Design of a Double Corbel Using the Strut-And-Tie Method

The strut-and-tie method can be used for the design of regions of structures where the basic assumptions of flexure theory, namely plane sections remaining plane before and after bending, are not applicable. Such regions occur near force discontinuities arising fromconcentrated forces or reactions and near geometric discontinuities such as abrupt changes in cross section etc. The strut-and-tie method of design is based on the assumption that appropriate regions in concrete structures can be analysed and designed using hypothetical pin-jointed trusses consisting of struts and ties connected at nodes. Although IS 456:2000 recommends the strut-and-tie method for design of corbels, no guidelines are given for determination of concrete strut and node dimensions and for the allowable stresses for design. The ACI Code 318-02 on the other hand, gives explicit and practical recommendations related to the design of structural members using the strut-and-tie method. To amplify the application of these recommendations to the design of structural concrete a complete example on the analysis and design of a double corbel using the strut-and-tie method has been presented.