Concrete-filled Rectangular Hollow Section Research Articles

Monte Carlo simulation study on the reliability of concrete-filled HSS beam-column design provisions

Revisions were recently proposed to the way in which concrete-filled hollow structural section (HSS) members are handled in CSA S16. These revisions were based on previous research, comparisons to experiments, and a first-order reliability method analysis of existing provisions for compression and flexural members. In this paper, this topic is further expanded by using Monte Carlo Simulations (MCS) to determine the inherent reliability of the previous and new design rules for concrete-filled rectangular hollow section (RHS) and circular hollow section (CHS) beam-columns. A representative set of concrete-filled RHS and CHS members with variations in concrete strength, wall slenderness, effective length, and loading eccentricity are analyzed. Using MCS, the reliability index (β+) of each is determined over a range of live-to-dead load (L/D) ratios. Inherent β+ values are compared to the code-specified target (i.e., β+ = 3.0 per Annex B of CSA S16) and the CSA S16:19 and AISC 360-16 provisions.

Experimental and numerical analyses on stress concentration factors of concrete-filled welded integral K-joints in steel truss bridges

A novel fully welded concrete-filled integral K-joint incorporating longitudinal perfobond ribs welded to the inner faces of the chord is proposed to improve the fatigue behavior. To evaluate the stress concentration factor (SCF) of such joints, a 1:5 scale truss specimen was fabricated and tested to measure the SCF distribution in the fatigue prone joint. A finite element model was also developed to evaluate the SCFmax of concrete-filled welded integral K-joints and was validated against the test results. A parametric study was carried out and a comprehensive database was obtained considering the effects of brace width-to-chord thickness ratio (2γ), brace-to-chord thickness ratio (τ), the angle between braces and chord (θ) on the SCFmax. Also, the following three basic loading conditions were examined: brace axial force, chord axial force and chord in-plane bending. Based on the results of 192 numerical models, new equations to predict the SCFmax of concrete-filled welded integral K-joint were derived for design purposes. Finally, the fatigue behavior of three different designs is compared in terms of SCFmax and hot spot stress range Sh-N curves. These systems are rectangular hollow section (RHS) K-joints, concrete-filled rectangular hollow section (CFRHS) K-joints and concrete-filled welded integral K-joint. It was shown that the concrete-filled integral welded K-joint has the best fatigue behavior, followed by the CFRHS K-joint, while the RHS K-joint has the poorest fatigue behavior.

Investigations into Structural Behavior of Concrete-Filled RHS Columns with Unequal Flange Thickness under Compressive Load.

Previous studies have shown that components with an unequal-walled concrete-filled rectangular hollow section (CFRHS) can achieve a greater resistance under bending than those with equal-walled CFRHS. However, the study on the compressive behavior of the CFRHS column is limited. Therefore, this paper investigates the performance of compressed CFRHS columns with unequal flange thickness, based on experimental and numerical approaches. In the test, the effects of slenderness and eccentricity on the compressive capacity of the CFRHS columns with unequal shell thickness are discussed. Numerical models based on the finite element method are established, to evaluate the resistance and failure pattern of each specimen in the test. Parametric studies are carried out based on the validated model, to investigate the effect of eccentricity, wall thickness, and steel and concrete material properties on the load-bearing capacity of the compressed CFRHS column. In addition, the analytical expressions of the resistance of CFRHS columns with unequal wall thickness are derived, and the prediction values are validated through comparing with the test results. It is found that eccentric compressed columns with unequal-walled CFRHS have a similar load-bearing capacity and better ductility when compared with the equal-walled CFRHS.

Flexural behavior of concrete-filled SHS and RHS aluminum alloy tubes strengthened with CFRP

Conventional concrete-filled aluminum alloy tube (CFAT) can effectively delay the inward local buckling of aluminum alloy tube (AA). This paper experimentally and numerically investigates the suitability of strengthening square and rectangular hollow section (SHS and RHS) CFAT beams with a layer of carbon-fiber reinforcement polymer (CFRP) under four-point bending. Among 40 beams, 30 square and rectangular CFAT beams were strengthened with CFRP comprising three arrangement schemes of CFRP and 10 conventional square and rectangular CFAT beams were treated as reference beams. Flexural stiffness of square and rectangular CFAT beams are remarkably enhanced by external bonded CFRP, while the ductility is decreased. The bottom flange-bonded CFRP scheme is less effective in enhancing ultimate strength of CFAT beams than that of four sides-bonded CFRP scheme. New design approaches for evaluating both initial and post-yield flexural stiffness of square and rectangular CFAT beams strengthened with CFRP are proposed. FE models are correctly simulated to analyze the flexural behavior of square and rectangular CFAT beams strengthened with CFRP. CFRP strengthening technique using in this study can remarkably enhance the ultimate strength of square and rectangular CFAT beams and effectively delay the outward local buckling of AA tubes.

