| 1. |
- Bravo, L, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
- Tabiri, S, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 3. |
- Simoes Cunha, Mafalda, et al.
(författare)
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Symptoms of anxiety and depression in patients with persistent asthma : a cross-sectional analysis of the INSPIRERS studies
- 2023
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Ingår i: BMJ Open. - : BMJ Publishing Group Ltd. - 2044-6055. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- ObjectivesAnxiety and depression are relevant comorbidities in asthma, but, in Portugal and Spain, data on this topic are scarce. We assessed, in patients with asthma, the frequency of anxiety and depression using the Hospital Anxiety and Depression Scale (HADS) and the European Quality of Life Five Dimension Questionnaire (EQ-5D); the level of agreement between these questionnaires, and the factors associated with these symptoms.MethodsThis is a secondary analysis of the INSPIRERS studies. A total of 614 adolescents and adults with persistent asthma (32.6 +/- 16.9 years, 64.7% female) were recruited from 30 primary care centres and 32 allergy, pulmonology and paediatric clinics. Demographic and clinical characteristics, HADS and EQ-5D were collected. A score >= 8 on Hospital Anxiety and Depression Scale-Anxiety/Hospital Anxiety and Depression Scale-Depression or a positive answer to EQ-5D item 5 indicated the presence of these symptoms. Agreement was determined by Cohen's kappa. Two multivariable logistic regressions were built.ResultsAccording to HADS, 36% of the participants had symptoms of anxiety and 12% of depression. According to EQ-5D, 36% of the participants had anxiety/depression. The agreement between questionnaires in identifying anxiety/depression was moderate (k=0.55, 95% CI 0.48 to 0.62). Late asthma diagnosis, comorbidities and female gender were predictors of anxiety/depression, while better asthma control, health-related quality of life and perception of health were associated with lower odds for anxiety/depression.ConclusionAt least 1/3 of the patients with persistent asthma experience symptoms of anxiety/depression, showing the relevance of screening these disorders in patients with asthma. EQ-5D and HADS questionnaires showed a moderate agreement in the identification of anxiety/depression symptoms. The identified associated factors need to be further investigated in long-term studies.
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| 4. |
- Cachim, Afonso, et al.
(författare)
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Measuring adherence to inhaled control medication in patients with asthma : Comparison among an asthma app, patient self-report and physician assessment
- 2023
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Ingår i: Clinical and Translational Allergy. - : John Wiley & Sons. - 2045-7022. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundPrevious studies have demonstrated the feasibility of using an asthma app to support medication management and adherence but failed to compare with other measures currently used in clinical practice. However, in a clinical setting, any additional adherence measurement must be evaluated in the context of both the patient and physician perspectives so that it can also help improve the process of shared decision making. Thus, we aimed to compare different measures of adherence to asthma control inhalers in clinical practice, namely through an app, patient self-report and physician assessment.MethodsThis study is a secondary analysis of three prospective multicentre observational studies with patients (≥13 years old) with persistent asthma recruited from 61 primary and secondary care centres in Portugal. Patients were invited to use the InspirerMundi app and register their inhaled medication. Adherence was measured by the app as the number of doses taken divided by the number of doses scheduled each day and two time points were considered for analysis: 1-week and 1-month. At baseline, patients and physicians independently assessed adherence to asthma control inhalers during the previous week using a Visual Analogue Scale (VAS 0–100).ResultsA total of 193 patients (72% female; median [P25–P75] age 28 [19–41] years old) were included in the analysis. Adherence measured by the app was lower (1 week: 31 [0–71]%; 1 month: 18 [0–48]%) than patient self-report (80 [60–95]) and physician assessment (82 [51–94]) (p < 0.001). A negligible non-significant correlation was found between the app and subjective measurements (ρ 0.118–0.156, p > 0.05). There was a moderate correlation between patient self-report and physician assessment (ρ = 0.596, p < 0.001).ConclusionsAdherence measured by the app was lower than that reported by the patient or the physician. This was expected as objective measurements are commonly lower than subjective evaluations, which tend to overestimate adherence. Nevertheless, the low adherence measured by the app may also be influenced by the use of the app itself and this needs to be considered in future studies.
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| 5. |
- Lopes, Fernanda, et al.
(författare)
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Behaviour of the reverse channel joint component at elevated temperature
- 2012
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Ingår i: Tubular Structures XIV. - London : CRC Press. - 9780203073100 ; , s. 645-651
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Konferensbidrag (refereegranskat)abstract
- The reverse channel connection appears to have the best combination of desirable feature underfire loading: moderate construction cost, ability to develop catenary action and extremely high ductilitythrough deformation of the web channel (Ding & Wang 2007). This paper presents the results of the experimentalinvestigation on a reverse channel component carried out at the University of Coimbra into the EuropeanRFCS COMPFIRE Project, which the main focus is to characterize the behaviour of steel joints betweensteel beams to concrete filled tubular columns under natural fire loading. A series of tension and compressiontests at ambient and elevated temperatures were tested. The aim of those experimental tests was to identify thestrength, stiffness and ductility of this joint component, establishing a relationship between force, displacementand temperature.
