## DETERMINATION OF R-FACTOR USING NONLINEAR ANALYSIS FOR R.C SPECIAL FRAMES CONSIDERING SPAN VARIABILITY

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##### Date

2022-07-31

##### Authors

Yacob abu Hantash

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##### Abstract

Background: The Response Modification factor (R-factor) consider as the most important seismic design parameters, it is describing the amount of damping and inherent ductility in the structural system during an earthquake and it is used in general to reduce the actual seismic force to a design force, due to the inelasticity of the structure. Each of the global building codes gives a different procedure to describe the R-factor and give a different value, moreover, the R-factor is a nonlinear factor and it is very complicated thus, any change in the structural system leads to a different value of the R-factor.
Objectives: This thesis gives a comprehensive procedure to calculate the R-factor and then highlights the relationship between the R-factor and the relative stiffness between beam and column. To date, there is no guideline as to how R-Factor would change due to variation of the relative stiffness between beam and column. This thesis comes as a step toward check the code values of the R-factor under the changing of relative stiffness between beam and column.
Methodology: To achieve the above mention goal, a nonlinear static pushover procedure is used to obtain the inelastic behavior of the structure. SAP2000 program is used to generate the nonlinear capacity curves through incremental displacement control nonlinear analysis with concentrated plasticity in the plastic hinge within the structural element, XTRACT program is used to generate all the moment curvature curves for all structural members that are used to define the plastic hinges in SAP2000 program. Tow building layouts were used in the study, one is a uniform span length with a different number of floors and a different number of bays, and the other is a nonuniform span length with a different length ratio between spans.
Results: The results show that the R-factor increase as the number of floors increases, also, as the number of bays increases the R-factor will increase and get close to a recommended code value, on the other hand, increasing the length of spans has a negligible effect on R-factor. The R-factor is minimum in the nonuniform cases, for example, the case with a nonuniform span length and three bays (6, 2, 6) meter length and with five floors has a value of R-factor 6.22 which is less than 8 (the IBC 2018 code R-factor for all SMRF). This means that using the IBC 2018 value of the R-factor would give lower induced seismic force for the design and may lead to a detailing level that does not warrant the realistic R-factor for the building being designed.
Conclusions: The study gives a methodology to study the relationship between the R-factor and any variable that affected the structure’s response. As a future topic, it is recommended to repeat the work using a nonlinear dynamic procedure like time history analysis using actual earthquake records to compare the result with the actual earthquake loads in these building.
Keywords: R-Factor, Pushover method, nonlinear procedure, Plastic hinge definition, ductility.