I-shaped Members Research Articles

Lateral-Torsional Buckling Modification Factors in Steel I-Shaped Members: Recommendations Using Energy-Based Formulations

Lateral torsional buckling (LTB) is of concern in long-span flexural members, particularly in the negative flexure regions of continuous-span, steel I-shaped members and during construction. While the elastic critical LTB capacity of a simply supported I-shaped member subjected to uniform moment has a closed-form solution, most LTB modification factors for beams subjected to moment gradients in the literature are empirical and work well only for specific loading and boundary conditions. This paper investigates the suitability of the different LTB modification factors in literature and design specifications for various loading and boundary conditions, accomplished via comparisons with analytical solutions using the Rayleigh-Ritz method and numerical solutions from finite element analyses. The analytical LTB modification factors are derived for doubly symmetric I-shaped members with different combinations of ideal flexural and torsional boundary conditions (simply supported and fixed) and subjected to different loading scenarios. The validity of the LTB modification factors determined using the Rayleigh-Ritz method and other formulae in the literature are also assessed for realistic intermediate restraint conditions, which are neither fully pinned nor fixed, by examining laterally continuous beams. Demonstrating that current design specifications for elastic critical LTB modifications are overly conservative

Numerical investigation of the influence of transverse welds on the strength of aluminum alloy I-shaped members – Columns

This paper presents a numerical investigation, using finite element analysis, of the effects of transverse welds on the structural behavior of aluminum-alloy compression members. A non-linear finite element (FE) model was developed, and validated using experimental tests, to simulate the behavior of 6061-T6 aluminum-alloy columns with an I-shaped AW6×4.03 section geometry. The FE model included different material properties for the heat-affected zone (HAZ) that occurs in the proximity of the weld and the remaining base material, and incorporated both geometric and material nonlinearities. A parametric study of 80 columns with and without transverse welds was conducted, which investigated ten unbraced lengths, three weld centerline locations along the member length, and two types of post-yield material stiffness models, including elastic-perfectly plastic and strain hardening materials. The FE results provide clear evidence of the significance of the HAZ strength reduction on the load carrying capacity of welded aluminum-alloy columns. Numerical results were compared with those obtained using the provisions within the Aluminum Association’s Specification for Aluminum Structures, and they were used to develop proposed modifications to these provisions, which can remove the degree conservatism observed. A similar study on beams is presented in a companion paper.

Elastic local buckling coefficients of I-shaped beams considering flange–web interaction

Since using high–strength and high–performance steels has become a more common structural design practice in building and bridge construction, there is an increased potential for designing extremely thin-walled I-shaped beam members to enhance the efficiency of the steel beam design. For a more accurate design approach for these thin-walled I-beam members, particularly when they are near noncompact limits, it is necessary to explore more rational methods for determining the elastic local buckling strength of I-beams. This study aimed to investigate the local buckling behavior and strength of I-shape structural sections by considering flange-web interactions through three-dimensional finite element analysis. The goal was to provide a more reasonable estimation of local buckling strength under uniform bending. To evaluate the local buckling behavior of flange and web panels and explain it reasonably, this study adopted the ratio of flange-web slenderness (λf/λw) and height-to-width ratio (H/bf) of I-shaped beams which can affect buckling mode shapes and local buckling strength of I-shaped beams induced by flange local and web bend bucklings. Finally, this study presented design equations for both flange local and web-bend buckling coefficients considering λf/λw and H/bf. It was expected that the presented local buckling coefficients (kf) for flanges and webs could lead to a more reasonable design, as compared to the existing AISC design provisions.

Transverse impact behavior of concrete filled steel tube simply supported members stiffened with encased I-shape CFRP

