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This paper aimed to study the compatibility between E-glass of chemical resistance (ECR-glass) fibers and the polymer matrix and the influence of different matrix types on the durability performance of ECR-glass fiber–reinforced polymer (GFRP) bars in a marine concrete environment. Two types of matrices, epoxy and vinyl ester, were employed to fabricate GFRP bars, which were then subjected to accelerated exposure by immersion in a simulated seawater sea-sand concrete (SWSSC) pore solution. The degradation performance and damage mechanism were thoroughly investigated. The results indicated that hydrolytic degradation of the cured epoxy and vinyl matrices and subsequent chemical etching to glass fibers are the primary damage mechanisms affecting GFRP bars in the SWSSC environment. Based on these mechanisms, two damage models were proposed: a chemical etching-based model and a hydroxyl ion diffusion-based model. These models enabled the prediction of the residual tensile strength of GFRP bars in the SWSSC pore solution environment at different temperatures. The accuracy of the proposed models was validated through comparisons with experimental data. [ABSTRACT FROM AUTHOR]

An iron-based shape memory alloy (Fe-SMA) can be used to conveniently apply prestress strengthening via a heating and cooling procedure. Material-level tests demonstrated that prestress of Fe-SMAs is sensitive to mechanical and thermal loading. Durability of steel structures strengthened by Fe-SMAs when subjected to harsh service conditions, such as coupled thermomechanical cycles is not fully understood. In this study, high-cycle fatigue tests were conducted on damaged steel plates retrofitted with Fe-SMA strips. Four temperature scenarios were adopted: room temperature (RT), a low temperature (LT) of −20°C , a high temperature (HT) of 60°C, and a cyclic temperature (CT) from −20°C to 60°C. Results showed that regardless of temperature variation, the Fe-SMA presented reliable repairing effects on steel plates, of which, the fatigue life was 2.1–3.5 times larger than that of the unstrengthened samples. The difference in coefficients of thermal expansion (CTEs) between the Fe-SMA and steel, as well as loss of prestress of the Fe-SMA due to fatigue and thermal loading, both affected the fatigue performance of the retrofitted specimens. [ABSTRACT FROM AUTHOR]

Self-drilling screws provide an efficient and cost-effective way of joining lightweight structural members. In this work, the performance of self-drilling screw connections for fiber-reinforced polymer (FRP) structural members is investigated, for use in joining panels or plates to square hollow sections (SHSs). To investigate the resistance to pullout loads, tensile tests were conducted on connection specimens consisting of an FRP plate joined to an FRP SHS at a right angle. The specimens were prepared in five configurations, with differences in pultrusion directions of the FRP plate, screw gauge size, and coarseness of the screw threads. The specimens having fibers oriented transversely in the FRP plate exhibited a flexural failure of the plate and the lowest connection strength. The specimens having fibers oriented longitudinally in the FRP plate failed by the screw being pulled out from the FRP SHS profiles; shearing out of the thread in the screw hole. An increase in screw gauge size and thread coarseness was found to be beneficial to the connection strength. Further analysis was carried out to estimate the initial stiffness and the connection strength, by finite-element and analytical modeling, respectively. In addition, these analyses are able to correlate the average shear stress at failure of the connection specimens to the screw gauge size, thread coarseness, and effective contact area of the screws. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio, and cross-sectional geometry were investigated. The experimental results suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history. [ABSTRACT FROM AUTHOR]

