• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.1-8
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• 2011

Concrete filled steel tubes(CFST) is considered as a column having better structural stability and better performance of fire resistance than that made with H-section and hollow section in itself. To get the fire resistance of the CFST, two kinds of concrete strength were used, 21 MPa, 40 MPa and 4 sorts of the applied loads were calculated and used to the specimens such as 3.5 m long, round and rectangular section. After various fire tests under 4 sorts of load ratios, the fire resistance of the CFST is not possible to get over 1 hour because of the rapid decrease of concrete strength. The below 50% of the applied load is recommended to obtain over 1 hour fire resistance of the CFST.

• International Journal of High-Rise Buildings
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• v.10 no.4
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• pp.335-344
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• 2021

In structural engineering practice, understanding the performance of composite columns under extreme loading conditions such as high-rise bulding, long span and heavy loads is essential to accuratly predicting of material responses under severe loads such as fires or earthquakes. Hitherto, the combined effect of partial axial loads and subsequent elevated temperatures on the performance of hollow steel column filled fly ash concrete have not been widely investigated. Comprehensive test was carried out to investigate the effect of elevated temperatures on partial axially loaded square hollow steel column filled fly ash concrete as reported in this paper. Four batches of hollow steel column filled fly ash concrete ( 30 percent replacement of fly ash), (HySC) and normal concrete (CFHS) were subjected to four different load levels, n_f of 20%, 30%, 40% and 50% based on ultimate column strength. Subsequently, all batches of the partially damage composite columns were exposed to transient elevated temperature up to 250℃, 450℃ and 650℃ for one hour. The overall stress - strain relationship for both types of composited columns with different concrete fillers were presented for each different partial load levels and elevated temperature exposure. Results show that CFHS column has better performance than HySC at ambient temperature with 1.03 relative difference. However, the residual ultimate compressive strength of HySC subjected to partial axial load and elevated temperature exposure present an improvement compared to CFHS column with percentage difference in range 1.9% to 18.3%. Most of HySC and CFHS column specimens failed due to local buckling at the top and middle section of the column caused by concrete crushing. The columns failed due to global buckling after prolong compression load. After the compression load was lengthened, the columns were found to fail due to global buckling except for HySC02.

• Steel and Composite Structures
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• v.18 no.6
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• pp.1569-1582
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• 2015

This study explores the lateral deflections of diagonal braces in concentrically-braced earthquake-resisting frames. The performance of this widely-used system is often compromised by the flexural buckling of slender braces in compression. In addition to reducing the compressive resistance, buckling may also cause these members to undergo sizeable lateral deflections which could damage surrounding structural components. Different approaches have been used in the past to predict the mid-length lateral deflections of cyclically loaded steel braces based on their theoretical deformed geometry or by using experimental data. Expressions have been proposed relating the mid-length lateral deflection to the axial displacement ductility of the member. Recent experiments were conducted on hollow and concrete-filled circular hollow section (CHS) braces of different lengths under cyclic loading. Very slender, concrete-filled tubular braces exhibited a highly ductile response, undergoing large axial displacements prior to failure. The presence of concrete infill did not influence the magnitude of lateral deflection in relation to the axial displacement, but did increase the number of cycles endured and the maximum axial displacement achieved. The corresponding lateral deflections exceeded the deflections observed in the majority of the previous experiments that were considered. Consequently, predictive expressions from previous research did not accurately predict the mid-height lateral deflections of these CHS members. Mid-length lateral deflections were found to be influenced by the member non-dimensional slenderness (${\bar{\lambda}}$) and hence a new expression was proposed for the lateral deflection in terms of member slenderness and axial displacement ductility.

