One-way shear strength of large footings

Results are presented from 23 shear tests on 1-m deep specimens made of low-strength concrete and tested with shear span-to-effective depth ratios between 1.4 and 2.4 to obtain information that is relevant to the one-way shear strength of footings. Based on these results and other test results from the literature, an amendment is proposed to the 1994 Canadian concrete code one-way shear strength provisions for members without stirrups. In order to account for the beneficial effects of strut-action in deep members such as footings, it is proposed that the reduction in shear strength due to size not be applied to sections located less than 2d from the face of a support or concentrated load when the applied shear introduces compression into the member. The strut-and-tie provisions in the Canadian code, which has stress limits to prevent concrete compression failures, normally should be used to design deep members, but should not be used to design members without minimum stirrups. The proposed revision eliminates the unnecessary increase in footing depths that is needed to meet the one-way shear strength requirements of the 1994 Canadian concrete code.