This study aims to produce a type of concrete with both good thermal and mechanical properties by using environmentally friendly and low cost materials. In addition, the resistance of this concrete to fire conditions was investigated. The experimental work comprises two parts. In the first part, recycled glass was used as a partial replacement for natural sand (at proportions 20%, 40% and 60%) together with basalt fibre having different volume fractions (0.1%, 0.3%, and 0.5%). The results obtained from the experimental work showed that the optimum content is 20% glass and at 28 days, there was a 4.23% and 15% enhancement in the compressive strength and the splitting tensile strength respectively. Above 20% glass there was a slight reduction (6.6% and 22%) in the compressive strength and the splitting tensile strength when 60% glass was used. The results also showed that when glass sand and basalt fibre content increase, there is a decrease in the thermal conductivity range from 4.35% to 50% at temperature levels between 60oC to 600oC. The structural behaviour of this type of concrete was investigated in the second part of this study by carrying out small-scale slab tests at ambient and elevated temperatures. The results show that there is an increase in the load carrying capacity above the theoretical yield line load, due to membrane action, for all percentages of glass and volume fractions of basalt fibre ranging from 1.35 to 1.68 for the slab tested at ambient temperature and from 3.13 to 3.26 for the slabs tested at elevated temperature. Also the slabs with higher glass sand and basalt fibre content had a higher load enhancement and failed at a higher displacement compared to the control mix.A comparison between the simplified method and the finite element software package ABAQUS showed that the ABAQUS model gives reasonable predictions for the load-vertical displacement and the temperature-displacement relationships at both ambient and elevated temperature conditions, while the simplified method gives conservative predictions for the maximum allowable vertical displacement for the slab at elevated temperature. A parametric study showed that a 10 mm cover depth is the optimum depth as well as the reinforcement temperature predicted reduced with increasing load ratio (applied load/yield line load).

This thesis investigates, using finite element modelling and experimental investigation, the fracture of mesh reinforcement in composite floor slabs at elevated temperatures. The main objective of the research is the study of the bond strength between the welded mesh reinforcement and concrete at elevated temperatures, since this was found to be the principal behaviour that governs the fracture of the reinforcement in a composite floor slab.The experimental programme included steady state and transient pull-out tests carried out at temperatures varying from 20°C to 1000°C. However, unlike previous work, which concentrated on the bond of single bars, rectangular normal concrete prisms were constructed with one longitudinal bar, ensuring a bond length of 200 mm, and one transverse bar welded centrally. As a result, the influence of the weld of the mesh reinforcement in the bond strength between reinforcement and concrete was studied. The bond strength-slip-temperature relationship was obtained for various sized ribbed and plain bars. It was found that the 6, 7 and 8mm diameter ribbed mesh failed by fracture of the longitudinal bar at all temperatures, including ambient temperature. It was shown that the reduction of bond strength of ribbed mesh was similar to the reduction in strength of the bar, which together with the observed modes of failure, lead to the conclusion that ribbed mesh can be assumed to be fully bonded at all temperatures. The 10mm diameter ribbed mesh failed by splitting due to the cover-bar diameter ratio being small. In contrast, all the plain bars failed by fracture of the weld followed by pull-out of the bar. Therefore the correct bond stress-slip relationship should be modelled for smooth bars to accurately predict global structural behaviour.The investigation using finite element modelling utilizes the DIANA program. The incorporation by the author of the bond strength-slip-temperature relationship within the models permits a better prediction of fracture of the reinforcement in composite floor slabs. It has been shown that smooth bars are more beneficial since the bond is broken before fracture of the bar allowing strains to be distributed along the bar. In the case of ribbed bars the bond is such that localised strain will occur in the bar at crack locations leading quickly to fracture of the reinforcement.

