Rating precast prestressed concrete bridges for shear

Final report; Oct. 2005-Dec. 2008.PDFTech ReportFHWA-OK-08-08ODOT Item Number 2186Prestressed concrete bridgesShear strengthStrength of materialsShear testsShear propertiesBuilding codesGirdersOklahomaOklahoma. Dept of TransportationPei, Jin-SongMartin, Randy D.Sandburg, Colby J.Kang, Thomas H.-K.University of Oklahoma. School of Civil Engineering and Environmental ScienceOklahoma. Dept. of Transportation. Planning & Research DivisionUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsNTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and PerformanceUS Transportation CollectionShear capacity of real-world prestressed concrete girders designed in the 1960\ue2\u20ac\u2122s and 1970\ue2\u20ac\u2122s is a concern becauseAASHTO Standard Specifications (AASHTO-STD) employed the quarter-point rule for shear design, which is lessconservative for shear demands than today's AASHTO LRFD.Shear tests were conducted on two full sized AASHTO Type II girders, one of which had been in service for nearlyforty years before being replaced due to irreparable damage.The comparison of nominal shear capacities according to the 11th Edition AASHTO-STD (1973), AASHTO LRFD(2004), ACI 318-08 including provisions for strut and tie models is carried out. By examining the ratios of nominal shearcapacity to demands for each code, considering all load and resistance factors, these code-to-code comparisons arebetter able to identify girders that may be deficient according to today's standards than a direct comparison of nominalcapacities alone. Experimental results for shear capacity of real-world girders are compared with the codes' nominalcapacities to check if the girders' are structurally sufficient. Additionally, LRFR is used to check the statistical safety forAASHTO inventory and legal loads.Preliminary results are presented on the estimation of effective prestressing force using static test data. Nominalshear capacity is particularly sensitive to effective prestressing force under current design codes, so it's important tohave accurate values when making calculations. In attempt to get more accurate results for effective prestressing force,span varying flexural stiffness is assumed. This assumption reflects that girders with long histories may be damaged,obvious or otherwise. Inverse problems are formulated where input and output are measured to determine systemproperties. Key challenges are discussed, and future work is identified.For a given girder, the ratio of nominal shear capacity to demands has generally decreased with newer codes.Girders having this ratio near one for the 11th Edition AASHTO-STD may be structurally deficient according to newercodes, however, LRFR results show that the girders in this study are safe for all AASHTO legal loads. Experimentalresults indicate that the girders\ue2\u20ac\u2122 actual capacity exceeds nominal capacity of current codes. Additional shear capacitytests should be performed on more real-world girders to get a more definitive conclusion