Stefano Podestà

Identification of Shear Parameters of Masonry Panels Through the In-Situ Diagonal Compression Test

This article deals with the mechanical interpretation of the in-situ diagonal compression test on masonry panels, through a non-linear numerical modeling, and proposes a methodology for the evaluation of the tensile strength and the shear modulus of masonry. The results of a wide experimental campaign on 24 masonry panels in the region of Tuscany (Italy) are presented; the obtained material parameters are classified according to the masonry typology. A critical review of the frequently used methodologies for the interpretation of the diagonal compression test, regulated by ASTM and RILEM (ASTM E 519-02, 2002; RILEM TC-76 LUM, 1994), has been made, showing the inaccuracy and incompleteness of both. The aims of this research are to simulate the behavior of different masonry typologies and to give a numerical interpretation of the tests, in order to determine the tensile strength of the panel. This parameter is very important for the seismic safety check of masonry panels in existing buildings, according to many seismic codes.

Seismic Vulnerability of Ancient Churches: I. Damage Assessment and Emergency Planning

This paper describes a new methodology used to assess seismic damage in the churches of Umbria and the Marches, which is based on 18 indicators, each representative of a possible collapse mechanism for a macroelement. The subdivision of the church into macroelements consists of the identification of architectonic elements in which the seismic behavior is almost independent from the rest of the structure (façade, apse, dome, bell tower, etc.). For each macroelement, by considering its typology and connection to the rest of the church, it is possible to identify the damage modes and the collapse mechanisms. During inspection operations, the surveyors must indicate: (a) the actual macroelements; (b) the damage level; and (c) the vulnerability of the church to that mechanism, related to some specific details of construction. From these data a damage score is defined, which is a number from 0 to 1, obtained as a normalized mean of the damage grades in each mechanism. The analysis of the collected data (more than 1,000 churches in Umbria) allows the definition of the correlation between macroseismic intensity and damage.

Seismic Vulnerability of Ancient Churches: II. Statistical Analysis of Surveyed Data and Methods for Risk Analysis

In the context of a seismic prevention strategy, vulnerability analysis has the aim of acquiring knowledge of the buildings in a region, with particular reference to their predisposition to be damaged by an earthquake. The goal may be both at a territorial level, to assess the damage scenario expected after an earthquake of given intensity, and at a detailed level, as a support to the planning of seismic improvement interventions. The latter objective is very important for ancient churches, due to their architectural and historical value. They definitely need a more profound analysis. The survey with the new form proposed in Part I of this paper allows us to highlight the specific vulnerability with regard to the different collapse mechanisms that are typical of earthquakes, taking into account, if present, the damage due to historical events as an observed vulnerability.

Damage and Vulnerability Assessment of Churches after the 2002 Molise, Italy, Earthquake

The 2002 Molise, Italy, earthquake sequence shocked the Italian public because it killed school children, but it also highlighted the fact that seismic vulnerability of historic masonry buildings has increased because of reinforcement work that has been done in the last 50 years. Replacing the original wooden roof structure with new reinforced concrete or steel elements, inserting reinforced concrete tie-beams in the masonry and new reinforced concrete floors, and using reinforced concrete jacketing on the shear walls are all widely used interventions. However, they lead to increased seismic force (because of greater weight) and to deformations incompatible with the masonry walls. The authors present results of an extensive survey of damage resulting from recent Italian seismic events (with particular reference to the Molise earthquake). We evaluate the effectiveness and applicability of some retrofitting methods in the hope that these findings will be taken into account in technical codes.

Experimental evaluation of the in-plane stiffness of timber diaphragms

The seismic response of unreinforced masonry (URM) buildings, in both their as-built or retrofitted configuration, is strongly dependent on the characteristics of wooden floors and, in particular, on their in-plane stiffness and on the quality of wall-to-floor connections. As part of the development of alternative performance-based retrofit strategies for URM buildings, experimental research has been carried out by the authors at the University of Canterbury, in order to distinguish the different elements contributing to the whole diaphragms stiffness. The results have been compared to the ones predicted through the use of international guidelines in order to highlight shortcomings and qualities and to propose a simplified formulation for the evaluation of the stiffness properties.

Seismic vulnerability assessment at urban scale for two typical Swiss cities using Risk-UE methodology

This paper contains a seismic assessment at urban scale of the cities of Sion and Martigny in Switzerland. These two cities have been identified for the present research based on their importance regarding size and the characteristics of the building stock for which information was available. Moreover, microzonation investigations are available for both cities. This results in a more accurate characterization of local expected ground shaking, which is expressed through specific response spectra. Sion and Martigny represent, respectively, the capital and second largest city of the canton of Valais. This region is characterized by the highest seismicity within Switzerland. The paper focuses on the assessment using Risk-UE methodology, namely the empirical method LM1 and the mechanical method LM2. The obtained results are compared in order to assess the related accuracy. Firstly, buildings of the two cities were surveyed in order to collect main structural characteristics in a database. Building stock is typical of that region and can be found similar to many other medium-sized Swiss cities. Around half of the buildings are unreinforced masonry buildings, while several others are reinforced concrete buildings with shear walls. Results show the most vulnerable part of the cities regarding earthquake. There are significant differences in global results between LM1 and LM2 methods. The mechanical LM2 method is more pessimistic since it predicts damage grades of about one degree higher than LM1 method. However, the main drawback of the empirical LM1 method is that an a priori determination of an adequate value of the macroseismic intensity is required. Nevertheless, LM2 method may lead to a global overestimation of damage prediction.