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| 6. |
- Lopes, Fernanda, et al.
(författare)
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Experimental behaviour of the reverse channel joint component at elevated and ambient temperatures
- 2013
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Ingår i: International Journal of Steel Structures. - : Springer Science and Business Media LLC. - 1598-2351 .- 2093-6311. ; 13:3, s. 459-472
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Tidskriftsartikel (refereegranskat)abstract
- The reverse channel connection appears to have the best combination of desirable features under fire loading: moderate construction cost, ability to develop catenary action and extremely high ductility through deformation of the web channel (Ding and Wang, 2007). This paper presents the results of an experimental investigation of a reverse channel component conducted at the University of Coimbra as part of the European RFCS COMPFIRE Project, the main focus of which is to characterise the behaviour of steel joints that connect steel beams to concrete-filled tubular columns under natural fire loading. A series of tensile and compressive tests at ambient and elevated temperatures was conducted. The purposes of the experimental tests were to characterise the strength, stiffness and ductility of this joint component and to establish a relationship between force, displacement and temperature.
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| 7. |
- Lopes, Fernanda, et al.
(författare)
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Sub-frames with reverse channel connections to cft composite columns –experimental evaluation
- 2015
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Ingår i: Advanced steel construction. - : Hong Kong Institute of Steel Construction. - 1816-112X. ; 11:1, s. 111-126
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the experimental results of the investigation on the coupled joint-structure behaviour of the composite sub-frame, using the reverse channel connections between an I-beam and the concrete filled tube (CFT) columns. This experimental programme includes seven full-scale tests: three tests at ambient temperature and four tests under heating-cooling curves. The parametric study was dedicated to: temperature-time curve and channel wall thickness (8, 10 and 12 mm). The main objective of these tests is to provide experimental information on the behaviour of the reverse channel joints and its influence on the structure under a heating-cooling fire. The restraining effects from the unaffected part of surrounding structure induce highly variable loading histories on the joints during fire; therefore the investigation on coupled joint-structure behaviour should lead to a realistic prediction of progressive collapse of the structure.
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| 8. |
- Rebelo, Carlos, et al.
(författare)
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Comparative life cycle assessment of tubular wind towers and foundations : Part 1: Structural design
- 2014
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 74, s. 283-291
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Tidskriftsartikel (refereegranskat)abstract
- The use of tubular towers made of steel, concrete or hybrid steel–concrete has become standard in the wind energy industry. However, more powerful wind energy generators are leading to the need for increasing the towers height. This implies rethinking of existing solutions for the support onshore structure composed of tower and foundation, including design concept, life cycle and environmental repercussion. The need for transportation of larger prefabricated elements and more complex processes of assembling on site become important issues. This paper addresses the comparative study concerning the influence of increasing height on the structural design and outcome of different structural solutions. Steel, concrete and hybrid steel–concrete wind towers with heights of 80, 100 and 150 m supporting multi-megawatt turbines of 2, 3.6 and 5 MW power respectively are addressed. The design of the towers is made in accordance with the structural Eurocodes. Two different scenarios are addressed, the first considering common lifetime of 20 years and the second considering increased lifetime of 40 years with reuse of tower parts. In-situ erection of steel tubular parts is achieved using flange connections or newly developed friction connections. Conclusions point out that, for towers up to 80 m, the use of steel tubular sections and flange connections are the most suitable. Friction connections are suitable for higher towers, leading to less material consumption. The use of concrete towers, particularly for heights above 100 m, is penalized when seismic risk is considered in special in the dimensions of the slab foundations
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Vicente, Guiomar, et al.
(författare)
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Sistema Inovador de Construção Metálica : FRAMEUP
- 2015
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Konferensbidrag (refereegranskat)abstract
- The methodology developed under the project FRAMEUP includes the construction of residential buildings from the top to the base, whose compartments are prefabricated modules. The construction begins with the execution of the roof, on the ground level, which is later on lifted, allowing from beneath the construction of the lower floors, while it protects them from the weather. The construction ends with the execution of the ground floor. It is adopted a framed structure with tubular sections for which the beam-to-column connections are developed and the columns-splices designed to facilitate and the use of this constructive methodology.
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| 13. |
- Eriksen, Jörgen, et al.
(författare)
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Guidelines to perform life cycle analysis of bridges
- 2008
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Ingår i: Proceedings of Seminar on Sustainability of Constructions - Integrated approach to life-time structural engineering. - 9783867800945 ; , s. 5.27-5.51
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 14. |
- Gervasio, Helena, et al.
