Browsing by Author "Costa, Alexandre A."
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- Advantages of structural inspection and diagnosis for traditional buildings’ refurbishment: A Life Cycle Assessment perspectivePublication . Silva, Renata; Surra, Elena; Quelhas, Bruno; Costa, Alexandre A.; Lapa, Nuno; Delerue-Matos, CristinaThis work demonstrated, through Life Cycle Assessment (LCA), the environmental advantages brought by the application of the Structural Inspection and Diagnosis (SID) methodology to the structural refurbishment of 7 traditional buildings located in the city of Porto (Portugal), when compared to the common total demolition and reconstruction approach. The early diagnosis of the conservation state of the existing structural elements, and their characterization provides fundamental information for optimizing the design of the refurbishment towards environmental sustainability. SID approach can reduce by 75.3%, on average, the demolished material and provide the lowest environmental burdens in the environmental categories of Global Warming, Acidification, Eutrophication, Ozone, and Abiotic Depletion, Photochemical Ozone Creation potential, Human Toxicity as well as Energy Demand when compared with the total demolition and reconstruction scenarios. In terms of relative environmental impact for the reconstruction scenarios, it was concluded that reinforced concrete, in the form of lightweight and solid slabs, presents the worst performance due to the concrete production process. Furthermore, timber structures show better environmental performance when compared to the use of glued laminated timber. The establishment of the SID tool as a consolidated methodology can be a unique opportunity to systematically include, in the refurbishment of traditional buildings, the principles of the environmental sustainability required by EU policies in the construction sector, providing a significant reduction of demolition wastes and the maximization of the preservation of existing structural materials.
- Analysis of the Out-Of-Plane Seismic Behavior of Unreinforced Masonry: A Literature ReviewPublication . Ferreira, Tiago Miguel; Costa, Alexandre A.; Costa, AníbalAlthough the issue of the out-of-plane response of unreinforced masonry structures under earthquake excitation is well known with consensus among the research community, this issue is simultaneously one of the more complex and most neglected areas on the seismic assessment of existing buildings. Nonetheless, its characterization should be found on the solid knowledge of the phenomenon and on the complete understanding of methodologies currently used to describe it. Based on this assumption, this article presents a general framework on the issue of the out-of-plane performance of unreinforced masonry structures, beginning with a brief introduction to the topic, followed by a compact state of art in which the principal methodologies proposed to assess the out-of-plane behavior of unreinforced masonry structures are presented. Different analytical approaches are presented, namely force and displacement-based, complemented with the presentation of existing numerical tools for the purpose presented above. Moreover, the most relevant experimental campaigns carried out in order to reproduce the phenomenon are reviewed and briefly discussed.
- Efficiency of strengthening techniques assessed for existing masonry buildingsPublication . Diz, Sérgio; Costa, Aníbal; Costa, Alexandre A.The Azores archipelago is a zone with a vast cultural heritage, presenting a building stock mainly constructed in traditional stone masonry. It is known that this type of construction exhibits poor behaviour under seismic excitations; however it is extensively used in seismic prone areas, such as this case. The 9th of July of 1998 earthquake was the last seismic event in the islands, leaving many traditional stone constructions severely damaged or totally destroyed. This scenario led to an effort by the local government of improving the seismic resistance of these constructions, with the application of several reinforcement techniques. This work aims to study some of the most used reinforcement schemes after the 1998 earthquake, and to assess their effectiveness in the mitigation of the construction’s seismic vulnerability. A brief evaluation of the cost versus benefit of these retrofitting techniques is also made, seeking to identify those that are most suitable for each building typology. Thus, it was sought to analyze the case of real structures with different geometrical and physical characteristics, by establishing a comparison between the seismic performance of reinforced and non-reinforced structures. The first section contains the analysis of a total of six reinforcement scenarios for each building chosen. Using the recorded 1998 earthquake accelerograms, a linear time-history analysis was performed for each reinforcement scenario. A comparison was then established between the maximum displacements, inter-storey drift and maximum stress obtained, in order to evaluate the global seismic response of each reinforced structure. In the second part of the work, the examination of the performance obtained in the previous section, in relation to the cost of implementing each reinforcement technique, allowed to draw conclusions concerning the viability of implementing each reinforcement method, based on the book value of the buildings in study.
- Experimental characterization of the out-of-plane performance of regular stone masonry walls, including test setups and axial load influencePublication . Ferreira, Tiago Miguel; Costa, Alexandre A.; Arêde, António; Gomes, Ana; Costa, AníbalStone masonry is one of the oldest and most worldwide used building techniques. Nevertheless, the structural response of masonry structures is complex and the effective knowledge about their mechanical behaviour is still limited. This fact is particularly notorious when dealing with the description of their out-of-plane behaviour under horizontal loadings, as is the case of the earthquake action. In this context, this paper describes an experimental program, conducted in laboratory environment, aiming at characterizing the out-of-plane behaviour of traditional unreinforced stone masonry walls. In the scope of this campaign, six full-scale sacco stone masonry specimens were fully characterised regarding their most important mechanic, geometric and dynamic features and were tested resorting to two different loading techniques under three distinct vertical pre-compression states; three of the specimens were subjected to an out-of-plane surface load by means of a system of airbags and the remaining were subjected to an out-of-plane horizontal line-load at the top. From the experiments it was possible to observe that both test setups were able to globally mobilize the out-of-plane response of the walls, which presented substantial displacement capacity, with ratios of ultimate displacement to the wall thickness ranging between 26 and 45 %, as well as good energy dissipation capacity. Finally, very interesting results were also obtained from a simple analytical model used herein to compute a set of experimental-based ratios, namely between the maximum stability displacement and the wall thickness for which a mean value of about 60 % was found.
