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

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treatment (counting the transverse reinforcement near the center of the end block) iswithin the intent of the AASHTO LRFD is discussed further in Section 2.7.5.2.7.2 Florida U-BeamAdapted from the Texas standard, the U-beam has existed as a standard section inFlorida since the mid-1990s. At present four depths have been standardized (rangingfrom 48 to 72 in), including a 54-in. section identical in cross section to the Texas U54(show previously in Figure 2.49). Up to three rows of 26 strands can be placed in thebottom flange.End-region transverse reinforcement within the webs of the Florida U-beam ismore substantial than that in the Texas U-beam, with one #5 bar in each web at 3 in.spacing. The larger bar size and the closer spacing combine for an 85% increase fortransverse web-reinforcement in the beam end region compared with the Texas standard.Transverse reinforcement within the void-projected area of the end block issimilar to the Texas U-beam (Figure 2.53), with three layers of transverse bars: one eachat the outer (6 – #5) and inner faces (6 – #4) of the end block, and one between (6 – #5).A recent Florida DOT design bulletin sets limits on the bonded prestressing forceat pretensioned beam ends in order to control end-region cracking: the limits for U-beamswere set such that the transverse-bar design stress is 18 ksi (Nickas, 2004). This designstress is 10% less than that prescribed by AASHTO.At skewed ends, the end blocks used in Florida U-beams are always skewed (likeFigure 2.51-b), never triangular (Figure 2.51-a). The maximum allowable skew is muchless than allowed in Texas: 15° vs. 45°. End blocks are 18 in. thick, regardless of thebeam skew.88
2.7.3 Colorado U-GirderThe Colorado U-girder (Figure 2.54) was developed in the late 1990s for beams48 to 84 in. deep. Webs are sloped similarly to Texas/Florida beams, but top flanges arewider. A major difference between the Colorado and Texas/Florida standard is the lack ofan end block in the Colorado beam. Diaphragms are provided at various locations in thebeam, but at the beam end, the diaphragms are cast integrally with the bridge bent caps(cast in place). The top flanges for the Colorado beam, shown in Figure 2.54 as muchwider than those of the Texas/Florida standard, are actually of variable width dependenton beam spacing. (The widest permissible flanges are depicted in the figure.)Section Propertiesy b23.3 in.A 1195 in. 2I 380,000 in. 2w1.25 kip/ftFigure 2.54 Colorado U-girder section properties(48 in. deep, pretensioned standard)Colorado beams may be solely pretensioned or prestressed by a combination ofpretensioning and post-tensioning. If the pretensioned/post-tensioned option is chosen, awider web width is used (7.5 or 10 in.) to accommodate the post-tensioning duct;otherwise the beam webs are similar to the Texas/Florida section (5 in. thick).89
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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
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 78 and 79: Figure 2.38 Typical gage locations
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 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 150 and 151: In order to use a pretensioning bed
Page 152 and 153: 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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