Stress concentration factor parametric formulae for concrete-filled rectangular hollow section K-joints with perfobond ribs

A new type of tubular joint made of rectangular hollow section (RHS) braces welded onto concrete-filled RHS (CFRHS) chords stiffened by longitudinally welding perfobond ribs to the inner faces has been studied earlier and demonstrated a better fatigue behaviour than a conventional empty RHS joint. In this paper, stress concentration factor (SCF) parametric design equations were developed for CFRHS K-joints with perfobond ribs through finite element (FE) analysis to fill a gap in current design guides for this type of K-joints. Three-dimensional FE models were developed using the ABAQUS software to simulate the hot spot stress distribution at the brace-chord intersection. FE results were successfully verified using experimental results of nine Y-joints from literature and one truss K-joint in this research. A comprehensive parametric study including 570 models was then carried out on CFRHS K-joints with perfobond ribs to examine the SCFs with five key dimensionless geometric parameters and three basic loading conditions involving axial loading in the chord and brace and bending in the chord. Consequently, a total of 36 SCF parametric equations were established using regression analysis. Subsequently, the number of formulae was reduced to six equations to predict the maximum SCFs for practical application.

Fatigue behaviour of non-integral Y-joint of concrete-filled rectangular hollow section continuous chord stiffened with perfobond ribs

This paper examines the fatigue behaviour of non-integral welded joint of rectangular hollow section (RHS) brace and a continuous concrete-filled RHS (CFRHS) chord stiffened by internal perfobond ribs. A total of eleven Y-joints, including two control specimens with hollow section chords, were tested under axial force in the brace. The effects of concrete infill and perfobond ribs on the stress concentration factors (SCFs) are examined. The crack-initiation fatigue life and loss-of-strength fatigue life were established. Comparisons of the measured fatigue life with existing experimental data of square hollow section (SHS) joints without concrete infill or perfobond ribs and with predictions made using design guides are also presented. The test results show that the same Sh-N curve based on the hot spot stress method can be adopted for RHS joints with and without concrete infill and perfobond ribs. However, a significant decrease of SCFs in CFRHS joints with perfobond ribs is observed compared to the RHS joints. In addition, for the full-width joints (β = 1), CIDECT and DNV design guides Sh-N curves overestimate the fatigue strength of CFRHS joint with perfobond ribs, while the API design guide underestimates its fatigue strength.

A review on application of composite truss bridges composed of hollow structural section members

Abstract Composite truss with hollow structural section (HSS) members is deemed as the structure applicable to large-span and heavily-loaded bridges. To promote the application of composite truss bridge with HSS members in China, this paper described its structural characteristics and technology in details. Besides, not only were 32 typical design cases of composite truss bridges with HSS members collected, but also the corresponding historical development was summed up. Comparisons on structural components, characteristics and engineering applications were made among composite truss bridges with HSS members in different structural forms. Then, the analysis on the characteristics of composite truss bridges with concrete-filled steel tubular (CFST) chords was conducted, and the challenges on the aspects of complicated joints and interfacial debonding were pointed out. To address these problems, the concrete-filled rectangular hollow section (CFRHS) stiffened with PBLs (Perfobond Ribs) was proposed to improve the reliability of confinement effect in CFST member and force transfer in joints. The advantages on the mechanical properties of CFRHS structure stiffened using PBLs were systematically expounded with respect to the behaviors of steel plate, interface, member and joint. Moreover, the structure design, construction technology, structural calculation and economic efficiency of the practical bridge with CFRHS chords stiffened using PBLs were comprehensively analyzed. The results demonstrated that composite truss bridge with PBL-stiffened CFRHS members was competitive in mechanical performance and construction.

