Luigi Sorrentino

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.

Review of Out-of-Plane Seismic Assessment Techniques Applied To Existing Masonry Buildings

ABSTRACT Observations after strong earthquakes show that out-of-plane failure of unreinforced masonry elements probably constitutes the most serious life-safety hazard for this type of construction. Existing unreinforced masonry buildings tend to be more vulnerable than new buildings, not only because they have been designed to little or no seismic loading requirements, but also because connections among load-bearing walls and with horizontal structures are not always adequate. Consequently, several types of mechanisms can be activated due to separation from the rest of the construction. Even when connections are effective, out-of-plane failure can be induced by excessive vertical and/or horizontal slenderness of walls (length/thickness ratio). The awareness of such vulnerability has encouraged research in the field, which is summarized in this article. An outline of past research on force-based and displacement-based assessment is given and their translation into international codes is summarized. Strong and weak points of codified assessment procedures are presented through a comparison with parametric nonlinear dynamic analyses of three recurring out-of-plane mechanisms. The assessment strategies are marked by substantial scatter, which can be reduced through an energy-based assessment.

Methods and Approaches for Blind Test Predictions of Out-of-Plane Behavior of Masonry Walls: A Numerical Comparative Study

ABSTRACT Earthquakes cause severe damage to masonry structures due to inertial forces acting in the normal direction to the plane of the walls. The out-of-plane behavior of masonry walls is complex and depends on several parameters, such as material and geometric properties of walls, connections between structural elements, the characteristics of the input motions, among others. Different analytical methods and advanced numerical modeling are usually used for evaluating the out-of-plane behavior of masonry structures. Furthermore, different types of structural analysis can be adopted for this complex behavior, such as limit analysis, pushover, or nonlinear dynamic analysis. Aiming to evaluate the capabilities of different approaches to similar problems, blind predictions were made using different approaches. For this purpose, two idealized structures were tested on a shaking table and several experts on masonry structures were invited to present blind predictions on the response of the structures, aiming at evaluating the available tools for the out-of-plane assessment of masonry structures. This article presents the results of the blind test predictions and the comparison with the experimental results, namely in terms of formed collapsed mechanisms and control outputs (PGA or maximum displacements), taking into account the selected tools to perform the analysis.

Out-of-Plane Seismic Response of Unreinforced Masonry Walls: Conceptual Discussion, Research Needs, and Modeling Issues

ABSTRACT Modeling unreinforced masonry walls, subjected to seismic loads applied normal to their plane, has received much attention in the past. Yet, there is a general lack of conformance with regard to what aspects of seismic response a computational model should reflect. Boundary conditions are certainly an important aspect, as the response can involve two-way bending or just one-way bending and, in the second case, along vertical or horizontal directions. In this respect, flexural restraint of wall intersections can be significant in addition to size and placement of openings. Moreover, in-plane damage can modify the boundary conditions and the overall out-of-plane performance. Proper modeling of actions is also relevant, as they can be a result of distortions imposed upon wall elements and/or inertial forces along the span of a wall. Axial forces can markedly affect the out-of-plane response of the wall, particularly vertical compressive forces, which can enhance out-of-plane strength. The outcome of static verifications can be more conservative than that of dynamic analyses, but the latter are much more complex to carry out. These topics are discussed with reference to previous research, observations in the field and in the laboratory, as well as numerical analyses on three-dimensional models.

Identifying Seismic Local Collapse Mechanisms in Unreinforced Masonry Buildings through 3D Laser Scanning

The surveys following severe earthquakes show that existing unreinforced masonry buildings are highly vulnerable to local collapse mechanisms. However, their assessment is strongly sensitive to the choice of the mechanism, whose boundary conditions are largely unknown. In the past the mechanism has been selected based on the crack survey alone, because the survey of the deformations is very difficult if traditional tools are used. In the last years advanced survey techniques have been developed, the most powerful of whom resorts to laser scanning. A laser scanner allows the acquisitions of a very large amount of information: building overall dimensions and single elements detailed survey, detection of anomalies, and identification of very limited deformations undetectable with the naked eye. Moreover, contrary to traditional procedures, it allows the survey of the façades without any direct contact with the building, which could be damaged after an earthquake. A laser-scanner survey has been performed in the whole historical centre of Rovere, in the municipality of Rocca di Mezzo, affected by the 2009 L’Aquila earthquake. This survey has been used to study the façades of three different building units, recognising the collapse mechanism triggered by the earthquake ground motion. The mechanisms are fairly different from what suggested by the crack pattern alone and pertain to deformations that cannot be recognised in the photos. Moreover, the faithful geometric models that can be generated from laser scanning allow accounting for deformations and out-of-plumb. Thus, the acceleration activating the mechanism can be estimated much more accurately compared to a perfectly vertical and parallelepiped wall.

