Sürdürülebilir Kalkınma Amaçları
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- MakaleYalnız künye2025Influences of chord pre-stress on CHS X-joints with high-strength-steel at various temperatures
Ozyurt, E.; Wang, Y.C.
This study examines the influence of chord pre-stress on the behaviour and load resistance of Circular Hollow Section (CHS) X-joints with High Strength Steel (HSS) at various temperatures. This investigation uses a total number of seven hundred and four Finite Element simulation results to evaluate the level of accuracy of current Eurocode and CIDECT design guidelines in predicting the high-temperature resistance of these joints. The numerical simulations investigate the effects of changing brace-to-chord diameter (β), chord semi-diameter-to-thickness (γ), and brace-to-chord thickness (τ) ratios, as well as different prestressing levels (np) and temperatures (θ). The γ and τ ratios have a limited effect on the normalised joint strength, but the β ratio, and the prestressing level are highly influential. At ambient temperature, the CIDECT design approach is a more suitable method for calculating the chord pre-stress reduction factors for S355 joints. For HSS X-joints, the constant modification coefficient of 0.80 is inadequate, and this paper has proposed a new modification coefficient as a function of the pre-stress level. At elevated temperatures, the ambient temperature resistance of CHS X-joints can be modified by the reduction factor of the Young's modulus for S355 steel and that of the yield stress for S960 steel.
- MakaleYalnız künye2024Hysteretic behaviour of square-hollow-section T- and X-joints with in-plane bending moment
Ozyurt, E.; Gunaydin, M.
This study examined the hysteretic behaviour of Square Hollow Section (SHS) T- and X-joints subjected to cyclic in-plane bending moments. A nonlinear finite element software, Abaqus, was used to investigate SHS T- and X-joint seismic performance. Prior to the parametric study, the numerical model was validated based on the available test results in the literature. A comprehensive parametric study employed validated finite element models to evaluate the influence of critical geometric parameters, including the brace-to-chord width ratio (β) and the chord width-to-thickness ratio (γ). The results of the finite element analyses regarding ductility, flexural strength, and energy dissipation behaviour of SHS T- and X-joints under quasi-static cyclic in-plane bending were evaluated. Based on the hysteretic curves, increasing β generally leaded to higher initial stiffness and moment capacity in SHS joints, considerably reducing joint rotation. Conversely, the joints with larger γ exhibited reduced initial stiffness and moment capacity. Besides, the Eurocode 3 EN1993-1-8 predictions for the ultimate flexural strength of the joints are found to be conservative compared to finite element results. The results also revealed that the SHS T- and X-joints showed satisfactory ductility levels under in-plane bending load. It was observed that the SHS T- and X-joints with high β and low γ are advantageous for absorbing energy under seismic loads. These findings offered valuable insights for the seismic-resistant design of structures incorporating SHS joints, aiding in selecting optimal configurations based on specific performance requirements.
- MakaleYalnız künye2024Axial resistance of elliptical hollow section K-joints made of high strength steel
Ozyurt, E.
The present study examined the axial resistance of welded elliptical hollow section (EHS) K-joints made of high-strength steel (HSS). The axial resistance of EHS K-joints was affected by a range of factors, including the geometrical parameters, orientations, chord pre-stress levels, and the mechanical properties of the high-strength steel grades. This research aimed to investigate the performance of welded EHS K-joints made of HSS under axial loading conditions with or without chord pre-stresses. Finite element analysis was employed for numerical simulations to analyze the nonlinear behaviour of EHS K-joints with HSS. It was observed from the numerical results that the orientation types significantly affected normalised resistance ratios. In contrast, β, γ, θ, and chord pre-stress levels had minimal impact, as comparisons were based on normalised resistance ratios. However, non-dimensional geometric parameters and chord pre-stress levels notably influenced the axial joint resistance of the HSS K-joints. As for predicting the axial resistances of EHS K-joints with HSS, the numerical results indicated that the existing reduction factor might be unsafe for the equivalent RHS method to be applied in the current design guides. Therefore, a new reduction factor was proposed for EHS K-joints with HSS that yield unsafe results.
- MakaleYalnız künye2023A Numerical Study to Evaluate the Changes in Dynamic Properties of Various Steel Truss Types Under Fire Conditions
Sibil, R.; Ozyurt, E.
