Extent of critical region and limited ductility design of high-strength reinforced concrete columns for hong kong practice

Abstract

Extent of critical region, which is usually referred to as plastic hinge length, of high-strength reinforced concrete (HSRC) columns, where extensive inelastic damages might occur under seismic loading, was experimentally investigated. A total of 6 HSRC columns that can be grouped into 2 series or 3 pairs, were tested under various axial load levels as well as reversed cyclic inelastic displacement excursions simulating seismic loading. The first series of columns contained transverse steel designed according to the shear resistance requirement of BS 8110, while the second series, representing limited ductile columns, to the authors' proposed equation. From test observation, progressive development and formation of the critical region in these columns were discussed. The extents of these critical regions were subsequently evaluated rigorously using direct (by physical observation or measured column curvature profiles) and indirect (by back calculation using an idealised column curvature profile) methods. From the results, it was evident that: (1) the critical region developed starting from the point of maximum bending moment over a finite length along the concrete spoiling area, (2) the extent of critical region was largely influenced by volumetric ratio of transverse steel, concrete strength and axial load level, (3) the extents of critical region evaluated using both methods were in good agreement, (4) the HSRC columns containing transverse steel calculated using the authors' proposed equation proved to behave in a limited ductile manner, and the extent of their critical regions was smaller than that of the counterpart columns designed complying with BS 8110. Finally, some guidelines for the design of limited ductile HSRC columns were proposed.