Seismic behaviour of reinforced concrete bridges. Modelling, numerical analysis and experimental assessment.Miranda Guedes, J. (1997). PhD Thesis.

This work was developed within the Prenormative Research in support of the EuroCode 8 (PREC8) programme of the European Commission. EuroCode 8 (EC8) is the provisional European standards for the design of civil engineering structures in seismic prone areas. The programme included a series of Pseudo-dynamic tests on a set of Reinforced Concrete (R/C) bridges designed according to EC8. The Pseudo-dynamic method is based on a hybrid formulation that combines the numerical integration of the equations of motion of a structure and the experimental measurement of the corresponding restoring forces. Application to bridges can be made using substructuring techniques where the deck is simulated numerically and only the piers are physically tested in the laboratory.
This was the first Pseudo-dynamic testing campaign performed in the world using the substructuring technique on large scale structures.
Numerical tests using a fibre model were performed to predict the bridges response. These preliminary results allowed us not only to verify the ability of the model to predict the behaviour of these structures under cyclic loading, but also to establish the maximum forces provided by the control system in the laboratory. The need to improve the fibre model for the non-linear behaviour in shear derived from the comparison between the experimental response and the numerical results. A strut-and-tie formulation coupled with the classic fibre model was developed. This formulation is based on the analogy between an R/C structure damaged with diagonal cracking and a truss made of concrete diagonals and steel ties.
Subsequently, the numerical analyses were repeated using the new model and the results were compared with the experimental response. These new results were analysed and discussed in detail. In order to understand the irregularity issue, a new set of bridges with increasing degree of irregularity was designed and their numerical response was evaluated for seismic actions of growing intensity.

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Seismic assessment of the out-of-plane performance of traditional stone masonry walls.Costa, A.A. (2012). PhD Thesis.

The present Thesis focuses on the experimental characterization and numerical study of the out-of-plane behaviour of stone masonry walls for quasi-static and dynamic loads.
Several in-situ experiments on existing constructions were performed in order to characterize the quasi-static behaviour of unreinforced and strengthened specimens with techniques commonly used in pre/post-earthquake interventions. For this purposes, a new test setup to perform field tests within reasonable time interval and costs was developed and validated with an extensive tests campaign on damaged constructions after the 1998 Azores earthquake. The efficiency of different strengthening techniques was assessed and compared among them and simple analytical calculations proved to be efficient and conservative solutions when applied to force-based assessment of existing masonry walls.
The dynamic behaviour of masonry walls was also evaluated resorting to shaking table tests as well as numerical simulations. Shaking table tests performed at LNEC (Lisbon, Portugal) on full scale ne-storey sacco stone masonry facades were made especially devoted to the out-of-plane behaviour, where the selection of the input ground motions revealed to be decisive to trigger the overturning mechanism. The behaviour of the facades was found to be significantly influenced by the presence of the masonry multiple leaves, being the instability achieved by the overturning of the outer leaf and local masonry assemblages’ effects.
A novel proposal for simulating the dynamic response of local mechanisms was made resorting to multibody dynamics, where masonry portions (of a given local mechanism) are simulated through kinematic chains (rigid bodies) with concentrated nonlinearity at contact surfaces. The restitution coefficient, an important parameter to correctly describe the dynamic rocking behavior of rigid bodies, was determined by lab experimental tests of cantilever masonry walls for 2-sided rocking, where the dynamic properties of the wall are reproduced by an equivalent structure based on a proposed methodology named as Equivalent Block Approach (EBA).
Finally, the multibody dynamics approach was validated against two shaking table test results: the shaking table test presented herein and the test performed on a two-storey height double leaf stone masonry facade tested at EUCENTRE (Pavia, Italy). Promising results were obtained and some comments are included regarding static and dynamic analysis of local mechanisms resorting to simplified models. At the end, a proposal for seismic assessment of existing structure is made, where both the in-plane and out-of-plane behaviours are taken into account.

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Pavimentos de madeira em edifícios antigos. Diagnóstico e intervenção estrutural.Ilharco, T. (2008). Master Thesis.

