Experimental study on column underpinning joints with inclined steel bars

Abstract

Column underpinning joints play an important role in monolithic moving, jacking up and renovation or reinforcing of buildings. However, existing methods of improving the bearing capacity of joints usually cause damage to columns and the constructions are complex. A new column underpinning method with inclined rectangular ribbed steel bars was thus developed. Six specimens were tested experimentally under vertical static load. The inclination angle and the number of inclined steel bars were considered as the main parameters. Tests were carried out to study the mechanical performance of the column underpinning joints, especially bearing capacity. The results indicate that, compared with a specimen without inclined bars, the addition of inclined bars in joints improves the bearing capacity by a maximum of 143·7%. Analysis revealed that the bearing capacity of joints with inclined bars is mainly composed of three parts – the vertical component of force in inclined bars, partial cohesion strength and the shear strength resulting from friction at the interface between new and old concrete. The failure of all specimens was sliding failure at the interface, except for one specimen that failed due to crushing of the columns.