Seismic Stability Response of Columns in Multi-Tiered Braced Steel Frames for Industrial Applications

Abstract

This paper presents a study on the seismic response of multi-tiered braced steel frames. The seismic demand and stability of the columns in a 4-tiered special X-braced frame structure located in a high seismic area and designed according to current AISC seismic provisions is evaluated. The drift demand in the individual bracing tiers and the combined column axial force and in-plane flexural demand are evaluated through nonlinear time history analysis. Detailed finite element analysis of one column under demands extracted from time history analysis is carried out to investigate the buckling response of the column. The results show that high in-plane bending demand is induced in the columns. Flexural yielding caused by non-uniform tier drift demand may detrimentally affect the torsional-flexural stability of the columns.

A New Seismic Design Method for Steel Multi-Tiered Braced Frames

“…Column is torsionally fixed at the tier level to simulate the torsional restraint provided by the strut. Additional detail is given in Imanpour et al (2013). The results of the analysis showed that flexural buckling takes place at a time t = 9 s, after brace tension yielding has developed in Tier 2 but before it occurred in Tier 1.…”

“…The analysis can therefore be used to assess the nonlinear seismic response of the frame example, including the expected force demand on the columns and tier drift response, such that the proposed design requirements can be validated. Detail of the modeling and analysis assumptions are given in Imanpour et al (2012aImanpour et al ( , 2013. Nonlinear incremental static (pushover) analysis of the frame is performed to determine member forces and tier drifts as the frame deforms up to the anticipated story deflection.…”

“…The braces in each tier are designed to resist in tension and compression the seismic story shear and two different HSS sizes are selected due to the different brace lengths. Additional design detail is given in Imanpour et al (2013). Brace properties are given in Table 1.…”

Three-Dimensional Finite Element Simulation of the Seismic Behavior of Multitier Concentrically Braced Frames

“…Prior studies on the seismic behavior of MTCBFs demonstrated that frames designed according to contemporary seismic provisions are susceptible to inelastic drift concentration within a single tier (Imanpour et al 2012a(Imanpour et al , 2012b(Imanpour et al , 2013Imanpour and Tremblay 2012). Concentration of inelastic drift within a single tier may result in brace fracture due to ultra low cycle fatigue (Roufegarinejad andTremblay 2012, Fell et al 2009), or weak-axis flexural yielding of the columns (Imanpour et al 2012a(Imanpour et al , 2012b(Imanpour et al , 2013Imanpour and Tremblay 2012;Stoakes and Fahnestock 2012b). In addition to compromising in-plane stability of the columns, previous research found that weak-axis flexural yielding may also lead to out-of-plane and/or torsional column instability (Imanpour et al 2012b;Stoakes and Fahnestock 2012b).…”

“…In addition, existing studies on the seismic behavior of MTCBFs have not fully accounted for column axial forces, or torsional loading and deformation of the columns in MTCBFs. In the studies by Imanpour et al (2012aImanpour et al ( , 2012bImanpour et al ( , 2013 and Imanpour and Tremblay (2012), torsion-induced shear stresses acting on the columns were not considered to interact with normal stresses due to axial and flexural demands. In the study by Stoakes and Fahnestock (2012b), the axial force was assumed uniform over the height of the columns.…”