Structural engineers and architects have a responsibility for incorporating fire safety into their building designs in order to minimize loss of life and property. To meet this requirement, extensive research has been carried out, aimed at obtaining better understanding of the performance of steel and composite structures under fire conditions. Recent research indicates that the robustness of steel connections is vitally important to the fire resistance of steel-framed composite buildings. The development of effective connection models is a key issue in this research field. This PhD research is focused on the development of robust connection elements, for modelling steel connections at elevated temperatures. In this work, a robust simplified two-node connection element has been developed, for modelling the behaviour of the bolted end-plate connections between steel beam and column at elevated temperatures. The proposed numerical procedure is based on the model proposed by Huang (2011), incorporating additional developments to more precisely determine the tension, compression, and bending moment capacities of end-plate connections in fire. The proper failure criteria are proposed to calculate the tension capacity for each individual bolt row. In this new model, the connection failure due to bending, axial tension, compression and shear are considered. The influence of the axial force of the connected beam on the connection is also taken into account. This new model has the advantages of both the simple and component-based models. A total of 22 tests are used to validate the model. From these validations, it is evident that this new connection model has ability to accurately predict the behaviour of the end-plate connection at elevated temperatures, and can be used to represent the end-plate connections in supporting performance-based fire resistance design of steel-framed composite buildings. For modelling the behaviour of partial end-plate connections between steel beams and columns under fire conditions, a simplified robust 2-node connection element has also been developed. The rotational response of a partial end-plate connection at elevated temperatures comprises of two stages. These stages are due to the shift of the compression centre of the connection from the end of end-plate, to the centre of the beam bottom flange at large rotation. The model proposed in this research accounts for these two stage behaviours, representing the partial end-plate iv connection as a 2-node non-linear spring element. Characteristics of the spring, such as stiffness, tension, compression, shear strengths and bending moment resistance, are determined based on a component-based approach. This model therefore retains the advantages of both the simple and component-based models. Compared to normal component-based models, this simplified model has very good numerical stability under static solver condition, and is computationally efficient. Fourteen tests are used to validate the model, showing that the model is capable of accurately predicting the behaviour of partial end-plate connections under fire conditions. A series of numerical studies has been conducted on a 2D steel frame, subjected to ISO834 Fire and Natural Fire, in order to investigate the influences of the connections on the behaviour of steel structures. It is clear that the model can be used to represent the partial end-plate connections in performance-based fire resistance design of steel-framed composite buildings. According to full-scale fire tests, tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into how vertical supports influence the tensile membrane actions of the slab. In this thesis, the performance of a generic three dimensional 45m x 45m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied, in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumed that the connections behave as pinned or rigid for simplicity, the two robust 2-node connection element models described above are used to model the semi-rigid behaviour of end-plate and partial end-plate connections within the fire compartment. The impact of connections on the 3D behaviour of composite floors is taken into consideration. The load-transfer mechanisms of a composite floor, when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed for enhancing the fire resistance of composite buildings.

A norma brasileira ABNT NBR 14323:2013 apresenta um método para o dimensionamento de lajes mistas de aço e concreto em situação de incêndio. No entanto, esse procedimento não inclui o efeito do comportamento de membrana da laje. Usando a teoria de placas para grandes deslocamentos, esta pesquisa estabelece que as altas temperaturas podem induzir uma considerável ação de membrana de tração, auxiliando na segurança da laje em situação de incêndio. No desenvolvimento de uma ferramenta para o dimensionamento a partir do método analítico de lajes mistas em situação de incêndio, uma série de estudos foi desenvolvida para a análise do comportamento de membrana de tração a altas temperaturas. O método analítico mais conhecido é o método de Bailey. Comparações entre os métodos de Bailey e da ABNT NBR 14323:2013, e análises empregando os programas Vulcan e MACS+ foram realizadas. Neste trabalho, compararam-se resultados empregando o método de Bailey e do programa de computador MACS+, que teve por base o próprio método de Bailey. Como esperado, os resultados foram similares. Ainda, neste trabalho, realizaram-se alguns estudos numéricos empregando o método dos elementos finitos, por meio do programa de computador Vulcan e compararam-se resultados entre o método de Bailey e Vulcan. Uma investigação sobre possíveis simplificações da formulação da ABNT NBR 14323:2013 também foi realizada. / The Brazilian standard ABNT NBR 14323:2013 presents a method for the composite slabs fire design. However, it doesnt include the effect of the slab behaving as a membrane. Using the theory of plates for large displacements, the research establishes that high temperatures can induce a considerable tensile membrane action, assisting in the safety of the slab in fire. In developing a tool for the analytical method composite slabs fire design, some studies were made to analyze the behavior of tensile membrane at high temperatures. The most popular analytical method is the Baileys method. In this study, analysis of the Baileys methods, the Brazilian standard and the Vulcan and MACS+ software were performed and the results were compared. As expected, the results were similar. Still, in this work, there have been some numerical studies employing the finite element method, using the computer program Vulcan, and results were compared between the Baileys method and Vulcan. An investigation about possible simplifications of the formulation presented by Brazilian standard were also developed.

