Transverse reinforcement for columns of RC frames to resist earthquakes

An approximate formulation to determine the amount of transverse reinforcement for columns of reinforced concrete (RC) frames in seismic areas is presented. It is based on observations that suggested that the main function of transverse reinforcement is to confine the core subjected to-a complex state of stress rather than simply resist shear or improve deformability under axial compression. The combined effects of shear and axial stresses are assumed to be a function of the maximum drift ratio and they are interpreted using Coulomb's failure criterion. A comparison between results obtained with the model developed and current design recommendations suggests that the required amount of transverse reinforcement specified in ACI 318-95 can be reduced safely for "flexible" columns (ratio of column height to effective depth congruent to 6) under low amplitude displacement cycles (ratio of lateral displacement to column height less than or equal to 3%) and "short" columns (ratio of column height to effective depth congruent to 4) under combinations of relatively low shear and axial stresses.