Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web (2010) / Chapter Skim
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Of those who experienced longitudinal web cracking, 56% do not have any official criteria for classifying it. The others use a combination of crack width and crack length.
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This is because usually the direction of the end zone cracks is normal to the direction of shear cracks, which means that the end zone cracks will be subject to diagonal compressive stresses that help to close them up. Of the 36 who experienced end zone cracking, 31 used flame cutting of individual strands as their only method or one of their methods for strand release.
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Bayshore Concrete Products, Cape Charles, Virginia Designed to fail in flexure ' cif = 6,000 psi, 'cf = 8,500 psi Bottom: 38 straight 0.6 in., 270 ksi, low relaxation strands jacked to 43.9 kips Top: 14 straight 0.6 in., 270 ksi, low relaxation strands jacked to 43.9 kips 4-in. thick, 47-in.
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diameter, 270 ksi, low relaxation prestressing strands, stressed to 33.8 kips per strand. They also contained two partially stressed 0.5-in.
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diameter, 270 ksi, low relaxation prestressing strands in the bottom portion of the girder, jacked to 43.9 kips per strand. At the top of the web, each specimen contains 20 additional straight 0.6-in diameter prestressing strands and 4 "temporary" post-tension 0.6-in diameter strands.
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high bulb-T girders with thirtyeight 0.6-in. diameter, 270 ksi, low relaxation prestressing strands in the bottom flange and fourteen 0.6-in.
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End zone reinforcement details of WA1L (proposed)
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#6 (604) 4' 8" 8" 1 1/2" 2" 2'-0" 3 1/2" 3" 7" 4'-0" 3" 2" 3 1/2"2'-2" 2'-9" 8" 3 1/2"9" 2" 1'-6" Cross Section Figure 3.9.
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Cross section details of Florida specimens.
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End zone reinforcement details of FL1L (FL) and FL1R (modified FL)
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25 3'-0" 5'-5 1/4" 12" (2) C12 x 20.7 steel shapes jack locked in at 54k 1" threaded rods 3/4" rubber pad 3'-9" 7 1/4" 1'-0" 9' (2)
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An example of the load-deflection relationship is presented in Figure 3.23, which shows how the test data far exceeds the estimated capacities. The curve is for End WA1R that was designed using LRFD specifications.
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27 (a) Classical Flexural Cracking (b)
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The end designed using the AASHTO LRFD specifications experienced the least amount of cracking. See Figure 3.24.
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However, the end designed using the LRFD experienced slightly more cracking than the proposed method. The two ends designed from Florida details were similarly cracked as well.
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the girders to contain only half the amount of shear reinforcement requested, leading to the premature failure of the ends in shear. One girder was observed to contain half of the specified shear reinforcement when it burst in shear failure.
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(a) General View (b)
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Specified release strength was 6,500 psi and final strength was 8,000 psi. The bottom flange was reinforced with thirty-two 0.6-in., 270 ksi, low relaxation straight strands in two rows, and the web top was reinforced with twelve 0.6-in., 270 ksi, low relaxation straight strands.
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Both ends of the second specimen were provided with special end zone reinforcement, where the left end was designed using the LRFD Specifications (18) and the right end was designed using the proposed end zone reinforcement detail that is given in Section 3.7 of this report, as shown in Figure 3.34.
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For Specimen #2, the end designed according to the AASHTO LRFD specifications experienced more severe cracking than the end designed using the proposed detail. The lack of bottom plate and bottom flange reinforcement contributed to increased cracking near the bottom flange.
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the specimens were shipped to the structures laboratory in Omaha, Nebraska, for testing. 3.3.3 Preparation of the Test Specimens The team's objective was to find the most suitable method of testing the cracked and repaired ends for tensile capacity, and to compare them with the capacity of the uncracked zone in the mid-length of the specimen.
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Table 3.3 provides the description and properties of each specimen. 3.3.4 Test Results 3.3.4.1 Specimen S1L (No End Zone Reinforcement, Repaired)
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3.3.4.2 Specimen S1R (No End Zone Reinforcement, Unrepaired) The specimen failed at a load of 109 kips with a maximum deflection of 0.236 in.
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3.3.4.5 Specimen S2R (Proposed End Zone Reinforcement, Unrepaired) The specimen contained four pairs of #6 bars and three pairs of #4 bars, as shown in Figure 3.48(a)
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Specimen S2L (LRFD end zone reinforcement, repaired specimen)
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Specimen S2R (UNL end zone reinforcement unrepaired specimen)
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Appendix D provides technical information on the sealants. Figure 3.50 shows the cylinders after being sealed with the five sealants.
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Specimens coated in sealants.
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Figure 3.51. Specimens with metal shims.
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DegaDeck® TranspoSealate® DuralPrep® A.C. SilACT®Crack Width (in.)
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Specimens coated with Transpo Sealate®. 45 Crack Width (in.)
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Specimens coated with SilACT®.
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3.4.4 Durability Test, Stage III For Stage III of the Durability Test, the research team repeated the procedure used in Stage II for DegaDeck®, DuralPrep® A.C., and SilACT® for the crack widths 0.007-in., 0.016-in., 0.033-in., and 0.054-in. Transpo Sealate® T-70 was removed from the testing because it did not perform well with a vertical application, as shown in Stage II.
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Crack Width (in.) Control DegaDeck® DuralPrep® A.C.
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The control group absorbed the highest volume of water, as expected. The results in Tables 3.10 through 3.13 also show a relationship between the amount of water absorbed and the crack width.
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, and they all experienced end zone cracking. The crack patterns, as well as the crack widths and lengths, were fairly consistent from one girder to another.
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The top section of cracks was caused by the prestressing force of strands in the bottom flange. Likewise, the collection of cracks on the bottom was caused by the prestressing strands 51
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near the top of the girder. This arrangement of prestressing strands in both the top and bottom portions of a girder creates increased stress on the girder end, amplifying the likelihood of increased end zone cracking.
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All girders were lightweight concrete of 120 pcf with a 28-day concrete strength of 8 ksi. Half-inch diameter, 270 ksi, low relaxation pretensioned strands were used in all spans.
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54 Figure 3.62. Cross section of the bridge (eastbound and westbound approaches)
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Half-inch diameter, 270 ksi, low relaxation strands were used in all spans. The bridge is made of eight VA New BT girders spaced at 9 ft, 6 in.
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The cross section of the bridge consists of 6 girders at 7 ft, 4 in., which support 8-in.-thick cast-in-place concrete slab, as shown in Figure 3.70. All of the girders are 54 in.
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57 (a) Cross Section of the Bridge (b)
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Specification of crack width limits and "z" value limits for flexural design have been dropped from recent editions of the ACI-318 Building Code and from the AASHTO specifications. This was done due to evidence that flexural cracking, which is normal to the flexural reinforcement, does not correlate to reinforcement corrosion.
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The end zone reinforcement is designed for 20 ksi allowable stress to control the crack size and is located within h/4 from the end of the girder, where h is total girder depth. The following recommendations offer improvements to the AASHTO provisions, especially for cases with high 59
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The full-scale testing confirmed that, although the AASHTO LRFD requirements provided acceptable performance in all cases, the proposed details provided better performance. More significantly, the proposed details lend themselves to optimal bar detailing with minimized end zone reinforcement congestion.
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68-82. Tadros, M.K., Badie, S.S., and Tuan, C., "Evaluation and Repair Procedures for Precast/Prestressed Concrete Girders with Longitudinal Cracking in the Web," NCHRP 18-14, Contractor's Final Report, November 2009 (published as NCHRP Report 654)
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