ABSTRACT
In spite of the numerous damages during the earthquakes in the past, partially infilled RC frames have not been adequately studied. There are only a handful of experimental studies and a very few analytical studies currently undertaken on the partially infilled RC frames. Chiou et al. (1999) carried out the full-scale tests on one-bay onestorey fully infilled, partially infilled and bare frames. The partial infill wall was found to induce short column effect leading to the severe damage of columns under the in-plane monotonic loading. To study the mitigation measures of the captive column effect, Babu et al. (2006) conducted the tests on two sets of partially infilled RC frames with and without masonry inserts. The performance of partially infilled frame with masonry inserts was reported to be better than without it. Similarly,
1 INTRODUCTION
The regular masonry infill walls in the Reinforced Concrete (RC) frame building are considered by many researchers as beneficial to the overall performance of the building. The infill wall increases the stiffness, strength and damping of the RC frame and in turn, reduces the lateral deformation. However, irregular arrangement of masonry infill wall in the RC frame causes a number of detrimental effects such as soft storey effect, captive column effect and torsional effect. The captive columns are the consequence of partially infilling the RC frame with the masonry walls. The lower portion of the column is kept captive by the surrounding infill wall leaving only the upper portion of the column for the potential deformation as shown in Figure 1. The total deformation that is designed to be sustained by the full height of the column, H is forced upon to the reduced height of the column, h. This results in the increase in column shear force and hence possibly severe damages to the upper free portion of the column during the earthquakes. In many previous earthquakes such as the 1985 Mexico earthquake, 2001 Gujarat earthquake, 2008 Wenchuan earthquake and 2015 Nepal earthquake, captive columns induced by the partially
Huang et al. (2006) tested two sets of one-bay one-storey RC frames consisting of full infill, partially infill walls and bare frames with and without wrapping the columns with the Carbon Fiber Reinforced Polymer (CFRP) sheets under the horizontal cyclic loads. They observed improvement in the lateral load capacity and reduction of captive column effect for the case where CFRP sheet is used. Jayaguru and Subramanian (2012) also tested two sets of two-bay two-storey non-ductile RC frame with partial infill wall on the ground floor. The first set was tested under the lateral load without reinforcing the columns while the second set was tested by wrapping the ground floor columns and a portion of the first floor beams by Glass Fiber Reinforced Polymer (GFRP) composites. It was observed that the RC frame retrofitted with GFRP exhibited increase in shear strength by approximately 60% leading to the overcoming of captive column effect. However, its effectiveness was limited by the bond between the column and GFRP sheet. Taher and Afefy (2008) investigated the seismic response of low, medium and high-rise buildings with partial infill walls and with various percentages of openings. They reported the increase in stiffness, strength and frequency of the buildings depending on the location and percentage of openings. They also observed that the infill walls located on the lower floor provide a higher contribution to shear strength and stiffness than those located on the upper floors. Pradhan et al. (2014) studied the effect of the partial infill wall using two sets of masonry strengths and also varying the height of the partial infill wall in the frame. He observed the increase in the shear force of columns by 1.5 times and recommended the full wall to be provided in the frame.
