For the connection of segments in tubular steel towers, some recently published literature promot... more For the connection of segments in tubular steel towers, some recently published literature promotes the use of friction connections as shown in Fig. 1 instead of the common flange connections [1]. Such friction connections consist of normal clearance holes with preinstalled bolts in one segment and long open slotted holes in the other segment. To facilitate assembly, the two segments differ in diameter. This allows for a certain deformability of the connection. The resistance of such a friction connection can simply follow the design rules of the European Standard EN1993-1-8 for friction connections with pretensioned bolts [2]. To investigate the behavior of the so called “fingers”, as which the steel plates between the long open slotted holes are designated, the following tests are going to be conducted: Two quadratic hollow sections of steel grade S355 will be connected with long open friction connections with 6 M24 bolts of grade 10.9 on two of their four sides, varying in distan...
Beam-to-column joints play an important role in the overall seismic behavior of steel frame struc... more Beam-to-column joints play an important role in the overall seismic behavior of steel frame structures, since the deformations in the panel zone of the beam-to-column joint region significantly affects the seismic behavior of steel joints. This paper aims to assess the seismic performance of dual concentrically braced steel frames (D-CBF) through static and incremental dynamic nonlinear analyses using different strategies to detailed modelling of the joints. A case study building with 6-storeys and 4 bays is used to illustrate the design of a D-CBF with different joint performance levels and to assess the influence of the joints. The frame studied is a perimeter seismic resistant system while the inner frames are designed for gravity loads only. The design and seismic performance of the joints is based on the pre-normative design recommendations achieved in the scope of the EQUALJOINTS project where different design procedures for beam-to-column joints are proposed in order to rende...
The Strategic Workshop on the trends and challenges for wind energy harvesting is the first open ... more The Strategic Workshop on the trends and challenges for wind energy harvesting is the first open forum organised within the framework of the activities of the TU1304 WINERCOST Action “Wind energy technology reconsideration to enhance the concept of smart future cities”. The state-of-the-art of the wind characteristics in disturbed and non-disturbed environment, the state-of-the-art of the wind energy structures and emerging applications as well as the society acceptance of wind energy technology and related topics are issues that were presented in details and discussed during the two days of the present Strategic Workshop.
This paper presents experimental and FE results of buckling study around door openings for steel ... more This paper presents experimental and FE results of buckling study around door openings for steel tubular wind turbine towers. Compression tests, using circular and polygonal down scale specimens with and without openings, have been performed in the approximately scale 1:10. A software package has been used to compare and analyse the images in order to gain insight into the local buckling development. Finite element analyses of the numerical models have been also performed and results have been compared with test results.
Increasing needs for taller wind turbines with bigger capacities, intended for places with high w... more Increasing needs for taller wind turbines with bigger capacities, intended for places with high wind velocities or at higher altitudes, have led to new technologies in the wind energy industry. A recently introduced structural system for onshore wind turbine towers is the hybrid steel tower. Comprehension of the environmental response of this hybrid steel structural system is warranted. Even though life cycle assessments (LCAs) for conventional wind turbine tubular towers exist, the environmental performance of this new hybrid structure has not been reported. The present paper examines the LCA of 185 m tall hybrid towers. Considerations made for the LCA procedure are meticulously described, including particular attention at the erection and transportation stage. The highest environmental impacts arise during the manufacturing stage followed by the erection stage. The tower is the component with the largest carbon emissions and energy requirements. The obtained LCA footprints of hybr...
Micropiles, which are small-diameter deep foundation solutions with diameters that can measure up... more Micropiles, which are small-diameter deep foundation solutions with diameters that can measure up to 300 mm, are often used to reinforce new and existing foundations. Their use in the foundations of structures with high eccentricity, such as wind towers when subjected to wind loads, may lead to more efficient and economical solutions. As the new generation of wind towers will reach more than 150 m tall, very large and uneconomical gravity foundations are required. In regions of high seismicity this problem is aggravated. To evaluate the behavior of micropiles under variable loading and predict the improvement of the reinforced solution, load tests were performed on steel micropiles under controlled laboratory conditions. A total of 36 tests were conducted on 3-m-long pipe micropiles, both while isolated and in 2 by 2 groups, with three different spacings. The micropiles were installed in a cylindrical container filled with calibrated sand and tested under monotonic and cyclic loading, first without grout, then when low-pressure grouted and retested, with the aim to evaluate the improvement caused by the grout injection, the micropile spacing, and application of cyclic loading both in terms of resistance and stiffness. An improvement both in stiffness and resistance due to the grouting was obtained and, for the applied cyclic loading, there was no clear reduction in micropile cyclic stiffness. The presented results provide a tool for the calibration of numerical models to estimate the behavior of real-scale micropiles installed in higher density sand.
