Edge Stiffeners Research Articles

Parametric study on cold-formed steel built-up columns using direct strength method

The use of built-up cold-formed channels in the metal lightweight industry increases for higher strengths offers in comparison with a single-channel section. However, their unavailability of design guidelines determining the axial strength had made most researchers seeking to formulate new designs rules for different built-up sections. This research aims to convey parametric study on built-up columns using a proposed Approach based on the direct strength method for further knowledge and to understand the behavior of cold-formed steel built-up columns. For that a nonlinear finite element was developed to perform a parametric study, a total of 93 finite elements models were analyzed to study the effects of the cross-section, the gap between the two channels, the spacing between battens, the addition of web stiffener, the angle variation in C-sections simple lip edge stiffener, different lengths of the profiles and the ratio (d/D), on the stability of built-up columns. An approach based on the direct strength method (DSM) was proposed, where elastic, local, distortional or global elastic buckling solutions are determined from finite element or finite strip procedures. The obtained results were compared with the current design standard the North American specifications and the Australia/New Zealand codes, the AISI specifications, and European code EC3. The results of the parametric study were compared with the values found by AISI, EC3 and proposed DSM approaches, it stated that, the design specification noted in the AISI are generally conservative for overall buckling mode and slightly conservative for local buckling mode columns. For EC3 specifications, there is a difference between open and closed sections. For open sections, the results are conservative for local buckling mode and slightly conservative for global buckling mode. For the proposed DSM approaches, the results are slightly conservative for global buckling columns and non-conservative for local buckling mode columns.

Experiments on perforated cold-formed built-up I-section beam-columns with longitudinal web and complex edge stiffeners

A built-up I-section with longitudinal web and complex edge stiffeners is expected to have better performance to resist against local and distortional buckling compared to built-up I-section without these. In this paper, the compression behavior of perforated cold-formed beams-columns with longitudinal web and complex edge stiffeners was experimentally studied between pined-ends. It contained 16 single section and 8 built-up section specimens, respectively. The above research was shown that the form of longitudinal stiffeners and built-up I-sections could effectively improve steel utilization and load-carrying capacity. For the single-limb section, effective centroid shift led to an eccentricity of the applied force and hence induced the maximum ultimate load achieved at a certain loading eccentricity, but not at concentricity. However, the built-up member was symmetrical along the center of the member and uniformly compressed on both sides, which was not affected by the above. It was noteworthy that the two adjacent single-limb webs of conventional built-up I-section exhibited some specific support to each other, but the deformation of the plate around the hole cannot be restricted. However, the section with web stiffeners shown an opposite result of the above situation. Meanwhile, the longitudinal stiffener can obviously resist the built-up members' elastic deformation under the same condition. In addition, a finite element model was developed and verified against experiments of perforated beam-columns. Finally, two different Direct Strength Method (DSM) formulas were used to calculate the ultimate bearing capacity of perforated beam-column members under eccentric load. The calculated results were compared. It can be seen that the DSM formula that considered the distortional and overall relative buckling was closer to the actual value.

Strength enhancements across various parts in intermediate and edge stiffened angle sections due to cold-forming

This study presents an experimental study on the strength characteristics of steel coupons extracted from various parts of Cold-Formed Steel (CFS) Intermediate and Edge Stiffened Angle Sections. The light gauge thin-walled CFS sections formed for specific design requisites are of different shapes, and often the profiles are stiffened by the employment of intermediate and edge stiffeners to resist elemental plate segment local buckling. As a result, these sections undergo modifications in their actual tensile strength characteristics across various regions, say the flat portions, corners and stiffened portions of the cross-section geometry due to the cold-forming from sheets into sections; hence is essential to know the stress-strain responses of the section before using them as structural members. Based on this study on various grades of stiffened angle sections, it is found that there is strength enhancement due to forming. Moreover, there is a notable increase in tensile capacities, say the maximum of 8% in the yield strength and a 5% increase in the ultimate strength in the corners and at the stiffened zones, with slightly less elongation capacity, in comparison with the tensile properties of flat parts. And also, there exists a marginal difference of 2–3% in the tensile properties between the partially stiffened and fully stiffened elemental parts of flat portions. These results can be effectively utilised while performing higher-order parametric studies by the Finite Element Analysis approach.

