Finite element modeling of bridges with equivalent orthotropic material method for multi-scale dynamic loads

An effective Finite Element (FE) model is important to evaluate the structural performance under multi-scale dynamic loads, for instance, the wind induced vibrations for the long span bridge in a kilo-meter scale and the vehicle induced dynamic impacts within limited influence areas in a meter scale. The superposition of the stresses from the multi-scale dynamic loads might cause serious fatigue damage accumulation for long-span bridges. This paper presents a multiple scale modeling and simulation scheme based on an equivalent orthotropic material modeling (EOMM) method that is capable of including the refined structural details. Bridge details with complicated multiple stiffeners are modeled as equivalent shell elements using equivalent orthotropic materials, resulting in the same longitudinal and lateral stiffness in the unit width and shear stiffness in the shell plane as the original configuration. The static and dynamic response and dynamic properties of a simplified short span bridge from the EOMM model are obtained. The results match well with those obtained from the original model with real geometry and materials. The EOMM model for a long-span cable-stayed bridge is built with good precision on dynamic properties and can be used for the wind induced fatigue analysis. Based on the modeling scheme, it is possible to predict a reasonable static and dynamic response of the bridge details due to the multi-scale dynamic loads effects, for instance, the wind induced low frequency vibrations in a kilo-meter scale and the vehicle induced high frequency vibrations in meter scale.