This project aims to study an innovative technique to improve the seismic behavior of structures. Steel devices are inserted in the beam-column connections to improve the connection capacity and to increase the energy dissipation by means of the plasticization of the material. The device is characterized by two steel elements, welded at 90° and fixed to the structural elements with constraints which aim to behave as a hinge. The effectiveness of this solution is evaluated with reference to an existing precast building. The application to the case study aims to highlight advantages and limits of the seismic device. Since the building is composed of two independent structural parts, two separate structural models are created using the software “Midas Gen”. The seismic capacity of the building is studied through modal and spectral analyses following the prescriptions of NTC 2008. The columns are verified under simple compression, P-Delta effects and combined compressive and bending stress; moreover, the structural pounding between the two buildings is analyzed. These verifications allow to define the seismic vulnerability of the building, which is intended to be reduced through the installation of the steel devices, placed at the top of the columns. The design of the seismic devices is performed on the basis of the study of the two-dimensional frame of the “Corpo 1”, defined as the “Prototype Frame”. The devices design is based on linear dynamic analyses with increasing q factor, from 2.5 to 5. The seismic response of the structure is preliminary evaluated in the non-linear range with a set of seven accelerograms compatible with the Code response spectrum. This evaluation aims to the choice of the geometry of the device. The effectiveness of the design with the devices at the columns top is evaluated by making a comparison with the original structure and with the retrofitted one with the devices inserted at the bottom of the columns. Finally, the effects due to the introduction of the steel devices are studied on the complete models of the two buildings. The results show that the devices have a beneficial influence on the displacements at the top of the columns which tend to decrease, reducing the possibility of a loss of support between beam and column. However, there is an increase of the values of the internal actions, especially of the shear force at the base of the columns. This problem might be solved by applying local strengthening in these critical points.
Il presente elaborato si pone l’obiettivo di valutare una tecnica innovativa di miglioramento sismico, caratterizzata da dispositivi in acciaio inseriti nella connessione trave-colonna allo scopo di rinforzare la struttura e di dissipare energia tramite la plasticizzazione del materiale. Il dispositivo è costituito da due elementi in acciaio saldati tra loro a novanta gradi e fissati agli elementi strutturali tramite vincoli che mirano a realizzare una cerniera. L’efficacia della soluzione proposta viene valutata con riferimento a un edificio prefabbricato esistente, con lo scopo di investigare pregi e limiti della soluzione proposta. Poiché l’edificio è suddiviso in due corpi strutturalmente indipendenti, viene creato un modello strutturale per ciascun corpo mediante il software di calcolo “Midas Gen”. Viene valutato lo stato di fatto della struttura, di cui si determinano le proprietà modali e si esegue l’analisi spettrale secondo le NTC 2008. Vengono quindi eseguite sui pilastri le verifiche a compressione semplice, sugli effetti P-Delta, a presso-flessione e viene analizzato il fenomeno del martellamento tra i due corpi. Tali verifiche consentono di valutare la vulnerabilità sismica dell’edificio, cui si vuole porre rimedio mediante l’inserimento dei dispositivi sulla sommità delle colonne. Il loro dimensionamento viene effettuato mediante lo studio di un telaio bidimensionale del Corpo 1 della struttura in esame, indicato come "Telaio Tipo". I dispositivi vengono dimensionati sulla base di analisi lineari con fattori di struttura q crescenti da 2.5 a 5. La risposta della struttura viene preliminarmente valutata in campo non lineare facendo uso di sette accelerogrammi spettro-compatibili. Tale valutazione porta alla scelta della geometria del dissipatore: l’efficacia del dimensionamento finale in sommità si ottiene per confronto con lo stato di fatto e con il caso dei dispositivi inseriti alla base. Da ultimo, l’effetto dei dispositivi viene valutato nei modelli completi dei due Corpi in esame. Le analisi effettuate evidenziano che a seguito dell’introduzione dei dispositivi lo spostamento in sommità dei pilastri tende a diminuire, riducendo la possibilità di perdita dell’appoggio. Tuttavia, si nota un aumento delle azioni interne, soprattutto dell’azione tagliante; aspetto che può essere controllato mediante l’inserimento di rinforzi locali.
Studio di una tecnica innovativa di miglioramento sismico per un edificio prefabbricato industriale
OSTI, SIMONE;DE DONNO, ROBERTA
2017/2018
Abstract
This project aims to study an innovative technique to improve the seismic behavior of structures. Steel devices are inserted in the beam-column connections to improve the connection capacity and to increase the energy dissipation by means of the plasticization of the material. The device is characterized by two steel elements, welded at 90° and fixed to the structural elements with constraints which aim to behave as a hinge. The effectiveness of this solution is evaluated with reference to an existing precast building. The application to the case study aims to highlight advantages and limits of the seismic device. Since the building is composed of two independent structural parts, two separate structural models are created using the software “Midas Gen”. The seismic capacity of the building is studied through modal and spectral analyses following the prescriptions of NTC 2008. The columns are verified under simple compression, P-Delta effects and combined compressive and bending stress; moreover, the structural pounding between the two buildings is analyzed. These verifications allow to define the seismic vulnerability of the building, which is intended to be reduced through the installation of the steel devices, placed at the top of the columns. The design of the seismic devices is performed on the basis of the study of the two-dimensional frame of the “Corpo 1”, defined as the “Prototype Frame”. The devices design is based on linear dynamic analyses with increasing q factor, from 2.5 to 5. The seismic response of the structure is preliminary evaluated in the non-linear range with a set of seven accelerograms compatible with the Code response spectrum. This evaluation aims to the choice of the geometry of the device. The effectiveness of the design with the devices at the columns top is evaluated by making a comparison with the original structure and with the retrofitted one with the devices inserted at the bottom of the columns. Finally, the effects due to the introduction of the steel devices are studied on the complete models of the two buildings. The results show that the devices have a beneficial influence on the displacements at the top of the columns which tend to decrease, reducing the possibility of a loss of support between beam and column. However, there is an increase of the values of the internal actions, especially of the shear force at the base of the columns. This problem might be solved by applying local strengthening in these critical points.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/142347