Concrete-filled Chord Research Articles

Stress Concentration Factors of Concrete-Filled T-Joints under In-Plane Bending: Experiments, FE Analysis and Formulae.

Experimental and numerical investigations on seven cold-formed steel square hollow section (SHS) T-joints with concrete-filled chords were conducted for the determination of stress concentration factors (SCFs). The SCFs were experimentally determined using strain gauges and then numerically determined using Abaqus finite element analysis (FEA) software under static in-plane brace bending. Good agreement was observed between the two investigations. After validating the FEA results, a parametric study was conducted on the SCFs of concrete-filled SHS-SHS T-joints using Abaqus FEA to evaluate the effects of the non-dimensional parameters on the SCFs. Subsequently, design formulae for predicting the SCF of concrete-filled SHS-SHS T-joints subjected to in-plane bending were proposed. Comparable results were obtained between the numerical SCFs with SCFs calculated from the proposed design equations. The maximum SCF of concrete-filled SHS T-joints under in-plane brace bending occurred at different locations. The overall mean of the experimental reduction percentage in peak SCF due to concrete infill is 22% and the overall mean of the numerical reduction percentage in peak SCF due to concrete infill is 19%. The determination of SCFs in concrete-filled SHS-SHS T-joints under in-plane bending has been the subject of little research, and more information regarding the behavior of concrete-filled T-joints with SHS under in-plane bending needs to be provided to practicing engineers.

Design formulae for predicting the stress concentration factors of concrete-filled T-joints under out-of-plane bending

An experimental study was carried out on seven square hollow section (SHS) T-joint specimens with concrete-filled chords to determine the stress concentration factor (SCF) at the hot spot locations. A parametric study was then carried out on concrete-filled SHS-SHS T-joint models using ABAQUS software to determine the numerical stress concentration factor (SCF) at the hot spot locations. Sixty SHS-SHS concrete-filled T-joints were modelled and analysed under out-plane bending on the brace to study the effect of the non-dimensional parameters on the SCFs. The numerical SCFs from FEA were validated as comparable results of SCFs were obtained between the numerical and experimental studies. Proposed design formulae were developed for determining the SCF in SHS concrete-filled T-joints under out-of-plane bending. This was achieved by carrying out non-linear multiple regression analysis using the results of the parametric study. The maximum SCF in SHS T-joints with concrete-filled chord subjected to out-of-plane brace bending commonly occurred along lines A, B and C.

Experimental and numerical investigation of square hollow section joints and members under static and fatigue loadings: a review

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 and numerical investigation of square hollow section joints and members under static and fatigue loadings: a review

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.

Fatigue Behavior of Integral Built-Up Box Y-Joints between Concrete-Filled Chords with Perfobond Ribs and Hollow Braces

AbstractA novel integral built-up box Y-joint welded to rectangular hollow section braces and concrete-filled square hollow section chord stiffened by perfobond ribs was proposed and studied in fat...

Stress concentration factors in joints of square hollow section (SHS) brace and concrete-filled SHS chord under axial tension in brace

It has been shown that concrete filling of square hollow section (SHS) chords in trusses increases fatigue life at the joint between the chord and the SHS brace. Nonetheless, currently there are no expressions for the stress concentration factor (SCF) at these joints. In this study, a robust finite element investigation is carried out to examine SCF in 90° joints made up of empty SHS braces and concrete-filled SHS (CFSHS) chords under axial tension in the brace. Results were validated against experimental data. A comprehensive parametric study was then carried out on 80 FE models to generate a large database for SCFs, considering the effects of key non-dimensional parameters, namely; width ratio between brace and chord of 0.4–1.0, width to wall thickness ratio of the chord of 12.5–25, and wall thickness ratio between brace and chord of 0.25–1.0. Using multiple regression analyses, a series of formulae for SCF were developed for practical design applications. A comparison of SCFs in joints with hollow and concrete filled chords shows a 10–26% reduction in SCFs in concrete-filled chords, leading to better fatigue behavior.

Experimental study on joint resistance and failure modes of concrete filled steel tubular (CFST) truss girders

Concrete Filled Steel Tubular (CFST) structures are increasingly used not only for columns in tall buildings but also in the arch trusses of many arch bridges and in the truss girders of buildings and bridge decks. Therefore, the chords of Circular Hollow Section (CHS) truss arches and girders are increasingly filled with concrete, effectively making them CFST structures. In addition to the strength and stiffness of the CFST members, the failure mode of the CFST joint connecting them to the tubular member is also affected by the concrete filling. In this study, truss girders with different web arrangements were tested, and their behaviour investigated. The girders were not slender because they were designed to attain the peak limiting state for joint failure rather than chord failure due to bending moments. Moreover, two other types of girders were tested: one without concrete-filled chords (CHS girder) and another with only the upper chord filled with concrete; thus allowing an investigation of how a concrete-filled chord affects joint failure mode. The geometry of the CHS girder joints was such that only chord face failure and punching shear failure could occur. The former required an inward deformation that was prevented by the concrete filling in a CFST girder with similar geometry. Finally, the study considers extending the Eurocode 3 and the AWS D1.1 code formulae, originally proposed for CHS joints, to calculate the resistance of CFST joints.

