Transverse Stiffeners Research Articles

Experimental investigation on stiffened plates with non-continuous longitudinal stiffeners ending within the panel

The present contribution investigates a construction method predominately applied in crane manufacturing known as non-continuous longitudinal stiffening. In this approach, the longitudinal stiffeners end within the panel, leaving a gap before reaching the transverse stiffener or the end of the girder. Current standardization is limited to conventional continuous stiffening. Therefore, the present study conducts an experimental test series of 50 close-to-reality scaled, non-continuously longitudinally stiffened plates subjected to uniform compression to characterize their structural behavior. The results are compared regarding different geometry parameters. One main conclusion is that the gap drastically governs the ultimate resistance, usually leading to a triangular-shaped buckling mode.

Analysis of beam web panels with full length transverse stiffener in compression

The web panels of metal sections subjected to compression have resistances that are often driven by local buckling. Transverse stiffeners are used to increase their resistance. These stiffeners can be arranged at different positions in relation to the edge of the metal section. The strength of the stiffened panel can be compared to that of a compressed element whose cross-section consists of the stiffener and a participating length of the web. To observe the behavior of these stiffened walls and to evaluate the existing analytical calculation methods, an experimental campaign was carried out on two metal sections of different heights, stiffened or not over their entire height of the web. Thus, 33 zones of stiffened or unstiffened panels are tested in double localized compression until failure. The stiffeners are placed near the edge or in the middle of the panel and welded on both sides of the web over its entire height and on the panel flanges. In parallel, a finite element model using shell elements and non-linear calculations considering the plasticity of the materials, the geometrical imperfections and the large displacements is set up. It is validated by comparing its force–displacement curves and modes of ruin with those obtained by tests. The model thus validated makes it possible to enrich the results of the experimental tests to better describe the behavior of stiffened walls subjected to compression. It also allows to discuss the observed failure modes and some analytical formulas which estimate the resistance capacities of the stiffened panels.

Fatigue life prediction of welded joints at sub-zero temperatures using modified Paris–Erdogan parameters

The fatigue life of welded steel components is usually determined by the weldment; in these cases, fracture mechanical approaches are widely used for their prediction. Ferritic steels are known to have a fatigue strength that is dependent on temperature. Therefore, this study evaluates fatigue tests of cruciform joints and transverse stiffeners at different sub-zero temperature levels regarding fatigue life. Simultaneously, the stress intensity factors over the crack length are calculated for the individual experiments using analytical solutions. Then, using the Paris–Erdogan relation with temperature- and material-specific C and m parameters as well as tabular values, the fatigue lives are calculated with analytical solutions and compared with the experimental results. It is shown that the prediction accuracy is significantly increased for the sub-zero temperature range by using temperature-adjusted Paris–Erdogan parameters, as long as the temperature is above the fatigue transition temperature.

Reliability of Cold-Formed Steel Sections Subjected to Web Crippling

This study aims to evaluate the structural safety of cold-formed steel sections subjected to concentrated loads in regions without transverse stiffeners, susceptible to web crippling, and dimensioned according to the North American Specification (AISI S100) and the Norma Brasileira (NBR 14762 2010) standard. Experimental data from various sections reported in the literature were analysed, obtaining professional factor statistics. Target reliability indices commonly used in the calibration of cold-formed steel standards were considered. A reliability analysis according to the First-Order Reliability Method (FORM) was developed for several action combinations found in the AISI and NBR standards. In addition to the scenarios prescribed by the AISI (2016), a scenario for the NBR 14762 (2010) standard is proposed, which, although it does not yet exist in the standard, was adopted for research purposes. In the proposed scenario, it was discovered that the resistance factor stipulated by the NBR 14762 (2010) standard did not produce satisfactory outcomes regarding a target reliability index of 2.5 in 10 out of 25 examined cases.

