Jelena Milosevic

Fragility curves for old masonry building types in Lisbon

AbstractImproving the seismic resistance of traditional buildings is essential for preserving cultural heritage and increasing their safety. This is especially important for old masonry buildings in Lisbon (“Pombalino”, “Gaioleiro” and “Placa”), which are still used for housing and services. Taking this into account, this paper is focused on the seismic assessment of these three types of buildings. The buildings were modelled based on the equivalent frame model approach, their dynamic characteristics were determined and non-linear static (pushover) analyses were performed. Furthermore, for the seismic demand of Lisbon, the seismic performance of such building classes was defined and compared. Finally, with the aim of supporting seismic risk and loss estimation studies, a probabilistic assessment was carried out and the fragility curves for each building type derived.

Seismic vulnerability assessment of a mixed masonry–RC building aggregate by linear and nonlinear analyses

From the beginning of the twentieth century, and due to the rapid increase of reinforced concrete (RC) usage, mixed masonry–RC buildings have emerged. In Lisbon, Portugal, old mixed masonry–RC buildings appeared between 1920 and 1960, representing the transition period between masonry and proper RC. These buildings are often integrated in blocks, and frequently share the side-walls, implying, thus, the need to assess the seismic vulnerability of building aggregates. The present paper approaches the seismic vulnerability assessment of a specific type of old mixed masonry–RC buildings in Lisbon. The study comprises the analysis of a building, both as an isolated structure and inserted in its aggregate, using two approaches: (1) linear dynamic analysis with SAP2000 and (2) nonlinear static analysis by means of 3Muri/Tremuri software. A comparison of both approaches derives a good matching between the obtained results. However, a nonlinear analysis is required to identify, in an adequate manner, the critical areas of the structure requiring strengthening.

Nonlinear Parametric Static Analysis of Rubble Stone Masonry Walls in Lisbon

Unreinforced masonry construction is predominant in many urban areas world-wide. Many of these constructions are vulnerable to earthquakes, which are the main cause of damage and loss of cultural heritage. Thus, seismic assessment should be provided in a reliable way by using proper mechanical parameters and an appropriate modeling approach. This paper focus on the numerical study of the in-plane behavior of rubble stone masonry walls with air lime mortar, which is a typical material for old masonry buildings in Lisbon. The first part of the paper is focused on the performance on nonlinear numerical static analysis in order to calibrate the static cyclic experimental tests carried out within the scope of a research project. In the second part, the calibrated models were used to carry out parametric analysis varying the geometrical parameter in terms of ratio h/l and axial load. The modelling approach was executed using software based on the finite element method, DIANA. This parametric assessment is a starting point for further analysis for the entire building with the aim to evaluate efficiently the influence of some input parameters. Regarding the obtained results, the good match between experimental and numerical results was obtained in terms of strength and ductility capacity, as well as in terms of stiffness and failure mode. Results obtained for parametric analysis are presented and discussed.

Seismic Behavior of Lisbon Mixed Masonry-RC Buildings With Historical Value: A Contribution for the Practical Assessment

The fact that linear analysis is still the most used procedure in the design engineering offices, studies which addresses issues associated to the estimation of the structural behavior factor values are relevant. In this study, the behavior factor of a particular type of mixed masonry-reinforced concrete buildings in Lisbon is estimated. The typology chosen in this study represents 30% of building stock in Lisbon; these buildings were built between 1930-60 and thus were designed without considering the seismic-design requirements proposed in current codes. The evaluation of the behavior factors was based on the use of nonlinear static analyses, performed in the form of the sensitivity analysis and following the criteria proposed in the current seismic codes and literature. In the scope of the sensitivity analysis, aleatory and epistemic uncertainties have been considered in terms of the mechanical parameters and structural details, respectively with the aim to take into account different characteristics of the structures. In order to derive the most reliable values of the behavior factor for this typology, extensive research in terms of the historical information, structural characterization and definition of the mechanical parameters has been performed. The study indicates that the final values of behavior factor are low and depend most on the type of connections between structural walls. Although the obtained values of the behavior factor for this typology match well with the ones proposed in most recent seismic codes, it is recommended that the assessment of such factor of a specific class for a particular structural type building should always be careful evaluated.

Seismic Assessment of Pombalino Buildings

Portuguese Pombalino masonry buildings were built mainly in Lisbon after the 1755s Lisbon Earthquake. These buildings are characterized by a mixed timber-masonry structure, known as the gaiola pombalina (cage), and were built aiming to withstand the horizontal seismic loads. The cage is composed of timber floors and improved mixed timber-masonry shear walls (“frontal” walls). It was arguably the first case in history of an entire town built with the purpose of providing seismic resistance to its buildings. In this paper, a description of the Pombalino buildings is presented, GIS mapping tool was developed to identify the main features of Pombalino buildings in Lisbon downtown area and the results of the seismic assessment of existing building are briefly discussed. A three-dimensional model was developed in Tremuri program based on the equivalent frame model approach. The building was modelled using non-linear beams for masonry panels. The “frontal” walls were modelled by a macro-element model developed and calibrated according to an experimental campaign. The seismic assessment of the global response of the building was determined through non-linear static (pushover) analyses. Due to the fact that building does not fulfil the safety requirements for the ultimate limit state, a strengthening solution was proposed in order to improve the seismic behavior of the building.