This paper presents a series of tests on high strength aluminum square hollow sections subjected to concentrated bearing load. A total of 64 web-bearing tests was conducted. The test specimens were fabricated by extrusion using 6061-T6 heat-treated aluminum alloy. The tests were carried out under end and interior loading conditions, where the specimens were seated on a fixed solid steel base plate. These tests closely simulated the support condition of the floor joist members seated on solid foundation. The test results were compared with the design strengths obtained using the American Aluminum Design Manual and European code for aluminum structures. It was shown that the design strengths predicted by these codes are either quite conservative or unconservative. Furthermore, the Australian Standard AS4100 and British Standard BS5950 Part 1 were used for aluminum square hollow section with sharp corners. The design rules of steel codes were modified to predict the web-bearing strength based on this study. It was shown that the design strengths calculated using the modified web-bearing design rules are generally conservative and agree well with the experimental results. Furthermore, the critical values of web slenderness were proposed beyond which web buckling governs. DOI: 10.1061/(ASCE)ST.1943-541X.0000015 CE Database subject headings: Aluminum: Concentrated loads: Investigation: Webs: Hollow sections: Structural design.

This paper determines new section slenderness limits suitable for design and construction of seismic resisting structural systems. It describes an experimental investigation of the cyclic inelastic flexural behavior of cold-formed circular hollow section (CHS) beams. Controlled-rotation, symmetrical cyclic bending tests were performed on different sizes compact CHS with section slenderness D/t ranging from 13 to 39. With continuous cycling, the growth of ovalization caused a progressive reduction in the bending rigidity of the tube and eventually an instability occurred. The CHS beams exhibited stable hysteresis behavior up to local buckling and then showed considerable degradation in strength and ductility depending upon the D/t ratio. Seismic capacity parameters are presented, including strength, stiffness, hysteresis loops and modes of failure for each specimen. Peak moments obtained in the cyclic tests were compared with those obtained in monotonic tests published previously and also with design moments predicted using a number of steel specifications. The deformation ductility demand was determined and used to derive new fully ductile section slenderness limits suitable for seismic design. A comparison is made between these seismic slenderness limits and the static limits available in the design codes. CE Database subject headings: Beams; Cold-formed steel; Tubes; Cyclic loads; Bending; Slenderness ratio.

This paper describes a series of tests to failure of fix-ended tubular braces subjected to cyclic concentric axial loading. The braces were made from cold-formed steel grade C350L0 (350 MPa nominal yield stress) circular hollow sections (CHS). Nine different diameter-to-thickness ratios in the range of 19 CE Database subject headings: Cold-formed Steel; Bracing; Tubes; Cyclic loads. DOI: 10.1061/(ASCE)0733-9445(2003)129:4(507)

Hollow structural steel (HSS) columns filled with concrete offer a number of benefits and are often used in tall buildings and other industrial structures. A mathematical model was developed and used to investigate the influence of important parameters that determine the fire resistance of concrete-filled hollow steel columns. The behavior of concrete-filled HSS columns with or without fire protection subjected to axial or eccentric loads was experimentally investigated and the results presented in this paper. The parametric and experimental studies provide information for the development of formulas for the calculation of the fire resistance and fire protection thickness of the composite columns. The main objectives of this work were threefold: First, to report a series of fire tests on composite columns; second, to analyze the influence of several parameters, such as the sectional dimension, load eccentricity ratio, and fire protection thickness on the fire resistance of the composite columns. It was found, in general, that the sectional dimension and the fire protection thickness have significant influence on the fire resistance of concrete-filled HSS columns; however, the load eccentricity ratio has moderate influence on the fire resistance. The final objective was to develop formulas for the calculation of the fire resistance and the fire protection thickness of the concrete-filled HSS columns. CE Database keywords: Steel columns; Fire resistance; Concrete; Beam columns; Hollow sections.

There is an increased use of thin-waslled (t DOI: 10.1061/(ASCE)0733-9445(2002) 128:11 (1413) CE Database keywords: Cyclic loads; Failure modes; Stress concentration; Connections, welded; Thin-wall sections; Hollow sections.

