Laura Liberatore

The performance of churches in the 2012 Emilia earthquakes

In this study the damage suffered by churches during the 2012 Emilia seismic sequence in Italy is analysed, based on surveys and inspections carried out in the area. Similarly to what was observed after other Italian earthquakes, the damage to churches was severe. However, the Emilia churches present some characteristic features such as the use of unreinforced clay brick masonry. In order to appropriately address the performance of this class of buildings, typical architectural layouts and construction techniques are described. Such techniques are interpreted also in the light of the local seismic catalogue. Fifty churches are then selected and their damage is studied, with reference to typical local-collapse mechanisms of different macro-elements. The study highlights that the damage is often concentrated at the top section of the façade, in the clerestory walls, in the vaults and in the bell towers. Structural analyses are performed to explain some of the observations. The overturning of the top section of the façade is analytically addressed, modelling the friction interlocking. With reference to the case study of San Francesco in Mirandola, non-linear static and dynamic analyses allow us to correlate the directionality of damage to the higher seismic demand along the NS direction, to point out the negligible role of the large vertical component of ground motion and to emphasise the relevance of the buttresses for the seismic response of the façade.

The behaviour of vernacular buildings in the 2012 Emilia earthquakes

Vernacular buildings are a relevant part of the building stock affected by the Emilia, 2012, earthquakes and they contribute to shape the rural landscape of the Po valley. Unfortunately, due to overall layout, constructive details and poor maintenance, they have shown a very poor seismic performance. Because most of these buildings are lightly used or abandoned, the risk that they will be demolished is rather high; this could be the most long-lasting outcome of the seismic sequence, deeply affecting the traditional landscape of this portion of the Po valley. In this paper a brief description of the architectural features of these buildings is given and their typical seismic performances are analysed. Because damage is usually related to local-collapse mechanisms, rocking spectra are computed for the near field accelerograms and they are compared with observed behaviours. Finally, suggestions are given to improve the earthquake response of these structures, with the aim of preserving important testimonies of the civilisation of the area.

Characterization of displacement demand for elastic and inelastic SDOF systems

Abstract The results of a research concerning the characterization of elastic and inelastic displacement spectral demand as a function of magnitude, source-to-site distance, and soil type are presented. The displacement spectra were computed for single degree of freedom systems subjected to a large set of strong ground motion records. In the elastic case, design displacement spectra, modeled in a simplified way with a bilinear shape in the period range 0–4 s, are then proposed for the estimation of the displacement demand to structures located on different local soil condition, at different distance from the causative fault, and for different levels of magnitude. In order to evaluate the reliability of the proposed design displacement spectra, probabilistic displacement spectra corresponding to different levels of probability of non-exceedance were also carried out. The inelastic displacement demand to elasto-plastic systems was analyzed through the ratio between inelastic and elastic spectral displacements. Simplified relationships of the inelastic displacement ratio are then proposed as a function of displacement ductility, soil condition and period of vibration. Finally, as a comparison, the inelastic displacement ratios were also estimated considering other constitutive models.

Performance of Reinforced Concrete Buildings During the 2002 Molise, Italy, Earthquake

About 10% of the almost 20,000 buildings damaged by the 2002 Molise, Italy, seismic sequence were reinforced concrete (RC). The most frequent type of damage affected the infill masonry walls, but in some cases cracks in concrete columns were observed. Heavy damage to both infills and structural elements was restricted to a few cases in the meizoseismal area. Almost all the affected municipalities were only classified as seismic in May 2003, following this earthquake. Consequently, construction generally used vertical-load-bearing moment-resisting frames with no explicit design for seismic lateral forces. In particular, the reinforced concrete buildings typically consist of cast-in-place unidirectional RC slabs lightened with hollow clay tiles, supported by RC beams and columns. Usually no shear walls are present, except in some cases for the elevator shaft. This paper covers: a) an overview and statistical analysis of damage to RC buildings, and b) a detailed analysis of two damaged buildings.

Strength and stiffness reduction factors for infilled frames with openings

Framed structures are usually infilled with masonry walls. They may cause a significant increase in both stiffness and strength, reducing the deformation demand and increasing the energy dissipation capacity of the system. On the other hand, irregular arrangements of the masonry panels may lead to the concentration of damage in some regions, with negative effects; for example soft story mechanisms and shear failures in short columns. Therefore, the presence of infill walls should not be neglected, especially in regions of moderate and high seismicity. To this aim, simple models are available for solid infills walls, such as the diagonal no-tension strut model, while infilled frames with openings have not been adequately investigated. In this study, the effect of openings on the strength and stiffness of infilled frames is investigated by means of about 150 experimental and numerical tests. The main parameters involved are identified and a simple model to take into account the openings in the infills is developed and compared with other models proposed by different researchers. The model, which is based on the use of strength and stiffness reduction factors, takes into account the opening dimensions and presence of reinforcing elements around the opening. An example of an application of the proposed reduction factors is also presented.

