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Tese de doutoramento em Civil Engineering, Contemporary architecture encourages the use of glass in structural applications. Glass industry has developed the thermal toughening to increase its tensile strength and lamination to prevent brittle failure. However, glass can still fail unexpectedly due to the growth of surface flaws. Recent studies have focused on glass composite systems, mainly using steel as reinforcement. Other reinforcement materials (e.g. CFRP and Fe-SMA) and application techniques (e.g. prestressing) need also to be explored, given their promising features to face the growing structural challenges. This thesis aimed at covering two main topics related to structural glass: (i) post-cracking performance and (ii) mechanical post-tensioning. Its main objective was to evaluate the feasibility of using CFRP and Fe-SMA as reinforcement in flexure to obtain ductile failure modes, as well as the application of post-tensioning to reduce the unpredictability of the glass fracture strength. The experimental programs included (i) tensile tests on double-lap joints to assess the bond performance of glass-to- CFRP adhesive connections, (ii) flexural tests on small-scale monolithic glass beams with externally bonded CFRP or Fe-SMA reinforcements, and (iii) flexural tests on large-scale laminated glass beams with hybrid (EBR + NSM) strengthening. It was possible to obtain ductile failure modes when glass was strengthened with CFRP and Fe-SMA. The post-cracking performance was sensitive to the adhesive type, reinforcement material, strengthening system and, in the case of Fe-SMA reinforced glass, the activation temperature. Hybrid strengthening systems prevented premature debonding of the reinforcement and made better use of its tensile capacity. NSM-CFRP composite systems were safely prestressed and FRP peeling-off failure was avoided during load releasing. Considering the importance of design rules for practitioners, numerical modelling was carried out to assess (i) the efficiency of different constitutive models to simulate the non-linear behaviour of glass in tension and (ii) the influence of design parameters on the numerical response of glass composite systems. Further numerical simulations were performed to better understand the structural performance of CFRP reinforced glass elements, including at the level of the glass-to-CFRP adhesive joint. The results obtained were promising, and although additional studies are needed, new perspectives were opened for a future safer and widespread use of glass as a structural material., A arquitetura contemporânea tem encorajado a aplicação estrutural do vidro. A indústria do vidro desenvolveu os processos de têmpera, de modo a aumentar a sua resistência à tração, e de laminação, com o propósito de evitar roturas frágeis. O vidro pode, ainda assim, romper inesperadamente devido à propagação de defeitos superficiais. Recentemente, os sistemas compósitos de vidro têm sido estudados como uma alternativa para prevenir roturas inesperadas, usando principalmente aço. Outros tipos de reforço recentes (ex: CFRP e Fe-SMA) e técnicas de aplicação (por exemplo, protensão) apresentam também características promissoras. Esta tese aborda dois tópicos cruciais no contexto do vidro estrutural: (i) o comportamento pósfissuração e (ii) o pré-esforço mecânico. A obtenção de modos de rotura dúcteis por via do reforço com CFRP e Fe-SMA e a redução da imprevisibilidade da resistência à tração do vidro por via da aplicação de pré-esforço foram os principais objetivos deste estudo. Os programas experimentais incluíram (i) ensaios em juntas de sobreposição dupla para caracterizar o desempenho de ligações adesivas vidro-CFRP, (ii) ensaios de flexão em vigas de vidro monolítico de pequena dimensão, reforçadas externamente com CFRP e Fe-SMA, e (iii) ensaios de flexão em vigas de vidro laminado de grande dimensão com sistemas de reforço híbridos (EBR + NSM). Foi possível obter roturas dúcteis em elementos estruturais de vidro reforçados com CFRP e Fe-SMA. O desempenho pós-fissuração mostrou ser sensível ao tipo de adesivo, ao material de reforço, ao sistema de reforço e, no caso de vidro reforçado com Fe-SMA, à temperatura de ativação. Os sistemas de reforço híbridos mostraram bons resultados na prevenção do destacamento prematuro do reforço. Considerando a importância das regras de projeto para os sistemas em estudo, realizaram-se simulações numéricas para avaliar (i) a eficácia de diferentes modelos constitutivos para simular o comportamento não-linear do vidro e (ii) a influência de parâmetros de projeto na resposta numérica de sistemas compósitos de vidro. Posteriormente realizaram-se ainda simulações numéricas adicionais para aprofundar o conhecimento sobre o desempenho estrutural de elementos de vidro reforçados com CFRP, incluindo simulações ao nível das juntas adesivas entre vidro e CFRP. Os resultados obtidos foram promissores e, embora sejam necessários estudos adicionais, abriram-se novas perspetivas para que a aplicação estrutural do vidro seja mais segura e generalizada no futuro., This work was financially supported by the Portuguese Foundation for the Science and Technology (Fundação para a Ciência e a Tecnologia, FCT) under the grant number SFRH/BD/122428/2016, which is gratefully acknowledged.

