The primary objective of this project is to obtain an indication of the structural response of five concrete ties instrumented with electrical resistance strain gages, when subjected to moving loads from BART trains.
In preparation for the collection of field data from strain gage readings of the ties in track, five concrete ties were removed from track in the Oakland area and delivered to the Structures Laboratory at San Jose State University. Twelve strain gages were attached to each of the five ties. The ties were then subjected to static loadings to produce positive and negative bending moments at both the rail seat and the centerline. Calibration curves relating strain to bending moment were produced. These calibration curves served as the basis for determining bending moments in the ties when placed in track and subjected to the structural effects of moving trains.
The five ties were installed in a section of outbound track west of the Lafayette Station. The exact location of the ties is at Milepost 10.8 on the C-1 track. The track at this location is on a horizontal curve with a radius of 3,115 feet. Also at this point, the track has a vertical curve with the ties being located on the uphill side with a slope of approximately 2%. The track has a superelevation of 7 inches. Figure 1 shows the test site, looking west. Figure 2 shows the five instrumented concrete ties in the foreground with the track leading toward the Lafayette Station.
Details of the laboratory testing program of the five concrete ties are described in the report, “Strain Gage Instrumentation and Calibration of BART Concrete Ties.” (1)