A mechanically derived vulnerability index method for seismic risk assessment of existing RC school buildings

La vulnerabilità sismica degli edifici scolastici in C.A. è un aspetto molto importante in Italia, come mostrato da recenti terremoti che hanno causato danni rilevanti in diverse scuole. La maggior parte delle scuole italiane è stata costruita tra gli anni ’50 e ’90, quindi in assenza o con basso livello di resistenza sismica. Nel presente studio è stata sviluppata una metodologia per la valutazione speditiva del rischio sismico è stata sviluppata. Essa si basa sul metodo dell’indice di vulnerabilità, assumendo 15 indicatori di vulnerabilità a cui assegnare dei punteggi sulla base di un giudizio esperto. I punteggi sono stati determinati mediante analisi pushover effettuate su diversi modelli strutturali rappresentativi delle principali caratteristiche dei due campioni di scuole Pre 1974 e Post 1974. A tal fine un set di circa 40 istituti scolastici superiori è stato analizzato per rilevare le vulnerabilità tipiche e specifiche, ed una progettazione simulata è stata effettuata in accordo ai Codici in vigore nei due periodi di riferimento. Delle correlazioni tra l’indice di vulnerabilità globale Iv e la capacità in termini di PGA, sia per lo stato di danno leggero che per il collasso, sono state determinate per ottenere curve di danno trilineari così come nel metodo GNDT. La validazione numerica del metodo proposto è stata effettuata confrontando le curve di danno trilineari ottenute per due edifici prototipo, rappresentativi in media delle classi Pre 1974 e Post 1974, con le curve di danno analitiche fornite per gli stessi edifici sia da analisi pushover che dinamiche incrementali. Inoltre, una validazione sperimentale è stata fatta confrontando, per le scuole superiori delle province di Ancona e Macerata, il danno subito a causa della sequenza sismica del centro Italia del 2016, con il danno stimato, per lo stesso livello di intensità, mediante il metodo proposto. Entrambe le procedure di validazione hanno confermato una buona affidabilità del metodo proposto per valutazioni rapide e di tipo comparativo. Infine, due tipologie di scenari di danno rapido sono state sviluppate per il campione di edifici, al fine di stimare le perdite fisiche, umane ed economiche. Il primo tipo considera una pericolosità sismica uniforme sull’intero territorio e livelli di intensità crescenti, invece l’altra tipologia considera tre singoli eventi sulla base del sistema di faglie presente nella zona di interesse (fissando per ognuno un epicentro, magnitudo e profondità), quindi i valori di PGA sono calcolati per ogni edificio mediante una legge di attenuazione.The seismic vulnerability of RC school buildings is a very important issue in Italy, as shown from recent earthquakes that caused heavy damage of several school buildings. Most of Italian schools were built between the 50s and the 90s, so without or with low seismic resistance criteria. In this study a methodology for rapid seismic risk assessment of RC school buildings is developed. It is based on the vulnerability index method, assuming 15 vulnerability indicators to which assign scores on the base of expert judgment. The scores were determined through pushover analyses performed on several structural models representative of the main characteristics of the Pre 1974 and Post 1974 school building stocks. To this aim a set of about 40 high schools were analysed to detect typical and specific vulnerabilities, and a simulated design procedure was carried according to the Codes in force in the two reference periods. Correlations between the global vulnerability index Iv and the capacity in terms of PGA, for both slight damage and collapse, were determined to obtain trilinear damage curves such as in GNDT method. The numerical validation of the proposed method was made by comparing the trilinear damage curves obtained for two prototype buildings, representative in average of the Pre 1974 and Post 1974 classes, with analytical damage curves provided for the same buildings by both pushover and incremental dynamic analyses. Also, experimental validation was carried out by comparing, for the high schools of the provinces of Ancona and Macerata, the damage occurred because of the Centre Italy 2016 seismic sequence, with the damage estimated, for the same intensity level, through the proposed method. Both validation procedures have confirmed a good reliability of the proposed method for rapid and comparative evaluations. Finally, two typologies of rapid damage scenarios were developed for the building stock, in order to estimate physical, human and economic losses. The first typology considers uniform seismic hazard on the whole territory and increasing intensity levels, instead the second one considers three single events on the base of the fault system of the region (fixing for each an epicentre, magnitude and depth), thus the PGA values are calculated for every school building by means an attenuation law

La vulnerabilità sismica degli edifici storici in muratura: dalla conoscenza agli interventi di consolidamento strutturale/Seismic vulnerability of historic masonry buildings: from knowledge to the interventions of structural consolidation

