Alternative Support Systems for Cantilever - National Transportation ...

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Figure 4-11. Fabricated pipe and plate apparatus one half of the size of the foundation that was investigated in a site visit for that project (1). However, based on the 30” diameter of the concrete shaft used in the previous design, it became apparent that the calculated torsional strength of the embedded pipe and plate apparatus would exceed the torsional strength of the lever arm utilized in the previous test. Therefore, the concrete shaft diameter was reduced to 26”. From there, the torsional and flexural capacity was determined using ACI 318-08 requirements, taking care to prevent failure before the concrete breakout or bearing strength was encountered and exceeded. A concrete strength of 5500 psi was utilized in the calculations, which is the strength indicated on FDOT standard drawings. 4.3.1 Concrete Shaft Diameter Design The starting point for the concrete shaft diameter was 30”, the same as that of the previous project. Using this concrete shaft diameter, the value of ca1 was determined to be approximately 5”. The calculated equivalent torsional concrete breakout strength was determined to be 296 kip- ft. The calculated equivalent torsional bearing strength was determined to be 446 kip-ft. The 52
torsional strength of the lever arm pipe was calculated to be only 359 kip-ft, which exceeds the concrete breakout strength and does not exceed the bearing strength. Since the estimated strength will likely lie between those values, the lever arm pipe does not provide enough strength. For the first test the concrete shaft diameter was reduced to 26” to decrease the concrete breakout and bearing strength to 212 kip-ft and 333 kip-ft, respectively. However, for the second test a 30” concrete shaft diameter was chosen because it was thought that the interaction of the flexural and torsional failure modes would reduce the overall strength of each failure mode and the increased value of ca1 would be compensated for. 4.3.2 Torsion Design The basic threshold torsional strength of the concrete shaft was calculated using ACI 318- 08 11.6.1(a) to be 18 kip-ft (5). The threshold torsional strength does not take into account the reinforcement present in the concrete shaft and therefore will likely be exceeded. Therefore, the nominal torsional strength, which does take into account reinforcement, was used as the design torsional strength. The cracking torsional strength was determined from ACI 318-08 R11.6.1 as 73 kip-ft (5). Since the concrete breakout and side-face blowout torsional strengths exceeded this value, it indicated that there would be torsional cracks in the concrete shaft before it fails. In order to calculate the nominal torsional strength of the concrete shaft, the reinforcement needed to be specified. The starting point was derived from the previous design, with the transverse hoop steel being comprised of #3 bars spaced at 2.5”. However, it became clear that the torsional strength with this reinforcement scheme, 191 kip-ft, was insufficient to exceed the concrete breakout or bearing strength of the section, 212 kip-ft or 333 kip-ft, respectively. Therefore, the hoop steel size was increased to #4 bars and the spacing decreased to 2” to yield a nominal torsional strength of 426 kip-ft, which exceeded the concrete breakout strength of the 53
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Report No. BDK75 977-04 Date: Augus
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Metric Conversion Table SYMBOL WHEN
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ALTERNATIVE SUPPORT SYSTEMS FOR CAN
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EXECUTIVE SUMMARY During the 2004 h
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CHAPTER TABLE OF CONTENTS 1 INTRODU
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Torsion Test Data .................
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LIST OF FIGURES Figure page Figure
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Figure 4-15. Arrangement of the LVD
Page 17 and 18: CHAPTER 1 INTRODUCTION This project
Page 19 and 20: CHAPTER 2 BACKGROUND The following
Page 21 and 22: information obtained in the late 19
Page 23 and 24: these problems. The concern with fa
Page 25 and 26: opposite side, see Figure 2-2 The s
Page 27 and 28: 2.2.4 Helical Pipes This option wou
Page 29 and 30: 2.3 Alternative Foundations from Ot
Page 31 and 32: Figure 2-10. Drilled concrete piles
Page 33 and 34: Figure 2-13. Grouted soil anchors G
Page 35 and 36: The pad and pier foundation, found
Page 37 and 38: comments and recommendations on pre
Page 39 and 40: CHAPTER 3 DESIGN IMPLICATIONS Based
Page 41 and 42: Figure 3-2. Differences between con
Page 43 and 44: 2 [ ] 2 2 ( r ) + 3. 25 ( r ) − (
Page 45 and 46: eakout surface for a single plate,
Page 47 and 48: strength of a headed anchor in tens
Page 49 and 50: Figure 3-9. Schematic of anticipate
Page 51 and 52: Vbfp l e tfp bfp f’c ca1 = the ba
Page 53 and 54: 3.2.2 Equivalent Side-Face Blowout
Page 55 and 56: computed. See Equation 3-14 below t
Page 57 and 58: One method to quantify the failure
Page 59 and 60: • An additional 12-4.5” long, 1
Page 61 and 62: Applied load Lever arm Figure 4-4.
