Search

The application of steel castings in earthquake engineering has increased significantly in recent years, and steel casting technology has been proven as a viable solution for the design and development of energy dissipative yielding elements. The first-generation of cast steel replaceable modular yielding links were recently proposed as an off-the-shelf energy dissipative product line for use in steel eccentrically braced frames (EBF). The performance of the links was validated through an extensive full-scale experimental program. These links featured a design approach in which the effective length of all links across the product line was identical. As a result of this design approach, a wide range was observed in the ductility capacity, with the smaller- to medium-capacity links achieving larger rotation capacities than the larger-capacity links. This paper presents the design and experimental validation of an alternative design of cast steel replaceable yielding links where, rather than ensuring equal length across the product line, a similar link ductility capacity is targeted for all link sizes. The new cast steel links with targeted ductility capacity are presented, and the performance of two link sizes is validated through large-scale experiments to confirm that the proposed design achieved the targeted design ductility. Each link size was tested twice: once as a standalone element and once as part of a one-story EBF system that imparted a large axial load to the link. Based on the results, the effect of axial load on the performance of EBF links is discussed. [ABSTRACT FROM AUTHOR]

Steel eccentrically braced frames (EBFs) combine the advantages of both moment-resisting frames and concentrically braced frames and provide an attractive seismic design solution. Shear-critical replaceable links were developed about a decade ago to improve the performance, design process, construction, and postearthquake repair process in EBFs. However, replaceable shear links are still susceptible to the commonly observed limit states in EBF links such as web fracture close to web stiffeners, local buckling, and lateral torsional buckling. This paper presents the experimental validation of a new generation of optimized cast steel replaceable yielding links for use in EBFs, which address the shortcomings of conventional and fabricated replaceable links. The performance of the proposed cast steel links is investigated through nine large-scale component-level and system-level experiments, covering a range of link sizes and loading conditions, while also studying the impact of other phenomena influencing the response such as the presence of axial load, the level of axial restraint in the links and the presence of a concrete slab. The tested series of cast links demonstrated enhanced ductility levels and low-cycle fatigue life when compared to fabricated links, achieving up to 0.21 radians of link rotation under the AISC protocol used for the qualification of EBF links. [ABSTRACT FROM AUTHOR]

The cast-steel yielding connector (YC) is a yielding fuse device designed to dissipate earthquake energy through inelastic deformations in specially designed distributed yielding regions, while ensuring primarily elastic behavior elsewhere in the structure. The YC exhibits a stable, symmetric hysteretic response with a characteristic postyield stiffness increase due to a combination of friction and second-order geometric effects. The ultimate limit state of the YC is governed by the ultralow-cycle fatigue (ULCF) fracture of the yielding sections, where fracture begins after a relatively low number of large inelastic cycles, followed by a slow strength degradation. This paper presents tests and finite-element analyses of small-scale coupons and full-scale tests of a variety of YCs. Detailed finite-element models of YCs are developed and a novel crack propagation simulation scheme is proposed to numerically simulate its ductile fracture initiation, propagation, and associated degradation and regaining of strength due to crack opening and closing. This simulation scheme is validated against 14 small-scale coupon tests and 11 full-scale YC tests. Full-scale test results and the validated model are then used to investigate the influence of in-plane rotation and out-of-plane demands on the overall performance of YC in a nonbuckling concentrically braced frame configuration. [ABSTRACT FROM AUTHOR]