- In situ Out-of-Plane Cyclic Testing of Original and Strengthened Traditional Stone Masonry Walls Using AirbagsPublication . Ferreira, Tiago Miguel; Costa, Alexandre A.; Arêde, António; Varum, Humberto; Costa, AníbalThis article presents a field experimental campaign carried out on an existing one-story stone masonry building, aiming at characterizing the out-of-plane behavior of its walls. A bidirectional test set-up based on a self-equilibrated airbag system was developed and used on three similarmasonry walls under distinct conditions: original, retrofitted, and strengthened. The results obtained and the main advantages and shortcomings found in the test set-up are discussed. Finally, some of the most popular retrofitting and/or strengthening techniques applied during the 1998 Azores reconstruction process are critically analyzed, aiming at suggesting quantifications for future interventions on existing unreinforced masonry buildings.
- Methods and Challenges on the Out-Of-Plane Assessment of Existing Masonry BuildingsPublication . Lourenço, Paulo B.; Mendes, Nuno; Costa, Alexandre A.; Campos-Costa, AlfredoHistoric masonry buildings were built for many centuries taking into account mostly vertical static loads according to the experience of the builder, usually, without much seismic concern. The seismic behavior of ancient masonry buildings is particularly difficult to characterize and depends on several factors, namely the materials properties, geometry of the structure, connections between structural and non-structural elements, stiffness of the horizontal diaphragms, and building condition. However, the different masonry types present common features that lead to high seismic vulnerability of these buildings, such as high specific mass, low tensile strength, low to moderate shear strength, and low to moderate ductility.
- A simplified four-branch model for the analytical study of the out-of-plane performance of regular stone URM wallsPublication . Ferreira, Tiago Miguel; Costa, Alexandre A.; Vicente, Romeu; Varum, HumbertoDuring the last years, several studies have been made aiming to assess the out-of-plane seismic response of unreinforced stone masonry structures. This fact led to the development of a wide variety of models and approaches, ranging from simple kinematic based analytical models up to complex numerical simulations. Nevertheless, for the sake of simplicity, the out-of-plane seismic response of a masonry wall pier may be obtained by means of a simple single-degree-of-freedom system while still providing good results. In fact, despite the assumptions associated with such a simple formulation, it is also true that the epistemic uncertainty inherent with the selection of appropriate input parameters in more complex models may render them truly ineffective. In this framework, this paper focuses on the study of the out-of-plane bending of unreinforced stone masonry walls (cantilevers) by proposing a simplified analytical approach based on the construction of a linearized four-branch model, which is used to characterize the linear and nonlinear response of such structural elements through an overturning moment-rotation relationship. The formulation of the four-branch model is presented and described in detail and the meaningful parameters used for its construction are obtained from a set of experimental laboratory tests performed on six full-scale unreinforced regular sacco stone masonry specimens. Moreover, a parametric analysis aiming to evaluate the effect of these parameters’ variation on the final configuration of the model is presented and critically discussed. Finally, the results obtained from the application of the developed four-branch model on real unreinforced regular sacco stone masonry walls are thoroughly analysed and the main conclusions obtained from its application are summarized.
- Simulation of masonry out-of-plane failure modes by multi-body dynamicsPublication . Costa, Alexandre A.; Penna, Andrea; Arêde, António; Costa, AníbalThe seismic assessment of the local failure modes in existing masonry buildings is currently based on the identification of the so-called local mechanisms, often associated with the out-of-plane wall behavior, whose stability is evaluated by static force-based approaches and, more recently, by some displacement-based proposals. Local mechanisms consist of kinematic chains of masonry portions, often regarded as rigid bodies, with geometric nonlinearity and concentrated nonlinearity in predefined contact regions (unilateral no-tension behavior, possible sliding with friction). In this work, the dynamic behavior of local mechanisms is simulated through multi-body dynamics, to obtain the nonlinear response with efficient time history analyses that directly take into account the characteristics of the ground motion. The amplification/filtering effects of the structure are considered within the input motion. The proposed approach is validated with experimental results of two full-scale shaking-table tests on stone masonry buildings: a sacco-stone masonry façade tested at Laboratório Nacional de Engenharia Civil and a two-storey double-leaf masonry building tested at European Centre for Training and Research in Earthquake Engineering (EUCENTRE).