United States Department of Transportation
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Influence of The Spacing of Longitudinal Reinforcement On The Performance of Laterally Loaded CIDH Piles : Analytical Investigation
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2015-12-21
[PDF-3.61 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Design;NTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATION;
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Abstract:For the construction of cast-in-drilled-hole (CIDH) piles in the presence of ground water, slurry is used before and during concrete placement to stabilize the drilled hole. When concrete is placed under slurry, defects may occur, affecting the structural integrity of the pile. In this situation, non-destructive testing, such as gamma-gamma testing, is to be conducted to detect potential anomalies in the concrete. These tests require the placement of inspection (PVC) tubes inside the pile. To accommodate the inspection tubes, the center-to-center spacing of the adjacent longitudinal bars in the pile has to be larger than the 8-in. maximum permitted by the Caltrans Bridge Design Specifications and the AASHTO LRFD Bridge Design Specifications. This report presents a numerical investigation to study the effect of the spacing of the longitudinal reinforcement in CIDH piles on their structural performance. It is aimed to confirm and generalize the experimental data obtained in this project, which has been reported elsewhere. To this end, three-dimensional nonlinear finite element (FE) models have been developed for RC pile shafts, and used for a numerical parametric study. The modeling method has been validated by experimental data. The parametric study considers piles of different diameters, with different lineal and angular spacings of the longitudinal bars, and with different levels of the axial load. To capture the strength degradation of piles under lateral loading, a phenomenological stress-strain law for steel that accounts for the low cycle fatigue of bars under large-amplitude cyclic strain reversals has been developed in this study. To model the nonlinear behavior of concrete, a damaged-plasticity model has been used. In addition, a microplane model for concrete has been implemented as an alternative. The latter has been found to be superior in that it does not require artificial remedies to capture the tensile unloading and reloading behavior of concrete and the compressive behavior of confined concrete. The bond-slip behavior between the longitudinal bars and the surrounding concrete is modeled with a phenomenological bond-slip law. The numerical study has shown that the spacing of the longitudinal bars in circular RC members can be larger than 8 in. without jeopardizing their structural performance. Similar to the experimental findings, the numerical parametric study has shown that the lineal spacing of the longitudinal bars does not have any impact on the ductility of an RC pile. However, the size of the longitudinal bars can affect the ductility of a pile. The load degradation in a pile is often associated with the spalling of the cover concrete, and the buckling and the fracture of the longitude bars in the plastic-hinge region of the pile. Larger-diameter bars are more resistant to buckling for the same spacing of the lateral reinforcement and therefore result in a more ductile behavior. The parametric study has also confirmed that a smaller lineal spacing with smaller-size longitudinal bars can lead to more closely spaced flexural cracks with smaller widths. These observations are true for piles of different diameters and subjected to different levels of axial loads.
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