A Probability-Based Methodology for Establishing Non-Extreme and Extreme Vertical Load Combinations for Multi-Hazard LRFD of Bridges

The current probability-based AASHTO LRFD Bridge Design Specifications are fully calibrated against gravity dead load and truck load. However, it does not cover extreme load effects in a consistent fashion. In this paper, a methodology is described to combine extreme and non-extreme loads. To illustrate this method, common truck load and earthquake load combinations are used. This illustration quantitatively shows that the current design practice is non-conservative if only considering peak truck load or peak earthquake load alone; and it is too conservative if the design is based on the combined peak truck and earthquake.