Web Holes Research Articles

The structural behavior of castellated beam with shape variation using finite element methods

Castella steel is an alternative material used in the structure of beams and columns in the construction of a building. Castella web holes in previous studies mentioned the following: hexagonal, honeycomb, octagonal, diamond, and hexagonal. The advantage of using the castella steel beam is that it has a higher web geometry without increasing its weight so that it could add up the inertia value of its profile. The purpose of this study is to analyze castella steel beams with various geometric shapes such as hexagonal, octagonal, and diamond with couple plates on the web weld joints to determine the behavior of castella steel beams when receiving axial loads using the finite element method of the abaqus. Analysis of the behavior of castella steel beams, with or without using of a plate, does not significantly influence the deflection that occurs. However, the addition of the coupled plate has a significant influence on the stress-strain value in the welded joints on the web. Hence, the addition of a plate coupled to the web joints of the castella steel beam profile is highly recommended to support strength resistance as a long-term structure. Analysis of the performance of castella steel beams by the addition of coupled plates for each castella hole with a load equal to 75 kN, resulting in the best capability on the value of the displacement is the hexagonal profile that is 12.839mm compared to other profile displacements of 14.433mm diamond hole profiles and 14.972 octagonal hole profiles.

Axial strength of back-to-back cold-formed steel channels with edge-stiffened holes, un-stiffened holes and plain webs

Cold-formed steel (CFS) back-to-back channels are becoming a popular choice for use in load-carrying members in building structures. These built-up channels often include web holes for installation of services. Traditional web holes are un-stiffened, which can restrict the size and spacing of holes. Recently, a new generation of CFS channels with edge-stiffened holes has been developed and used widely in New Zealand. No research has been reported in the literature to investigate the axial strength of back-to-back channels with edge-stiffened holes. Experiments are required on back-to-back channels with edge-stiffened holes so to understand the effects of composite actions between the back-to-back channels on the axial strength of such channels. This paper presents a total of 162 new results comprising 27 axial compression tests and 135 finite element analysis (FEA) results on the axial strength of back-to-back channels with edge-stiffened holes, un-stiffened holes and plain webs. Prior to compression tests, initial geometric imperfections were measured using a laser scanner. Tensile coupon tests were also conducted to determine the material properties of both the flat and corner portions of the channels. The test results show that for the case of back-to-back channels with edge-stiffened holes, the axial strength increased by 6.6% on average, compared to a back-to-back plain channel. For comparison, the same section with un-stiffened holes had a 12.4% reduction on average in axial strength, compared to a back-to-back plain channel. A nonlinear elasto-plastic finite element (FE) model was then developed, and the results showed good agreement with the test results. The validated FE model was used to conduct a parametric study involving 135 FE models to investigate the effects of column slenderness, diameter of hole, screw spacing, stiffener lengths and stiffener fillet radius on the axial strength of such channels. Finally, the tests and parametric study results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) (2016) and Australian and New Zealand Standards (AS/NZS) (2018) for back-to-back plain channels and against the design equations of Moen and Schafer (2011) for back-to-back channels with un-stiffened holes. It was found that the AISI (2016) and AS/NZS (2018) are only 3% conservative to the test results. The Moen and Schafer equations (2008, 2009, 2011) are conservative by 21% on average for back-to-back channels with un-stiffened holes.

Parametric study for shear design of cold-formed channels with elongated web openings

Cold-formed steel members are commonly perforated with elongated web openings in practice to allow more access for the building service systems. The presence of such extended web holes in the members, when subjected to high shear forces, influences the shear buckling characteristics, the shear failure modes and generally leads to a reduction of shear capacity as well. In order to provide a better insight into the shear behaviour of cold-formed members with elongated web cut-outs, this paper presents a numerical study using finite element method (FEM) models employing ABAQUS/Standard to investigate the elastic shear buckling and post-buckling behaviour of cold-formed members in the form of thin channel sections. A full non-linear FEM model is developed and calibrated against previous shear tests with elongated web holes carried out using a dual actuator test rig. Based on the successful calibration against the tests, a parametric investigation is conducted to extend the resulting database. Further, a new proposal for the Direct Strength Method (DSM) of design of perforated channels in shear with both non-elongated and elongated web holes is further validated by using the results from the parametric study. A comparison between the empirical approach (“qs” method) and the new DSM of design derived from the Vierendeel mechanism approach is also provided to enhance the applicability of the new proposal to different cases of perforated channel members in shear with a wider range of sectional dimension and thicknesses.

