Masters Theses

Date of Award

12-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Edwin G. Burdette

Committee Members

Harold Deatherage, David W. Goodpasture

Abstract

The Tennessee Department of Transportation uses a program called SEISAB to determine the dynamic response of bridges. In addition to the properties of the bridge, SEISAB allows spring stiffnesses to be input to represent soil stiffnesses at the foundation. Since current modeling techniques by TNDOT assume fixed foundations, it was desired to determine the implications of adding spring stiffnesses to the bridges being modeled. These stiffnesses were calculated using results of pluck tests performed on a single pile. The tests were conducted in loess, a soil which is predominant in West Tennessee, which is an area of high seismic risk. As a result of the pluck tests, a stiffness of 30 kips/inch was used to calculate stiffnesses which were applied to SEISAB for four different bridges. Each bridge was modeled with fixed bent foundations and with spring stiffnesses at the foundations. The bridges modeled were of two foundation types. Two of the bridges had bent foundations consisting of a pile cap supported by a pile group, while the other two bridge foundations consisted of a row of free-standing pile bents. Once the dynamic analyses were complete, it was evident that the bridges with the free-standing pile bents experienced a greater percent difference in forces and deflections than the bridges with the pile cap/pile group foundations. In all cases, the moments and axial forces in the bridge bents decreased, by a large amount in some cases, while the deflections of the structure increased. These results show that the assumptions of fixed conditions at the bent foundations are conservative for forces and unconservative for deflections.

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