The developed research was structured into five progressive stages, corresponding to the main scientific activities:
- Characterisation of the risk areas and main housing typologies;
- Experimental characterization (in situ);
- Numerical modelling and parametric studies;
- Identification and description of the most efficient seismic resistant reinforcement solutions;
- Recommendations for the awareness and strengthening of Local Seismic Culture.
a. Characterization of the risk areas and main housing typologies
It constitutes mainly in the definition of the areas of study, according to the seismic hazard. This activity was undertaken throughout survey missions and preliminary analysis. This task assumed the analysis of the state of the art of Local Seismic Culture, and its adaptation to Portugal actual context, which was still an unexplored research field. The def inition of the areas and their limits were executed under two premises: 1-According to the intensity and frequency of the register earthquakes, the impact of these events on the building environment, and the level of the community preparedness to the occurrence; 2-The implementation of Survey Missions to understand and to confirm the actual state of conservation and authenticity of in-use Vernacular Architecture. This was accomplished by the analyses of a uniform sample and the inclusion of isolated case studies with documental evidence for the extrapolation of solutions. The task was developed with the study of six specific regions, plus Lisbon downtown, which the preliminary analyses highlighted as striking reference for the Portuguese community.
Lisbon was assumed as an isolated reference, given the significance that the 1755’s earthquake had on Portugal and the world. There is much information published on that earthquake, both from written accounts of that time, immediately following the earthquake, and all throughout the 20th century. After considering the information regarding the 6 proposed sites, the team developed a comprehensive understanding of the vernacular housing typologies, through the characterisation of their morphological and construction components, with special focus on prevention and reactive solutions.
This 1st phase of the research, coordinated by ESG, consituted the first technical report of the Seismic-V Project.
b. Experimental characterisation, to study the materials and their application through benchmarking in paradigmatic cases
Vernacular buildings are often complex structures, both in terms of structural behaviour, and the mechanical properties of their components and materials. Moreover, usually, specific provisions for seismic demands are not present in this type of construction. However, recent earthquakes all over the world show that, in many cases, vernacular constructions may show an adequate seismic performance. Therefore, the identification and understanding of construction solutions and the detailing that may enhance their seismic performance should be analysed, and such solutions should be studied for eventual application to existing structures (traditional masonry, rammed earth or adobe constructions), so as to reduce their vulnerability to earthquakes.
A comprehensive study of the geometry, structural solutions and constituent materials of vernacular buildings was fundamental to study how these parameters can influence their seismic performance, as well as to determine the more adequate repair and/or retrofitting solutions. Excessively intrusive assessment techniques should be avoided, in order to prevent these constructions from losing their “vernacular value”.
In this task, existing vernacular buildings were selected as case-studies, analysing different situations in terms of construction materials (adobe, masonry, and timber), structural solutions (type of connections between wall-floor, wall-roof, etc.), building conf igurations and dimensions. The selection of the case studies considered the location and period of construction. In this way, the case studies would be representative of the existing vernacular construction in different regions of Portugal. Non-destructive tests were performed in situ, on the structures selected, aiming particularly at their dynamic properties characterisation. To this end, natural frequencies were measured, and modal shapes were identified.
The collected data was analysed and comparisons were established between the results obtained for the different case-studies, leading to the conclusions on the influence of the type of construction material, and the structural solutions adopted, in the dynamic behaviour of the structures. In particular, the results analysis allowed preliminary conclusions about the construction solutions in vernacular constructions that may improve their seismic performance. The results obtained within this task also contributed to a better definition and understating of the structural fragilities of the case studies assessed. Moreover, the results provided valuable information for the calibration of the numerical models and parametric studies, which were, subsequently, developed within Task 3. This task was coordinated by the University of Aveiro research team, under the supervision of Professor Humberto Varum. More detailed information is available in the second technical report
c. Numerical modelling and parametric studies
As aforementioned, the project focuses on the use of vernacular architecture and its behaviour response in earthquake events. Different constructive systems are envisaged, namely buildings of the following building techniques, fired brick, adobe and stone masonry, wattle-and-daub and rammed earth. Besides, an important goal of the project is the design of retrofitting solutions for vernacular architecture buildings, in order for their mechanical behaviour to be improved under seismic actions, taking into account the particularities of each constructive system.
