Application of a PIP Slip Joint Consisting of Square Hollow Sections: A Numerical Approach

The structural behaviour and design of stainless steel hollow sections in fire, including stainless steel (i) circular hollow sections (CHS), (ii) elliptical hollow sections (EHS), (iii) square hollow sections (SHS) and (iv) rectangular hollow sections (RHS), are explored in this paper. Shell finite element models of stainless steel CHS, EHS, SHS and RHS able to replicate their structural response at elevated temperatures are created. Numerical parametric studies are performed on cold‐formed and hot‐rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS subjected to (i) pure compression, (ii) pure bending, (iii) combined axial compression and bending and (iv) combined bending and shear in fire, covering different cross‐section slendernesses and elevated temperature levels. Calibrated against the benchmark structural performance data obtained from the numerical parametric studies, the new design proposals for predicting the ultimate resistances of stainless steel CHS, EHS, SHS and RHS in fire put forward in Quan and Kucukler [1,2] are set out. It is demonstrated that relative to the design recommendations provided in the European structural steel fire design standard EN 1993‐1‐2, the proposed cross‐section design methods provide more accurate and safe‐sided ultimate resistance predictions for stainless steel CHS, EHS, SHS and RHS at elevated temperatures.

Behaviour of square hollow section brace-H-shaped steel chord T-joints under axial compression

This chapter focuses on the mechanical performance of fibre reinforced polymer (FRP) columns with square hollow sections (SHS) in axial compression. Width-thickness ratio (b/t) is an important geometric parameter for the local buckling of plates and therefore also for such SHS columns. The effects of b/t on the failure modes and load-carrying capacities of pultruded glass fibre reinforced polymer (GFRP) SHS columns are investigated in this chapter. Two SHS with different b/t values of 10.7 and 15.9 respectively are examined under axial compression. Experimental results reveal that local buckling occurs in section B (b/t = 15.9) but not in section A (b/t = 10.7). From a theoretical analysis, a formulation of critical b/t values is established at the boundaries between the failure modes of such GFRP SHS columns under compression, considering the different boundary conditions of the SHS side plates. It is commonly understood that global buckling occurs in columns with higher non-dimensional slenderness λ. This is only true when the width-thickness ratio b/t is less than the derived critical value. Experimental results from this study and previous literature are consistent with the developed theoretical estimations of failure modes and load-carrying capacities for GFRP SHS columns, considering the effects of both non-dimensional slenderness, λ, and width-thickness ratio, b/t.

Welded tubular square hollow section (SHS) joints are widely used in numerous structures such as steel bridges and tower structures. These structures are susceptible to fatigue failure caused by cyclic axial loadings, in-plane and out-of-plane loadings. Concrete filling the hollow section of the joints' chord is necessary to improve the strength of structures and their fatigue life and decreases stresses at the hot spot locations of the joints. Concrete-filled SHS/RHS members are also briefly included in the review to show the benefits of concrete-filled tubes under fire impact and bearing. There is no existing fatigue design guide for welded composite tubular joints due to limited results relating to the concrete grades, size range of hollow structural steel sections and joint types. The purpose of this paper is to summarise and present researches that have been conducted on empty and composite SHS joints under static and fatigue loadings and highlight the research gap. Previous experimental studies and/or numerical studies on tubular SHS joints with concrete-filled chords and empty joints with SHS are studied and summarised. Recommendations for future work are given.

Experimental study on additive manufactured 304L stainless steel tubular sections: Material properties and cross-sectional behavior

Wire arc additive manufacturing (WAAM), a method of directed energy deposition (DED) for metal 3D printing, is capable of producing intricate parts at a relatively high rate and low cost. Despite the great potential of WAAM for applications in construction, knowledge of the performance of WAAM structural elements is still lacking, and the geometric freedom is yet to be fully harnessed. This study is therefore aimed at investigating the local buckling behaviour of carbon steel WAAM elements and exploring the opportunity for improved structural efficiency through optimisation. An optimisation study was initially conducted to derive optimal stiffener layouts for square hollow sections (SHS) under compression. A total of six plain SHS with a broad range of width-to-thickness ratios, along with two SHS strengthened with optimised stiffeners, were manufactured via WAAM and tested. The six benchmark WAAM SHS profiles were examined to allow direct comparisons with conventionally-produced SHS. 3D laser-scanning was carried out to capture the geometric features of the WAAM specimens, and digital image correlation (DIC) was adopted for the full-field measurement of their structural responses during testing. The WAAM SHS stub columns were shown to have comparable load-carrying capacities to conventionally-produced SHS in the stocky range, but exhibited inferior local buckling behaviour in the slender range. Comparisons with the Eurocode 3 (EC3) resistance predictions showed that the existing Class 3 slenderness limit and effective width method specified in EC3 for plated structures may be overly optimistic for WAAM steel elements owing to their typically larger geometric imperfections. Finally, the SHS strengthened with optimised stiffeners were shown to exhibit significantly improved structural efficiency over both the WAAM and conventionally-manufactured plain SHS, bringing disproportionate increases in load-carrying and deformation capacity relative to the increases in mass.

