Seismic Induced Floor Accelerations and Diaphragm Forces for Buckling Restrained Braced Frames


Abstract eng:
Floor and roof diaphragms are essential part of seismic force resisting systems in building structures. They must be designed to withstand and transfer forces that are induced by floor acceleration in an event of strong earthquakes. Reconnaissance reports of major earthquakes have shown that diaphragms structural integrity is one of the key factors to obtain satisfactory seismic performance of structural systems. This article presents a comparison between Canadian and U.S. building code provisions regarding diaphragm seismic design forces and a case of 10-storey buckling-restrained braced frame is elaborated as an example. Despite the general similarities, building codes in the two countries prescribed significantly different design values for the case studied. The results of nonlinear time history analysis conducted on 3 to 15-storey codeconforming ductile steel braced frames are then compared to the Canadian code (NBCC) specified design values. These analyses show that diaphragm forces exceed the design values by a significant margin and diaphragms overload can be repeated many times during a typical design level earthquake. Current peak floor accelerations defined in NBCC for the design of non-structural elements and building components is also shown to be overlay conservative, especially at the roof level. Large diaphragm forces are generated as a result of time delays between storey shear forces in adjacent storeys with maximum values occurring during elastic phases of the response. This delay is strongly related to the ground motion intensity and frequency content. Based on the observations made in this study, possible avenues are proposed to improve design provisions for peak floor accelerations and diaphragm inertia forces.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2423.:
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