Strength Reduction Factor Of RC Frames Including The Effects Of Masonry Infills

The Masonry infilled reinforced concrete(RC) buildings constitute a popular building typology in many cities of China.Primary reasons for the same are easily available construction materials,flexibility in layout, and the traditional practices in some cases. As shown in the existing studies which focus on the study of simplified analytic model and the seismic behavior of the masonry-infilled RC frames,the mechanical characteristics and failure modes of different types of masonry-infilled RC frames are obviously different, but the judgement of different infilled frames has not been perfertly proposed. The strength reduction factors are not only the key factors in determining design seismic force in force-based seismic design,but also the cornerstone of the performance-based seismic design.However, Seismic code of China take a unified values as strength reduction factor,which neglects the influence of structure system and ductility etc.Besides,there are a few studies on the strength reduction factor of RC frames. Therefore, research on the judgement of different types of masonry-infilled RC frames and strength reduction factors was carried out in this paper, the following studies include:(1) The ratio between shear capacity of column and masonry infill wall is used to judge the type of masonry-infilled RC frames based on the data collected and compiled from different tests.The masonry-infilled RC frames are divided into two types,one is ‘strong frame with weak infill wall,the other is ‘weak frame with strong infill wall’. In addition,the characteristics of the backbone curve, failure modes and the influence of the infill wall’s physical properties are also studied respectly.(2) A new hysteretic model is established by using the backbone curve obtained in previous studies combined with certain hysteretic rules.The model is more suitable for the study on the masonry-infilled RC frames. The infulences of period of vibration,ductility factor,site class and the parameters of the backbone curve on the constant ductility strength reduction factor are analyzed. Besides,the results of the hysteretic model established in this paper are also compared with other hysteretic models.(3) The influence of Physical properties of the masonry infill walls on the constant ductility strength reduction factor is fully analyzed. The differences in physical properties of the masonry infill including: the difference in the strength of bricks or blocks which consist of the infill wall, difference in opening configurations(window or door),the difference in window opening locations,the difference in the size of window and door, the difference in aspect ratio. After analyzing their effects on strength reduction factor, a simplified equation of constant ductility strength reduction factor which considers the effects of masonry infill wall is suggested.