Compression Flange Research Articles

Flexural Strength of cold-formed steel built-up composite beams with rectangular compression flanges

The past research on cold-formed steel (CFS) flexural members have proved that rectangular hollow flanged sections perform better than conventional I-sections due to their higher torsional rigidity over the later ones. However, CFS members are vulnerable to local buckling, substantially due to their thin-walled features. The use of packing, such as firmly connected timber planks, to the flanges of conventional CFS lipped I-sections can drastically improve their flexural performance as well as structural efficiency. Whilst several CFS composites have been developed so far, only limited packing materials have been tried. This paper presents a series of tests carried out on different rectangular hollow compression flanged sections with innovative packing materials. Four-point flexural tests were carried out to assess the flexural capacity, failure modes and deformed shapes of the CFS composite beam specimens. The geometric imperfections were measured and reported. The North American Specifications and Indian Standard for cold-formed steel structures were used to compare the design strengths of the experimental specimen. The test results indicate clearly that CFS rectangular \'compression\' flanged composite beams perform significantly better than the conventional rectangular hollow flanged CFS sections.

About the influence of fiber on the deformation of compressed flanges at 3.6 h′f, 4.8 h′f, 8 h′f overhangs of reinforced rubber concrete t-beams with reinforcement of 2.50%

The aim of this study is to determine the effect of fiber reinforcement on deformations arising from the applied load in the compressed flanges of reinforced rubber concrete beams of a T-section.This article presents the results of testing prototypes of rubber concrete and fiber rubber concrete beams of a T-section, tested to a pure bending. The strain curves for compressed flanges (3.6h’f , 4.8h’f , 8h’f overhangs) of reinforced rubber concrete beams of T-section are obtained.

Effect of longitudinal stiffeners’ spacing in lateral-torsional buckling

This study focused on the experimental assessment of the effect of the spacing between longitudinal stiffeners welded to I-shaped beams under the action of lateral-torsional buckling. In this procedure, 192 aluminum beams on a 1:9 scale were tested under simple-support conditions with a laterally unbraced length ranging from 0.55 m through 1.95 m. Moreover, the stiffeners’ spacing was also ranged from 3 to 9 times the depth of section. The structural behavior of the beams is discussed in terms of their flexural capacity, spacing between longitudinal stiffeners, lateral displacement of compression flange and failure angle twist. Results show that the spacing of longitudinal stiffeners influences the flexural capacity of I-shaped beams, so that, when the spacing of longitudinal stiffeners decreases, flexural capacity tends to increase, especially in the elastic buckling zone.

COMPRESSED FLANGES OF ARCHED STEEL THIN-WALLED COLD-ROLLED PROFILED SHEETS: DETERMINATION OF RESIDUAL STRESSES

Introduction. The construction sphere widely uses steel thin-walled cold-formed profiles. In arched steel coldformed trapezoidal section profiles, residual normal stresses oriented along the profile occur at the stage of manufacturing arched blanks from flat profiled sheets and are caused by the cold bending process involving the extreme zones of the profile in the plastic stage with unloading without subsequent heat treatment. According to preliminary estimates, the residual stresses are up to one third of the calculated resistance of sheet steel at small radii of the arch profile. At present, the researchers do not take into account the residual technological stresses of the longitudinal bending when designing structures from thin-walled longitudinally bent rolled trapezoidal sections. The purpose of the paper is to develop a method for determining residual stresses in compressed flanges of arched steel thin-walled cold-rolled profiled sheets, which provides simplicity of the measurement and calculation methods, reliability and high accuracy of the obtained stress values.Materials and methods. The authors made the analysis of previously published materials and identified the advantages and disadvantages of previous studies. Moreover, the authors showed the advantages of the proposed method for determining the residual technological normal stresses in compressed flanges of arched steel thin-rolled profiled steel.Results. The researches formed a new method for making sections of a compressed shelf and measuring residual normal stresses in the compressed flanges of an arched steel sheet of cold-rolled profiled steel. The proposed method greatly simplified the existing method of determining residual technological normal stresses in compressed profile flanges, improved the accuracy of measuring normal stresses in compressed profile flanges.Discussion and conclusions. The method of measuring residual process stresses allows improving existing methods for determining residual stresses, simplifying calculations, as well as improving the accuracy of stresses. In the future, the authors will make a numerical simulation of the bending arch profiles, as well as an experimental assessment of the adequacy of the proposed method.The authors have read and approved the final manuscript. Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.