Application of improved element-free Galerkin combining with finite strip method for buckling analysis of channel-section beams with openings

In this paper, a coupling of improved element-free Galerkin with the finite strip (IEFG-FS) is used to investigate the buckling analysis of cold-formed steel (CFS) channel-section beam with web holes. For this purpose, three sections of the CFS channel are considered under bending loading. These sections are divided into two sub-domains in which the IEFG method is used in sub-domain with openings, and the finite strip (FS) method is applied for another sub-domain. In the IEFG domain, the boundary conditions are enforced using the Lagrange multiplier method. In the following, hole size effects are investigated on the moment buckling load of sections. The results show that the IEFG-FS is an efficient method for buckling analysis of channel-section beams. Moreover, the presence of holes in CFS channel section reduces the moment buckling load, so that the decrease in the local buckling is more than the distortional and global buckling loads.

Web crippling behaviour of cold-formed steel channel sections with edge-stiffened and unstiffened circular holes under interior-two-flange loading condition

Abstract Recently, a new generation of cold-formed steel (CFS) channel sections with edge-stiffened circular holes have been developed by industry in New Zealand. No previous research, however, has considered the web crippling strength of CFS channel sections with edge-stiffened circular web holes under the interior-two-flange (ITF) loading conditions. In this paper, a combination of experimental investigation and non-linear finite element analysis (FEA) are used to investigate the effect of edge-stiffened holes under ITF loading conditions; for comparison, channel sections without holes and with unstiffened holes are also considered. In total, 30 web crippling test results are reported. A non-linear finite element (FE) model is described, and the results were compared against the test results, which showed a good agreement in terms of both the web crippling strength and failure modes. The results indicate that the stiffened web holes can significantly improve the web crippling strength of CFS channel sections. Using the validated FE model, a parametric study was conducted which include 1116 FE analyses, covering the effect of different hole sizes, edge-stiffener lengths and fillet radii, length of the bearing plates and position of the holes in the web. From the results of the parametric study, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and FE results.

Parametric study and simplified design equations for cold-formed steel channels with edge-stiffened holes under axial compression

The use of cold-formed steel (CFS) channels with web holes are becoming increasingly popular. Such holes, however, result in sections becoming more susceptible to lower axial compressive resistance. Traditional holes are normally punched at the web and un-stiffened. Recently, a new generation of CFS channels with edge-stiffened holes has been developed by the CFS industry but no information is available in the literature to accurately predict the axial capacity of such sections. The current design guidelines in accordance with the American Iron and Steel Institute (AISI 2016) and Australia New Zealand standards (AS/NZ 4600:2018) do not provide any design rules for CFS channels with edge-stiffened holes. In this paper, a numerical model that accurately simulated results from the experimental testing of CFS channels with edge-stiffened holes under axial compression as published in a previous paper by the authors was employed to carry out a parametric study which involved 348 finite element (FE) models. Variables which were examined included column slenderness, stiffener length, fillet radius, hole size, hole location and hole spacing. A comparison of the numerical results with current design rules for CFS channels with un-stiffened holes revealed that the design equations were not accurate for such sections; design equations are therefore proposed in which an enhancement factor is applied to the original equations. The enhancement factor was obtained using bivariate linear regression analysis. The proposed design equations closely predict the enhanced axial capacity of CFS channels with edge-stiffened holes.

Non-linear finite element analysis of reinforced concrete deep beam with web opening

The use of Reinforced Concrete (RC) deep beams in building may requires web openings or holes for electrical and mechanical utilities passage. This web opening will change the behavior of RC deep beam and may resulted in early cracks even at service load. Hence, it is important to use a suitable tool to predict the full response of RC deep beam with opening. For that purpose, nonlinear finite element method using 3D-NLFEA software package which utilize a plasticity-fracture model is used to predict the behavior of RC deep beam. One deep beam specimen available in the literature is investigated. To study the effect of using structured and unstructured mesh, as well as different element types on the load deflection curve, hexahedral and tetrahedral solid element was used. From the comparisons, it was observed that the crack pattern between two different meshes was not similar. Structured mesh often has straighter crack propagation compared to the unstructured mesh. The load deflection curve for both models are similar and both models were performed satisfactorily in predicting the peak load of the deep beam.