Friction connections with long open slotted holes have been proven to be a competitive alternativ... more Friction connections with long open slotted holes have been proven to be a competitive alternative to the conventional flange connections in steel tubular towers for wind energy converters. As full-scale tests are not available, results of Finite Element Analysis (FEA) of the real-scale tower geometry are used in this paper to investigate the influence of tower cross section shape, execution tolerance (gap between the shells) and length of the connection on the bending resistance. Buckling behaviour of the shell in the vicinity of the friction connection in circular and polygonal towers is compared. The friction connection is thoroughly examined and recommendations for execution tolerances are given. The influence of two types of the execution tolerances on the connection strength is considered: inward bended "fingers", leading to inclined gaps, and a parallel gap created by different tower diameters.
This article presents some results of the experimental monotonic bending tests on the behaviour o... more This article presents some results of the experimental monotonic bending tests on the behaviour of the tubular columns and the reverse channel, effected based on a parametric variation of the most significant characteristics of the tubular profiles. The parameters considered are the thicknesses and the widths of the tubular columns faces, the filling with concrete and the axial load. The experimental tests program, included in the framework of the Doctoral Program Thesis in the scientific domain of the Steel Composite Structures, were performed on a test layout, corresponds to a framed structure, in the Structural Mechanic Laboratory of the Department of Civil Engineering of the University of Coimbra. The objective is to determine the characteristics of the nonlinear cyclic behaviour of the principal components of the tubular columns and the reverse channel, in this shape of joints. These components are related to the tubular columns walls, and to the web and flanges of the reverse ...
This paper describes a study of the S650 high strength steel material properties including the ef... more This paper describes a study of the S650 high strength steel material properties including the effect of cold-formed angle. Coupon specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160° and 180°) and different thicknesses (4 mm and 6 mm) were examined. Relationships between cold-formed angle and yield stress as well as tensile stress of the material were determined, based on the tensile coupon test results. Yield and tensile stresses assessed by consid ering the influence of the cold-formed angles were compared with those without considering this influence. Analyses revealed that both yield and tensile stresses decreased with increasing cold-formed angle. Ductile-damage material models available in the finite element analysis software ABAQUS were used to simulate tensile coupon tests. The experimental and numerical results showed good agreements.
This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-s... more This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-six specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160°, and 170°) and different thicknesses (4 mm and 6 mm) were considered. The initial geometric imperfections of the specimens were determined using the 3D laser scanning method. The magnitudes of these geometric imperfections for torsional and torsional-flexural buckling and flexural buckling analyses were proposed. The commercial finite element analysis (FEA) programme ABAQUS with sh ell elements S4R was used for finite element analyses. Different material strengths in corner and flat parts along with different proof stresses (0.2%, 0.01%, and 0.006%) were considered in the numerical models. The experimental and FEA results showed good agreement. Influence of cold-formed angle on non-dimensional slenderness and reduction factor curves of the 4 mm thick columns with 90° and 120° cold-formed angles was analysed.
The special issue of the Wind Engineering journal gathers a set of invited papers presented in th... more The special issue of the Wind Engineering journal gathers a set of invited papers presented in the International Conference on Wind Energy Harvesting that took place on 20–21 April 2017 in the University of Coimbra in Portugal and organized in the scope of the TUD COST Action TU1304 Wind energy technology reconsideration to enhance the concept of smart cities (WINERCOST). This conference and the COST action provided a forum for the presentation and discussion of different aspects of wind energy and wind energy technologies. Its principal objective was to collect the existing expertise on the Built environment Wind energy Technology (BWT) recently developed as a follow-up of the Onshore/Offshore Wind Energy Technology (ON/OFF-WET) and to investigate effective adoption methods for enabling the concept of Smart Future Cities. In addition, the utmost important issue of the social acceptance strategy will be scrutinized in close collaboration with municipality authorities, industry, manu...
