The cyclic loading program was designed to generate
large horizontal shear force ranges within the composite
connection between the girder and the deck. A four-stage
loading program was used (Fig. 6). The first three stages
subjected each test specimen to more than 2 million cycles
of structural loading. The final stage subjected each test
specimen to more than 5 million additional cycles of structural
loading. The vertical shear force range was increased
by approximately one-third at each stage, resulting in the
final stage applying twice the vertical shear force range as
the initial stage. In this final stage, the vertical shear force
range was 94 kip (418 kN).
The design of the composite connection in a slab-onstringer
bridge is frequently driven by service-level fatigue
load considerations. Section 6.10.10 of the AASHTO
LRFD specifications provides guidance on the design of a
shear stud composite connection. These provisions were
used to determine the amount of steel crossing all of the
girder-to-haunch composite connection interfaces. The
goal was to simulate the resistance of the design bridge
while imparting loads exceeding those that the bridge
may experience. Figure 7 shows that the horizontal shear
fatigue load range per unit length generated in the first
phase of the cyclic testing exceeded the anticipated load
range for the design bridge as well as the design resistances
at the girder-haunch and haunch-deck interfaces.
Each successive loading step surpassed the design capacities
by a larger margin. In the figure, ΔVf indicates the
range of vertical shear force on the beam, which is equal
to half the live load applied through the actuators onto the
beam. The circle-arrow marker indicates that the specimen
capacity was sufficient to resist the applied loads
throughout each loading phase, constituting a fatigue
runout at that load.
After the cyclic loading program, each specimen was
subjected to static loading in the second phase of the testing.
The basic loading setup was the same as that used for
the cyclic loading, with additional static hydraulic actuators
added to achieve the necessary higher loads. The test
specimens were loaded in a stepwise fashion until failure.