This study numerically examines the changes in dynamic properties of fire-damaged steel trusses made of square hollow sections subjected to uniform and non-uniform heating scenarios. After verifying the numerical models at both ambient and elevated temperatures, a vast number of the simulations were analysed using non-linear finite element software to evaluate the effects of fire scenarios, truss types, and fire-damaged levels on the fire dynamic characteristics of square hollow section Warren, Howe, and Pratt trusses. The results indicated that the natural frequency of steel trusses significantly decreased as the fire-damaged level increased. In the case of local fire, the natural frequencies of the trusses began to drop suddenly at temperatures above 550 °C. Whereas the drop in the natural frequency of the uniformly heated trusses started at even much lower temperature levels. Moreover, the decrease in the natural fundamental frequencies of the uniformly heated trusses was lower than the reduction rate of the modulus of elasticity at high temperatures due to the large non-linear deformations. Since the modification of the stiffness of the truss by simply the reduction factor of the elastic modulus of the steel may be inappropriate to calculate the fundamental frequency of the trusses in the local and global fires, a new method was introduced to calculate the fundamental frequency value of the steel trusses in the fire.
- MakaleYalnız künye2022A Parametric Study on Earthquake-Damaged Square Hollow Section T-Joints under Fire Conditions
Ozyurt, E.
This study numerically investigated the elevated temperature resistance of earthquake-damaged square hollow section (SHS) T-joints subjected to brace axial compressive load. The residual stresses and deformations due to the earthquake were obtained from a pushover analysis. The extensive numerical simulations were analyzed using nonlinear finite-element software to examine the effects of the beta ratio, gamma ratio, damage level ((D) over cap), and initial applied load (n(f)) on the fire resistance of SHS T-joints after verification of the numerical simulations based on the available test results in the literature. The results indicated that the fire resistance of SHS T-joints with axial compressive load in the brace member decreased significantly due to the residual stresses and deformations from the earthquake. This situation worsened in all numerical models as the damage level increased. The reduction rate of the critical temperature at various damage rates was independent of the initially applied load ratio, but the loading rate directly affected the fire resistance of the joint regardless of the earthquake. As the beta ratio decreased, the yielded area at the brace-to-chord intersection region increased. Thus, the critical temperature of the joints at a constant damage level was inversely proportional to the beta ratio. Joints with a large gamma ratio had larger residual stresses and deformations than those of corresponding joints with a small. ratio. Therefore, the fire resistance of the joints after the earthquake decreased as the chord-wall thickness decreased. The critical temperature of the joints with either a large beta or gamma ratio was limited by the deformation limit at high damage levels. The fire resistance of the SHS T-joints after the earthquake decreased due to residual stresses and deformations. That effect increased even more in joints with high beta and. ratios. (C) 2022 American Society of Civil Engineers.
- MakaleYalnız künye2021Static resistance of axially loaded multiplanar gap KK-joints of Circular Hollow sections at elevated temperatures
Wang, Y.C.; Ozyurt, E.
This paper presents the results of a numerical investigation of the behaviour, and proposes a method to calculate the static resistance of axially loaded Circular Hollow Section Double K-joints (DKK) at elevated temperatures. This type of joints is widely used in building construction, but currently, there is no method to calculate their static resistance at elevated temperatures. The numerical investigations of this paper cover a wide range of design parameters, including brace axial load combination, joint temperature, angles between brace members, longitudinal and transverse gap sizes, chord diameter to thickness ratio and brace diameter to chord diameter ratio. The results of this paper indicate that the ratio of joint elevated temperature resistance to ambient temperature resistance may be lower than the reduction factor for the yield strength of steel at elevated temperatures. There are two joint failure modes, one for small and one for large transverse gap. These failure modes and the demarcation between small and large gaps are independent of joint temperature. For joints with large gap, the ratio of joint resistance at elevated temperature to that at ambient temperature is close to the average of steel yield strength and Young's modulus reduction factors at elevated temperature. For joints with small gap, the joint resistance ratio follows the steel Young's modulus factor variation at elevated temperature if all four braces are under compression, but the trend changes to the average ratio of steel Young's modulus and yield strength reduction factors if the axial brace loads are balanced (compression in two brace members equal to tension force in the other two brace members). Linear interpolation can be applied between these two different loading cases.