Concrete-filled steel tubular simply supported members stiffened with encased I-shaped CFRP (CFSTS-CFRP members) have been developed due to their excellent mechanical performance, promoting promising applications in bridge and building structures. However, these members are susceptible to collision impacts during service, leading to serious accidents. This paper aims to investigate the structural behavior of CFSTS-CFRP members subjected to transverse impact loading, utilizing experimental, numerical, and theoretical studies. Drop hammer impact tests were conducted on three CFSTS-CFRP specimens with varying impact velocities, while a CFST specimen was used as the benchmark. The experimental results demonstrate that all CFSTS-CFRP specimens experienced bending failure. The cooperation between the I-shaped CFRP and CFST members was observed, with the mechanical properties of CFSTS-CFRP specimens being fully utilized. The working mechanism of CFSTS-CFRP members is revealed by numerical simulation results obtained from the FE models of the tested CFSTS-CFRP members, which consist of the analyses of failure mode, inertia force, sectional moment, energy absorption, etc. Furthermore, by investigating the effects of different parameters on the structural response of CFSTS-CFRP members, predicted models for dynamic flexural capacity and maximum deflection are proposed for the purpose of impact design. Additionally, the contribution of the steel tube, concrete, and I-shaped CFRP to the transverse impact resistance of CFSTS-CFRP members is clarified. This clarification provides a scientific basis for determining the respective weight coefficients in subsequent damage assessment research. The findings from the experimental, numerical, and theoretical analyses contribute to the understanding of their mechanical performance and assist in the development of more efficient design approaches.

Verification of the Ramberg-Osgood Material Model for the Fire Design of Steel Members

Abstract In this paper, the modified Ramberg-Osgood constitutive equations for calculating the stress-strain of steel at elevated temperatures using the parameters determined based on the transient state tensile test results achieved at the Helsinki University of Technology are verified. This is done by numerically comparing the global and local buckling capacities of I-shaped steel members incorporating the modified Ramberg-Osgood model along with the material model given in the fire section of Eurocode EN1993-1-2. For this purpose, a numerical model using the ABAQUS software was developed. Then, nonlinear analyses with imperfections (GMNIA) were performed to compare the buckling capacities of the steel columns and beams of four different hot-rolled cross-sections (IPE160, IPE180, HE100B, HE500B), made of steel grade S355, at three different temperatures (400°C, 500°C, 600°C). The results showed that adopting the modified Ramberg-Osgood model can lead to the same buckling capacities resulting when using the EN1993-1-2 material model for steel temperatures of less than 400°C. However, adopting this model for 600°C overestimates the buckling capacities in most cases.

Shear performance and design rules for welded stainless steel I-shaped members with web openings

The use of stainless steel I-shaped members as primary load-bearing members has become increasingly popular, particularly in acidic environments, owing to their corrosion resistance and other advantages. Openings on the web are often introduced for ease of installation. The presence of web openings can reduce the shear resistance and produce high stresses around the openings, limiting their application. However, no previous study has investigated the shear resistance and design rules of such welded stainless steel I-shaped members with web openings. This work presents a detailed numerical analysis to examine the shear performance of perforated stainless steel members. Finite element (FE) models considering material nonlinearity and initial geometric imperfections were developed and verified using corresponding test data presented by the authors and many researchers. A parametric study including 434 FE models was undertaken to analyse the influence of web openings on the shear resistance of such members. The results suggested that for members with a hole diameter–web height ratio of 0.7, web openings can reduce the shear resistance by 61.4% on average, when compared to unperforated members. The generated numerical results were used to evaluate the current design recommendations given in the Eurocode (EN 1993-1-4+A1) (2015), American standard (ANSI/AISC 370-21) (2021), and those design rules proposed by Chen et al. (2018), although they were designed only for unperforated members. The comparisons demonstrated that the current design guidelines provided non-conservative predictions for calculating the shear resistance of perforated members. New design formulas were proposed using the strength reduction factor. A reliability analysis was undertaken, which indicated that the new design formulas were reliable for predicting the shear resistance of such members.

Finite element analysis and proposed design rules for 304D high-strength stainless steel I-shaped members in shear

The stainless steel I-shaped members are extensively used as plate girders due to their excellent performance. However, traditional stainless steel is often expensive and has a relatively low yield strength, limiting their application. In recent years, a new type of austenitic high-strength stainless steel named 304D (08Cr19Mn6Ni3Cu2N) was developed and extensively used. This new material has similar anti-corrosion properties as S30408 stainless steel, but has a lower cost and higher yield strength. However, no work has been undertaken on the shear resistance and design of such members. The material property and chemical property of such 304D members are quite different from those of traditional stainless steel, which may result in different performance in shear resistance. Hence, a total of six tensile coupon tests were performed to obtain the material properties of 304D high-strength stainless steel. Finite element (FE) models were established and validated against the corresponding test data reported by the authors and other researchers, although they are only traditional stainless steel. A comprehensive parametric analysis including 576 FE models was performed to examine the influences of the critical parameters on the shear resistance of such members. The results suggested that the shear resistance of 304D members increased by 61% on average, compared to S30408 members. The parametric analysis results were further used to assess the existing design methods in the GB 50017 (2017), EN 1993-1-4 + A1 (2015), ANSI/AISC 360–16 (2016), ANSI/AISC 370–21 (2021) and those proposed by Chen et al. (2018). Upon comparison, it was demonstrated that the existing design methods were generally over-conservative for predicting the shear resistance of such members. Design formulas were therefore proposed by modifying the original design eqs. A reliability analysis was then performed, indicating that the modified equations can closely predict the shear resistance of such members.

