Investigation into the floor diaphragm flexibility in rectangular reinforced concrete buildings and error formula

Building structures are typically designed on the assumption that the floor systems serve as rigid diaphragms that span between the vertical resisting elements. Such an assumption is normally perfectly adequate for the seismic analysis of most buildings, but some structural forms, typically those comprising long, thin floor plans and perimeter lateral resisting elements, can exhibit significant in plane flexibility in their floor systems. The dynamic behavior of this latter class of structures is dissimilar to the behavior expected of typical structures and can lead to unexpected force and drift patterns. The main purpose of this paper is to use the finite element method to investigate the influence of floor diaphragm flexibility on the behavior of concrete structures. Initially a parametric study is undertaken on a variety of reinforced concrete structures with rectangular plan form, perimeter shear walls and slabs that contain openings. In the second part of the paper, a number of response spectrum analyses are performed on the structures assuming both rigid and flexible diaphragm assumptions. A regression analysis is then performed on the results to obtain an error formula that can be used to estimate the error involved in using the rigid diaphragm assumption on structures similar to those tested.