This paper presents how performance-based design (PBD) approaches can help to improve the structural performance and cost effectiveness in design of floor diaphragms of tall buildings under earthquakes. In contrast to the prescriptive design approaches, performance-based design provides a systematic methodology for assessing the performance capability of overall building system and its components. The performance-based design explicitly evaluates the response of the building under the potential seismic hazard, considering the probable site-specific seismic demands as well as the uncertainties in the post-yielding response and behaviour of the building under seismic events. Case study of 57-story reinforced concrete residential building with 4 basement levels is presented. The building was designed for Design Basis Earthquake (DBE) level in accordance with traditional code-based design procedures at the preliminary design stage. After preliminary design, the performance of the building was checked explicitly at Service Level Earthquake (SLE) (43-year return period) and Maximum Considered Earthquake (MCE) level (2475-year return period), using linear and nonlinear response history procedures. Diaphragm design forces at podium level and tower levels were explicitly checked at site-specific MCE level event rather than application of code-specified modification factors to estimate the forces and deformation under code-specified earthquake level. Cost effectiveness of the design was evaluated by comparison of the indicative quantities and parameters between the code-based design and the modified design based on PBD.
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