Experimental and computational strategies for the seismic behavior evaluation of frames with infill walls

Experimental and computational strategies for the evaluation of the seismic performance of frames with concrete block masonry infill walls were investigated. The work is divided into three main parts: quasi-static experimentation, pseudo-dynamic experimentation, and computational methods.; In the quasi-static experiments, reduced scale, one-story Gravity Load Designed (GLD) infilled frames were subjected to cyclic loading with increasing amplitude. Observed failure modes consisted of masonry crushing in the infill corners, and mortar joint cracking and slipping. The experiments included undamaged and previously damaged infills. These results were used to quantify the straining actions in the frame members arising from frame/infill interaction.; In the pseudo-dynamic experimentation part, an experimental procedure and the corresponding controlling algorithm were developed and refined until the inherent experimental and numerical errors were minimized. The importance of the proper consideration of the residual force and the step-by-step integration method used in the control algorithm was shown. The resulting experimental procedure was used in testing a reduced scale two-story GLD frame with infills. Experimental findings demonstrated the infill crack evolution, and the results were used to establish the distribution of energy terms for different intensity levels of earthquake loading. It was shown that dissipated and imparted energies can serve as a useful damage indicator.; In the third part, several computational techniques were developed to calculate the response of frame with masonry infill walls. Two finite element approaches were investigated. In the first, masonry was treated as a composite material where the cracking and slipping of mortar joints were treated as the source of material nonlinearities. The numerical discretization consisted of interface elements for the mortar joints and plane stress elements for the blocks.; In the second finite element approach, masonry was idealized by an equivalent homogeneous material with properties derived from either a homogenization procedure or a system identification technique. Cracking was accounted for using the smeared cracking formulation, in which the concept of the evolution of the crack band width was developed and implemented.; Two simplified techniques for modeling infilled structures were also evaluated. One was based on equivalent nonlinear trusses to replace the infills. In the other, the response of the infilled frame was obtained using a nonlinear single degree of freedom system with properties derived from the static response of the original structure. This system was shown to be an excellent approach for establishing the seismic fragility of low-rise infilled frames.