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Title: Inelastic Shear Distribution in Prestressed Concrete Girder Bridges

Author(s): Ben Dymond

Publication: Web Session



Appears on pages(s):



Date: 3/24/2019

American Association of State Highway and Transportation Officials (AASHTO) requirements for the consideration of shear in prestressed concrete girders have changed considerably over the last 50 years. Some prestressed concrete bridge girders designed using older specifications may rate poorly for shear when load rated with current methods. AASHTO allows the shear rating to be neglected if the bridges do not show signs of distress under normal traffic conditions. The primary goal of this research was to determine whether linear elastic shear distribution principles are conservative for load rating at ultimate capacity. Within this investigation, a secondary goal was to determine if initial web-shear cracking was visible in an unloaded state. Two tests on a full-scale prestressed concrete girder laboratory bridge were conducted (one with an end diaphragm and one without) to determine if an interior girder shed shear force to adjacent girders as the beam carrying the most load transitioned from uncracked to cracked to ultimate behavior. The end diaphragm acted to slightly increase the amount of shear in the loaded beam, but the end diaphragm did not have a significant effect on the failure load or shear distribution near failure. Inelastic shear distribution results indicated that the girder carrying the most load redistributed shear to the other girders as the loaded girder lost stiffness due to web-shear and flexural cracking. The redistribution of shear continued to increase as the damaged girder stiffness decreased. Use of linear elastic load distribution factors was conservative considering shear distribution at ultimate capacity. Furthermore, initial web-shear cracks were visible in an unloaded state when the stirrup spacing was 24 in. (61 cm), but web-shear cracks were not visible in an unloaded state when the stirrup spacing was 8 in. (20 cm).