New distortional buckling design rules for slotted perforated cold-formed steel beams

Cold-Formed Steel (CFS) members with slotted perforations in webs are used in civil construction to amplify the thermal and energy performance of structures. However, the slotted webs reduce the structural performance of the element, prominently their shear, bending and combined bending and shear strengths. Many research studies have been undertaken to examine the behaviour of CFS channel sections subject to bending. Yet, no research has been performed to investigate the distortional buckling behaviour of slotted perforated CFS flexural members. Finite Element (FE) models of CFS channels with staggered slotted perforations were developed herein to investigate their distortional buckling under bending stress. A parametric study was conducted in detail by developing 432 slotted perforated CFS FE models based on the validation process with available experimental results. In particular, this paper presents the FE analysis details of CFS flexural members with slotted perforations subject to distortional buckling and results. The reliability of the current Direct Strength Method (DSM) for CFS flexural members with web holes subject to distortional buckling in accordance with the North American Specification (AISI S100) (2016) and the Australian/New Zealand Standards (AS/NZ 4600) (2018) was investigated. Modified DSM formulae for slotted perforated CFS flexural members subject to distortional buckling were also proposed.

Effect of web holes on the web crippling capacity of cold-formed LiteSteel beams under End-Two-Flange load case

LiteSteel (LSB) beams are made of two rectangular hollow flanges and a slender web. Although the flexural capacity and bending stiffness are enhanced due to hollow flanges, they are vulnerable to the web crippling failure under concentrated loads and reactions due to high web slenderness values. In current steel buildings, cold-formed steel sections with web holes have been used to accommodate service ducts in floor systems. These LiteSteel beams (LSBs) are innovative new sections, hence current web crippling equations cannot be used to predict the web crippling capacities of them. Keerthan et al. (2014, 2016) and Steau et al. (2015) proposed coefficients to the unified web crippling equation which is available in Australian/New Zealand standard (AS/NZS 4600) and North American Specification (AISI S100) for unfastened and fastened supports, respectively for LSB sections without web holes under four load cases based on their experimental studies. However web crippling behaviour of these sections with web holes is still unknown under all four load cases. In past studies, the web holes are classified into two groups such as centred beneath and offset web holes to investigate their effect on the web crippling behaviour. This study investigates web crippling behaviour of LiteSteel beams with centred beneath and offset circular web holes with unfastened supports under End-Two-Flange load case (ETF) using finite element analysis in ANSYS. Accurate validations have been performed for five different web crippling datasets, and the parametric study was conducted using validated FE models. Web crippling equations were proposed for LiteSteel beams with centred beneath and offset web holes and without web holes based on 1067 FE model values.

Shear Strengthening of Composite Concrete Steel Plate Girders with Web Openings Using Steel Strips

The study aims to investigate behaviour plus influence on the final load resistance of strengthen girders containing openings in web which were 40% of web height. This paper presents an experimental study of applying of five steel-concrete composite plate girder specimens that were loaded in shear predominantly. Three of those girders were considered as control girders, without web openings, containing circular web holes, and containing square web holes, respectively. Other two girders were strengthen girders. The slab reinforcement, dimensions of girders and compressive strength of concrete slabs were constant. Strengthening was made by using steel rings and strips which were welded to webs of strengthen girders to investigate influence of strengthening plan by steel welding on behaviour and final load strength for these girders. Findings illustrate increasing in final load strength of strengthen girders with circular and square web holes with about 57.38% and 43.75%, respectively in comparing to that for control girders. Moreover, the final shear capacity for the tested girders was also compared with that predicted by von Mises stresses.

Evaluation of OSB webbed laminated bamboo lumber box-shaped joists with a circular web hole

Openings are frequently required in the web of oriented strand board (OSB) webbed laminated bamboo lumber (LBL) box-shaped joists for passage of service ducts, plumbing, and wiring. A total of 105 joists with a circular web hole were tested and compared with 7 joists without a web opening (control joists). It was found that for smaller circular holes (D/hw ≤ 30%), the effect of the hole was negligible and did not cause strength and stiffness reductions. The unreinforced joists with larger web holes (D/hw>30%) failed in a brittle and sudden shear mode, resulting in a reduction in strength. Reinforcing of joists with an opening to stop or prevent crack formation or propagation could be accomplished by using one of three methods including collar shaped oriented strand board patches (C-OSB), two “U” shaped oriented strand board patches (TU-OSB), or collar shaped steel patches (C-SP). Results showed that the C-OSB worked most effectively and returned 2 of 5 series of joists to a strength and stiffness equivalent to the “no hole” condition. The mechanical performance and deformation properties of joists with a web opening could be improved by C-SP, but the improvement was only a small percentage of the total load-carrying capacity. TU-OSB worked effectively for a limited opening diameter (D/hw ≤ 50%), and was easier to install without removing the service pipes and less expensive than the C-OSB or C-SP options. Good correlation was obtained between experimental results and numerical simulations.

