Out-of-plane seismic response of masonry façades some comparisons among full dynamic and pushover analysis = Risposta sismica fuori del piano di facciate in muratura: Confronto tra analisi dinamiche non-lineari e analisi pushover

Within the framework of the seismic risk assessment of monumental masonry buildings, we focus on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the façade of churches or basilicas. A full non-linear dynamic analysis is performed by adopting a rigid body and spring model (RBSM), where damage is entirely ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including plastic energy dissipation and mechanical damage. Then, a comparison is made with a non-linear static pushover analysis, which is performed by means of the same RBSM under quasi-static loading, incrementally applied. The generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand. As a case study, the church of Rosario in Guastalla was chosen, that was damaged by the Emilia Romagna Earthquake in 1987. A number of analyses have been performed, by adopting artificially generated accelerograms with different destroying potential, in order to investigate the correlation between the damage indicators obtained with the two procedures. The two methodologies showed a good agreement in the evaluation of the seismic response for low-medium seismic demands, even if NSPs tends to overestimate the damage, especially for high seismic levels.

Nell’ambito del tema della valutazione del rischio sismico degli edifici monumentali in muratura, si presenta una ricerca incentrata sull’analisi dei meccanismi di collasso fuori-piano. Due differenti metodologie di anali-si sono applicate e confrontate. Da un lato si effettua un’analisi dinamica non-lineare completa (NLD) adot-tando un modello specifico a elementi rigidi e molle (RBSM – Rigid Body and Spring Model) in cui la pro-gressione del danneggiamento è determinata dal meccanismo flessionale fuori-piano ed il comportamento costitutivo ciclico del materiale è definito attraverso una descrizione fenomenologica che include la dissipa-zione plastica e il degrado dei parametri meccanici. Dall’altro, con lo stesso modello RSBM, si effettua un’analisi statica non-lineare pushover (NSP) valutando la curva forza generalizzata-spostamento e lo spo-stamento limite ultimo, poi comparati con la domanda sismica espressa in termini di coordinate spettrali. Co-me caso di studio viene considerata la chiesa del Rosario a Guastalla, danneggiata dal terremoto dell’Emilia Romagna nel 1987, adottando accelerogrammi di diverso potenziale distruttivo e valutando la loro correlazio-ne con i parametri rappresentativi del danno. Le due metodologie messe a confronto hanno mostrato una buo-na corrispondenza per quanto riguarda la valutazione della risposta nelle zone a bassa e media sismicità, con una tendenza delle NSP a sovrastimare il danno, specialmente per i livelli maggiori di azione sismica. *** Within the framework of the seismic risk assessment of monumental masonry buildings, we focus on the analysis of out-of-plane mechanisms which actually represent the most recurrent collapse mode for the façade of churches or basilicas. A full non-linear dynamic analysis is performed by adopting a rigid body and spring model (RBSM), where damage is entirely ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including plastic energy dissipation and mechanical damage. Then, a comparison is made with a non-linear static pushover analysis, which is performed by means of the same RBSM under quasi-static loading, incrementally applied. The generalized force-displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand. As a case study, the church of Rosario in Guastalla was chosen, that was damaged by the Emilia Romagna Earthquake in 1987. A number of analyses have been performed, by adopting artificially generated accelerograms with different destroying potential, in order to investigate the correlation between the damage indicators obtained with the two procedures. The two methodologies showed a good agreement in the evaluation of the seismic response for low-medium seismic demands, even if NSPs tends to overestimate the damage, especially for high seismic levels.