The Relationship Between Damage and Peak Accelerations in Ripabottoni During the 2002 Molise, Italy, Earthquake

After the main shocks of the 2002 Molise, Italy, earthquake sequence, the University of Genoa Geophysical Section (Dip. Te. Ris) installed a temporary seismic network, composed of two velocimetric and two accelerometric stations, in the village of Ripabottoni (Campobasso Province), near the epicentral area. These stations were implemented in the regional network of seismic instruments installed after November 1 by geophysical institutes from Rome and Trieste, Italy. The network registered more than 2,000 aftershocks with magnitudes ranging from 1.0–4.0. A DISEG Group also participated in a survey coordinated by the Larino Emergency Operations Center to examine damaged churches. The preliminary data, which correlates the waveform of the available recordings from aftershocks with damaged masonry pillars, indicates that the damage may relate not only to the intrinsic vulnerability of this building type, but also to the high energy in the high frequency range observed in the vertical component of the earthquakes.

Simplified Mechanical Model for the Seismic Vulnerability Evaluation of Belfries

The systematic observation of damage caused by recent Italian earthquakes has highlighted the high seismic vulnerability of belfries, the inner part of bell towers. In this study, the authors propose a simplified methodology for safety checks of belfries that is usable for risk analysis at territorial level for the whole bell tower, according to the method proposed by the Italian Directive of October 12, 2007, Guidelines for the Evaluation and the Reduction of the Seismic Vulnerability of Cultural Heritage. The new mechanical method takes into account the possible activation of two different collapse mechanisms, connected to combined actions of compression and bending or shear action, supposing different static schemes in relation to the real belfry configuration. The seismic force at the base of the belfry is calculated also considering the influence of the second mode of vibration through a correction factor obtained by spectral analyses on several bell towers damaged by the 1976 Friuli earthquake. A validation of the proposed approach has been shown for two belfries damaged by the 2002 Molise earthquake and by the 2009 Abruzzi earthquakes, to highlight the reliability of the method in comparison to the simplified approach proposed in the literature.

Validation and improvement of Risk-UE LM2 capacity curves for URM buildings with stiff floors and RC shear walls buildings

This paper addresses seismic vulnerability assessment at an urban scale and more specifically the capacity curves involved for building damage prediction. Standard capacity curves are a function of predefined building typology and are proposed in the Risk-UE LM2 method for computation of the corresponding damage grades. However, these capacity curves have been mainly developed for building stock of southern European cities and the accuracy of their application with different building features, such as the ones of cities of northern Europe should be assessed. A recent research project of seismic scenarios for the cities of Sion and Martigny in Switzerland provided the opportunity to check the capacity curves of Risk-UE LM2 method. Within the framework of this project, a detailed analysis was achieved for more than 500 buildings. These buildings were typical Swiss buildings and were composed of both unreinforced masonry buildings with stiff floors and reinforced concrete buildings. The construction drawings of each building were collected in order to have the most accurate information about their main structural characteristics. The typological classification that has been adopted was developed in a recent research project. Based on the individual features of the buildings, individual capacity curves were defined. Results of the seismic assessment applied to the 500 buildings compare very well with those obtained by using Risk-UE LM2 method for unreinforced masonry buildings with stiff floors. A slight improvement may be proposed for buildings with three stories through their introduction to the category of low-rise instead of mid-rise buildings. By contrast, accuracy for reinforced concrete buildings with shear walls is very poor. Damage prediction using related capacity curves of Risk-UE LM2 method does not correspond to reality. Prediction is too pessimistic and moreover damage grades increase with the height category (low-rise, mid-rise and high-rise) of these buildings which is in contradiction with the observed damages for this type of buildings. Improvements are proposed to increase the accuracy of the seismic vulnerability assessment for northern European building stock. For unreinforced masonry buildings, a slight modification of the limits of the height category of buildings using the ones defined for RC buildings improves the damage prediction. For reinforced concrete buildings with shear walls improved capacity curves derived from the typological curves of the specific typology C are proposed.

The Post-Earthquake Reconstruction Process of Monumental Masonry Buildings: Suggestions from the Molise Event (Italy)

After the 2002 Molise earthquake in southern Italy, several issues related to seismic risk of a wide building stock (both cultural heritage and public facilities) were stressed. The Italian scientific community and the national and regional regulatory authorities — involved in this kind of research over the past 10 years — were quite responsive to this event. The need for new tools to deal with the complex regulatory, technical, and economic matters arose. This article addresses the reconstruction course of the Molise areas struck by the earthquake, with special interest in monumental buildings and in churches in particular. The decision and technical procedures, carried out to assess the seismic risk for historic structures, to ensure the correct funding distribution, and to prevent inadequate interventions (in relation to preservation criteria) are revised. Moreover, on the basis of a large amount of data related to churches, suggestions for the planning of the final stage of the reconstruction process (definitive seismic strengthening intervention design) are put forward: a quality check on the seismic upgrading designs proposed in the preliminary phase is provided. In particular, some closer examination and discussion is devoted to possible mechanical methods aiming to verify the vulnerability for out-of-plane mechanisms and effectiveness of the retrofitting interventions quantitatively.