- MakaleYalnız künye2020Finite element study on axially loaded reinforced Square Hollow Section T-joints at elevated temperatures
Ozyurt, E.
This study numerically investigates the elevated temperature resistance of collar plate and doubler plate reinforced Square Hollow Section (SHS) T-joints subjected to brace axial compressive load. The extensive numerical simulations were performed to examine the effects of the geometrical parameters of main members and reinforcing plate on the fire resistance of reinforced SHS T-joints after verification of the numerical models based on the available test results. The corresponding unreinforced joints were also analysed as reference resistance at five different temperature levels (20 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Results indicate that the elevated temperature capacity of SHS T-joints can be significantly increased by using a collar plate or a doubler plate. Although the initial stiffness of the doubler plate reinforced joints was higher than the collar plate reinforced joints, their capacity was similar to each other. Also, the fire resistance of the reinforced joints mainly depended on the brace-to-chord width ratio and reinforcing plate thickness to chord wall thickness ratio. However, there was no beneficial effect on the fire resistance of reinforced joints when the thickness of the reinforcing plate was greater than 1.5 times the chord wall thickness. Moreover, there was an insignificant effect of half-width to thickness ratio of the chord, reinforcing length and reinforcing type as long as the required limit values of the reinforcing length and width were used based on the Eurocode 3 EN 1993-1-8. It is worth mentioning that modifying the steel yield strength in the ambient temperature design method to calculate the capacity of the reinforced SHS T-joints at elevated temperatures may be unsafe. A new design method was developed to predict the capacity of a collar plate and doubler plate reinforced SHS T-joints subjected to brace compressive load in fire.
- MakaleAçık Erişim2019Experimental and numerical studies on axially loaded reinforced square hollow section T-joints
Ozyurt, E.; Das, S.
This paper presents outcomes of experimental and numerical studies completed on unreinforced, collar plate reinforced and doubler plate reinforced Square Hollow Section (SHS)T-joints subjected to axial compressive loading on the brace member. A total of nine full-scale SHS T-joint specimens were fabricated and tested, in which six specimens were reinforced with collar plate and doubler plate. Non-linear finite element (FE)models were developed using finite element code, ABAQUS. Test data was used to validate these FE models. Subsequently, validated FE models were used to conduct an extensive parametric study to investigate the effect of various geometrical parameters of main members and reinforcement plates on the ultimate capacity of reinforced SHS T-joints. The parametric study found that use of both collar and doubler plate reinforcements significantly increase the ultimate capacity of SHS T-joints. Thickness of the reinforcing plate has a positive effect if the thickness of the reinforcing plate is limited to twice the thickness of the chord member. This study, however, found that the capacity of a reinforced SHS T-joint is not dependent on the type of reinforcing plate. The study concludes that the maximum capacity that can be achieved from a reinforced joint is about double the capacity of a similar unreinforced joint. It was found that the Eurocode EN 1993-1-8 overestimates the capacity of reinforced SHS T-joints. Therefore, a new design method for predicting the ultimate capacity of the collar plate and doubler plate reinforced SHS T-joints was developed and this new design method is presented in this paper.
- MakaleAçık Erişim2019A numerical investigation of static resistance of welded planar steel tubular joints under in-plane and out-of-plane bending at elevated temperatures
Ozyurt, E.; Wang, Y.C.
This study presents the results of a numerical investigation on static resistance of welded planar steel tubular joints under in-plane and out-of-plane bending moments at elevated temperatures. The numerical simulations were carried out using the commercial finite Element software ABAQUS v6.14-1 and the simulation model was validated by comparing against test results for CHS joints under brace in-plane bending at elevated temperatures. Extensive numerical parametric simulations were performed for CHS/SHS/EHS joints under in-plane and out-of-plane bending at elevated temperatures, to establish a database of results covering a wide range of geometrical parameters, including brace to chord diameter ratio, the angle between brace to chord members, and chord diameter to twice chord thickness ratio. The ratios of joint elevated temperature resistance to ambient temperature resistance were compared to the steel yield strength reduction factor, the steel Young's modulus reduction factor, and the average of the above these reduction factors at different elevated temperatures. Based on the comparisons, it has been found that using the reduction factor for the yield strength of steel to modify the ambient temperature equations will overestimate the resistance of joints at elevated temperatures. As a simplified and safe recommendation, the ambient temperature joint resistance equations can be modified by the average reduction factors for the Young's modulus and yield strength at elevated temperatures. This modification factor can be increased to the yield strength reduction factor when the brace and chord widths/diameters are the same.