(författare)
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Comparative analysis of an integral abutment composite bridge and a concrete bridge with expansion joints
- 2008
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Ingår i: Steel bridges : advanced solutions & technologies. - Brussels : European Convention for Constructional Steelwork, ECCS.
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Konferensbidrag (refereegranskat)abstract
- Bridge engineers very often face economic restrictions on their designs in addition to technical requirements. Those requirements are related not only to initial construction costs but also the cost to maintain the bridge condition at the level required by the bridge administration. In standard bridge structures, expansion joints are one of the most expensive components to maintain. In this regard, jointless bridges have major advantages. Integral bridges are built without joints, they span from one abutment to the other abutment, possibly over intermediate piers, without any joints in the deck. The absence of joints and bearings results in savings in initial costs and reduce maintenance efforts. Apart from economical benefits, the reduction of maintenance leads to less disturbance of the traffic over the bridge and thus to smaller environmental and social impacts. In this paper a case study is presented with the purpose of making a comparative life cycle analysis between an integral composite bridge and a concrete bridge with expansion joints. The result of this life cycle analysis will enhance the advantages of the former solution in regard of economical and environmental aspects.
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| 15. |
- Gervásio, Helena, et al.
(författare)
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Comparative life cycle assessment of tubular wind towers and foundations : Part 2: Life cycle analysis
- 2014
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 74, s. 292-299
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Tidskriftsartikel (refereegranskat)abstract
- In the first part of the paper the design of tubular towers and respective onshore foundations was addressed. The considered solutions were based on steel, concrete and hybrid steel-concrete tubular towers supporting multi-megawatt turbines of 2, 3.6 and 5 MW power with hub heights of 80, 100 and 150 m respectively. In this second part of the paper, the life cycle analysis of the designed case studies is performed and conclusions about their environmental impact are drawn. Two different scenarios concerning the lifetime of the towers were established. The first scenario considers 20 years lifetime and two different construction methods for the connection of the steel segments, the first based in current technology using flange connections and the second using newly developed friction connections. Assuming equal importance for all environmental categories in this scenario, it may be concluded that for heights up to 100 m hybrid towers with friction connections are the most efficient solution. For higher heights, the concrete tower becomes more efficient. The second scenario considers an increased total lifetime of 40 years, assuming the reuse of the tower after 20 years of operation. In this case, the use of friction connections in steel towers enhances the possibility of dismantling and reusing the tower potentiating much better performance in relation to the environmental category of global warming.
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| 16. |
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| 17. |
- Heistermann, Christine, et al.
(författare)
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Influence of execution tolerances for friction connections in circular and polygonal towers for wind converters
- 2017
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Ingår i: Advanced steel construction. - : Hong Kong Institute of Steel Construction. - 1816-112X. ; 13:4, s. 343-360
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 18. |
- Heistermann, Tim, et al.
(författare)
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Initial stiffness evaluation of reverse channel connections in tension and compression
- 2015
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Ingår i: Journal of constructional steel research. - : Elsevier BV. - 0143-974X .- 1873-5983. ; 114, s. 119-128
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Tidskriftsartikel (refereegranskat)abstract
- The so-called Reverse Channel connection has been conceived for the purpose of accommodating the thermal expansion of beams so that premature failure due to thermal buckling is avoided. The connection is made of a channel-shaped element, welded along the tips of its flanges onto the face of a hollow section column; an endplate welded on the beam is bolted onto the web of the channel. In a fire situation, the thermal expansion of a reverse-channel supported beam causes extensive bending deformation of the connection, therefore preventing the development of significant axial stress in the beam. Furthermore, this connection offers a high rotational capacity, if designed properly, which is beneficial in a fire situation where excessive deflections of beams can be expected. This paper aims to provide analytical stiffness assessment tools for reverse channel connections in compression and tension under uniform temperatures. The proposed analytical models are compared to results of Finite Element simulations, which in turn have been benchmarked with experiments. In addition, a comprehensive parametric study is conducted in order to identify all influencing factors on the initial stiffness response: reverse channel geometry and thickness, plate thickness, bolt position, and bolt diameter. Correction factors that account for 3D effects and bolt size are presented and discussed. The obtained expressions for the reverse channel stiffness are found to provide an accuracy that is acceptable for structural applications and can, therefore, be used as a design tool.
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| 19. |
- Heistermann, Tim, et al.
