Inelastic behavior of eccentric braces in steel structure

ABSTRACT: The performance of eccentric braces is to some extent considered as a new subject amongst Civil Engineers. In general, braces are the members that resist against lateral forces in a steel structure while the structures are under seismic excitation. Although the height of a structure and the structural system are the two parameters which can affect the inelastic behavior and response of the structure but these parameters have not been taken into consideration in the current design codes for designing of Eccentric Braced Frames (EBFs). In this study nine frames were exerted which were braced with three different eccentric braces (V, Inverted-V and Diagonal) in three different heights (4, 8 and 12 story).Then the frames were assessed by nonlinear static (pushover) analysis mainly based on FEMA 440 (2005). As a result of these frame analysis, it can be observed that the plastic hinges firstly occur at the fuse section of braces and then at the compressive members of the eccentric braces. Regarding the analyses conducted on the 4 story frames it can be inferred that eccentric Diagonal braced frames have better performance than the eccentric Inverted-V braced frames and in the same way the Inverted-V braced frames have better behavior than the eccentric V braced frames. This is also true for the 8_story and 12_ story models in this study. Furthermore, a comparison relevant to the total weight of the frames has been conducted among the above mentioned frames and this lead to the conclusion that using eccentric diagonal bracing system for the 12 story model will yield to the heaviest frame which is not economical in terms of frame weight. But on the other hand using the eccentric diagonal braces for low and medium rise structures is more logical and acceptable from economical point of view as this type of bracing system absorbs considerably more energy when compared with eccentric V and Inverted V bracing systems. …………………………………………………………………………………………………………………………………………………………………………………………………………