Structural and economic comparison of 4, 8 and 16-storey reinforced concrete frames with varying steel ratios

In areas of low and moderate seismicity, a significant number of buildings are constructed with framed reinforced concrete (RC) structures. These structures are characterised by their low cost and the small amount of material used, due to their small sections (columns and beams). The smaller amount of material in the sections results in reduced resistance and structural properties, requiring the use of stiffening elements such as bracing or walls (infill or structural walls). These characteristics mean that the structural sections require a certain minimum amount of steel and concrete (as proposed by the many world HA Standards). This means that acceptable structural behaviour can be achieved in the face of events such as high winds or earthquakes, improving the ductility and lateral resistance of the structures. On the other hand, earthquakes such as those in Turkey (2023) or Lorca (2011), have revealed that many of these buildings were designed with less steel than that estimated in the structural codes, without considering criteria such as the ductility; they only considered low lateral resistance. The objective of this work is to determine the optimal amount of steel (1%, 2%, 3%, 5% and 8%) necessary in the structural sections (beams and columns) that make up the frames, according to several factors: resistance, plastic and ultimate deformation, ductility, CO2 emissions and cost. The paper concludes that there is a need to introduce a certain minimum amount of steel in structural sections, the optimal amount being between 3-5%.