Seismic force distribution in members of confined masonry buildings

Abstract

Seismic design codes for confined masonry (CM) buildings are few; therefore, in many places these buildings are generally designed and constructed using simplified guidelines or handbooks. For brevity, it is assumed that masonry walls resist all possible loads imparted on CM buildings, while the only role of reinforced concrete (RC) confining members, also known as tie-members, is to provide the confinement and stability (both in-plane as well as out-of-plane) to the masonry walls. Though such an assumption simplifies the design process, it results in missing out on significant material strength that the tie-members can potentially add up to the structural strength. On the other extreme, such a simplification can also result in construction of weaker tie-members, especially the tie-columns, because the seismic design forces are generally not distributed to different members of the CM buildings. In the present study, a methodology was developed to distribute the seismic design forces to different members of CM buildings such that the tie-columns can be formally designed to not only provide confinement and stability to the masonry walls, but also provide reserved strength that may be utilized in case of failure of masonry walls. Empirical and numerical approaches were followed in developing the methodology. The approaches utilized all the available empirical methods for lateral strength estimation of CM walls and results reported in large number of past experimental studies, including three tests carried out by the authors. An extensive parametric finite element study was carried out considering the influence of several important parameters, and a methodology was developed for relative distribution of shear forces in tie-columns and masonry walls of CM walls.