Alternative Support Systems for Cantilever - National Transportation ...

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These most common foundation systems utilize anchor bolts to transfer torsional and flexural moments from the monopole to the support structure. Figure 2-1 depicts how the torsional and flexural moments are transferred in the current anchor bolt design. American Association of State and Highway Transportation Officials(AASHTO) provides guidance in their Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (Supports Specifications) for the design of signal/sign supports (3). Many problems have been detected with the signal/sign support structures and the following will cover the history and problems associated with cantilever signal/signs and their support structures. Applied Torsion Torsion Resolved into Shear Parallel to the Edge Concrete Cracking Figure 2-1. How torsional and flexural moments are transferred using anchor bolts (1) In 1994, the National Cooperative Highway Research Program (NCHRP) initiated Project 17-10 at the University of Alabama at Birmingham (4). The scope of Project 17-10 was to update all aspects, excluding vibration and fatigue, of the 1994 Supports Specifications (4). One element of the Supports Specifications that required immediate updating was the information on anchorage systems. The 1994 Supports Specifications’ information on anchor bolts was based on 4 Applied Flexure Flexure Resolved into Tension and Compression
information obtained in the late 1960s and late 1970s (4). The updated anchor bolt information contained in Report 411 included an Appendix C which addressed minimum embedment length of headed cast-in-place anchor bolts, effect of edge distance, and the effect of spacing between anchor bolts (4). However, Appendix C of NCHRP Report 411 was not included in the 2001 Supports Specifications (2). A second phase of Project 17-10 was initiated and published as NCHRP Report 494 in 2003. NCHRP Report 494 addressed additional updates to the Supports Specifications. In NCHRP Report 494, further information is provided regarding anchorage to concrete. In addition to restating the information in Appendix C of NCHRP Report 411, NCHRP Report 494 provided a simplified design method for design of anchorage to concrete based on the then recently added Appendix D to American Concrete Institute (ACI) 318-02 (2). The simplified design method for anchorage required the following conditions be met (2): • Anchor bolts be hooked or headed • Foundations have vertical reinforcing steel and vertical confinement, with anchor bolts placed inside of the reinforcement • Foundation reinforcing steel is uncoated • If hooked anchor bolts are used, the length of the hook is at least 4.5 times the anchor bolt diameter The simplified design method would design the diameter and bearing area of a headed anchor or the required anchor bolt diameter of a hooked anchor as well as the bolt length so that the failure plane would intersect the foundation’s reinforcing steel below the point at which the reinforcing steel is fully developed (2). The transfer of flexural moment is thoroughly addressed in the simplified design method through its treatment of tension. While the simplified method does well to address anchor bearing on concrete, it makes the assumption that if confining reinforcement is provided, failure by concrete breakout and concrete side-face blowout can be 5
Page 1 and 2: Report No. BDK75 977-04 Date: Augus
Page 3 and 4: Metric Conversion Table SYMBOL WHEN
Page 5 and 6: ALTERNATIVE SUPPORT SYSTEMS FOR CAN
Page 7 and 8: EXECUTIVE SUMMARY During the 2004 h
Page 9 and 10: CHAPTER TABLE OF CONTENTS 1 INTRODU
Page 11 and 12: Torsion Test Data .................
Page 13 and 14: LIST OF FIGURES Figure page Figure
Page 15 and 16: Figure 4-15. Arrangement of the LVD
Page 17 and 18: CHAPTER 1 INTRODUCTION This project
Page 19: CHAPTER 2 BACKGROUND The following
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 and 68: 4.2.4 Annular Base Plate Design The
Page 69 and 70: torsional strength of the lever arm
Page 71 and 72:
4.4 Concrete Block and Tie-Down Des
Page 73 and 74:
Figure 4-13. Arrangement of the LVD
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4.7 Summary of Torsion and Flexure
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foundation displayed the predicted
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Figure 5-5. Specimen at failure 5.1
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Figure 5-7. Torsional moment and ro
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torsional 45 degree crack formation
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Figure 5-11. Widening of concrete b
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Failure cracks widen Bond loosens F
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Rear of shaft Figure 5-14. Load and
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testing, signifying that the predic
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provided in NCHRP Report 412 were i
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6.2.2 Tapered Embedded Steel Pipe a
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Figure 6-3. FDOT Design Standards I
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This option provides a possible alt
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6.2.5 Cast-in-Place Solid Concrete
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This option does have some disadvan
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Figure 6-9. Embedded steel pipe and
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However, the fillet welds are susce
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APPENDIX A TEST APPARATUS DRAWINGS
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Figure A-3. Dimensioned side elevat
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Figure A-5. Dimensioned drawings of
Page 115 and 116:
Figure A-7. Dimensioned plan drawin
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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
Page 127 and 128:
β 1 f c Calculations Using ACI Str
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Determine Flexural Capacity of Roun
Page 131 and 132:
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
Page 201 and 202:
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
Page 211 and 212:
REFERENCES 1. Cook, R.A., and Halco
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