Estimation of near-source ground motion and seismic behaviour of RC framed structures damaged by the 1999 Athens earthquake

On September 7, 1999 an earthquake with magnitude M W =5.9 occurred close to the city of Athens in Greece. More than 80 buildings collapsed, about 150 deaths and hundreds of injuries were reported. Soon after the event a damage investigation was carried out by two of the authors in the most heavily struck areas. The most serious damages were observed in the northern suburbs of Athens, where reinforced concrete frames and masonry buildings represent the prevalent construction systems. The hysteretic energy demands imposed on RC buildings should have been rather severe considering the structural systems characteristics and the inadequate construction details. However, over-strengths, redundancy and especially the presence of infill walls, provided a significant increase of the seismic capacity and contributed to the survival of many buildings. The objective of the present work is to reproduce and analyse the response of typical RC frames subjected to the 1999 Athens earthquake in areas where the observed damage was particularly severe but no recordings of the ground motion were available. After a general overview of the seismotectonic environment, seismological data, observed macro-seismic intensities, structural typologies and observed building behaviour, an attempt is made to identify representative excitations in the meizoseismal area. Specifically, the required accelerograms are obtained by modifying available records so as to reproduce a given global energy content and to be consistent with the observed damage. To study the seismic response of RC models, the obtained accelerograms are used to perform nonlinear dynamic analyses.

Finite-discrete element modelling of masonry infill walls subjected to out-of-plane loads

In this paper, the out-of-plane response of infill walls is investigated by means of non-linear monotonic (push-over) analyses through a combined finite and discrete modelling approach. The model accounts for material deformability, crack formation, sliding, separation and formation of new contacts. Masonry units are modelled as finite elements, and different material models are assumed for the masonry. Contact between masonry units, and between masonry and frame elements is modelled by means of interfaces, which permit tangential motion with frictional sliding. Frame elements are modelled by means of a linearelastic material. The results of the numerical analyses are compared with those of experimental tests available in the literature. The advantages and disadvantages of the adopted modelling strategy are investigated.

Seismic Demand on Historical Constructions During the 2016–2017 Central Italy Earthquake Sequence

Between August 2016 and January 2017 nine shallow events with moment magnitude between 5.0 and 6.5 occurred in Central Italy, with largest magnitude being the most severe in Italy since 1980. Several thousands of heritage buildings have been affected to a different degree by the ground motion shaking, highlighting some specific behaviours in the most stricken areas. In and around Amatrice extensive masonry fragmentation, cracking of large walls without openings, as well as survival of tall towers and slender bell gables have been observed. On the contrary, in and around Norcia bell gables and churches collapsed. In this paper, surveyed response is interpreted both in terms of construction characteristics and by means of conventional (pseudo-acceleration) and unconventional (energy and rocking) spectra. It is shown that in Amatrice high frequency content of the first earthquake affected short masonry structures with very poor quality mortar, whereas in Norcia low-frequency content affected structures undergoing out-of-plane rocking or local mechanisms.

COMPARATIVE ASSESSMENT OF STRUT MODELS FOR THE MODELLING OF IN-PLANE SEISMIC RESPONSE OF INFILL WALLS

The influence of infills on the seismic response of frame structures has long been recognised. Typically, stiffness and strength of the infill and connections between infill and frame are such that the infill affects the global seismic behaviour of the structure. Hence, the presence of infills should be considered in the analysis and design of new buildings and in the seismic assessment of existing ones. To this aim, simple models for infill walls, such as the equivalent diagonal no-tension strut model, have been developed in the last decades. The objective of the present study is to assess the validity of different strut models. To this aim, 162 experimental tests available in the literature are considered. The data set includes both reinforced concrete and steel frames, as well as confined masonry structures. The mechanical characteristics of masonry and the boundary conditions between frames and infills of the test specimens take into account a large set of situations, reflecting the great variability in the materials and in the construction techniques adopted in different countries. Moreover, the type of tests and the related results are not uniform; in some cases monotonic experiments are performed, whereas in other cases cyclic tests are carried out. As expected, the presence of different types of infill-frame systems results in a large scatter of the data. However, the comparison between experimental results and predictions show that, on the average, the infill strength can be adequately estimated by resorting to the strut model whereas major uncertainties are found for the stiffness prediction. 3255 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3255-3268

Non Linear Analyses for the Evaluation of Seismic Behavior of Mixed R.C.-Masonry Structures

In this work the seismic behavior of masonry buildings with mixed structural system, consisting of perimeter masonry walls and internal r.c. frames, is studied by means of non linear static (pushover) analyses. Several aspects, like the distribution of seismic action between masonry and r.c. elements, the local and global behavior of the structure, the crisis of the connections and the attainment of the ultimate strength of the whole structure are examined. The influence of some parameters, such as the masonry compressive and tensile strength, on the structural behavior is investigated. The numerical analyses are also repeated on a building in which the r.c. internal frames are replaced with masonry walls.