• Steel and Composite Structures
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• v.7 no.1
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• pp.19-34
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• 2007

This paper presents results of a non-linear finite element analysis of axially loaded slender hollow structural section (HSS) columns, strengthened using high modulus carbon-fiber reinforced polymer (CFRP) longitudinal sheets. The model was developed and verified against both experimental and other analytical models. Both geometric and material nonlinearities, which are attributed to the column's initial imperfection and plasticity of steel, respectively, are accounted for. Residual stresses have also been modeled. The axial strength in the experimental study was found to be highly dependent on the column's imperfection. Consequently, no specific correlation was established experimentally between strength gain and amount of CFRP. The model predicted the ultimate loads and failure modes quite reasonably and was used to isolate the effects of CFRP strengthening from the columns' imperfections. It was then used in a parametric study to examine columns of different slenderness ratios, imperfections, number of CFRP layers, and level of residual stresses. The study demonstrated the effectiveness of high modulus CFRP in increasing stiffness and strength of slender columns. While the columns' imperfections affect their actual strengths before and after strengthening,the percentage gain in strength is highly dependent on slenderness ratio and CFRP reinforcement ratio, rather than the value of imperfection.

• Steel and Composite Structures
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• v.5 no.6
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• pp.459-484
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• 2005

In recent years, the use of steel tube confined concrete (STCC) columns has been the interests of many structural engineers. The present study is an attempt to study the monotonic and cyclic behaviours of STCC columns. For the monotonic behaviours, a series of tests on STCC stub columns (twenty one), and beam-columns (twenty) were carried out. The main parameters varied in the tests are: (1) column section types, circular and square; (2) tube diameter (or width) to thickness ratio, from 40 to 162, and (3) load eccentricity ratio (e/r), from 0 to 0.5. For the cyclic behaviours, the test parameters included the sectional types and the axial load level (n). Twelve STCC column specimens, including 6 specimens with circular sections and 6 specimens with square sections were tested under constant axial load and cyclically increasing flexural loading. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes. It was found that STCC columns exhibit very high levels of energy dissipation and ductility, particularly when subjected to high axial loads. Generally, the energy dissipation ability of the columns with circular sections was much higher than those of the specimens with square sections. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes such as AIJ-1997, AISCLRFD- 1994, BS5400-1979 and EC4-1994.

• Structural Engineering and Mechanics
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• v.53 no.1
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• pp.17-26
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• 2015

The cross sections of hollow cylindrical tubes ovalise under a pure bending condition, and this reduces their flexural stiffness as their curvatures increase. It is important to accurately evaluate this phenomenon, known as the 'Brazier effect', to understand the bending behaviour of the systems considered. However, if the tubes are supported by an elastic medium or foundation, the ovalisation displacements of their cross sections may decrease. From this point of view, the purpose of this research is to analytically investigate the bending characteristics of single- and double-walled elastic tubes contacted by an elastic material by considering the Brazier effect. The Brazier moment, which is the maximum moment-carrying capacity of the ovalised cross section, can be calculated by introducing the strain energy per unit length of the tube in terms of the degree of ovalisation for the tube and the curvature. The total strain energy of the double-walled system is the sum of the strain energies of the outer and inner tubes and that of the compliant core. Results are comparatively presented to show the variation in the degree of ovalisation and the Brazier moment for single- and double-walled tubes.

• Steel and Composite Structures
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• v.12 no.1
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• pp.73-92
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• 2012

The effect of element interaction and material nonlinearity on the ultimate capacity of stainless steel plated cross-sections is investigated in this paper. The focus of the research lies in cross-sections failing by local buckling; member instabilities, distortional buckling and interactions thereof with local buckling are not considered. The cross-sections investigated include rectangular hollow sections (RHS), I sections and parallel flange channels (PFC). Based on previous finite element investigations of structural stainless steel stub columns, parametric studies were conducted and the ultimate capacity of the aforementioned cross-sections with a range of element slendernesses and aspect ratios has been obtained. Various design methods, including the effective width approach, the direct strength method (DSM), the continuous strength method (CSM) and a design method based on regression analysis, which accounts for element interaction, were assessed on the basis of the numerical results, and the relative merits and weaknesses of each design approach have been highlighted. Element interaction has been shown to be significant for slender cross-sections, whilst the behaviour of stocky cross-sections is more strongly influenced by the material strain-hardening characteristics. A modification to the continuous strength method has been proposed to allow for the effect of element interaction, which leads to more reliable ultimate capacity predictions. Comparisons with available test data have also been made to demonstrate the enhanced accuracy of the proposed method and its suitability for the treatment of local buckling in stainless steel cross-sections.

