The Non-Linear Behavior of Mixed Reinforced Concrete–Steel Frames under Strong Earthquakes

Abstract

Mixed building frames constructed using reinforced concrete (RC) in the lower stories and structural steel in the higher ones meet great scientific interest as forming a common and often constructed building type. However, the current seismic regulations do not provide special guidelines for the aforementioned vertically mixed building type, but only for building frames constructed with the same material throughout. In addition, a small number of respective works in the literature can be found, thus underlining the need for the thorough examination of the nonlinear response of mixed reinforced concrete and structural steel frames subjected to strong ground excitations. Due to space limitations, selected cases of mixed RC–steel 3D frames are analyzed here via nonlinear dynamic analysis under selected intense earthquakes, considering appropriate nonlinear mechanical models for structural elements. A comparison of nonlinear response results is performed for two considered connection types of the steel part on the RC part, which are called “fixed” and “fixed-pinned” connections here. In this way, the nonlinear response of mixed-frame cases is studied under extreme ground motions, towards the utmost unfavorable conditions. Selected comparative nonlinear response results and plots are presented to estimate the behavior of mixed frames. Qualitative remarks arise from the current described investigation, resulting in practical suggestions for the design enhancement of mixed buildings, available for the upgrade of current codes.

Keywords

• mixed frames
• reinforced concrete
• steel
• time–history analysis
• non-linear behavior
• strong earthquakes