Response modification factors for concentrically braced steel frames

Abstract

The verification of the response modification factors (R) for concentrically inverted- V and X-braced 2D steel frames (for which there is no distinction for the R values in TEC- 2006) is the scope of this study. In this thesis, response modification factors of Inverted V Braced Frames and XBraced Frames were calculated with the modified approaches in formulation of (R) factor, with the procedure of nonlinear static (pushover) analysis stated in FEMA 356 Prestandard (since TEC-2006 provides nonlinear static analyses for concrete structures only). For this parametric study, twelve different systems with 3-Story and 6-Story are designed as per EC-3; Structural systems are investigated as per “strong column-weak beam” and “strong beam-weak brace” design concept. The brace sections are chosen to be rectangular hollow sections, since they are the most efficient ones among other shapes. Lateral Loading of the steel frames are determined under the requirements of TEC-2006. Spectrum coefficient, S(T), was computed by using Z3 soil profile type. Plastic hinge modeling is done as per FEMA-356 Pre-standard. From the capacity curve, the ductility ratio and the overstrength factor is calculated. After calculating the response modification factors of these frames, the results are compared with the design response modification factors given in TEC-2006, EC-8, NEHRP and ATC-19. It is found out that (R) factors of X-braced frames have higher R factors than the Inverted V-braced frames. Different R values are found for these frames and suggested to be used also in TEC-2006.