• Steel and Composite Structures
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• v.32 no.1
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• pp.141-156
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• 2019

This paper presents the flexural behaviour of stainless steel beam-to-tubular column joints with extended endplates subjected to static loading. Moment-rotation relationships were investigated numerically by using Abaqus software with geometric and material nonlinearity considered. The prediction of damages among components was achieved through ductile damage models, and the influence of initial geometric imperfections and residual stresses was evaluated in large fabricated stainless steel joints involving hollow columns and concrete-filled columns. Parametric analysis was subsequently conducted to assess critical factors that could affect the flexural performance significantly in terms of the initial stiffness and moment resistance. A comparison between codes of practice and numerical results was thereafter made, and design recommendations were proposed for further applications. Results suggest that the finite element model can predict the structural behaviour reasonably well with the component damage consistent with test outcomes. Initial geometric imperfections and residual stresses are shown to have little effect on the moment-rotation responses. A series of parameters that can influence the joint behaviour remarkably include the strain-hardening exponents, stainless steel strength, diameter of bolts, thickness of endplates, position of bolts, section of beams and columns. AS/NZS 2327 is more reliable to predict the joint performance regarding the initial stiffness and moment capacity compared to EN 1993-1-8.

• Journal of Korean Society of Steel Construction
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• v.22 no.2
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• pp.109-119
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• 2010

There are many restrictions in the application of high-strength HSSs, including yield strength and yield ratio for the 600-MPa steel. The AISC and Canadian codes recommend that the yield strength and yield ratio of HSS members be 360 MPa and 80%, respectively. It is important to understand the true buckling behaviors of HSSs using high-strength steel at the limit states. There are many experimental data regarding the rectangular HSSs, and the circular ones are not enough for high-strength steel. Therefore, this study was conducted to create a better understanding of the buckling behaviors of the 600- and 400-MPa steels based on the results of the finite-element analysis that was done before the experiment. To understand the structural behaviors of the aforementioned steels, the width-to-thickness ratios, the angle of the web members, the yield strength, and the gap of the web members were selected as the main parameters in this study, and ABAQUS, a general finite-element program, was used.As a result, the compression web member reached elastic buckling in the 600-MPa steel and inelastic buckling in the 400-MPa steel. A brittle fracture occurred in the case where the yield ratio was greater than 80%. At the same time, it was found that the limit strength determined via FEM analysis had a higher value compared to the code evaluation with the variation of the width-to-thickness ratio in the main code member. The change in the connection load in high-strength steels was not identified by the other factors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.12-23
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• 2024

In this study, a structural concrete square beam was developed using the centrifugal molding technique. In order to secure the bending stiffness of the cross section, the hollow rate of the cross section was set to 10% or less. Instead of using the current poor mixture of concrete and a concrete mixing ratio with a high slump (150-200) and a design strength of 100 MPa or more was developed and applied. In order to investigate the durability of centrifugally formed PSC square beams to be used as the superstructure of the avalanch tunnel or ramen bridge, the durability performance of ultra-high-strength centrifugally formed concrete with a compressive strength of 100 MPa was evaluated in terms of deterioration and chemical resistance properties.Concrete durability tests, including chloride penetration resistance, accelerated carbonation, sulfate erosion resistance, freeze-thaw resistance, and scaling resistance, were performed on centrifugally formed square beam test specimens produced in 2022 and 2023. Considering the information verified in this study, the durability of centrifugally molded concrete, which has increased watertightness in the later manufacturing stage, was found to be superior to that of general concrete.