After the accidents occurred during the first decade of this millennium, such as the World Trade ... more After the accidents occurred during the first decade of this millennium, such as the World Trade Center (2001), London (2005) and Madrid (2004), special attention was given to the study of robust structures subjected to different accidental loads. The World Trade Center attack highlighted troublesome weakness in connections, which exhibited poor performance caused by brittle failure. Structural details played a very significant behavioural role when the structure is subjected to impulsive loads [1]. Concerning the behaviour of steel joint, the literature presents several studies on steel connections under both static and cyclic loads [2, 3]; many results of these studies have contributed for improving the current standards, such as the Eurocode 3, part 1-8 [4]. However, only scarce information exists concerning the behaviour of these joints directly loaded by higher loading rates [5]. This paper is devoted to the report of an experimental programme on steel joints under impact loadi...
The purpose of this study is to address a way of predicting the ductility capacity of steel joint... more The purpose of this study is to address a way of predicting the ductility capacity of steel joints. Recent research studies show that a joints’ ability to perform under elevated deformations, without fracturing, is a key factor in enabling mechanisms preventing collapse to be developed, and thus, improve the overall robustness of steel framed structures. This theme is becoming rather timely as building owners and insurers try to assess the collapse risk of their buildings, and the probability of a wide spread collapse if subjected to extreme events, either due to natural or terrorist causes. However, regarding this matter, current design code guidelines are limited to a prescriptive approach, by recommending a nominal tying force to be met, or quantifying a force that reproduces accidental scenarios, such as an impact of a vehicle, ships or helicopters, which do not address the overall behavior and performance of the structure.
Abstract The accuracy of structural fire design of cold-formed steel structures depends on the av... more Abstract The accuracy of structural fire design of cold-formed steel structures depends on the available predictive models regarding mechanical and thermal properties. The deterioration of mechanical properties, such as yield strength and modulus of elasticity, and the evolution of thermal properties, such as thermal conductivity, thermal elongation and specific heat, with temperature is a key issue in the assessment of the performance of cold-formed steel structural elements in fire. An experimental campaign was undertaken to determine both mechanical and thermal properties of the S280GD+Z steel used in cold-formed steel building construction industry. Tensile coupon tests were carried out to determine the mechanical properties of the S280 GD+Z steel with 2.5 mm thickness at temperatures ranging from 20 to 800 °C. Thermal properties were assessed using the Transient Plane Source (TPS) equipment. Test results were compared with current design standards and with the ones available in the literature. The proposed predictive equations based on the Ramberg–Osgood model show very good agreement with the experimental results for temperatures beyond 300 °C. It was found that some predictive models presented in the EN 1993-1-2:2005 regarding mechanical and thermal properties should be improved. Hence new proposals are presented for both thermal and mechanical properties. Also a modified stress–strain model based on the EN 1993-1-2:2005 formulation is proposed for the S280GD+Z steel.
Steel beam behaviour in standard and natural fires : Comparison of FE modelling and hand calculat... more Steel beam behaviour in standard and natural fires : Comparison of FE modelling and hand calculation procedures
In order to address the complex loading condition of steel joints in fire, and based on the exper... more In order to address the complex loading condition of steel joints in fire, and based on the experimental fire tests on steel frames with different joint typologies, performed at the University of Coimbra (Santiago et al. 2008), a detailed three-dimensional model was developed and calibrated to simulate the behaviour of welded and bolted end plate beam-to-column joints. The structural frame is modeled combining 3D shell, solid and joint elements, thereby taking into account the effect of the local failure modes, and the realistic behaviour of the frame exposed to a natural fire. The numerical model accounts for the initial geometrical imperfections, non-linear temperature gradient, geometrical and material nonlinearity and temperature dependent material properties. The results show the performance of each individual structural joint component under heating and cooling conditions and identify the main dependencies of the geometrical and mechanical variables of the components on the joint behaviour. The global behaviour of the frame and the joint failure modes are compared and discussed with the experimental observations.
Abstract Nanotechnology is a growing field of application by the use of particles at the nanoscal... more Abstract Nanotechnology is a growing field of application by the use of particles at the nanoscale. The application of extremely small particles based on identical grain-size particles can result in materials with enhanced properties. Studies have been carried out on cement-based materials and showed their advantages regarding their rheological, mechanical and durability characteristics. This paper presents a collection of the state-of-the-art on the recent progress of using different nanoparticles in cementitious materials both for structural purposes and for fire protection construction materials succinctly. Therefore, the findings of the current state of knowledge on this topic are summarised and discussed. Limitations and recommendations are also underlined for future research. Based on recent research works it is clear that the strength level, porosity, mix composition and type, water content, specimen geometry, nano size scale, nanoparticle type, nanoparticle content, the combination of nanoparticles and material age take a crucial role in the physical properties of cementitious materials modified with nanoparticles. It is recommended that different sizes of nanoparticles should be used in such materials as well as polypropylene fibres when subjected to high temperatures. The content of nanoparticles in such materials should be also lower for fire applications than for only ambient temperature purposes. Additionally, there is still an absence of knowledge and comprehension of the response of such materials under high temperatures, which highlights the urgent need for further research into this topic.
