ABSTRACT
The goal of present contribution refers to the effectiveness of seismic mitigation of 3D steel multi-storey structures via base isolation. The effectiveness of seismic mitigation is regarded as a seismic performance parameter and it is expressed in terms of reduction in the amplitudes of kinematical parameters associated to seismically induced vibratory motion of the analyzed structures. The “reduction” in the seismic response of protected structures is expressed via Seismic Protection Envelope Curves (SPEC’s) that collect the peak values of several parameters (such as lateral displacements, accelerations, etc.) and extend over the duration of seismic action (Prodan et al., 2010a; Prodan et al., 2010b). Also, the efficiency of base isolators on seismically induced kinetic energy into the structure is presented via hysteretic type constitutive (force-displacements) curves. The displacements, accelerations and story drifts are studied along both, orthogonal directions (x and y) of the structure. The mitigation effect of base isolators is exhibited by the above mentioned SPEC’s that are expressed in time, highlighting the length of the interval, amplitudes, their variation/ decrease in time, and the beginning of the induced short pseudo-steady state motion. The mitigation interval via the descending slope of SPEC and the values of associated parameter emphasizes the effectiveness of seismic protection. The shorter is the interval and greater is the reduction in the
1 INTRODUCTION
Seismic mitigation of skeletal structures located in seismic areas, in spite of being a day-by-day design practice in Civil Engineering is, still, a much debated subject. An important aspect of the design activity associated to passive seismic protection is the assessment of the effectiveness of this protection. Effectiveness of applied seismic protection may be viewed in several aspects out of which the investment and maintenance costs-benefit ratio seems to govern the decision in the design activity. There is no doubt that the fulfilling by the seismically protected structure of the entire spectrum of parameters associated to performance based design has to be ensured. On a large extent, the structure will observe the imposed limits of several of these parameters-first of all-by a proper conception and a correct sectional dimensioning (Romanian seismic design code, 2006). Nevertheless, many structures located in seismic areas will exhibit an apriori imposed seismic behaviour, as required by design codes, only if they are equipped with seismic protection devices (Kasai et al., 2009).