(författare)
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Initial Stiffness of Reverse Channel Connections
- 2014
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Ingår i: Eurosteel 2014. - Brussels : European Convention for Constructional Steelwork, ECCS. - 9789291471218
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Konferensbidrag (refereegranskat)abstract
- The robustness of a structure in a fire situation greatly depends on the rotational capacity of the connection region. High rotational capacity is required at elevated temperatures since the steel beams lose their bending stiffness and exhibit increasingly large deflections under constant load. Beam deflections result in increasing rotations at the supports and may lead to collapse due to connection failure. The reverse channel has been proposed as a practical alternative to assemble beams to tubular columns. In a simple implementation, the bending moment generated in the joint due to rotation of the beam may be neglected; however, research efforts are being attempted to quantify the level of constraint. The typical arrangement of the connection type consists of a reverse channel with its flanges welded onto the face of concrete-filled tubular columns and the web bolted to the endplate of a beam. Thicknesses and depths of the reverse channel determine the level of rotational restraint at high temperature. The reverse channel has the ability to undergo catenary deformation in the tensile zone due to the applied rotation at the support and similarly it is relatively ductile in the compression zone. Overall, the reverse channel connection response is rather ductile in terms of its ability to undergo large rotational deformation as long as bolt failure is avoided through proper design.Various tests have been performed to study the behaviour of this type of connection such as full scale buildings, sub-frames, isolated joints and individual sections. The aim of these tests was to capture the connection behaviour in relation to other structural components in fire. This paper, however, focuses on the derivation and verification of analytical models to assess the initial stiffness of reverse channel/partial-depth endplate connections. The results from finite element analyses have been utilized to validate analytical models that describe the behaviour of this type of connection at ambient and elevated temperature. Insight into the analytical models provides proper background to a structural designer to estimate the initial stiffness and understand the behaviour of the reverse channel in the connection.
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| 20. |
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| 21. |
- Iqbal, Naveed, et al.
(författare)
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Axial Force And Deformation Of A Restrained Steel Beam In Fire : Description and validation of a simplified analytical procedure
- 2016
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Ingår i: Advanced steel construction. - 1816-112X. ; 12:2, s. 174-193
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Tidskriftsartikel (refereegranskat)abstract
- Structural fire design is exceedingly adopting the performance based approach. There are evidentadvantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on thereal performance, must accurately predict the beam behaviour in fire. The study presented here proposes one suchsimplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analyticalprocedure is validated through FE Analysis using FE models validated through test results. The study also attempts toestablish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviorof the restrained beam at catenary stage.
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| 22. |
- Iqbal, Naveed, et al.
(författare)
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Axial force and deformation of a restrained steel beam in fire: Description and validation of a simplified analytical procedure
- 2016
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Ingår i: Advanced steel construction. - : Hong Kong Institute of Steel Construction. - 1816-112X. ; 12:2, s. 174-193
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Tidskriftsartikel (refereegranskat)abstract
- Structural fire design is exceedingly adopting the performance based approach. There are evident advantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on the real performance, must accurately predict the beam behaviour in fire. The study presented here proposes one such simplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analytical procedure is validated through FE Analysis using FE models validated through test results. The study also attempts to establish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviour of the restrained beam at catenary stage.
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| 23. |
- Iqbal, Naveed, et al.
(författare)
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Numerical Investigation of the Behaviour of Steel Beams in Steel-Concrete Composite Frames
- 2016
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Ingår i: Composite Construction in Steel and Concrete VII. - New York : American Society of Civil Engineers (ASCE). - 9780784479735 ; , s. 199-213
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Konferensbidrag (refereegranskat)abstract
- The methods proposed by the design codes for single member design in fire situation assume that these members are isolated in their response. The real response of structural members such as beams is, however, more complex due to thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of structure at high temperature in a way which includes its interaction with its surroundings such as in a full-scale fire test and in numerical analysis. This paper focuses on the numerical investigation of steel beams, with a concrete slab and connected to concrete filled tubular (CFT) columns through reverse channel connections. The finite element software ABAQUS has been used in this study. The aim of the investigation is to study the behaviour of the composite steel-concrete beam exposed to increasing temperature in fire.
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| 24. |
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| 25. |
- Iqbal, Naveed, et al.
(författare)
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Numerical Study of Steel Beams in Sub-frame Assembly Validation of Existing Hand Calculation Procedures
- 2015
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Ingår i: Journal of Structural Fire Engineering. - : Emerald. - 2040-2317 .- 2040-2325. ; 6:2, s. 123-140
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Tidskriftsartikel (refereegranskat)abstract
- The design methods currently proposed by the codes prescribe the strength assessment of structures to be based on their strength limit state. These design methods can be applied to isolated steel members to determine their design strengthin fire. The real response of a structural member is, however, more complex due to the thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of a structural member at high temperature in a way which includes its interaction with its surroundings. This paper focus on the numerical investigation of steel beams in structural frames connected to concrete filled tubular (CFT) columns through reverse channel connections and comparison to hand calculation procedures. Finite element models (FEM) of the sub-frames were validated against fire tests conducted on sub-frames and then their results were compared to the proposed simplified hand calculation procedures (HCM).
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| 26. |
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| 27. |
- Limam, Marouene, et al.