I tragici eventi sismici che da agosto 2016 a gennaio 2017 hanno colpito una vasta area del Centro Italia, hanno nuovamente acceso i riflettori sull’elevata vulnerabilità del patrimonio storico-architettonico ampiamente diffuso sul territorio italiano.Con un taglio il più divulgativo e meno tecnico possibile, e nei limiti di lunghezza richiesti, si vogliono illustrare le principali questioni legate alla mitigazione del rischio sismico, a partire dalla scarsa qualità muraria che rappresenta il maggior elemento di vulnerabilità, fino alle tecniche di intervento, passando per gli altri elementi di vulnerabilità, per la conoscenza dell’edificio, irrinunciabile per comprenderne il comportamento, e per le analisi strutturali necessarie per una affidabile ed oggettiva valutazione della vulnerabilità sismica. The tragic seismic events that hit a large area of the Centre Italy, from August 2016 to January 2017, have again highlighted the high vulnerability of the historical and architectonical heritage widely spread on the Italian land.With an exposition the most informative and the less technical possible, in the required length limit, the main issues regarding the seismic risk mitigation are treated. Starting from the poor quality of the masonry, which represents the main vulnerability factor, up to the intervention techniques, the paper deals about the other vulnerability factors, the knowledge of the building as the indispensable process to understand the seismic behaviour, and the structural analyses as necessary to provide a reliable and objective seismic vulnerability assessment

The Influence of Dowel-Pin Connections on the Seismic Fragility Assessment of RC Precast Industrial Buildings

Background:Recent major earthquakes in the centre of the Italy, between August and October 2016, have reaffirmed the seismic vulnerability of precast industrial buildings with a lot of collapse recorded. This is typical due to the past Italian building practices, where structural deficiencies are mainly related to the capacity to transfer horizontal forces between primary structural elements.Objectives and Methods:In these types of structures, a key role is played by the dowel pin connections which allow to transfer lateral horizontal forces from the beam to the column, without losing load carrying capacity. For this reason, in this work, the assessment of the seismic fragility of single-story reinforced concrete precast building located not far from the epicentres of the two aforementioned earthquakes was done.Results and Conclusion:The seismic risk was evaluated in terms of annual frequency of exceedance for three performance levels provided by the European and Italian seismic codes, considering the mean hazard curves for the site. The comparison between the fragility of different structural models shows the importance in the choice of the column-beam connection modelling to obtain reliable results on the structural safety assessment.</jats:sec

Seismic Assessment of a Monumental Building through Nonlinear Analyses of a 3D Solid Model

The paper analyzes the static behavior and the seismic vulnerability of the “San Francesco ad Alto” building in Ancona (Italy), which is currently used as a Regional Headquarter of the Marche Region by the Italian Army and was formerly a monastery. The global static structural behavior and the dynamic properties have been evaluated using the Finite Element modeling technique, in which the nonlinear behavior of masonry has been taken into account by proper constitutive laws. The concepts of homogenized material and smeared cracking are used to evaluate the capacity of the monastery to withstand lateral loads together with the expected demands resulting from seismic actions (N2 method), using a nonlinear static analysis (pushover). The comparison of seismic demand and capacity confirms the susceptibility of these types of buildings to extensive damage and collapse, as frequently observed in similar buildings. This paper aims to point out that advanced numerical analyses can offer significant information on the understanding of the actual structural behavior of historical buildings. It is believed that the methodology and the overall conclusions of this case study are valid for many historical monasteries in Europe

One-year monitoring of a reinforced concrete school building: Evolution of dynamic behavior during retrofitting works

This work illustrates the results of a one-year structural monitoring campaign of a Reinforced Concrete (RC) school building subjected to a substantial retrofitting works. Through Operational Modal Analysis (OMA) techniques, it has been possible to follow the dynamic evolution of the structure, using Finite Element Method (FEM) model refinement as a valuable tool for non-invasive structural assessment. The long-term Ambient Vibration Survey (AVS) highlighted the increasing of building performance in terms of natural frequencies following the retrofitting works. This relevant data collection can be extremely helpful in calibrating of other similar retrofitting interventions and provides useful guidelines that can assist in the planning of Structural Health Monitoring (SHM) applications

Modelling and analysis of an ancient monastery under earthquake loading: assessment of seismic resistance

The paper discusses the static behaviour and the seismic vulnerability of a historical building, in particular a monastery currently used as a Regional Headquarter of the Marche Region by the Italian Army. The building is located in Ancona, a site characterized with a medium-high seismic risk. Monasteries, as churches, represent a large portion of the Italian (and European) cultural heritage particularly susceptible to damage and prone to partial or total collapse under earthquake loads; for these reasons they are of economic and engineering concern. The high seismic vulnerability of this type of buildings is due to both the specific mechanical properties of masonry materials (characterized by a very small tensile strength) and the particular configuration of the buildings itself, which are characterized by an open plan layout often with perimeter slender walls. Moreover the vulnerability of these historical masonry buildings is enhanced by the absence of adequate connections between the various parts constituting the structural complex and by the presence of thrusting horizontal structures (triumphal arches, etc.) as already discussed in several studies [1,2]. Furthermore, it is no longer used as a monastery, a fact that changes the hazard aspects [3]. A finite element methodology for the static and dynamic analysis of historical masonry structures is described and applied to the case study. In particular 3D linear and nonlinear analyses (which take into account the nonlinear behaviour of masonry) are performed. Also constitutive assumptions, characterized by elasticity, damage and friction, are done. The behaviour of the masonry is simulated by use of solid elements which can have their stiffness modified by the development of cracking and crushing. The comparison demand vs. capacity confirms the susceptibility of this type of buildings to extensive damage and possibly to collapse. At the end, we have conducted some analyses of active failure mechanisms in the light of the observed state of damage and of the FEM results