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

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Figure 2.38 Typical gage locations (O’Callaghan, 2007)Cracking in the bursting zones of the Tx girder specimens was extensive(Figure 2.39). Typically a wide crack of 0.007 to 0.009 in. formed at the bottomweb/flange junction. This crack would begin a few inches into the beam and extend 30 to40 in. For 7 of the 8 end regions, the AASHTO stress limit (20 ksi) was exceeded at thisdepth: in most cases, by more than one bar. Bars stressed beyond 20 ksi were located 15to 30 in. into the beam. Near the beam end, where supplemental bundled reinforcementwas provided, no bar was observed to exceed the stress limit. Cracks also formed in theside of the flange, but these cracks were not as wide. One beam was instrumented at thisdepth, but the stresses found there were much lower than those at the bottom flange/webjunction.Cracking in the spalling zone was limited to one or two fine cracks extending afew inches into the beam. The most extensive spalling cracks were seen in the deepest62
eam (70 in. deep), confirming the correlation between eccentricity and spalling. Spallingstresses reached a maximum of approximately 10 ksi at mid-depth of this beam.Figure 2.39 Typical crack pattern with widths (O’Callaghan, 2007)For the beams of this study, bursting effects were clearly more significant thanspalling effects. These beams were more highly stressed than most others, and hadprestressing force applied close to the bottom flange/web junction. Perhaps mostsignificantly, though, the beams employed gages in the bursting zone, without which thesignificance of the bursting stresses could have been missed.In recognition of the high observed bursting stresses in the transversereinforcement, O’Callaghan recommended extending the bundled straight-barreinforcement out to one transfer length (36 in.) from the end of the beam, at whichlocation the stresses were judged to have diminished sufficiently. This recommendationwas adopted by the TxDOT in the design standards for the new beams (2007).63
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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
Page 27 and 28: As splitting stress is bond-related
Page 29 and 30: Figure 2.6 Effect of bursting & spa
Page 31 and 32: magnitude of the end-region transve
Page 33 and 34: FEA can readily output color maps o
Page 35 and 36: 2.3.1.3 Plastic Analysis of Beam En
Page 38 and 39: force can increase by 400% (Yettram
Page 40 and 41: 2.4 EXPERIMENTAL STUDIES OF BURSTIN
Page 42 and 43: The trial specimens included one 40
Page 44 and 45: mechanical gage (2 in. gage length)
Page 46 and 47: Bursting stress(normalized by prest
Page 48 and 49: proprietary post-tensioning anchors
Page 50 and 51: Though Marshall and Mattock placed
Page 52 and 53: ectangular beam” (p. 21). At high
Page 54 and 55: Most beams observed to crack did so
Page 56 and 57: The behavior of these beams was dom
Page 58 and 59: 2.4.2 Studies of End-Region Transve
Page 60 and 61: Figure 2.28 I-beams studied by Mars
Page 62 and 63: transverse forces compared to those
Page 64 and 65: (a) Actual spalling stress variatio
Page 66 and 67: stirrups in Gergely, Sozen and Sies
Page 68 and 69: 50% more reinforcement than require
Page 70 and 71: strength concrete, increasingly hig
Page 72 and 73: the reinforcement located within th
Page 74 and 75: Typical crack patterns for the beam
Page 76 and 77: “Very common”crack locationPred
Page 80 and 81: 2.4.2.7 Smith et al., 2008Most rece
Page 82 and 83: the provided transverse reinforceme
Page 84 and 85: Itani and Galbraith (1986) reported
Page 86 and 87: Figure 2.45 Confining reinforcement
Page 88 and 89: cracks located along lines of prest
Page 90 and 91: odies relevant to pretensioned conc
Page 92 and 93: than that in another shape. For thi
Page 94 and 95: Figure 2.47 Required splitting rein
Page 96 and 97: No attempt was made in the Tentativ
Page 98 and 99: 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
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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
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Figure 3.33 Installing the interior
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In order to use a pretensioning bed
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standardside-formprofilespecialtape
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Figure 3.41 Strands installed, tens
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Correspondence between the values o
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Figures 3.45 to 3.50 show the fabri
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Figure 3.49 Casting end block (and
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Figure 3.52 Detensioning by gradual
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CHAPTER 4Results & Discussion4.1 OV
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The strain time history for each ga
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1DNorthSouth1E18 ksi1C1C,E1D1521B1B
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Figure 4.4 Beam 1 prestress losses
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crack adjacent to this location was
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The temperatures in the end blocks
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Table 4.4 Beam 2 applied prestressi
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Figure 4.10 Beam 2 prestress losses
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terms of force distribution seems t
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limits were only exceeded at locati
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spalling stresses were measured in
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transverse reinforcement contained
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Based on Figure 4.18, the 4% Pi des
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Uniform and linearly-decreasing tra
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4.3.5 Contributing Factors to High
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stress ratio multiplied by a typica
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Figure 4.25 Relation between total
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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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Bursting and Spalling in Pretensioned U-Beams - Ferguson ...

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