(författare)
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Modeling three dimensional friction connection for wind towers using finite element methods
- 2011
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Ingår i: Proceedings of the 6th European Conference on Steel and Composite Structures. - Budapest : European Convention for Constructional Steelwork, ECCS. - 9789291471034
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Konferensbidrag (refereegranskat)abstract
- The tubular steel towers supporting wind turbines account for about 15 to 20% of the total installation costs and their optimization may lead to substantial savings with regard to costs and use of material. An innovative solution for assembling joints of a tubular tower for wind turbines has been studied in an European research project called HISTWIN (High-Strength Steel Tower for Wind Turbine). This solution is simpler to produce and 80% less expensive than the traditional flange connection.The paper deals with connections used to assemble sections of tubular steel towers supporting wind turbines. The starting point is a rather simple lap joint connection .This connection is chosen for the sake of simplicity but still having possibility of general conclusions. After that more realistic connection between two tower segments is presented, each section has about 3m high and 2 m in diameter and they are connected by 222 M30 high-strength bolts.Modeling such FE models, which consists of several parts in contact, requires knowledge in contact mechanics with friction, meshing techniques as well as stability and convergence algorithms.A short parametric study is made to evaluate influence of number of bolts and the pretension force on the tubular tower failure mode.Results of FEA and resistance according to European codes, series EN1993-1-8 is considered. Keywords: Finite Element Model, Gap, High Strength Friction Grip Connection, Tubular Steel Tower, contact.
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| 28. |
- Matos, Rui, et al.
(författare)
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Cyclic performance of single and group micropiles on loose sand
- 2015
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Ingår i: Front Matter. - Reston, VA : American Society of Civil Engineers (ASCE). - 9780784479087 ; , s. 1751-1763
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Konferensbidrag (refereegranskat)abstract
- An increase in the height of new generation of wind towers is foreseen in order to improve their performance. This will imply larger shallow foundations, which represent a substantial percentage of the overall budget. Consequently, it is of interest to develop alternative foundation solutions, with a smaller environmental impact, in particular in terms of the required volume of excavation and reinforced concrete. The proposed improvement consists in the use of micropiles placed along the foundation perimeter as a way to increase the overturning resistance of the system as well as the foundation behavior. The main focus of this paper is the characterization of the behavior of single and groups of micropiles, tested under controlled conditions. An extensive set of experimental tests were conducted on single and 2x2 groups of micropiles under monotonic or cyclic loading installed in loose sand. The effect of the cyclic loading on the behavior of the micropiles was assessed as well as the effect of the grouting on the improvement of the micropile resistance and stiffness and also on the improvement of the soil mechanical properties. The assembly and procedure of the tests are described and the corresponding resistance and stiffness are presented and compared
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| 29. |
- Pavlovic, Marko, et al.
(författare)
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Connections in towers for wind converters : part I: Evaluation of down-scaled experiments
- 2015
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Ingår i: Journal of constructional steel research. - : Elsevier BV. - 0143-974X .- 1873-5983. ; 115, s. 445-457
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Tidskriftsartikel (refereegranskat)abstract
- The cost of a tubular steel tower supporting a wind converter becomes increasingly important in a competitive energy market. In-situ connection between tower segments is an important factor of the design. The tower segments are usually connected by welded ring flanges. An alternative solution based on a novel single lap friction connection is analysed. The purpose of the research presented in this paper is to thoroughly analyse the behaviour of both connections by an experimental testing programme and advanced finite element analysis (FEA). Down-scaled experiments of ring flange and friction connection in circular towers were performed using a 4-point bending test set-up. Altogether eight connections joining cylindrical shell, 1 m diameter, plate thickness 8 mm and total span of about 7 m were tested. A friction connection with long open slotted holes and two different cases of the ring flange connection are considered: with perfectly flat flanges and flanges with geometric imperfection. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experiments. Failure modes, bolt forces and distribution of meridional membrane stresses in the shell in the vicinity of connections are analysed. Existing hand-calculation models, for the bolt force and normal stress distribution in the shell are validated by experiments and FEA.
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| 30. |
- Pavlovic, Marko, et al.