Cold-formed steel channel sections under end-two-flange loading condition: Design for edge-stiffened holes, unstiffened holes and plain webs

Abstract In cold-formed steel (CFS) channel sections, web holes are becoming increasingly popular. Such holes, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web holes. Traditional web holes are normally punched or bored and are unstiffened. Recently, a new generation of CFS channel sections with edge-stiffened web holes has been developed by the CFS industry and is being widely used. However, no research is available in the literature which investigated the web crippling strength of CFS channel sections with edge-stiffened circular web holes under the end-two-flange (ETF) loading conditions. A combination of experimental tests and non-linear FEA were used to investigate the effect of such stiffened holes on web crippling behaviour under ETF loading conditions. The results of 30 web crippling tests are presented. Non-linear FE models are described, and the results are compared against the laboratory test results; a good agreement was obtained in terms of both the strength and failure modes. The results indicate that the stiffened holes can significantly improve the web crippling strength of CFS channel sections. A parametric study involving 1116 FEA was then performed, covering the effect of different hole sizes, edge-stiffener lengths and fillet radii, length of the bearing plates and position of holes in the web. Finally, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and FE results.

Experimental investigation of high strength cold-formed channel sections in shear with rectangular and slotted web openings

Cold-formed steel channels with web openings in shear have been thoroughly investigated mainly with circular and square holes. However, web cut-outs are likely to be enlarged along the span length of members due to a limited web depth to provide more access for the building services in practice. The design of cold-formed sections with elongated web holes in shear was investigated and retained in the AISI S100–16 and the AS/NZS 4600:2018 using the empirical approach. This paper presents an experimental investigation of perforated channel sections with rectangular and slotted web openings in shear using a dual actuator test rig to minimise the effects of bending moments and obtain the predominantly shear capacity with an aspect ratio up to 2.0. The commercially available plain C-lipped channel sections with a depth of 200 mm and a thickness of 1.5 mm were chosen with varying sizes of central cut-outs. A new strategy for determination of the shear yield loads (Vy) together with the Vierendeel mechanism approach is presented in this study to propose a modified design for perforated channels with web openings having aspect ratios of holes up to 3.0 for the Direct Strength Method (DSM) of design of channel members in shear with elongated web openings. In addition, as required in the DSM method, the shear elastic buckling loads (Vcr) are extracted from the linear elastic buckling analyses using finite element method in this paper.

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

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

Shear Strength Experiments and Design of Cold-Formed Steel Channels with Web Holes

AbstractIn the latest North American specification for the design of cold-formed steel (CFS) structural members and the Australian/New Zealand standard for cold-formed steel structures, an empirica...

Flexural behaviour of composite slim floor beams

Composite slim floor beams consist of a steel section embedded in a concrete slab, offering the advantages of a steel-concrete composite structure combined with a reduced floor depth. Several mechanisms contribute to the shear connection in this type of beam, such as headed studs, friction and clamping effects and the using of reinforcement bars passing through holes in the steel beam web. However, to date, nobody has systematically identified these mechanisms and Eurocode 4 does not provide specific design guidance for slim floor beams. A series of shear beam tests and flexural beam tests, using different arrangements of shear connectors, were carried out in order to assess the degree of shear connection and connector capacity in these beams. Most of the specimens used a novel shear connector, comprising a transverse steel bar surrounded by concrete, passing through a hole in the steel section web. This paper presents the findings from the flexural beam tests and draws comparisons with those from the previous shear beam tests. Numerical models will be developed in future to extend the data and include a wider range of parameters. The data will also be used to improve understanding of this type of beam and will lead to the provision of specific design guidelines for slim floor beams.

