Combined Seismic plus Live Load Analysis of Highway Bridges

The combination of seismic and vehicle live loadings on bridges is an important design consideration. There are well-established design provisions for how the individual loadings affect bridge response: structural components that carry vertical live loads are designed to remain well within the linear-elastic range while lateral load carrying components are designed to yield under large seismic excitations. The weight of the bridge superstructure is taken in to account as dead load in structural analysis for seismic loads; however, the effects of additional mass and damping of live loads on the bridge deck are neglected. To improve the design of highway…

The combination of seismic and vehicle live loadings on bridges is an important design consideration. There are well-established design provisions for how the individual loadings affect bridge response: structural components that carry vertical live loads are designed to remain well within the linear-elastic range while lateral load carrying components are designed to yield under large seismic excitations. The weight of the bridge superstructure is taken in to account as dead load in structural analysis for seismic loads; however, the effects of additional mass and damping of live loads on the bridge deck are neglected. To improve the design of highway bridges for multi-hazard effects of seismic plus live load, the following questions arise:

- Would a bridge with low seismic risk experience significant and unexpected damage during an earthquake event where there are numerous heavy vehicles on the bridge deck?
- Does traffic moving over a bridge change its earthquake response?
- Is there a dependence of a bridge’s earthquake response on vehicle speed, i.e., will a bridge experience significantly different earthquake response for stand-still and normal speed traffic?

The proposed research, based entirely on numerical simulations of short span bridges, will lead to recommendations for when to include live loads in the seismic analysis of bridges. In addition to these recommendations, parametric studies will shed light on vehicle speeds and axle configurations that will produce the largest increase in seismic response; and response sensitivity analyses will show the effect of parameter variations and their importance ranking on the bridge response.  Upon successful completion of the research, the methodology can be extended to long span bridges whose seismic response is more heavily influenced by mass on the bridge deck.