EFFECT OF FOUNDATION SOIL ON STRUCTURAL ECONOMICS OF EARTHQUAKE RESISTANT DESIGN OF RC BUILDINGS

Abstract

For a particular building, the magnitude of the lateral loads due to earthquakes will depend on the zone in which the building is located and the type .of soil upon which the building is supported. The variation in the design lateral loads due to seismic zone and the type of soil will affect the size of the structural members like beams, columns and foundations, which in turn will influence the structural cost of the building. Here, the structural cost refers to the cost of the materials that are structural steel and concrete. This excludes other factors such as labour, non-structural members, electrical and water fittings, etc. An attempt has been made to study the structural economics of the building, i.e., the change in the structural cost when a four-storied RC building in the same zone (zone IV) and with the same geometry is analyzed, designed and detailed for varying soil types [15]* For simplicity, symmetrical buildings with no openings are taken, and three dimensional frame models of the buildings are generated in SAP (Structural analysis program) [28] software. Apart from it, the analysis of buildings incorporates SSI (Soil-structure Interaction) effects as per the guidelines given in FEMA-440 [6], FEMA-356 [5] and ATC-40 [3]. Then seismic analysis is done for the response of the building as per IS : 1893 [15]. Thereafter, the design and ductile detailing of members of the building are carried out as per IS : 456 [I1] and IS : 13920 [21]. The quantity of steel and concrete for each case has been computed. and structural costs of these two materials are found. The comparison of the structural cost has been done among the considered cases.