Evaluation of response modification factor for different types of stainless steel frames

Abstract

The application of stainless steel in construction industries is increasing for its environmental and mechanical advantages such as corrosion resistance, heat resistance, pleasant in appearance, higher ductility, and low maintenance cost. The stress-strain curve of stainless steel is different from that of ordinary carbon steel. Stainless steel shows early nonlinearity and higher strain hardening. Stainless steel specially, Austenitic and Duplex grade exhibit higher ductility compared to that of carbon steel. Stainless steel exhibits ultimate to yield stress ratios generally1.7–2 where these values are 1.2–1.4 for carbon steel. The Stainless steel shows elongation at fracture, generally 40–60%. The currently available design guidelines for stainless steel such as SEI/ASCE-8-02, AS/NZS 4673, and EN, 1993-1-4 generally supplement or modify the equivalent carbon steel provisions. However, none of these codes recommend the value of response modification factor (R) for stainless steel structures. Currently, the value of R recommended for carbon steel frames are being used for stainless steel structures, which undermines the advantages of stainless steel and makes the design more conservative. To incorporate the advantageous properties of stainless steel, the determination of R value for frames made of stainless steel is necessary. This study has investigated the performance of different structural steel frames such as Special Moment Resisting Frames (SMRF) and Special Concentric Bracing Frames (SCBF) made of stainless steel. To evaluate a more realistic response of the frames, the study uses proper simulation with refined finite element models of structural members followed by a structural level analysis. The SMRF and SCBF of 4, 8, and 12 stories have been investigated in this study. First, the frames have been designed according to the seismic provision of Bangladesh National Building Code, BNBC-2020. Then the finite element simulation has been done for each member of the frames such as beam, column, and brace under cyclic loading to develop the backbone curves of these members. Using these element level results, the nonlinear pushover analysis has been performed on the frames. The response modification factors of all frames have been calculated and compared. It has been found that the response modification factor of frames made of stainless steel is higher than that of carbon steel. The recommended value of R by code was found conservative both for carbon steel and stainless steel. Hence, the obtained results from the study show that the uses of stainless steel as a structural material enhance the seismic performance of steel frames. It was also observed that the values of R were gradually decreased with the increase of stories. The R values of SMRF stainless steel frames were 1.30 to 1.55 times the values found for carbon steel. For SCBF, the values were found 1.25 to 1.39. From results obtained from the study, it can be suggested that the R value recommended in code may be increased for SMRF and SCBF made of SS.