Enhancing the cyclic performance of shear links using longitudinal stiffeners

Shear links constitute the most crucial part of eccentrically braced frames. Their main responsibility is to dissipate the earthquake input energy away from the main structural members; therefore, keeping them responding within the elastic stage. However, the rotation capacity of vertical shear links directly influences the allowable interstorey drift of the eccentrically braced frame and the energy dissipation capacity. To enhance their rotation capacity and performance, transverse stiffeners in vertical shear links are proposed to be replaced with longitudinal stiffeners in this research. A numerical study is conducted, using Ansys Workbench, on fourteen shear links with different parameters to investigate their cyclic behaviour. The considered parameters are the stiffener configuration (transverse or longitudinal), web thickness, stiffeners number, stiffeners thickness, flanges width, and web aspect ratio. The influence of these parameters on the failure mode, hysteretic response, mechanical parameters (strength, rotation capacity, etc.), ductility, cyclic web shear buckling, and energy dissipation is analysed and discussed. The results demonstrate that longitudinally stiffened shear links surpass conventional transversely stiffened ones in terms of strength, overstrength, rotation capacity, ductility, web shear buckling resistance, and energy dissipation. Additionally, it is found that the current design provisions of EN 1998–1 cannot accurately predict the yield shear strength of longitudinally stiffened shear links. Moreover, numerous remarks involved with the influence of different parameters on the cyclic performance of longitudinally stiffened shear links are presented and discussed.

Numerical study on steel plate girders ‐ Intermediate transverse stiffeners axial force

AbstractTransverse stiffeners are used in steel plate girders with slender webs to provide lateral support to the web along the span and thus increase the plate girder shear resistance. Furthermore, transverse stiffeners anchor the tension field, resulting in axial compression in the stiffener. Despite this, it is widely assumed that the design axial force provided by the FprEN 1993‐1‐5 [1] for the transverse stiffeners is significantly greater than that observed in experimental testing and numerical simulations.The results of 550 nonlinear numerical simulations of plate girders loaded in shear up to failure are presented. Shear resistance and axial stiffener forces are evaluated while the effects of a wide parameter range as web aspect ratio and thickness, flange‐to‐web area ratio, and steel grade are investigated. The numerical results are compared to the European standard design values. Finally, a statistical analysis of the set of results is presented.The numerical analyses show that the axial forces installed in the intermediate transverse stiffeners are significantly lower than those specified by FprEN 1993‐1‐5 [1].

Design optimisation of welded I‐beams made of high strength steels

AbstractNowadays, hot rolled steel sections are used in practice. The cross‐sectional dimensions are therefore fixed and catalogued by the steel manufacturers. However, when the span of the members and/or the applied load becomes significant, such hot rolled steel sections can no longer meet the ultimate and/or service design criteria and the use of a built‐up welded I‐beam should be considered. They are typically made of three steel plates welded together to form a monolithic I‐beam. By varying the dimensions of these plates, an infinite amount of cross‐section geometries can be defined. But face to this high variability of solutions, the designers encounter difficulties in identifying the most appropriate combination of geometrical and mechanical properties for the constitutive plates.To study and optimise these profiles, a MATLAB® routine has been developed at the University of Liege. It allows, for different load cases, to find suitable cross‐sectional dimensions that minimise the weight and/or the total cost of the element. This routine follows the current recommendations prescribed in prEN1993‐1‐5 and evaluates the possibility of using transverse stiffeners along the web to further reduce the weight and cost of the element. The so‐developed routine is presented in the present paper. Also, the advantage of considering the use of high strength steels for such structural members is discussed to propose recommendations to the designers for the selection of the most appropriate steel grade.

Numerical study on the impact of longitudinal stiffeners ending within the buckling field

AbstractTypically, longitudinal stiffeners of plated structures pass through the entire girder (continuously) or span from one transverse stiffener to another (discontinuously). The present research deals with a design method predominantly executed in crane manufacturing – non‐continuous longitudinal stiffening. Non‐continuous longitudinal stiffeners end within the buckling field, i.e., leaving a gap ahead of the transverse stiffener or the end of the girder. To date, the standardization in EN1993‐1‐5 is limited to conventional longitudinal stiffening (continuous and discontinuous), as defined above. This paper deals with a numerical study aiming to obtain initial insights into the load‐bearing behavior of non‐continuously stiffened plates. Geometrically and materially nonlinear buckling analyses with imperfections (GMNIA) are performed to provide the foundation for a series of experimental tests. Alongside the realization of realistic boundary conditions, estimating the most realistic ultimate load‐bearing capacity is of particular importance to comply with the constraints in the laboratory. The simulations reveal a significant load‐bearing behavior and capacity modification compared with conventional longitudinal stiffening.

