Behavior of Prestressed Pile to Bent Cap Connections and Damage Evaluation with Acoustic Emission

The state of South Carolina employs a unique connection detail between precast prestressed piles to cast in place bent caps. This detail is constructed by plainly embedding piles to a specified depth into bent caps. Typically in regions of high seismicity such as South Carolina connections between these two elements require special detailing which increases both the time and cost of construction. Although connection behavior between piles and bent caps has been studied significantly, a low amount of this effort has focused on the plain pile embedment detail. In an effort to better understand the connection behavior as well as to provide damage assessment tools a series of studies was conducted. The first study investigated the behavior of the plain pile embedment detail at exterior connections using cast in place (CIP) bent caps. During seismic events, exterior connections are subjected to both axial compressive and axial tensile loads. Prior to this study the behavior of these connections under the loading scheme described had not been studied and design engineers have to date typically considered these locations to perform as a hinged connection. In this study, four full-scale specimens were constructed and tested an analytical model that considers confinement was also created. The results showed that the current SCDOT state of practice performed inadequately with an undesired failure mechanism. Two design methodologies are presented which allow for full development of the embedded pile and thus moment transfer between the pile and bent cap elements. An alternative idealized hinge design is also presented. The second investigation discusses the results of a test specimen constructed at full scale which was comprised of three piles connected to a single bent cap. This specimen was tested as a means of validation of eight single pile specimens tested previously. The connection detail of a plain pile embedment is shown again to behave favorably under different loading conditions. The results of the specimen provided a direct comparison of the two design methodologies for exterior connections presented in the previous study, and further proved the ability of the simple connection to withstand seismic loading while performing as expected given the requirements set forth by the SCDOT. In the third study, the behavior of plain embedment connection between piles and precast bent caps was examined. It has been documented that the use of precast bent caps may save significant amount of time during the construction process while improving worker safety and environmental impact. However, prior to this study, the behavior of this connection had not been studied. Therefore, two single piles were plainly embedded in an interior and an exterior precast bent caps and tested at full-scale. The results of this study showed that the connection detail is a possible connection method when using precast bent caps subjected to seismic loading. The performance of the tested systems not only met the design requirements and expectations but also performed better than similar CIP bent cap specimens. The last of the investigations presented uses Acoustic Emission (AE) as a means of non-destructive evaluation (NDE) of the test specimens presented in the previous works. In this work three previously proposed AE analysis techniques are examined. Two damage evaluation models are created based on the results of single pile specimens and validated with the results of the three pile specimen. These models are able to assess sustained damage in the specimens and predict remaining capacity. The outcomes of these studies showed that a plain pile embedment is a viable solution in areas of seismic activity when proper design considerations are considered. This is shown to be true of both CIP and precast bent cap specimens. Additionally, AE is shown to be an effective method of damage evaluation for these systems where multiple evaluation models are presented