Web Stiffeners Research Articles

Behavior of Steel Plate Girders with Deep Section under Dynamic Effect

Having a minimum mass, equal-sized flanges and no web stiffeners is the most economical plate girder to fabricate. As with rolled I-sections, for a given section modulus a section with a greater depth will have a lower mass than one with a smaller depth, except in some instances where a thicker web is required in the deeper section. A wider flange plate to resist the buckling tendency may be necessary to use, when the compression flange is laterally unrestrained, but this will add to the cost because of the more difficult assembly procedure. In order to arrive at a minimum-mass cross section as much as possible of the material should be located in the flanges and as little as possible in the web, consistent with shear requirements. There is usually an advantage, however, in using a somewhat thicker web in order to reduce welding distortion, or to avoid the use of or number of stiffeners. It can be shown that for a given web depth to thickness ratio the minimum-mass cross section is that in which the area of the two flanges combined equals that of the web, i.e. 2Af = Aw.An important consideration in cost reduction is the use of preferred plate widths and thicknesses for the flange and web elements.

Numerical investigation of cold-formed stainless steel lipped channels with longitudinal stiffeners subjected to shear

The shear response of the cold-formed stainless steel lipped channel sections with longitudinal stiffeners has not been investigated adequately in the past. Therefore, this paper presents the details of numerical investigations conducted to study the shear behaviour of longitudinally stiffened cold-formed stainless steel lipped channel sections. Following a validation study of the finite element models of lipped channel sections, the effect of return lips and web stiffeners on the shear response of lipped channel sections was examined through comprehensive numerical parametric studies. In addition, numerical investigations were conducted to study the elastic shear buckling response of the sections and the shear buckling coefficients were back-calculated. It was found that the longitudinal web stiffeners enhance the shear buckling resistance of lipped channel sections considerably with increased stiffener depth. However, the shear capacity increment is not significant compared to plain lipped channel sections. The presence of the web stiffeners is found to be not preventing the out-of-plane buckling of the sections. The evaluation of Eurocode 3 and the direct strength method shear provisions for stainless steel channel sections with longitudinal stiffeners illustrates inaccurate capacity predictions. Therefore, modifications were proposed and comparisons reveal that the proposed provisions enhance the shear resistance predictions with good accuracy over the codified provisions.

Shear Response of Glass Fibre Reinforced Polymer (GFRP) Built-Up Hollow and Lightweight Concrete Filled Beams: An Experimental and Numerical Study.

This paper investigated the static behaviour of glass fibre reinforced polymer (GFRP) built-up hollow and concrete filled built-up beams tested under four-point bending with a span-to-depth ratio of 1.67, therefore focusing their shear performance. Two parameters considered for hollow sections were longitudinal web stiffener and strengthening at the web–flange junction. The experimental results indicated that the GFRP hollow beams failed by web crushing at supports; therefore, the longitudinal web stiffener has an insignificant effect on improving the maximum load. Strengthening web–flange junctions using rectangular hollow sections increased the maximum load by 47%. Concrete infill could effectively prevent the web crushing, and it demonstrated the highest load increment of 162%. The concrete filled GFRP composite beam failed by diagonal tension in the lightweight concrete core. The finite element models adopting Hashin damage criteria yielded are in good agreement with the experimental results in terms of maximum load and failure mode. Based on the numerical study, the longitudinal web stiffener could prevent the web buckling of the slender GFRP beam and improved the maximum load by 136%. The maximum load may be further improved by increasing the thickness of the GFRP section and the size of rectangular hollow sections used for strengthening. It was found that the bond–slip at the concrete–GFRP interface affected the shear resistance of concrete–GFRP composite beam.

Optimal Design Parameters of Stiffeners for Improving Seismic Performance of Links in EBFs

In eccentrically braced frames (EBFs), the link beam is the main factor determining the behavior of this type of system. In order to enhance the ductility and delaying the web and flange buckling, the link beam is reinforced using intermediate web stiffeners to improve its performance and energy dissipation capacity. The web stiffeners spacing criteria is based on short links under pure shear, which have been applied without considering the bending effect on intermediate links. In this paper, first the effects of stiffener details and section geometry on the link behavior are investigated using finite element modeling, and then by proposing an optimization model, new spacing is proposed for stiffeners of intermediate links that is also consistent with bending distribution, and enhances the performance of intermediate links significantly. To further investigate the results of the optimization model and sensitivity analyses results, the behavior of a total of 52 short, intermediate and long links with different lengths and sections is simulated and investigated under cyclic loading based on ANSI/AISC 341-10 (Seismic provisions for structural steel buildings, Chicago, American Institute of Steel Construction, 2010) using ABAQUS. The results show that the section geometry in W-beams affects the stiffeners spacing and thereby, the behavior of intermediate and long links. According to the obtained results in short links, stiffeners spacing are very conservative and can be increased, and for intermediate links, adjusting the stiffeners spacing based on the proposed optimization model can significantly enhance the performance of the link beam.