The behaviour of standard bolted steel connections submitted to monotonic loads, through the use ... more The behaviour of standard bolted steel connections submitted to monotonic loads, through the use of numerical models, is presented in the current paper. The bolted connections allow speed up constructive processes in an increasingly competitive and globalized world in which the costs are a decisive factor in the development of a project. The use of computational tools in the analysis of bolted connections becomes determinant, mainly for new solutions or solutions less explored in terms of design codes. Throughout the years, bolted connections have been suffering transformations resulting from research activities performed by many authors. Rivets have been replaced by bolts, the main achievement being the pre-stressed bolts. Methodologies based on finite element analyses were proposed for double shear bolted connection. The non-linear behaviour of these connections is investigated and their performances are compared. In the numerical modelling of the bolted connection, linear elastic...
Nowadays, many buildings with steel Moment Resisting Frames (MRF) are built in seismic zones when... more Nowadays, many buildings with steel Moment Resisting Frames (MRF) are built in seismic zones when seismic codes are at its early stages of development, and as such, these structures are often designed solely to resist lateral wind loads without providing an overall ductile mechanism. On the other hand, current seismic design criteria based on hierarchy of resistance allow enhancing the structural ductility and controlling the structural plastic behaviour. Therefore, seismic design criteria might also be beneficial to improve the structural robustness. In order to investigate this issue for steel MRF, a parametric study based on pushdown analysis and on the Energy Balance Method is described and discussed in the present paper. With this regard, the following cases are examined: (i) MRF not designed for seismic actions and (ii) MRF designed for seismic actions. The investigated parameters are (i) the number of storeys, (ii) the interstorey height, (iii) the span length, (iv) the build...
The recent technological advances on steel production process allowed introducing in construction... more The recent technological advances on steel production process allowed introducing in construction market steel grades with significantly high yield strength. These new materials are known as High Strength Steel (HSS). The use of these steel grades offers economical and mechanical benefits compared with mild carbon steel (MCS). Consequently, their use is constantly increasing especially for seismic applications that are the rational field to exploit the high performance of HSS, by means of the “dual-steel” concept, which combines the HSS with MCS in order to provide overstrength to non-dissipative element and ductility to dissipative ones, thus controlling the global frame behaviour into a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic performance of Eurocode 8 compliant dual-steel chevron Dual-Concentrically Braced Frames (D-CBF) is presented and discussed. This structural typology is composed of two dissipative sub-s...
A steel hybrid structural solution for onshore wind turbine towers was proposed in the European p... more A steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration.
Mechanical models have the potential to characterize the behavior of complex steel joints, using ... more Mechanical models have the potential to characterize the behavior of complex steel joints, using for that the isolated behavior of its components, assembled according to their geometry. However, the mechanical models implemented in the current design codes are not prepared to deal with cyclically loaded joints, due to the complexity associated to load reversal. To overcome this difficulty this work makes to use of detailed finite elements models, to extract the needed force-displacement components response. The FE models are capable of representing the various connections components and the several sources of nonlinearity associated to them and are validated against existing experimental data. The discretized nature of the FE models is able to provide all the relevant information of any element, and even provide data that is typically unavailable from experimental tests, such as the contact or friction forces. Several models of bolted end plate beam-to column joints, with partial-strength classification in relation to the connected beam, have been developed using the ABAQUS FE package. A methodology to extract the needed force-displacement relationships of the column web components of the joint is presented and applied to the joints, through integration of stress and displacement fields. The results, presented in this paper, allow setting the base for a component-based model to simulate the dissipative behavior of steel connections subjected to cyclic loading conditions.
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
In this paper a detailed FE model of a bolted steel beam-to-column end-plate connection developed... more In this paper a detailed FE model of a bolted steel beam-to-column end-plate connection developed in ABAQUS is presented. The model is capable of simulating the behaviour of partial-strength joints subjected to both monotonic and cyclic loading. The model is validated by comparing the numerical results with available experimental data and also with results derived with simpler 2D models. The modelling approach is then employed to undertake extensive non-linear time history analyses on a set of partial-strength joints using several earthquake records and considering increasing levels of ductility demand, for a range of connections capable of representing the behaviour of the three ductile failure modes defined in Eurocode 3. Relationships between ductility and equivalent viscous damping are determined, which can be used in the application of the Direct Displacement-Based Design procedure to the seismic design of steel moment resisting framed structures with partial-strength connections.
