The effects of integrated exposed strands on the behavior of prestressed concrete piles in integral abutments

The Tennessee Department of Transportation (TOOT) has a history of designing and constructing integral abutments with prestressed concrete piles. Initially, the design of the integral abutments called for the prestressing strands to be cut along the top of the pile. The integration of the pile into the abutment was achieved by pouring the abutment around a length of the pile. This practice has been replaced. The current practice is to leave the prestressing strands intact above the pile and integrate them as well as a length of the pile in the abutment. Both types of integral abutments are still in use in Tennessee. TDOT contracted The University of Tennessee, Knoxville (UTK) to research the behavior of concrete piles in integral abutments. This research provided an opportunity to compare abutments with and without exposed strands. Three integral abutments with prestressed concrete piles were tested. The strands were left exposed in two piles. Two theoretical models have been created to determine the effects of exposed strands. The first model determines the maximum stress that may be developed in a prestressing strand at a particular location based on th� exposed strand length and the distance to the top of the pile. The second model predicts the axial load and moment capacity of the pile based on the prestressing strand stress, pile geometry, and material properties. Both models agree with the test data collected. The models show that axial load and moment capacity of the pile may be increased by changing the maximum stress in the strands. Similar increases in strand stress may be achieved by lengthening the pile embedment in the abutment or by lengthening the exposed strands, but the effects on the pile's axial load and moment capacity are not the same.