Effect of material strength on the cost of RCC building frames

In this study, the influence of twelve concrete mix ratios and two rebar grades on the cost of 3, 7, 12 and 20 story RC building frames was investigated. Cylindrical concrete specimens having different mix ratios (by mass) were prepared with Ordinary Portland Cement and locally available fine and coarse aggregates. The compressive strength of concrete was tested on the 28th day of curing. A linear equation is proposed to predict the compressive strength of concrete keeping it as the function of the percentage of cement and the ratio of coarse and fine aggregate. Based on the compressive strengths obtained from different mix ratios, buildings of the same model were designed using the ETABS, as per the provision in Bangladesh National Building Code-2006 (which has a great similarity with the latest ACI code). Also, each building was evaluated individually for the two most conventionally used rebar grades. Therefore, in total 96 buildings were evaluated to obtain the total materials cost for each of the mix ratios and rebar grades. It was seen that (1) for low rise building the cost becomes lower when the lower strength concrete is used, (2) for medium to high rise building high strength concrete can be considered cost-efficient, (3) the mix ratios having a higher coarse aggregate/fine aggregate ratio tends to increase the cost, and (4) 500 MPa rebar was found cost-effective compared to 400 MPa rebar.