Analytical study and experimental tests on innovative steel-concrete composite floorings

Composite floor systems, when compared to reinforced concrete slabs, are a more cost-effective structural solution. The overall behaviour of these composite members depends on the shear connection between steel and the concrete encasement. The pre-cast composite flooring system with hollow-core section presents an efficient and useful solution that helps to reduce the flooring height. This paper reports the results of composite connection push-out and the associated composite beams full-scale tests. The system was composed of a partially encased asymmetric steel beam, and the shear transfer mechanism was established through an innovative shear connection by chemical bonding, friction, and dowel action (by transversal reinforcing bars passing through the web's holes). The tests results indicated that a rigid connection was produced by the chemical bonding and friction of the embedded flange profile in the concrete slab, as well as the composite beam's ability to develop its plastic bending moment capacity. The proposed analytical model provides an efficient way for analysing and designing a composite beam with encased compression flanges. Based on the results from the ultimate flexural resistance analytically obtained, a sensitivity study was also developed to evaluate the most competitive cases in terms of structural efficiency.

An experimental study on the flexural behavior of cold-formed steel composite beams

Local buckling instability under compressive stresses is common in cold-formed steel (CFS) members and generally occurs well before the material has reached its yield strength. This results in under-utilization of the cross-section, compared to its full capacity governed by strength failure. Under flexural loading these CFS members possess sufficient inelastic reserve strength up to the ultimate stage. A recent study indicated that plate girders with tubular flanges offer higher flexural and torsional strengths compared to the ones with flat flanges. Upon packing of the tubular compression flange of CFS beams with hard materials like concrete/ timber etc., there will be a substantial delay in early local buckling instabilities, thus improving their load carrying capacity considerably. Although, numerous CFS composite sections have been developed recently, very limited lightweight packing materials have been adopted. The current study presents an experimental investigation carried out on CFS beams with flanges and webs possessing rectangular box geometry, packed with suitable low-cost lightweight packing materials, resulting in novel light-weight CFS composite beams. Four point flexural tests were conducted on these beams with simply supported end conditions. The ultimate strengths, modes of failure, load vs. displacement plots were obtained to study their flexural behavior, in order to evaluate the structural efficiency of the different packing materials. Lastly, the North American Specifications and Australian New Zealand Standard for CFS structures were also used for determining the design strengths of the specimens for comparison sake. This study proved that these novel CFS composite beams have shown better performance considerably.

Torsional Brace Strength Requirements for Steel I-Girder Systems

AbstractEffective stability bracing of beams can be achieved by either preventing lateral movement of the compression flange or restraining twist of the beam cross section. Bracing that restrains t...

Simplified method for lateral‐torsional buckling of beams with lateral restraints

AbstractSelected, extended paper from the SDSS 2019 special session ECCS/TC8 – Structural StabilityThis paper discusses the simplified method for the lateral‐torsional buckling design of I‐shaped beams with discrete lateral restraints. This popular method, also adopted in Eurocode 3, Part 1‐1:2005, consists of verifying the resistance of the compressed “flange” of the beam subjected to major‐axis bending. In this case the compressed flange is considered to be composed of the flange itself plus 1/3 of the compressed part of the web. This paper summarizes the analytical derivation of the simplified method and its key assumptions. It then presents inconsistencies arising if the simplified method is compared with the more generally applicable design methods for lateral‐torsional buckling given in Eurocode 3, Part 1‐1:2005. In addition, the design methods are compared with numerical simulations to reveal the lack of conservatism in the simplified method in some cases. The final part of the paper discusses how the simplified method may be modified in order to ensure a sufficient level of safety.

