Design for Shear Based on Loading Conditions

Tests show that shear failure can occur in reinforced concrete (RC) beams at levels of load that are lower than indicated by ACI 318-05. This article reports on a database of 1200 tests, compiled to examine the effects of loading type and position of the load on the shear strength of reinforced concrete beams. The authors also conducted 24 additional tests to examine the differences in shear response due to concentrated and uniform loads where data were lacking. Their results indicated that shear strength can be affected by the type of loading. A significant number of beams subjected to concentrated loads applied between 2d and 6d from the face of the support failed at loads below the nominal strengths calculated using current design provisions. Based on these findings, the authors propose a modification to current design procedures for shear; a modification that addresses member geometry and load configurations. These proposed provisions are applicable only to structural members subjected to a narrowly-defined type of loading. The shear design of many structural components is left unchanged. The primary impact of the proposed provisions will be to increase the size of transfer girders or other elements under concentrated loads (and hence increase the shear strength of such critical structural elements).

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