Shear behaviour of doubly symmetric rectangular hollow flange beam with circular edge-stiffened openings

Cold-Formed Steel (CFS) sections are evolved through the last two decades compromising various aspects of construction needs. Doubly symmetric Rectangular Hollow Flange Beam (RHFB) is one of the innovative CFS sections, which was introduced to eliminate the drawbacks of conventional open CFS sections such as prone to complex buckling and torsional effects. Edge-stiffened web holes are recently recommended and available for extensive usage in the floor beams. Even though previous studies conducted researches on various kinds of stiffeners, there is no definite design equation or findings that were presented on shear behaviour. Therefore, this study focuses on the effect of edge-stiffened circular web openings on the shear capacity of doubly symmetric RHFB. Non-linear numerical models were developed using the ABAQUS software package for validation purposes and then comprehensive parametric studies were carried out for doubly symmetric RHFB with edge-stiffened openings. A total of 558 models consisting of edge-stiffeners, un-stiffened openings and plain webs were analysed in this study. Parametric results of with edge stiffeners exhibited shear capacity increment (1–90%) compared to unstiffened web openings. Hence, new design equations were proposed in the form of reduction factor and based on Direct Strength Method (DSM). Finally, optimum edge-stiffener length of 15 mm was recommended regardless of web opening size.

Local and distortional buckling of extruded aluminium alloy lipped angle columns

The outstand flanges of aluminium alloy angles are sensitive to local buckling due to the low elastic modulus of material. To improve the sectional buckling stress, lips could be introduced to improve the stability behaviour of the outstand flanges. This paper presents an equilibrium approach and a simplified energy method for the local and distortional buckling of extruded aluminium alloy lipped angle columns. Closed form solutions for local buckling and distortional buckling are proposed. The equivalent flexural rigidity and torsional rigidity of the lip are two main factors affecting the sectional buckling behaviour. As distinct from double-sided symmetrical edge stiffeners, the bending of a single-sided edge stiffener can lead to in-plane compressive deformation of the adjacent flange. Based on the edge-stiffened flange model, the equivalent flexural rigidity of the lip is obtained from finite element (FE) analysis. To validate the proposed analytical methods, the elastic buckling coefficients of lipped angles with varying dimensions are obtained from eigenvalue buckling analysis. Lips of different thicknesses are considered to study the effect of torsional rigidity. Comparing with FE results, the proposed equilibrium approach shows excellent accuracy for both local and distortional buckling stresses. The closed form solution given by energy method can also well predict the sectional buckling stress. Finally, parametric studies are carried out to further investigate the effects of flexural and torsional rigidities of lips and the slenderness ratios of flanges on the elastic buckling behaviour. Some design remarks are concluded to provide valuable reference for the application of extruded aluminium alloy lipped angles in practice.

Comparing Fire Behaviour of Restrained Cold‐Formed Steel Columns with Stiffened and Unstiffened Sections

AbstractAlthough, some experimental investigations have already been conducted and reported in the literature on cold‐formed steel columns under fire conditions, tests on the structural response of CFS columns in compression with intermediate and edge stiffeners and with restrained thermal elongation are rarely found in the literature, hence the relevance of the current investigation. In the present study, the effect of i) cross‐section shape (including single and built‐up sections), ii) web and edge stiffener configurations (webs with and without intermediate stiffeners and flanges with single edge fold stiffeners and double edge fold stiffeners), iii) slenderness (columns with different boundary conditions: pinned and fixed ends), and iv) stiffness of the surrounding structure to the thermal elongation of such columns have been investigated using an experimental campaign. Based on the research results it is clear that the overlapping regions, composite action, number of stiffeners, section geometry and load level take a crucial role in the fire structural behavior of CFS columns.

Numerical 3D Finite Element Assessment of Bending Moment-Resisting Frame Equipped with Semi-Disconnected Steel Plate Shear Wall and Yielding Plate Connection

Steel plate shear walls (SPSWs) have advantages such as high elastic stiffness, stable hysteresis behavior, high energy absorption capacity, and decent ductility. However, one of the main drawbacks of SPSWs is their buckling under lateral loading. To address this issue, a simple and practical solution in the form of using a trapezoidal plate moment connection (PMC) and a narrow gap between the infill plate and columns is presented. The PMC will act as an energy absorber, similar to a yielding steel plate, and keep the other structural members in an elastic state. Extensive three-dimensional finite element (FE) models of the SPSW system were investigated under monotonic and cyclic loading. The results revealed that by separating the infill plate from the vertical boundary elements and using two vertical edge stiffeners at both edges of the wall, the same lateral bearing capacity of the conventional system can be achieved. In addition, by increasing the thickness of the PMC from 6.5 to 26 mm, the load-bearing capacity, energy dissipation, and elastic stiffness increased approximately 2, 2.5, and 3.2 times, respectively. It was also found that the flexural capacity ratio of the connection to the beam had little effect on the overall force–displacement behavior. However, it can affect the system failure mechanism. Finally, the tension field inclination angle for such SPSWs was proposed in the range of 30 to 35°.

