Practical Advanced Analysis for Eccentrically Braced Frames

Abstract

Under severe earthquakes, flexural or shear yielding of the inelastic links in eccentrically braced frames (EBFs) was often observed. The behavior of links could not be well predicted by the traditional advanced analysis method when they experienced shear yielding and strain hardening. In this paper, the analytical model of links is obtained by using three rotational subsprings and three translational subsprings with zero-length, respectively, at each element end to simulate the flexural and shear yielding behavior with strain hardening effect. For the other elements in EBFs, a spring with zero-length is provided at each end to consider yielding on the cross-sectional level. The yield functions for the links and other elements are derived based on the section assemblage concept, and a practical advanced analysis method for EBFs is proposed. The proposed elements have the same nodal degree of freedom as conventional element by condensing the non-nodal degree of freedom that introduced in the derivation. Numerical analysis shows that the proposed method has a high efficiency and accuracy as well as easy determination of the element yielding sequence.Keywords: Eccentrically braced frames (EBFs), Advanced analysis, Shear link, Section assemblage concept, Yield function, Strain hardening INTRODUCTIONEccentrically braced frames (EBFs), which combine the advantages of moment resisting frame (MRF) and concentrically braced frame (CBF), are one type of hybrid structural system with good ductility and lateral stiffness. The links in EBFs are generally designed to yield prior to frame structures, acting as the "structural fuse" member. The ductility of EBFs depends on links, which is determined by the plastic rotational capacity [1]-3]. Under severe earthquake, the main structures are generally designed to be elastic with yielding of links only so that damage on the structures can be minimized.From previous studies, the links had three types, which were shear links, flexural links and shear-flexural links. It is also known that the behavior of links had a significance effect on the seismic behavior of EBFs and the links might experience shear or/and flexural yielding [4][5]. Detailed researches on the static and dynamic behavior of links were conducted by Ricles et al.[6], Ramadan et al. [7] and Richards et al. [8], in which the analytical model of links considering the flexural yielding, shear yielding and strain hardening were obtained. These models were regarded as the "complete element", in which a plastic hinge with zero-length was assumed at each end of link while the middle of link remained elastic without yielding. For each plastic hinge, moment hinge and shear hinge were used to simulate the rotational and horizontal deformations. Multiple subsprings with elastic-perfectly plastic model were provided at each link end to simulate the strain hardening effect. However, there were no easy methods to determine whether the design requirements and expected goals were met even though the performances of all the ...

Effect of the Bracing System on the Probability of Collapse of Steel Structures under Maximum Credible Earthquake

“…Main beams in these frames can have simple connections to the columns in cases where the link beam is located in the middle of the beam and away from the columns and connection zones [2]. Considering the mentioned effects, as mentioned by Hu et al, it is possible not to assume an interaction between shear and flexural behavior in the beam [27] because according to the classification in AISC360-16 and Code 360 of Iran, the behavior of link beams in modeled frames according to their length of 50 cm is in the category of shear behavior. It should be noted that according to Popov's research, e � 1.6 * Mp/Vp is the boundary between shear and flexural behavior in these frames [3,28].…”