Report No.: CCEER-97-3
Title: Determination of In-Situ Footing Stiffness Using Full-Scale Dynamic Field Testing
Authors: I. Darwish, M. Saiidi, G. Norris, and E. Maragakis
Date: October 1997
Nevada Department of Transportation
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
This report presents the results of an experimental and analytical study, which was conducted on three footings of an existing bridge in order to determine their in-situ stiffnesses. The bridge is located on Interstate 80 south east of Verdi, Nevada. Six tests were conducted by shaking each footing in the longitudinal and the short direction. Each footing was subjected to sinusoidal vibration force, which was applied through an eccentric mass shaker. Twenty-three accelerometers were used to measure the response of the soil, bridge footings, and the bent cap of the bridge during shaking.
A three-dimensional finite element model of the last two spans of the bridge was developed using computer program COSMOS/M. Then, a linear response history analysis was performed to determine the steady state acceleration response of the three footings. During the analysis, the soil-footing interaction was modeled using a spring-dashpot model. Several refinements were applied to the response history analysis until the predicted steady state peak acceleration at the footing level matched the measured steady state peak acceleration on the corresponding footing during the dynamic field test.
A design guideline and recommendations, which provide the basis for the computation of footing stiffness using spring models, were developed based on the experimental and the analytical results (Abstract by authors).