Vulnerability Assessment of Unreinforced Masonry Churches Following the 2010–2011 Canterbury Earthquake Sequence

The 2010–2011 Canterbury, New Zealand earthquake sequence caused extensive damage to unreinforced masonry churches. A sample of 80 affected buildings was analysed and their performance statistically interpreted. Structural behaviour is described in terms of mechanisms affecting the so-called macro-elements, and damage probability matrices are computed. Regression models correlating mean damage level against macroseismic intensity are also developed for all observed mechanisms, improving the initial simple-linear formulations through use of multiple-linear regressions accounting for vulnerability modifiers, whose influence is evaluated via statistical procedures. Results presented herein will support the future development of predictive tools for decision-makers, also contributing to seismic vulnerability mitigation at a territorial scale.

Seismic Risk Assessment of New Zealand Unreinforced Masonry Churches using Statistical Procedures

ABSTRACT The 2010–2011 Canterbury earthquake sequence provided extensive evidence of the significant seismic vulnerability of New Zealand unreinforced masonry (URM) churches. Given the high seismicity of the country, the exposure of human lives and the societal significance of ecclesiastic buildings, for both historical and religious reasons, the reduction in seismic vulnerability of this building type is of primary importance. By analyzing the seismic performance of a sample of 80 affected buildings, regression models correlating mean damage levels against ground-motion parameters were developed for observed collapse mechanisms, accounting for vulnerability modifiers whose influence was estimated via statistical procedures. Considering the homogeneity of New Zealand URM churches, the vulnerability models developed for the Canterbury region were extended to the whole country inventory, and a synthetic index was proposed to summarise damage related to several mechanisms. Territorial scale assessment of the seismic vulnerability of churches can assist emergency management efforts and facilitate the identification of priorities for more in-depth analysis of individual buildings. After proper calibration, the proposed approach can be applied to other countries with similar building heritage.

Simulation Of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (II): Combined Finite-Discrete Elements

ABSTRACT Out-of-plane response of unreinforced masonry elements is frequently the most critical aspect of the seismic performance of existing masonry buildings. The response of such elements is usually governed by equilibrium rather than strength. Hence, it is customary to resort to rigid-body models, accounting for possible rotations, and/or sliding. However, the results of such analyses depend on the initial choice of the mechanism. In this article, the shaking-table experiments on a brick-masonry specimen, and on a stone-masonry specimen have been modeled by resorting to a combined finite-discrete element strategy. Despite the coarse discretization of both discrete and finite elements, the three-dimensional models are able to capture the experimentally observed multi-degree-of-freedom mechanisms, without any a priori assumption on the mechanism. A sensitivity analysis is carried out, addressing eight different parameters. The identification of the mechanism is sufficiently robust, but the assessment of its activation and failure is best done by combining the finite-discrete element model with a simplified model of the recognised mechanism.

Simplified survey form of unreinforced masonry buildings calibrated on data from the 2009 L’Aquila earthquake

The 2009 L’Aquila earthquake in southern Italy affected a rather large number of buildings, which experienced macroseismic intensities between V and IX on the Mercalli–Cancani–Sieberg scale. Almost sixty thousand unreinforced masonry constructions were officially inspected and almost half of them ended up losing their usability status temporarily, partially or completely, where the term usability refers to the suitability of a building for habitation or occupancy after a seismic event. A fairly detailed damage and usability form was compiled thanks to the work of a large number of volunteers. However, when pre-event surveys are carried out, data collection needs to be confined to the most relevant information in order to save time and manpower. The main aim of this article is, thus, the definition of a simplified form for pre-earthquake territorial-scale surveys of buildings, one containing fewer usability parameters and categories than the form compiled after the earthquake in L’Aquila. Analysis shows similar usability for buildings with more than two storeys above ground, those with construction timespans after 1962, and structural types with a specific combination of vertical and horizontal structures. Therefore, a simplified tool is recommended, one with just three categories for number of storeys instead of the thirteen in the current form, five construction timespan categories instead of eight, four structural classes instead of the current thirty. Other parameters, such as the presence of isolated columns or of mixed structures, have been removed altogether.