Laminated Aluminum Composite Structure (LACS) has shown great potential for replacing traditional bulk aluminum parts, due to its ability to maintain low manufacturing costs and create complex geometries. In this study, a LACS, that consists of 20 aluminum layers joined by a structural tape adhesive, was fabricated and tested to understand its impact performance. Three impact tests were conducted: axial drop, normal and transverse three-point bending drop tests. Numerical simulations were performed to predict the peak loads and failure modes during impacts. Material models with failure properties were used to simulate the cohesive failure, interfacial failure, and aluminum fracture. Various failure modes were observed experimentally (large plastic deformation, axial buckling, local wrinkling, aluminum fracture and delamination) and captured by simulations. Cross-section size of the axial drop model was varied to understand the LACS buckling direction and force response. For three-point bending drop simulations, the mechanism causing the maximum plastic strain at various locations in the aluminum and adhesive layers was discussed. This study presents an insight to understand the axial and flexural responses under dynamic loading, and the failure modes in LACS. The developed simulation methodology can be used to predict the performance of LACS with more complex geometries.

An analytical solution has been developed developed in this research for electro-mechanical flexural response of smart laminated piezoelectric composite rectangular plates encompassing flexible-spring boundary conditions at two opposite edges. Flexible-spring boundary structure is introduced to the system by inclusion of rotational springs of adjustable stiffness which can vary depending on changes in the rotational fixity factor of the springs. To add to the case study complexity, the two other edges are kept free. Three advantages of employing the proposed analytical method include: (1) the electro-mechanical flexural coupling between the piezoelectric actuators and the plate’s rotational springs of adjustable stiffness is addressed; (2) there is no need for trial deformation and characteristic function—therefore, it has higher accuracy than conventional semi-inverse methods; (3) there is no restriction imposed to the position, type, and number of applied loads. The Linear Theory of Piezoelectricity and Classical Plate Theory are adopted to derive the exact elasticity equation. The higher-order Fourier integral and higher-order unit step function differential equations are combined to derive the analytical equations. The analytical results are validated against those obtained from Abaqus Finite Element (FE) package. The results comparison showed good agreement. The proposed smart plates can potentially be applied to real-life structural systems such as smart floors and bridges and the proposed analytical solution can be used to analyze the flexural deformation response.

