“Computational Civil Engineering - "Intersections" International Journal

58 P. Alexa, H. Mociran, and A. Mathe4. CONCLUSIONSThe above numerical results – presented for the six story one bay frame – can notbe generalized. Nevertheless, the associated results are in line with other numericalresults obtained from other case studies. The main aspect that can be emphasized isthe benneficial effect of base isolators in all cases. This is – in fact – the generalexpectation. Whatever comparisson is inferred from the numerical results, it has tobe mention that the ultimate bending capacity of the semirigid connection is about80% of the bending capacity of the connected beam. A reduction of 20% in thebending capacity of the connecting section proves to be to much, since thesemirigid structure (Case 3 – Non-isolated semirigid structure) leads to theformation of plastic hinges in the middle span sections of the beams (Fig. 10). Thisfact has to be viewed correctly: the semirigid connecting sections are placed in theimmediate vicinity of the column flange (not in the vicinity of the column axix).This real model leads to a “delay” in the loading of the semirigid connections dueto smaller values of the (bending) moments at column flanges.Another feature of the non-isolated semirigid structure (Fig. 10) versus the nonisolatedrigid case (Fig. 6) is the higher number of plastic hinges (19 versus 12)developed over approximately the same duration – about 16 seconds) which leadsto a higher quantity of dissipated (through plastic hinges) of induced kineticenergy.The two cases of base isolated structures (Case 2 and, respectively, Case 4)emphisize the higher benefit obtained in the case of isolating semirigid structurethan in the case of rigid structure: no plastic hinges in the middle span sections ofthe beams. This benefit has to be assesed together that obtained from thepossibility of post – seism rehabilitation.References1. Gioncu, V. Influence of strain – rate on the behaviour of steel members, Proceedings of the 3 rInternational Conference STESSA 2000, A. A. Balkema, Rotterdam, 2000, pp. 19 – 26.2. De Martino, A. State of the art report on the basic problems of seismic behaviour of steelstructures: Genaral Report, Behaviour of Steel Structures in Seismic Areas, Aug. 1997, Kyoto,Edizzioni 10/17, 1997, pp. 3-20.3. Akiyama, H. An overview of global ductility, Proceedings of the International WorkshopSTESSA, Timisoara, 1994, E & FN Spon, London, 1995, pp. 519 - 534.4. Alexa, P. et al. Ductility via semirigidity, Proceedings of th 9 th Conference on Metal Structures,Timisoara 200, edited by M. Ivan, Orizonturi Universitare, Timisoara 2000, pp. 361 – 366.5. Georgescu, D. Semirigidity: General report, Proceedings of the International WorkshopSTESSA, Timisoara, 1994, E & FN Spon, London, 1995, pp. 519 - 534.6. www.fip-group.it/