Square Hollow Section Research Articles

Fatigue Performance of Bird-Beak SHS Gap K-Joints under Brace In-Plane Force

This paper presents a test campaign concerning the fatigue behavior of the bird-beak square hollow section (SHS) gap K-joints subjected to brace in-plane force. A total of four bird-beak SHS gap K-joint specimens were tested. Prior to the high-cycle fatigue tests, static in-plane force was applied to the braces of K-joint to determine the hot-line strain distributions and the stress concentration factors (SCFs) via extrapolation. Based on the results of static loading tests, the amplitude of cyclic load can be further determined. Subsequently, high-cycle fatigue tests were performed on the square and diamond bird-beak SHS gap K-joints to investigate the fatigue behavior from different perspectives, such as failure mode, fatigue life, crack propagation, and stiffness degradation. The test results demonstrate that the brace crown region always possessed the most severe stress concentration, which coincided with the location of crack initiation. This implies that the experimentally obtained SCFs can accurately predict the crack initiation location. The test fatigue lives of bird-beak gap K-joints were compared with the predictions by the International Institute of Welding (IIW) Srhs–N design curves originally developed for the conventional joints.

Axial-Load Resistance of a Novel UHPFRC Grouted SHS Tube-Sleeve Connection: Experimental, Numerical, and Theoretical Approaches

Experimental, numerical, and theoretical analyses were conducted of the axial load resistance of a novel ultrahigh-performance fiber-reinforced concrete (UHPFRC) grouted square hollow section (SHS) tube sleeve connection. The experimental study tested 10 full-scale specimens with varying shear key spacings, grout thicknesses, grout lengths, and volume proportions of steel fiber in the UHPFRC. Two types of failure modes were observed: (1) for the connection with high strength of the grouted part, the failure mode was fracture of the inner tube; and (2) for the connection with lower strength of the grouted part, the failure mode was grout shear crushing with significant bond-slip between grout and steel tube. To understand further the load transfer mechanism of the connection, an advanced three-dimensional (3D) nonlinear finite-element (FE) model was built to simulate the axial load–displacement behavior, state of stress and strain, and crack development of the grout. Based on the test and FE results, a new theoretical model was derived to predict the axial-load resistance of the connection. The proposed model considers the effect of section shape and material parameters, and is applicable to UHPFRC grouted SHS tube sleeve connection with different corner radii. Validation versus the test results showed that the new model can provide reasonably effective and accurate predictions of the axial-load resistance of the novel grouted sleeve connection subjected to tension.

Experimental, numerical and parametric studies on stress concentration factors of T-joints under tension

This paper investigates the behaviour of square hollow section (SHS) T-joints under static axial tension for the determination of stress concentration factors (SCFs) at the hot spot locations. Five empty and corresponding concrete-filled SHS-SHS T-joint connections were tested experimentally and numerically. The experimental investigation was carried out by attaching strain gauges onto the SHS-SHS T-joint specimens. The numerical study was then conducted by developing three-dimensional finite element (FE) T-joint models using ABAQUS finite element analysis software for capturing the distribution of the SCFs at the hot spot locations. The results showed that there is a good agreement between the experimental and numerical SCFs. A series of formulae for the prediction of SCF in concrete-filled SHS T-joints under tension were proposed, and good agreement was achieved between the maximum SCFs in SHS T-joints calculated from FE T-joint models and those from the predicted formulae.

An Efficient Approach to Describe the Fiber Effect on Mechanical Performance of Pultruded GFRP Profiles

This study focuses on the flexural behavior of pultruded glass fiber-reinforced polymer (GFRP) profiles developed for structural applications. Fiber content is a commonly accepted measure for estimating the resistance of such components, and technical datasheets describe this essential parameter. However, its direct implementation to the numerical simulations can face substantial problems because of the limitations of standard test protocols. Furthermore, the fiber mass percentage understandable for producers is unsuitable for typical software considered the volumetric reinforcement content. This manuscript exemplifies the above situation both experimentally and analytically, investigating two GFRP square hollow section (SHS) profiles available at the market. A three-point bending test determines the mechanical performance of the profiles in this experimental program; a digital image correlation system captures deformations and failure mechanisms of the SHS specimens; a standard tensile test defines the material properties. A simplified finite element (FE) model is developed based on the smeared reinforcement concept to predict the stiffness and load-bearing capacity of the profiles. An efficient balance between the prediction accuracy and computation time characterizes the developed FE approach that does not require specific descriptions of reinforcement geometry and refined meshes necessary for modeling the discrete fibers. The proposed FE approach is also used to analyze the fiber efficiency in reinforcing the polymer matrix. The efficiency is understood as the model’s ability to resist mechanical load proportional to the dry filaments’ content and experimental elastic modulus value. Scanning electron microscopy relates the composite microstructure and the mechanical performance of the selected profiles in this study.

