Steel Square Hollow Section Research Articles

Push-out tests of concrete-filled stainless steel SHS tubes

A total of 32 push-out tests were conducted in this paper on concrete-filled stainless steel square hollow section (SHS) tubes with different values of height-to-width ratio, width-to-thickness ratio and concrete strength. The bond-slip behaviour of all specimens and the strain distribution on the exterior of stainless steel tubes along the longitudinal height direction were carefully investigated. Shear failure loads of bonding slip and the interface friction resistance generally decreased with more loading cycles of the repeated push-out test employed in the same direction. It can be concluded that 70% of the bonding strength at the interface was taken by the friction force of the interface elements, while the remaining 30% of the bonding strength at the interface was sustained by the chemical adhesive force and the mechanical interlock force. Furthermore, the strains at the locations close to the free end and loading end of the specimens increased with the increase of the axial load, in which the increase of the strains at the location close to the free end is much greater. On the other hand, it is demonstrated that the height-to-width ratio and the width-to-thickness ratio of the stainless steel SHS tube have insignificant influence on the shear resistance of the bonding strength of the interface elements, which generally decreased with the increase of the concrete strength. In addition, the current design rules of concrete-filled carbon steel SHS tubes were found to be inapplicable to the shear resistance of the bonding strength of concrete-filled stainless steel SHS tubes.

Experimental and numerical investigation of strengtheneddeficient steel SHS columns under axial compressive loads

In past years, numerous problems have vexed engineers with regard to buckling, corrosion, bending, and over-loading in damaged steel structures. This article sets out to investigate the possible effects of carbon fiber reinforced polymer (CFRP) and steel plates for retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position and shape of deficient region on the length of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. A total of 14 specimens was tested for failure under axial compression in a laboratory and simulated using finite element (FE) analysis based on a numerical approach. The results indicate that the application of CFRP sheets and steel plates also caused a reduction in stress in the damaged region and prevented or retarded local deformation around the deficiency. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns. Finally, this research showed that the CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.

Numerical investigation of continuous hollow steel beam strengthened using CFRP

This paper presents a numerical study on the behavior of continuous hollow steel beam strengthened using carbon fiber reinforced polymers (CFRP). Most previous studies on the CFRP strengthening of steel beams have been carried out on the steel beams with simple boundary conditions. No independent study, to the researcher\'s knowledge, has studied on the CFRP strengthening of square hollow section (SHS) continuous steel beam. However, this study explored the effect of the use of adhesively bonded CFRP flexible sheets on the behavior of the continuous SHS steel beams. Finite Element Method (FEM) has been employed for modeling. Eleven specimens, ten of which were strengthened using CFRP sheets, were analyzed under different coverage length, the number of layers, and the location of CFRP composite. ANSYS software was used to analyze the SHS steel beams. The results showed that the coverage length, the number of layers, and the location of CFRP composite are effective in increasing the ultimate load capacity of the continuous SHS steel beams. Application of CFRP composite also caused the ductility increase some strengthened specimens.

Investigation of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression

An experimental investigation was conducted on empty and grouted stainless steel square hollow section (SHS) tubular X- and T-joints subjected to axial compression. A total of 24 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors (β, τ, grouting and grout strength) on the behaviour of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel SHS tubular X- and T-joints generally increased with the increase of the β and τ values. The enhancement of joint strengths obtained from grouting both brace and chord members is much greater than that obtained from grouting chord member only. In addition, the ultimate strengths of stainless steel SHS tubular X- and T-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel SHS tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally conservative for the design of empty stainless steel SHS tubular X- and T-joints subjected to axial compression, but unconservative for the design of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate.

Structural performance of additive manufactured metallic material and cross-sections

Additive manufacturing, a common example of which is 3D printing, has become more prevalent in recent years with it now being possible to form metallic structural elements in this way. There are, however, limited available experimental data on the material behaviour of powder bed fusion (PBF) additive manufactured metallic structural elements and no existing data at the cross-section level; this is addressed in the present paper through a series of tests on additive manufactured stainless steel material and cross-sections. Tensile and compressive coupon tests were used to assess anisotropy, symmetry of stress-strain behaviour and the influence of building direction on the material properties. The yield and ultimate tensile strengths were seen to generally decrease in magnitude with increasing build angle, while a reduction in ductility was observed in some building orientations, and the Young's moduli were typically insensitive to the build angle. The structural behaviour of PBF additive manufactured cross-sections was investigated through a series of square hollow section (SHS) stub column tests, and the results compared with conventionally produced stainless steel SHS. The generated test results have been used to evaluate the applicability of existing design guidance for conventionally produced sections to additive manufactured sections.