Shear response of trapezoidal profiled webs in girders with concrete-filled RHS flanges

The present paper deals with the shear buckling response of trapezoidal profiled webs in girders with concrete-filled rectangular hollow section (RHS) flanges. It outlines an experimental work of four girders with shear buckled trapezoidal profiled webs in interactive and global manners. Characteristic strain distributions on the trapezoidal profiled webs are reported. The analysis of load-deformation responses indicates that the trapezoidal profiled web buckled in the global manner suffered greater strength drops at early stage and less strength improvement contributed by the concrete-filled RHS flange in contrast to those buckled in interactive manner with partial local buckling. Finite element models explicitly allowing for isolated trapezoidal profiled webs with varied side boundaries and visual girder models with proposed design ratios are then presented for 572 cases. It is shown that the first eigenmode shape and critical stressing of the trapezoidal profiled webs are most likely influenced when the shear buckling in local manner takes place. Related geometric ratios involved with shear span, web slenderness, trapezoid altitude and subpanel height are examined through a parametric study. Afterwards, an analytical formula incorporating a proposed rigidity ratio as well as a correlated contribution coefficient is proposed for the determining shear buckling strength of trapezoidal profiled webs in the girders with concrete-filled RHS flanges. The proposed formula is verified in contrast to referred ones through a comparative study which can be deemed suitable for the design of trapezoidal profiled webs in girders with concrete-filled rectangular hollow section (RHS) flanges.

Behaviour and analysis of concrete-filled rectangular hollow sections subject to blast loading

Concrete-filled Rectangular Hollow Sections have been tested under large-scale, far-field, air-blast loading for the first time. The concrete-filled, cold-formed steel tubes performed well under the blast loads, with a significant reduction in the global and local displacements compared to unfilled RHS members. The heavily instrumented tests provided a large quantity of response data that was used for the validation of numerical models. Numerical models of the concrete-filled steel tubes were first developed using explicit finite element methodologies. A parametric study was conducted with the validated finite element model to further characterize the response of the concrete-filled steel tubes under air-blast loading. The influence of several key variables on the response of the tubular members was determined and preliminary design guidance is provided. Finally, the test and finite element results were used to develop an idealized single-degree-of-freedom numerical model that is well-suited to future use in design problems.

Flexural behaviour of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP

This paper presents the experimental and numerical investigations on concrete-filled stainless steel square and rectangular hollow section (SHS and RHS) tubes subjected to in-plane bending. A total of 32 specimens were tested, in which one fourth of test specimens were unstrengthened for comparison. The ultimate strengths, failure modes, flexural stiffness, ductility and longitudinal strains of test specimens are reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. An extensive parametric study was carried out by using the verified finite element model to investigate the strengthening effect of CFRP on the flexural behaviour of concrete-filled stainless steel SHS and RHS tubes. It is shown from the comparison that the strengthening effect of CFRP was improved with the increase of the β value. Whereas, the ductility ratio was greatly deteriorated. Furthermore, the secant stiffness at 0.6Mu was recommended to be the flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP in the practical applications. On the other hand, the flexural strength and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes were increased with the increase of interface friction coefficient between stainless steel tube and concrete up to 0.6. The design formulae are also proposed for the flexural strengths and flexural stiffness of concrete-filled stainless steel SHS and RHS tubes strengthened by CFRP based on the current design rules for concrete-filled steel tubes by further considering the flexural strengths and flexural stiffness of the CFRP, which were verified to be accurate by the finite element analysis results.

Flexural behaviour of concrete-filled aluminium alloy thin-walled SHS and RHS tubes

This paper presents an experimental study on flexural behaviour of concrete-filled aluminium alloy thin-walled square and rectangular hollow section (SHS and RHS) tubes subjected to in-plane bending. A total of 30 specimens including 20 concrete-filled aluminium alloy tubes (CFAT) and 10 bare aluminium alloy tubes (BAT) were tested. The ultimate strengths, failure modes, flexural stiffness, ductility, bending moment-midspan deflection curves, overall deflection curves, bending moment-longitudinal strain curves and longitudinal strain distribution curves of test specimens are reported. It is demonstrated that the ultimate strength, flexural stiffness and ductility of the BAT specimens are significantly enhanced by filling the concrete in the specimen along its full length. Furthermore, the enhancement is increased with the increase of the concrete strength, but the increase of enhancement is insignificant. The measured flexural stiffness including both initial flexural stiffness and post-yield flexural stiffness were compared with the design flexural stiffness calculated using the current AIJ standard, BS 5400, Eurocode 4 and AISC specification. It is shown from the comparison that the current design rules for the bare steel tube (BST) and concrete-filled steel tube (CFST) are generally inappropriate for the flexural stiffness of the BAT and CFAT under pure in-plane bending with high scatter of predictions. Furthermore, the design equations were proposed for the ultimate strengths of CFAT under in-plane bending, which were verified to be applicable.

