Seismic-resistant steel eccentrically braced frames (EBFs) are designed so that that yielding during earthquake loading is restricted primarily to the ductile links. To achieve this behavior, all members other than the link are designed to be stronger than the link, i.e. to develop the capacity of the link. However, satisfying these capacity design requirements for the beam segment outside of the link can be difficult in the overall design process of an EBF. In some cases, it may be necessary to make significant changes to the configuration of the EBF in order to satisfy beam design requirements. If this discovery is made late in the design process, such changes can be costly. The overall goal of this research was to develop guidelines for preliminary design of EBFs that will result in configurations where the beam is likely to satisfy capacity design requirements. Simplified approximate equations were developed to predict the axial force and moment in the beam segment outside of the link when link ultimate strength is developed. These equations, although approximate, provided significant insight into variables that affect capacity design of the beam. These equations were then used to conduct an extensive series of parametric studies on a wide variety of EBF configurations. The results of these studies show that the most important variables affecting beam design are 1) the nondimensional link length, 2) the ratio of web area to total area for the wide flange section used for the beam and link, 3) the angle between the brace and the beam, and 4) the flexural stiffness of the brace relative to the beam. Recommendations are provided for selection of values for these variables in preliminary design. / text

The catastrophic damage to the infrastructure due to the most recent major earthquakes around the world demonstrated the seismic vulnerability of many existing reinforced concrete buildings. Accordingly, this thesis is focused on a proposed seismic retrofitting system (PSRS) configured to upgrade the performance of seismically vulnerable reinforced concrete buildings. The proposed system is composed of a rigid steel frame with chevron braces and a conventional energy dissipating shear link. The retrofitting system is installed within the bays of a reinforced concrete building frame. A retrofitting design procedure using the proposed seismic retrofitting system is also developed as part of this study. The developed design methodology is based on performance-based design procedure. The retrofitting design procedure is configured to provide a uniform dissipation of earthquake input energy along the height of the reinforced concrete building. The PSRS and a conventional retrofitting system using squat infill shear panels are applied to an existing school and an office building. Nonlinear time history analyses of the buildings in the original and retrofitted conditions are conducted to assess the efficiency of the PSRS. The analyses results revealed that the PSRS can efficiently alleviate the detrimental effects of earthquakes on the buildings. The building retrofitted with PSRS has a more stable lateral force-deformation behavior with enhanced energy dissipation capability than that of the one retrofitted with squat infill shear panels. For small intensity ground motions, the maximum inter-story drift of the building retrofitted with the PSRS is comparable to that of the one retrofitted with squat infill shear panels. But for moderate to high intensity ground motions, the maximum inter-story drift of the building retrofitted with the PSRS is considerably smaller than that of the one retrofitted with squat infill shear panels.

Shear links are used as fuse elements in lateral load resisting systems to provide ductility and dissipate seismic energy. These links have traditionally been employed in eccentrically braced frames, but have more recently been suggested for use in the innovative linked column frame system (LCF). Current design specifications for shear links require intermediate web stiffeners to provide out-of-plane web stability so ductility requirements can be achieved. This research focused on moving from discrete transverse web stiffening to continuously stiffened webs in built up shear links. Built up links were designed to yield in shear when subjected to severe cyclic loading, however the webs of the links were designed using two metal sheets joined by an elastic core. These composite "sandwich" webs allowed for an increase in web thickness (and inherent flexural rigidity) without increasing the shear strength of the links. Numerical and experimental investigations were conducted to assess the performance of composite sandwich links subjected to severe loading. Numerical results showed improved web behavior in sandwich links in which the core material was assigned an elastic modulus greater than 5000psi. Due to fabrication limitations, experimental specimens were fabricated with a core material elastic modulus of 1000psi. These specimens did not perform as well as unstiffened base case links in terms global hysteretic behavior or ductility.

In current design of steel eccentrically braced frames (EBFs), the yielding link is coupled with the floor beam. This often results in oversized link elements, which leads to over-designed structures and foundations. In addition, the beams are expected to sustain significant damage through repeated inelastic deformations under design level earthquakes, and thus the structure may require extensive repair or need to be replaced. These drawbacks can be mitigated by designing EBFs with replaceable shear links. Two different replaceable link types with alternate section profiles, connection configurations, welding details and intermediate stiffener spacing were tested. A total of 13 cyclic quasi-static full-scale cyclic tests were performed, which included tests on eccentrically braced frames with the replaceable shear links, to study their inelastic seismic performance. The links exhibited a very good ductile behaviour, developing stable and repeatable yielding. Additional inelastic rotation capacity can be achieved with bolted replaceable links when allowing bolt bearing deformations to occur. The on-site replaceability of the link sections is confirmed even in the presence of residual deformations of 0.5% drift.

In current design of steel eccentrically braced frames (EBFs), the yielding link is coupled with the floor beam. This often results in oversized link elements, which leads to over-designed structures and foundations. In addition, the beams are expected to sustain significant damage through repeated inelastic deformations under design level earthquakes, and thus the structure may require extensive repair or need to be replaced. These drawbacks can be mitigated by designing EBFs with replaceable shear links. Two different replaceable link types with alternate section profiles, connection configurations, welding details and intermediate stiffener spacing were tested. A total of 13 cyclic quasi-static full-scale cyclic tests were performed, which included tests on eccentrically braced frames with the replaceable shear links, to study their inelastic seismic performance. The links exhibited a very good ductile behaviour, developing stable and repeatable yielding. Additional inelastic rotation capacity can be achieved with bolted replaceable links when allowing bolt bearing deformations to occur. The on-site replaceability of the link sections is confirmed even in the presence of residual deformations of 0.5% drift.