Effects of end-plate on the critical moment of I-section cantilever beam with free end restrained laterally

Effects of end-plate on the lateral buckling of doubly symmetrical I-section cantilever beam with free end restrained laterally are analyzed using the software COMSOL and linear shell finite elements. The torsional stiffness of the end-plate prevents the free warping of flanges and decreases the warping effective length of the cantilever beam. A parametric study is conducted on 3231 cantilever beams under uniform bending to propose an approximative formula to determine the warping effective length factor which depends on the ratio between the torsional constant of the end-plate and the warping stiffness of the beam. The small standard deviation and high coefficient of determination show a very good correlation between analytical formulas and numerical results. Numerical applications are applied to analyze some cantilever beams subjected to uniform bending to demonstrate the reliability of the proposed formula and the effects of the end-plate on the enhancement of the global stability of cantilever beams with free end restrained laterally.
 Keywords:
 cantilever lateral buckling; end-plate; edge stiffener; flexural-torsional buckling; warping effective length; warping effective length factor.

Torsional ductility spectrum for predicting ductility distribution in simple asymmetric‐plan structures

SummaryAn analytical procedure is developed for predicting the ductility demands in simple asymmetric‐plan structures under earthquake ground motions. The procedure governs regular structures dominated by the lower vibration modes where inelastic response occurs only at the bases of first story columns and at the beam ends, in conformance with the capacity design principles. Torsional ductility spectra are generated for expressing the maximum ductility response of torsionally coupled, generic, single‐story, 2‐degree‐of‐freedom inelastic parametric systems. Five parameters characterize the parametric systems: first mode period, uncoupled frequency ratio, stiffness eccentricity, stiff‐to‐flexible edge strength ratio, and ductility reduction factor. A surrogate modeling approach is developed for converting the properties of the actual systems to those of the parametric system. Mean maximum ductilities of torsionally stiff, equally stiff, and torsionally flexible systems are calculated under a set of design spectrum compatible strong motions for the possible combinations of characteristic parameters. The results obtained from case studies revealed reasonable accuracy of the estimations. The results have indicated that the flexible side frames of torsionally stiff and equally stiff code conforming designs are mainly responsible for providing the intended ductility and energy dissipation capacity whereas the stiff side frames play a secondary role, particularly when the stiff edge is significantly stronger than the flexible edge. However, ductility demands in torsionally flexible systems are significantly larger at both sides compared with torsionally stiff systems.

Parametric modal analysis of an induced-strain actuated wing-like plate for pitch and heave coupling response

This article investigates the feasibility of a plate-like flapping wing with varying geometric and boundary conditions actuated by surface-bonded piezoelectric material devices. The most influential structural parameters that vary dynamic response and heave–pitch mode coupling are investigated. An analytically and experimentally validated dynamic finite element model is developed to analyze the structure. A parametric analysis is conducted by varying critical geometric parameters and boundary conditions, such as aspect ratio, actuator position, actuator angle, clamp size, and position; substrate thickness variation; and substrate-to-actuator-thickness ratio. Response metrics representing heave and pitch motions are taken as longitudinal curvature and lateral slope, respectively—the surface regression analysis and results leading to these choices are presented. Maximum longitudinal curvature and lateral slope amplitudes and phase shifts are reported for key parameter choices. Longitudinal curvature to lateral slope coupling is achieved with the introduction of a leading edge stiffener to the otherwise uniform thickness plate. Conditions and parameters that lead to and influence heave–pitch coupling are presented and discussed in detail. This article presents a unique approach to flapping mode of flight compared to the literature. The article proposes a purely induced-strain actuation approach rather than the typical “mechanisms” based approach.

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.

Experimental investigation and finite element analysis of cold-formed steel channel columns with complex edge stiffeners

Abstract Presented in this paper are results obtained from experimental and numerical investigations on the axial behavior of cold-formed thin-walled steel channel columns with complex edge stiffeners, which are referred to as G-section columns. In the experimental investigation, a total of 36 G-section columns, with and without perforations, were tested under pin-ended boundary conditions, and their structural behavior was described. In these tests, the perforations were found to affect the ultimate strength and deformed shape of the G-section columns. In the numerical investigation, finite element models for G-section columns with and without perforations were developed with use of ABAQUS. The models were validated based on the test results. The calibrated finite element model was subsequently adopted for an extensive parametric study by varying the dimensions and locations of perforations. The numerical results indicated that increasing the perforation dimension resulted in a greater reduction on the column ultimate strength than changing the perforation location. But the location of the perforation could affect the deformed shape of the column significantly. Based on the results obtained from the parametric analysis, it is recommended that the spacing of circular holes is between three and six times the nominal diameter of the hole for engineering practice.