Post-fire residual strength of steel tubular T-joint with concrete-filled chord

The post-fire behavior of steel tubular T-joints with a concrete-filled chord (CFC) was experimentally and numerically investigated. One specimen was tested at ambient temperature while the other two were tested after a heating and cooling process. The experimental results revealed that the failure mode was chord plastification, rather than local buckling of the chord wall, due to the support provided by the in-filled concrete. A finite-element (FE) method was then developed to simulate the structural response of the post-fire joints under compressive load. The comparison between the FE simulation and experimental data illustrated that the FE method reliably and accurately predicted the failure modes, the measured load-displacement curves and the residual strength of the T-joints. The verified FE method was then used in a detailed parametric analysis, which systematically varied the geometric and material parameters including α, β, τ, γ, fc, fy and the highest temperature of fire exposure-Tmax. The results indicated that filling concrete into the chord increased the fire resistance and bearing capacity of the joints, but had an appreciably negative impact on the post-fire behavior, as the damage to concrete in fire was irreparable. Moreover, the residual strength increased significantly with increasing fy, but decreased with increasing α and γ. β and fc showed slight influence, while changing τ had negligible effect. The effect of each parameter could be quantitatively simulated by a function. A parametric equation based on the effect was proposed, and its accuracy was verified through error analysis against the numerical and experimental results.

Fatigue behavior and design of welded tubular T-joints with CHS brace and concrete-filled chord

Concrete-filled welded tubular structures have been increasingly used in large-span constructions such as truss bridges where fatigue failure is always a critical issue that should be focused on. This paper deals with fatigue behavior of CHS-CFSHS T-joints, which are made up of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. Experimental results on stress concentration factor (SCF) were briefly summarized. Fatigue tests were conducted under cyclic tensile force in the brace, so that cracking patterns, failure modes and fatigue data of such joints were recorded. The tested CHS-CFSHS T-joints suffered from one of the following three failure modes: (i) brace-90°-side failure, (ii) chord-90°-side failure, (iii) chord-0°-side failure. Based on the fatigue data in terms of hot spot stress range (Sr,hs) versus number of cycles (N), fatigue design Sr,hs-N curves were determined using the deterministic and least-squares methods, respectively. It was found that most of the existing Sr,hs-N curves are unsafe for fatigue design of CHS-CFSHS T-joints, except for the X´ Sr,hs-N curve recommended by American Petroleum Institute [32] and American Welding Society [36]. In addition, the fatigue data of the CHS-CFSHS T-joints were found comparable with CHS-CFCHS T-joints (T-joints with CHS brace and concrete-filled CHS chord), hence a new fatigue design Sr,hs-N curve was proposed for the both types of concrete-filled joints. A comparison between CHS-CFSHS T-joints and empty CHS-SHS T-joints showed that CHS-CFSHS T-joints generally have better fatigue behavior compared to their empty counterparts except for the case of extremely large ratio of brace diameter to chord width (β).

Stress concentration factors test of reinforced concrete-filled tubular Y-joints under in-plane bending

To study the stress concentration factors (SCFs) of concrete-filled tubular Y-joints subject to in-plane bending, experiments were used to investigate the hot spot stress distribution along the intersection between chord and brace. Three concrete-filled tubular chords forming Y-joints were tested with different reinforcing components, including doubler-plate, sleeve, and haunch-plate reinforcement. In addition, an unreinforced joint was also tested for comparison. Test results indicate that the three different forms of reinforcement effectively reduce the peak SCFs compared with the unreinforced joint. The current research suggests that the linear extrapolation method can be used for chords, whereas the quadratic extrapolation method must be used for braces. The SCF is effectively reduced and more evenly distributed when the value of the axial compression ratio in the chord is increased. Furthermore, the SCFs obtained from the test results were compared to predictions from some well-established SCF equations. Generally, the predictions from those equations are very consistent for braces, but very conservative for concretefilled chords.

Investigation on SCFs of concrete-filled circular chord and square braces K-joints under balanced axial loading

Most of the research work has been conducted on K-joints under static loading. Very limited information is available in consideration of fatigue strength of K-joints with concrete-filled chord. This paper aims to describe experimental and numerical investigations on stress concentration factors (SCFs) of concrete-filled circular chord and square braces K-joints under balanced axial loading. Experiment was conducted to study the hot spot stress distribution along the intersection of chord and braces in the two specimens with compacting concrete filled in the chord. The test results of stress distribution curves of two specimens were reported. SCFs of concrete-filled circular chord and square braces K-joints were lower than those of corresponding hollow circular chord and square brace K-joints. The corresponding finite element analysis was also conducted to simulate stress distribution along the brace and chord intersection region of joints. It was achieved that experimental and finite element analysis results had good agreement. Therefore, an extensive parametric study was carried out by using the calibrated finite element model to evaluate the effects of main geometric parameters and concrete strength on the behavior of concrete-filled circular chord and square braces K-joints under balanced axial loading. The SCFs at the hot spot locations obtained from ABAQUS were compared with those calculated by using design formula given in the CIDECT for hollow SHS-SHS K-joints. CIDECT Design Guide was generally quite conservative for predicting SCFs of braces and was dangerous for predicting SCFs of chord in concrete-filled circular chord and square braces K-joints. Finally SCF formulae were proposed for circular chord and square braces K-joints with concrete-filled in the chord under balanced axial loading. It is shown that the SCFs calculated from the proposed design equation are generally in agreement with the values derived from finite element analysis, which were proved to be reliable and accurate.

