Angelo Garofano

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.

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.

Seismic Assessment of a Historical Masonry Building in Switzerland: The “Ancien Hôpital De Sion”

ABSTRACT This article presents the results of the evaluation of the seismic safety of the Ancien Hôpital de Sion, an important Swiss architectural heritage building, situated in the Canton of Valais, the region with the highest seismic hazard in Switzerland. Three-dimensional Applied Element (AEM) modeling of the whole structure has been performed and validated. The adopted modeling strategy, together with nonlinear dynamic analysis, was able to represent the actual behavior and failure mechanisms typical of complex masonry structures, in addition to a good computational efficiency compared to other available numerical approaches. The local collapse mechanisms have been also studied through a kinematic limit analysis based on rigid block rotation. Both linear and nonlinear approaches have been followed together with the capacity spectrum method. The results provided by the different methodologies have been compared with the aim to provide possible insights concerning a general procedure for the assessment of the safety of such type of structures.

Evaluating seismic retrofitting efficiency through ambient vibration tests and analytical models

Economic and environmental imperatives lead to an ever growing need to extend the service life of the existing building stock without putting the users at risk. In zones prone to moderate seismic hazard, many buildings were built without considering seismic actions. The design and assessment of efficient seismic retrofitting rely on physical models of the buildings. However, model errors resulting from simplifications and other assumptions might lead to a biased and thus unreliable diagnosis. Therefore, structural measurements are interpreted to reduce the uncertainty related to the ambiguous task of inferring the real structural response of existing buildings, even in the linear elastic range. This contribution includes the assessment of the retrofitting of an existing masonry building through ambient vibration field measurements. Measured frequencies and mode shapes are interpreted using an error-domain model-falsification framework that allows explicit representation of uncertainties related to modelling and measurement errors. A simple continuous Timoshenko cantilever beam, characterizing the linear elastic dynamic response of the building, is used to model the building. It is concluded that such interpretation of ambient vibration data is useful to assess the efficiency of seismic retrofitting.

EVALUATION OF THE SEISMIC VULNERABILITY OF THE “ANCIEN HÔPITAL DE SION” USING APPLIED ELEMENT MODELLING (AEM) AND LOCAL MECHANISM ANALYSIS

The evaluation of the seismic vulnerability of monumental buildings is a difficult task and presents significantly higher level of complexity if compared to the case of new or current existing structures. This is due to the inherent uncertainty characterizing ancient buildings, regarding structural characteristics and constructive techniques, material properties, damages due to past actions, which should be properly handled in their seismic assessment. For this reason, the approach to the study of such buildings unavoidably involves the completion of different assessment methods and their comparison, in order to represent the characteristics of a complex structure, its local and global behaviour. This paper describes the first results of the evaluation of the seismic safety of the “Ancien Hôpital de Sion”, an important building belonging to the Swiss architectural heritage, sited in the Canton of Valais, the region with the highest seismic hazard in Switzerland. For the analysis of the building, three-dimensional Applied Element (AEM) modelling of the whole structure has been achieved and validated. The proposed modelling strategy, together with non-linear dynamic analysis, has been adopted on the basis of its capability to represent the actual behaviour and failure mechanisms of complex masonry structures, in addition to a good computational efficiency compared to other available numerical approaches. The local seismic collapse mechanisms have been also analysed through a kinematic limit analysis based on rigid block rotation. Both linear and non-linear approaches have been followed together with the capacity spectrum method. The results provided by the different methodologies have been compared with the aim to provide possible insights concerning a general procedure for the assessment of the safety of such type of structures.

In-plane behaviour of earthen materials: a numerical comparison between adobe masonry, rammed earth and cob

The paper presents a comparison between different numerical modelling ap-proaches aiming to simulate the in-plain behaviour of three types of earthen materials, name-ly adobe masonry, rammed earth and cob. For this purpose, uniaxial and diagonal compression tests were carried out, which allowed determining important mechanical param-eters, such as compressive strength, Young’s modulus, Poisson’s ratio, shear strength and shear modulus. Furthermore, the tests allowed assessing the level of non-linear behaviour of the respective stress–strain relationships as well as the failure modes. The experimental results were then used for the calibration of numerical models (based on the finite element method) for simulating the non-linear behaviour of the earth materials under in-plane shear loading. Both macro- and micro-modelling approaches were considered for this purpose. The procedures adopted for model calibration established the reliability of various modelling strategies for the different loading conditions. The simplified approach based on macro-modelling shows a satisfactory accuracy and low computational costs. The results reproduc-ing the uniaxial compression are in good correspondence with the post-elastic behaviour ob-served in the experimental campaign. The micro-modelling approach adopted to reproduce the shear behaviour, even with higher computational cost, represents a suitable tool to pre-dict the adobe masonry and rammed earth collapse mechanisms