Date of Award

Spring 5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Chuanbing Shawn Sun

Abstract

Precast prestressed concrete girders have been widely used to construct bridges in the United States. Recent advancements in high-performance concrete and newly developed girder sections allow the span of girders to be extended significantly. Generally, bridges with longer spans require deeper girders and use more prestressing strands; the latter exacerbates the end zone cracking in pretensioned concrete girders when prestressing strands are released. Various types of end zone cracks have been observed, including horizontal and inclined cracks in the web, and bottom flange cracks.

This dissertation explores two possible options to mitigate the end zone cracking in precast prestressed concrete girders, including the use of shape memory alloys (SMAs) and ultra-high performance concrete (UHPC) at the girder ends. Experimental work was conducted on the use of SMA wires to apply vertical prestress in the end zone of prestressed girders to counter the bursting stresses as a result of prestress transfer. The end zone behavior of UHPC in prestressed girders was also studied to evaluate its effect on enhanced splitting resistance. The relationship between the splitting resistance from the vertical reinforcement and UHPC at the girder ends and applied prestressing force was examined experimentally and analytically.

The experimental study indicated that the use of SMAs successfully introduced vertical prestress at the prestressed concrete beam ends, and therefore can increase the splitting resistance and concrete cracking at prestress can be possibly mitigated or eliminated. The laboratory tests showed that splitting resistance was significantly increased due to the use of UHPC at girder ends. It is suggested to keep the tensile stress limit of 20 ksi in the reinforcing bars to control the crack width, as specified for conventional concrete girders. The collected test data showed that the resulting splitting stresses in the prestressed UHPC girder ends were acceptable.

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