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

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4.4.1 Recommended Texas U-Beam Reinforcing Details for TestingOne of the tasks in TxDOT Research Project 5831 was to recommend better endregionreinforcement details and to test these new details, as discussed in Section 1.1. Asthe project is only partly complete (Year 2 of 5), the details here recommended are of apreliminary nature and may undergo changes as testing continues in the coming months.The high transverse-bar stresses measured in both the bursting (Beam 2) andspalling zones (Beams 1 and 2), coupled with the inadequate web reinforcementcompared to other DOT standards, lead to the recommendation to provide additionaltransverse reinforcement in the U-beam standard design. The addition of thisreinforcement would help to control cracking at transfer of prestress, and could improveshear performance.An end-region detail presently under consideration is shown in Figure 4.27. Thetwo main components of this detail are additional transverse reinforcement, bundled withthe existing steel and installed at the interior face of the web; and thickened webs in theend region. While the web would be thickened primarily for shear purposes, theadditional concrete could decrease average transverse-bar stresses slightly by carrying aportion of the transverse stress between cracks.182
Full-heighttransverse bar,bundled withexisting R barThickened web inend regionPartial-heighttransverse bar atinterior face of webFigure 4.27 Proposed end-region detail (cross-section)The additional steel should be extended through the spalling zone (near the beamend) into the bursting zone, as shown in Figure 4.28. While the maximum burstingstresses were measured closer to 20 in. into the beam (two-thirds of the transfer length forthese specimens), it is conservatively recommended to extend the supplementalreinforcement out to one transfer length from the beam end. As 0.6-in strand is the largestcommonly used in Texas beams, it would be safe to use 36 in. as the end-reinforcing zonebased on bursting and spalling considerations. Shear demands, however, may require thespecial detailing to be extended further into the beam.Lateral end-region reinforcement in the bottom flange, though substantially lessthan that required by AASHTO LRFD (Section 2.7.1), was not observed to experiencehigh stresses, nor was severe longitudinal cracking noted in the bottom flange. As such,no supplemental lateral reinforcement is recommended based on bursting and spallingconsiderations.183
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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
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Section Propertiesy b22.4 in.A 1120
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minimum for greater skews. For beam
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treatment (counting the transverse
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Pretensioned/post-tensioned beams h
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Figure 2.57 Harped strands in webs
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transversereinforcementwithin voidp
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2.8 SUMMARYIn this chapter, literat
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3.2.1.1 Linear and Nonlinear Stress
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Empirical expressions can be used t
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where: 0.021 = spalling force,
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3.3 CONCRETE PROPERTIES3.3.1 Concre
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It was reasoned that the dimensiona
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Splitting tensile-strength testing
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For temperature-match curing, therm
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3.4.1 Reinforcing-Bar Mechanical Te
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Grade 60 rebar yielded at 65 ksi an
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Equation 3.10where:ε1,2 = gage str
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Figure 3.17 Typical strand failure
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SouthNorth North120NorthSouthFigure
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Beam 1 also included an additional
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Figure 3.22 Strand strain-gage inst
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Figure 3.25 Interface board used to
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eam has a “hot spot” (measureme
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3.6 BEAM FABRICATION3.6.1 Beam Cast
Page 148 and 149: Figure 3.33 Installing the interior
Page 150 and 151: In order to use a pretensioning bed
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 200 and 201: Figure 4.28 Proposed end-region det
Page 202 and 203: At present, AASHTO LRFD (2009) lack
Page 204 and 205: CHAPTER 5Conclusions5.1 SUMMARY OF
Page 206 and 207: tested at transfer and under shear
Page 208 and 209: APPENDIX ADatabase of Transverse-Ba
Page 210 and 211: 194Figure A.1 U-beam with skewed en
Page 212 and 213: 196Figure A.3 Shallow Texas bulb te
Page 214 and 215: 198Figure A.5 Lightweight-concrete
Page 216 and 217: 200Figure A.7 Washington bulb tee (
Page 218 and 219: 202Figure A.9 Nebraska bulb tees an
Page 220 and 221: 204Figure A.11 Nebraska bulb tees a
Page 222 and 223: 206Figure A.13 Shallow I-beams
Page 224 and 225: where:= lower-bound concrete tensil
Page 226 and 227: B.3.4 Transmission Length (Clause 6
Page 228 and 229: Equation B.11where:= bursting force
Page 230 and 231: 50High Web gage4030Max Moment heigh
Page 232 and 233: C.2 CONCRETE RELEASE STRENGTHA bott
Page 234 and 235: Table C.1 Specimen Design for Beams
Page 236 and 237: Table D.1 Beam 1 match-cured cylind
Page 238 and 239: D.1.2 Beam 28Release-Point Cylinder
Page 240 and 241: Cylinder Strength (ksi)131197Ambien
Page 242 and 243: D.2 REINFORCING-BAR MODULUS & STREN
Page 244 and 245: APPENDIX EEnd-Block Temperature Pro
Page 246 and 247: 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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