Seismic behavior of composite coupled wall systems

A coordinated experimental and analytical study was carried out to develop a basic understanding of cyclic behavior of steel-concrete composite coupling beams, and to examine issues related to the connections of such members to reinforced concrete walls. The research presented is focused on a hybrid wall system in which conventionally reinforced concrete walls are coupled by steel/steel-concrete composite coupling beams.; The study revolved around a 20-story reinforced concrete structure with a central core formed by coupling three individual walls. A number of subassemblies were extracted from the structure for laboratory testing.; The experimental phase was conducted in two phases. All the specimens were 1/3-scale models. In the first phase, four specimens consisting of one-half of a coupling beam and a small portion of wall pier were fabricated and tested. The wall segment was subjected to a constant axial load equal to that due to gravity loads. A more complete set of subassemblies were tested in the second phase. The specimens in the second phase included one-half of a coupling beam and an approximately one and a half-story high wall pier. The coupling beam was subjected to cyclic shear, and the wall was subjected to overturning moment as well as gravity axial load. The main test variables were (a) presence or lack of nominally-reinforced encasement around steel coupling beams, (b) number and spacing of web stiffener plates, (c) method by which the required embedment length is calculated, and (d) floor slab.; Static and dynamic linear and nonlinear analyses were completed in an effort to identify the test specimens, their configuration, and their loading techniques.; The experimental data suggest that nominal encasement around steel coupling beams provide an effective means for preventing web buckling. The increased strength and stiffness due to the surrounding concrete encasement could be detrimental if not incorporated in design. The additional stiffness increases the level of coupling between walls, which affects the distribution of demands on the walls and foundation systems. The contribution of floor slab towards stiffness of steel-concrete composite coupling beams is lost after rather small deformations.; Available techniques for computing the embedment length of steel brackets inside reinforced concrete columns can reliably be used for steel-concrete composite coupling beams. Satisfactory energy dissipation characteristics, ductility, and load-carrying capacity of composite coupling beams are possible if the embedment length is calculated to develop 1.56 times the sum of the shear capacity of the steel beam and encasement. The contribution of floor slab towards capacity of composite coupling beams depends on the direction of bending. Under positive bending the capacity is larger. Floor slabs can apparently prevent the formation of plastic hinges in the connection region, and their contribution towards capacity of steel-concrete composite coupling beams may be ignored when the embedment length is computed.; Inelastic static and dynamic analyses show that the maximum expected coupling beam shear angle in coupled walls is considerably less than the assumed value in current design provisions. A simple procedure is proposed to compute a more reliable estimate of the expected coupling beam shear angle demands. (Abstract shortened by UMI.)...