Alternative Support Systems for Cantilever - National Transportation ...

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prevented (2). It also assumes that the shear force will not control because of the greater flexural moment. These simplified design guidelines have not been included in the Support Structures. However, the information obtained on anchor bolts by the FDOT under contract number BD545 RPWO #54 entitled Anchor Embedment Requirements for Signal/Sign Structures indicates that concrete breakout is a problem even if confining reinforcement is provided. The reason for the report was several cantilever support structure failures in Florida during the 2004 hurricane season (See Figure 1-1 and Figure 1-2). The project predicted that the reason for the failure of the cantilever signal/sign foundations was the hurricane wind loads applied excessive torsional force on the foundation. The torsional force could be resolved into shear force acting on the anchors parallel to the edge of the foundation (See Figure 2-2). The shear force acting parallel to the edge was causing an anchor break-out phenomena that is described in Section D.5.2 of ACI 318-08 (5). Testing confirmed the prediction and an evaluation guideline as well as a CFRP wrap retrofit design guideline were detailed in the report. Clearly, the information gathered on the present system shows a need to rethink the design where anchors are concerned. While the NCHRP Reports are designed to modify the Supports Specifications for the current anchor bolt design, the purpose for this research is to identify an alternative method of transferring torsional and flexural moments from the monopole to the concrete shaft other than through an anchor bolt connection. The main concern addressed in this research project is the failure of concrete due to shear load on the anchor bolts parallel to the edge resulting from torsion on the anchor group. Therefore, a viable alternative will be one that avoids transferring shear through anchor bolts. Other concerns that have been identified are design practice and construction related. While these concerns are not the main objective of this research project, a new design may address 6
these problems. The concern with fatigue has also been identified and is addressed in other research projects and is not in the scope of this project (6; 7). Recommendations for future testing regarding fatigue concerns will be addressed in Chapter 6. 2.2 Alternative Foundation Systems The following alternatives are based upon the recommendations of the FDOT Report BD545 RPWO #54 (1). There are three cast-in-place concrete foundation alternatives and a drilled helical pipe alternative recommended from FDOT Report BD545 RPWO #54. Also included in this section is an embedded tapered section that was not included in the previous report but has been used in other DOT applications. 2.2.1 Steel Pipes with Plates Welded at Four Locations This foundation system would use an embedded pipe with stiffener plates. Figure 2-2 shows the configuration of this system (1). The stiffener plates will be attached symmetrically around the shaft of the steel pipe. The purpose of the stiffener plates would be to provide for the transfer of torsional loading between the steel pipe and the concrete by bearing on the concrete during twisting. The installation of this foundation would be relatively simple. After excavation for the concrete foundation, a reinforcement cage would be lowered into the excavation and aligned properly. The steel pipe and plate assembly would be lowered into the excavation and aligned. The concrete would then be poured into the excavation. Then the superstructure would be erected on top of the foundation (8). The superstructure could be aligned and leveled using a leveling nut detail shown in Figure 2-3. This connection would also eliminate problems with grout installation because none would be required. 7
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 and 20: CHAPTER 2 BACKGROUND The following
Page 21: information obtained in the late 19
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
Page 75 and 76:
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
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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
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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
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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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