Evaluating mechanical efficiency of glass fibres in a polymer profile

This study focuses on the mechanical performance of pultruded glass fibre-reinforced polymer (GFRP) profiles developed for structural applications. Fibre content determines the tensile resistance of such components, and technical specifications describe this essential parameter. However, it does not determine the actual reinforcement efficiency. This manuscript illustrates the above inference both experimentally and analytically, investigating a GFRP square hollow section (SHS) profile available at the market. Standard tensile coupon test defines the material characteristics; a three-point-bending test determines the mechanical performance of the profile. A digital image correlation system captures deformations and failure mechanism of the SHS bending specimen. The developed finite element model with smeared reinforcement estimates the efficiency of the glass filaments, i.e. the ability to predict the actual mechanical resistance (flexural stiffness) under the assumption of the experimentally determined elasticity modulus of bare fibres. Scanning electron microscopy relates the composite microstructure and mechanical performance of the selected profile.

Structural performance evaluation of square hollow section column under compressive axial force with bending moment having different width‐thickness ratio

AbstractThe square hollow section (SHS) is commonly used for the column of the steel building structures in Japan. The moment‐resisting frame will resist the lateral force with the flexural manner of the columns. Under the seismic event, the bending moment will be significant, and the plastic hinge may be formed in the columns. It is crucial to understand the structural behavior at the component level to capture the structure system's ultimate limit state by computational simulation. Understanding the strength and the ductility is one of the essential aspects, but it is also crucial to know the structural elasto‐plastic behavior until the ultimate limit state. It is worthwhile to conduct the testing of the members under combined loading conditions. In this paper, the test results obtained from the different width‐thickness ratio SHS were reported. The forces subjected to the specimen were axial force and cyclic bending moment; therefore, the member was under combined loading condition. Collapse mode, maximum bending moment, and plastic deformation capacity were evaluated in consideration of the effect of the width‐thickness ratio; comparison study between the current design recommendation was also shown.

Shake Table Testing of Self‐Centring Concentrically Braced Frames

AbstractThe self‐centring system presented in this paper is a novel damage control technique designed to improve the resilience of concentrically braced frames (CBF) under seismic action. Namely, traditional CBFs can undergo large residual drifts following an earthquake event which can limit the opportunity for cost‐effective repair of the structure. Additionally, the gusset plates connecting the brace members to beams and/or columns can experience substantial rotations as a result of the compression buckling of the bracing members. Through the utilisation of post‐tensioning strands placed between flanges of beams, the novel self‐centring concentrically braced frame (SC‐CBF) system can return the frame to its original position after significant inelastic deformations experienced during large earthquakes, resulting in minimum residual drifts.In this paper, shake table testing of the aforementioned SC‐CBF system subjected to realistic earthquake loading is presented. The research is carried out as part of the H2020 “Seismology and earthquake engineering research infrastructure alliance for Europe” SERA project. Four sets of bracing configurations, incorporating varying square hollow section (SHS) braces and gusset plates were utilised in the shake table testing. Uniaxial loading with varying shake table accelerations was executed and the structural response evaluated using data from strain gauges (SG), load cells (LC), displacement transducers and accelerometers. The measured results provide information on the important parameters such as the tensile and compressive strength of the braces, post‐buckling capacity, gusset plate strains and post‐tensioning force. These findings are then presented and the crucial local and global response performance emphasised.

Experimental study on stainless steel blind bolted T-stub to square hollow section connections

This paper presents an experimental study on blind bolted T-stub to square hollow section (SHS) connections made by stainless steel. Experiments were conducted to investigate the structural behaviour (e.g., failure mode, load–displacement curve and load-carrying capacity) of T-to-SHS connections and their basic components, including bolts, T-stubs and SHSs. The effects of key parameters, such as bolt types, bolt layouts, tube thicknesses and specimen configurations, on the performance of T-to-SHS connections and the components were identified. Design formulas were proposed to estimate the load-carrying capacities of T-stubs and SHSs, which agree well with the experimental results. The experimental results on connections between T-stub and steel hollow sections will provide a basis for verifying numerical simulations and theoretical analysis to derive design equations for such stainless-steel connections.