This paper describes a series of tests on empty and void-filled rectangular hollow section (RHS) braces subjected to static and cyclic axial loading. The braces were made from cold-formed C450 (450 MPa nominal yield stress) RHS with two different plate slenderness ratios. The filler material used was normal concrete and light-weight concrete. Two loading protocols were applied, namely Cyclic-Direct (full axial displacement applied and load oscillated) and Cyclic-Incremental (load oscillated at several accumulating axial displacement increments). First-cycle buckling loads were compared with design loads predicted using various national standards. The effects of filler material and section slenderness on the load-deflection response, first cycle peak load, postpeak residual strength, ductility, and energy absorption of void-filled RHS braces are studied in the paper. The effect of the loading scheme is also discussed. CE Database keywords: Bracing; Cold-formed steel; Cyclic loads; Hollow sections; Thin wall sections.

Thin-walled tubular sections (t < 4 mm) are increasingly being used in the road transportation industry and agricultural industry for applications such as lighting poles, traffic sign supports, truck trailers, swing-ploughs, haymakers, and linkage graders. These structures are subjected to fatigue loading and some failures have been observed. Both the International Institute of Welding and International Committee for the Development and Study of Tubular Construction fatigue guides for welded tubular joints apply only to tubes with a thickness above 4 mm. This paper deals with the fatigue design of tube-to-plate T joints under cyclic in-plane bending using the classification method. Forty-eight specimens, made up by welding a square hollow section tube (t < 4 mm) to a plate, are fatigue tested. The effects of in-line galvanizing, steel grade, stress ratio, and tube wall thickness on the fatigue life of these joints are investigated. The design stress range-to-number of cycles (S - N) curves, derived from the least squares method of analysis, show that the S - N curves for the tube-to-plate joints lie above the existing S - N curves in the Australian, European, and Canadian standards. DOI: 10.1061/(ASCE)0733-9445(2002) 128:1(22) CE Database keywords: Fatigue tests; Hollow sections; Thin wall sections; Welded joints; and Bending.

Local buckling and plastic hinges may occur in the compression flange of square hollow-section (SHS) beams under high amplitude cyclic bending arising from earthquakes. Once a local mechanism forms, residual strength rapidly reduces within a few cycles. This is even true for compact sections that have adequate rotation capacity under static bending. This paper compares the behavior of empty, and void-filled, cold-formed square hollow sections subjected to large deformation cyclic bending. A model is developed to estimate the ultimate moment capacity of void-filled SHS beams. The filler material used was normal concrete, low strength concrete, lightweight concrete and polyurethane. Experimental results show that void filling significantly increases ductility - and thus the number of bending cycles SHS beams can be subjected to - in overloaded situations.

This paper describes a series of tests on longitudinal fillet welds in high-strength (450 MPa nominal yield stress), cold-formed rectangular hollow section (RHS) members that have a thickness less than 3 mm. The effect of load conditions, end return welds, and RHS orientation on weld strength is investigated. The experimental weld strength is compared with the predicted strength using existing Australian, American, Canadian, and European design standards. The test results are also compared with the proposed design rules for longitudinal fillet welds in RHS members derived from the previous research project on C350 (350 MPa nominal yield stress) RHS members. A reliability analysis method is used for calibration. All load and resistance factor design standards produce adequate reliability indices. A nonlinear finite-element analysis is carried out to simulate the failure mode and load carrying capacity. The finite-element model has given reasonable predictions in load-deflection curves, stress values, failure mode, and local deformed shape. Design rules are recommended for longitudinal fillet welds in thin-walled, high-strength, cold-formed RHS members.

This paper describes welded connection tests that were performed on square (SHS) and rectangular hollow sections (RHS) with a thickness ranging from 1.6 to 3.0 mm. Longitudinal fillet welds were tested. The test results are compared with existing American, Australian, Canadian, and European design formulas. The effect of the direction of loading, the weld length, the end return welds, and the orientation of an RHS on the weld strength are studied. Proposed design formulas are given. The reliability analysis method is used to calibrate the existing and proposed design formulas.

This paper describes welded-connection tests that were performed on rectangular hollow sections (RHS). The thickness of the RHS sections varied from 1.6 to 3.0 mm. Both butt welds and transverse fillet welds were tested where the tension load was perpendicular to the direction of the weld. The test results are compared with existing American, Australian, Canadian, and European design formulas, and proposed design formulas are given. The reliability analysis method is used to calibrate the existing and proposed design formulas.

