Experimental and numerical study of seismic performance of high-strength steel fabricated framed-tube structures with replaceable shear links

Abstract

Steel moment-resisting frames (MRFs) dissipate earthquake energy via the deformation of plastic hinges at beam-ends. To ensure that such plastic hinges are long enough to serve their purpose, their designs are based on a minimum span–depth ratio of beams as per seismic design codes. However, in steel framed-tube structures (SFTSs), deep spandrel beams having large cross-sections with flexural plastic hinges at beam-ends cannot be adequately developed, which is the reason behind SFTSs presenting lower ductility and energy dissipation capacities. To address this issue, high-strength steel (HS)-fabricated SFTSs with bolted web-connected replaceable shear links (HS-FTS-RSLs) have been proposed. In HS-FTS-RSLs, shear links are fabricated from conventional steel and placed in the middle of the deep spandrel beams to behave as ductile fuses that dissipate seismic energy, and the spandrel beams and columns use HS. In this study, a 2/3-scaled HS-FTS-RSL specimen with a very short shear link was fabricated, and cyclic loading tests were performed to investigate the hysteretic behavior of the specimen. The finite-element models (FEMs) of four full-scale sub-structures of HS-FTS-RSLs were established. Subsequently, the effects of the length of the very short bolted web-connected shear links on the cyclic performance of the HS-FTS-RSLs were investigated via nonlinear numerical analyses. The test results showed that the specimen developed the expected failure modes and showed good ductility and energy dissipation capacities. The shear link entered the plastic stage to dissipate energy, while spandrel beams and columns remained in the elastic stage under the cyclic loads. Moreover, the use of a shorter shear link was shown to yield a higher load-carrying capacity and initial elastic lateral stiffness; however, a lower ductility and energy dissipation capacity for HS-FTS-RSLs were induced. The performance of the specimen was comparable to that of the original sub-structure specimen after replacement of the shear link. The expected post-earthquake recoverability and resilience of the structure could be achieved via replacement of the shear link. The acceptable residual interstory drift, which simplifies the replacement of the bolted web-connected shear link, was 0.23%. The length ratios e/(Mp/Vp) of very short bolted web-connected shear links should not be lower than 0.53 in HS-FTS-RSLs, as per the numerical analysis results. The overstrength factor of the very short bolted web-connected shear link could reach 1.9, which is much higher than the proposed value of 1.5 for the shear link in the eccentrically braced frame in AISC 341–16.