Strength Versus Drift Limitation Effects on Code-Compliant Seismic-Resistant Flat Slab Buildings

Abstract eng:
This paper quantifies the relative contribution of minimum stiffness (i.e., code drift limit) versus minimum strength requirements to an economic and reliable design of low- to mid-rise flat slab buildings located in moderate seismic zones (0.25g) and dimensioned as per the emerging version of the seismic design code in Egypt. Two building schemes are considered: “columns-only” and “columns-shear walls” reinforced concrete flat slab buildings. Three versions of each type, namely 4-, 8- and 12-story are investigated with a theme layout representative of typical office building construction. The procedure starts by designing the flat slab buildings for “gravity only” loadings. Then, each building is checked for compliance to code seismic design requirements for strength (“No-collapse Limitation”) and stiffness (“Damage Limitation”) through bi-directional multi-mode response spectrum analysis performed on three dimensional computer models of the structure. Re-dimensioning of lateral resisting structural members is applied in order to achieve code-compliant structures under the code estimated seismic demand. In a final step, the design of all studied buildings is revisited and lateral load carrying elements are once more re-dimensioned to satisfy strength requirements only, thus completely ignoring code drift limitation. Buildings are then compared in terms of relative quantities of construction materials to estimate (1) the benefit of adding shear walls to the somehow inherently flexible flat slab buildings; and (2) the penalty which stringent design code analysis constraints may impose on the design economy of such building systems.

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