پیشینه، طراحی و استفاده های مهاربند کمانش ناپذیر

ABSTRACT Buckling-Restrained Brace: History, Design and Applications

The buckling-restrained brace (BRB) is a seismic device consisting of an axially yielding core and axially decoupled restraining mechanism, which suppresses the overall buckling. The hysteretic characteristics are stable and nearly symmetric once the full cross section of the core has yielded, differing only slightly from the base material hysteresis. Because buckling is restrained, no associated degradation should be appeared during the compression cycles. For this unique behavior, BRBs can be modeled using truss elements and uniaxial material hysteresis rules, assuming strain is distributed along the full plastic core length. The basic concepts of buckling-restrained braces appeared from the 1970s, when limited successes were reported by several researchers in Japan and India [1–3]. The first practical BRB was achieved by Saeki, Wada, et al. [4, 5] in 1988. They employed rectangular steel tubes with in-filled mortar for the restrainer, and determined the optimal debonding material specifications to obtain stable and symmetric hysteretic behavior. In addition, the basic theory to design the restrainer was established and the first project application soon followed. In 1989, these BRBs (unbonded braces) were applied to two 10- and 15-story steel frame office buildings, in the first project to use BRBs [6]. BRBs increased in popularity and other configurations soon followed, notably the all steel tube-in-tube type.

Through the 1990s, BRBs were used in approximately 160 buildings in Japan. In July 1995, the concept of “damage tolerant structure” was proposed by Wada, Iwata, et al. [7], which uses BRBs as energy dissipating elasto-plastic dampers within an elastic main frame. The AIJ design recommendations included BRBs design guidelines for the first time in 1996 [8].

Collaboration with researchers in US soon led to the first international application, with the construction of a building at UC Davis in 1998, followed by an experiment at UC Berkeley in 2000 [9]. Numerous other buildings with BRBs were soon constructed throughout California, including some in seismic retrofit applications. In 2002, a design guidance for the buckling-restrained braced frame (BRBF) was included in the Seismic Provisions for Structural Steel Buildings (ANSI/AISC 341-05) [10]. During these early years of technology transfer to international markets, a series of symposiums on passively controlled structures were held at Tokyo Tech, sharing code developments, BRB designs, and novel applications [11]. Through the following decade, BRBs increased in popularity in numerous countries, from Taiwan in the early 2000s [12] to the recent implementations in New Zealand as part of the Christchurch rebuild. BRBs are now widely known in seismic areas throughout the world, with research ongoing in countries such as Japan, Taiwan, China, USA, Canada, Turkey, Iran, Italy, Romania, New Zealand, and Chile.