Optimal design of cold roll formed steel channel sections under bending considering both geometry and cold work effects

Optimal design of a structural member is a design process of selecting alternative forms to obtain its maximum strength while maintaining the same weight, leading to the most economical and efficient structure. Amongst steel structures, cold rolled steel ones can effectively gain this requirement as they are thin-walled structures that offer the high ratio of strength over weight. However, the design is very challenging as these members are prone to buckling and failure at low loads. In this paper, the buckling and ultimate strength of cold rolled channel sections was studied using numerical modelling. In order to improve the section strength, the development of various alternative cold rolled formed sections included additional bends such as intermediate stiffeners. The section strength was optimised through a practical approach which altered the stiffener's position and shape and searched for maximum buckling and ultimate strength under bending. In this approach, a nonlinear Finite Element model was first developed for an industrial channel beam subjected to four-point bending tests and this model was validated against experimental test data. The verified model was then used to conduct a parametric study in which the effects of a stiffener's properties on the section strength including its position, shape, size and material properties by the cold work at bends were investigated in detail. Several different cold rolled channel sections having intermediate stiffeners at web and flanges with and without the cold work effect on material properties at the stiffener's bends were considered for this investigation. In addition, a design method, the Direct Strength Method (DSM), was utilised to take into account the effects of a stiffener's properties on the section strength and results were compared with the Finite Element modelling results. It was found that some significant improvements were obtained for the section strength of the optimised sections in comparison to the original sections. An optimal shape for the channel section with maximum ultimate strength in distortional buckling could be obtained with both the stiffeners' position, shape, size and quantity, and the cold work effect. The cold work effect was found most significant in the cases of changing the width of the web stiffeners and the position of the flange stiffeners. It also revealed that, the currently available DSM beam design curve for distortional buckling provided good agreement in predicting buckling load and ultimate strength capacity for most of the considered sections with and without the cold work effect included; however, the DSM provided overestimate results compared to the Finite Element model results in the sections with web intermediate stiffeners, in particular, when the tip of web intermediate stiffener moved away from the web-flange junction in the horizontal direction.

Behaviour of thin-walled intermediate stiffened back-to-back columns under axial compression

The axial load carrying abilities and the buckling behaviour of Cold-Formed Steel (CFS) Stiffened Built-up Columns (SBC) has been presented in this paper. In total, the results from 8 actual experiments and 64 finite element models in the parametric studies on CFS back-to-back channels built-up screw fastened SBCs with different cross-sections are reported. The specimens were tested with fixed end condition under axial compression. Sections with lip and web stiffeners predominantly failed due to distortional buckling mode whereas all the other sections failed due local or global flexural buckling mode or interaction of local and global modes of failure. The inclusion of intermediate stiffeners and global stiffeners supported in resisting buckling. The results obtained from this study were compared with the estimated load carrying capacities using Direct Strength Method (DSM) design equations. It was found that for built-up SBC members the method of calculating its compression capacity was over-conservative. SBC sections made of lipped channels along with longitudinal stiffeners exhibited highest load carrying ability. Providing stiffeners at the junction of flange and web portions did not radically increase in load carrying ability when compared to sections having stiffeners in the webs and lip portions. SBC sections made of lipped channels also failed in similar buckling phenomenon like in other sections but the plate element local buckling predominantly occurred at the lip portions.

Optimisation of Trapezoidal Corrugated Plate Girder

Trapezoidal Corrugated web girders is a newly developed structural design. The major advantage of such design of web is that the corrugated webs enhance the stability of beam against buckling, which results in a very economical design by the reduction in the use of web stiffeners. The flanges are made up of flat plates and welded to the trapezoidal web sheet with the modern manufacturing process and modern advance welding technology. The flanges are mainly used to provide flexural strength to the beam and web are used to increase the shear capacity of the beam. Main reason for the failure of the web is the steel yielding or web buckling. Other possible failure reasons are lateral torsional buckling of the girder and local flange buckling, separately or in combination. This paper presents a new technological solution of such a system, composed by web made of trapezoidal shape. The buckling strength of the girder is studied under different geometrical modifications performing a nonlinear finite element analysis in ANSYS.

