Asian Research Thesis Index

Abstract

Infill walls are normally considered as nonstructural components in Reinforce Concrete (RC) frames, and are often neglected in the structural analysis and design because of their complex behavior. In Pakistan, which is the 6th most populous country of the world, RC frames with infill walls is popular form of construction. Therefore, the principal objective of this research is to investigate the effect of infill walls on RC frame structures under lateral loading designed to BCP-SP2007.  To achieve the desired objectives, this research was conducted in two phases. In the first phase, six full scale, single story and single bay RC frames were tested. The variables, in these frames were opening type, opening location and quantity of infilled material used. These frames were representative of typical construction in Pakistan. Before the construction of the frames, engineering properties of the constituent materials were determined according to the ASTM standards. Frames were tested in displacement-control under quasi-static loading arrangement and crack propagation, collapse hierarchy and damaged levels were studied in detail. Discussion includes crack and failure patterns, hysteresis curves, energy dissipation, back bone curve, stiffness degradation, strength, displacement ductility, ductility factor, over strength factor, response modification factor and performance levels obtained. It was concluded from this phase that infill wall increased the strength and stiffness of the reinforced concrete frame. By providing door opening at the center, not at the side of infilled wall strength increased but stiffness decreased. Strength and stiffness are related to quantity of infilled wall used. Energy dissipation and performance levels are affected by infilled wall, and also affected by opening type and opening location in the infilled wall. It was also concluded that response modification factor is more sensitive to material strength and geometric configuration (period of structure) as compared to the single value of 8.5 for concrete special moment resisting frame being adopted by Building Code of Pakistan Seismic Provisions (BCP SP-2007).  In the second phase of this research, a half scale model of two story and two bay prototype was tested on a 6DOF/60-ton capacity shake table. The prototype was designed for Zone IV as per BCP SP-2007. Similitude relations based on dimensional analysis were drawn before the construction of the model. It was the first large scaled model designed according to BCP SP2007. It was tested on newly installed largest shake table in the history of Pakistan. Acquisition  ii   of material was done according to the scale of the models. Before the construction of model on the shake table, it was validated with 18-ton and 48-ton service loads, because the shake table was operated for the first time and it was necessary for design of experimental testing of program. Infill walls were provided at various locations with different combinations of door and window openings.  Three different test runs were performed on the model, using shake table. Before and after performing each run of high intensity, ambient and free vibration tests were performed to compute the natural frequency and damping of the model. To capture full range of the performance of the model, it was subjected to a series of sinusoidal motion with increasing frequency starting from 0.4, 0.5, 0.75 to 7.5 Hz with the increment of 0.25 Hz. The duration of the sinusoidal motion was kept around 20 seconds, and the data was recorded for 25 seconds at a sampling frequency of 200 Hz without applying any anti-aliasing filter.  Acceleration response histories and displacement response histories from the respective accelerometer and displacement transducers installed at the top, mid and base/bottom of the model were interpreted from which hysteretic curves were drawn. Energy dissipation was calculated for the first story, second story and for whole structure by finding area enclosed by the hysteretic curves.  It was concluded from this phase that masonry infilled panel wall alters the global response of the structure by decreasing the natural time period of the structure. After the generation of the cracks and dislodging of portions of infill walls, the natural frequency of the structure decreases and it follows different patterns depending on the properties and geometry of the infilled panel. Infilled panel with door and window openings is more vulnerable to lateral loadings, and nonuniform distribution of the infilled wall produces torsion in the structure.  The RC frame design behaved well (expect in fills) thus showing worthiness of BCP-SP 2007, however update to codes are needed based on this research and special attention to Nonstructure components is needed.

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