Page 63 and 64: Figure 4-8. Isometric view of embed
Page 65 and 66: Flexural plate breakout area Torsio
Page 67: 4.2.4 Annular Base Plate Design The
Page 71 and 72: 4.4 Concrete Block and Tie-Down Des
Page 73 and 74: Figure 4-13. Arrangement of the LVD
Page 75 and 76: 4.7 Summary of Torsion and Flexure
Page 77 and 78: foundation displayed the predicted
Page 79 and 80: Figure 5-5. Specimen at failure 5.1
Page 81 and 82: Figure 5-7. Torsional moment and ro
Page 83 and 84: torsional 45 degree crack formation
Page 85 and 86: Figure 5-11. Widening of concrete b
Page 87 and 88: Failure cracks widen Bond loosens F
Page 89 and 90: Rear of shaft Figure 5-14. Load and
Page 91 and 92: testing, signifying that the predic
Page 93 and 94: provided in NCHRP Report 412 were i
Page 95 and 96: 6.2.2 Tapered Embedded Steel Pipe a
Page 97 and 98: Figure 6-3. FDOT Design Standards I
Page 99 and 100: This option provides a possible alt
Page 101 and 102: 6.2.5 Cast-in-Place Solid Concrete
Page 103 and 104: This option does have some disadvan
Page 105 and 106: Figure 6-9. Embedded steel pipe and
Page 107 and 108: However, the fillet welds are susce
Page 109 and 110: APPENDIX A TEST APPARATUS DRAWINGS
Page 111 and 112: Figure A-3. Dimensioned side elevat
Page 113 and 114: Figure A-5. Dimensioned drawings of
Page 115 and 116: Figure A-7. Dimensioned plan drawin
Page 117 and 118: Figure A-9. Dimensioned drawing of
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Figure A-11. Dimensioned view of em
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STIFFENER DESIGN Calculation of Cap
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L breakout Concrete Breakout Equiva
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Abrg L⋅b 7 in 2 := = .5 Nsb 200
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β 1 f c Calculations Using ACI Str
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Determine Flexural Capacity of Roun
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DEVELOPMENT LENGTHS OF FLEXURAL REI
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Short Pipe Design Flexural Strength
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Long Pipe Design Flexural Strength
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Superstructure Assembly Strength -
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Weld Design Tn_blowout Vweld := Tor
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Check_Bolt_Shear := "Sufficient Str
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Check Reinforcement No_Bars_Block_R
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Tie-Down Design Block Properties Wi
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Vmax Total Load that the Tie-down m
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λpf := .38⋅ λpw := 3.76⋅ E F
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Input and Properties Shaft Torsion
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ψcV := 1.4 ψecV := 1.0 ψedV := 1
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lbreakout := L + 2⋅1.5ca1 lbreako
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Rn_weld := Throat⋅FW Rn_weld 11.1
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⎛ ⎜ ⎜⎜⎜⎜⎜⎜⎜ 9.250
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Flexural Capacity of T-Plates Using
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FAILURE EQUATIONS Torsion Threshold
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Required Length of Shaft Based on B
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Design Axial Strength ϕcomp := .90
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Design Axial Strength ϕcomp := .90
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Zp := ⎛ ⎜ ⎝ bp tp⋅ 2 ⎞
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Bolt Properties - D1" ASTM A325 Cen
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CONCRETE BLOCK Concrete Block Desig
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Check Shear Check_Shear_B := "Suffi
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7'-4" 8" 5'-4" 8" 1'-3" Calculate s
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Required Capacity of the Channel As
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Check_Flange_Compact_Unit := "Compa
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Rear of Shaft Face of Shaft Figure
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Bolt slippage ends Predicted failur
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APPENDIX D DESIGN GUIDELINES For th
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The designer should then use this i
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• Determine the angle required fo
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Superstructure Base Connection Foun
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1.5ca1 1.5ca1 Length of bearing are
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Vu = 9.04 kip T .u = 198.88 ft·kip
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Increase threaded rod diameter to 2
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Embedded Pipe and Torsion Plates De
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⎝ ⎠ Check_Breakout_Torsion := "
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Lbreakout := tflex.plate + 2⋅1.5c
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( ) .85 if fc < 4000psi β 1 f c .6
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REFERENCES 1. Cook, R.A., and Halco
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