EFFECT OF SEISMIC ZONES AND SOIL TYPES ON STRUCTURAL ECONOMICS IN EARTHQUAKE RESISTANT DESIGN OF RC BUILDINGS

Abstract

Reinforced concrete buildings are conventionally analyzed and designed for gravity and other imposed loads. Such buildings possess adequate strength and stiffness to resist these vertical loads but do not have adequate strength and stiffness when subjected to additional lateral loads induced by earthquakes. The Indian subcontinent has experienced a number of devastating earthquakes in the past, repeatedly reminding us about the high level of seismic hazard and risk prevailing in India. Incorporation of seismic forces in the design though puts additional burden on the structural economics but it also ensures greater safety levels for occupants in the advent of any seismic disturbance. The lateral forces induce additional stress in structural members of the buildings, thus influencing their design and structural cost. Also, level of additional lateral force exerted on the building depends upon its seismic zone and on the type of soil profile existing in the region. Various combinations of seismic zones and soil types will result in difference in the design and hence in cost of the building. Quantification of differences in the cost is subjected to analysis and design of the buildings for each of these combinations followed by detailed cost. analysis. In the present study, a regular RC building is analyzed and designed for the different combinations of seismic zones and soil types as per IS 1893 (Part I): 2002. Zones III, -IV and -V are considered in combination with hard, medium and soft soils. Sizes of beams and columns are kept same in all the possible nine combinations. Cost of the steel reinforcement for all the cases is then calculated to study the effect of seismic zones and soil types on the structural economics in earthquake resistant design of RC buildings. It should be noted that structural economics refers to the cost of steel reinforcement in beams and columns of the building. Buildings are modeled and analyzed in SAP 2000 software while their design conforms to IS 456, IS 13920 and IS 1893 (Part I): 2000.