Finite element analysis of vehicle–bridge interaction

Abstract

This paper presents results of the finite element (FE) analysis of dynamic interaction between a heavy truck and a selected highway bridge on US 90 in Florida. FE analysis of vehicle–bridge interaction was conducted using commercial program LS-DYNA and the super computer at the Florida State University. Development and implementation of a detailed FE truck model with 3D suspension systems, pneumatic and rotating wheels, appropriate contact algorithms, allowed for realistic representation of the actual vehicle dynamic loading. Several static and dynamic field tests were performed on the same bridge. The experimental data was used for validation of the FE models of the bridge and the truck. Numerical results were found to match well with the experimental data. Results presented in the paper demonstrate a significant potential of using computational mechanics and LS-DYNA code for thorough investigation of the vehicle–bridge interaction, dynamic impact factors, and the ultimate loading of bridges.

Introduction

Nonlinear finite element (FE) methods are nowadays commonly used to solve engineering problems. One such engineering area is the efficient management of highway facilities, especially bridges, where the knowledge of actual dynamic load effects, load carrying capacity, and current condition is critical in making management decisions and in establishing permissible weight limits. Significant dynamic effects can be triggered by increasingly heavier vehicles, which are now used on our highways [1], [2]. Additional dynamic effects are accounted for by dynamic impact factors introduced in bridge design codes. The impact factor IM [13], also referred to as dynamic load allowance [20], is defined as a ratio of the dynamic increment ($R_{\mathrm{D}}-R_{\mathrm{S}}$) in structure response to the static response:

$$\mathit{IM}=\frac{R_{\mathrm{D}}-R_{\mathrm{S}}}{R_{\mathrm{S}}}100\%\text{,}$$

where $R_{\mathrm{D}}$ is the dynamic response and $R_{\mathrm{S}}$ the static response. There is a large number of studies on this topic including experimental impact factors, analytical methods and code specifications. Nowak and Kim conducted tests on two bridges over Huron River to study impact factors, distribution factors and development of lateral cracks in bridge decks [3]. Chowdhury and Ray performed a series of load tests on a continuous span, multi-girder steel bridge and a single span concrete T-beam bridge to quantify physical and structural behavior of bridges due to moving vehicles [4]. A two-lane highway bridge over the River Lodden at Lower Earley was selected for testing by Green and Cebon to validate their proposed analytical procedure [5]. More examples of experimental studies can also be found in [6]. These experiments show that bridges exhibit a wide range of structural, dynamic responses and resulting impact factors depend on several different parameters related to bridge and vehicle characteristics.

Field tests are still the most reliable source of information on bridge dynamic responses, and the only method of final validation of the FE analysis. However, the high cost of such experiments and difficulties with collecting extensive data from field tests lead to growing interest in analytical and computational methods. A reliable, analytical investigation can reduce such costs dramatically and allow for faster introduction of new design improvements and maintenance decisions.

The analytical investigation of bridge dynamic response is based on numerous simplifications of its geometry, material models, boundary conditions, and loading. The interaction between a vehicle and bridge structure is usually reduced in analyses to a simplified mass–spring–damper system crossing a beam or grillage including road surface roughness [7], [8], [9], [10], [11], [12]. Current bridge design codes present some formulas estimating the dynamic effects [13], [14]. However, these formulas are oversimplified and, in many cases, are questioned by engineers [15].

An FE analysis by an explicit, dynamic computer program was used in this research to study dynamic response of medium span (20–30 m long) highway bridges subjected to moving vehicles. The paper describes comprehensive research efforts focused on development of the FE models of the selected highway bridge and the vehicle, computational mechanics study of vehicle–bridge interaction, and validation of the FE models using the field test results.