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原文传递 Influence of the Spacing of Longitudinal Reinforcement on the Performance of Laterally Loaded CIDH Piles – Experimental Investigation.

题名：	Influence of the Spacing of Longitudinal Reinforcement on the Performance of Laterally Loaded CIDH Piles – Experimental Investigation.
作者：	Papadopoulos, V.; Shing, P. B.
关键词：	Cast-in-drilled-hole (CIDH), Concrete placement, Structural performance, Bridge design specifications, American Association of State Highway Transportation Officials (AASHTO), Reinforcement spacing, Slurry displacement method, Vertical reinforcement, Confinement, Crack spacing, Crack width, Inspection tubes, Ductility, Flexural behavior
摘要：	In the presence of ground water, the slurry displacement method is normally used for the placement of concrete during the construction of cast-in-drilled-hole (CIDH) piles to ensure the stability of the drilled hole before concrete placement. When concrete is placed under water without compaction, defects or cavities 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. The impact of this increased spacing on the structural performance of the pile was not well understood. This report presents an experimental study that investigated the effect of the circumferential spacing of longitudinal reinforcement in CIDH piles on their structural performance. In this study, two 28-in.-diameter piles were tested under a constant vertical compressive load with lateral displacement cycles of increasing amplitudes. The two specimens had the same quantity and spacing of transverse reinforcement and similar quantities of longitudinal reinforcement. Specimen #1 had 6 #11 longitudinal bars spaced at 11 in. on center, which exceeded that maximum spacing permitted by the current design specifications. Specimen #2 had 10 #9 bars spaced at 6.75 in. on center. The total cross-sectional area of the longitudinal steel in Specimen #1 was 1.52% of that of the pile, while it was 1.62% in Specimen #2. The experimental results have shown that the spacing of longitudinal bars in circular RC members can be larger than 8 in. without a detrimental effect on structural performance. This spacing does not affect the effectiveness of the confinement on the concrete core and the ductility of the member. However, the results have shown that the diameter of longitudinal bars can affect the flexural ductility of a member. Flexural ductility in a plastic-hinge zone is often limited by the buckling of the longitudinal bars after the spalling of the concrete cover, which leads to severe bar strains causing the fracture of the bars. Larger-diameter bars have better buckling resistance for the same spacing of the transverse reinforcement, and can therefore result in more ductile flexural behavior. Furthermore, the spacing and the diameter of longitudinal bars have a clear influence on the spacing and the width of flexural cracks. Increasing the diameter and the spacing of longitudinal bars can lead to wider crack spacing and larger crack widths as also shown in other studies.
报告类型：	科技报告