The Need of Proper Code Specifications of Lateral Strength and Displacements for the Seismic Design of Buildings

Abstract eng:
Recorded ground motions in several earthquakes in different urban areas around the world exceeded the design basis earthquake considered by building codes in such areas. This has been for example the cases of the 1985 Mexico City earthquake, 2010 Chile earthquake and the 2010 and 2011 Christchurch earthquakes in New Zealand. These earthquakes in Mexico, Chile and New Zealand are studied in this research. Results show the need of revising existing current seismic design procedures specified by building codes. Nonlinear time-history analyses were performed using a SDOF system subjected to typical recorded ground accelerations in these earthquakes, and considering typical structural features of buildings in these earthquakes. Demands of lateral strengths and roof drift ratios in these buildings were obtained from such analyses. In addition, a seismic damage index previously proposed by the author was computed for the selected earthquakes. Results of the evaluation of this damage index showed the importance of properly considering the type of soil and proper amplification of ground movements due to the type of soils when specifying seismic design strength and displacement demands for the seismic design of buildings. These results also showed the importance of specifying both proper drift demands and a type of structural system capable of controlling building displacements during earthquakes. This research reached the simple conclusion that seismic design codes should specify a clear and explicit seismic design procedure using proper values of demand and capacity of inelastic displacements in a building for the design earthquake. Such procedure calls for a displacement-based design as a first step in the seismic design of a building.

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