ECONOMIC CONSIDERATION OF HSC IN MULTI-STOREY BUILDINGS

Abstract

There are several advantages in using high strength concrete in building construction, the principal one being the economic benefits derived from its use in primary structural members such as columns. With an increase in concrete strength, the engineer can design a smaller member size to carry the same loads that a large member of ordinary strength concrete would carry. Reduced member size increases the amount of rentable space and is specially beneficial when there are architectural restrictions on column sizes. Moreover, high strength concrete adds to saving by allowing construction forms to be stripped sooner, due to early high concrete strength and lighter foundations. In this era of high construction costs, the shorter the time period between project beginning and occupation of the building by paying tenants, the greater the savings to the developer. In this study, economical feasibility of using high strength concretes in columns for 10, 15, 20 and 25 storey buildings were carried out. A typical square building plans with frame cum shear walls was selected and the normal design loads were assumed to be uniform. Because of the uniformity of the loads and the repetition of the frames, 2-D computer analysis of frames permitted the computation of forces and displacements with sufficient accuracy. In the study, material characteristics in terms of concrete strength and number of stories in the building were varied. Normal design loads comprising of dead load, live load, wind and earthquake have been considered. Concrete grades of 27, 42 and 52 MPa cylinder compressive strength were considered for comparative cost analysis. For the design of columns, critical load combinations from the three load cases of earthquake, wind and live load (on all spans) plus dead load were considered. As a part of this study, a computer program for "optimized" column design was developed to design both uniaxial and biaxial columns. The program also calculates the cost of columns in a block of five storey each from the unit cost of constituent materials and the shuttering cost.