This paper presents the bending and buckling analyses of simply supported nanowires using various classical and non-classical higher-order shear deformation theories (HSDTs). The one dimensional structure is modeled with including the surface effects based on the Gurtin–Murdoch surface elasticity theory (non-classical beam theory) and the small scale effect based on the Eringen nonlocal theory (nonlocal beam theory), the transverse displacement is divided into two bending and shear components. A system of governing equations is derived with the help of the minimum total potential energy principle and resolved via Navier’s solutions. Several numerical results are presented and compared with those given in the literature. The results showed that the influence of the surface effects on the bending and buckling load of nanowires is more than that of the nonlocal parameter., В статье представлен анализ поперечного и продольного изгиба свободно опертых нанопроволок в рамках классических и неклассических теорий сдвиговых деформаций высшего порядка. Одномерная структура моделируется с учетом эффектов поверхности на основе теории поверхностной упругости Gurtin–Murdoch (неклассическая теория балок) и масштабного фактора на основе нелокальной теории Eringen (нелокальная теория балок), при этом поперечное смещение делится на две компоненты изгиба и сдвига. На основе принципа минимума полной потенциальной энергии получены система определяющих уравнений и ее решение с помощью решений Навье. Проведено сравнение некоторых полученных результатов с литературными данными. Показано, что поверхностные эффекты оказывают большее влияние при поперечном и продольном изгибе нанопроволок по сравнению с влиянием нелокального параметра.

In this paper, the flexural response of extruded wrought aluminium girders is presented. This structural element is intended for usage in marine structures such as light docks, marinas and yacht ports. Ease of use, durability, reduced weight, manoeuvrability and the potential development of bespoke sections are appealing properties in such structures that are fulfilled satisfactorily by this type of aluminium elements. Both experimental and numerical analyses are presented. Experimentally, modules of the girders are tested with loading about both minor and major axes. Numerically, the tests are satisfactorily reproduced for the sake of validation and a subsequent exploitation of the model is addressed for further study of the structural response of the girders. A discussion of the results is presented with some design recommendations of these particular structural elements.

The purpose of the work was the study of the structural safety of R.C. beams subjected to corrosion processes though the derivation of moment-curvature diagrams and moment-to-shear interaction diagrams. Normal-strength reinforced concrete beams with longitudinal bars in the presence of transverse stirrups and subjected to corrosion processed are considered. Experimental results available in the literature related to corrosion processes, for steel bars, crack openings and bond degradation due to rust formation are reviewed. Then analytical laws relating to crack opening, bond degradation with attack penetration depth, through a rearranged form of Faraday’s law, are presented. An analytical model for cross-section analysis and shear strength prediction including the main effect due to rust formation is developed and verified against experimental data. Finally, a case study is added giving moment-curvature diagrams and moment-to-shear interaction diagrams to show the effects of different scenarios of natural corrosion increasing with time on beam elements.

Most of the composite materials that are used in aerospace structures have been manufactured using a thermostable matrix, as epoxy resin. The region of stability of these polymers is defined by the glass transition temperature (Tg). However, operating temperatures close and above the Tg can cause a variation in the properties of the polymer and consequently, modify the mechanical properties of the composite material. Therefore, it is necessary to understand the failure mechanisms that occur in the material in order to ensure stability and durability. The effect of temperature and time of exposure on the impact and flexural mechanical responses of carbon/epoxy composites are studied in this work. For that purpose, ageing treatments at temperatures below and above the Tg have been considered and then, impact and flexural tests have been performed. It was observed that thermal ageing cause two different effects: at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect, however, the mechanical properties decrease at higher temperatures of thermal ageing due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface.