Critical study of steel beams with web openings

ABSTRACT In this study, experimental and numerical approaches are adopted to comprehensively investigate the flexural strength capacity and failure modes of I-shaped steel members with various web openings geometry. To validate the results, the finite element models are established using ABAQUS with the same configurations as the test specimens. Based on the experimental and numerical investigation it is observed that, the web openings not only weaken the practical section but also destroy its continuity. The common mode of failure observed in beams with web openings is excessive bending, Vierendeel mechanism and web post buckling. When the opening ratio exceeds 0.75, the openings greatly affect the stability of the components, which results in reduction in strength capacity of perforated beams. In contrast, when the opening ratio is less than 0.5, the openings have negligible impact on the stability and strength component. The web openings also have a significant impact on the bearing strength of the members when the provided web post width is less than 200 mm. In contrast, when the web post width exceeded 200 mm, the web opening ratio had only a small effect on the member bearing capacity. The response of the perforated beams was presented in terms of load-deflection and moment-deflection curves. .

Cyclic Response of Bolted and Hybrid Pultruded FRP Beam-Column Joints between I-Shaped Sections

This paper presents cyclic behaviour of bolted and hybrid–combined bolted and bonded fibre reinforced polymer (FRP) beam-to-column joints between I-shaped members using steel and FRP cleats. Five full-scale cyclic tests are carried out to study moment-rotation behaviour, cyclic response, and failure patterns. The test parameters include position of cleat (flange or combined web and flange), fastening method (bolting or hybrid–combining bolting and bonding) and cleat material (steel or FRP). First two tests had bolted and hybrid joints with steel flange and web double angles. Next two tests had the same joint detailing but with no web cleats. Last test used bolted joint only with FRP web and flange cleats. Three failure modes were observed: shear-out failure of the beam’s bolted zone, adhesive debonding with shear-out failure and delamination cracking. Cyclic performance of the joints was assessed by hysteresis moment-rotation curves and accumulated dissipated energy. Hybrid joints showed the best overall cyclic performance with accumulated dissipated energy about 75% higher than the bolted joints. Bolted joints with FRP cleats exhibited the worst cyclic performance. Flange cleated joints showed similar performance to web and flange cleated joints.

Technical Note: Unbraced Length Requirements for Steel Special Cantilever Column Systems

AISC Seismic Provisions Section E6.4b for steel special cantilever column systems (SCCS) requires clarification based on inquiries to the AISC Steel Solution Center. In the 2016 edition, it is unclear if bracing is required for all special cantilever columns or for columns with unbraced lengths that exceed the maximum beam brace spacing of Lb per Section D1.2a for moderately ductile members. Instead of using Equation D1-2, which is applicable to I-shaped beams only, equations for SCCS columns have been derived for both I-shaped members and rectangular HSS or box-shaped members. The proposed revision provides specific situations when bracing is required.

Basınç Elemanları İçin Yardımcı Abaklar

Bu çalışma yapısal tasarımcıların sıcak haddelenmiş I-enkesitli profillerden teşkil edilmiş basınç elemanlarını Çelik Yapıların Tasarım, Hesap ve Yapım Esasları’na (ÇYTHYE’na) göre hızlı ve etkin bir şekilde boyutlandırılabilmeleri için yardımcı abaklar sunmaktadır. Bu amaç için ÇYTHYE’de tanımlanan yük ve dayanım katsayıları ile tasarım (YDKT) esaslarına göre uygulamada en çok tercih edilen S235, S275 ve S355 malzeme sınıflarından teşkil edilmiş HEA, HEB, IPE ve IPN profilleri için ayrı ayrı basınç taşıma kapasiteleri belirlenmiş ve narinlik değerlerine göre değişimlerini gösteren abaklar oluşturulmuştur. Hazırlanan bu abaklar sayesinde malzeme sınıfına ve enkesit tipine göre istenilen narinlik değerlerinde elemanların tasarım basınç kuvveti dayanımlarına ulaşıla bilinecektir.