Specific distortion‐induced fatigue failure at main girders of a railway bridge – efficiency of different reinforcements based on strain measurements

AbstractAt the main girders of a three span continuous girder railway bridge, built in the 1960s, through‐thickness cracks were detected in the web, at the location of the transverse stiffener to main girder connections. The transverse stiffeners are not welded to the girder flange, in order to increase their fatigue resistance. Instead, fitting strips between the stiffeners and the bottom flanges were used.First of all, the paper presents the results of local strain measurements at the original detail, without any reinforcement, for individual train passages. These results confirm a distortion‐induced fatigue failure, due to an unexpected high‐frequency oscillation of the web plate. Based on that, three different types of reinforcement were developed and installed at the bridge. For each type of reinforcement further strain measurements were done during regular train service. Also, a weigh‐in‐motion‐system was installed, to specify a representative passenger and freight train each. From the local strain measurements, during the passage of these two trains, the stress‐spectra were evaluated for all three types of reinforcement. Furthermore, existing fatigue test data of a similar connection detail from the literature were reassessed in order to provide an accurate fatigue resistance for the damage accumulation. The comparison of the evaluated fatigue damage of these individual stress spectra indicates the efficiency of each type of reinforcement.Finally, also representative reduction factors of the initial stress ranges without reinforcement, were developed for each type of reinforcement. This allows a more generalized assessment, regarding the efficiency of the different types of reinforcement, not just valid for individual trains but also for the whole train traffic.

Fatigue Verification Concept for Details containing Weld Imperfections

AbstractSteel structures subjected to repeated stress variations must be verified against fatigue in accordance with EN 1993‐1‐9 on the basis of a detail catalog. As one major concern, the background of the detail classification in terms of an extensive database does not provide information on the considered quality of welds. Certain weld imperfections are present in every construction. However, the extent of imperfection sizes that can be tolerated to provide sufficient fatigue resistance has not yet been scientifically determined.On an experimental and numerical basis, the presented concept allows the quantitative connection of fatigue classes with sizes of weld imperfections. For the two representative details of the load‐carrying‐cruciform joint and the non‐load‐carrying transverse stiffener, basic fatigue classes without explicit imperfections are calculated first. Furthermore, stress increase factors were determined that indicate the decrease in fatigue strength for weld imperfections of different type and size.A combination model is used to determine the fatigue strength of a detail with multiple weld imperfections. Using a simple formula and reading fatigue classes and reduction factors in tables, the fatigue strength of an imperfect detail can be easily determined.

Fatigue strength of tubular welded connections in offshore floating platforms

AbstractThe work reported in the present paper is part of a European research program aimed at developing a hybrid tension‐leg floating platform, suitable for combined offshore wind and wave energy exploitation. Eight (8) fatigue tests on welded tubular joint specimens are performed, which represent the full penetration brace‐to‐cylindrical column welded connections of the project prototype structure. The large‐diameter columns are reinforced internally with a grid of longitudinal and transverse stiffeners fillet welded to the shell. The specimens are approximately 1/6‐scale physical models made of S355 grade steel, and subjected to cyclic loading under constant load amplitude histories. The brace‐to‐cylinder welds are semiautomatic, and high‐frequency mechanical impact treatment is applied in four specimens. The experiments are supported by post‐fracture metallographic examination and finite element analyses. The results indicate two locations for fatigue crack initiation: brace‐to‐cylinder crown and cylinder‐to‐stiffener connection.

On the fatigue behaviour and reliability assessment of high strength welded details

This research focusses on the fatigue behaviour of welded components made of high strength duplex (EN 1.4162) and carbon steel. It starts by investigating the base material alongside welded cruciform joints submitted to cyclic loading through experiments and finite element models. The obtained results are then compared with existing research on high strength (carbon and stainless) steel equivalents. This collated database of >500 reference test results is then used to assess the applicability of the current Eurocode and IIW provisions to predict the fatigue life of higher strength steels and to propose new rules that include the benefit of their higher material strength. Proposals are made to upgrade certain fatigue classes (e.g., transverse stiffeners and butt welds) when high strength steel grades are employed. The reliability of these proposals is then supported by the use Weibull models, commonly used in survival analysis.