Finite Element Analysis of Concrete-Filled Rectangular Steel Tubular Y-Connections under Tension

Rectangular steel truss Y-connections, whose chord is filled in concrete, is described. The behavior of Y-connections include hollow structural section and concrete-filled section loaded in tension is analyzed by means of finite element analysis. It is shown that there is a significant improvement in strength and stiffness of Y-connections with concrete-filled chord.

Fatigue and residual strength of concrete-filled tubular X-joints with full capacity welds

This paper presents the experimental findings on the fatigue performance and residual strength of the circular hollow section X-joints with a concrete-filled chord. The welding profile along the brace-to-chord intersection employs a recently proposed set of welding details, namely the full capacity tubular joint welds. The experimental investigation focuses on: 1) the stress concentration comparison corresponding to different stages of the specimen preparation, 2) the fatigue crack initiation life and propagation life; and 3) the comparison of the measured fatigue life with respect to the design S-N curves. The experimental measurement reveals that the fatigue crack propagation life contributes to a significant portion of the total fatigue life for both the hollow section tubular joints and the concrete-filled tubular joints. The total fatigue life of the test specimens complies with the life estimation based on the existing design S-N curves, originally developed for tubular joints fabricated using the complete joint penetration welds. The residual strength of the fatigue-cracked tubular joints follows approximately a linear relationship with respect to the percentage of the crack area along the brace-to-chord intersection.

Experiment investigation of stress concentration factor of concrete-filled tubular T joints

The aim of this paper is to study the stress concentration factors of concrete-filled tubular T joints subject to axial loading and in-plane bending. Experimental investigation was performed to investigate the Hot Spot Stress distribution along the intersection of chord and brace. Five tubular T joint specimens with self compacting concrete-filled chords were tested. In addition, three hollow steel tubular T joint specimens were also tested for comparison. Generally, it is shown that the concrete filling effectively reduces the peak stress concentration factors. The stress concentration factors obtained from the test results were compared against predictions from some well-established existing stress concentration factor equations. Generally, the predictions from those equations are very conservative for concrete-filled specimens.

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

In recent years, there has been an increased use of concrete-filled composite tubular joints in bridge construction. The reliability of these joints under fatigue therefore need to be investigated to avoid any catastrophic failures. In this paper, hollow section T-joints made up of square hollow section (SHS) chords and braces are investigated. The chords of the SHS–SHS T-joints were concrete-filled thereby forming welded composite tubular T-joints. The SHS–SHS T-joints with concrete-filled chords were strain gauged and tested under static loading to determine stress concentration factors (SCFs) at hot spot locations, where cracks are likely to propagate. Fatigue tests of the welded composite joints were also carried out under cyclic in-plane bending in the brace to obtain stress range vs. number of cycles ( S– N) data. The maximum stress concentration factor (SCF) at hot spot locations in a welded composite tubular T-joint was found to be generally lower than the maximum SCF in an empty (or called unfilled) hollow section SHS–SHS T-joint. Fatigue failure in welded composite tubular T-joints occurred through the initiation and propagation of cracks at weld toes in either the chord or brace member, with the majority of tests exhibiting the first visual crack at weld toes in the chord. The welded composite tubular T-joints were found to have better fatigue strength compared to the empty hollow section SHS–SHS T-joints. Design rules are recommended for the SHS–SHS T-joints with concrete-filled chords through analysis of fatigue test data using the hot spot stress method.

Investigation of concrete-filled stainless steel tubular X-joints

Experimental and numerical investigation of concrete-filled stainless steel tubular X-joints were conducted. The specimens were fabricated from square and rectangular hollow sections (SHS and RHS) with nominal concrete cylinder strength of 30 MPa filled in the chord members. The tests were performed by using steel bearing plates to transmit transverse compression force to the concrete-filled chord members. A numerical study was performed using finite element analysis. The geometric and material nonlinearities of stainless steel tubes as well as the concrete infill were carefully incorporated in the finite element model. The numerical results showed good agreement with the experimental results. Therefore, the parametric study was performed using the verified finite element model to investigate the strength and behaviour of concrete-filled stainless steel tubular X-joints. Chord face failure and chord side wall failure as well as crushing of concrete were the main failure modes observed in the parametric study. The joint strengths obtained from the parametric study and tests were compared with the design strengths calculated using the CIDECT design rules for concrete-filled carbon steel tubular joints. It is shown that the design strengths calculated using the existing design equations are quite conservative.