Overall stability of steel web-tapered frame members

The solution to the problem of fully nonlinear stability analysis of web-tapered I-shaped members is presented in the paper. In order to accelerate the analysis, an analytical- numerical approach was applied in the solution. Nonlinear stability analysis in the elastic range is carried out by the use of the analytical procedure (so-called “Member” procedure) which is based on the combination of the results of buckling and linear analyses. The growth of the plastic deformations is taken into account by adding extra displacements in the “Member” procedure. These displacements are determined numerically in the process of incremental loading (so-called “Section” procedure). The proposed approach allows the calculation of all displacements at each load step and the estimating of the member’s overall stability capacity, rapidly (up to 20 times faster than using shell-FEM) and accurately enough. The overall stability calculation results, depending on the different variables (slenderness, load eccentricities and their ratios, rigidity variations) under different load cases, are given in the paper. The stability capacity comparison between tapered and prismatic members is presented. Also the comparison with existent experimental researches’ results is provided in the paper.

Design of welded stainless steel I-shaped members subjected to shear

Abstract This paper aims to develop design methods for the shear strength of welded stainless steel I-shaped members. The current American AISC Design Guide 27 has been published for Structural Stainless Steel, and it refers to the specification ANSI/AISC 360-16 for structural steel buildings for the shear strength without considering tension field action (TFA). All the available test data on stainless steel plate girders were collected from literatures and employed to assess the provisions in the Design Guide 27, as well as the codified ones in Eurocode 3 Part 1.4. Based on the test results and obtained comparisons, two new proposals for unstiffened webs or webs with transverse stiffeners widely spaced (without TFA), and for interior webs with stiffeners spaced at 3hw or smaller (considering TFA) were developed and presented to match the format of the expressions in ANSI/AISC 360-16 for stainless steel webs under shear. Reliability analysis was further performed to calculate the Load and Resistance Factor Design (LRFD) resistance factors determined by the new proposals and to further justify the target factor in AISC Design Guide 27 for structural stainless steel.

Lateral torsional buckling of doubly symmetric I-shaped steel members under linear moment gradient

Lateral torsional buckling of doubly symmetric I-shaped steel members under linear moment gradient

Elastic Lateral Torsional Buckling of Simply Supported Beams under Concentrated Load and Linear Moment Gradient

Lateral torsional buckling is a limit state for I-shaped steel beams that may often be a controlling issue in structural steel design. When these members are not appropriately braced so as to prevent lateral deformations and torsion, they are subjected to risk of failure by lateral torsional buckling before reaching their ultimate capacity. This paper investigates elastic lateral torsional buckling of simply supported I-shaped steel beams under concentrated load and linear moment gradient using design standards and codes, approaches from the literature and finite element analysis. Several unbraced member lengths and end moment values are taken into account to compare and evaluate these approaches in terms of elastic critical moment and end moment ratios. Analysis results show that lateral torsional buckling is a crucial stability problem for I-shaped steel members that are under flexure and it is reflected with adequate safety in the design codes and standards considering finite element analysis outcomes.

Residual welding stress of I-section members beyond the limits of width-thickness ratio

Despite the extensive studies on the effect of width-thickness ratio and residual stress on member behavior, few scholars have probed into the residual stress distribution on the I-section members. Based on the principle of blind hole drilling, this paper conducts an experimental study of the residual welding stresses of eight welded I-shaped members. Through the analysis of the test results, the author draws the following conclusion: it is safe to use I-section members beyond the limits of width-thickness ratio because the residual stress distribution is not severely affected by width-thickness ratio.

