Development of an amplified added stiffening and damping system for wood-frame shear walls

Abstract

SEISMIC DAMPERS ARE COMMONLY USED AS A TOOL TO IMPROVE THE LATERAL PERFORMANCE OF TIMBER STRUCTURES BY INCREASING THEIR DAMPING PROPERTIES UNDER CYCLIC REVERSED LOADS. HOWEVER, THE EFFECTIVENESS OF THESE DEVICES MAY BE HEAVILY DIMINISHED IF RESTRICTIVE LATERAL DRIFT LIMITS GOVERN THE DESIGN OF THE STRUCTURE. THEREFORE, THIS PAPER PRESENTS AN INNOVATIVE APPROACH TO IMPROVE THE PERFORMANCE OF SEISMIC DAMPERS WHEN INSTALLED IN STIFF WOOD FRAME STRUCTURES WITH LOW LATERAL DEFORMATION LEVELS. AS PART OF THE INVESTIGATION, U-SHAPE FLEXURAL PLATE DAMPERS WERE INSTALLED IN A 4880X2475 MM WOOD FRAME WALL ALONG WITH AN ECCENTRIC LEVER-ARM SYSTEM, WHICH AIMED AT AMPLIFYING THE DISPLACEMENTS TRANSFERRED FROM THE WALL TO THE DAMPERS. FOUR CYCLIC TESTS WITH DIFFERENT CONFIGURATIONS WERE CONDUCTED ON THE WALL TO EVALUATE THE PERFORMANCE OF THE SPECIMEN BEFORE AND AFTER THE RETROFITTING. RESULTS SHOWED THAT THIS APPROACH PROVIDES A FEASIBLE SOLUTION TO ENHANCE THE LATERAL PERFORMANCE OF WOOD FRAME STRUCTURES, IMPROVING THEIR STRENGTH, STIFFNESS, ENERGY DISSIPATION CAPACITY, AND POST-PEAK BEHAVIOR. HOWEVER, ESPECIALLY, A GREAT BENEFIT IN TERMS OR RESILIENCE WAS FOUND FOR THE DAMPED WALLS, AS THE DROPS OF STRENGTH, STIFFNESS AND ENERGY DISSIPATION WERE ONLY ABOUT 40% AFTER SIMULATING TWO MAJOR EARTHQUAKES. IN CONTRAST, FOR UNPROTECTED TIMBER SHEAR WALLS, THE DROPS IN STRENGTH, STIFFNESS AND ENERGY DISSIPATION AFTERSHOCK CAN BE AS LARGE AS 90%. BESIDES, IT WAS FOUND THAT THE INTERSTORY DRIFTS OF MID-RISE TIMBER BUILDINGS COULD DECREASE ABOUT 30% USING DISSIPATION DEVICES, WHICH SIGNIFICANTLY MAY ENHANCE THE STRUCTURAL DESIGN FEASIBILITY OF TIMBER BUILDINGS IN SEISMIC AREAS. THE TESTS RESULTS SHOWED, HOWEVER, THAT THE PRESENTED DESIGN OF DAMPED SHEAR WALLS SUFFERED CONCENTRATED LOSSES OF STIFFNESS AT SEVERAL CONNECTIONS OF THE DISPLACEMENT AMPLIFICATION SYSTEM, RECUDING ITS REAL EFFICIENCY ABOUT 37% IN COMPARSION TO THE THEORETICAL PREDICTIONS. YET, THE LOSSESS AT THE CONNECTIONS BETWEEN THE TIMBERFRAME AND THE AMPLIFICATION SYSTEM WERE NEGLIGIBLE, SUCH THAT THE OVERSIZING OF THE AMPLIFICATION SYSTEM SHOULD GREATLY CORRECT POTENTIAL INEFFICIENCIES IN THE AMPLIFICATION OF DISPLACEMENTS. FUTURE INVESTIGATIONS SHOULD FOCUS ON IMPROVING SUCH EFFICIENCY AS PROPOSING SIMPLIFIED DESIGN METHODS FOR DAMPED TIMBER SHEAR WALLS, WHICH SHOULD GREATLY EXPAND ITS APPLICATION AS THEY COULD BE A GREAT IMPROVEMENT IN ENABLING THE STRUCTURAL DESIGN FEASIBILITY OF TIMBER BUILDINGS.