The simplified method of the equivalent compression flange

AbstractExtended version of the Tomáš Vraný SDSS Award 2019The method of the equivalent compression flange simplifies the verification of lateral torsional buckling of steel beams to flexural buckling of an equivalent part of the cross‐section that is in compression. The current simplified method is based on outdated normative rules and the design results may be both, uneconomic and non‐conservative. To remedy these shortcomings, the simplified method is modified based on the basic structural behaviour of steel beams taking into account the effects of material, cross‐sectional geometry and residual stresses. This paper presents a comprehensive experimental study on the lateral torsional buckling behaviour and residual stresses of welded doubly‐ and mono‐symmetric I‐shaped steel beams. Moreover, an improved simplified method of the equivalent compression flange is proposed for design purposes.

Effectiveness of CFRP composites on compression flange of structural I-beam

Purpose This study aims to use carbon fiber-reinforced polymer (CFRP) laminates to strengthen the compression flange of structural I-beam so as to avoid local failure of compression flange and to take a load to its full capacity. Light weight beam (LB) 100 at 5.1 kg/m and LB 115 at 8.1 kg/m are used for this purpose. The compression flange of a beam is well prepared to ensure a rust-free surface so as to achieve proper bonding between the flange and fiber sheet to avoid de-bonding at the time of testing. A flange of the beam is strengthened using CFRP sheets applied to it with the help of adhesive. The beam with CFRP is cured in air for 48 h before testing. Experiments are performed in a loading frame of 100 T capacity. Results show that the load carrying capacity of the strengthened beam increased by 25-30 per cent compared to the control beam (non-strengthened), and the local failure of the compression flange due to the applied load is totally avoided. The elastic behavior of the strengthened beam is also increased compared to the non-strengthened beam, which gives a higher yield point. Design/methodology/approach Different methods exist for strengthening various structures. Use of CFRP appears to be an excellent solution. Vast research has been conducted on the use of CFRP for strengthening and retrofitting of steel structures. The load carrying capacities of steel beams can be increased by strengthening their compression flange by using CFRP and avoiding the local failure of beams at early stages. Findings The load carrying capacity of a beam strengthened with CFRP increased by 25-30 per cent compared to the non-strengthened beam. In addition, the elastic behavior of the strengthened beam is also improved. Originality/value The compression flange of the steel beam is strengthened using different layers of CFRP strips to avoid the local failure, and its deflection is observed using linear variable deformation transducer.

Flexural Strength of Composite HSB690 I-Girders in Negative Moment

The flexural behaviors of composite I-girders made of a high performance steel, HSB690, having a yield strength of 690 MPa in negative moment, were numerically investigated by applying an incremental ultimate strength analysis with material and geometrical nonlinearities. A total of twenty-nine example sections with various slenderness ratios of compression flanges and webs were carefully selected such that they meet the requirements in Appendix A6 of AASHTO LRFD, except the first requirement that the yield strength not exceed 485 MPa (70 ksi). Results of the numerical scheme adopted in this study were verified by comparing the flexural strengths computed by FEA to those of experimental results produced by other researchers. Numerical results for moment versus rotation curves, stress distributions, and failure modes were investigated and presented. The effects of initial imperfections, residual stresses, and mechanical properties of reinforcing steels on the ultimate flexural behavior of the girders were also closely investigated. The applicability of the negative flexural resistance equations in AASHTO LRFD for HSB690 composite I-girders was examined by comparison of the ultimate flexural strengths obtained from the numerical analyses. It was found that the upper limit on the yield strength of 485 MPa as one of the three major prerequisites to using the Appendix A6 in AASHTO LRFD can be removed from the provisions. Therefore, the flexural resistances of HSB690 girders in negative moment can be more efficiently evaluated by utilizing the procedures in Appendix A6 of AASHTO LRFD than those of Article 6.10.8 in AASHTO.