For the connection of segments in tubular steel towers, some recently published literature promot... more For the connection of segments in tubular steel towers, some recently published literature promotes the use of friction connections as shown in Fig. 1 instead of the common flange connections [1]. Such friction connections consist of normal clearance holes with preinstalled bolts in one segment and long open slotted holes in the other segment. To facilitate assembly, the two segments differ in diameter. This allows for a certain deformability of the connection. The resistance of such a friction connection can simply follow the design rules of the European Standard EN1993-1-8 for friction connections with pretensioned bolts [2]. To investigate the behavior of the so called “fingers”, as which the steel plates between the long open slotted holes are designated, the following tests are going to be conducted: Two quadratic hollow sections of steel grade S355 will be connected with long open friction connections with 6 M24 bolts of grade 10.9 on two of their four sides, varying in distan...
Beam-to-column joints play an important role in the overall seismic behavior of steel frame struc... more Beam-to-column joints play an important role in the overall seismic behavior of steel frame structures, since the deformations in the panel zone of the beam-to-column joint region significantly affects the seismic behavior of steel joints. This paper aims to assess the seismic performance of dual concentrically braced steel frames (D-CBF) through static and incremental dynamic nonlinear analyses using different strategies to detailed modelling of the joints. A case study building with 6-storeys and 4 bays is used to illustrate the design of a D-CBF with different joint performance levels and to assess the influence of the joints. The frame studied is a perimeter seismic resistant system while the inner frames are designed for gravity loads only. The design and seismic performance of the joints is based on the pre-normative design recommendations achieved in the scope of the EQUALJOINTS project where different design procedures for beam-to-column joints are proposed in order to rende...
The Strategic Workshop on the trends and challenges for wind energy harvesting is the first open ... more The Strategic Workshop on the trends and challenges for wind energy harvesting is the first open forum organised within the framework of the activities of the TU1304 WINERCOST Action “Wind energy technology reconsideration to enhance the concept of smart future cities”. The state-of-the-art of the wind characteristics in disturbed and non-disturbed environment, the state-of-the-art of the wind energy structures and emerging applications as well as the society acceptance of wind energy technology and related topics are issues that were presented in details and discussed during the two days of the present Strategic Workshop.
This paper presents experimental and FE results of buckling study around door openings for steel ... more This paper presents experimental and FE results of buckling study around door openings for steel tubular wind turbine towers. Compression tests, using circular and polygonal down scale specimens with and without openings, have been performed in the approximately scale 1:10. A software package has been used to compare and analyse the images in order to gain insight into the local buckling development. Finite element analyses of the numerical models have been also performed and results have been compared with test results.
Increasing needs for taller wind turbines with bigger capacities, intended for places with high w... more Increasing needs for taller wind turbines with bigger capacities, intended for places with high wind velocities or at higher altitudes, have led to new technologies in the wind energy industry. A recently introduced structural system for onshore wind turbine towers is the hybrid steel tower. Comprehension of the environmental response of this hybrid steel structural system is warranted. Even though life cycle assessments (LCAs) for conventional wind turbine tubular towers exist, the environmental performance of this new hybrid structure has not been reported. The present paper examines the LCA of 185 m tall hybrid towers. Considerations made for the LCA procedure are meticulously described, including particular attention at the erection and transportation stage. The highest environmental impacts arise during the manufacturing stage followed by the erection stage. The tower is the component with the largest carbon emissions and energy requirements. The obtained LCA footprints of hybr...
Micropiles, which are small-diameter deep foundation solutions with diameters that can measure up... more Micropiles, which are small-diameter deep foundation solutions with diameters that can measure up to 300 mm, are often used to reinforce new and existing foundations. Their use in the foundations of structures with high eccentricity, such as wind towers when subjected to wind loads, may lead to more efficient and economical solutions. As the new generation of wind towers will reach more than 150 m tall, very large and uneconomical gravity foundations are required. In regions of high seismicity this problem is aggravated. To evaluate the behavior of micropiles under variable loading and predict the improvement of the reinforced solution, load tests were performed on steel micropiles under controlled laboratory conditions. A total of 36 tests were conducted on 3-m-long pipe micropiles, both while isolated and in 2 by 2 groups, with three different spacings. The micropiles were installed in a cylindrical container filled with calibrated sand and tested under monotonic and cyclic loading, first without grout, then when low-pressure grouted and retested, with the aim to evaluate the improvement caused by the grout injection, the micropile spacing, and application of cyclic loading both in terms of resistance and stiffness. An improvement both in stiffness and resistance due to the grouting was obtained and, for the applied cyclic loading, there was no clear reduction in micropile cyclic stiffness. The presented results provide a tool for the calibration of numerical models to estimate the behavior of real-scale micropiles installed in higher density sand.