This paper provides a tensile stress-strain (σ-ε) relationship for High-Strength Steel Fiber Reinforced Concrete (HSFRC). Load-deflection (P-δ) behavior of HSFRC beams tested under four-point flexural load were used with inverse analysis to calculate the tensile σ-ε relationship for various tested concrete grades (70 and 90MPa) containing 60 kg/m3 (0.76 %) of hook-end steel fibers. A first estimate of the tensile (σ-ε) relationship is obtained using RILEM TC 162-TDF and other methods available in literature, frequently used for determining tensile σ-ε relationship of Normal-Strength Concrete (NSC) Non-Linear Finite Element Analysis (NLFEA) package ABAQUS® is used to model the beam’s P-δ behavior. The results have shown that an element-size dependent tensile σ-ε relationship for HSFRC can be successfully generated and adopted for further analyses involving HSFRC structures., {"references":["Aldossari kMA. Behavior of High Strength Steel Fibers Reinforced Concrete Ground Slabs. Kingdom of Saudi Arabia: King Saud University, 2014.","Vandewalle L, Nemegeer D, Balazs L, Barr B, Barros J, Bartos P, et al. RILEM TC162-TDF: Test and Design Methods for Steel Fibre Reinforced Concrete: sigma-epsilon design method (final recommendation). Materials and Structures. 2003;36(262):560-7.","Barros JAO, Cunha VMCF, Ribeiro AF, Antunes JAB. Post-cracking behaviour of steel fibre reinforced concrete. Materials and Structures. 2005;38(1):47-56.","Kohoutkova, A., V. Kristek, and I. Broukalova, \"Material model of FRC-inverse analysis\" in Proc. 6th International RILEM Symposium, Italy, 2004, pp. 857–864.","Elsaigh W, Robberts J, Kearsley E, di Prisco M, Felicetti R, Plizzari G, \"Modeling non-linear behavior of steel fibre reinforced concrete\" in Proc. 6th International RILEM Symposium, Italy, 2004, pp. 837-846.","Tlemat H, Pilakoutas K, Neocleous K. Modelling of SFRC using inverse finite element analysis. Materials and Structures. 2006;39(2):221-33.","Labib WA. An experimental study and finite analysis of punching shear failure in steel fibre-reinforced concrete ground-suspended floor slabs: Liverpool John Moores University, 2008.","Hemmy O. Recommendations for finite element analysis of FRC–report of subtask 3.5. Brite-Euram project BRPR-CT98-0813: Test and Design Methods for Steel Fibre Reinforced Concrete, Project funded by the European Community under the Industrial and Materials Technologies Programme (Brite-Euram II). 2002.","Blazejowski M. Flexural Behaviour of Steel Fibre Reinforced Concrete Tunnel Linings. 2012.\n[10]\tSimulia D. ABAQUS 6.11 analysis user's manual. Abaqus. 2011;6:22.2.\n[11]\tKmiecik P, KamiŃSki M. Modelling of reinforced concrete structures and composite structures with concrete strength degradation taken into consideration. Archives of Civil and Mechanical Engineering. 2011;11(3):623-36.\n[12]\tJankowiak T, Lodygowski T. Identification of parameters of concrete damage plasticity constitutive model. 2013.\n[13]\tAnderson TL, Anderson T. Fracture mechanics: fundamentals and applications: CRC press, 2005."]}

In the present paper the experimental results relative to three-point bending tests on multilayer glass beams and on semi-rigid connections realised with stainless double web angles are presented and discussed. Small and medium size glass beams were tested and load–deflection curves and crack patterns at failure were recorded. The laminated glass specimens, of equal cross-section, were characterised by three different combinations of annealed float and fully thermally tempered glass plies and different interlayers. Steel joints constituted by double web angles to connect two glass beams were tested adopting several geometrical configurations and using stainless steel bolts preloaded with two different preloading values. The results obtained highlight the brittleness of glass beams with fail safe mechanism in the case of multilayer glasses with PVB. The joints tested were the semi-rigid type, which only make it possible to activate small percentages of the flexural capacity of beams. In all cases examined brittle failure in the glass beams was observed due to stress concentration near the hole, highlighting the importance of the choice of an adequate distance from the hole and the edges of the beams and of the study of an appropriate interface material for connections between glass panels and steel members in the case of both preloaded and non-preloaded bolts.

The response to fire of concrete structural members depends on the thermal, mechanical, and deformation properties of concrete. These properties vary significantly with temperature depending on the composition and characteristics of the concrete batch mix as well as heating rate and other environmental conditions. The paper presents the effects of a high temperature on selected physical properties of concrete. The main aim of the article is the evaluation of monitoring concrete properties loaded in a few thermal steps up to 1200 °C. Therefore, the concrete specimens were heated in a programmable laboratory furnace at a heating rate of 5 °C/min. The specimens were loaded at six temperatures, 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C, and 1200 °C maintained for 60 minutes. The acoustic emission activity and some material characteristics were evaluated in a three-point bending test.

