Influence of Seismic Hazard and Importance Class on The Behavior of Reinforced Concrete Structural Elements

Abstract

A significant step forward in structural engineering in our country is the implementation of European standards (Eurocodes) for structural design of buildings, which tend to be the only valid ones. For that reason, in this research it is decided the provisions of these standards to be applied to a real, reinforced concrete structure, which is a four – story residential building located in Skopje. Knowing that the region in which we live is extremely seismically active, special attention is paid to the seismic action and its influence on the behavior of reinforced concrete structural elements. It is a numerical analysis that is realized by varying certain parameters that define the seismic action. Firstly, the seismic hazard is analyzed, which according to EN 1998-1 is described in terms of a single parameter, i.e. the value of peak ground acceleration agR (PGA). According to the seismic zone map for our country, its territory is divided into five seismic zones, so that PGA takes the following values: agR={0,1g; 0,15g; 0,2g; 0,25g; 0,3g}. By implementing an analysis for each of the listed values, it is realized how and to what extent the location affects the behavior of reinforced concrete structural elements. The second variable parameter is the importance factor that according to EN 1998-1 takes different values, depending the importance class in which the building is classified. For the purposes of this part of the research, these importance classes are analyzed: Class II (residential building), Class III (school) and Class IV (hospital). It is expected that by increasing the variable parameters, the design values of the effects of actions in beams and columns also increase. As a consequence to that, the geometric reinforcement ratio increases, too. When PGA varies, the design values of bending moment in beams, and thus the reinforcement ratio increase by 2-3 times. At the column sections, this ratio reaches an increase of 40 % when PGA varies and 35 % when importance factor varies. Common feature for all column sections is the ductile failure, so that the strain in steel decreases up to 34 % in the sections where the ultimate strain in concrete is achieved, and the strain in concrete increases up to 94 % when the ultimate strain in steel is achieved. Overall, it may be said that seismic action has a huge impact on the structural elements and the behavior of the structure at all. Therefore, it is necessary to pay special attention when designing buildings that are located in seismically active areas.