This paper presents experimental and numerical investigations on the tensile performance of the elliptical one-sided bolted joints in building applications. Two types of joints are examined including the T-stub joints and T-hollow joints, where T-stub joints are formed by two T-stubs connected together through elliptical one-sided bolts at their flanges; and T-hollow joints are formed by two T-stubs connected to a square hollow section (SHS) member with the help of the elliptical one-sided bolts. A group of T-stub joints with ordinary bolts is also comparatively studied. Similar failure modes were observed for either elliptical one-sided or ordinary bolted joints while the yield capacity for elliptical one-sided joints was 9% lower than that of ordinary bolted joints for the T-stub joints. Parametric studies are further carried out on the key parameters such as flange thickness of the T-stubs and wall thickness of the hollow section members in the T-stub and T-hollow joints. It is found that the joint stiffness and strength can be improved with the increase of flange thickness or wall thickness for T-stub and T-hollow joints. Analytical models based on the yield line mechanisms are then presented, providing mechanism-based understanding for such elliptical one-sided joints in structural assembly. Detailed finite element (FE) models were constructed with considerations of bolt pre-tensioning and contact behaviours such as those between T-stub flange and bolt head. The deformed configurations of specimens can be successfully described by the FE modelling and the differences on initial stiffness and yield capacity between experimental and FE results are within about 10%.

The aim of this rigorous parametric study is to explore the influence of perforations on the local buckling behavior of square hollow sections (SHSs) possessing non-uniform wall thickness. A finite element procedure followed in the current study has been first validated against existing test results documented for the local buckling behavior of the perforated SHS with uniform web and flange segment thickness under axial compression. The linear elastic eigenvalue buckling and elastoplastic buckling analyses have been implemented using the Abaqus engineering finite element code. The verification of the numerical procedure has been achieved by favorably comparing the finite element results with the existing test results in terms of the first local buckling mode shape and load-end shortening curves of the perforated SHS with uniform wall thickness. . The verified numerical procedure has been applied to the problem of finding the perforation effect on the local buckling response of the SHS with non-uniform thickness. Finite element analyses have been performed for four various web width-to-perforation diameter ratios ranging from 0.3 to 0.9. Finite element analysis results have revealed that the presence of perforations does not influence the local buckling mode shape of the SHS but considerably affects the critical local buckling loads. The results have put forth that increasing perforation diameter leads to a more pronounced and drastic decrease in the critical local buckling load. The outcomes of the study have also shown that the critical post-buckling load of the SHS with non-uniform wall thickness is less susceptible to perforations compared to the SHS with uniform wall thickness. The results obtained in the context of this parametric study have been made available to practical engineering for use in actual design of the perforated SHSs.

This article presents a study of the wind-resistance and seismic behavior of steel frame elevator structures with square hollow section (SHS) members. The study was conducted by numerical analysis, it begins by examining the semi-rigid performance of SHS T-joints (beam-column joints) under in-plane bending moment, proposes a semi-rigid connection model for the joints, and then investigates the influence of semi-rigid joint effect on the performance of the steel elevators. Finite element (FE) results showed that the semi-rigid model can predict the moment-rotation response of the beam-column joints. The results also showed that the natural vibration period of the elevator with semi-rigid joints is 20% higher than that of an elevator with rigid joints. The semi-rigid joint effect causes the lateral drift of the elevator to increase by more than 47% under wind load, causing the maximum story drift of the elevator to exceed the limit specified in the current code. The semi-rigid joint effect causes the lateral displacement of the elevator to increase by approximately 15%–30% under the seismic waves of a rare earthquake.

Square hollow section (SHS) T-joints with concrete-filled chords subjected to in-plane fatigue loading in the brace

This parametric study examines the influence of residual stresses from light and heavy welding on the local elastic buckling behavior of square hollow sections (SHSs) with welded corners, under axial compression and major axis bending. By analyzing various SHS sizes with a constant height-to-thickness ratio of 40, this investigation provides insights into how residual stress levels impact load-bearing capacity. Findings reveal a pronounced impact of heavy welding-induced residual stresses, notably diminishing the critical buckling loads across both loading conditions. Specifically, under axial compression, heavy welding led to a significant reduction in bifurcation loads by approximately 15.3%, while light welding caused a reduction of around 7.5%. In major axis bending, the effects were similarly considerable, with bifurcation moments reduced by approximately 12.78% for heavy welding and by 6.16% for light welding. The findings underscore the substantial effect of residual stress, particularly from heavy welding, on axial compression, indicating a greater sensitivity of SHSs to this loading condition relative to major axis bending. This study emphasizes the need for careful consideration of welding type in design practices to ensure structural reliability.