Experimental and numerical investigation on the complex behaviour of the localised seismic response in a multi-storey plan-asymmetric structure

Asymmetric structures experience higher seismic damage compared with their symmetric counterparts. This damage is mainly attributed to the coupled torsional vibrations, which tend to induce twisting in the structural floors and increase the shear demands in the corner column of the flexible side (CCFE) of asymmetric structures with in-plan stiffness eccentricity. Such floor twisting consequently leads towards the damage concentration in the critical region of CCFE and produce relatively higher local deformations and stiffness degradation of the structural component. Therefore, the investigation of such damage concentration is important as it can potentially lead towards local and global seismic failure. In this regard, this research aims at evaluating the damage behaviour of CCFE of a plan-asymmetric reinforced concrete (RC) structure. For this purpose, a quarter scaled asymmetric structure with in-plan stiffness eccentricity was experimentally tested under progressive seismic excitations. Internal seismic damage in the critical region of CCFE was monitored using Fibre Bragg grating (FBG) sensors during the structure’s transformation from elastic state to a highly plastic state. To validate the experimental findings, a calibrated finite element model was established in ABAQUS and a comparison of the damage behaviour of CCFE is presented to highlight the influence of stiffness eccentricity on damage concentration in the critical structural element. Finally, based on the experimental and numerical investigations, the mechanism of the local response behaviour both at the flexible and stiff edge of the plan-asymmetric structure is discussed and compared. This research concludes that CCFE in plan-asymmetric structures requires substantial design redundancy and special seismic detailing to resist extreme seismic events.

Numerical study on effect of stiffeners on the Gusset-plates using buckling restrained braced frame

Buckling restrained braces (BRB) is a popular and promising ductile damper in terms of higher ductility, energy dissipation, symmetrical hysteresis response and ability to yield in tension as well as compression. The BRB core element is made of three segments, namely, yielding length, transition zones, and elastic ends. The elastic-end of BRB is connected to the gusset plates, which are connected to the framing members. The gusset plates are playing an essential role in the stability of BRB members at the transition segments. Besides, the higher sizing of the gusset plate used in BRB as per current code recommendation is tending to failure in the connections before reaching the BRB to the ultimate ductility. A finite element (FE) modeling has been carried out using ABAQUS software on one bay and one-story frame under lateral cyclic loading using a diagonal BRB, the FE modelling result has been validated with the experimental result Chou et al. [10]. The parametric study has been carried on the gusset plate with different free edge stiffener. The comparison of hysteresis response, backbone curves, and shear/normal stress behaviour at the beam-column connection of the different gusset plates have been investigated. The gusset plate with a free edge stiffener has been recommended for the design of the BRB frame.

Finite Element Analysis of Cold Formed Steel Channel Columns with Complex Edge Stiffeners and Web Holes using Abaqus

The present theory work means to think about the numerical examination on models of channel segment with middle and complex edge stiffeners and web gaps under pivotal pressure. A wide scope of parameters, for example, slimness proportion, spine width and thickness have been considered in the investigation. An aggregate of 12 channel models with various parameters, for example, length, thickness and rib width are reenacted. The limited component non-direct examination program ABAQUS V6.14-2 is utilized to reproduce the models. The material properties are acquired from Coupon test. Component type utilized in this non-straight examination is SHELL. A Static, Riks step is utilized to complete examination. The Failure modes, extreme burden and the pressure conveyance around web gaps are inquired about. The relocation parts in every augmentation of burden along X, Y and Z bearings and Rotation segment about X course are gathered. The Von-Mises pressure forms, Deformed shapes and disappointment modes including nearby, horizontal distortional and parallel torsional clasping modes are acquired. The pivotal burden limits of pressure individuals with various parameters are looked at.

