A system is described, aiming at reducing the seismic excitation of structures, based on pure struc- tural solutions. The basic idea is to exploit the phase lag of the incident seismic waves along the foundation and, accordingly, to design it in order to possess the adequate stiffness and strength. The longer the foundation is, the larger the phase lag becomes. It is, therefore, well understandable that under this requirement, foundations of the maximum possible length must be designed. The presented methodology might be proved quite valuable for exist- ing structures and especially for monuments, where, in most cases, it is not possible to proceed to the necessary strengthening interventions in the structure above its foundation. As a technical support of the present investigation, the size of the foundation as a two dimensional elastic beam and the velocity of the propagation of the ground motion are examined as basic parameters. Two strong ground motions have been used, each one with quite differ- ent characteristics compared to the other one: an artificial time history of rather high frequency, fitting to EC8, Type 1, ground class A and a natural ground motion of the Edessa, Greece 1990, M = 5.9, earthquake. The Edessa earthquake is characterized by much longer predominant periods of vibration compared to the artificial one. Vari- ous lengths of the foundation beam have been examined in combination with the velocity of the propagation of the ground motion along the longitudinal direction of the beam. The achieved motions at the center of gravity of the beam as well as the pertinent response spectra are calculated. These spectra are compared to the free field ones. At the beginning of the paper, it is tried to explain the inconsistency between macroseismic observations and earth- quake code requirements concerning the effects of the size of the building foundation. At the end of the paper, the results of the described methodology are demonstrated in several practical case studies.
existing buildings
Il cambiamento di scala delle strutture per la verifica sismica su tavola vibrante: un telaio in c.a. progettato per carichi verticali
The work presented here is one of the fundamental phases of a research programme on seismic evaluation of existing buildings, funded by the Department of Civil Protection and developed at the European Centre for Training and Research in Earthquake Engineering (Eucentre). The present article contains a brief summary of the general theory on scaling: this concepts are then specialised for RC structures to be tested on shaking tables. These ideas are finally applied to the numerical model of the studied building and actually under testing on the Eucentre shaking table.
This paper is available in Italian only.
Concezione strutturale e risposta sismica delle strutture lignee di copertura
In view of assessing the seismic vulnerability of timber roof structures, it is necessary to define evaluation criteria for the various elements and features that influence the structural response. Ths work focuses on the structural concept, particularly interesting because of the numerous existing solutions; indeed, these structures, originally conceived for vertical loads, may be more or less apt to respond to seismic action. With the classic tools of modal and response spectrum analysis the effect of the structural concept has been investigated, in order to define a basis for classification criteria. The aspects that appeared to affect positively the seismic response are a suitable association of the design parameters, according to the traditional construction practice, and the effectiveness of the connections that realize the threedimensionality of the structure.
This paper is available in Italian only.