Concrete-filled rectangular hollow section X joint with Perfobond Leister rib structural performance study: Ultimate and fatigue experimental Investigation

This paper presents a series of ultimate and fatigue experimental investigation on concrete-filled rectangular hollow section (CRHS) X joints with Perfobond Leister rib (PBR) under tension. A total of 15 specimens were fabricated, in which 12 specimens were tested under ultimate tension and 3 specimens were investigated in fatigue test. Different parameters including PBR stiffening, brace-to-chord ratio (β) and inclined angle (&$952;) were considered in the test. Each joint was tested to failure under tension load. Obtained from test result, PBR was found to improve the tension strength and fatigue durability of CRHS joint substantially. Concrete dowel consisted by PBR and concrete inside the chord stiffened the joint, which leaded to a combination failure mode of punching shear and chord plastification of CRHS joint under tension. Finite element analysis validated the compound failure mode. Stress concentration on typical spot of CRHS joint was mitigated by PBR which was observed from fatigue test. Initial fatigue crack presented in CRHS joint with PBR also differentiated with the counterpart without PBR.

Flexural behaviour of concrete-filled stainless steel SHS and RHS tubes

This paper presents an experimental investigation on flexural behaviour of concrete-filled stainless steel square and rectangular hollow section (SHS and RHS) tubes under uniaxial bending. A total of 24 specimens including 16 concrete-filled stainless steel SHS and RHS flexural members and 8 empty stainless steel SHS and RHS flexural members were tested. The ultimate strengths, failure modes, flexural stiffness, ductility, bending moment-midspan deflection curves, overall deflection curves and strain distribution curves of test specimens are reported. It is demonstrated that the ultimate strength, initial stiffness and ductility of empty stainless steel SHS and RHS flexural members are significantly enhanced by filling the concrete in the specimen along its full length. The enhancement is increased with the increase of the thickness of the SHS and RHS tube. Furthermore, the concrete strength has little influence on the ultimate strength, initial stiffness and ductility of concrete-filled stainless steel SHS and RHS flexural members. The test flexural stiffness including both initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel SHS and RHS tubes under uniaxial bending are compared with the design flexural stiffness calculated using the current AIJ standard, BS 5400, Eurocode 4 and AISC specification for concrete-filled steel tubes. It is shown from the comparison that the current design rules are all unconservative for initial flexural stiffness and flexural stiffness at the serviceability limit state of concrete-filled stainless steel SHS and RHS tubes under uniaxial bending with high scatter of predictions.

Experimental investigation on fatigue strength of joints between SRC beams and concrete-filled RHS columns

Fatigue behavior, failure mechanism and fatigue strength of joints between steel reinforced concrete (SRC) beams and Concrete Filled Rectangular Hollow Section (CFRHS) columns is discussed in this paper. Three identical beam-to-column joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, they were loaded to failure under increased fatigue load in order to know failure mechanism and fatigue strength. It is found that the joints satisfied design requirements when subjected to static loading and design fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading. The crack initiated at the weld toe of stud or stirrup hole in the upper flange of I-shaped steel in certain SRC beam, and then it propagated along flange width in winding trajectory until fatigue fracture occurred. Stress amplitude of tension flange in SRC beam can be regarded as the parameter representing fatigue strength of the joints. S-N curves in related codes are selected to evaluate fatigue strength of the joints. The design method is suggested to consider fatigue design of the joints.

Component-Based Mechanical Models for Concrete-Filled RHS Connections with Diaphragms under Bending Moment

One component-based mechanical model is presented in this paper to predict the flexural strength of through-diaphragm connections between concrete-filled RHS columns and H-beams. Three parts are contributed to the overall flexural strength of the connections: the failure of the through-diaphragm, the bending action of the column tube, and the tensile membrane action of the column tube. The component-based strength model is based upon defining a rigid plate deformation pattern for the connection under bending moment and then applying the virtual work principle. The proposed model is capable of predicting the ultimate flexural strength of the connections. The developed model is validated against a series of experiments with varied dimensions of column tubes and diaphragms. The results showed that the derived strength equation provided a reasonable prediction.

Component-based mechanical models for axially-loaded through-diaphragm connections to concrete-filled RHS columns

This paper presents the results of theoretical studies into the behavior of the through-diaphragm to concrete-filled rectangular hollow section (RHS) columns subjected to tensile force. Component-based models have been developed and used for predicting the strength of the column component of concrete-filled RHS columns under tensile load imparted through a through-diaphragm connection. The strength models are based upon defining a rigid plate deformation pattern for the column face and then applying the virtual work principle, taking into account the membrane action and strain hardening. The hand calculation procedures for yield and ultimate deflection were also developed. The load–deformation curve consists of three segments: the first representing the elastic behavior from the classic plate theory, the second obtained by plotting the deformation at the ultimate strength against the maximum load, and the third a horizontal line stretching to the failure point. The mechanical models were compared with a large range of experimental results and good agreement was shown between them. The proposed method can be used in the component-based method for connections involving a through-diaphragm component in tension.