Local buckling analysis of cold-formed steel webs with stiffened rectangular openings

The cold-formed steel members often require web openings to allow for building services such as mechanical piping, electrical wiring, and air conditioning systems pass through the ceiling and therefore reduce the building overall height and as a result, lateral forces induced on the building. Stress distribution in members with openings is different from members without holes and therefore characteristics, shape and modes of their buckling are dissimilar which results in reduced buckling capacity and ultimate strength. In order to compensate some of the lost capacity, edge and intermediate stiffeners are fabricated into the web which complicates the characteristics and buckling mode. In this study, a set of analytical solutions for the local buckling of cold-formed steel webs with rectangular openings stiffened by intermediate and edge stiffeners subjected to compression, bending and their combination is developed, and summarized. The main variables are elastic modulus, Poisson's ratio, height of openings to height of web, aspect ratio of openings, moment of inertia of intermediate and edge stiffeners to moment of inertia of reduced web section, and stress distribution gradient above or under the hole. The proposed solutions can be used for a wide range of rectangular web openings. Analyses are conducted using energy based methods and the results are compared with numerical data obtained from the commercial finite element software (Abaqus). The numerical results demonstrate that one of the eight proposed formulas with minor modification can be successfully used to predict the critical buckling stress.

Experimental analysis of cold-formed steel columns with intermediate and edge stiffeners in fire

Abstract Although the use of longitudinal stiffeners in cold-formed steel members in compression is known to increase their ultimate strength at ambient temperatures, it is expected that the rigidity of such stiffeners and the strength of steel decreases when the cold-formed steel members are exposed to high temperatures. Therefore, this paper presents and discusses the results of an experimental investigation on the structural response of cold-formed steel columns with intermediate and edge stiffeners under fire conditions for assessing mainly their critical temperatures, critical times (fire resistance) and failure modes. The main variables studied included the: (a) cross-section shape, (b) boundary conditions, (c) edge stiffener configuration and (d) stiffness of the surrounding structure to the thermal elongation of such columns. Additionally, European fire design predictions (EN 1993-1-2:2005) were compared with the experimental results, in order to observe their accuracy. Finally, based on the findings of this research work it is obvious the advantage of using CFS sections with double edge fold stiffeners over the sections with single edge fold stiffeners. Moreover, built-up sections had lower critical temperatures than those for single sections, but with slightly higher fire resistance time. Furthermore, existing analytical methods have been shown to be incapable to predict sufficiently realistic the complex buckling behaviour of restrained CFS columns under fire conditions.

Behaviour of cold-formed steel built-up closed columns composed by angle profiles

This paper presents the experimental investigation of cold-formed built-up closed sections with intermediate web stiffeners under axial compression with hinged end conditions. The specimens were formed using two angle sections with edge and intermediate stiffeners, connected by self-tapping screws. Three series of tests were conducted by varying the width of the intermediate web element. Twelve columns were tested by varying the column length. The specimens were failed by local, flexural, and interaction of these buckling modes. Non-linear Finite-element Analysis (FEA) was carried out using ANSYS. FEA results were compared with the experimental results. It is observed that FEA results closely resemble to experimental results. An extensive parametric study was carried out using validated finite-element model by varying the cross-sectional geometries of cold-formed built-up closed section with intermediate stiffeners. The column strengths predicted from the FEA was compared with the design strengths calculated using the AISI specification of cold-formed steel structures. The reliability of the current design method was assessed by reliability analysis.

Evaluating out-of-plane stability for welded BRBs considering flexural restrainer and gusset rotations

Buckling-restrained braces (BRB) have been widely used as cost-effective energy dissipators in seismic designs of steel buildings. However, several issues of out-of-plane (OOP) instability have been observed in previous research. The stability evaluation method commonly used in seismic design practice applies three limit states to check the stability of the steel casing, connections, and gussets separately. Nevertheless, they appear to be over-simplified, by adopting unreasonable end conditions and neglecting coupling effects among them. Therefore, this study adapts an advanced stability assessment procedure and proposes a new stability model that considers the flexural deformation of the restrainer, gusset rotations, and the aforementioned coupling effects. In addition, an evaluation method is developed for finite-element model analysis to compute the gussets' rotational stiffness and strength. To verify the effectiveness of the proposed model, four full-scale BRB specimens each 5.8 m long with a 988-kN nominal yielding strength, varying restrainer stiffness, gusset thickness, and with/without edge stiffeners or OOP end drift are tested. The proposed model satisfactorily predicts specimens' failure modes and buckling strengths with errors less than 6%. Test results show a 9% drop in buckling strength due to a 57-mm OOP end drift, highlighting the significant impact from the OOP end drift. The proposed model exhibits an improvement in the buckling strength of over 80% with a 24% enlargement in the restrainer diameter, indicating the critical effects of the restrainer's flexural stiffness. The research results can be adopted to improve the practice of BRB frame design.

Experimental and numerical investigation of perforated cold-formed steel built-up I-section columns with web stiffeners and complex edge stiffeners

A built-up I-section with web stiffeners and complex edge stiffeners is expected to have better performance to resist against local and distortional buckling compared to conventional built-up I-sec...