In this paper, tests on the lateral buckling of cold-formed rectangular hollow sections (RHS) beams under uniform bending moment are described. The section size chosen for testing is 75 x 25 x 2.5 mm, which is the largest depth/width ratio manufactured in Australia. The beam spans varied from 2,000 to 7,000 mm to produce a large range of beam-slenderness ratios. Carefully designed loading and support systems were used in the tests to apply gravity load through the centroid of the section and to ensure that simply supported end conditions were achieved. The test results are compared with existing design models and standards. An improved design rule is given for the lateral buckling of cold-formed RHS beams.

This paper describes tests on a range of cold-formed square and rectangular hollow section members subject to end-bearing force. The concentrated force was applied by means of a bearing plate, which acted across the full flange width of the section. The parameters varied in the tests included (1) the bearing length; (2) the slenderness of the member; and (3) the shape of the section [rectangular hollow sections (RHS) or square hollow sections (SHS)]. The results are compared with existing American, Australian, Canadian, and European design formulas. The results are also compared with the formulas given by the writers, which were based on tests of SHS and RHS sections under interior bearing force. A design model is proposed for SHS and RHS sections under end-bearing force. The reliability analysis method is used to calibrate the existing and proposed design formulas.

A large number of tests on a range of cold-formed square and rectangular hollow sections subjected to pure bending, pure concentrated force and combined bending, and concentrated force are described. The concentrated force is applied by means of a bearing plate that acts across the full flange width of the section. The ratio ([Gamma]) of the bearing length to the width of the bearing plate used varies from 0.5 to 1.0 in order to show the effects of the bearing length on the failure loads. The current tests are compared with previous T-joint tests performed at the University of Sydney on similar sections to demonstrate the significant reductions in failure loads and the more severe interaction between bending moment and concentrated force for the tests using bearing plates. The test results are compared with the existing Australian, European, and American design procedures. Improved design procedures are also proposed., Pure bending, pure concentrated force and combined bending and concentrated force tests conducted on cold-formed square and rectangular hollow section members showed that better designs are needed for cold-formed members. Research parameters such as bearing length, slenderness and shape of the section and ratio of the bending moment to the concentrated force were varied during testing. The concentrated force was applied using a bearing plate acting across the full flange width of the member section. Comparison of results with other design procedures are also presented.

Axial load-bearing structural members often experience significant damage or failure when subjected to moving-vehicle or vessel collisions. Hollow steel tubular columns are highly vulnerable under transverse impact loading. Thus, strengthening/retrofitting of existing steel tubular columns may be required if these members are not designed to withstand expected transverse impact from transport accidents. This paper investigates the performance of full-scale circular-hollow-section (CHS) tubular columns strengthened with fiber-reinforced polymer (FRP) and subjected to vehicular impact. Initially, finite-element (FE) models of bare and FRP-strengthened CHS medium-scale specimens were developed to conduct transverse impact analysis for the model validation purpose. The impact simulation results were compared with the drop-mass impact test results and good agreements were found between the FE and experimental tests. The validated FE models were extended to full-scale bare and FRP-wrapped CHS columns. The full-column vehicle collisions were simulated using a realistic vehicle model by considering varying axial static forces and vehicle impact velocities. The results showed that strengthening with carbon-fiber-reinforced polymer (CFRP) improved the impact resistance capacity of a bare CHS column by preventing plastic hinge formation due to excessive local buckling when subjected to accidental vehicular impact. Three-layer CFRP strengthening proved to be an effective strengthening system compared with two-layer CFRP strengthening system. The effect of load eccentricity was assessed further, and it was found that CFRP strengthening contributed significantly to preventing the failure of CHS columns with varying eccentricities when subjected to credible vehicular impact events. [ABSTRACT FROM AUTHOR]

