Sergio Lagomarsino

Forecast models for damping and vibration periods of buildings

Abstract The buildings dynamic parameters (vibration periods, damping) are examined in three sequential phases: (a) the study of physical-theoretical aspects and of the existing forecast models; (b) the collection of a broad experimental data base; (c) the definition of new simple forecast models. The bending and torsion periods are, with a good approximation, related to the height of the building. The damping resuting from low intensity vibrations follows Rayleighs law; growth of the damping due to the increase of vibration amplitude depends on the structural material. The confidence intervals are supplied to all proposed models with the scope of defining cautionary criteria for application in the codes.

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.

PERPETUATE guidelines for seismic performance-based assessment of cultural heritage masonry structures

Ancient monumental masonry buildings are complex structures that were not based on an engineered design, underwent many transformations during their life and often present lack of connections among the structural elements. Earthquakes are the main cause of damage for ancient masonry structures and, in order to reduce their vulnerability with compatible and light interventions, it is necessary to have accurate models for the seismic analysis, able to simulate the nonlinear behavior of masonry, and a well defined performance-based assessment procedure, aimed to guarantee the acceptable level of risk for the occupants and for the conservation of the monument itself. The paper outlines the guidelines that were developed within the PERPETUATE European research project. The wide variety of architectural assets is classified and the related proper modeling strategies are identified; moreover, immovable artistic assets are considered in the assessment. A displacement-based approach is adopted, because these structures crack even for low intensity earthquakes and can survive severe ones only if they have a sufficient displacement capacity. Safety and conservation requirements are proposed by considering distinct sets of performance levels, related to use and safety of people, conservation of the building and of the artistic assets that might be present. Some indications on the seismic hazard assessment are provided, considering the distinctive features of some types of ancient structures. Within the fundamental knowledge phase, sensitivity analysis is proposed in order to address and optimize the in-situ investigation and to define proper confidence factors, aimed to consider epistemic and statistical uncertainties. Different modeling approaches and methods of analysis are considered, depending on the characteristics of the structure; both static pushover and incremental dynamic nonlinear analyses are considered. Related verification procedures are defined to evaluate the seismic intensity measure, and the corresponding return period, which is compatible with each performance level that must be fulfilled.

Seismic assessment of rocking masonry structures

The seismic assessment of rocking masonry structures is a complex task, due to the high sensitivity of the behavior to the characteristics of the input motion. The paper compares the results offered by different models and the reliability of widely used intensity measures. A displacement-based approach based on an incremental limit analysis of rigid blocks is proposed for the performance-based assessment of rocking masonry structures, such as: rocky structures (archeological remains, obelisks, columns, trilithons), arch-piers systems (e.g. triumphal arches, belfries), out-of-plane mechanisms of walls (standing out walls, façades in buildings or churches etc.) or artistic assets prone to overturn (pinnacles, statues etc.). The method is compatible with the format of the PERPETUATE performance-based assessment method for cultural heritage assets

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 assessment of churches after L’Aquila earthquake (2009)

L’Aquila earthquake, which occurred on April 6, 2009, proved the high vulnerability of cultural heritage, with particular reference to churches. Damage assessment in the emergency was carried out on more than 700 churches with a methodology aimed at recognizing the collapse mechanisms in the different architectonic elements of the church. The method was developed after the earthquake in Umbria and the Marches (1997) and has been widely used in the last decade; this approach is also very useful for seismic prevention, as it allows one to single out the most vulnerable structures. Some examples are presented in this paper, representative of recurrent damage in the main elements of the church: the façade, the roof, the apse and the belfry. It emerges that, for a correct interpretation of damage and vulnerability, it is necessary a deep knowledge of local construction techniques and of the historic transformation sequence. Moreover, the bad behaviour of churches strengthened by modern techniques, such as the substitution of original timber roofs with stiff and heavy r.c. slabs, was observed. Starting from the observation of some case studies, the paper achieves some worth results, which may be useful for correctly driving future strengthening interventions.

The Assessment of Damage Limitation State in the Seismic Analysis of Monumental Buildings

The structural safety evaluation of monumental and historical buildings in seismic prone areas requires the availability of appropriate verification tools, in order to ensure both a realistic estimation and the feasibility of the method. In the case of historical masonry structures, such as palaces or churches, local damage mechanisms often take place (e.g., out-of-plane overturning). A procedure to assess the seismic vulnerability of these mechanisms, focusing on the damage limitation state, is developed through equilibrium limit analysis. Moreover, the possibility of enriching the formulation, including constructive and technological aspects, which may modify structural response, is shown.

Damage assessment of fortresses after the 2012 Emilia earthquake (Italy)

The medieval fortresses are a very common and distinctive type among the Emilian historical constructions and the earthquake of May 20 and 29, 2012 highlighted their high vulnerability. Starting from the analysis of the geometrical and constructive features, the interpretation of their seismic vulnerability has been based on an accurate damage assessment and supported by the numerical results of typical configurations. An abacus of recurring seismic damage mechanisms in fortresses has been proposed: it in particular concerns the towers and their interaction with the fortress perimeter walls. Moreover, the seismic response of the most important fortresses in the epicentral area has been described referring to their historical notes, the recent interventions and their influence on the seismic damage.

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.