Strength evaluation of intersection between stiffeners and primary supporting members in double hull structure

In this previous study, a consistent theoretical formula was established in single hull structure, taking account of all the structural components affecting the load share of each member, in combination with the combined load effect of direct force from the longitudinal stiffener and shear force on the primary supporting member. What's more, it has been known qualitatively that the bending moment at the root of the web stiffener in double hull structure is less than that in single hull structure. However, the difference between double hull and single hull structures has not been achieved. In this study, the authors develop a theoretical formulation to represent the stresses at the root of the web stiffener due to the load from both the longitudinal stiffener and the shear force on the primary supporting member in the double hull structure. Then, the results calculated by the derived formulae are compared with the results obtained by finite element analysis, and good accuracy of the proposed formula was verified. Finally, the calculated stresses were compared between double hull and single hull structures. On one hand, the share of loading born by the web stiffener is almost comparable between the double hull and single hull structures. On the other hand, the bending moment at the root of the web stiffener is smaller in the double hull structure than in single hull structure, and therefore, the maximum stress is smaller.

Numerical assessment of lateral distortional buckling in steel-concrete composite beams

Steel-concrete composite beams, when requested by negative moment, can fail due to Lateral Distortional Buckling (LDB), local buckling, or by the combination of these stability modes. LDB is a mode of stability in which the web must distort in order for the compression flange to displace and twist during buckling. The standard procedures that address this phenomenon use the conventional lateral-torsional buckling theories for the buckling of partially restrained beams or the U-frame model. This study investigates, through the development of refined physical and geometrical nonlinear numerical analyzes with the ABAQUS software, the strength of steel-concrete composite beams under the action of negative moment. The influences of several parameters are analyzed, such as: steel profile cross section, longitudinal reinforcement rate, unrestrained length, presence of the web stiffeners and the distribution of negative moment along the span. The results are compared with standard procedures and analytical methods. It can be concluded that the cross section and the presence of web stiffeners are the parameters that most influence the LDB strength. Regarding the standard procedures, it was found that both those who adopt the conventional lateral-torsional buckling theories and those who use the U-frame model provide conservative results. Therefore, further investigations are necessary to better understand the behavior of these elements under the action of negative moment.

Flexural capacity of gapped built-up cold-formed steel channel sections including web stiffeners

This paper describes an experimental and numerical investigation to study the flexural capacity of back-to-back gapped built-up cold-formed steel (CFS) channel sections under four-point bending. The gap between the back-to-back channels was formed through intermediate link-channels which were screwed to the webs of the back-to-back channels. A total of 90 results comprising 18 laboratory tests and 72 finite element (FE) analysis results are reported on the flexural capacity of back-to-back gapped built-up CFS channel sections under four-point bending. Three different types of channels were considered to form the built-up channels: plain channels, channels with one web stiffener and channels with two web stiffeners. Two different beam spans as 1000 mm and 2000 mm were tested. Initial geometric imperfections were also measured prior to bending tests for all test specimens. A nonlinear FE model was then developed, the results of which showed good agreement against the laboratory test results. Using the validated FE model, an extensive parametric study was conducted to investigate the effects of web stiffeners and link-channel spacing on the flexural capacity of such gapped built-up beams. It is shown that design in accordance with the American Iron and Steel Institute, AISI (2016) and Australia/New-Zealand standards, AS/NZS (2018) can be conservative by as much as 27%. The flexural capacity of back-to-back gapped built-up sections with two web stiffeners was increased by 10% on average, when compared to the capacity of gapped built-up beams with plain channel sections.

Research on static performance of T-shaped stiffener Reinforced Box Space joints under Spatial Loading

The problem of inner partition reinforced box column are the weld quality, time-consuming and laborious. In view of the problem, T-shaped stiffener externally reinforced box space beam-column joinst are proposed in this paper. The finite element simulation was used to study the evolution of the initial stiffness of the T-shaped stiffener reinforced joints under spatial static loading, and the mechanism of the mutual force transfer between the T-shaped stiffener and the H-shaped beam and square column are revealed. The beam section height, the width of the T-shaped stiffener web, the height of the T-shaped stiffener flange are analyzed which are the T-shaped stiffener geometric parameters. The static performance of the reinforced box space joints are gained. The results show that the plastic hinge of the T-shaped stiffener reinforced the space joint is formed in the distance from the beam flange which is the point connecting with the end of the T-shaped stiffener. Such as the stress distribution is reasonable. The bearing capacity, plastic limit bending moment and initial stiffness of the box space joint can be effectively improved with increasing of the beam section height, stiffener web width and stiffener flange height. Therefore, the external T-shaped stiffener reinforced square steel column H-beam space joint has good static performance.

