Pushover Analysis: A New Procedure to Include Torsional Effects in Buildings

Non-linear Static analysis or Pushover analysis is a very practical method fit for day-to-day use in the structural design field when compared to Non-linear Time History analysis due to its computational intensity and experienced judgement required. However, it is found that Non-linear Time History analysis is more accurate than Pushover analysis, the disadvantage being more pronounced in the case of irregular and torsional buildings. Here a new PoA method by which the eigenvectors naturally translate to force/moment vectors is proposed and investigated to find whether it predicts the responses of a torsional structure closer to NL-THA than the conventional PoA. The proposed procedure was applied to structures with different configurations, including a non-torsional one, and the results obtained were compared with those of NL-THA. The analyses were done using the structural analysis package of SAP2000 which has inbuilt functions for PoA based on both the Capacity Spectrum Method and the Displacement Coefficient Method. With conventional PoA, the torsional effects are mostly pronounced in the elastic range and early stages of plastic behaviour and tend to decrease with an increase in plastic deformations, thus failing to capture the effects of torsion in buildings. The obvious answer is the inclusion of torsional elements in the lateral load pattern, a new method by which the eigenvectors are translated to their corresponding lateral load vectors with the torsional aspect included is proposed. On investigation, it is found to overcome the above drawback and gives results closer to that of Non-linear Time History analysis, especially for irregular torsional buildings. Results obtained from the Proposed PoA method show that for torsional buildings responses are closer than the Conventional PoA method to the Time History results, while for non-torsional buildings, both methods have been found to give more or less the same result, suggesting that the proposed method can be applied to torsional buildings to get more accurate results.