Assessment of web crippling design provisions for application to proprietary soldier beams

Structures used for temporary works are lightweight so that they are easy to transport, erect and dismantle. Particular care should be taken in their design as local instabilities could arise due to their thin-walled nature. This article presents 12 tests on proprietary soldier beams subjected to two concentrate opposing loads applied simultaneously. The geometry of the proprietary beams feature cold-formed C-shaped sections with web holes connected back to back with internal spacers. In the absence of design rules for application to such members, the experimental results are used in the present investigation to assess the suitability of the provisions for the web crippling design of cold-formed steel members as well as existing design methods from the literature, which account for the effect of perforations in the web. Experimental and predicted resistances are compared and design recommendations are provided.

On Problem of Torsional Characteristics of Thin-walled Steel Beams with Web Openings

The current trend in the design of steel structures leads, due to the saving of the material, to the frequent use of thin-walled cold formed steel sections. The thin-walled cold-formed steel profiles are often manufactured with web holes. In the design of such a thin-walled steel members with web openings arises a question of correct determination of the real crosssectional properties. This paper focuses on the problem of the real torsional characteristics determination, which are parameters needed for the design of members subjected to the bending with respect to lateral torsional buckling or for the design of the compressed members prone to torsional buckling or flexural torsional buckling. These torsional characteristics include St. Venant torsion constant and warping constant. In the forthcoming European Standard specifying the rules for the design of beams with holes, it is recommended to use the cross-sectional characteristics of the most weakened section of the member with web openings. This paper deals with the possibility of introduction of “substitute cross-section” whose cross-sectional characteristics are determined as the weighted average of the properties of full section and the most weakened section. The solution with substitute cross-section is validated by the series of tests focusing on the experimental verification of the both real torsional stiffness –- St. Venant torsion stiffness and warping torsion stiffness. Based on the results of test series with twisted beams freely supported in torsion, the St. Venant torsion constant is being derived, respectively from the results of the test series with twisted beams fixed in torsion (the warping is restrained at both beam ends), the warping constant is being derived. Both torsional characteristics are verified by tests executed on three different lengths (L=2.0m, L=3.0m and L=4.0m) of beams with sigma cross-section with large circular web openings.

Tests and direct strength design on cold-formed steel channel beams with web holes

To investigate the flexural behaviors of cold-formed steel channel beams with web holes and assess the reliability of the current direct strength method (DSM) for design of cold-formed steel beams with web holes stipulated in North American Specification (NAS) (2016), ten groups of specimens with various sizes of web holes and lips were tested under four-point bending. Among them, each kind of specimens with short lips or long lips have five kinds of hole height-to-web depth ratios, 0, 0.2, 0.4, 0.6 and 0.8. It is shown that the web holes change the failure modes of beams from only distortional buckling or only local buckling to distortional-local buckling interaction controlled by distortional buckling or local-distortional buckling interaction controlled by local buckling. It is found that the moment capacities reduce slightly with a maximum reduction value of 7.0% when the ratio of hole height-to-web depth increases from 0 to 0.4, and that the moment capacities reduce dramatically with a maximum reduction value of 16.3% when the ratio of hole height-to-web depth further increases to 0.8. Moreover, ANSYS finite element (FE) program was used to simulate the beam tests, the simulation results show good agreement with the test results in terms of moment capacities and failure modes. Extensive ANSYS FE parametric analysis were carried out to verify the accurateness of critical elastic distortional buckling stress prediction method using CUFSM finite strip program and to modify the existed approximate prediction formulas of critical elastic local buckling stress applying to such beams with web holes. Furthermore, the test results and parametric analysis results were compared with the current DSM prediction results of cold-formed steel beams with web holes. It is found that the DSM in NAS (2016) provides unconservative predictions for most cold-formed steel channel beams with web holes, especially for beams failed by local-distortional buckling interaction controlled by local buckling. Therefore, the modified direct strength method formulas for cold-formed steel beams with web holes were proposed.

Decrease of cold-formed slotted studs heat conductivity by slots shape modification

Cold-formed steel framing is gaining ground in Russia. Now it’s making attempts to adopt curtain wall panels with cold-formed slotted steel members in residential building. In view of cold Russian climate, a problem of mitigation of the cold bridge effect created by the steel have appeared. It’s proposed to improve steel members’ thermal performance by choice a new web holes shape. Stud models with different web holes configuration were investigated by means of fine element analysis in COMSOL Multiphysics software. Their thermal and load-carrying performance was compared with a standard slotted stud. Two promising pilot models were chosen for further experimental research. An experiment to compare heat conduction capacity of these pilot models and a standard slotted stud was carried out in the Laboratory of glass and facade constructions. The results of this experiment are presented in this article.