Elastic Critical Moment of Lateral-Distortional Buckling of Steel-Concrete Composite Beams under Uniform Hogging Moment

Great attention has been given in the last few years to steel–concrete composite beams due to the gains in strength that can be obtained with the small cost of installing a shear connection between the steel profile and the concrete slab. In continuous and semicontinuous composite beams close to the internal supports, hogging bending moments are developed and the compressed bottom flange may buckle laterally in an unstable way known as the lateral-distortional buckling, characterized by a horizontal displacement and twist of the bottom flange with an out-of-plane distortion of the web. In the literature, several formulations were proposed to determine the critical moment for this type of buckling. Among them, some of the most relevant are presented by [K. Roik, G. Hanswille and J. Kina, Solution for the lateral torsional buckling problem of composite beams (in German), Stahlbau 59 (1990)] and [G. Hanswille, J. Lindner and D. Munich, Lateral torsional buckling of composite beams (in German), Stahlbau 67 (1998)]. In the present work, a new procedure is developed to determine the elastic critical moment of lateral–distortional buckling of composite beams under uniform hogging moment. To assess and calibrate this procedure, 7[Formula: see text]772 numerical models were analyzed by the finite element code ANSYS and the results were compared with the ones obtained from the new proposed formulas. The procedure presented excellent agreement with the numerical results, with an average deviation of 2.33% from the computational simulations. The formulations of [K. Roik, G. Hanswille and J. Kina, Solution for the lateral torsional buckling problem of composite beams (in German), Stahlbau 59 (1990)] and [G. Hanswille, J. Lindner and D. Munich, Lateral torsional buckling of composite beams (in German), Stahlbau 67 (1998)] did not lead to such satisfactory results, presenting an average deviation of 12.41% and 16.51%, respectively.

EXPERIMENTAL STUDY ON INTERNAL FORCE VARIATION OF STEEL-CONCRETE COMPOSITE BEAM UNDER FIRE

In practical engineering, most steel-concrete composite beams have axial constraints, which cause the composite beam to produce catenary action to continue bearing more external loads at large deformations. To study the mechanism of catenary action of steel-concrete composite beam under fire, two full-scale tests of steel-concrete composite beams were carried out to obtain the internal force variations with the time. The test designation, loading scheme and measurement contents are presented in this paper. The experimental phenomena and failure characteristics are also described. The test results show that the temperature gradient distribution of the composite beam section changes greatly under fire, and so it is easy to generate additional bending moment, which has an adverse effect on the ultimate bearing capacity of the composite beam. The failure mode of the composite beam is mainly the formation of obvious plastic hinge at the negative bending moment area at the beam ends, and the overall lateral instability occurs on the tensioned lower flange of the steel beam at the bottom of the beam, which is contrary to the common phenomenon that overall unstability of a steel beam is usually attributed to the compression flange buckling of a steel beam. The load ratio is one of the important parameters affecting the fire resistance of the composite beam. Through the actual measurement, the changing process of the internal force of the composite beam in fire is obtained. It is found that a larger load value leads to more obvious catenary action of the composite beam at the same time under the same conditions.

Flexural behavior of corroded HPS beams

Experimental research is conducted to investigate the flexural behavior of corroded High Performance Steel (HPS) beams. Four beams with various corrosion damage are designed and subjected to electrochemical accelerated corrosion process. 3D scanning technology is employed to analyze the geometric features affected by the corrosion damage. Flexural tests are carried out, and the impact of corrosion on the flexural response is discussed. Considering the randomness of corrosion pits in each area, predictive models are proposed for the flexural strength of corroded beams with an idealized elastic-plastic and linear-hardening constitutive relationship model. An analysis comparing the proposed models with Chinese and American codes is made. Results show that increasing the corrosion damage leads to a decrease of discreteness in the residual sectional area and causes a transformation in the compressed flange from noncompact to slender. A corrosion loss less than 10% leads to slight deterioration of both strength and stiffness degradation, while further corrosion damage results in a significant decrease. The depth and length of the buckling wavelength for corroded beams decreases gradually as the corrosion damage become more serious. The analytical models IEM and LHM or the GB50017-2017 may be suitable for predicting the lower and upper limit values of the ultimate flexural moment, respectively, and results predicted by AISC are conservative.

