The Effects of Coupled Translational - Torsional Dynamic Response on Buildings

Abstract

<p>An investigation is made into the coupled lateral - torsional response on frame buildings to horizontally directed earthquake excitation. Attention is confined to the accuracy of the static code provision on torsional effect with special reference to the National Building Code of Canada 1977 (NBC 77).</p> <p>A mathematical model to compute the dynamic response of a building is presented. The formulation of the general equation of motion to a monosymmetrical building is developed in detail. The static storey torque is compared with the dynamic torque computed by using the response spectrum technique as outlined in the Commentary K of NBC 77. It has been found that the sympathetic coupled translational torsional resonance occurs at the buildings with small eccentricities. To uniform structure, the static code torque estimate is good if the effect of sympathetic coupled resonance is not significant. To building with large eccentricities, sympathetic resonance is unlikely to occur and the current NBC requirement of doubling the computed torque for design is a very conservative requirement.</p> <p>To buildings with eccentrical offset, NBC 80 proposes a modification on the definition of structural eccentricity. A study in this aspect is made through the floor torques comparison between dynamic analysis and static codes calculations. The results show that the improvement by NBC 80 is only partial. Buildings with eccentric offsets are irregular buildings, only a dynamic approach can lead to a realistic estimate of the torque distributions.</p>