(författare)
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Connections in towers for wind converters : Part II: The friction connection behaviour
- 2015
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Ingår i: Journal of constructional steel research. - : Elsevier BV. - 0143-974X .- 1873-5983. ; 115, s. 458-466
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Tidskriftsartikel (refereegranskat)abstract
- A novel friction connection consisting of a single lap joint with long open slotted holes is proposed for use in tubular towers for wind converters for in-situ connections. This is a competitive alternative to the common ring flange connection as it has been shown in the European Project “HISTWIN”. Two sets of experiments are analysed: the down-scaled tubular steel tower 4-point bending experiments using high-strength bolts M20 and a single lap joint using plate thickness 25 mm and tension control bolts M30.The main motivation for this paper is a much higher bending resistance obtained in the 4-point bending experiments compared to predictions based on hand-calculation models.Results of experiments are used to validate finite element analysis (FEA). Explicit solver and the most realistic geometry of the bolts are the main characteristics of the FEA performed. Very good agreement between the experiments and FEA results is obtained, which provides credibility of the computational approach used to thoroughly examine experimental results. New evidences of the friction connection behaviour are provided: a short-term loss of preloading force due to external loading, transfer of shear force in the single lap joint and influence of the slotted hole on the joint resistance.Results obtained from hand-calculation models are used to predict the loss of preloading, the bending resistance of the connection and meridional stresses in the tower shell in the vicinity of the connection, which are compared to the experiments and the FEA. Recommendations related to use of the hand-calculation models in the design are provided.
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| 31. |
- Pavlović, Marko, et al.
(författare)
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Friction connection vs. ring flange connection in steel towers for wind converters
- 2015
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Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 98, s. 151-162
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Tidskriftsartikel (refereegranskat)abstract
- Tubular steel towers are the most commonly used structures to support wind converters. Towers are fabricated in welded segments, complying with the traffic requirements for transportation, and in-situ assembled. Ring flange connections are used to connect two segments. Fatigue endurance of the ring flange to the shell weld, class 71, is often the design criterion and imposes a limit on the shell thickness. Recently studied friction connections with long opened slotted holes, in HISTWIN and HISTWIN2 projects, provides a remedy for this limitation. The main purpose of this paper is to compare performance of the ring flange connection and the novel friction considering connection of a real tubular tower segment 3.37 m in diameter and 24 mm shell thickness. This cross-section is designed for the ultimate load MEd = 45.8 MNm and the steel grade S355. Finite Element Method is used to investigate possible failure modes of the connection. Advanced FEA comprise the realistic geometry of the connection, ductile damage material model and element removal using explicit dynamic solver. This allows sophisticated analysis of the behaviour and direct comparison of the results for both connection alternatives. The FEA is validated by down-scaled experiments performed previously within the HISTWIN project. The friction connection is thoroughly examined: geometry of the connection, influence of the shell imperfection in the vicinity of the connection and possible use of higher resistance steel grades. By focusing on key issues of the friction connection recommendations for the design are provided together with a numerical example.
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| 32. |
- Pinto da Silva, André, et al.
(författare)
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Climate and anthropogenic factors determine site occupancy in Scotland's Northern-range badger population : implications of context-dependent responses under environmental change
- 2017
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Ingår i: Diversity & distributions. - : Wiley. - 1366-9516 .- 1472-4642. ; 23:6, s. 627-639
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Tidskriftsartikel (refereegranskat)abstract
- Aim: In the light of human-induced rapid environmental change (HIREC), populations are exposed to ever-greater bioclimatic stress at the edge of a species' historic range. The distribution dynamics of European badgers (Meles meles) at their southern edge are linked tightly to climatic variability. We contribute critical data on how climatic context and local factors determine site occupancy in a northern-range population.Location: Eleven study areas (averaging similar to 21.3km(2)) spread over similar to 50,000km(2) in Northern Scotland.Methods: While accounting for heterogeneous detectability, we applied single-season occupancy models to broad-scale camera-trapping data (168 stations) to evaluate how Autumn-Winter weather conditions interact with land-cover type (including agricultural land) and human disturbance to determine badger occupancy.Results: Mean minimum daily winter temperature and elevation influenced inter-site occupancy. When clustering study areas into two distinct topo-climatic types, badger occupancy was associated with agriculture in areas with lower mean minimum winter temperatures (<0.3 degrees C) at higher elevation (>246m). In areas with higher mean minimum winter temperature (>1.2 degrees C) at lower elevation (<133m), badgers selected sites further away from human infrastructures (settlements and main roads). Climatic factors and human disturbance interact in intricate, context-dependent patterns to determine badger site occupancy.Main Conclusions: The UKCP09 Medium Emissions Scenario projects a winter mean minimum temperature increase of between 1 and 3 degrees C (central estimate) for Northern Scotland by the 2050s. Although warmer weather should benefit badger occupancy, this may be counteracted by up to a predicted 5% human population increase in the Scottish highlands, by 2037, which is likely to disturb badgers. We show that even in instances where species' regional responses to climate change are positive, these effects can be neutralized by other anthropogenic pressures. Our findings add to the growing body of evidence advocating that interactive effects should be taken into account when planning conservation management.
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| 33. |
- Santiago, Aldina, et al.
