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

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spalling stresses were measured in transverse reinforcing bars within the end regions ofpretensioned concrete beams.4.3.1 Studies of Bursting & SpallingPast studies included in the transverse-bar bursting and spalling stress database,previously discussed in Section 2.4.2, are listed in Table 4.5.Table 4.5 Specimens examined in past studies of bursting and/or spalling stressesSource Year End-Region Type Number of Strain-Gage LinesMarshall & Mattock 1962 14 I-beams SingleItani & Galbraith 1986 3 I-beams Multiple (3 or 4)Tuan et al. * 2004 18 I- and 8 IT-beams SingleCrispino 2007 2 I-beams Multiple (4)O’Callaghan 2007 8 I-beams Multiple (3 or 4)* For additional information on the layout of transverse reinforcement in thesespecimens, Tadros, Yehia and Jongpitaksseel (2003) was consulted.While all these studies investigated stresses in transverse reinforcement at transferof prestress, they did so by slightly different methods. Notable among the methodologicaldifferences is the number of distinct strain-gage lines (along the beam length) used withinthe end region. In the case of beam end regions instrumented with all their strain gages ina single line, in order for the maximum transverse stress to be measured, a researcherwould need to know a priori the maximum-width crack locations in a pretensioned beamspecimen. When the inherent randomness of cracking in concrete is considered, itbecomes clear that the use of multiple lines of strain gages is more likely to yield highermeasurements of stress. The additional gages do not induce high stresses, but rather allowfor their measurement.168
Most studies of transverse-bar stresses at transfer have been conducted using asingle strain-gage line per specimen; these studies focused on spalling behavior. Studiesexamining bursting behavior have also included strain gages in the spalling zone. Assuch, a disparity exists between the database size for spalling and bursting behavior, asshown in Figure 4.16. Spalling behavior was measured for each beam end regionincluded in the database (57), bursting behavior for 30% of them (17 of 57 end regions).Specimens inwhich SpallingBehavior wasexaminedBurstingBehaviorFigure 4.16 Proportion of database in whichbursting & spalling behaviors were examinedBecause of differences between studies and randomness in material properties,high variation is expected between specimens. The primary purpose of the database is toexamine general trends in behavior, to assess the conservatism of existing designequations rather than develop new ones.4.3.2 Assembly of DatabaseFor specimens in the literature, section properties, material properties andprestressing strand patterns were readily available. From these properties, the top- andbottom-fiber stresses at prestress transfer could be determined. The transversereinforcement layout was also inputted in the database. For the U-beam specimens, all169
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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
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 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 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
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
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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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