Analysis of photographically measured crack development from shear tests on large bridge girders

摘要

>The angle, spacing, and width of shear cracks, and the loads at which shear cracks form, are all informative and externally measurable data for assessing the condition of structural concrete members. Unfortunately, there is little data on crack development from experiments on full-sized prestressed concrete bridge members. A large experimental research program was conducted on the shear behavior of 63-in.-deep and 72-in. deep (1600 mm and 1850 mm) bulb-tee girders that were simply supported and subjected to uniformly distributed loads. In this program, a crack-recording method, based on the principles of close-range digital photogrammetry, was used to create complete and accurate crack maps that tracked the development of cracking. It was observed in this research that the angle of diagonal cracking could be predicted using Mohr’s circle of stress. The research also found that the 17th edition of the American Association of State Highway and Transportation Officials’ Standard Specifications for Highway Bridges provided a reasonably accurate but somewhat conservative estimate of the web-shear racking load V_cw and a marginally overestimated value of the flexure-shear cracking load V_ci . The flexural cracking loads were reasonably predicted by the calculated cracking moment M_cr when the tensile cracking stress was taken as 6 sqrt(f_c'), where f_c' is the specified compressive strength of concrete. Based on test data, equations for computing the average spacing and maximum crack width of inclined cracks were proposed to overcome the deficiencies of current methods.