Test Setup and Instrumentation
Two 440 kips (1957 KN) MTS hydraulic actuators were used to apply a concentrated load to each span simultaneously to simulate the effect of a truck wheel load. Two 10 x 20 in. (254 x 508 mm) steel plates were used to transfer the load from the actuator to comply with the AASHTO LRFD Bridge Design Specifications for tire contact area. A 1/2 in. (13 mm) thick neoprene pad was placed under each loading plate to prevent possible local crushing of the concrete. The supporting girders were supported by concrete blocks to transfer the applied load to the strong floor resulting in a clear span of 96 in. (2438 mm). The clear span of supporting girders was determined based on the equivalency of the torsional stiffness of the supporting girders to that of the steel girders used in the actual bridge. Figure 3 shows an isometric view of the test setup and the first bridge deck prior to testing.
A total of 72 channels were used for instrumentation of each bridge deck. A 440 kips (1957 KN) load cell was mounted to each actuator to measure the applied load. Twenty-four string potentiometers (string pots) were used to measure the bridge deck deflection profiles along the longitudinal and transverse directions. In addition, six linear potentiometers were used to measure the girders deflections and rotations. Twenty PI gages were used to measure the concrete strain at various locations. The measured strains were used to determine the strain profiles of the sections at the measured locations. Twenty electrical resistance strain gages of 120 ohm and 6 mm gage length were attached to selected reinforcing bars to determine the strains in these bars. Data were electronically recorded by an Optim Megadac data acquisition system. Figure 4 shows the locations of the PI gages used and establishes the notation adopted hereafter.
(a) Test setup (b) First bridge deck prior to testing
Fig. 3. Test setup and the first bridge deck prior to testing.
Fig. 4. PI gages locations and notations for the three bridge decks.