Seismic design of special moment‐resisting steel frame with prevention of soft‐storey mechanism failure

Abstract

Most structures with masonry infills that are continuous along their height, which are interrupted in the lowest storey, are damaged by earthquakes. These structures are anticipated to collapse due to the undesirable soft-storey mechanism formed by lateral stiffness of masonry infills in other storeys. The seismic design criteria of UBC97 code for special moment-resisting steel frame (SMRSF) are reviewed. In this paper, a new criterion for seismic design of such structures is presented. The proposed criteria are used to design three SMRSFs: 5, 8 and 15 storeys. Nonlinear time-history dynamic analyses are applied for the designed SMRSFs based on the proposed criteria. Displacements and storey drifts, which are obtained by the proposed method, are compared with nonlinear time-history dynamic analysis results, finally.Step 1: SMRSF structure is designed according to the criteria of common seismic design codes, e.g.UBC97, using ductile-compact sections/ignoring the frame-infill interaction.Since the proposed method is an iterative method, it is necessary to assume the initial size of the members. The best sections for the initial design are those obtained according to the criteria of seismic design codes. For the three moment-resisting steel frames 5SSB, 8SSB and 15SSB, the initial profiles of the members are those in 5GM, 8GM and 15GM moment-resisting steel frames that are shown in Figure 2.Step 2: Analytical natural period related to the first vibration mode of the structure is calculated. This period is based on the mathematical model of beam and column sections determined in the previous section as well as modelling the lateral behaviour of masonry infills.Considering the basic differences of SMRSF designed based on general failure mechanism with soft-storey failure mechanism in the lowest storey, common seismic design codes could not be used for calculating the natural period of the structure. A mathematical model should be used in which all affecting parameters on lateral stiffness of structure are considered. Figure 2. Member sizing 5GM, 8GM and 15GM.

An innovative infill wall utilizing light expanded clay aggregate: An experimental and numerical study

“…Researchers have investigated the negative effect of infill walls on the structure behavior, which indicates the destructive effects of frames on the behavior of structures. Those studies were included: shear fracture of columns, beam, and connections, [ 2–6 ] create strength beam‐week column, [ 7 ] reduction of natural period, [ 8–13 ] soft storey mechanism, [ 14–16 ] create short column that is vulnerable under shear load, [ 6–8,17–19 ] suddenly change of the distribution of stiffness and create a torsion, [ 17,20 ] degradation in load–displacement curve of frame. [ 21 ] The mentioned studies have proposed methods to solve the negative effect of infill wall on the structure behavior.…”