(författare)
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Numerical study of a steel sub-frame in fire
- 2008
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Ingår i: Computers & structures. - : Elsevier BV. - 0045-7949 .- 1879-2243. ; 86:15-16, s. 1619-1632
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Tidskriftsartikel (refereegranskat)abstract
- Steel framed buildings are generally designed with "simple" shear-resisting connections, and lateral forces are resisted by vertical bracing and shear walls. When a beam is considered then the effects of the longitudinal restraints by the adjacent structure and the rotational restraint by the connections has to be taken into account. Because of structural interaction, the beam behaviour at elevated temperature is rather complex. This paper presents a numerical parametric study of a structural system consisting of an exposed steel beam restrained between a pair of fire protected steel columns. The structural sub-frame is modelled using 3D shell elements, thereby taking into account the effect of the local failure modes, and the realistic behaviour of the sub-frame exposed to natural fire. The numerical model accounts for the initial geometrical imperfections, non-linear temperature gradient over the cross-section, geometrical and material nonlinearity and temperature dependent material properties. Results obtained using a general Finite Element software - LUSAS and a fire dedicated software - SAFIR, are compared. The influence of following variables: beam span/depth ratio, lateral restraint, gradient temperature within the cross-section and mechanical load level is presented in the paper. The failure modes, the development of the internal forces and displacements throughout the analysis are considered to exemplify the effects of the variables considered.
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| 34. |
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| 35. |
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| 36. |
- Tran, Anh Tuan, et al.
(författare)
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Influence of cold-formed angle on high strength steel material properties
- 2019
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Ingår i: Advanced steel construction. - : The Hong Kong Institute of Steel Construction. - 1816-112X. ; 15:4, s. 316-322
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Tidskriftsartikel (refereegranskat)abstract
- 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 considering 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.
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| 37. |
- Tran, Anh Tuan, et al.
(författare)
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Influence of Geometrical Imperfections on Analyses of Door Openings in Tubular Steel Towers for Wind Turbines.
- 2014
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Ingår i: Eurosteel 2014.
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Konferensbidrag (refereegranskat)abstract
- Towers for wind turbines are very sensitive to geometrical imperfections. Pattern and amplitude of imperfections significantly influence the strength of the towers. Rather limited number of experiments exists on a tubular tower like structure and no experiments are available considering door opening in towers with cylindrical or polygonal cross-section. One of the objectives of the RFCS research project “HIGH STEEL TUBULAR TOWERS FOR WIND TURBINES, HISTIWIN2” was to investigate current practice for design of door openings and propose a competitive solution, possibly using higher strength steel grades. A comprehensive experimental program was conceived to gain experimental evidence for the design of stiffening of the door openings.The following compression tests were evaluated in the paper:•4 static down-scaled compression tests of components of circular tubes •4 static down-scaled compression tests of components of polygonal tubes•4 static down-scaled compression tests of components of circular tubes with opening•4 static down-scaled compression tests of components of polygonal tubes with openingPlate thickness is down-scaled to 4 mm thick plate made of S650 steel grade.Most of FE nonlinear analyses of thin walled shell structures were performed using geometrical imperfections according to Eurocode 3. In this approach, geometrical imperfections are based on the pattern that coincides with the critical buckling mode. A comprehensive numerical investigation was made to conclude whether there is need to use a real geometrical imperfection pattern. The real geometry of the imperfections was obtained by laser scan measurements. Both, the measured geometrical imperfections and the geometrical imperfections according to Eurocode 3 were considered. Furthermore, results obtained from polygonal specimens were compared with specimens with circular cross sections.
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| 38. |
- Tran, Anh Tuan, et al.
(författare)
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Resistance of cold-formed high strength steel angles
- 2019
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Ingår i: Advanced steel construction. - : The Hong Kong Institute of Steel Construction. - 1816-112X. ; 15:3, s. 242-251
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Tidskriftsartikel (refereegranskat)abstract
- 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 shell 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.
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| 39. |
- Tran, Anh Tuan, et al.
(författare)
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Resistance of cold-formed high strength steel circular and polygonal sections : Part 1: Experimental investigations
- 2016
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Ingår i: Journal of constructional steel research. - : Elsevier BV. - 0143-974X .- 1873-5983. ; 120, s. 245-257
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results from experiments performed on cold-formed high strength steel circular and polygonal sections. The test specimens were conceived to provide necessary information for development of tubular towers for wind turbines. A total of 32 high strength steel specimens were tested under uniaxial compression. Various thicknesses, openings and geometric imperfections were studied. Sixteen specimens without opening and sixteen specimens with opening were tested under axial compression in order to investigate influences of opening on the resistances. Tensile tests of coupon specimens taken from flat part, circular part and corner part were used to investigate basic properties of high strength steel material S650 and to evaluate influence of corner on the material strength and ductility. Initial geometric imperfections of the specimens were determined by using a 3D laser scanning method. The coupon test results were used to calibrate the ductile damage material models for modelling of fracture. Results from the experiments are fully described in this paper
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| 40. |
- Tran, Anh Tuan, et al.
