An analytical model for determining the shear strength of concrete pile caps under the failure mode of diagonal-compression originally based on the softened strut-and-tie model is proposed. The failure probabilities of reinforced concrete pile caps are investigated by Monte Carlo method. The results indicate that the proposed model can accurately predict the shear strength of the pile caps. The distribution of the failure probabilities for pile caps designed to ACI 318-02 Appendix A and the proposed design method are more uniform than that designed to the ACI 318-99. The ACI 318-99 is very conservative and cannot provide a consistent safety for pile caps design. It is suggested that the procedures in the ACI 318-02 Appendix A should be moved to the main body of ACI 318-02 and the proposed design method should be incorporated into the current reinforced concrete pile cap design methods.