Friction connections with long open slotted holes have been proven to be a competitive alternativ... more Friction connections with long open slotted holes have been proven to be a competitive alternative to the conventional flange connections in steel tubular towers for wind energy converters. As full-scale tests are not available, results of Finite Element Analysis (FEA) of the real-scale tower geometry are used in this paper to investigate the influence of tower cross section shape, execution tolerance (gap between the shells) and length of the connection on the bending resistance. Buckling behaviour of the shell in the vicinity of the friction connection in circular and polygonal towers is compared. The friction connection is thoroughly examined and recommendations for execution tolerances are given. The influence of two types of the execution tolerances on the connection strength is considered: inward bended "fingers", leading to inclined gaps, and a parallel gap created by different tower diameters.
This article presents some results of the experimental monotonic bending tests on the behaviour o... more This article presents some results of the experimental monotonic bending tests on the behaviour of the tubular columns and the reverse channel, effected based on a parametric variation of the most significant characteristics of the tubular profiles. The parameters considered are the thicknesses and the widths of the tubular columns faces, the filling with concrete and the axial load. The experimental tests program, included in the framework of the Doctoral Program Thesis in the scientific domain of the Steel Composite Structures, were performed on a test layout, corresponds to a framed structure, in the Structural Mechanic Laboratory of the Department of Civil Engineering of the University of Coimbra. The objective is to determine the characteristics of the nonlinear cyclic behaviour of the principal components of the tubular columns and the reverse channel, in this shape of joints. These components are related to the tubular columns walls, and to the web and flanges of the reverse ...
This paper describes a study of the S650 high strength steel material properties including the ef... more This paper describes a study of the S650 high strength steel material properties including the effect of cold-formed angle. Coupon specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160° and 180°) and different thicknesses (4 mm and 6 mm) were examined. Relationships between cold-formed angle and yield stress as well as tensile stress of the material were determined, based on the tensile coupon test results. Yield and tensile stresses assessed by consid ering the influence of the cold-formed angles were compared with those without considering this influence. Analyses revealed that both yield and tensile stresses decreased with increasing cold-formed angle. Ductile-damage material models available in the finite element analysis software ABAQUS were used to simulate tensile coupon tests. The experimental and numerical results showed good agreements.
This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-s... more This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-six specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160°, and 170°) and different thicknesses (4 mm and 6 mm) were considered. The initial geometric imperfections of the specimens were determined using the 3D laser scanning method. The magnitudes of these geometric imperfections for torsional and torsional-flexural buckling and flexural buckling analyses were proposed. The commercial finite element analysis (FEA) programme ABAQUS with sh ell elements S4R was used for finite element analyses. Different material strengths in corner and flat parts along with different proof stresses (0.2%, 0.01%, and 0.006%) were considered in the numerical models. The experimental and FEA results showed good agreement. Influence of cold-formed angle on non-dimensional slenderness and reduction factor curves of the 4 mm thick columns with 90° and 120° cold-formed angles was analysed.
The special issue of the Wind Engineering journal gathers a set of invited papers presented in th... more The special issue of the Wind Engineering journal gathers a set of invited papers presented in the International Conference on Wind Energy Harvesting that took place on 20–21 April 2017 in the University of Coimbra in Portugal and organized in the scope of the TUD COST Action TU1304 Wind energy technology reconsideration to enhance the concept of smart cities (WINERCOST). This conference and the COST action provided a forum for the presentation and discussion of different aspects of wind energy and wind energy technologies. Its principal objective was to collect the existing expertise on the Built environment Wind energy Technology (BWT) recently developed as a follow-up of the Onshore/Offshore Wind Energy Technology (ON/OFF-WET) and to investigate effective adoption methods for enabling the concept of Smart Future Cities. In addition, the utmost important issue of the social acceptance strategy will be scrutinized in close collaboration with municipality authorities, industry, manu...