Experimental study of concrete filled cold-formed steel tubular stub columns

An experimental programme was conducted to investigate the compressive behaviour of concrete-filled cold-formed steel tubular (CFCFST) stub columns with thicker tubes. A total of 30 CFCFST stub columns were tested. The cold-formed square hollow section (SHS) tubes included unstiffened sections and longitudinally inner-stiffened sections using different stiffening methods. Two tubular thicknesses of 6mm and 10mm were considered. The overall nominal dimension of the steel section was 200×200mm, and the length of the stub columns was 600mm. Normal concrete and self-consolidating concrete with a nominal compressive strength of 30MPa were used to fill the cold-formed SHS steel tubes. The effects of the stiffeners on the rigidity, ductility, failure mode and average sectional strength of the CFCFST specimens were examined. The measured strengths of the CFCFST specimens were also compared with the predicted capacities using methods in various codes including AISC, BS5400, EC4, and DBJ and from a finite element (FE) analysis. Results demonstrate that the inner stiffeners affect the deformability, failure mode and overall strength of the stub columns with the 6mm-thick tubes more significantly. The DBJ code method is comparatively the best in predicting the strength capacity. Using the validated FE model, an extended analysis has been conducted and this has provided further insight into the mechanical behaviour of the CFCFST specimens.

CFRP strengthening of steel columns subjected to eccentric compression loading

Steel structures often require strengthening due to the increasing life loads, or repair caused by corrosion or fatigue cracking. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been carried out on steel beams and steel columns under centric compression load. No independent article, to the author's knowledge, has studied the effect of CFRP strengthening on steel columns under eccentric compression load, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel columns under eccentric compression load. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel columns under the eccentric compression load, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine ultimate load of SHS steel columns, eight specimens with two types of section (Type A and B), strengthened using CFRP sheets, were analyzed under different coverage lengths, the number of layers, and the location of CFRP composites. Two specimens were analyzed without strengthening (control) to determine the increasing rate of the ultimate load in strengthened steel columns. ANSYS was used to analyze the SHS steel columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel columns.

Numerical investigation of SHS steel beam-columns strengthened using CFRP composite

Carbon Fiber Reinforced Polymer (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been done on steel beams and steel columns. No independent study, to the researcher\' s knowledge, has studied the effect of CFRP strengthening on steel beam-columns, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel beam-columns. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel beam-columns, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine the ultimate load of SHS steel beam-columns, ten specimens, eight of which were strengthened with the different coverage length and with one and two CFRP layers, with two types of section (Type A and B) were analyzed. ANSYS was used to analyze the SHS steel beam-columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel beam-columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel beam-columns.

Numerical investigation on the behavior of SHS steel frames strengthened using CFRP

Steel frames are widely used in steel structures. Exiting steel structures may be needed to strengthen for various reasons. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials that are used to strengthen steel structures. Most studies on strengthening steel structures have been done on beams and steel columns. No independent study, to the researcher's knowledge, has studied the effect of CFRP strengthening on steel frames. This study explored the use of CFRP composite on retrofitting square hollow section (SHS) steel frames, using numerical investigations. Ten Finite Element (FE) models, which were strengthened with CFRP sheets, were analyzed under different coverage length, number of layers, and location of CFRP composite. One FE model without strengthening was analyzed as a control FE model to determine the increase of the ultimate load in the strengthened steel frames. ANSYS software was used to analyze the SHS steel frames. The results showed that the coverage length and the number of layers of CFRP composite have a significant effect on increasing the ultimate load of the SHS steel frames. The results also showed that the location of CFRP composite had no similar effect on increasing the ultimate load and the amount of mid span deflection of the SHS steel frames.

Structural behaviors of deficient steel SHS short columns strengthened using CFRP

This paper presents the experimental and numerical investigations on the structural behaviors of steel square hollow section (SHS) compression members having initial horizontal or vertical deficiencies which were strengthened using Carbon Fiber Reinforced Polymer (CFRP) sheets. One non-strengthened control column and twelve specimens with different lengths and orientation of deficiencies were investigated. Eight of the deficient specimens were repaired using CFRP sheets. To study the effects of CFRP strengthening method on recovering the strength-lost in the deficient specimens, both experimental test and simulation modeling methods were used. In the experimental test, axial static gradual loading was utilized. To simulate the specimens, three dimensional (3D) modeling and non-linear static analysis methods using ABAQUS software were applied. The results indicated that application of CFRP sheets for strengthening of deficient steel short SHS columns could recover the strength-lost due to deficiency, significantly. Increment on the load-bearing capacity and delaying local buckling were also observed. Good accurateness between the experimental and numerical results were seen.

