Abstract:

Past studies assert that the code-specified response modification factor (R) for structures may not always be suitable due to variations in material properties, geometric configuration and site characteristics. This study presents a method that may be used to optimize the design of reinforced concrete (RC) dual systems utilizing R obtained from incremental dynamic analysis (IDA). A regular nine-story three-dimensional building with a dual system in y-direction and a special moment-resisting frame in x- direction was designed as per NSCP 2015. A nonlinear model of the building was created by defining hinges based on design results. Nonlinear M3-hinges for girders, fiber P-M2-M3 hinge for columns and fiber P-M3 hinge for walls were employed in ETABS. Incremental dynamic analyses for the building case were then performed utilizing seven (7) ground motions obtained from the Pacific Earthquake Engineering Research online database. Capacity curves were generated for each ground motion by recording the maximum base shear and roof displacement obtained from each time-history analysis. Roughly, a total of 150 time-history analyses were conducted to determine the building’s overstrength factor (Ω) and ductility factor (R_μ ). For each ground motion, the IDA-based response modification factor (R_D ) was computed as the product of Ω and R_μ. Results have shown that the actual R for the building employed varies from 8.0 to 10. Values of R in this range were used to redesign the building, and it was found out that for the building case considered,the building-specific response modification factor R_b=9.5 resulted in the largest reduction of 10.24% in weight and volume of concrete. The proposed method can be used to investigate further the quantification of R for other building configurations and types.