Behavior of partially concrete-filled X-joints with CHS braces and SHS chord under axial compression

The paper experimentally studies the static behavior of partially concrete-filled X-joints with circular hollow section (CHS) braces and square hollow section (SHS) chord under axial compression. Totally 40 partially concrete-filled CHS-SHS X-joints were designed, including 20 X-joints with concrete-filled CHS braces and hollow SHS chord (CFCHS-SHS) and 20 X-joints with hollow CHS braces and concrete-filled SHS chord (CHS-CFSHS). The impacts of the brace diameter to chord width ratio (β = d/b) and chord width to double chord thickness ratio (γ = b/2 T) on the static behavior of CHS-SHS X-joints were experimentally studied. At the same time, the corresponding finite element analysis (FEA) models were established and validated by comparison with test results, and then an extensive parametric investigation was performed to study the effects of three main influential factors (τ, concrete filling position, and in-filled concrete strength) on the ultimate strength of CHS-SHS X-joints under axial compression. The test results show that the CFCHS-SHS X-joints and CHS-CFSHS X-joints exhibit completely different failure modes under axial compression. All CFCHS-SHS X-joints are failed with chord plasticization, while the local buckling of the brace members is the primary failure mode for the CHS-CFSHS X-joints. The ultimate strength and axial stiffness of CHS-CFSHS X-joints are significantly higher than those of CFCHS-SHS X-joints. However, the ductility of CHS-CFSHS X-joints is slightly superior to that of CFCHS-SHS X-joints. Based on the analyses of test results, the design equations derived from the simplified yield line model were put forward for the estimation of the ultimate strength of CFCHS-SHS X-joints, which was verified to be reasonable and accurate. In addition, the study also revealed that the total cross-section yield strength of the brace could be utilized to accurately predict the ultimate strength of CHS-CFSHS X-joints.

Static bearing capacity investigation of grouted square hollow section sleeve connection

As a pilot research for an aimed beam-column joint of steel prefabricated prefinished volumetric construction (PPVC) buildings, this study investigates the axial static bearing capacity of grouted square hollow section (SHS) sleeve connections via carrying out experimental tests. Ten specimens with different dimensions were tested to failure under monotonic axial compressive loading and their loading-displacement curves were measured and recorded. The effect of the grouted length, the shear-key spacing, and the grout strength to the bearing capacity of the grouted SHS sleeve connections are investigated in this study. It is found that the axial static bearing capacity of the specimens tested increases approximately in a linear manner with the grouted length increases and can reach the bearing capacity of the outer tube’s cross-section when the grouted length is sufficient. Besides, the benefits brought by the increment of the grout strength to the axial bearing capacity of the grouted SHS sleeve connection may depend on other parameters such as the shear-key size and spacing, the gap between two tubes, and the thickness of the outer tube. Therefore, more experimental tests are required to understand the effect of the grout strength comprehensively.

Numerical investigation and design rules for stress concentration factors of stainless-steel hybrid tubular joints

This paper describes a numerical study on stress concentration factors (SCFs) of stainless-steel hybrid tubular T-, Y- and X-joints with circular hollow sections (CHSs) and with square hollow sections (SHSs). The finite element models (FE models) were developed and validated against the corresponding test results available in the literature. The validated FE models were then utilized to perform an extensive parametric study containing 47 FE models for T-joints, 47 FE models for Y-joints and 47 FE models for X-joints. In total, 141 FE models were analyzed in the parametric study. The brace diameter to chord width ratio (β=d1∕b0), brace to chord thickness ratio (τ=t1∕t0) and chord width to thickness ratio (2γ=b0∕t0) were selected as the key geometric parameters in the parametric study. The SCFs at the hot spot locations obtained from the parametric study were compared against those calculated from the design formulae specified in the current design guidelines of the International Committee for the Development and Study of Tubular Structures (CIDECT). The comparison results show that the design formulae given in the CIDECT specification are not appropriate for predicting the SCFs of stainless-steel CHS-to-SHS hybrid tubular T-, Y- and X-joints. Therefore, new design equations were proposed in this study. It is shown that the values of SCFs calculated from the proposed design equations are generally in good agreement with the values obtained from the FEA.

Parametric study on axially loaded square hollow section T-joints at elevated temperature

The paper presents the numerical study of tubular square T-joints under fire conditions. The sequentially coupled thermal-displacement numerical model was proposed to examine the performance of square hollow section (SHS) joints. The developed finite element (FE) model was validated against available experimental test results and applied to study the influence of dimensionless parameters on the strength of SHS tubular T-joints at elevated temperatures. These parameters include brace-to-chord width ratio β, chord-width-to-thickness ratio γ, chord-to-brace thickness ratio τ and loading ratio nF. The obtained results show that the critical temperature of T-joints is mostly influenced by the loading ratio nF and β parameter. Different methods to obtain the joint resistance are presented. The strength of the joint obtained based on EN 1993-1-8 was compared with FE analysis, which showed that the decrease in the joint resistance in brace axial compression follows the curve of Young's modulus reduction factors. Finally, the strength of the joint was calculated based on the component method, with a temperature increase specified for each individual component. This method gave higher results in joint strength, when the non-uniform temperature distribution within the joint was taken into account.