Performance of concrete-filled RHS columns exposed to fire on 3 sides

The behaviour of concrete-filled steel tubular (CFST) columns subjected to uniform fires has been well studied over the past few decades. However, knowledge of the performance of concrete-filled rectangular hollow section (RHS) columns exposed to fire on 3 sides, which is a common scenario in practice, is limited. Hence, this paper presents an experimental and numerical study into the response of concrete-filled RHS columns subjected to 3-sided fire exposure. Three full-scale concrete-filled RHS columns, two of which were exposed to fire on 3 sides and the other on 4 sides, were tested to failure. The temperature distributions, axial displacements, lateral displacements and failure modes were all recorded and discussed. Following the experiments, a sequentially coupled thermal–stress numerical model was developed, featuring heat transfer analysis and stress analysis. The FE model was validated against the test results, and used to assist in the understanding of the observed failure mechanisms and to extend the investigated range of key parameters. These parameters included load ratio, load eccentricity, cross-sectional dimensions, slenderness ratio, steel ratio and strengths of the constituent materials. It was found that the load ratio, cross-sectional dimensions and load eccentricity have a significant influence on the fire resistance. Based on the results of the parametric studies, a simplified design formula was developed for predicting the fire resistance of concrete-filled RHS columns subjected to 3-sided exposure. Furthermore, a reduction factor method was proposed for the design of concrete-filled RHS columns exposed to 3-sided fire, based on fire safety design methods for concrete-filled RHS columns in uniform fire, which may be more convenient for engineering applications.

Behaviour of Filled Rectangular Steel HSS Composite Columns under Bi-Axial Bending

The purpose of this study was to investigate the behaviour of concrete-filled rectangular steel hollow structural section (HSS) columns formed by slender plates with large depth-to-width ratio subjected to bi-axial bending. As part of this study, four large concrete-filled thin-walled rib-stiffened rectangular HSS columns have been tested. Their steel tubes possess a depth-to-width ratio of 2.38 and a depth-to-thickness ratio of 175. Rib stiffeners were welded to the plate walls such that the stiffened plate width-to-thickness ratio (= 45) was less than that specified (= 60) in the Chinese design code. The results showed that local buckling of steel plate appeared after the specimen reached the ultimate capacity. Also, the fiber element analysis method is adapted to analyze the behaviour of specimen, in which the change of neutral axis position is considered. At last, the experimental results are compared with the values calculated from design codes, namely EC4, LRFD, CECS and DBJ. The results show that all codes provide safe ultimate capacities. Among them, the capacities calculated from DBJ yield results closest to the experimental ones and the other three design codes produce safety over 20%.

Design of Concrete-Filled Stainless Steel Tubular Connections

A numerical study was performed on concrete-filled stainless steel tubular T- and X-joints using finite element analysis. The specimens were fabricated from square and rectangular hollow sections (SHS and RHS) with concrete-filled in the chord members. The geometric and material nonlinearities of stainless steel tubes as well as the concrete infill were carefully incorporated in the finite element models. The nominal compressive concrete strengths were ranged from 30 to 110 MPa. The numerical results showed good agreement with the experimental results for the concrete-filled stainless steel SHS and RHS tubular T- and X-joints. Therefore, an extensive parametric study was performed using the verified finite element models to investigate the strength and behaviour of concrete-filled stainless steel tubular connections. The joint strengths obtained from the parametric study and tests were compared with the current design strengths calculated using the CIDECT design rules for concrete-filled carbon steel tubular joints, which is the only existing design guideline for concrete-filled tubular joints. It should be noted that the current CIDECT design rules ignore the contribution of the steel tubes in the calculation of the joint strengths. In this study, design formulae of concrete-filled stainless steel tubular T- and X-joints are proposed. The proposed design formulae include the contribution of the stainless steel tubes. 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 accurate and reliable.

Energy Absorption Capacity of Composite Beams

Local buckling may occur in the compression flange of rectangular hollow-section beams under cyclic repeated loading arising from earthquakes. Once a local mechanism forms, residual strength rapidly reduces within a few cycles. This is true even for compact sections under static bending. This paper aims to study the experimental behaviour and ultimate moment capacity of unfilled and concrete-filled rectangular hollow sections subjected to cyclic reversible loading. Two types of filler material were used - normal mix concrete and fly ash concrete. The effect of filler materials, section slenderness, loaddeflection response, moment-strain behaviour, first cycle peak load, ductility, stiffness degradation and energy absorption of concrete –filled RHS beams are studied.