Precise control of tube deformation during rotary draw bending is critical for automotive, structural, and piping applications to avoid rework and scrap. This study investigates the deformation behavior of circular (CHS) and square (SHS) tubes during rotary draw bending to provide practical guidelines for defect-free manufacturing. This study investigates the deformation behavior of circular hollow section (CHS) and square hollow section (SHS) tubes during rotary draw bending, focusing on springback, ovalization, and wrinkling phenomena. The experimental specimens consisted of ASTM A36 tubes: circular hollow sections (CHS) with an outer diameter of Ø25 mm and square hollow sections (SHS) with a nominal cross-section of 25 × 25 mm. Each geometry was tested at wall thicknesses of 0.7, 0.8, and 1.0 mm. The specimens were bent at angles of 30°, 60°, and 90° under controlled conditions. Experimental results reveal that CHS consistently exhibits lower springback (≈ 2.5–5.0°) and ovalization (≈ 7–14%) than SHS, which reached up to 7.0° springback and 16.6% ovalization. Wrinkling defects were observed exclusively in SHS, occurring in 100% of specimens at 90° with 0.7–0.8 mm wall thickness. ANOVA confirmed tube geometry as the dominant parameter (F = 764, p 0.001), followed by bending angle and wall thickness, with no significant interactions. Unlike prior studies analyzing CHS or SHS individually, this work provides a systematic comparison under identical conditions, bridging experimental validation with practical guidelines. The findings highlight the decisive role of cross-sectional geometry in tube bending mechanics and suggest minimum thickness thresholds and compensatory tooling strategies for defect-free manufacturing.

Welded tubular square hollow section (SHS) joints are widely used in numerous structures such as steel bridges and tower structures. These structures are susceptible to fatigue failure caused by cyclic axial loadings, in-plane and out-of-plane loadings. Concrete filling the hollow section of the joints' chord is necessary to improve the strength of structures and their fatigue life and decreases stresses at the hot spot locations of the joints. Concrete-filled SHS/RHS members are also briefly included in the review to show the benefits of concrete-filled tubes under fire impact and bearing. There is no existing fatigue design guide for welded composite tubular joints due to limited results relating to the concrete grades, size range of hollow structural steel sections and joint types. The purpose of this paper is to summarise and present researches that have been conducted on empty and composite SHS joints under static and fatigue loadings and highlight the research gap. Previous experimental studies and/or numerical studies on tubular SHS joints with concrete-filled chords and empty joints with SHS are studied and summarised. Recommendations for future work are given.

The provisions in the design guides such as BS7910 (2005) and RP579/ASME FFS–1 (2007) are applicable only for uni-planar tubular circular hollow section (CHS) joints, and it is strictly not applicable for cracked square hollow section (SHS) joints. In this study, a completely new and robust finite element (FE) mesh generator is developed to model cracked SHS joints. The new automatic FE mesh generator is validated using the previous experimental test data as well as with the existing commercial software results. The new FE mesh generator is able to overcome the drawbacks of the previous mesh generator approaches as well as achieves convergence of solutions even at a very high plastic deformation. The new FE mesh generator is further used in the parametric study and a new set of equations are proposed for determining the weld toe magnification factor of cracked double-sided T-butt joints and cruciform X-joints subjected to both axial and bending loading. Extensive parametric study is carried out for uni-planar SHS T-, Y- and K-joints and multi-planar SHS TT-, YT- and KT-joints subjected to axial tensile loading at the brace end. Subsequently, new equations for determining the reduction factor (FAR) of above mentioned SHS joints are proposed. The results reveal that the crack area and the brace to chord width ratio (β) have a significant influence on the plastic collapse load (Pc) of the cracked SHS joints. It is also concluded that the additional multi-planar brace increases the Pc load of cracked SHS joints. The highest level, Level 3C failure assessment diagram (FAD) curve of cracked SHS joints is constructed using the full numerical results of the elastic J-integral (Je), elastic-plastic J-integral (Jep) values and Pc load. It is found that standard Level 2A curve of the BS7910 (2005) is not always safe in assessing the safety and integrity of cracked SHS joints. Therefore, penalty factors of 1.2 and 1.1 for Pc load are recommended to move all the constructed Level 3C FAD curves above the standard Level 2A curve for cracked uni-planar and multi-planar SHS joints. These new Level 3C FAD curves are found to produce optimal solutions and they can be used to assess the safety and integrity of cracked uni-planar SHS T-, Y- and K-joints, and multi-planar SHS TT-, YT- and KT-joints.

In order to investigate the effect of fiber reinforced plastic (FRP) and rubber layers on the static and dynamic behaviour of aluminium square hollow section (SHS) member five different specimens have been tested by measuring the static deflection and vibration damping. The FRP layers increase the bending stiffness but have no significant effect on damping. The damping can be increased by a rubber layer at the neutral axis of two combined hollow sections, but this layer decreases the bending stiffness. The static and dynamic bending theory of sandwich beams with thick faces is suitable for the calculation of deflections and loss factors of beams constructed from two SHS profiles, a rubber layer glued between them and FRP layers.