Experimental study and analysis of inner-stiffened cold-formed SHS steel stub columns

A series of axial compression tests was conducted to investigate the compressive behaviour of cold-formed steel stub columns with relatively thick walls (6mm and 10mm, respectively). Four different inner-stiffener arrangements were considered. Tensile coupons were cut from different parts of the square hollow section (SHS) sections to obtain a full picture of the enhanced material properties due to the cold-forming process. A finite element model was also developed and employed to provide a numerical perspective of the behaviour of the SHS columns. The applicability of two code-specified methods for the calculation of the strength of thin-walled cold-formed SHS columns for the present thick-walled cases is examined. The comparison shows that the AISI (and similarly AS/NZS) method tends to overestimate the sectional strength for the unstiffened and partially stiffened 6-mm thick columns, but predicts generally well (with slight underestimate) in the cases of well-stiffened 6-mm columns and all the 10-mm thick columns. The GB method, on the other hand, appears to predict well for all cases where the stiffening effect was less significant, but underestimates the sectional strength in the well-stiffened cases.

Tests of cold-formed duplex stainless steel SHS beam–columns

Stainless steel is gaining widespread use in construction due to its obvious special characteristics – attractive appearance, corrosion resistance and ease of maintenance, whilst beneficial mechanical properties such as high ductility, better fire resistance than carbon steel and high strength demonstrated by the duplex grades add value to its aesthetics. Reliable experimental investigation is a prerequisite to explore the full potential of stainless steel members and to evaluate the performance of the existing design rules. The current study describes a test program on cold-formed stainless steel square hollow section (SHS) members subjected to eccentric compression to examine the beam–column interaction, which is one of the least explored fields in structural stainless steel. Cross-sections are produced from duplex stainless steel grade with the measured yield stress up to 700MPa, for which material properties were obtained by tensile coupons cut from within the cross-sections. A total of 20 specimens are tested with initial geometric imperfection being measured at mid-height of each beam–column specimen. The specimens were placed between knife-edge supports to simulate an ideal pin-ended boundary condition at both ends. The column lengths were 550 and 1100mm, and each specimen was subjected to compression loading with eccentricity varying from 0 to 60mm. The test results were compared with those predicted using the American and the Australian/New Zealand design specifications for cold-formed stainless steel structures. It is observed that the code predictions are mostly conservative for stainless steel beam–columns with rooms for improvement in the current design guidance.

Inclined concrete-filled SHS steel column to steel beam joints under monotonic and cyclic loading: Experiments

Inclined concrete-filled steel tubular (CFST) columns have been applied in some construction projects recently, and they are usually connected with either I-shape or box steel beams in buildings. This paper presents a serial of test results of joints consist of inclined concrete-filled square hollow section (SHS) steel columns and box steel beams. A total of 24 specimens modelled as exterior joints were tested in the program. The parameters investigated included the column type, the joint type and the loading type. The failure modes, the strength and stiffness degradation and the energy dissipation of these composite joints were studied. Discussions on classification of these composite joints were made referencing existing codes. The test results showed that these composite joints reached more than 0.04rad before loads dropped to 85% of the ultimate strength under monotonic loading, and the specimens with both internal and external diaphragms exhibited the most favourable seismic performance among these joints.

Mathematical modelling of yielding shear panel device

Passive control devices are used in structures to dissipate seismic energy with a view to minimise damages to the major structural components. A relatively new device, yielding shear panel device (YSPD), to exploit the shear deformation of thin metal plates to absorb energy has recently been developed. YSPD is formed by welding a thin steel plate within a steel square hollow section (SHS) and its behaviour is determined by complex interactions among the thin diaphragm plate, the surrounding SHS and the boundary conditions. Available experimental results show that YSPD produces nonlinear pinching hysteretic force–displacement response when subjected to cyclic loading. This paper proposes a mathematical model to predict the hysteretic response using easily available parameters, i.e. the geometry of the YSPD and the properties of the material. Results obtained from the verified finite element (FE) models are used to calibrate the proposed models, which should facilitate the full scale modelling of building frames retrofitted with YSPD.

Capacities of Concrete-filled Steel Beams of Unequal Double Spans by Testing and Code

This paper presents an experimental investigation on flexural capacity of square hollow section (SHS) steel and concrete-filled square hollow section (SHS) steel tube. Beams with unequal double spans and subjected to point loads at the middle of each span were tested. Comparison was made on the flexural capacity and ductility of bare SHS steel and concrete-filled SHS steel tubes. The moment capacities obtained by the design method in code of practice for structural uses of steel 2005 – CoPHK were compared with experimental results reported in this paper.