Optimization of Cold-Formed Steel Channel Columns

Sixteen cold-formed steel channel columns with different combinations of edge and web stiffeners under axial compression forces up to failure were numerically investigated using finite element (FE) analysis program, ANSYS. The behavior characteristics; the ultimate load, stiffness, ductility and energy absorption have been selected and separately analyzed in relation to column parameters. To determine the single-performance optimization of each characteristic, Taguchi method was applied. The multi-performance optimization was also investigated using Taguchi method coupled with grey relational analysis to achieve the favorable column characteristics and to investigate the multiple-performance characteristics index of each column. The results indicated that for multi-response and a single response, the predicted results are confirmed and the errors in the predicted values using the Taguchi method with respect to the numerical values using ANSYS are acceptable and also they indicated that broken straight line web stiffener factor (WS3) was the highest contributing parameters for variation of the ultimate load of CFS columns.

Enhancing flange local buckling strength of pultruded GFRP open-section beams

In this work, the use of pultruded GFRP web stiffeners to enhance the flange local buckling behavior of pultruded GFRP open-section beams was proposed and demonstrated through a numerical study. The buckling strength of the GFRP I-beam was successfully increased by up to 207% via this approach. The influences of the stiffener geometry and spacing were investigated. The buckling strength of the GFRP I-beam increased as the stiffener width increased and the stiffener spacing decreased. Epoxy adhesive was found to provide a sufficient bonding effect between the web stiffeners and the beams. In addition, a design approach was proposed to predict the increased buckling strength of GFRP I-beams strengthened with web stiffeners. A comparison with finite element analysis and experimental results showed that the design equation was able to provide uniformly conservative predictions. Additionally, practical design suggestions were provided to ensure the best performance of the web stiffeners. The strengthening approach addressed in this work could potentially permit a longer span of GFRP profiles and a wider application of GFRP structures.

Seismic behaviour of combined steel framed-tube substructure with replaceable shear links

A combined steel framed-tube structure with replaceable shear links (SFTS-links) can make plasticity isolated to links for rapid replacement of damaged links and improve the applicability of SFTS-links with enhanced ductility in high-seismic zones. In this paper, the seismic performance of thirty-storey SFTS-links and SFTS was compared by elasto-plastic time history and nonlinear static analyses. A 2/3-scale double half-storey, one-bay substructure was tested under cyclic loading in two stages. The substructure was repaired by replacing the damaged link in Stage I. Then the substructure restored to its original position was loaded to destruction in Stage II. Analysis of the substructure was conducted for two stages. The results indicate that ductility of SFTS-links is 34% higher than that of SFTS; the link can be replaced even at the story drift angle of 0.43%; replacing the damaged link can substantially improve the performance of the damaged structure; the ductile factor and the maximum viscous damping ratio of the specimen are 3.92, 0.39, respectively, and the maximum rotation angle and overstrength factor of the link are 0.147 rad, 1.54, respectively; the failure mode of the link is that expansion of the weld crack at the chamfer position of stiffeners causes tearing of link web and fracture of stiffeners. A numerical model is developed and verified with the test results. With increasing link length, initial stiffness, peak strength and cumulative energy dissipation decrease. It is recommended that the length ratio of the link should be 0.93–1.26 in SFTS-links.

Elastic Critical Stress for Trapezoidal Sheeting with Flange and Web Stiffeners

Elastic Critical Stress for Trapezoidal Sheeting with Flange and Web Stiffeners

Longitudinally stiffened web purlins under shear and bending moment

Abstract This paper aims to better understand the influence of longitudinal web stiffeners in the structural behavior of cold-formed steel purlins. A set of specimens with stiffened web and plain web cross-sections were tested on predominantly shear, combined bending and shear, and bending only. Numerical analyses carried out in CUFSM and ANSYS investigated the buckling behavior of the sections, allowing the determination of elastic critical stresses and the calculation of the resistance for the tested specimens by Direct Strength Method (DSM). Numerical results showed that the intermediate web stiffeners improve the buckling strength in loading cases of pure bending and pure shear. Experimental and numerical data were used to evaluate the interaction between bending moment and shear force, and showed that the circular interaction diagram was conservative and the results were closer to the trilinear interaction diagram. The comparison between experimental data and DSM predictions demonstrated that DSM provides accurate estimates for shear and flexural strengths of purlins with stiffened web cross-section.

