SHEAR CAPACITY OF CONCRETE PRISMS WITH INTERFACE JOINTS

Abstract

Construction joints are frequently used in engineering structures for various reasons. When the size of the structure is relatively large stoppage of concrete casting at certain locations is necessary. Stoppage of casting may also occurs due to sudden failure of mixing machines, or when the concrete stock ingredients runs out of materials, or when weather conditions do not permit casting operations to continue. If stoppage of concreting occurs, a joint between old and new concrete forms, it is then necessary to evaluate the horizontal shear capacity at the interface between old and new concretes to prevent progressive slip from taking place and to insure satisfactory performance of the structure.
A total of 16 push-off tests were performed to quantify the shear strength capacity at the interface between old and new concretes and to recommend the necessary practice for such circumstances. Test parameters include different interface surfaces smooth and rough with and without shear keys. The variables also include presence of shear reinforcement across the interface surfaces.
Test results have indicated that leaving concrete surface at the end of casting rough with shear keys is essential to restore part of shear resistance between old and new concretes. Presence of shear reinforcement further improves the shear resistance at the interfaces. It was found that the average nominal shear capacity of concrete at the interface relative to the nominal shear capacity of control specimens cast monolithically is about 43% for rough surfaces having amplitude of 6mm and 55% for rough surfaces with shear keys. When 3-Φ10 shear reinforcement is used along rough interface, shear resistance increased to 62% relative to the shear capacity of control specimens cast monolithically.