This paper is focused on the vibration effects produced by an array of decentralised velocity feedback loops that are evenly distributed over a rectangular thin plate to minimise its flexural response. The velocity feedback loops are formed by collocated ideal velocity sensor and point force actuator pairs, which are unconditionally stable and produce ‘sky-hook’ damping on the plate. The study compares how the overall flexural vibration of the plate and the local absorption of vibration power by the feedback loops vary with the control gains. The analysis is carried out both considering a typical frequency-domain formulation based on kinetic energy and structural power physical quantities, which is normally used to study vibration and noise problems, and a time-domain formulation also based on kinetic energy and structural power, which is usually implemented to investigate control problems. The time-domain formulation shows to be much more computationally efficient and robust with reference to truncation errors. Thus it has been used to perform a parametric study to assess if, and under which conditions, the minimum of the kinetic energy and the maximum of the absorbed power cost functions match with reference to: (a) the number of feedback control loops, (b) the structural damping in the plate, (c) the mutual distance of a pair of control loops and (d) the mutual gains implemented in a pair of feedback loops.

In the present paper the compressive and flexural behavior of R.C. columns externally wrapped with FRP layers is examined. The investigation refers to a short compressed R.C. member having circular transverse cross-section and reinforced with longitudinal bars and transverse hoops or spirals. A first phase of the investigation was addressed to describing the constitutive laws of constituent materials (confined concrete core, steel bars in compression and in tension, FRP in tension). The second phase of the research was addressed to deriving the compressive and flexural responses in terms of load-axial shortening curves and momentaxial force interaction domain, to be compared with experimental data available in the literature.

Punching shear reinforcement is an efficient method to increase not only the strength but also the deformation capacity of flat slabs supported by columns. Especially, the increase in deformation capacity is desired so that the load can be distributed to other supports preventing a total collapse of the structure in the case of the occurrence of a local failure. Thus, the research presented herein addresses the punching strength as well as the deformation capacity of flat slabs. Thereby, the focus is set on the analysis of the maximum increase in strength and rotation capacity due to punching shear reinforcement. Therefore, the principal aim is the analysis of flat slabs with large amounts of punching shear reinforcement. In addition to an experimental and numerical investigation of flat slabs, another principal objective of the research project was the development of an analytical model that enables accurate predictions of the punching strength and the rotation capacity of flat slabs with large amounts of shear reinforcement. Thus, the research presented herein can basically be divided into three main parts. An experimental investigation of sixteen flat slab specimens with and without shear reinforcement leads to new findings with respect to the punching strength and the load-deformation response of flat slabs. The results of the tests serve for the validation of current design codes and the Critical Shear Crack Theory. In addition to the specimens tested within this research project, tests found in literature are used to investigate the influence of certain parameters on the prediction of the punching strength. A non-linear numerical model on the basis of the Finite Element Method enables the modeling of the test specimens. This approach uses plane stress fields to calculate the moment-curvature response of a discrete slab element. The thereby obtained flexural and torsional stiffness serve as input parameters for a linear-elastic finite element analysis. This analysis enables the modeling of the load-deformation response of the tested slab specimens leading to valuable information regarding the state of deformation at different load levels. The findings of the experimental and the numerical investigation support the development of an analytical model. The theoretical background of this model is the Critical Shear Crack Theory, which describes the punching strength as a function of the slab rotation. Thus, the developed analytical model enables the calculation of the load-rotation response of flat slab specimens. Moreover, the developed failure criteria enable the prediction of the punching strength as well as the maximum rotation capacity. Finally, it is shown that the results obtained from the developed model are in good agreement with results of tests performed within this research project and of tests found in literature.