The main goals of this work are to analyse timber floors, in particular from old buildings, describe the most common damages and present rehabilitation and strengthening procedures. Furthermore, it presents the results of in situ and laboratory tests made on a timber floor of an early XX century building. Most of the information gathered in this work resulted of the experience obtained on structural analysis performed under protocols established with public and private institutions and NCREP (Nucleus for the Conservation and Rehabilitation of Buildings and Built Heritage) of FEUP (Engineering Faculty of the Porto University). Although these collaborations and protocols were extended beyond the city of Porto, the analysed examples and the final case study report to buildings mainly localized in this city.
Pros and cons of the rehabilitation of old timber floors are discussed, in opposition to the option of their total demolition. Study cases of old buildings analysed by NCREP, with original timber floors performing its functions, are presented. The different structural elements of timber floors, their function and main characteristics are studied. The importance of the Analysis and Diagnosis phases, as fundamental assets for the support of rehabilitation/strengthening intervention, is focussed, and the verification method of timber floors recommended by Eurocode 5 is analysed. Rehabilitation and strengthening techniques of timber floors are described, associating its use to structural damages or specific needs, and a comparative analysis that allows the definition of its suitability for each situation is made.
Within the scope of an extensive campaign of tests performed in a timber floor of a Porto old building, the liability and compatibility of results obtained from different test methods of evaluation of physical and mechanical properties of wood are analysed. Both non destructive in situ tests (Resistograph, Pilodyn, Seismographs, load test) and laboratory destructive tests (in small specimens without defects and in natural size specimens) were applied. A finite elements model of the floor is made, in order to evaluate its liability for the prevision of the mechanical behavior of timber floors.
The presented work aims to define an evaluation and execution procedure for old timber floors, in order to provide simplified ways of supporting the intervention decision, namely with instruments that allow a simple and non intrusive evaluation. Since not only the façades are heritage, the presented work is able to show that a vast range of rehabilitation/strengthening solutions is nowadays available, therefore enabling a simple maintenance of the legacy that old timber floors represent.

Identificação mecânica e avaliação do comportamento sísmico de chaminés em alvenaria.Lopes, V. (2009). Master Thesis.

This work analyses the seismic behaviour of brick masonry chimneys. A case study of a chimney located near Porto city is presented after a brief historical characterization of these structures in Portugal, which were mainly constructed between the ending of the XIX century and the beginning of the XX century. The geometrical characterization of the chimney was done through laser scanning technology, and the mechanical assessment through in situ dynamic testing using ambient vibration and visual inspection. These results were used to calibrate two different numerical models built under this work. The dynamic testing characteristics and particulars are presented, as well as the signal processing procedures and the model calibration strategies. The consideration of different material characteristics in the numerical modelling, in agreement to the results of the visual inspection, is analysed and the numerical dynamic response of each model is compared to the experimental data.
The numerical simulation of the chimney seismic behaviour is then done following different strategies: considering or not different material zones in the chimney model, and considering for the masonry behaviour a linear elastic or a non-linear plastic law using a continuum damage model, both for tension and compression. The different premises found in the literature for the masonry behaviour, which provide the necessary information for the calibration of the non linear material model are presented and discussed. The main results obtained from each model are compared, focusing mainly on the importance of considering the material damage state and the non linear behaviour. Finally, a possible retrofitting solution is tested in order to evaluate its benefits to the chimney seismic behaviour.
The presented work aims to define procedures for the assessment of the damage state and the response of old masonry structures, involving, in particular, in situ dynamic testing using ambient vibration as a non destructive tool for the assessment of the mechanical properties of the masonry, and the use of non-linear numerical tools, supported by damage type behavior models, to analyse the numerical response of such structures under code actions.

Experimental testing of lateral capacity of masonry piers. An application to seismic assessment of AAC masonry buildings.Costa, A.A. (2007). Master Thesis.

The aim of this work was to develop and propose a new experimental test setup to evaluate the in-plane resistance of masonry panels, and also analyse the lateral resistance of autoclaved aerated concrete (AAC) walls through experimental tests and subsequent numerical simulations of buildings with the aim of provide some recommendations to design AAC masonry buildings.
In order to propose a new experimental test setup, a literature review is presented regarding different test setups which create different loading and boundary conditions. Based on these test setups and taking into account a desired boundary condition (fixed-ended) a new proposal and two alternatives is presented.
Moreover, and using an old test setup, the lateral resistance of AAC panels with different slenderness ratios and reinforcement is evaluated and, using these results, a new material model based on Gambarotta and Lagomarsino [1996] macro-element is calibrated. Hence, the dynamic response of AAC masonry buildings is presented using non-linear analyses, with an innovative algorithm called Seismic Adaptative Pushover (SDAP), the capacity response method and non-linear dynamic analyses.
In the end of this work some conclusions regarding the results obtained in the numerical simulations are commented, and some recommendations are presented regarding the design of new AAC masonry buildings subjected to seismic excitations.

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Diagnosis and strengthening of historical masonry structures: Numerical and experimental analyses.Silva, B. (2012). PhD Thesis.

