Instrumentation for long term testing of abutments on stub piles

The Tennessee Department of Transportation has been designing and constructing jointless bridges with integral abutments for some time. The particular concern with the integral abutment is the pile which supports it. As the span of the bridge increases, the lateral loads imposed by thermal movements can cause large deflections in the pile supporting the integral abutment. The University of Tennessee under contract with TDOT is investigating the effects of these deflections on the pile supporting the abutment.

Full scale lateral load tests were performed on a 40 foot pile supporting an abutment. The testing was performed over several months, and the instrumentation requirements were extensive. The pile was instrumented on the top 20 feet with weldable strain gages and pressure sensors. The loads and deflections were monitored with load cells and linear displacement voltage transducers (LVDT’s), respectively. There were a total of 72 instrumentation devices to be monitored for each test.

The device known as the Optim MEGADAC used in conjunction with the Test Control Software (TCS) was invaluable to the data collection process. The MEGADAC converts the signals coming in from the gages and sensors into readings of strain, psi, kips. or inches. The sampling rate can be adjusted from test to test, and 1 sample per second was used for the two tests presented herein.

From the analysis of the data, it is shown that the most useful and reliable data obtained are from the strain gages. The pressure sensors simply do not hold up over time, and the results from them are not very consistent. Data reduction should therefore focus on the strain gage data, and the conversion of the strains into moments and pressures.