Investigation of joist floor diaphragm flexibility on inelastic behavior of steel braced structures

The flexibility of floor diaphragms has a significant influence on the behavior of buildingstructures. commonly, in analyzing structures, floor diaphragms are considered rigid. this assumptiondistributes lateral loads between the resistant elements according to their rigidities, and decreases thedegree of freedom that creates easier analysis. however, in steel structures with braced frames and longspan floors, diaphragms usually behave flexibly. the seismic responses of such structures vary to theexpected response of typical rigid floor structures. ignoring the effects of diaphragm flexibility can lead tonon-economic or unsafe structural design. in this paper, the nonlinear responses of braced steel buildingswith flexible concrete block-joist floor diaphragms are investigated under both static lateral load anddynamic ground motion, and they are compared with the responses of structures with the assumptionof rigid diaphragms. this study demonstrates that span ratio is an important parameter in the flexibilityof floor diaphragms, and if this ratio exceeds three, the variation of results between the two assumptionsof flexible and rigid diaphragms may not be ignored. in addition, results show that diaphragm flexibilitychanges the seismic response of the structures and linear analysis is not sufficient to explain this behavior.