Interactive buckling failure modes of hybrid steel flexural members

The flexural strength of steel I-beams is influenced by the local and lateral-torsional instabilities, where the presence of shear also reduces the moment carrying capacity. The objective of this research is to investigate the interactive buckling modes for hybrid steel I-shaped flexural members subjected to uniform moment loading. A three-dimensional finite element (FE) model subjected to monotonic loading is developed using nonlinear buckling analysis. The analytical model was experimentally verified based on the results of six full-scale 3m beams that were tested previously. An extensive parametric study is conducted for 526 FE models and different instability modes including local buckling, lateral-torsional buckling, and shear buckling modes are identified. Subsequently a classification is proposed based on slenderness to predict buckling mode shapes of flexural member. Attention is given to the interaction between shear and flexural buckling modes, and their effect on inelastic flexural capacity. The flexural strength is evaluated based on local and overall slenderness and interactive buckling behavior. Based on the obtained buckling modes as well as local and overall slenderness ratios, some mathematical expressions are developed and presented to determine the ultimate shear-moment capacity when lateral torsional buckling is also associated with interactive buckling modes in hybrid and non-hybrid I-shaped flexural members.

Shear strength of tapered I-shaped steel members

Steel plate girders with long or unstiffened web panels are often tapered to produce optimized members in buildings and bridges. Web shear strength is a critical limit state for these members because they usually have slender webs.Historically, shear has been apportioned to the web using two methods. The most common method is to assign the entire shear to the web. Alternatively, the Modified Shear Method considers the vertical component of each flange force resulting in web shear force not equal to the total shear. The first objective of this research was to experimentally determine the accuracy of these methods. It was found that the Modified Shear Method accurately predicted the shear resisted by the web at all 18 instrumented cross-sections in ten tested specimens.Several methods for predicting shear strength of unstiffened and long prismatic web panels are available in the literature. The second major objective of this research was to determine if one or more of these methods accurately predicts tapered member shear strength. Measured ultimate shear strengths were compared to predictions. Methods based on Basler's method provided inaccurate predictions. Methods based on Höglund's method and the method by Lee and colleagues provided accurate predictions.

Comparison on Calculation Method for Post-Buckling Strength of Thin-Webbed I-Shape Member

The thin-webbed I-shaped members are used as the basic members for beams and columns of steel buildings in order to increase utilization ratio of steel. The local buckling can occur for these members because of the large width-thickness ratio and these members have a substantial post-buckling strength which can be used. Different codes in China have different estimation method for substantial post-buckling strength of thin-webbed I-shaped members. So it is very necessary to establish the same calculation method to consider post-buckling strength for different china codes. In this paper the effective width estimation methods of technical specification for steel structure of light weight buildings with gabled frames (CECS 102-2002), code for design of steel structures (GB50017-2003), technical code of cold-formed thin-wall steel structures (GB50018-2002), America specification (AISC: 2005), European specification (E3-1.5:2006), and Winter equation are introduced simply. The effective area of thin-webbed I-shaped members with different width-thickness ratio in web and slenderness ratio are estimated using these codes. Comparison of these estimated results show that CECS 102-2002, GB50017-2003, AISC: 2005, Winter equation, and E3-1.5:2006 may be conservative or unsafe for members with different slenderness ratio or width-thickness ratio of web. GB50018-2002 is applicable for members with different slenderness ratio or width-thickness ratio of web without considering interaction between flange and web of members and can be used to estimate the effective area of thin-webbed I-shaped members. At the same time, the calculated method of post-buckling strength of thin-webbed I-shaped members in CECS 102-2002 and GB50017-2003 could use the same method as GB50018-2002.

Tangent moduli of hot-rolled I-shaped axial members considering various residual stress distributions

This paper presents an equation for the effective tangent moduli for steel axial members of hot-rolled I-shaped section subjected to various residual stress distributions. Because of the existence of residual stresses, the cross section yields gradually even when the member is subjected to uniform axial stresses. In the elasto-plastic stage, the structural response can be easily traced using rational tangent modulus of the member. In this study, the equations for rational tangent moduli for hot-rolled I-shaped steel members in the elasto-plastic stage were derived based on the general principle of force-equilibrium. For practical purpose, the equations for the tangent modulus were presented for conventional patterns of the residual stress distribution of hot-rolled I-shaped steel members. Through a series of material nonlinear analyses for steel axial members modeled by shell elements, the derived equations were numerically verified, and the presented equations were compared with the CRC tangent modulus equation, the most frequently used equation so far. The comparative study shows that the presented equations are extremely effective for accurately analyzing elasto-plastic behavior of the axially loaded members in a simple manner without using complex shell element models.