Out-of-Plane Ambient Vibration Tests of an Infill Wall in RC Frame Subjected to Previous In-Plane Damage

Masonry infill walls are widely used as enclosure elements in reinforced concrete (RC) buildings to provide thermal and acoustic insulation. Past earthquakes have identified the masonry infill walls’ out-of-plane collapse as one of the predominant modes of failure. Out-of-plane failure is characterized by brittle behavior and it is, therefore, a threat to human safety. Moreover, the out-of-plane capacity is significantly affected by the presence of cracks due to the in-plane damage related to the interstorey drift. In order to identify the out-of-plane behavior of infill walls depending on the in-plane damage, an experimental campaign based on cyclic quasi-static tests has been initiated on a full-scale infilled RC portal frame at the Laboratory of Structures of the University of Basilicata. The one-bay (4.5 m span), one story (3 m height) frame infilled with two layers of hollow clay brick walls 8 and 12 cm thick, has been subjected to in-plane loading by means of three reversed cycles for each increasing amplitude, until the story drift was equal to 2% and extensive damage occurred to both the infills and the RC members. After each set of three in-plane cycles, a dynamic identification of the infills’ layers has been carried out based on ambient vibrations in order to detect changes in its dynamic behavior. This latter, using nine accelerometers placed on the infills’ surface. The identification tests provided valuable information regarding the out-of-plane (OOP) frequencies during the test as a function of the in-plane drift. The paper describes the results of in-plane tests in correlation with the results of the ambient vibration tests