Seismic behaviour of reinforced concrete frames with different configurations of masonry infill : experimental study

Abstract

It is well known that the seismic effect of masonry infills is not fully considered in the reinforced concrete frame structures worldwide and especially in European countries, even if it provides a relevant support on the overall structural behaviour during earthquake events. The purpose of this research is to analyse the influence provided by the infill wall on the RC frame response under reversed cyclic load and to study new solution on the interaction between infilled wall and surrounding RC frame in order to enhance ductility and energy dissipation of the system. To pursue this goal four scaled specimens with different configuration of infills and a bare frame as a reference specimen have been tested. The design of the frames was not made for a gravity load configuration, but according to the seismic load design specification of medium ductility (DCM) behaviour structure in the current Eurocode8. A more effective connection has been designed in such a way that lateral gaps were introduced between the formwork panel and the frame to provide enhancement in lateral displacement and ductility while mild steel the connectors with various diameter were inserted to avoid the out-of-plane failure without transferring any lateral load from the wall to the columns. The differences in results regarding stiffness, ductility and energy dissipation were obtained varying the frame-to-infill interaction effect. Hysteretic loops have been drawn to provide a better understanding of the energetic behaviour of the frames and a precise explanation of crack pattern directly observed on the specimens has been detailed. Therefore, from the experimental results, it is possible to conclude that by isolating the columns from the infills, the ductility factor enhances significantly as well as the energy dissipate during the loading while the slitted walls one didn’t provide enough rigidity. Moreover it has been verified that stronger connection causes greater damage in the infill with the appearance of diagonal cracks and sliding surfaces along mortar joints compared to weaker ones and it can break, losing then its role of avoiding the out-of-plane collapse of the wall. The irregular positioning or eccentric arrangement of the opening can influence greatly the load-transfer path and crack propagation into the wall; further studies are needed to recover the high level of uncertainties on this topic. As recommendations for future design and implementation of current seismic codes it can be suggested that the lateral gaps width should not be lower than 2,5% of lateral inter-storey drift or 100mm to obtain the desired level of ductility. Furthermore the lateral connectors should be selected to be weak enough for not transferring any stress from the wall to the columns and vice versa but strong enough to satisfy infill wall safety requirements. Panels opening need particular attention and further studies with suggested corrections on the design of the columns particularly against shear forces.

Date of Award	2015
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology