Design rules for shear in concrete bridges have varied over the years. Currently, the design of prestressed concrete bridge beams is carried out according to BS 5400: Part 4 which requires a minimum amount of shear reinforcement to be present in the webs in the form of links. The Department of Transport Standard, BD 44/90, relaxes this requirement for the assessment of existing bridges. The present series of tests was carried out before this standard was issued. A number of pre-tensioned I-beams wihout links were recovered from a 30-year-old M63 underbridge during demolition and tested to establish their shear strength. The results indicate that the beams possessed reserves of strength because of conservative assumptions in the method of calculation in BS 5400: Part 4, and the high strength of the concrete. The beams showed no ill effects from the absence of links, nor from 30 years of traffic. The test results support the case for relaxing the requirement for minimum links in assessment. Further tests on damaged and repaired beams indicated that their strength compared favourably with the strength of the intact beams, although precracked webs may present a problem. (A)
Abstract