Experimental and numerical study of notched SHS made of different S355 steels

This study compares the mechanical behaviour of square hollow sections (SHS) made of three different types of S355: cold-formed, hot-rolled and offshore steel. A material model and failure criterion for each steel type were calibrated based on quasi-static uniaxial tensile tests. The failure criterion applies a recently proposed through-thickness damage regularisation model with the purpose of accurately describing the load-bearing capacity using shell elements. Experimental three-point bending tests were conducted at both quasi-static and dynamic conditions. Notches were used to trigger failure in the tests. The cold-formed steel exhibited the highest yield stress of the three steel types, while the offshore steel displayed better ductility than the other two. The numerical simulations showed that a shell element model of the SHS incorporating the regularisation scheme was able to describe the material behaviour and predict failure.

Finite element analysis on the residual bearing capacity of axially preloaded tubular T-joints subjected to impacts

Understanding the dynamic behavior of tubular members is necessary for ensuring their safety, even when damaged after an impact. A nonlinear finite element analysis (FEA) was performed to evaluate the residual bearing capacity of axially preloaded square hollow section (SHS) T-joints subjected to impact loading. First, the Bao–Wierzbicki fracture criterion was used to simulate the failure modes and behavior of specimens subjected to static axial compression and impacts, and the numerical results were compared with experimental results in the literature. The bearing capacity error between the numerical and experimental results was within 10%, which verified the accuracy of the finite element (FE) model. Then, the local and global displacements of joints were distinguished with the central line displacement method, and 40 FE models were created. The dynamic responses of joints under impact loading were used to study the resistance mechanism. Joint deformation mainly manifested as outward buckling of the chord webs and indentation of the chord upper flange. The in-plane restraint and support by the brace of the chord increased with the brace–chord width ratio. Finally, the ultimate residual bearing capacity coefficient ψ was defined as the ratio of the ultimate bearing capacities of the impacted and reference specimen, and the influence of different parameters, including axial preloading, impact energy, brace–chord width ratio, and chord diameter, was explored. Axial preloading and impact energy showed a negative correlation with ψ, while the brace–chord width ratio and chord diameter showed a significant positive correlation with ψ.

FRP strengthened SHS beam-column connection under monotonic and large-deformation cyclic loading

Many civil applications use square hollow sections (SHSs) as members in beam-column connections which can be vulnerable under cyclic loading. Cyclic loadings from earthquakes, wind, waves and currents affect onshore and offshore civil infrastructure. In addition, these beam-column connections can become structurally inadequate through incremental service loads, design/fabrication errors and material property degradation over time. Due to this, it will be necessary to strengthen SHS beam-column connections to improve their performance under sustained monotonic and cyclic loadings. This paper treats the performance of SHS beam-column connections strengthened with externally bonded carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). Experimental investigations have been conducted on the bare, CFRP and GFRP strengthened SHS connections under monotonic and cyclic loading. Results show that under cyclic loading, both CFRP and GFRP strengthened SHS beam-column connections exhibit improved ultimate moment capacity, moment degradation behaviour, secant stiffness, energy dissipation capacity and plastic hinge behaviour compared to their bare counterparts. Under monotonic loading, both types of strengthened connections show higher moment capacity, secant stiffness and ductility. In addition, CFRP strengthening enhances the ultimate strength, while GFRP strengthening enhances the ductility.

Behaviour of Precast Concrete Beam-to-Column Connection with SHS Hidden Corbel Subjected to Monotonic Load

Beam-to-column connection is the most critical part of a precast concrete (PC) structure as it governs the integrity of the entire structure. In this study, a beam-to-column connection with square hollow section (SHS) hidden corbel was developed. A full-scale test was conducted on eleven T-subframe specimens with various configurations to investigate the behaviour of the connection under an incremental static load. The behaviour of the connection was evaluated in terms of the moment-rotation response and the mechanical properties were obtained by using the beam-line method. Due to the extensive usage of steel elements, the PC connect possessed a higher ultimate strength than the reinforced concrete (RC) connection. The moment resistance of the connection was largely contributed to by the hidden corbel embedded in the beam and column. However, the PC connection gave a lower stiffness, which resulted in a larger rotation deformation than the RC connection, and thus lowered its design strength. The PC connection was classified as semi-rigid and partial strength, and only specimen PC-3 was considered feasible for PC structures.