The welded truss composed of circular hollow section (CHS) braces and concrete-filled circular hollow-section (CFCHS) chords is a new kind of structural system that has been increasingly applied in large span arch bridges in China. It is necessary to have a good knowledge of fatigue strength of the welded CHS-to-CFCHS joints for the design of this kind of composite bridge. This paper reports on a series of tests on welded CHS-to-CFCHS T-joints subjected to axial cyclic fatigue loading in the brace. Eleven joints were designed to investigate various influence factors such as different nondimensional geometric parameters of circular hollow sections and different concrete strength grades. The quality of welds connecting brace and chord members were examined using the magnetic particle and radiographic inspection methods. The conditions of hot spot stress at both the crown and saddle positions in brace and chord members were determined by means of linear and nonlinear extrapolation methods. During the fatigue testing process, the number of cycles relating to several stages of failure, the crack initiation positions, crack propagation patterns, and the final failure modes were recorded. Fatigue strength of the CHS-to-CFCHS T-joints was compared with that of CHS-to-CHS T-joints. It is concluded that the CHS-to-CFCHS T-joints have a much lower stress concentration factor and consequently have better fatigue strength than the CHS-to-CHS T-joints, when both kinds of joints have the same nondimensional geometrical parameters and same nominal stresses on the brace. The curves in the Comité International pour le Développement et l'Étude de la Construction Tubulaire guidelines used for CHS-to-CHS joints are not appropriate for the reliable fatigue assessment of CHS-to-CFCHS T-joints based on the current test data. [ABSTRACT FROM AUTHOR]

In this paper, steel plates with longitudinal weld attachments strengthened by carbon fiber reinforced polymer (CFRP) laminates on one side were analyzed based on the boundary element method and compared with test data from the literature. Good agreement with the data indicated that the numerical analysis was reliable for estimation of the fatigue crack propagation of CFRP-bonded steel plates with longitudinal weld attachments. The effects of double-sided strengthening, double-sided weld attachment and CFRP stiffness on the fatigue behavior of retrofitted welded joints were also investigated. The results showed that double-sided strengthening was much more efficient than single-sided application. It was observed that the crack propagation of steel plates with weld attachments on both sides was accelerated compared with those with attachments on only one side. In comparison with steel plates without a weld attachment, the retrofitting efficiency, in terms of the fatigue life extension ratio, was significantly lowered in welded plates with single-sided repair, whereas only a slight difference was observed in those with double-sided strengthening. The effect of an increased modulus of the composite materials could result in better fatigue performance, especially with double-sided application. [ABSTRACT FROM AUTHOR]

Bird-beak joints are a type of welded square hollow section (SHS) joint, the static strength of which is higher than that of conventional joints. Experimental analyses were conducted on the stress concentration factors (SCFs) of square bird-beak joints to obtain more information regarding their fatigue behavior. Twelve specimens, i.e., three conventional joints and nine square bird-beak joints, are separately tested by considering chord and brace axial force load cases. Both conventional and square bird-beak joints tested have a T-shape and are simply supported at their chord ends. Elastic strain distributions near the crown and saddle areas are measured, and strain concentration factors (SNCFs) at potential hot spots are calculated using an extrapolation approach. Quadratic extrapolation is suggested for the square bird-beak joints because linear extrapolation may underestimate SNCFs by up to 35%. Furthermore, critical locations are identified for square bird-beak joints subjected to chord and brace axial forces. A comparison indicates that the square bird-beak joints can produce lower stress concentration factors than the conventional or the diamond bird-beak joints with identical nondimensional parameters, especially when brace-to-chord width ratios are relatively small. [ABSTRACT FROM AUTHOR]

Presents a discussion on longitudinal fillet welds in thin cold-formed rectangular hollow-section members. Correlation between fillet weld resistance and direction of loading; Longitudinal and normal forces; Transmission of stress by welds; Distinction between lap-joint and T-joint fillet welds.