A norma brasileira ABNT NBR 14323:2013 apresenta um método para o dimensionamento de lajes mistas de aço e concreto em situação de incêndio. No entanto, esse procedimento não inclui o efeito do comportamento de membrana da laje. Usando a teoria de placas para grandes deslocamentos, esta pesquisa estabelece que as altas temperaturas podem induzir uma considerável ação de membrana de tração, auxiliando na segurança da laje em situação de incêndio. No desenvolvimento de uma ferramenta para o dimensionamento a partir do método analítico de lajes mistas em situação de incêndio, uma série de estudos foi desenvolvida para a análise do comportamento de membrana de tração a altas temperaturas. O método analítico mais conhecido é o método de Bailey. Comparações entre os métodos de Bailey e da ABNT NBR 14323:2013, e análises empregando os programas Vulcan e MACS+ foram realizadas. Neste trabalho, compararam-se resultados empregando o método de Bailey e do programa de computador MACS+, que teve por base o próprio método de Bailey. Como esperado, os resultados foram similares. Ainda, neste trabalho, realizaram-se alguns estudos numéricos empregando o método dos elementos finitos, por meio do programa de computador Vulcan e compararam-se resultados entre o método de Bailey e Vulcan. Uma investigação sobre possíveis simplificações da formulação da ABNT NBR 14323:2013 também foi realizada. / The Brazilian standard ABNT NBR 14323:2013 presents a method for the composite slabs fire design. However, it doesnt include the effect of the slab behaving as a membrane. Using the theory of plates for large displacements, the research establishes that high temperatures can induce a considerable tensile membrane action, assisting in the safety of the slab in fire. In developing a tool for the analytical method composite slabs fire design, some studies were made to analyze the behavior of tensile membrane at high temperatures. The most popular analytical method is the Baileys method. In this study, analysis of the Baileys methods, the Brazilian standard and the Vulcan and MACS+ software were performed and the results were compared. As expected, the results were similar. Still, in this work, there have been some numerical studies employing the finite element method, using the computer program Vulcan, and results were compared between the Baileys method and Vulcan. An investigation about possible simplifications of the formulation presented by Brazilian standard were also developed.

En situation d’incendie, la dégradation des propriétés mécaniques des matériaux constitutifs d’une structure peut sensiblement en modifier le comportement global. Ainsi, lors d’essais au feu ou de sinistres réels, des flèches significatives sont observées sans ruine globale du plancher. Ceci traduit l’activation d’un mécanisme basé sur une borne supérieure de plasticité en grands déplacements et appelé effet membrane. Ainsi, malgré la perte des propriétés du béton, de l’acier d’armatures et de l’acier de construction des poutres connectées à une dalle en béton armé ou mixte acier-béton, la capacité portante de cette dalle se définit comme une fonction croissante de sa flèche. En pratique, le comportement complexe des planchers mixtes acier-béton peut être appréhendé par des modèles dits simplifiés ou avancés, suivant le niveau de précision souhaité. La méthode analytique FRACOF permet par exemple d’étudier un plancher global à température élevée, en se basant sur les modèles de comportement simplifiés des matériaux, acier et béton, définis dans les Eurocodes. Par cette méthode, la capacité portante d’une dalle peut alors être déterminée en tenant compte des profilés métalliques connectés à la dalle, et de l’activation d’un effet membrane en grands déplacements. Cette méthode analytique a été validée par une comparaison à des modèles éléments finis, ainsi qu’à des résultats d’essais au feu en grandeur nature. Elle est applicable à des profilés en acier laminé à chaud avec des portées pouvant atteindre 20 m. Or le franchissement de ces portées nécessite des sections de poutre à forte inertie, afin de limiter les flèches du plancher en service. Pour limiter la quantité d’acier que requerraient de telles poutres, le recours à des poutres cellulaires est une solution pratique et esthétique. Un modèle élément finis de poutres cellulaires en acier seul et mixtes est proposé dans le cadre de la thèse de doctorat. Le comportement thermo-mécanique des poutres cellulaires en acier seul