Earthquake resistant foundation system of low rise building

Abstract

Most low rise buildings in Bangladesh are reinforced concrete frame with unreinforced solid clay brick infill wall as a partition. The frames are designed as the primary lateral force resisting system; the stiffness and strength of brick infill walls are not conventionally considered in analysis and design. So isolated column footing is commonly provided in low rise buildings. Infill brick wall significantly affect the response of RC frame structure during earthquake. The change in lateral stiffness, strength and natural period of the frame structure due to the presence of infills change the behavior of the building under seismic action. Therefore, continuous wall footing for a low rise building can be an earthquake resistant foundation system because of (i) infill wall between foundation and grade beam (ii) symmetry in elevation (iii) uniformity and continuity in horizontal and vertical direction and (iv) integral action of foundation and super-structure. To investigate the seismic resistant behavior, a 3-storied frame structured building was studied under conventional method and confined method. In conventional method brick wall is considered as loads on beams and slab. Stiffness and strength is completely ignored in analysis and design. So conventional method did not shows real behavior of the buildings during earthquake. In confined method masonry brick wall was modeled as structural element. Compressive strength and stiffness of masonry wall was considered in analysis and design. Also confined masonry construction method was adopted for construction which based on ―first brick wall and then frame‖. Based on this study it was found that confined continuous masonry wall footing is the better seismic resistant foundation than conventionally designed isolated column footing for low rise buildings. Also consideration of infill brick wall in analysis and design of RC frame structured building and adopting confined method of construction increases lateral resistance, storey shear capacity, lateral stiffness, energy dissipation capacity, improve ductility behavior and decreases storey displacement of the structure rather than conventional bare frame method of analysis and design. Performance of confined masonry building and conventional bare frame building in several part earthquake already proof these benefits. Also confined method reduces the foundation cost approximately by 21.5% and total cost of the building by 15% rather than conventional method of low rise building. Finally it is concluded that the confined method of analysis, design and construction of RC frame structured low rise building is more seismic resistant than conventional bare frame method.