Seismic performance and new design procedure for chevron‐braced frames

Abstract

SUMMARYThe paper is concerned with the seismic design of steel-braced frames in which the braces are conÿgured in a chevron pattern. According to EuroCode 8 (EC8), the behaviour factor q, which allows for the tradeo between the strength and ductility, is set at 2.5 for chevron-braced frames, while 6.5 is assigned for most ductile steel moment-resisting frames. Strength deterioration in post-buckling regime varies with the brace's slenderness, but EC8 adopts a unique q value irrespective of the brace slenderness. The study focuses on reevaluation of the q value adequate for the seismic design of chevron-braced frames. The present EC8 method for the calculation of brace strength supplies signiÿcantly di erent elastic sti nesses and actual strengths for di erent values of brace slenderness. A new method to estimate the strength of a chevron brace pair is proposed, in which the yield strength (for the brace in tension) and the post-buckling strength (for the brace in compression) are considered. The new method ensures an identical elastic sti ness and a similar strength regardless of the brace slenderness. The advantage of the proposed method over the conventional EC8 method is demonstrated for the capacity of the proposed method to control the maximum inter-storey drift. The q values adequate for the chevron-braced frames are examined in reference to the maximum inter-storey drifts sustained by most ductile moment-resisting frames. When the proposed method is employed for strength calculation, the q value of 3.5 is found to be reasonable. It is notable that the proposed method does not require larger cross-sections for the braces compared to the cross-sections required for the present EC8 method.

Design of steel frames equipped with BRBs in the framework of Eurocode 8

“…The obtained values of the behaviour factor generally decrease with the increase in the height of the building. This finding is consistent with the results of other studies concerning the evaluation of the response modification factor of frames endowed with BRBs [23,25,24] or other braced frames [45,[50][51][52][53][54]. However, the values of q obtained here are much lower than those reported in [23][24][25], especially in the 4-storey systems.…”

High strength steel in chevron concentrically braced frames designed according to Eurocode 8

“…Indeed, the EC8 limits on the brace slenderness and the requirement on the variability of design overstrength ratios X i lead to select stocky bracing members. Conversely, the EC8 hierarchy rule for the brace-intercepted beam does not guarantee adequate strength and stiffness to prevent large vertical deflection at the intersection with braces, as also highlighted by [55][56][57].…”

Effect of gravity columns on mitigation of drift concentration for braced frames

“…The shear strength of a brace pair was estimated to be the sum of the yielding strength of a brace in tension (N y ) and the post-buckling strength of a brace in compression (N u ) [2]. The post-buckling strength N u was taken to be 30% of the brace yielding strength N y [9].…”

“…Steel braces are known to be very effective structural components that can provide lateral stiffness and strength, and concentrically braced frames (CBFs) are thus among the most cost-effective and commonly used systems in earthquake-prone regions [1,2]. An extensive survey of brace tests [3], however, indicates that typical steel braces are susceptible to buckling, and fracture is prone to develop at the mid-span when the braces are stretched in tension after local buckling.…”