CFRP strengthening of steel beam curved in plan

Nowadays, one of the practical, fast and easy ways to strengthen steel elements is the use of Carbon Fiber Reinforced Polymer (CFRP). Most previous research in the CFRP strengthening of steel members has carried out on straight steel members. The main difference between horizontal curved beams and straight beams under vertical load is the presence of torsional moment in the horizontal curved beams. In the other words, the horizontal curved beams are analyzed and designed for simultaneous internal forces included bending moment, torsional moment, and shear force. The horizontal curved steel beams are usually used in buildings, bridges, trusses, and others. This study explored the effect of the CFRP strengthening on the behavior of the horizontal curved square hollow section (SHS) steel beams. Four specimens were analyzed, one non-strengthened curved steel beam as a control column and three horizontal curved steel beams strengthened using CFRP sheets (under concentrated load and uniform distributed load). To analyze the horizontal curved steel beams, three dimensional (3D) modeling and nonlinear static analysis methods using ANSYS software were applied. The results indicated that application of CFRP sheets in some specific locations of the horizontal curved steel beams could increase the ultimate capacity of these beams, significantly. Also, the results indicated when the horizontal curved steel beams were under distributed load, the increase rate in the ultimate capacity was more than in the case when these beams were under concentrated load.

Cold-formed high strength steel tubular beam-columns

High strength steel is used more often in a variety of civil engineering applications due to its high strength-to-weight ratio and cost effectiveness. This paper presents the experimental investigation on cold-formed high strength carbon steel tubular members subjected to combined compression and bending. The nominal 0.2% proof stresses of the test specimens were 700 and 900 MPa. The test specimens consisted of square hollow sections (SHS), rectangular hollow sections (RHS) and circular hollow sections (CHS). The material properties, global geometric imperfections of the specimens were measured. The behaviour of the beam-column members was investigated through testing 32 specimens which had a nominal member length of 1480 mm. The second order effects were also considered by measuring the mid-height deflections for all specimens. The compression and bending capacities, load-deformation histories and failure modes of the test specimens were also reported. The test results were compared with the values predicted from the American, Australian and European standards. Improved design recommendation is provided for cold-formed high strength steel tubular beam-columns. Based on the experimental results, finite element modelling methodology is also proposed.

Experimental study on material properties and stress concentration factors of stainless-steel hybrid tubular joints

This paper presents an experimental investigation to determine the stress concentration factors (SCFs) of stainless-steel hybrid tubular joints, connecting circular hollow sections (CHSs) with square hollow sections (SHSs) under axial loads. Austenitic stainless-steel (AISI 304 grade) was used to manufacture all specimens. In total, twelve experiments were conducted comprising T, Y and X joints. To obtain the material properties of stainless-steel hybrid tubular joints, tensile coupon tests were conducted. For each joint, eight unidirectional strain gauges were placed to measure the hot spot strain perpendicular to the weld toe and the strain parallel to the weld toe. To analyze the strain gauge data from experiments, the hot spot stress method was used, adopting the quadratic extrapolation method, to determine the SCFs of stainless-steel hybrid tubular joints. From the results of experiments, strain concentration factors and conversion coefficients were recommended for stainless-steel hybrid tubular joints. The maximum SCFs recorded from the experiments on the SHS chord and CHS brace of stainless-steel hybrid tubular joints were then compared against the design values calculated in accordance with the CIDECT Guideline 8 and the proposed design formulas by Tong et al. and Yin et al. for carbon steel hybrid tubular joints. It is shown that the current design formulas as prescribed in CIDECT Guideline 8, are conservative by around 20%, while determining SCFs of such stainless-steel hybrid tubular joints.

Experimental and numerical analysis of circular concrete-filled double steel tubular stub columns with inner square hollow section

A circular concrete-filled double steel tubular column (CFDST) with a square hollow section (SHS) as an inner tube is introduced as a new form of a composite column in the paper. A series of axial compression tests that are carried out on this new type of composite column is reported in this study. Three-dimensional models based on the finite element (FE) program ABAQUS are also developed for such columns employing a modified confined concrete constitutive model for the core concrete. The accuracy of the model is verified by comparing the FE model with the experimental results. The effects of various parameters on the load-axial strain response of CFDST short columns are studied by using the validated FE model. The suggested formulas based on the confined concrete model for calculating the bearing capacity of CFDST short columns are proposed.