EFFECT OF THE BUILDING ASPECT RATIO ON RESPONSE MODIFICATION FACTOR FOR REINFORCED CONCRETE MOMENT RESISTING FRAMES
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Date
2023-07-02
Authors
Dana Issam Abdul Kareem Nassar
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Abstract
Abstract
The response modification factor (R) is one of the essential factors in seismic design and is used to define the nonlinear behavior of buildings during an earthquake. International codes such as IBC 2016 provide a constant value for “R” for a particular structural system. However, the value of "R" may change based on parameters including zone factor, soil site class, aspect ratio of the frame, column orientation, and type of slabs. This study investigates the effect of building aspect ratio on the value of "R". In addition, it checks if the values of the R factor recommended by the IBC-2016 code are conservative. A single cycle for calculating the R factor is applied by pushover analysis (nonlinear response analysis) to achieve this goal. It was applied to many 3-D intermediate moment-resisting frame systems with different aspect ratios as the key parameter and different seismic zone factors and sites as secondary parameters to determine the behavior of the frame with increasing lateral force until collapse. The researcher selected 30 cases with different aspect ratios, zone factors, site classes, and building plans. Then, the ETABS2016 program is used to design and analyze (elastic analysis) the 3-D frames as per previous code requirements. Finite element software (ABAQUS) performs the nonlinear analysis via incremental Elasto-Plastic analysis. The reinforced concrete elements are presented in the program as line elements. Afterwards, the Xtract program is used to evaluate the inelastic properties of the sections fed to ABAQUS for the frame analysis. The obtained results of "R" are compared to the values suggested by international codes (IBC 2016). The results demonstrate an influence of the aspect ratio, zone factor, and site class on the R factor. An equation was derived to calculate the R factor through the aspect ratio of the building and the seismicity of the region. Consequently, the computed values for the cases depending on the pushover curve are larger than or equal to those recommended by the IBC2016 code. So, the international code is conservative, in term of the total base shear, force because it considers the period of the building in the calculation of the R factor. However, further ductility investigation is needed as the required R values are higher than code ones.
Keywords: Nonlinear static analysis; ABAQUS program; response modification factor