Parapet Load Distribution to the Bearing Pads of Prestressed Concrete Girders in a Simple Span Bridge

Author

Calvin Austiff, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2014

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Hsiao, J. Kent

Abstract

In current bridge engineering an idealized model is used to apply the parapet load to the bearing pads of a bridge. In this idealized model it is assumed that the parapet load is evenly distributed across all of the bridge bearing pads. However, this assumption is incorrect. The purpose of this study is to demonstrate that the parapet load distribution is more complicated than an evenly distributed load. Instead, this study shows that a majority of the parapet load is applied to the exterior bearing pad. This means that the real world exterior bearing pad reactions will be much larger than the reactions found using the idealized, evenly distributed model. This study utilizes the finite element program, NISA, to model and analyze a simple span bridge. The bridge used in this study was developed using a prestressed concrete girder design example from the Texas Department of Transportation. The design example specified the span length, clear roadway width, prestressed girder type, and girder spacing of the bridge. The bridge is modeled under two different loading conditions to ensure a comprehensive array of results is obtained. The two loading conditions were carefully designed to compare the idealized model, utilized by the Federal Highway Administration, to the real world parapet load distribution. The focus of this study is to determine how the parapet load distribution will affect the bearing pad reactions in a simple span bridge. The results of this study are provided in several tables depicting the bearing pad reactions obtained from the finite element models. The results of each parapet load distribution are compared to one another and percent differences are calculated between each condition. This allows for the use of a single number to define the effect the parapet load distribution has on the bearing pad reactions. A secondary focus of this study is to determine how a bearing pad's deformation, and thus its stiffness, will affect the bearing pad reactions of a simple span bridge. The results of this study are provided in several tables depicting the bearing pad reactions obtained from the finite element models. The results of each bearing pad stiffness condition are compared to one another and percent differences are calculated between each configuration. This allows for the use of a single number to define the effect of bearing pad stiffness on the parapet load distribution. This portion was completed first and the best model was chosen to be used in the main part of the study.