(författare)
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Resistance of cold-formed high strength steel circular and polygonal sections : Part 2: Numerical investigations
- 2016
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Ingår i: Journal of constructional steel research. - : Elsevier BV. - 0143-974X .- 1873-5983. ; 125, s. 227-238
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Tidskriftsartikel (refereegranskat)abstract
- This paper is the second part of the study on the cold-formed high strength steel circular and polygonal sections intended to be used in tubular wind towers. Results from 32 numerical finite element analysis (FEA) models were compared with and calibrated against results of the tests on 32 corresponding specimens. The FEA results agreed well with the experimental results in terms of resistances and load-displacement curves. Further investigations on the numerical models were performed. Yield stress used in the FEA significantly affected the resistances of the numerical models. Using 0.2% proof stress leaded to higher resistance than the experimental results. Corners significantly influenced buckling behaviour in the polygonal section models. Analyses of an oval opening in the tubular specimens showed that peak stresses around the opening were considerably higher in the polygonal section models than in the circular section models. Finally, investigation of sensitivity to geometrical imperfections indicated that failure modes of numerical models with geometrical imperfections according to EC3 significantly differed from those of tested specimens and numerical models with geometrical imperfections obtained from the 3D scans.
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| 41. |
- Tran, Anh Tuan, et al.
(författare)
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Resistance of Door Opening in Towers for Wind Turbines
- 2013
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Ingår i: SEECCM III. ; , s. 312-324
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Konferensbidrag (refereegranskat)abstract
- In this paper, a study of resistance of a lower part of a wind tower including a door opening is presented. Nonlinear 3-D shell element models with real geometry of lower tower segment have been used to simulate the thin walled shell structure in order to study the influence of door opening on the strength of the tower. Two possible alternatives for strengthening the door openings were considered: (i) increasing thicknesses of plate around the opening and (ii)stiffening the opening by a stiffener. Buckling analysis and nonlinear analysis were performed to obtain critical buckling modes and strength of the tower segment. Nominal material properties of different steel grades were considered to investigate possibility of using higher strength steels. A parametric study considering possible local shell imperfections according to EN1993-1-6 has been considered. Additionally, comparative studies have been performed based on the FE model without door opening.
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| 42. |
- Veljkovic, Milan, et al.
(författare)
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Feasibility study of friction connection in tubular towers for wind turbines
- 2010
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Ingår i: Steel structures: culture & sustainability 2010. - Istanbul : Turkish Constructional Steelwork Association. - 9789759246129
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Konferensbidrag (refereegranskat)abstract
- In steel tubular towers flange connections are used to assemble two segments of the tower. As an alternative for these fatigue-sensitive joints a new type of friction connection has been investigated both in laboratory and at a production plant where the feasibility study was performed. The specimen used in the feasibility test consists of two tower segments, each about 3m high and 2 m in diameter. The segments are connected by 222 M30 high-strength bolts. The production process and tolerances achieved are briefly explained. The assembling process is modeled using a realistic FEA model to predict the stress in the segments during pretensioning. A simplified FE analysis was performed to assess the influence of the compressive strength of the specimens. This paper presents results of a short parametric study on the influence of the gap between two tower segments exploring possibilities to use higher-strength steel in the towers. Keywords: Finite Element Model, Gap, High Strength Friction Grip Connection, Tubular Steel Tower, Wind Energy Converter
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| 43. |
- Veljkovic, Milan, et al.
(författare)
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Friction connection in tubular towers for a wind turbine
- 2010
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Ingår i: Stahlbau. - : Wiley. - 0038-9145 .- 1437-1049. ; 79:9, s. 660-668
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Tidskriftsartikel (refereegranskat)abstract
- Innovative solution for assembling joints of a tubular tower for wind turbines has been studied by a European consortium since 2005 and the HISTWIN (High-Strength Steel Tower for Wind Turbine) project provides background for design of the friction connection considered. This solution is simpler to produce and 80% less expensive than traditional flange connection. A feasibility study at the production plant indicates that the towers would be easy to assemble in-situ. In addition to the direct costs savings due to technical simplicity of the solution, the higher fatigue endurance than the flange connection is experimentally established. The loss of pretension forces in the friction connection with long opened slotted holes is studied using segment short-term and long-term static tests, fatigue tests, down-scaled bending tests and by a specimen used in a feasibility study. The total reduction of the costs for tower is estimated to about 10% to 15% compared to the traditional tower with the flange connection.
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| 44. |
- Veljkovic, Milan, et al.
(författare)
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Structural member behaviour and analysis in case of fire
- 2008
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Ingår i: Urban Habitat Constructions under Catastrophic Events. - Valetta : Editura Universitatii de Vest din Timisoara / University of the West Timisoara Publishing House. - 9789990944402 ; , s. 45-50
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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