Applicability of the direct displacement-based design method to steel moment resisting frames with setbacks

Abstract

While quite extensive research has been undertaken during the last decades to extend the direct displacement-based design (DDBD) method to a wide range of structural types and materials, it is recognized that there are still some areas requiring further study and development. Steel structures and, more specifically, steel moment resisting frames with setbacks are one of these and, therefore, this work aims to investigate the seismic response of such structures designed according to the DDBD procedure currently prescribed for regular frames and to elaborate specific recommendations based on the results obtained. The main aspects to be considered are the adequacy of the displacement profile and higher mode reduction factor to be used, as well as the suitable strength distribution required. In a trial application of the current DDBD procedure, two two-dimensional 12-storey frames with setbacks are designed, and the solutions obtained are used to develop models of the structures, which are then subject to a series of non-linear time-history analyses at increasing levels of intensity, using spectrum-compatible scaled accelerograms. The results obtained are contrasted with those of Karavasilis et al. (J Constr Steel Res 64:644-654, 2008), which were developed for steel frames designed via code methods. It is recognized that the DDBD method can benefit from the expressions developed by these authors, and recommendations for the adjustment of the DDBD higher mode reduction factors are subsequently proposed. The efficacy of the latter is evaluated by the design and verification at a range of diverse intensities of a set of two-dimensional frames of 6, 9 and 12 storeys, and satisfactory outcomes are obtained. These results have been fundamental in revealing the need for future research regarding the influence of the design spectral shapes, ductility demand and P-Delta instability in the dynamic amplification of drifts due to higher mode effects.

Vibration control of steel frames with setback irregularities equipped with semi-active tuned mass dampers

“…Furthermore, the seismic response of structures with setbacks that are located on the soft soil was more complex and should be considered when designing this type of structure (Shakib and Homaei 2017). Nievas and Sullivan (2015) successfully proposed the use of a direct displacement-based design method for MRFs with setbacks. A simple and economical procedure for evaluating the seismic performance of steel MRFs with setbacks that depends on reliability-performance-based methods was proposed by Pirizadeh and Shakib (2019).…”

Seismic performance of irregular RC frames designed according to the DDBD approach

“…After the column base moments are identified, a bottom-to-top sequence of member equilibrium is followed to determine the required flexural strength in other locations. Nievas and Sullivan (2015) introduced a modification of the sequence to encompass the effect of setbacks at the corresponding joints.…”

“…However, irregular RC frames have received comparatively little attention within the context of the DDBD approach. Nievas and Sullivan (2015) modified the higher mode effects reduction factor ! " for steel plane frames with setbacks.…”

Modified direct displacement‐based design approach for structures equipped with fluid viscous damper

“…However, Chopra and Goel 9 implemented DDBD approach using the inelastic design spectrum without equalizing the dissipated hysteretic energy with a damping ratio. Effectiveness of DDBD approach in the achievement of a predictable performance level has been shown in different structural systems such as reinforced concrete (RC) moment-resisting frames, 10 concentrically braced frame structures, [11][12][13][14][15] RC frame-wall structures, 16 eccentrically braced frame structures, 17,18 steel moment-resisting frames, [19][20][21] and steel-braced RC frames. 22 DDBD approach has been also employed for designing different structural control systems such as selfcentering energy-dissipative braces, 23 hysteretic damped braces, 24 base isolation system, 25 and viscoelastic dampers.…”