- BildiriYalnız künye2018Behavior of T and X joints of elliptical hollow sections at both ambient and high temperatures
Ozyurt, E.; Wang, Y.C.; Heidarpour, A.; Zhao, X.-L.
This paper presents the results of a numerical study to develop a method to calculate the ultimate load carrying capacity of welded Elliptical Hollow Section (EHS) joints at elevated temperatures. Extensive numerical simulations, using the non-linear finite element package ABAQUS v6.14-1, have been conducted on EHS T-and X-joints subjected to brace axial compression or tension, considering a wide range of geometrical parameters, pre-stress in chord member and different type of joint orientations. The FE simulation results indicates that the equivalent RHS method is not appropriate for calculating the load carrying capacity of EHS joints at ambient temperature. At elevated temperatures, for T-and X-joints with braces welded to wide sides of chord, replacing the ambient temperature yield strength of steel by the elevated temperature value overestimates the ultimate load carrying capacity of axially loaded EHS T-and X-joints with compressive brace. Alternative design methods have been proposed.
- MakaleAçık Erişim2018Resistance of Axially Loaded T- and X-Joints of Elliptical Hollow Sections at Elevated Temperatures – A Finite Element Study
Ozyurt, E.; Wang, Y.C.
This study presents the results of a numerical study to develop a method to calculate the static strength of welded Elliptical Hollow Section (EHS) joints at elevated temperatures. Extensive numerical simulations using the non-linear finite element package, ABAQUS v6.14–1 on EHS T- and X-joints under brace axial compression or tension and pre-stress in chord member with different type of joint orientations at elevated temperatures over a wide range of diameter ratio have been conducted. The adjustments required to be made to the equations of joint resistance under ambient temperature conditions for estimating joint resistance at elevated temperature conditions are investigated in this study. The FE simulation results have been compared with the calculation results of a number of existing methods at ambient temperature. It has been found that the method proposed by Packer et al. gives the best agreement with the authors' simulation results at ambient temperature. At elevated temperatures, for T- and X- joints with braces in compression welded to the wide sides of chords, replacing the ambient temperature yield strength of steel by the elevated temperature value in the current design method overestimates the ultimate load carrying capacity of axially loaded EHS T- and X-joints due to inability of the ambient temperature calculation equations to take into consideration EHS flattening at high temperatures. For these cases, it is recommended to calculate the joint strength reduction factor at elevated temperatures according to the Young's modulus of steel.
- MakaleYayıncıda açık erişim2016Effects of non-uniform temperature distribution on critical member temperature of steel tubular truss
Ozyurt, E.; Wang, Y.C.
This paper examines the effects of thermal restraint, caused by non-uniform temperature distribution in different members, on the failure temperatures of critical members of steel tubular trusses. Non-uniform temperature distribution develops in trusses exposed to localised fire attack. The truss member nearest to the fire source experiences the highest temperature, with reduced temperatures in the nearby members. The number of the nearby truss members being heated and their temperatures will affect the failure temperature of the critical truss member which has the highest temperature. The aim of this paper is to develop a simplified method to account for the effects of different numbers of members being simultaneously heated to different temperatures on the development of compression force and failure temperature of the critical member. Finite Element (FE) simulations were carried out for Circular Hollow Section (CHS) trusses using the commercial Finite Element software ABAQUS v6.10-1 which has previously been validated by the authors. The simulation trusses were subjected to constant mechanical loads and then increasing temperatures until failure. The elevated temperature stress-strain curves were based on EN-1993-1-2 [1]. Initial geometrical imperfections were included, based on the lowest buckling mode from eigenvalue analysis.The numerical study examined the effects of truss type, critical member slenderness, applied load ratio and axial restraint stiffness ratio on the failure temperatures of the critical truss members. The numerical simulation results were used to check the accuracy of a proposed simplified calculation method, combining linear elastic static truss analysis at ambient temperature and analytical equations to calculated the failure temperatures of thermally restrained truss members based on the regression equations of Wang et al. [2]. The calculation method was shown to be sufficiently accurate for fire resistant design purpose.