Date of Award
Master of Science (MS)
The South Carolina Department of Transportation (SCDOT) is currently in the process of load rating every bridge in their inventory. Two types of short-span precast concrete bridges built around the 1960s are prevalent throughout the state, exhibiting different levels of deterioration. In order to better understand how these bridge typologies behave under loading, two test types were conducted and will be discussed in this thesis. The first test conducted was a live load test on an in-service bridge containing flat precast concrete slabs. This test was used to evaluate transverse load distribution and efficiency of the longitudinal slab-to-slab joints. The precast slabs span fifteen feet and are five and a half feet wide, and they have slab-to-slab joints consisting of v-shaped interlocking shear keys. The live load test consisted of a crawling (< 5 mph) loaded dump truck at several critical locations while simultaneously measuring vertical displacement in the slabs. From the deflection data, joint efficiency and experimental distribution factors for moments (DFMs) were calculated. Based on the test results it is recommended that 0.55 should be the minimum distribution factor used when calculating moment demand. Having a high DFM proves that this in-service bridge lacks transverse distribution between adjacent slabs as each slab will carry 55% of a trucks load. These results demonstrated that the interlocking shear keys along the transverse joints are not capable of distributing loads transversely in their current state, and each slab acts independently. The second group of tests conducted were laboratory tests on “arch” beams. They are so-named because the cross-section includes an arch-shaped void between two stems and below the top flange. To better understand the capacity of these bridges’ service and strength tests were conducted—a service load test, a flexural test taken to failure, and an autopsy of the specimen tested. The service load tests were performed on three bolt-connected arch beams to determine transverse load distribution as well as the bolt connection efficacy; the failure test was performed on a single arch beam in order to determine the flexural capacity; and the autopsy was performed to determine number, size and location of the steel reinforcement. The service load tests indicated the bolt connections provided minimal transverse load distribution. The data from these tests indicate a DFM of 0.5 should be used to calculate moment demand during load rating. Thus an arch beam will support as much as 50% of a truck’s weight due to the lack of transverse load distribution from the bolt connections. The arch beam failed at 597 kip-ft during the flexural failure test. Based on assumed material properties and the reinforcement pattern found during the autopsy, the beam has a much higher capacity than should be expected. Original assumptions about the material properties were based on the SCDOT construction practices of the 1960s which indicated concrete compressive strength of 4 ksi and steel yield stress of 40 ksi. It was determined that the material properties were closer to a concrete compressive strength of 7.5 ksi and a steel yield stress of 60 ksi.
Crabtree, Brianna, "Strength and Behavior of Rural Short-Span Precast Concrete Bridges in South Carolina" (2020). All Theses. 3443.