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

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Section Propertiesy b22.4 in.A 1120 in. 2I 403,000 in. 2w1.17 kip/ftFigure 2.49 Texas/Florida U-beam section properties (54 in. standard)Figure 2.50 Two- & three-strand-row design standards for 54-in. Texas U-beam(Ralls, Ybanez & Panak, 1993)84
Ralls, Ybanez and Panak (1993) state that finite element analyses for beams withsquare and skewed ends were conducted during design development. No details of theseanalyses were published, but “no unusual behavior” was observed (p. 27). One set ofTexas U-beams were examined for end-region cracking at transfer by Barrios (1994,previously described in Section 2.5.1), but no measurements of bursting or spallingstresses were made. Since their introduction, Texas U-beams have been tested forprestress losses by Gross and Burns (2000) and Tadros et al. (2003).End blocks are provided primarily as diaphragms: for adequate bearing area at thesupports and for lateral stability of the thin U-beam webs. The end blocks also serve todistribute internal forces. In square end regions, the end-block thickness is specified as 18in. minimum. For skewed end regions, two end-block designs are acceptable.The design typically chosen by fabricators consists of a triangular end block, itsinterior face normal to the beam direction (Figure 2.51-a). For large skews, the triangularend block is massive: for a 45° skew, nearly 8 ft. long. Large end blocks are vulnerable toexcessive internal curing temperatures and materials problems such as delayed ettringiteformation (DEF), which can cause extensive cracking (as shown in Section 1.1). DEFmay be triggered in concretes whose internal temperature exceeds 160°F (a softconversion of the 70°C limit). While the triangular end-block design may lead to largemasses of concrete at beam ends, the end block itself cannot be classified as “massconcrete” according to the TxDOT: a minimum dimension of 5 ft. in each direction isrequired for this designation per the TxDOT Standard Specifications (Section 420.4.14).The other alternative consists of a smaller end block with its interior face parallelto the skew (Figure 2.51-b). For skewed ends, end-block size is specified not as the endblockthickness, but as a longitudinal distance (Figure 2.52). The specified dimensionincreases as a function of skew: 18 in. minimum for skews under 30° and 24 in.85
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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
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 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 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
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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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