius, a = 1.25 in Standard, 1.375 in Light Shaft Circumference = 2%b = 9.42 in Minimum Steel Tensile Strength, ) t = 62 ksi Approximate Steel Ultimate Shear Strength, ) s = 0.7 x ) t Bolt Hole Diameter, d h = 1 in Polar Moment of Inertia, J = %(b 4 - a 4 )/2 J = 4.12 in 4 Standard, J = 2.34 in 4 Light Shaft Torsional Strength = ) s J/b = 0.7(62)(4.12)/(1.5) 120 kip-in Standard, 68 kip-in Light Reduction due to Bolt Holes = (1 in)(2 holes)/(9.42) = 21% Standard Coupling Torsional Strength = 94 kip-in = 7,800 ft-lbs Light Coupling Torsional Strength = 53 kip-in = 4,400 ft-lbs Ultimate coupling torsional strength is theoretically governed by inner shaft shear and is = 7,800 ft-lbs and 4,400 ft-lbs for the Standard and Light Duty Single-Sleeve Connectors, Respectively Heavy Duty Double-Sleeve Connector Torsional Shear Inner sleeve prevents shearing of inner shaft Consequently, the coupling is stronger than the shaft itself Thus, the torsional strength is given by Shaft Torsional Strength = 120 kip-in = 10,000 ft-lbs Ultimate coupling torsional strength is theoretically governed by total shaft shear and is = 10,000 ft-lbs for the Heavy Duty Double-Sleeve Connector -9-
Coupling Torsional Strength Test Materials: Test Specimen sections of helix shaft connected with external sleeve coupling and bolt Load Fixture floor mounted torque reaction plate Test Equipment: Test Location: 12,000 ft-lb Eskridge Hydraulic Torque Motor CASE Backhoe Magnum Shear Pin Torque Indicator Hydraulic Pressure Gauges Magnum Headquarters - West Chester, OH Test Procedures: Magnum Shear Pin Indicator Shear Pin Calibration 1. Calibrate shear pin indicator 2. Draw axial and circumferential grid lines on test specimen 3. Mount one end of test specimen to torque reaction plate and the other end to the shear pin indicator 4. Photograph both sides of test specimen prior to start of test 5. Insert appropriate number of shear pins for a torque equal to significantly less than the theoretical torque value 6. Gradually increase hydraulic pressure to torque motor until shear pin failure 7. Photograph and sketch any strains observed in test specimen 8. Record input and output hydraulic pressure and backhoe throttle settings 9. Increase number of shear pins by 1 10. Repeat steps 6 through 9 until coupling failure 11. Remove connector and disassemble on test bench 12. Observe, sketch, and photograph failure modes -10-
Coupling Torsion Test Results Example Disassembled Tested Connectors Torsion Test in Progress Double-Sleeve Connector Calibrated Strength of Test Pins = 550 ft-lbs Summary of Test Results Connector Type Number of Pins Ultimate Torsional Strength Magnum Light Duty (Single-Sleeve) Magnum Standard Duty (Single-Sleeve) Magnum Heavy Duty (Double-Sleeve) 7 3,900 ft-lbs 15 8,300 ft-lbs 19 10,000 ft-lbs -11-
Theoretical Bracket Mechanical Capacity SECTION 4. Bracket Mechanical Capacity The capacity of foundation brackets is a function of mechanical strength of bracket components, strength of concrete anchors, and integrity of the structure upon which the bracket is affixed. A structural engineer and/or an experienced installer must judge the integrity of an existing structure. This section regards tests conducted by Magnum Piering, Inc. to evaluate mechanical strength of bracket components. Weld Shear: Bracket Plate Dimensions = 21 in x 8 in x 3/8 in Length of welds, L = 8 in Minimum Weld Thickness, t w = 0.25 in x 2 (both sides) Minimum Steel Yield Strength, ) y = 36 ksi Approximate Steel Shear Strength, ) s = 0.7 x ) y Weld strength = L t w ) s = (8)(0.5)(0.7)(36) = 100 kips Inner Shaft Bolt-Hole Shear: Length of Shear Path, l = 1.7 in x 2 paths x 1 side = 3.4 in Thickness of Shaft, t s = 0.25 in Stnd, 0.13 in Light Minimum Steel Yield Strength, ) ys = 46 ksi Approximate Steel Shear Strength, ) ss = 0.7 x ) ys Shaft Strength = l t s ) ss x 2 bolt holes = following Standard Duty: (3.4)(0.25)(0.7)(46)(2) = 55 kips Light Duty: (3.4)(0.13)(0.7)(46)(2) = 28 kips Bolt Shear: Bolt Diameter, d b = 3/4 in Bolt Grade = SAE 8 Minimum Bolt Yield Strength, ) y = 130 ksi Approximate Bolt Shear Strength, ) s = 0.7 x ) y Bolt Area = 1/4 % d b 2 x 2 bolts = 0.88 in 2 Bolt Strength = 1/4 % d b 2 )s = (0.88)(0.7)(130) = 80 kips Bracket mechanical capacity is theoretically governed by inner shaft bolt-hole shear and is = 55 kips and 28 kips for double bolted standard and light duty shaft, respectively. -12-
Bracket Mechanical Capacity Testing Materials: Test Specimen Magnum plate bracket Load Fixture 12" thick, high-strength concrete slab-on-grade Test Equipment: Test Location: Twin 25 ton hydraulic power packs Horizontal Load Frame Vibrating wire load cell Optical displacement monitoring equipment Magnum Headquarters - West Chester, OH Test Procedures: 1. Mount bracket to concrete slab 2. Set-up horizontal load frame 3. Photograph mounted bracket and load frame configuration prior to start of test 4. Apply pressure in increments to the bracket using the hydraulic rams 5. Monitor bracket displacement and measure applied load 6. Record maximum capacity of bracket 7. Plot load vs. displacement and establish yield point 8. Sketch and photograph bracket failure modes -13-
