A comparative investigation on experimental lateral behaviour of bare RC frame, non-strengthened and ferrocement strengthened masonry infilled RC frame

Abstract

Although concrete framed structures are widely used with masonry infills, the contribution of masonry infills in structural design is limited to their dead loads only. Therefore, the full-fledged stiffness characteristics of masonry infill are not often considered. However, recent earthquakes showed the impact of masonry infill on the lateral behavior of surrounding RC frames. Moreover, sometimes existing masonry infills are strengthened using Ferrocement (FC), Textile Reinforced Mortar (TRM), Carbon Fiber Reinforced Polymer (CFRP), etc., which might also have a similar impact on surrounding RC frames. The impact includes enhanced shear demand, damage, etc. However, the effect of the enhanced shear demand on RC columns is a relatively less investigated issue. In this context, an experimental program was designed to compare the effect of non-strengthened and FC strengthened masonry infill on the behavior of the surrounding RC frame in terms of lateral strength, hinge formation, shear demand enhancement, and damage to columns. The test specimens, including a bare RC frame, a masonry infilled RC frame, and a FC strengthened masonry infilled RC frame, were subjected to a quasi-static cyclic lateral loads. The experimental result showed that the masonry infill and FC strengthened masonry infill increased lateral strength, on average, by 81% and 244%, respectively, when compared to that of the bare RC frame. Meanwhile, FC strengthening of masonry infill improved the lateral strength, on average, by 90% when compared with the masonry infilled RC frame’s lateral strength. In this study, low-strength masonry infill caused the formation of a short column on the tension column of the RC frame. The application of ferrocement to low-strength masonry altered the position of the plastic hinge formed on the tension column of the RC frame when compared to that of the masonry infilled RC frame. Therefore, ferrocement strengthening of masonry eliminated the short column phenomenon in this particular study. Nevertheless, the shear demand (in terms of strain on the column tie) enhancement of the tension column was not substantial due to the ferrocement strengthening of the masonry infill when compared to that of the masonry infilled RC frame. Moreover, the damage concentration on RC columns (i.e., residual crack width) after insertion of masonry infill and ferrocement strengthened masonry infill changed to a smaller extent when compared to the bare RC frame damages, where the residual crack widths were within 1.0 ~ 2.0 mm.