11.50: Modelling hysteretic behaviour of U-shaped steel dampers

Conventional approach to earthquake resistant building design relies upon strength, stiffness, and inelastic deformation capacity, which are great enough to withstand a given level of design earthquake effects. However, modern approach in today's designs aims to mitigate seismic energy before the input energy reaches the structural elements. Dissipating seismic energy through the inelastic deformation of metallic dampers is one of the cost effective solutions. After appearing concept of dissipating energy through the inelastic deformation (mainly yielding and post yielding) of metallic dampers, numerous types of metallic dampers, such as X-shaped, J-shaped, U-shaped, shear panel, triangular plate dampers have been developed and their effectivenesses have been proved both theoretically and experimentally. Inelastic hysteretic behaviour of U-shaped devices is somewhat complex and varies with geometry of the damper. To address this issue and possibly attain some practical results, this present paper focuses on modelling hysteretic behaviour of U-shaped dampers. ABAQUS has been used as the computational tool in which a finite element model made of the C3DR8 solid element is adopted. Nonlinear kinematic and isotropic hardening material assumptions are considered to determine cyclic behaviour at 0o, 45o and 90o loading directions. For each analysis, effective stiffness, effective damping ratio, and maximum reaction forces (i.e. horizontal strengths) of the damper are calculated to evaluate performance. As an additional parameter, two different loading protocols are taken into consideration. Hysteretic curves and deformed shapes of a selected damper type taken from an existing experimental work and this numerical study show very good agreement proving that the modelling assumptions made during the analyses are appropriate and sufficient for a better prediction of behaviour. Additional numerical analyses on several dampers under various loading protocols reveal that effective damping ratio of the damper is more than ξeff =40% at the maximum displacement level due to significant energy dissipation through plastic deformation of the damper. A numerical example of mixed use of U-shaped steel dampers and rubber isolation bearings on a selected two story steel framed building is also discussed.