“Computational Civil Engineering - "Intersections" International Journal

“Computational Civil Engineering 2005”, International SymposiumIaşi, România, May 27, 2005Passive control of semirigid steel structuresPavel Alexa 1 , Horatiu Mociran 2 and Aliz Mathe 31 Faculty of Civ. Eng., Technical University, Cluj Napoca, 3400, Romania2 Faculty of Civ. Eng., Technical University, Cluj Napoca, 3400, Romania3 Faculty of Civ. Eng., Technical University, Cluj Napoca, 3400, RomaniaSummaryThe present contribution refers to the possibility and efficiency of applying passivecontrol to the seismic behavior of steel skeletal structures with semirigid beam –column connections. The semirigidity is a way on its own to introduce a certainlevel of ductility into the steel structures of the frame type. Nevertheless, thesemirigidity accounts for other beneficial effects during seismic action on this typeof structures. The Northridge 1994 earthquake emphasized the difficult and, even,impossible technical approach to the rehabilitation of seismically damaged steelwelded beam – column connections. It proved the advantage of using bolted(replacable) beam – column connectionsThe study presents in a comparative manner several sets of numerical resultsregarding the kinematic and static paramenters that govern the seismicalbehaviour of steel frames. A six story one bay steel frame rigidly connected isconsidered in both situation: withthout base isolation and with base isolation. Thesame structure is, then, taken with semirigidly beam – column connections. Themechanical semirigid model of the beam - column connections are of the usualtypes: web angles, top and seat angles and top and seat and web angles. Also,several analytical bending moment – relative rotation M - θ r have been considered.The semirigid connected structure is than analyzed in both situations, without baseisolators and with base isolators. The analysis is of the time history type conductedin the elasto – plastic domain. The dead load is taken into the analysis when theaccelerograme is applied. The parameters that are considered relevant for theseismic behaviour of the frames are: the natural periods of vibration, theacclerationand displacements induced into the top floor nodes, the lateraldisplacements variation , the base shear variation, the elasto – plastic mechanisms,(location and history of plastic hinges formation), the ductility levels.The conclusions inferred from the numerical results are focused on the role of thepasive seismic control via base isolators. The base isolators used into the analysisare of the elastomeric type chossen from FIP INDUSTRIALE catalog.Keywords: steel frames, semirigidity, passive control, base isolators, time historyanalysis, elasto – plastic mechanism, ductility.