Axial load limit considerations for 14 in. square prestressed concrete piles

[摘要] From the 1997 Uniform Building Code (UBC)1 to the 2015 International Building Code (IBC),2 the required quantity of confinement spiral ρs for 14 in. (350 mm) square prestressed concrete piles was capped at 0.021. This upper bound appears to be related to conclusions made by Banerjee et al.,3 who found that 14 in. piles with a quantity of confinement spiral ρs greater than 0.020 were expected to have “virtually unlimited curvature capacity.”4 The usability of the curvature capacity was recently brought into question by Sritharan et al.5 based on results obtained while performing a parametric study of pile ductility. Their research was funded by PCI and aimed at developing updated minimum spiral confinement equations intended for inclusion in the update of the PCI Prestressed Concrete Piling Committee’s “Recommended Practice for Design, Manufacture, and Installation of Prestressed Concrete Piling”6 and for possible consideration during future code development deliberations. When reviewing their research results, Sritharan et al. were concerned about the significant drop in moment capacity that occurs when the pile’s cover spalls as part of the pile hinge process. In response, the researchers established a threshold of 40% as the maximum permitted drop in moment capacity that they would permit for 14 in. piles. For cases where the 40% drop was exceeded, published results are not available and the researchers recommended against the use of these piles. Because the percent drop is related to the axial load on the pile, the 40% drop was found by the researchers to occur in some cases when the axial load exceeded 0.2 fc ' Ag , where fc ' is the specified 28-day concrete strength and Ag is the gross cross-sectional area, or 20% of the nominal concrete compressive capacity of the 14 in. prestressed concrete pile.

[学科分类] 建筑学