After the accidents occurred during the first decade of this millennium, such as the World Trade ... more After the accidents occurred during the first decade of this millennium, such as the World Trade Center (2001), London (2005) and Madrid (2004), special attention was given to the study of robust structures subjected to different accidental loads. The World Trade Center attack highlighted troublesome weakness in connections, which exhibited poor performance caused by brittle failure. Structural details played a very significant behavioural role when the structure is subjected to impulsive loads [1]. Concerning the behaviour of steel joint, the literature presents several studies on steel connections under both static and cyclic loads [2, 3]; many results of these studies have contributed for improving the current standards, such as the Eurocode 3, part 1-8 [4]. However, only scarce information exists concerning the behaviour of these joints directly loaded by higher loading rates [5]. This paper is devoted to the report of an experimental programme on steel joints under impact loadi...
The purpose of this study is to address a way of predicting the ductility capacity of steel joint... more The purpose of this study is to address a way of predicting the ductility capacity of steel joints. Recent research studies show that a joints’ ability to perform under elevated deformations, without fracturing, is a key factor in enabling mechanisms preventing collapse to be developed, and thus, improve the overall robustness of steel framed structures. This theme is becoming rather timely as building owners and insurers try to assess the collapse risk of their buildings, and the probability of a wide spread collapse if subjected to extreme events, either due to natural or terrorist causes. However, regarding this matter, current design code guidelines are limited to a prescriptive approach, by recommending a nominal tying force to be met, or quantifying a force that reproduces accidental scenarios, such as an impact of a vehicle, ships or helicopters, which do not address the overall behavior and performance of the structure.
Abstract The accuracy of structural fire design of cold-formed steel structures depends on the av... more Abstract The accuracy of structural fire design of cold-formed steel structures depends on the available predictive models regarding mechanical and thermal properties. The deterioration of mechanical properties, such as yield strength and modulus of elasticity, and the evolution of thermal properties, such as thermal conductivity, thermal elongation and specific heat, with temperature is a key issue in the assessment of the performance of cold-formed steel structural elements in fire. An experimental campaign was undertaken to determine both mechanical and thermal properties of the S280GD+Z steel used in cold-formed steel building construction industry. Tensile coupon tests were carried out to determine the mechanical properties of the S280 GD+Z steel with 2.5 mm thickness at temperatures ranging from 20 to 800 °C. Thermal properties were assessed using the Transient Plane Source (TPS) equipment. Test results were compared with current design standards and with the ones available in the literature. The proposed predictive equations based on the Ramberg–Osgood model show very good agreement with the experimental results for temperatures beyond 300 °C. It was found that some predictive models presented in the EN 1993-1-2:2005 regarding mechanical and thermal properties should be improved. Hence new proposals are presented for both thermal and mechanical properties. Also a modified stress–strain model based on the EN 1993-1-2:2005 formulation is proposed for the S280GD+Z steel.
Steel beam behaviour in standard and natural fires : Comparison of FE modelling and hand calculat... more Steel beam behaviour in standard and natural fires : Comparison of FE modelling and hand calculation procedures
In order to address the complex loading condition of steel joints in fire, and based on the exper... more In order to address the complex loading condition of steel joints in fire, and based on the experimental fire tests on steel frames with different joint typologies, performed at the University of Coimbra (Santiago et al. 2008), a detailed three-dimensional model was developed and calibrated to simulate the behaviour of welded and bolted end plate beam-to-column joints. The structural frame is modeled combining 3D shell, solid and joint elements, thereby taking into account the effect of the local failure modes, and the realistic behaviour of the frame exposed to a natural fire. The numerical model accounts for the initial geometrical imperfections, non-linear temperature gradient, geometrical and material nonlinearity and temperature dependent material properties. The results show the performance of each individual structural joint component under heating and cooling conditions and identify the main dependencies of the geometrical and mechanical variables of the components on the joint behaviour. The global behaviour of the frame and the joint failure modes are compared and discussed with the experimental observations.
Abstract Nanotechnology is a growing field of application by the use of particles at the nanoscal... more Abstract Nanotechnology is a growing field of application by the use of particles at the nanoscale. The application of extremely small particles based on identical grain-size particles can result in materials with enhanced properties. Studies have been carried out on cement-based materials and showed their advantages regarding their rheological, mechanical and durability characteristics. This paper presents a collection of the state-of-the-art on the recent progress of using different nanoparticles in cementitious materials both for structural purposes and for fire protection construction materials succinctly. Therefore, the findings of the current state of knowledge on this topic are summarised and discussed. Limitations and recommendations are also underlined for future research. Based on recent research works it is clear that the strength level, porosity, mix composition and type, water content, specimen geometry, nano size scale, nanoparticle type, nanoparticle content, the combination of nanoparticles and material age take a crucial role in the physical properties of cementitious materials modified with nanoparticles. It is recommended that different sizes of nanoparticles should be used in such materials as well as polypropylene fibres when subjected to high temperatures. The content of nanoparticles in such materials should be also lower for fire applications than for only ambient temperature purposes. Additionally, there is still an absence of knowledge and comprehension of the response of such materials under high temperatures, which highlights the urgent need for further research into this topic.
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