Simulation of flexural behaviour and design of cold-formed steel closed built-up beams composed of two sigma sections for local buckling

This study focused on the structural behaviour of cold-formed steel (CFS) closed Built-up beams composed of two sigma sections primarily fail due to local buckling under four-point bending about the major axis. It is aimed to establish accurate finite element models for CFS built-up I-beam subjected to a transverse load. The numerical model was developed by using Finite Element (FE) software ABAQUS 6.13. The numerical models were discretized with S4R element, end condition as simply supported and non-linear analysis which includes material, geometric, contact non-linearities and geometric imperfections. The numerical model is validated by means of comparison with the experimental results published in the literature in terms of moment capacities, moment versus deflection curve and failure mode of specimens. For different cross-section geometries and different thickness of the built-up closed beam, the numerical parametric study has been carried out by using the verified FE model, and the obtained flexural resistances were compared with those predicted by using current DSM and DSM proposed for built-up beams. The moment capacity decreases with increase in compression flange width to thickness ratio. In general, the moment of resistance of the section increases with decreasing the aspect ratio. There is no significant effect in flexural strength of the built-up closed beams due to the change in depth of web stiffener. Based on the comparison of results, suitable modifications are proposed herein for DSM, especially for the closed built-up beams made of two sigma sections normally failed by local buckling and also the performance of the current DSM, DSM proposed for built-up beams and the DSM proposed by this study are assessed by reliability analysis.

The effects of residual stresses and strains on lateral-torsional buckling behavior of cold-formed steel channel and built-up I-sections beams

Purpose The purpose of this paper is to focus on the influences of residual stresses which were induced during roll-forming sections on lateral-torsional buckling of thin-walled cold-formed steel channel and built-up I-sections beams. Built-up I section is made up of two back-to-back cold-formed channel beams. In this direction, at the primary stage, the roll-forming process of a channel section was simulated in ABAQUS environment and the accuracy of the result was verified with those existing experiments. Residual stresses and strains in both longitudinal and circumferential transverse directions were extracted and considered in the lateral-torsional buckling analysis under uniform end moments. The contribution of the current research is devoted to the numerical simulation of the rolling process in ABAQUS software enabling to restore the remaining stresses and strains for the buckling analysis in the identical software. The results showed that the residual stresses decrease considerably the lateral-torsional buckling strength as they have a major impact on short-span beams for channel sections and larger span for built-up I sections. The obtained moment capacity from the buckling analysis was compared to the predictions by American Iron and Steel Institute design code and it is found to be conservative. Design/methodology/approach This paper has explained a numerical study on the roll-forming process of a channel section and member moment capacities related to the lateral-torsional buckling of the rolled form channel and built-up I-sections beams under uniform bending about its major axis. It has also investigated the effects of residual stresses and strains on the behaviour of this buckling mode. Findings The residuals decrease the moment capacities of the channel beams and have major effect on shorter spans and also increase the local buckling strength of compression flange. But the residuals have major effect on larger spans for built-up I sections. It could be seen that the ratio of moment (with residuals and without residuals) for singly symmetric sections is more pronounced than doubly symmetric sections. So it is recommended to use doubly symmetric section of cold-formed section beams. Originality/value The incorporation of residual stresses and strains in the process of numerical simulation of rolled forming of cold-formed steel sections under end moments is the main contribution of the current work. The effect of residual stresses and strains on the lateral-torsional buckling is, for the first time, addressed in the paper.

Behaviour of concrete filled glass fibre-reinforced polymer tubes under static and flexural fatigue loading

Abstract Concrete-filled glass fibre-reinforced polymer tubes (CFFTs) have reportedly been considered for industrial applications such as fender piling for marine structures and bridge girders. Even though previous investigations of the flexural fatigue behaviour of circular sectioned CFFTs have been reported in the literature, no such study has been carried out for square or rectangular sectioned tubes. In order to address this research gap, an experimental programme was carried out to investigate the flexural fatigue behaviour of square sectioned CFFTs, considering fatigue deformation cycles equal to 75%, 80%, 85% and 90% of the deformation corresponding to the static flexural failure of the tested CFFTs. The used glass fibre-reinforced polymer (GFRP) tubes contained reinforcements at the longitudinal direction and ±45° to the longitudinal axis of tubes. They were also specified to have much larger longitudinal tensile and compressive strength compared to typical rectangular GFRP tubes. Self-compacting concrete was used for the core-infill of the tested CFFTs. In total, eight static flexural tests and sixteen flexural fatigue tests were conducted under displacement-control fatigue loading using two loading arrangements, namely three-point and four-point bending. All CFFTs beams subjected to the fatigue loading failed due to buckling of the compression flange of CFFT. It was observed that the number of cycles to failure for the employed fatigue deformation ranges were quite low and decreased with increasing the amplitude of fatigue deformation. The bending stiffness of the tested specimens was observed to decrease as the fatigue loading progressed. It was also found that the amount of dissipated energy in a given cycle and the rate of stiffness degradation increases with an increase in the amplitude of fatigue deformation, especially for specimens tested under four-point bending. Furthermore, the bending stiffness at failure for the specimens tested under four-point bending was found to be approximately 80–90% of its initial value.

