1,721,035 research outputs found
Seismic retrofit of a prestressed concrete road bridge
No full textThe paper deals with the proposal of a procedure for the seismic retrofit of an existing prestressed concrete bridge. First, the seismic vulnerability assessment of the bridge was carried out. With this aim, a Nonlinear Static Procedure based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra was applied. According to the Performance-Based Earthquake Engineering principles, this procedure makes it possible to explicitly correlate the different performance levels to the varying intensities of seismic action. A seismic protection strategy based on the use of isolating system located between pier top and deck was subsequently applied. A design process consisting of an appropriate application of capacity-design principles and the Direct Displacement-Based Design approach was implemented. Finally, the seismic response of the bridge, modeled with an “exact” damping matrix, was evaluated through a linear time-history analysis involving a solution of the complete set of equilibrium equations at each time increment. The results obtained highlight the effectiveness of the seismic retrofit strateg
Damping Effect on the Seismic Response of Base-Isolated Structures with LRB Devices
No full textThe introduction of high energy dissipation in base-isolated structures is often prescribed to minimize the device displacements as well as the effects of near-field earthquakes. The identification of effects on the superstructure due to the high energy dissipation is, therefore, an important aspect of the base-isolated structure design. In this study, the seismic response of base-isolated structures with Lead Rubber Bearing (LRB) devices is estimated aiming at the evaluation of the adverse effect of damping on the structural response parameters. Four base-isolated structures are considered taking into account a complete damping matrix. Their structural seismic response evaluation is first performed using nonlinear response history analysis (NRHA) by considering a bilinear device behaviour. The increase in the superstructure response parameters is detected. A structural analysis by considering an equivalent linear viscoelastic LRB behaviour was also performed. A frequency domain method through transmissibility was applied to explain the influence of isolation damping on the higher mode effects and inter-storey drift ratios. The comparison between the NRHA results and response spectrum analysis (RSA) results highlights meaningful differences between the values of some structural response parameters (displacements of the isolation system and inter-storey drift ratio). A seismic analysis of base-isolated structures with High Damping Rubber Bearing (HDRB) and supplemental linear viscous damping (VD) devices is also carried out. The results point out that the use of HDRB devices with linear viscous dampers, as compared to LRB devices, lead to a reduction of the devices displacements and to a beneficial or least detrimental effects on the superstructure response parameters in base-isolated structures
Seismic performance assessment of masonry structures with a modified “concrete” model
No full textThis paper deals with the proposal of a constitutive model for the FEM nonlinear analysis of masonry structures as well as the use of a nonlinear static adaptive procedure in order to estimate the inelastic response and seismic performance ofmasonry buildings. In particular, the mechanical behaviour of masonry was simulated as a continuous, homogeneous and isotropic material, using a “concrete” smeared-crack model modified by an interaction with the plasticity Drucker–Prager domain as well as the definition of a new compression failure surface. The calibration and validation of the FEM model was carried out through a sensitivity analysis of the different mechanical parameters, which were based on the experimental data available in current literature. Subsequently, the proposed material constitutive model was used for the seismic performance evaluation of masonry buildings.With this aim, an incremental non-iterative procedure based on the capacity spectrum method and inelastic demand response spectra was applied. According to performance-based engineering, this procedure allows for the correlation between the different risk levels and the expected performance levels for each limit state to be taken into account. In conclusion, the results obtained
from the FEM model were compared with those from a well-known macro-element model
Prestazioni sismiche di strutture in c.a. rinforzate mediante controventi metallici dissipativi
No full textIn this paper, the performance-based seismic rehabilitation of RC buildings using dissipative
steel braces was carried out. At this aim, a damage-controlled nonlinear static procedure was used to estimate
maximum lateral displacement and plastic dissipated energy, control damage indices in structural elements
and keep them within tolerable limits at each performance level. These multi-level objectives were pursued
with a procedure based on the Capacity Spectrum Method, the Inelastic Demand Response Spectra and the estimation
of the duration-related damage that is a function of the energy absorbed in the structure. This procedure
retains the conceptual simplicity and computational effectiveness of pushover analysis and accounts
for the cumulative inelastic deformation under displacement reversals. Its accuracy in reproducing the dynamic
performance of RC frames rehabilitated with eccentric dissipative braces is finally investigated
Modellazione sperimentazione e caratterizzazione dinamica di un ponte a tre arcate sul fiume Volturno
No full textBase Isolation Seismic Retrofit of a Hospital Building in Italy
No full textThe paper deals on a significant retrofit project currently under construction of an existing hospital building in Avellino (Italy). The seismic retrofit was realized by connecting together the first floors of the three existing structures and by creating a unique isolation system composed of high damping rubber bearings and sliding devices. The base isolation is achieved by gradually cutting the building from foundation and installing the isolators at the level of upper edge of the columns. The study allows the verification of the adequacy of the isolation system, showing the benefits of the application of the isolation devices, the limitations and the characteristics of their performance
Annotazioni sulla risposta di strutture in c.a. isolate alla base con dispositivi elastomerici ad elevatissimo smorzamento
No full textStrutture in c.a. isolate alla base con dispositivi LRB ad elevato smorzamento: valutazione della risposta e analisi di confronto
Full text linkNel caso di strutture sismicamente isolate è in genere richiesta la presenza di importanti capacità dissipative nei dispositivi di isolamento, al fine di controllarne la risposta in termini di spostamento. A tal riguardo alcuni codici sismici di nuova generazione (FEMA-451; Eurocodice 8; NTC2008) aprono fortemente all’impiego di dispositivi elastomerici “ad elevatissimo smorzamento” (Lead Rubber Bearing - LRB) per il controllo passivo della risposta di edifici sotto sisma. Essi consentono inoltre di valutare la risposta strutturale con una procedura semplice e di generale diffusione (analisi modale con spettro assegnato) fino a valori del rapporto di smorzamento ξ pari a 0.30. Tuttavia, come è noto: (a) i dispositivi LRB presentano una risposta di tipo marcatamente non lineare; (b) secondo alcuni Autori, valori elevati di ξ producono l’effetto di amplificare la risposta della sovrastruttura. In tale contesto, il presente lavoro affronta lo studio della risposta di strutture isolate alla base mediante dispositivi elastomerici LRB con valori del rapporto di smorzamento ξ compresi nell’intervallo 0.2-0.3. Con riferimento a sistemi MDOF corrispondenti ad organismi resistenti in cemento armato modellati con una matrice di smorzamento “completa” ed isolati alla base con dispositivi LRB, sono state valutate in primo luogo le risposte strutturali mediante analisi time-history con integrazione frontale delle equazioni del moto, considerando per i dispositivi una schematizzazione sia lineare che non lineare. Sono stati a tal fine impiegati segnali accelerometrici artificiali e registrazioni di terremoti storici significativi. I risultati delle analisi mostrano, in alcuni casi, un incremento nei parametri di risposta della sovrastruttura per valori del rapporto di smorzamento dei dispositivi superiori al 20%. Sono state infine condotte valutazioni di confronto tra le risposte di cui innanzi e quelle ottenute attraverso l’analisi modale con spettro assegnato, che evidenziano come quest’ultima procedura conduce a stime non conservative sia del massimo spostamento dei dispositivi di isolamento che dei parametri di risposta della sovrastruttura
- …
