Shear transfer resistance in high-strength concrete girders

As part of a national research programme, a series of 18 shear-friction tests and 20 beam shear tests were conducted. The concrete compressive strength in these test specimens ranged from 92 to 121 MPa and the level of transverse reinforcement ranged from a code-specified minimum to very heavy. This research was conducted with the aim of generating the experimental data that were needed for the extension of the American Association of State Highway and Transportation Officials load and resistance factor design (AASHTO LRFD) bridge design specifications to high-strength concrete; these specifications currently limit the compressive strength of concrete that may be used in shear design to 70 MPa. An important component of the research programme was the evaluation and comparison of interface shear-friction demand and capacity. This was because the concrete contribution to shear resistance in the LRFD specifications is limited by shear slip resistance along cracks. The results of the shear-friction tests indicate that the experimentally measured resistance is typically larger than that used in the derivation of the LRFD shear provisions. However, it was also found that the demand on shear cracks in the large 1·85 m deep bridge girders could be considerably larger than that assumed in the derivation of this shear design procedure.