Bursting and Spalling in Pretensioned U-Beams - Ferguson ...

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In order to use a pretensioning bed designed for I-beams to fabricate U-beams,some modifications to the bed were required. The existing bulkheads at the stressing andfixed ends were neither wide enough nor contained an appropriate strand pattern forU-beams, so new plates were purchased to replace them.Figure 3.36 FSEL pretensioning bed (O’Callaghan, 2007)The new bulkheads were 12 in. thick, A36 steel plates measuring 91 by 52 in. insection. This thickness was deemed appropriate based on FEA suggesting that, at 12 in.thickness, the bulkhead would not yield during U-beam or box-beam fabrication. Theplates were drilled with ¾-in. through-holes to match the U-beam and box-beam strandpatterns. The stressing-end bulkhead was mounted on 8-in. angles, which rested on steelplates. Polytetrafluoroethylene (PTFE) sheets were epoxied on both sides of theangle/plate interface to allow the bulkhead to slide during stressing (Figure 3.37).134
U-beamstrandpatternFigure 3.37 Wider bulkhead in place at stressing endCustom U-beam steel forms were designed and fabricated by Hamilton Form. Theside forms differ from typical designs in that the custom forms are tapered (Figure 3.38)for better fit within the existing pretensioning bed. Steel beam headers were used;wooden headers are typically used at precast fabrication facilities. With the providedformwork, a variety of beams could be constructed, with square ends or skewed ends(20° or 45°) and with either end-block detail (triangular or skewed) at the skewed ends.The formwork set up for a beam with one square end (near end) and one 45°skewedend (far) is shown in Figure 3.39.135
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CopyrightbyDavid Andrew Dunkman2009
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Bursting and Spalling in Pretension
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Bursting and Spalling in Pretension
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2.4.2.3 Itani & Galbraith, 1986 ...
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4.2.2.4 Beam 1: Lateral-Bar Burstin
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List of TablesTable 2.1 Range of st
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Figure 2.25 Mechanical gage points
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Figure 3.30 Thermocouple placement
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CHAPTER 1Introduction1.1 IMPETUS FO
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At present, current end-region deta
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Figure 2.1 Severe cracking in a pre
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through use of tensioned, high-stre
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As splitting stress is bond-related
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Figure 2.6 Effect of bursting & spa
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magnitude of the end-region transve
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FEA can readily output color maps o
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2.3.1.3 Plastic Analysis of Beam En
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force can increase by 400% (Yettram
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2.4 EXPERIMENTAL STUDIES OF BURSTIN
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The trial specimens included one 40
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mechanical gage (2 in. gage length)
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Bursting stress(normalized by prest
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proprietary post-tensioning anchors
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Though Marshall and Mattock placed
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ectangular beam” (p. 21). At high
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Most beams observed to crack did so
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The behavior of these beams was dom
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2.4.2 Studies of End-Region Transve
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Figure 2.28 I-beams studied by Mars
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transverse forces compared to those
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(a) Actual spalling stress variatio
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stirrups in Gergely, Sozen and Sies
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50% more reinforcement than require
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strength concrete, increasingly hig
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the reinforcement located within th
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Typical crack patterns for the beam
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“Very common”crack locationPred
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Figure 2.38 Typical gage locations
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2.4.2.7 Smith et al., 2008Most rece
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the provided transverse reinforceme
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Itani and Galbraith (1986) reported
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Figure 2.45 Confining reinforcement
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cracks located along lines of prest
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odies relevant to pretensioned conc