The behaviour of standard bolted steel connections submitted to monotonic loads, through the use ... more The behaviour of standard bolted steel connections submitted to monotonic loads, through the use of numerical models, is presented in the current paper. The bolted connections allow speed up constructive processes in an increasingly competitive and globalized world in which the costs are a decisive factor in the development of a project. The use of computational tools in the analysis of bolted connections becomes determinant, mainly for new solutions or solutions less explored in terms of design codes. Throughout the years, bolted connections have been suffering transformations resulting from research activities performed by many authors. Rivets have been replaced by bolts, the main achievement being the pre-stressed bolts. Methodologies based on finite element analyses were proposed for double shear bolted connection. The non-linear behaviour of these connections is investigated and their performances are compared. In the numerical modelling of the bolted connection, linear elastic...
Nowadays, many buildings with steel Moment Resisting Frames (MRF) are built in seismic zones when... more Nowadays, many buildings with steel Moment Resisting Frames (MRF) are built in seismic zones when seismic codes are at its early stages of development, and as such, these structures are often designed solely to resist lateral wind loads without providing an overall ductile mechanism. On the other hand, current seismic design criteria based on hierarchy of resistance allow enhancing the structural ductility and controlling the structural plastic behaviour. Therefore, seismic design criteria might also be beneficial to improve the structural robustness. In order to investigate this issue for steel MRF, a parametric study based on pushdown analysis and on the Energy Balance Method is described and discussed in the present paper. With this regard, the following cases are examined: (i) MRF not designed for seismic actions and (ii) MRF designed for seismic actions. The investigated parameters are (i) the number of storeys, (ii) the interstorey height, (iii) the span length, (iv) the build...
The recent technological advances on steel production process allowed introducing in construction... more The recent technological advances on steel production process allowed introducing in construction market steel grades with significantly high yield strength. These new materials are known as High Strength Steel (HSS). The use of these steel grades offers economical and mechanical benefits compared with mild carbon steel (MCS). Consequently, their use is constantly increasing especially for seismic applications that are the rational field to exploit the high performance of HSS, by means of the “dual-steel” concept, which combines the HSS with MCS in order to provide overstrength to non-dissipative element and ductility to dissipative ones, thus controlling the global frame behaviour into a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic performance of Eurocode 8 compliant dual-steel chevron Dual-Concentrically Braced Frames (D-CBF) is presented and discussed. This structural typology is composed of two dissipative sub-s...
A steel hybrid structural solution for onshore wind turbine towers was proposed in the European p... more A steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration.
Mechanical models have the potential to characterize the behavior of complex steel joints, using ... more Mechanical models have the potential to characterize the behavior of complex steel joints, using for that the isolated behavior of its components, assembled according to their geometry. However, the mechanical models implemented in the current design codes are not prepared to deal with cyclically loaded joints, due to the complexity associated to load reversal. To overcome this difficulty this work makes to use of detailed finite elements models, to extract the needed force-displacement components response. The FE models are capable of representing the various connections components and the several sources of nonlinearity associated to them and are validated against existing experimental data. The discretized nature of the FE models is able to provide all the relevant information of any element, and even provide data that is typically unavailable from experimental tests, such as the contact or friction forces. Several models of bolted end plate beam-to column joints, with partial-strength classification in relation to the connected beam, have been developed using the ABAQUS FE package. A methodology to extract the needed force-displacement relationships of the column web components of the joint is presented and applied to the joints, through integration of stress and displacement fields. The results, presented in this paper, allow setting the base for a component-based model to simulate the dissipative behavior of steel connections subjected to cyclic loading conditions.
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
In this paper a detailed FE model of a bolted steel beam-to-column end-plate connection developed... more In this paper a detailed FE model of a bolted steel beam-to-column end-plate connection developed in ABAQUS is presented. The model is capable of simulating the behaviour of partial-strength joints subjected to both monotonic and cyclic loading. The model is validated by comparing the numerical results with available experimental data and also with results derived with simpler 2D models. The modelling approach is then employed to undertake extensive non-linear time history analyses on a set of partial-strength joints using several earthquake records and considering increasing levels of ductility demand, for a range of connections capable of representing the behaviour of the three ductile failure modes defined in Eurocode 3. Relationships between ductility and equivalent viscous damping are determined, which can be used in the application of the Direct Displacement-Based Design procedure to the seismic design of steel moment resisting framed structures with partial-strength connections.
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Papers by Carlos Rebelo