Experimental Investigation of Size Effect in Shear Critical Reinforced Concrete Pile Caps

Abstract

This paper presents experimental results of a test campaign that examined the strength of shear critical RC pile caps in the ultimate limit state. The campaign comprised test specimens of different sizes - all scaled with identical geometrical ratios. The specimens simulated quadratic four-pile Pile Caps with concentric loading. This unique scaling allowed for an investigation of the effect of increased dimensions on the capacity of the solid RC structure in the ultimate limit state. The specimens scaled from overall dimensions of 450 × 450 × 230 mm3 (L × L × h) to 1188 × 1188 × 575 mm3 and the load carrying capacity increased from around 0.6 MN to 3.8 MN. Nevertheless, the average ultimate shear stress decreased with increasing depth. A novel two-camera setup for independent 2D Digital Image Correlation on two sides of the specimens was established to relate the crack development with characteristic points on the load-displacement relationship. This led to the identification of the first bending cracks and eventually development of shear cracks that contributed to the failure mode in the ultimate limit state. All specimens failed in a shear/punching-shear like manner, with several of the specimens failed in a mechanism involving shearing of one corner of the square pile cap. Based on the experimental findings, the paper investigates applicability of a rigid plastic upper bound solution - including the empirical account for size effect - to predict the strength and compare to the experimentally observed collapse mechanisms.