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than that in another shape. For thi
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Figure 2.47 Required splitting rein
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No attempt was made in the Tentativ
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No citation is provided in the PCI
Page 100 and 101: Section Propertiesy b22.4 in.A 1120
Page 102 and 103: minimum for greater skews. For beam
Page 104 and 105: treatment (counting the transverse
Page 106 and 107: Pretensioned/post-tensioned beams h
Page 108 and 109: Figure 2.57 Harped strands in webs
Page 110 and 111: transversereinforcementwithin voidp
Page 112 and 113: 2.8 SUMMARYIn this chapter, literat
Page 114 and 115: 3.2.1.1 Linear and Nonlinear Stress
Page 116 and 117: Empirical expressions can be used t
Page 118 and 119: where: 0.021 = spalling force,
Page 120 and 121: 3.3 CONCRETE PROPERTIES3.3.1 Concre
Page 122 and 123: It was reasoned that the dimensiona
Page 124 and 125: Splitting tensile-strength testing
Page 126 and 127: For temperature-match curing, therm
Page 128 and 129: 3.4.1 Reinforcing-Bar Mechanical Te
Page 130 and 131: Grade 60 rebar yielded at 65 ksi an
Page 132 and 133: Equation 3.10where:ε1,2 = gage str
Page 134 and 135: Figure 3.17 Typical strand failure
Page 136 and 137: SouthNorth North120NorthSouthFigure
Page 138 and 139: Beam 1 also included an additional
Page 140 and 141: Figure 3.22 Strand strain-gage inst
Page 142 and 143: Figure 3.25 Interface board used to
Page 144 and 145: eam has a “hot spot” (measureme
Page 146 and 147: 3.6 BEAM FABRICATION3.6.1 Beam Cast
Page 148 and 149: Figure 3.33 Installing the interior
Page 152 and 153: standardside-formprofilespecialtape
Page 154 and 155: Figure 3.41 Strands installed, tens
Page 156 and 157: Correspondence between the values o
Page 158 and 159: Figures 3.45 to 3.50 show the fabri
Page 160 and 161: Figure 3.49 Casting end block (and
Page 162 and 163: Figure 3.52 Detensioning by gradual
Page 164 and 165: CHAPTER 4Results & Discussion4.1 OV
Page 166 and 167: The strain time history for each ga
Page 168 and 169: 1DNorthSouth1E18 ksi1C1C,E1D1521B1B
Page 170 and 171: Figure 4.4 Beam 1 prestress losses
Page 172 and 173: crack adjacent to this location was
Page 174 and 175: The temperatures in the end blocks
Page 176 and 177: Table 4.4 Beam 2 applied prestressi
Page 178 and 179: Figure 4.10 Beam 2 prestress losses
Page 180 and 181: terms of force distribution seems t
Page 182 and 183: limits were only exceeded at locati
Page 184 and 185: spalling stresses were measured in
Page 186 and 187: transverse reinforcement contained
Page 188 and 189: Based on Figure 4.18, the 4% Pi des
Page 190 and 191: Uniform and linearly-decreasing tra
Page 192 and 193: 4.3.5 Contributing Factors to High
Page 194 and 195: stress ratio multiplied by a typica
Page 196 and 197: Figure 4.25 Relation between total
Page 198 and 199: 4.4.1 Recommended Texas U-Beam Rein
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Figure 4.28 Proposed end-region det
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At present, AASHTO LRFD (2009) lack
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CHAPTER 5Conclusions5.1 SUMMARY OF
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tested at transfer and under shear
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APPENDIX ADatabase of Transverse-Ba
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194Figure A.1 U-beam with skewed en
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196Figure A.3 Shallow Texas bulb te
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198Figure A.5 Lightweight-concrete
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200Figure A.7 Washington bulb tee (
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202Figure A.9 Nebraska bulb tees an
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204Figure A.11 Nebraska bulb tees a
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206Figure A.13 Shallow I-beams
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where:= lower-bound concrete tensil
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B.3.4 Transmission Length (Clause 6
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Equation B.11where:= bursting force
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50High Web gage4030Max Moment heigh
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C.2 CONCRETE RELEASE STRENGTHA bott
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Table C.1 Specimen Design for Beams
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Table D.1 Beam 1 match-cured cylind
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D.1.2 Beam 28Release-Point Cylinder
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Cylinder Strength (ksi)131197Ambien
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D.2 REINFORCING-BAR MODULUS & STREN
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APPENDIX EEnd-Block Temperature Pro
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E.2 BEAM 2T max = 142°F∆T = 30°
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REFERENCESREFERENCED STANDARDSAmeri
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Fédération Internationale du Bét
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Davis, R.T.; Buckner, C.D. & Ozyild
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Lin, T.Y. & Burns, N.H. (1981), Des
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Stone, W.C. & Breen, J.E. (1984),
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VITADavid Andrew Dunkman was born 2
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