An experimental and numerical investigation of reduced beam section connections with horizontal and vertical web stiffeners

Following the 1994 Northridge earthquake, reduced beam section (RBS) was presented as a novel connection detail in the steel moment-resisting frames. Proposed detail aims to debilitate the beam at a limited interval from the connection so that less moment and force are assigned to the connection. Cutting of the beam flange, especially in the narrow sections such as IPE, leads to an increase in the potential for the web local buckling, beam lateral-torsional buckling, and reduction in the beam strength. The hysteresis curve of IPE profiles, particularly in medium and large sections, is highly declining after the buckling. In this paper, a simple method was presented to amend the efficiency of IPE beams with an arched cutting in the flange, using horizontal and vertical stiffeners of the beam web. The experimental results and those of finite element in IPE beams revealed that the simultaneous application of horizontal and vertical stiffeners of the beam web largely prevented the declining of the beam hysteresis curve and left a full effect on its behavior. Therefore, the use of these types of connections in seismic areas with high relative risks is recommended.

A numerical model for evaluating fire performance of composite box bridge girders

This paper presents an approach for evaluating fire performance of composite box bridge girders exposed to fire. The model takes into account critical parameters, namely, fire scenario, fire exposure length, load level, numbers of longitudinal stiffeners in web and bottom flange and web pattern, that influence fire performance of bridges. A three dimensional finite element model, developed in the computer program ANSYS, is applied to model the fire response of composite box bridge girders. The finite element model is validated by comparing predicted sectional temperatures and deflections from the model with fire test data generated from a test on box bridge girder. The applicability of the numerical model in practical application is illustrated through numerical analysis on a composite box bridge girder subjected to simultaneous structural loading and fire exposure. Results from the numerical study clearly show that fire severity, fire exposure length, load level, number of longitudinal stiffeners and web slenderness have significant influence on the fire resistance of composite bridge girders. Provision of longitudinal stiffeners can result in lower deflections; thus enhancing fire resistance. Further, inclined web (configuration) incorporated into sectional shape can enhance fire resistance of composite box bridge girders.

Effect of multiple longitudinal stiffeners on ultimate strength of steel plate girders

In the present paper, the effect of multiple longitudinal web stiffeners (up to four) located at their optimum location on the ultimate strength of steel plate girders subjected to predominant shear loading, and combined bending and shear loading is investigated by using nonlinear inelastic analysis. Three dimensional (3D) finite element (FE) models of the steel plate girder are developed and analyzed by using ABAQUS commercial software. The accuracy of the FE models is validated by comparing their results with analogous experimental data. An extensive parametric analysis has been carried out to estimate the influence of specific geometric parameters on the ultimate strength. It has been shown that the shear resistance obtained from AASHTO LRFD equation is conservative since the influence of the longitudinal stiffeners was not considered in computing the shear resistance of the web plate girders under predominant shear loading and combined bending and shear. In addition, it has been demonstrated that the variation of the ultimate strength of the girder is almost monotonic against the various dimensionless geometric parameters, enabling thus the design of girder beams based on interpolation of tabulated data. Finally the results indicate that by adding not more than four stiffeners at the web of a steel plate girder subject either to predominant shear or combined shear and bending loads, an increase in its ultimate strength between 8% and 105% can be achieved.

Post‐buckling Strength of Plate Girders subjected to Shear: New Design Method

ABSTRACTThis paper describes a calculation method for steel plate girders with transverse web stiffeners subjected to shear. It may be used for predicting the failure load or, as a design method, to determine the optimal amount of internal web stiffeners. The method is based on the theory of plasticity. Many other theories have been developed, but the method presented differs from these theories by incorporating the strength of the transverse stiffeners and by the assumption that the tensile bands may pass the transverse stiffeners, which often is observed in tests. Other methods have only dealt with a single web field between two stiffeners.The method is called the plastic tension field method. It is based on the theory of plasticity and is analogous to the so‐called diagonal compression field method developed for reinforced concrete beams with transverse stirrups, which was adopted in EC2.