A static pushover method for identifying weak areas of earthquake resistant space frame structures

The occurrence of weak areas in a space frame structure under strong earthquakes is because the internal forces of the members in this area under earthquakes are considerably different from their non-seismic design internal forces that determine the configuration of cross-section, and the internal force difference mainly comes from the contribution of a few modes. Using the most unfavorable internal forces of both non-seismic design and frequently occurred earthquake check, a simple method for judging the suspected members in weak areas is proposed. Based on the structural responses under frequently occurred earthquakes obtained by the mode-superposition response spectrum method, the modes mainly contributing to the seismic internal forces of suspected members in weak areas can also be determined. Considering these main contribution modes and referring to the modal participating mass ratios, an integrated mode that can approximately reflect the most unfavorable unidirectional seismic response is established, and the equivalent static pushover load corresponding to the intensity of rare earthquakes is determined based on the principle of equivalent structural strain energy. A static pushover strategy that includes the contributions of three-dimensional ground motions is suggested, and a pushover analysis is carried out for an illustrative three-centered double-layer reticulated dome. By comparing with the results obtained by the dynamic elasto-plastic time-history analysis, it is revealed that the possible weak areas in the structure under rare earthquakes can be effectively identified using the proposed static pushover method as long as the main contribution modes to the seismic internal forces of the suspected members in weak areas are included in the combination modes and the sum of the modal participating mass ratios of all the combined modes is greater than 90% when constructing the pushover loads.