Date of Award:

5-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Paul J. Barr

Committee

Paul J. Barr

Committee

Marvin W. Halling

Committee

Joseph A. Caliendo

Abstract

In order to minimize traffic delays on the nation’s bridges, precast concrete bridge decks have been utilized to quickly and efficiently construct bridges. These precast concrete decks are cast off site and transported to the bridge after they have cured. The decks are then placed onto the bridge and grouted into place. These precast panels have an inherent weakness in that the joints between adjacent panels tend to leak. In order to mitigate leaking of the joints, two adjacent panels are typically post-tensioned together. A variation on the standard post-tensioning in use by some DOT’s was designed and investigated in order to find the viability of implementing this connection in the field. The proposed curved strand connection was found to behave similarly to the standard post-tensioned connection.

The proposed curved strand connection was investigated in four distinct areas: 1) Flexural Capacity, 2) Shear Capacity, 3) Capacity of Composite Section in Negative Flexure, and 4) Loss of Post-Tensioning Force over Time. The flexural capacity of the proposed curved strand connection was found by applying two loads, via a spreader beam, at equidistant points on either side of the joint. This test set up created a constant moment region with theoretically zero shear. Externally applied load and the corresponding deflections were monitored during testing and the capacity of the connection was found to be 31 k-ft. The shear test was conducted by applying a line load parallel to the joint at a distance d. This distance d was chosen in order to reduce any flexural stresses that may have occurred during testing. The externally applied load and corresponding deflection were monitored and used to find the shear capacity. The ultimate shear capacity was found to be 133.3 k-ft. The composite section was made by placing two precast concrete deck panels on steel I-girders, and grouting the concrete decks to the girders via shear studs. The test specimen was set onto supports at one end of the girders and at the joint. The load was then applied to the overhanging end. This loading pattern was chosen because it induced the maximum tensile stresses at the top of the joint that was pre-stressed using the proposed connection. The ultimate capacity of the specimen in composite negative bending was found to be 500 k. Pre-stress losses were measured by measuring the load in the strands from the initial stressing of the specimen to a time of approximately two months. The change in strand load was then recorded over time. A regression curve was fit to the loss data, and loss of prestressing force was extrapolated out to 75 years. The fit curve had a coefficient of correlation equal to 0.97, and predicted a loss value equal to 6% at 75 years.

These capacities were compared to those design capacities calculated in the AASHTO LRFD Bridge Specifications (2010). The proposed curved strand connection was found to behave stronger than the calculated values, and so the current bridge code was found to be conservative. The results of the three test specimens were used to calibrate a finite-element model of the connection. The finite-element models were found to behave similarly to the behavior observed in the physical test specimens. The finite-element models could then be used for further design and testing of the proposed connection.

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Comments

This work made publicly available electronically on May 11, 2012.

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