Isolare conviene: valutazioni su un edificio di nuova costruzione

Isolare conviene
(download pdf)
Il confronto in termini di costi di costruzione tra due soluzioni strutturali, l’una a base fissa e l’altra con isolamento sismico, per la realizzazione di un edificio di uso plurimo in Avezzano, caratterizzato da complessità distributiva in pianta ed in elevazione, ha mostrato un sensibile vantaggio economico nella realizzazione della seconda rispetto alla prima. Ciò va ad aggiungersi al superiore livello di prestazione offerto nei confronti del sisma della struttura con isolamento sismico che, pertanto, può conseguire un superiore valore di mercato

 

Isolation system is convenient: estimates of a new building

The paper presents the technical and economic comparison between two possible solutions, one with base isolation and the other with a fixed base, for a reinforced concrete building, for civil and commercial use in Avezzano, Italy, characterized by high seismic hazard. The requests of the customer and urban constraints, the presence of an adjacent building, make that the structure has an irregular plan-volumetric layout; then the design of the fixed base structure requires foundations of large size as well as of pillars and beams. By using the design spectrum requested by the Italian Technical Code (NTC 2008), with the following data: VS30=399 m/sec, class of use II (ordinary building), life of the structure 50 years (corresponding to a return period equal to 475 years), linear dynamic analysis of 3D model of the structure showed that the natural periods range from 0.42 sec to 0.13 sec, 88% of participating mass, with torsional and torsional-translational modal shapes and strong coupling of the higher modes.
Trying to get a better dynamic behavior of the structure, preserving the geometry, it has been designed by inserting base isolation pendulum devices between foundation and the superstructure. The choice of the pendulum seismic isolation ensures correspondence between the projection of the mass gravity-center and stiffness-center in any operating condition, since the horizontal stiffness is linked to the axial load at the level of the devices. According to Italian Technical Code the structure has been designed as it was located in seismic zone 4 of the previous Code, very low level of seismic hazard, obtaining relevant reduction of the dimension of pillars and beams, with FIP isolators FIP-D L 310/600-3700 and FIP-D L 510/600-3700. Dynamic Linear analysis carried out on base-isolated framed building showed two first translational modal shapes, with periods Tis = 2.85 sec and mass participation > 91% with total decoupling of the higher modes. The achievement of periods T > 2.8 sec allows to avoid any possible effect of local amplification due to soil resonance phenomena.
The costs of building the two structures have been estimated. The fixed base one has a cost higher than the similar base isolated one even considering the additional cost of the isolation system. In addition a higher market value can be achieved with a structure that offers resistance levels unfeasible with the fixed base one. Finally, it is worth to mention that the fixed base structure is exposed to damages in case of earthquake with consequent repair costs and loose of functionality while this is not expected for the base isolated one

 

 

 

W. Bellotta, F. Amatilli

DOI 10.12910/EAI2015-086

Contact person: Walter Bellotta  - w.bellotta@alice.it