Design of cold-formed stainless steel tubular T- and X-joints

This paper describes the numerical investigation of cold-formed stainless steel tubular T-joints, X-joints and X-joints with chord preload using finite element analysis. The stainless steel joints were fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. The geometric and material nonlinearities of stainless steel tubular joints were carefully incorporated in the finite element models. The joint strengths, failure modes as well as load-deformation curves of stainless steel tubular joints were obtained from the numerical analysis. The nonlinear finite element models were calibrated against experimental results of cold-formed stainless steel SHS and RHS tubular T- and X-joints. Good agreement between the experimental and finite element analysis results was achieved. Therefore, an extensive parametric study of 172 T- and X-joints was then carried out using the verified finite element models to evaluate the effects of the strength and behaviour of cold-formed stainless steel tubular joints. The joint strengths obtained from the parametric study and tests were compared with the current design strengths calculated using the Australian/New Zealand Standard for stainless steel structures, CIDECT and Eurocode design rules for carbon steel tubular structures. Furthermore, design formulae of cold-formed stainless steel tubular T- and X-joints are proposed. A reliability analysis was performed to assess the reliability of the current and proposed design rules. It is shown that the design strengths calculated using the proposed equations are generally more accurate and reliable than those calculated using the current design rules.

Recycled aggregate concrete filled steel SHS beam-columns subjected to cyclic loading

The present paper provides test data to evaluate the seismic performance of recycled aggregate concrete (RAC) filled steel square hollow section (SHS) beam-columns. Fifteen specimens, including 12 RAC filled steel tubular (RACFST) columns and 3 reference conventional concrete filled steel tubular (CFST) columns, were tested under reversed cyclic flexural loading while subjected to constant axially compressive load. The test parameters include: (1) axial load level (n), from 0.05 to 0.47; and (2) recycled coarse aggregate replacement ratio (r), from 0 to 50%. It was found that, generally, the seismic performance of RACFST columns was similar to that of the reference conventional CFST columns, and RACFST columns exhibited high levels of bearing capacity and ductility. Comparisons are made with predicted RACFST beam-column bearing capacities and flexural stiffness using current design codes. A theoretical model for conventional CFST beam-columns is employed in this paper for square RACFST beam-columns. The predicted load versus deformation hysteretic curves are found to exhibit satisfactory agreement with test results.

Composite steel–CFRP SHS tubes under axial impact

Abstract Composite steel–carbon fibre reinforced polymer (CFRP) tubes combine the benefits of the stable, ductile plastic collapse mechanism of the steel and the high strength to weight ratio of the fibre/resin composite, to form a composite tube with high energy absorption capability. This paper presents experimental results of square hollow section (SHS) composite steel–CFRP tubes subjected to axial impact. A number of different steel SHS geometries and two different matrix layouts of the CFRP are investigated. The dynamic results are compared with quasi-static results of composite steel–CFRP SHS and dynamic results of steel SHS and CFRP SHS. It is shown that the crashworthiness properties of load uniformity and specific energy absorption of the composite steel–CFRP tubes exceed those of the steel-only and CFRP-only tubes. An additional advantage of the CFRP application technique is that the CFRP may be retro-fitted to existing steel tubes, and the energy absorption capacity is shown to be markedly improved by such application. A theoretical method to calculate the dynamic mean crushing load which includes the effects of strain-rate is shown to compare well with the experimental results.

Plastic mechanism analysis of steel SHS strengthened with CFRP under large axial deformation

Carbon fibre reinforced polymer (CFRP) strengthening of structures has been gaining increasing interest, traditionally in application with concrete structures, and more recently in application with steel structures. This paper presents experiments and plastic mechanism analysis of steel square hollow section (SHS) tubes strengthened using externally bonded CFRP, deforming in an axi-symmetric collapse mode under quasi-static large deformation axial compression. The fold formation process of the stub column was such that the flat sides formed the well-known roof mechanism. The collapse proceeded progressively by folding about concentrated hinge lines and yielding of the four corners. An expression for the plastic collapse axial load was obtained by equating the total energy absorbed in bending and yielding to the external work carried out during deformation of the composite tube. The predicted instantaneous post-buckling and mean collapse loads are shown to compare well with the experimental results.

Nonlinear analysis of concrete-filled steel SHS and RHS columns

This paper presents an accurate nonlinear finite element model for the behaviour and design of axially loaded concrete-filled square hollow section (SHS) and rectangular hollow section (RHS) steel tube columns. The nonlinear material models for confined concrete and steel tubes were carefully modeled in the finite element analysis. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled SHS and RHS steel tube columns. The study was conducted over a wide range of concrete cube strengths ranged from 30 to 110 MPa. The overall depth of the steel tube-to-plate thickness ratio ranged from 10 to 40 covering compact SHS and RHS steel tube sections. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results obtained from the parametric study, it is found that the design strengths calculated using the American Specifications and Australian Standards are conservative, while the design strengths calculated using the European Code are accurate, except for the concrete-filled RHS compact steel tube columns having the overall depth of the steel tube-to-plate thickness ratio of 40.