The present Thesis focuses on the experimental characterization and numerical study of the out-of-plane behaviour of stone masonry walls for quasi-static and dynamic loads.
Several in-situ experiments on existing constructions were performed in order to characterize the quasi-static behaviour of unreinforced and strengthened specimens with techniques commonly used in pre/post-earthquake interventions. For this purposes, a new test setup to perform field tests within reasonable time interval and costs was developed and validated with an extensive tests campaign on damaged constructions after the 1998 Azores earthquake. The efficiency of different strengthening techniques was assessed and compared among them and simple analytical calculations proved to be efficient and conservative solutions when applied to force-based assessment of existing masonry walls.
The dynamic behaviour of masonry walls was also evaluated resorting to shaking table tests as well as numerical simulations. Shaking table tests performed at LNEC (Lisbon, Portugal) on full scale ne-storey sacco stone masonry facades were made especially devoted to the out-of-plane behaviour, where the selection of the input ground motions revealed to be decisive to trigger the overturning mechanism. The behaviour of the facades was found to be significantly influenced by the presence of the masonry multiple leaves, being the instability achieved by the overturning of the outer leaf and local masonry assemblages’ effects.
A novel proposal for simulating the dynamic response of local mechanisms was made resorting to multibody dynamics, where masonry portions (of a given local mechanism) are simulated through kinematic chains (rigid bodies) with concentrated nonlinearity at contact surfaces. The restitution coefficient, an important parameter to correctly describe the dynamic rocking behavior of rigid bodies, was determined by lab experimental tests of cantilever masonry walls for 2-sided rocking, where the dynamic properties of the wall are reproduced by an equivalent structure based on a proposed methodology named as Equivalent Block Approach (EBA).
Finally, the multibody dynamics approach was validated against two shaking table test results: the shaking table test presented herein and the test performed on a two-storey height double leaf stone masonry facade tested at EUCENTRE (Pavia, Italy). Promising results were obtained and some comments are included regarding static and dynamic analysis of local mechanisms resorting to simplified models. At the end, a proposal for seismic assessment of existing structure is made, where both the in-plane and out-of-plane behaviours are taken into account.

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Aplicação de um modelo de dano contínuo na modelação de estruturas de alvenaria de pedra. Igreja de Gondar - um caso de estudo.Silva, B. (2008). Master Thesis.

Stone masonry is one of the oldest constructive solutions still in use; it was used on a huge diversity of constructions (houses, temples, bridges…) that can be found all throughout Portugal, mainly on structures labelled as historical heritage. The analysis of stone masonry structures creates important challenges, due to the fact that this material is very heterogeneous, with unknown internal geometry and characterized by a big mechanical variability and uncertainty. Therefore, understanding how these structures behave is very important, especially under dynamic loads, in order to evaluate possible collapse mechanisms and damage progression along the structure.
In this work, it’s analysed the seismic behaviour of an ancient 17th century church, located in Gondar, in the north of Portugal. Consists on a tri dimensional finite element dynamic analysis using the program Cast3M (CEA, 1990) and considering two different modelling strategies in terms of geometrical complexity. It adopted two types of masonry material behaviour: (a) linear and (b) non linear. The non linear model adopted to simulate the stone masonry behaviour was a continuum damage model (Faria, 1994), initially developed for the analyse of large volumes concrete structures, like dams. The first step to assess the model applicability to such a heterogeneous and anisotropic material like stone masonry was a parametric sensitivity analysis. The model numerical adjustment was preformed based on the experimental tests results made on masonry walls at LESE and on experimental results available on the bibliography.
With this in mind an experimental study was preformed concerning the structural behaviour of stone masonry walls built at the Laboratory of Seismic and Structural Engineering (LESE) of the Faculty of Engineering of Porto University. The walls were tested under constant vertical load and cyclic horizontal loads applied on the top of the wall, in order to simulate the effects of a horizontal seismic type action. The experimental tests results and its analysis, besides allowing a better understanding of the walls structural cyclic behaviour, in particular the estimation of the energy dissipation, ductility capacity, strength and stiffness, it also represented an important contribution towards the definition of data for using in advanced numerical models, such as the continuum damage model adopted in this work.
The church was then analysed considering a rigid foundation and submitted to its self-weight and to artificial generated accelerograms based on a normalized response spectra EN 1998-1:2005 (CEN, 2005) and on the zoning proposed in the Document of National Application (DNA).
The results of the different seismic modelling strategies, namely the stress and the deformation state of the structural elements, the assessment of the structures seismic response and the identification the most vulnerable spots, were compared, allowing us to assess the differences and to give answers to questions such as: Is it really necessary to perform highly complex and time consuming non linear analysis, when studying this type of structures? Do they bring any advantages or additional important information to the study? What are the main differences?
Finally some seismic strengthening solutions applied at the top of the church walls and on the roof were analysed and its performance and efficiency were evaluated and compared.

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