engleski

Damage Control of Masonry Infills in Seismic Design

The limitation of damage to non-structural masonry infills in RC structures induced by earthquake ground motions is of major interest for the prevention of extensive economic losses and possible threats to human lives. Field observations after major seismic events repeatedly point towards the high seismic vulnerability of masonry infills, not only in older buildings but also in more recently designed RC frame structures. In the last decade, several strong earthquakes have occurred on the Italian territory and problems related to the performance of masonry infill typologies and construction techniques typically adopted in Italy and other European countries, prone to seismic activity, have been identified. Although measures for the prevention of infill damage are to some extent included in modern seismic design codes, an effective design procedure has not yet been achieved. This work focuses on a specific group of infills widely adopted in European (and in particular Italian) construction practise, representing traditional unreinforced clay masonry infill typologies, with masonry panels constructed in complete contact with the surrounding RC frame. The main objectives of this work are related to (i) improvements in the understanding of the seismic response of newly designed masonry infilled RC structures in function of relevant design parameters and infill typologies and (ii) the development of recommendations for a refined verification procedure in order to provide enhanced damage control for masonry infills. The two principal objectives of the research are achieved through an extensive analytical parametric study on newly designed RC structural configurations with different masonry infill typologies. Based on numerical models, calibrated with reference to the representation of masonry infills, based on test results from previous experimental studies, a series of nonlinear time-history analyses has been carried out. The structural response is evaluated primarily in terms of inter-storey drift demands closely related to the masonry infill damage. The influence of several design parameters on the seismic response of masonry infilled RC structures and in particular, the infill performance is investigated, including building height, ground motion intensity, ductility class, and masonry typology. Given that in current force-based seismic design practise the design of RC structures with masonry infills is commonly carried out on bare frame configurations, with reference to European and Italian national seismic design provisions, particular attention is devoted to the presently existing inter-storey drift limitations, imposed on the RC structure during the design procedure. The introduction of refined inter-storey drift limitations as a function of various design conditions is proposed, based on the prediction of drifts for infilled structures derived from drifts of the corresponding bare structural configurations, with the aim to ensure a more effective infill damage control without overly penalising the RC structure. Bearing in mind the strong relation of in-plane and out-of-plane damage and the significant reduction of out-of-plane resistance due to previous in-plane damage, the present work is primarily focusing on the in-plane structural response and infill damage control. However, issues related to the currently adopted codified verification of the outof-plane stability of non-structural elements are addressed and a simplified method for the evaluation of the out-of-plane resistance accounting for reduced strength due to previous in-plane damage is proposed, starting from available test results. The verification of possible local effects on the columns of RC frame structures due to the presence of masonry infills is examined, and a procedure for the evaluation of design column shear demands as a function of expected inter-storey drifts of the infilled structure is introduced. The proposed design approach may be supplemented in the future with further experimental evidence and required design parameters. An extensive experimental campaign related to the response of clay masonry infill typologies is in progress at the Department of Civil Engineering and Architecture of the University of Pavia and at EUCENTRE of Pavia.

masonry infills; damage limitation; seismic design; nonlinear analysis

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