SEISMIC EVALUATION OF REINFORCED CONCRETE BUILDING WITH SOFT STOREY

Abstract

A G+ 10 RC building frame with one and two bay has been taken for the study of soft storey problem, analyzed and designed using the five different approaches, viz., (i) IS 1893(Part 1):2002 Code criteria, (ii) Capacity Based Design, (iii) Energy Based Design, (iv) Equal Displacement Based Design, (v) Direct Displacement Based Design. Analysis has been performed without considering the stiffness of infills in first method. Capacity based design has been carried out using the results obtained from the previous analysis of the frame for further revision of capacity. In energy based design, multiplication factors has been determined by assuming that sections of all columns are kept same in all floors for uniform structure as those from the initial analysis and infills are added for analysis of rigid structures. Equal and direct displacement based designs has been carried out with an assumed spectral velocity. The design of members has been carried out using SP-16. The design carried out by IS 1893(Part 1):2002 design criteria yielded that the soft storey can resist up to 76% and 69% of the base shear of the maximum considered earthquake with out any reduction factor (i.e., R=l) for one and two bay frames respectively. The observations from the results of capacity based design method are (i) the moment magnification factors are (a) nearly equal to 1.0 at the joints of top and bottom storeys, (b) maximum at the joints of intermediate storeys, (c) nearly equal at all the exterior joints of 2-bay and 1-bay frames, and (d) higher near the interior joints compared to exterior joints of 2-bay frame. In energy based design, (i) the multiplying factors for the design of soft storey elements of 1-bay and 2-bay framed buildings are 1.825 and 1.928 respectively. (ii) soft storey can resist 55 % and 46% of the base shear of maximum considered earthquake with reduction factor of R=1 for 1-bay and 2-bay frames respectively. From equal displacement based design, the design base shears are found to be 52% of the design base shear of the design base earthquake with R = 5 for both one and two bay frames. Direct displacement based design, the design base shears are found to be 79% and 84% of the design base shear of the design base earthquake with R =5 for one and two bay frames respectively.