Alternative Support Systems for Cantilever - National Transportation ...

More documents

Recommendations

Info

6.2.1 Introduction and Background 6.2 Recommendations for Future Testing Cantilever sign/signal structures typically have a single monopole supported by a cast-in- place foundation. As was mentioned in Chapter 2, the most common method of connecting the monopole to the foundation is through the use of anchor bolts attached to an annular plate welded to the monopole (See Figure 6-1). Although this connection is the most widely used, many studies in the past few years have reported that fatigue of the annular plate and anchor bolt configuration is a significant concern. Figure 6-1. Typical sign/signal base connection In the early 1990s it became evident that the Supports Specifications were not providing enough guidance on designing for vibration and fatigue. In response to the large problems with vibration and fatigue in cantilever signal/sign support structures, the National Cooperative Highway Research Program (NCHRP) initiated project 10-38 in 1993 (6). The information obtained from project 10-38 was published as NCHRP Report 412. The recommendations 76 Anchor bolt Welded base plate Monopole Concrete foundation
provided in NCHRP Report 412 were incorporated into the design provisions in the 2001 Supports Specifications. NCHRP Report 412 found that galloping, vortex shedding, natural wind gusts, and truck- induced wind gusts were the primary wind-loading mechanisms that were responsible for most vibration and fatigue-related stresses on cantilever structures (7). Based on this information, importance factors were assigned for each of the four wind-loading mechanisms on three fatigue categories. Report 412 describes, “Structures classified as Category I would present a high hazard in the event of failure and should be designed to resist rarely occurring wind loading and vibration phenomena” (7). The fatigue design approach recommended by NCHRP Report 412, and adopted by the 2001 Supports Specifications, was to design cantilever support structures to resist specified static wind loads, modified by the importance factors (3). The stresses obtained from the modified static wind loads would be designed to satisfy the requirements of their recommended detail categories for an infinite life fatigue design (3). Due to the lack of proper guidance on vibration and fatigue design in the Supports Specifications until the 2001 edition, many of the supports structures designed prior to the 2001 edition are now experiencing fatigue problems, particularly on the welded annular base plate and anchor bolt connection (3). Despite the fact that NCHRP Report 412 finally gave guidance to designers on fatigue design for cantilever signal/sign support structures, the rate of fatigue cracking and failure has continued and may have even increased (6). Because of this, NCHRP Project 10-38(2) was initiated to further address fatigue-resistant design of the cantilever support structures. The information obtained from Project 10-38(2) was published as NCHRP Report 469. NCHRP 77
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 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 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
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: testing, signifying that the predic
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
Page 119 and 120: Figure A-11. Dimensioned view of em
Page 121 and 122: STIFFENER DESIGN Calculation of Cap
Page 123 and 124: L breakout Concrete Breakout Equiva
Page 125 and 126: Abrg L⋅b 7 in 2 := = .5 Nsb 200
Page 127 and 128: β 1 f c Calculations Using ACI Str
Page 129 and 130: Determine Flexural Capacity of Roun
Page 131 and 132: DEVELOPMENT LENGTHS OF FLEXURAL REI
Page 133 and 134: Short Pipe Design Flexural Strength
Page 135 and 136: Long Pipe Design Flexural Strength
Page 137 and 138: Superstructure Assembly Strength -
Page 139 and 140: Weld Design Tn_blowout Vweld := Tor
Page 141 and 142: Check_Bolt_Shear := "Sufficient Str
Page 143 and 144:
Check Reinforcement No_Bars_Block_R
Page 145 and 146:
Tie-Down Design Block Properties Wi
Page 147 and 148:
Vmax Total Load that the Tie-down m
Page 149 and 150:
λpf := .38⋅ λpw := 3.76⋅ E F
Page 151 and 152:
Input and Properties Shaft Torsion
Page 153 and 154:
ψcV := 1.4 ψecV := 1.0 ψedV := 1
Page 155 and 156:
lbreakout := L + 2⋅1.5ca1 lbreako
Page 157 and 158:
Rn_weld := Throat⋅FW Rn_weld 11.1
Page 159 and 160:
⎛ ⎜ ⎜⎜⎜⎜⎜⎜⎜ 9.250
Page 161 and 162:
Flexural Capacity of T-Plates Using
Page 163 and 164:
FAILURE EQUATIONS Torsion Threshold
Page 165 and 166:
Required Length of Shaft Based on B
Page 167 and 168:
Design Axial Strength ϕcomp := .90
Page 169 and 170:
Design Axial Strength ϕcomp := .90
Page 171 and 172:
Zp := ⎛ ⎜ ⎝ bp tp⋅ 2 ⎞
Page 173 and 174:
Bolt Properties - D1" ASTM A325 Cen
Page 175 and 176:
CONCRETE BLOCK Concrete Block Desig
Page 177 and 178:
Check Shear Check_Shear_B := "Suffi
Page 179 and 180:
7'-4" 8" 5'-4" 8" 1'-3" Calculate s
Page 181 and 182:
Required Capacity of the Channel As
Page 183 and 184:
Check_Flange_Compact_Unit := "Compa
Page 185 and 186:
Rear of Shaft Face of Shaft Figure
Page 187 and 188:
Bolt slippage ends Predicted failur
Page 189 and 190:
APPENDIX D DESIGN GUIDELINES For th
Page 191 and 192:
The designer should then use this i
Page 193 and 194:
• Determine the angle required fo
Page 195 and 196:
Superstructure Base Connection Foun
Page 197 and 198:
1.5ca1 1.5ca1 Length of bearing are
Page 199 and 200:
Vu = 9.04 kip T .u = 198.88 ft·kip
Page 201 and 202:
Increase threaded rod diameter to 2
Page 203 and 204:
Embedded Pipe and Torsion Plates De
Page 205 and 206:
⎝ ⎠ Check_Breakout_Torsion := "
Page 207 and 208:
Lbreakout := tflex.plate + 2⋅1.5c
Page 209 and 210:
( ) .85 if fc < 4000psi β 1 f c .6
Page 211 and 212:
REFERENCES 1. Cook, R.A., and Halco
show all

Alternative Support Systems for Cantilever - National Transportation ...

Create successful ePaper yourself

Delete template?

Save as template?