Bracket Mechanical Capacity Test Results As anticipated, the failure mode for the plate bracket was observed to be shearing of the bolt holes. The strength of the bolted connection is approximately double for two bolts compared with one bolt. Sample results of the tests are given in the table below. Summary of Results Test Specimen Single-Bolt Strength Double-Bolt Strength Bracket Mounted to Light Duty Pier (1/8" Wall Shaft) Bracket Mounted to Standard Duty Pier (1/4" Wall Shaft) Bracket Mounted to Heavy Duty Pier (1/4" Wall Shaft) 14 kips 34 kips 25 kips 58 kips 25 kips 58 kips -14-
Theoretical Bracket Concrete Anchor Capacity SECTION 5. Bracket Concrete Anchor Capacity The capacity of foundation brackets is a function of mechanical strength of bracket components, strength of concrete anchors, and integrity of the structure upon which the bracket is affixed. A structural engineer and/or an experienced installer must judge the integrity of an existing structure. This section regards tests conducted by Magnum Piering, Inc. to evaluate the strength of concrete anchors used to attach a bracket to an existing structure. Quantity of anchors = 18 Anchor type = ½ in diam., 5- ½ in long, Zinc Plated Trubolt Carbon Steel Shear strength in 2,000 psi concrete = 7,240 lbs ea. Load factor to account for close spacing = 0.40 Load factor to account for edge distance = 0.20 Shear strength of anchors: top row = (6 anchors)(7.24 kips ea)(0.20 factor) = middle row = (6 anchors)(7.24 kips ea)(0.4 factor) = bottom row = neglect due to test geometry* = 9 kips 17 kips 0 kips Total = (9 + 17 + 0) = 26 kips *due to unbalanced moments, bottom row of anchors can be placed in tension, therefore shear contribution of bottom row should be neglected when structure lacks lateral and moment resistance -15-
Bracket Concrete Anchor Capacity Testing Materials: Test Specimen Magnum Heavy Duty bracket Load Fixture 8" thick 2,000 psi concrete field-test footing Test Equipment: Twin 25 ton hydraulic power packs Magnum Load Frame Vibrating wire load cell Optical displacement monitoring equipment Test Location: Magnum Headquarters - West Chester, OH Test Procedures: 1. Select test site and clear utilities 2. Layout pins for reaction piers in a 6'x6' square 3. Layout pin for test pier offset from center location 4. Cast concrete test footing so that edge is below hydraulic ram location 5. Cure concrete for prescribed time period 6. Install reaction piers and test pier to similar depths 7. Periodically record torque and depth during installation 8. Photograph installation of piers 9. Set-up load frame 10. Mount bracket over test pier and attach to concrete footing 11. Photograph mounted bracket and load frame configuration prior to start of test 12. Apply an initial pressure to the concrete footing using the hydraulic rams so that the pressure is approximately 1/3 the ultimate capacity of the bracket 13. Record vertical position of bracket under initial pressure 14. Apply lifting pressure to bracket until failure 15. Monitor bracket displacement during lifting pressure application 16. Record maximum capacity of bracket attached to concrete footing 17. Sketch and photograph bracket or concrete footing failure modes -16-
Bracket Concrete Anchor Capacity Test Results Close-Up of Concrete Failure Close-Up of Concrete Failure Measured concrete anchor capacity for example shown above = 20 kips Note: See table contained in Section 4 of Magnum Helix Foundation Technical Reference Guide for more information on connection of helix foundations to structures and more test results for the plate bracket. -17-
MAGNUM HELIX FOUNDATION INSTALLATION AND FIELD TEST February 2, 2001 SECTION 6. Full-Scale Field Capacity TEST PIER DESCRIPTION 3-Inch O.D. Shaft 8" and 12" Helical Blades on 5' Lead 2-5' Extensions Final Depth = 15 feet Magnum Moment Balanced Blade Style REACTION PIER DESCRIPTION 3-Inch O.D. Shaft 8" and 12" Helical Blades on 5' Lead 2-5' Extensions Final Depths = 11-14 feet Different Orientations of Circular Blades and One Magnum Blade Style SITE The test was conducted at the North edge of the parking lot at Dwyer Companies construction yard in West Chester, Ohio. INSTALLATION The helix piers were installed using a CAT Backhoe with Eskridge 12,000 ft-lb Hydraulic Torque Motor Test Pier Installation Torque (Based on Hydraulic Pressure) Depth (ft) Input Pressure (psi) Approximate Torque (ft-lbs) 1 200 500 4 1100 4000 6 1000 3500 9 1100 3700 11 1200 4200 14 1700 6000 15 1100 3700 PREDICTED PERFORMANCE Final Installation Torque = 3700 ft-lbs Theoretical Capacity/Torque Ratio = 8 ft -1 Theoretical Ultimate Capacity = 8 x 3700 = 29,600 lbs -18-
FULL-SCALE FIELD TEST RESULTS Setting-up Magnum Load Frame Bearing Capacity Test in Progress SUMMARY OF TEST RESULTS Measured Ultimate Capacity in Bearing = 35 kips Measured Ultimate Capacity in Tension = 30 kips 40 Magnum Full-Scale Field Load Test 35 30 Applied Load (kips) 25 20 15 10 5 0 0-0.5-1 -1.5-2 -2.5 Displacement (in) -19-