Theoretical modeling for predicting the shear strength of partially-encased composite members with multiple transverse stiffeners

Partially encased composite (PEC) members are frequently used as girders in heavily-loaded or long-span structures. In PEC members, the steel web is encased in web concrete between the top and bottom flanges. When PEC members are used in continuous beam spans, the intermediate support area is subjected to significant shear force and negative bending, which is more critical than the span center. As a result, accurate prediction of shear strength is crucial for structural safety in practical design. Unlike traditional concrete or steel beams, PEC beams have multiple shear transfer mechanisms consisting of concrete, steel flanges, axial steel web, and transverse stiffeners (if necessary), and it is essential to investigate the shear contributions of the different mechanisms and how they work together as a composite structure. To solve this problem, this paper presents a novel shear strength model, in which the global shear strength is composed of two main components: the composite truss (steel flanges, web concrete, and transverse stiffeners) and the axial steel web, and these two components are unified by strain compatibility to show the composite action. Then, the proposed model is compared with existing shear equations using 25 existing specimens in the literature, and the results indicate that the proposed model can predict the shear strength of PEC beams with sufficient accuracy. Finally, the paper presents a simplified design method after validating the shear contributions of different anti-shear mechanisms, and the simplified method can facilitate practical design in engineering practices.

STRENGTH AND DUCTILITY EVALUATION OF THIN-WALLED STEEL TUBULAR BRIDGE PIERS UNDER CYCLIC LOADING

Numerical simulations are being conducted on the behavior of thin-walled steel tubular bridge piers under cyclic lateral loading in the presence of constant axial compression loads. The effects of cyclic lateral loading on the behavior of the thin-walled steel tubular bridge piers have been evaluated through analysis of the hysteresis curve, envelope curve, stiffness, and strength degradation characteristics, and energy-dissipating capacity, including interaction effects of local buckling and flexural buckling, and post-buckling regimes. This study also compares the numerical analysis with experimental results available in the literature to validate the accuracy of the proposed finite element model. Based on this model, a range of relevant material and structural parameters will be investigated in future work. Numerous numerical specimens will be designed and analyzed, gaining further information about the influence of width-to-thickness ratio, Rt, column slenderness ratio, , material properties of the embedded shell plate, spacing of transverse stiffening ribs of the shell, height, and properties of partially infill concrete, and axial compression load.

An experimental investigation into the influence of incorrect root gaps in welded-in transverse stiffeners on fatigue performance

The paper presents a comprehensive set of special experimental fatigue tests designed to determine the fatigue strength sensitivity of steel components, under circumstances where fabrication quality levels deviate from regulatory standards. Precise monitoring of the manufacturing process of test specimens containing internal imperfections facilitates accurate documentation of the phenomena that contribute to the eventual shape of the imperfection. Welded-in stiffeners with incorrect root gaps of varying sizes were subjected to fatigue testing, as such studies have never been carried out in experimental form before, as the background data to EN 1993-1-9 disclosed. The experimental investigation confirms numerical estimations, which predicted that even large root gaps do not result in lower fatigue strength values, when compared to stiffeners that were properly fitted. Moreover, details in welded beams that feature an intersection of three welds at the stiffener exhibit no discernible decrease in fatigue performance compared to rolled sections.

Experimental and numerical investigation of axially loaded L-shaped box-T section columns

L-shaped box-T section column (named ‘the Column’ in this paper) is increasingly used in the corner to avoid the column protruding indoors and increase the indoor area, but few pieces of research were conducted to study the Column’s axial loaded performance. This research investigated the axially loaded performance of the Column, proposed design suggestions, and modified design curves through experimental and numerical studies. In the experimental studies, 12 columns were axially loaded, and results were reported. According to experiments, distortional buckling decreasing column buckling strength was observed unless midspan transverse stiffeners were set. Based on the experimental and numerical analysis, one stiffener was recommended to be placed at the midspan. A parametric study was also conducted using the verified finite element (FE) method to assess column curves in Chinese, European, and American codes and provide reasonable design suggestions. Ultimately, modified design curves were put forward according to the Chinese and European codes’ theoretical basis, respectively.

