Ductile Design Approach for Reinforced Concrete Frames

In the design of multistorey moment-resisting reinforced concrete frames to resist severe earthquakes the emphasis should be on good structural concepts and detailing of reinforcement. Poor structural concepts can lead to major damage or collapse due to column sidesway mechanisms or excessive twisting as a result of soft storeys or lack of structural symmetry or uniformity. Poor detailing of reinforcement can lead to brittle connections, inadequate anchorage of reinforcement, or insufficient transverse reinforcement to prevent shear failure, premature buckling of compressed bars or crushing of compressed concrete. In the seismic provisions of the New Zealand concrete design code special considerations are given to the ratio of column flexural strength to beam flexural strength necessary to reduce the likelihood of plastic hinges forming simultaneously in the top and bottom of columns, the ratio of shear strength to flexural strength necessary to avoid shear failures in beams and columns at large inelastic deformations, the detailing of beams and columns for adequate flexural strength and ductility, and the detailing of beams, columns and beam-column joints for adequate shear resistance and bar anchorage. Differences exist between current United States and New Zealand code provisions for detailing beams and columns for ductility and for the design of beam-column joints.