Flexural and bond-slip behaviours of engineered cementitious composites encased steel composite beams

This paper studies the flexural and bond-slip behaviour of composite beams fabricated by encasing universal steel beams with Polyvinyl Alcohol-Engineered Cementitious Composite (PVA-ECC) and Light Weight Concrete (LWC). Four-point bending tests were conducted on one bare steel and four composite beams with different ECC and LWC encasement configurations. Test results showed that the ECC and LWC encasements could enhance the flexural strength and ductility of bare steel beams significantly. Furthermore, it was found that the weight of the encased beams could be further reduced by either replacing the bottom ECC layer with LWC or even only encasing the compression flange of the steel section without reducing the flexural strength of the beam significantly. The bond-slip behaviour between the ECC matrix and the steel section was also investigated. The experimental study is complemented by a non-linear finite element (FE) model which was validated against the test results. A small scale parametric study was then conducted by using the validated FE model to investigate the performances of beams formed by the steel sections with yield strengths ranging from 350 MPa to 960 MPa.

Lateral-Torsional Buckling Behaviour of Triangularly Corrugated Web Beam

Lateral torsional buckling (LTB) is a common failure mode of large span beams. In this phenomenon, the beam becomes unstable along the unbraced length. This instability of beams can be identified by out-of-plane deflection and twisting. In this paper LTB strength of triangularly corrugated web beams under bending condition is investigated. Examined steel beams consist of two flanges and a thin triangularly corrugated web, connected by automatic welding. In the literature, the LTB strength problem of steel beams was dealt with mostly for steel beams with plate, sinusoidal and trapezoidal corrugated webs. Researches of the LTB behaviour of beams with triangularly corrugated webs were found out to be very limited. A parametric study is carried out for various beam spans and corrugation densities. A general-purpose finite element program (ABAQUS) was used. The corrugation densities adopted in this study represent practical geometries, which are common used for such structures in building practice. Plot showing the influence of compressed flange slenderness on value of reduction factor for LTB is presented. It is determined that existing buckling curves poorly describe the change of reduction factor depending on slenderness of compressed flange for triangularly corrugated web beams. Finally, recommendations were proposed for the design of simple supported steel beams with corrugated webs against lateral torsional buckling in accordance with numerical results.

Testing and evaluation of full scale fiber-reinforced polymer bridge deck panels incorporating a polyurethane foam core

A fiber-reinforced polymer (FRP) bridge deck panel that incorporates a polyurethane foam core was developed for accelerated bridge construction and repair. This low cost panel was tested under monotonic loading and compared to applicable FRP design equations. This new prototype system consisted of two stiff facesheets of stitch bonded plain-weave woven E-glass fabric with sloping webs of E-glass woven fabric that are separated by trapezoidal-shaped, low-density polyurethane foam. The polyurethane foam was used in an attempt to reduce initial costs. The panels used in this study were manufactured using a one-step, vacuum-assisted, resin transfer molding process (VARTM) using a newly formulated, two-part, thermoset, polyurethane resin developed by Bayer MaterialScience to facilitate the infusion process. The results of the flexural and shear testing indicated that the prototype panels significantly exceeded the AASHTO Design Code Strength requirements by nearly three times. Even more importantly, the panels behaved linearly-elastically throughout the full range of loading and possessed significant post-buckling strength. In addition, the results of these full-scale panels were used to evaluate the applicability of existing FRP design equations when used for the design of the VARTM- manufactured, prototype FRP bridge deck. Results showed that the existing FRP design equations correctly predicted a flexural failure due to local buckling of the compression flange and a bearing failure due local buckling of the webs beneath the concentrated load.