The sound understanding of the seismic behaviour (resisting and ductility features), regarding vernacular architecture buildings, and the proposal of retrofitting solutions should be backed by numerical modelling. Moreover, numerical modelling based on nonlinear static numerical analysis of ancient masonry buildings represents a step forward in the technical and scientific knowledge, as few results are available in literature. In this task, it is planned to use finite element modelling (FEM) for the global seismic analysis (walls, floors, spandrels, connections), by following the common macro-modelling approach, and considering masonry as an isotropic and homogeneous media. The mechanical nonlinear behaviour of masonry was based on advanced plastic constitutive models. The numerical simulation intends to: (1) calibrate the numerical models based on the in situ experimental testing (task 2); (2) understand, in a more thorough way, the resisting mechanisms of the different structural elements of the masonry buildings under seismic loading; (3) assess the influence of distinct factors on the seismic behaviour of masonry buildings, based on a parametric study; (4) evaluate distinct retrofitting techniques of ancient masonry buildings.
The calibration of the numerical model was possible by comparing the numerical results with the experimental results attained in Task 2, in terms of stress and strain fields, crack patterns, and nonlinear force-displacement diagrams. The numerical models were based on nonlinear static (pushover) analysis. In relation to pushover analysis, alongside with the conventional procedures in terms of applied loads (proportional to mass, and proportional to the first mode), it was also intended to follow a more advanced procedure, based on an adaptive procedure, taking into account the damage progress on the shape of the first mode of vibration. After the completion of calibration of numerical model, it was possible to carry out parametric analysis, aiming at identifying the influence of possible parameters on the seismic response masonry buildings.
Distinct parameters were considered in the parametric analysis, namely: (1) distinct loading conditions; (2) distinct geometric configurations (plan and side views, and variation of the openings size); (3) modelling of the proposed retrofitting techniques, and comparative analysis on the seismic performance of each one. The results obtained in this task were essentialforTask5,whereretrofittingguidelinesforancient vernacular masonry buildings were provided. The main output of this task included: (1) experimental assessment of the global seismic behaviour of old masonry buildings; (2) valuation of the main parameters influencing the seismic response; (3) assessment of the seismic performance of distinct retrofitting techniques. Given the large expertise in the numerical analysis of masonry structures, the task was led by ISISE (UMinho), under supervision of Professors Paulo B. Lourenço and Graça Vasconcelos. More detailed information is available in the third technical report
d. Identification and description of the most efficient seismic resistant reinforcement solutions
An important part of the research was dedicated to the description of the most efficient seismic-resistant strengthening solutions, as well as the most frequent faults and errors found in implemented solutions. Since Vernacular Architecture is based on empiric knowledge transference, sometimes the origin of the solution is lost, and its principles are perverted along the generations. According to Task 2 and Task 3 it was possible to identify and to confirm, which solution presented a satisfactory improvement in the resistance of the construction, which were incipient, or even which of them were deceivingly harmful to the Seismic resistance of the buildings.
This task was of an overall importance for the building culture of the considered sites, as the gap between master builders and current repair professionals is huge, and sometimes impossible to fill in. First of all, there was a dissection between the preventive or reactive seismic retrofitting nature of each selected solution. To achieve this, it was essential understanding the cause that originated the solution, the real effect of it and, most of all, the expected result.
Considering the characterisation method, the solutions were systemised by sort of reinforcement, and then classified under the respective construction system. This would be more assertive in terms of material characterisation, and before constructive techniques comparison. This task furnished the possibility to classify the observed solution, under determined and specific typologies (timber wall trusses, halfburied floors, vaulted ceilings, counter arches, buttresses, Tie-rods, etc.), foundation grim systems, or even to recognise original ones (regarding the Vernacular Architecture flexibility to adapt to very particular contexts). There was an attempt to correspond solution types to the identified risk areas, addressed in the VSC Atlas.
e. Recommendations for the awareness and strengthening of Local Seismic Culture
The final task consisted in the Systematisation of all the collected and produced data, concerning the analysed solutions. It also provided findings, emerging from buildings performance under earthquakes, and based on simulation variables, in order to reinforce solutions for in-use vernacular architecture, regarding the seismic resistant features.