11.48: An experimental study on welded overlap core: Steel encased buckling‐restrained braces

Abstract

Buckling restrained braced frames (BRBFs) can be used as a lateral load resisting system in seismic regions. A typical buckling restrained brace (BRB) is composed of a core segment, debonding material and a buckling restraining mechanism (BRM). The cross-section of the core segment can be changed along the length to constrain yielding in a limited domain. Most of the BRBs utilize a rectangular core segment which is reduced in width throughout yielding length. The gradual reduction in the width of the core segment produces stress concentrations and employs costly CNC cutting. A novel type of BRB named the welded overlap core steel encased BRB was developed to provide an alternative that does not require CNC cutting of the core plate. This type of a BRB is formed by welding flat bars with different widths to each other. The yielding and non-yielding segment lengths and areas can be easily tailored to meet the stiffness and strength requirements. An experimental program has been undertaken to study the performance of welded overlap core steel encased BRBs.Pursuant to this goal four BRBs were manufactured and subjected to sub-assemblage testing. All specimens were tested using the loading protocol recommended in the AISC Seismic Provisions for Structural Steel Buildings (AISC341-10). Welding detail used to connect the built-up BRM members was considered as the primary test variable. The experimental results indicated that the proposed core segment concept can be an alternative to more traditional core segment designs. The weld configurations used to connect the buckling restraining mechanisms affected the response significantly. According to the results, properly detailed and inspected welded overlap core BRBs can provide acceptable performance by sustaining cumulative strains in excess of 400 times the yield strain.