Analyses of Box Bridge and Comparison of Structural Behavior using 3D Finite Element and Typical 1D Line Models

Abstract

Abstract: In civil engineering practice, 1D modeling (also called line modeling) is often the most common method of modeling used for the analyses of structures. It is easy to create the model and saves time without loss of significant accuracy in the results. However, these line models are ideally not a true representation of the behavior of the structure as they are overly simplified versions. Though this simplification leads to quick modeling and reduces analyses-design cycle time, this oversimplification can lead to inaccuracies and over- design that can impact the economy of construction in repeat projects. Also, in the current era of precast modular construction, it would be prudent to analyze a structure as precisely as it can be so that optimal solution is achieved before designing as standard member that can be reused across an array of projects. In this study an effort is made to model a box bridge structure to analyze and compare the behavior of the bridge under railway vehicular train loading. A Road under Bridge (RUB) of 25m barrel length is considered and analysis is carried out by creating two models subjected to IRS vehicular rail axle loading using STAAD.PRO commercial software. A comparison of flexural forces in the culvert structure is made between results of 1D line model versus 3D box finite element model. It was found that flexure at the critical sections of the box based on line model analysis are much higher than those from 3D finite element analysis. In this particular example, a 14% excess of flexural reinforcement and a 40% excess shear reinforcement are required if we design the structure based on line model of analysis. Thus it is inferred that a design based on line model analysis can be overly conservative and uneconomical. It is suggested that detailed 3D finite element analysis be performed for the design of modular and reusable members especially for precast construction and engineering.