b'FEATURECAST STEEL REPLACEABLE Links for use in Steel Eccentrically Braced Frames By Pedram Mortazavi, Oh-Sung Kwon, Constantin Christopoulos, Eden Lee,University of Torontoand Justin Binder, Michael Gray,Cast Connex CorporationSTEELECCENTRICALLYBraced Frames (EBFs) have been proposed as LateralMLoad Resisting Systems (LLRS) for seismic appli- Beamcations since the early 1970s [1-2]. They provideFormation of Tension FieldsanattractivealternativetomorecommonlyV Corner CracPVaralleeksrtical Crl to acWks eldsused LLRS in steel structures such as MomentBeamResistingFrames(MRFs)andConcentricallyPBraced Frames (CBFs), by combining the struc- Beamtural advantages of both systems. Compared toMRFs,EBFsexhibithigherlateralstiff-ness and, therefore, the inter-storey drifts are controlled much more effectively. In compar-ison with CBFs, EBFs demonstrate a more flexible response, leading to lower internal forces and reducing the challenges with the design of the capacity protected elements, including the foundations. In addition, EBFs providemorefreedominarchitectural design by allowing for larger architecturalFIGURE 1 : (a) Conventional EBFs, (b) Deformed Shape of Shear-Critical EBFs and (c) Distribution of openings such as windows and doors withinInternal Forces in EBFs.thebracedbay,comparedtoCBFsand Buckling-Restrained Braced Frames (BRBFs).to prevent web buckling and lateral supportreplaceable shear links have steadily gained Duringearthquakes,themechanismfortopreventlateraltorsionalbuckling,shearattentionfromtheengineeringcommunity energy dissipation in EBFs is achieved throughcritical EBF links can provide a stable energyin seismically active regions and, in particular, yieldingofthesegmentofthefloorbeamdissipation as they take advantage of uniformhave been used in rebuilding of Christchurch betweenthebraces[seeFigures1(a)andweb yielding instead of local flexural hinging[5]. Despite providing several advantages over (c)]. This portion of the beam that undergoes[3]. Therefore, shear critical links are preferredconventional EBFs, replaceable EBF links have controlled yielding is referred to as the link.inthedesignofconventionalEBFs.Whileboth complex detailing and stringent welding Dependingonthelengthofthelinkbeamconventionalshearlinkstypicallyproviderequirements and are still limited to 0.08 rad comparedtothebaylength,conventionalstableenergydissipation,theirultimatemaximum plastic rotation. EBFs are classified into flexural EBFs and shear- response is limited by weld cracks and webThe present study, which is a joint project critical EBFs. In flexural EBFs, the link beam isfracturing close to the stiffeners and thus thebetweentheUniversityofTorontoand long enough to develop significant bendingallowable link rotation during design is limitedCastConnexCorporation,investigatesthe moments and form flexural plastic hinges atto 0.08 radians. performance of a new generation of energy bothendswhenthebuildingissubjectedAbout a decade ago through a joint projectdissipative links in EBFs known as Replaceable to lateral loads. In shear-critical EBFs, on thebetween the University of Toronto and coleCast Steel Links. The system benefits from other hand, the yielding mechanism is primarilyPolytechnique of Montreal, replaceable shearsteelcastingtechnologywhichoffers through shear yielding of the web. This can belinks were proposed for seismic applicationsfreedom of geometry in structural design as better understood by considering the loading[4].Theproposedsystemfacilitatedpost- well as highly improved response attributes state of an EBF link under lateral loads, which isearthquakerepairsandsimplifiedthesuch as significantly increased ductility and shown in Figure 1 (c). By adding web stiffenersdesign and construction of EBFs. Since then,material low-cycle fatigue life. These new links 22|WINTER 2020 ADVANTAGE STEEL'