est modélisé sous le code Cast3M. Les poutres mixtes sont modélisées en combinant un calcul de transfert thermique sous Cast3M et une analyse mécanique sous ANSYS. Les poutres en acier et la dalle en béton ou mixte sont représentées par des éléments de type coque. Les connecteurs sont représentés par des éléments de type poutre. Ce modèle tridimensionnel tient par ailleurs compte des non-linéarités matérielle et géométrique. Il est confronté à des résultats d’essais à températures normale et élevée. La validation du modèle est suivie d’une comparaison à une méthode analytique existante pour en vérifier la précision et le degré de conservatisme. Les poutres cellulaires sont ensuite étudiées en tant que partie intégrante de planchers mixtes acier-béton sous incendie. Un essai en grandeur nature sous feu réel met en évidence l’activation d’un effet membrane en présence de poutres cellulaires non-protégées, sans ruine du plancher. Les résultats de l’essai sont utilisés pour calibrer un modèle élément fini tridimensionnel. La calibration est effectuée en s’appuyant sur la distribution des températures dans les différents composants du plancher, la durée de résistance au feu, la forme des déformées et les modes de ruine. Ensuite, le modèle, qui peut reproduire le comportement thermo-mécanique d’un plancher mixte, est utilisé pour évaluer une proposition d’extension de la méthode FRACOF à des planchers mixtes comportant des poutres cellulaires. / In a fire situation, the decrease of the material properties of a structure can significantly modify its overall behaviour. Hence, during fire tests or real fires, very large deflections can be observed on a floor without any global collapse. This highlights the activation of a large-displacement plastic upper bound mechanism called membrane action. Thus, in spite of the property loss of concrete, reinforcement steel and constructional steel of the beams connected to a reinforced concrete or composite slab, the load bearing capacity of this slab is defined as an increasing function of its vertical deflection. In practice, the behaviour of composite steel and concrete floors can be assessed with simplified or advanced models, depending on the expected level of precision. For instance, the analytical method named FRACOF enables to study a whole floor at elevated temperatures, on the basis of the Eurocodes simplified models for the behaviour of steel and concrete. With this method, the load bearing capacity of a slab can then be estimated taking account of steel profiles connected to the slab and tensile membrane action in large displacements. This analytical method has been validated against finite elements models as well as results from full scale fire tests. It applies to hot-rolled steel profiles spanning up to 20 m. However, such spans require sections with a great moment of area to limit the floor deflection in serviceability state. In order to limit the amount of steel required, cellular beams can be utilized as a practical and aesthetical solution. A finite element model for steel and composite steel and concrete cellular beams is proposed in the scope of the PhD thesis. The thermo-mechanical behaviour of steel cellular beams is modelled under Cast3M code. Composite beams are modelled combining a heat transfer calculation under Cast3M to a mechanical analysis under ANSYS. The steel beams and the reinforced or composite slab are modelled with shell elements. The shear studs are modelled with beam elements. Besides, this 3D model takes into account both material and geometrical nonlinearities. It is compared with tests results at both normal and elevated temperatures. Once validated, the model is compared to an existing analytical method in order to check the precision and the level of conservatism of the latter. Then, cellular beams are studied as part of composite steel and concrete floors in a fire situation. A full-scale natural fire test puts into evidence tensile membrane action with unprotected cellular beams, without any overall collapse. The test results are used for calibrating a 3D finite element model. This calibration relies on the temperature distribution in the different parts of the floor components, the fire resistance degree, the deformed shape and the failure modes. The model, which can reproduce the thermo-mechanical behaviour of a composite floor, is then utilized for assessing an extension proposal of the FRACOF method to composite floors made of cellular beams.