Optimum Reliability-Based Design Loads Due to Natural Hazard

The reliability concept is now widely accepted in structural engineering as a tool to find the most appropriate structural system for a particular site in terms of safety and economy. The probability of failure Pf, or the reliability index , are explicitly cited in some codes to determine design loads. However, target reliability tends to be a standard value specified by code writers, mainly based on calibration with established design regulations. Instead of calibration, the degree of safety against natural hazards can be represented in terms of optimum reliability, as determined by the minimum total cost principle, with a reliability index obtained as a closed-form solution of a simplified model. Such simplified models can include parameters for the cost-up ratio, the load effect coefficient of vibration cov, the separation factor and the normalized failure cost. Through the examination of the cost-up ratio and estimation of the normalized failure cost, design loads can be determined using a simple first order, second moment reliability index formula. This procedure for determining target safety or design load levels for snow, wind and earthquake loads is discussed. The effects of availability on statistical information of these loads are also presented.