Experimental behaviour of plate girders in steel – Internal forces in intermediate transverse stiffeners

Economical design of steel plate girders usually adopts slender web panels sometimes combined with large panel aspect ratio, which determines the elastic stability of the web panel. The adoption of transverse stiffeners is one efficient strategy to retard the web buckling due to shear. The primary role of intermediate transverse stiffener is clear: divide the web into panels providing lateral support to the web plate along the span – This increases the shear strength of the web. However, FprEN 1993-1-5: 2022 [1] stiffener design approach is based mainly on direct compressive forces resulting from the tension filed action in post buckling phase. According to multiple investigations, this area requirement is much higher than that found in laboratory testing and numerical simulations. The findings of experimental testing on eight plate girders with thin webs and two configurations of transverse stiffeners under ultimate load are presented. Using the web and stiffener measure strains, the internal stiffener forces are calculated past the shear failure of the plate girders. These results show that the axial compression and bending moment measured in the intermediate transverse stiffeners are considerably lower than those specified for the design by the FprEN 1993-1-5: 2022 [1].

Proposed Stiffener Spacing Requirements for the Seismic Design of Short Links in Eccentrically Braced Steel Frames

Links in eccentrically braced frames (EBFs) are designed with transverse web stiffeners to achieve the desired seismic performance targets established in current design standards. Prior studies have suggested that stiffener spacing requirements in the standards may be conservative. This paper proposes new stiffener spacing design requirements for short EBF links. The proposed limits were established on the basis of a methodology that combines a numerical solution of the classical problem of inelastic plate buckling of a thick plate under shear thrusts along with comparisons with available experimental data. The resultant design equation was verified through complementary continuum finite-element simulations of 18 wide-flange short links under symmetric cyclic loading. The finite-element simulations suggested that the proposed design equation reduce the stiffener requirements by about 35%, on average, relative to the current stiffener spacing requirements for short EBF links. Limitations and suggestions of future work are discussed.

A compound strip method based on the Mindlin plate theory for static and buckling analyses of thin-walled members with transverse stiffeners

The compound strip method origins from the finite strip method (FSM) aimed to analyze thin-walled members with additional parts such as bolts and stiffeners. Traditionally, FSM mainly solves the buckling problem of prismatic members with longitudinally uniform sections. However, existing FSM could not take into account the stiffeners’ effect in the present form. The paper proposes a compound strip method based on the Mindlin plate theory (MCSM), in which members are modeled by finite strips while stiffeners are by MITC4 shell elements. This combination can effectively connect the stiffeners with the flange/web of the members. Meanwhile, the contribution from the thickness of stiffeners to buckling strengths could be considered accurately. The validity of MCSM is demonstrated through the comparison of the deformation and capacity from static and buckling analyses with solutions of the finite element method (FEM). The developed MCSM is then used to explore the impact of the number and thickness of stiffeners on the members. Besides, the discussion on how sectional characteristics affect stiffeners in improving the buckling loads is carried out. To ensure the calculation in MCSM is accurate and efficient, a study on meshing schemes is also presented.

Experimental and numerical study on the failure modes of ship stiffened plate structure under projectile perforation

Four sets of experiments were carried out on penetrating the ship stiffened plate structures which were made of panel plates with different thicknesses and stiffeners with different sizes. Ballistic characteristics of projectiles were recorded by a high-speed camera system. Through analysis, it has been found that stiffeners can reduce the overall plastic deformation of the panel and make projectile attitude change significantly. The failure modes of stiffened plates, which are obviously different from the homogeneous plates, change accordingly with the change of impact points. In order to analyze the problem better, the stiffened plate is assumed to be composed by four parts, namely main panel plate, transverse large stiffener ventral plate, transverse large stiffener flange plate and longitudinal weak stiffener. The penetration process has been simulated by 3D analysis using ANSYS/LS-DYNA which was verified by experiments, and numerical simulations were carried out. Through the numerical and experimental results, a variety of failure modes have been observed. Failure modes of stiffened plates are found to be composed by four types and summarized.