Elasto-plastic Finite Element Model Research Articles

Axial capacity of cold-formed steel channel sections with slits

Cold-formed steel (CFS) studs often include slits in their webs to improve thermal performance. However, the inclusion of such slits reduces their axial capacity. The literature contains limited experimental studies on the axial capacity of these studs with slits, and no non-linear elasto-plastic finite element studies have been reported. This research aims to address this gap. Non-linear elasto-plastic finite element models were developed and validated against experimental test results. A parametric study consisting of 960 finite element analysis (FEA) models was then conducted, covering the effects of different channel dimensions, slit sizes, section thicknesses, and stud lengths. Ultimate axial capacities obtained from these analyses were compared to the current codified direct strength method (DSM) predictions as per the Australian/New Zealand Standard AS/NZS 4600. Finally, design recommendations in the form of strength reduction factors are proposed. Based on these recommendations, modified DSM design equations with a reliability index above 2.5 are presented.

Effects of anisotropy and infill pattern on compression properties of 3D printed CFRP: mechanical analysis and elasto-plastic finite element modelling

PurposeFinite element (FE) analysis can be used for both design and verification of components. In the case of 3D-printed materials, a proper characterization of properties, accounting for anisotropy and raster angles, can help develop efficient material models. This study aims to use compression tests to characterize short carbon-reinforced PA12 made by fused filament fabrication (FFF) and to model its behaviour by the FE method.Design/methodology/approachIn this work, the authors focus on compression tests, using post-processed specimens to overcome external defects introduced by the FFF process. The material’s elastoplastic mechanical behaviour is modelled by an elastic stiffness matrix, Hill’s anisotropic yield criterion and Voce’s isotropic hardening law, considering the stacking sequence of raster angles. A FE analysis is conducted to reproduce the material’s compressive behaviour through the LS-DYNA software.FindingsThe proposed model can capture stress values at different deformation levels and peculiar aspects of deformed shapes until the onset of damage mechanisms. Deformation and damage mechanisms are strictly correlated to orientation and raster angle.Originality/valueThe paper aims to contribute to the understanding of 3D-printed material’s behaviour through compression tests on bulk 3D-printed material. The methodology proposed, enriched with an anisotropic damage criterion, could be effectively used for design and verification purposes in the field of 3D-printed components through FE analysis.

Assessment of Thermal Osteonecrosis during Bone Drilling Using a Three-Dimensional Finite Element Model.

Bone drilling is a common procedure used to create pilot holes for inserting screws to secure implants for fracture fixation. However, this process can increase bone temperature and the excessive heat can lead to cell death and thermal osteonecrosis, potentially causing early fixation failure or complications. We applied a three-dimensional dynamic elastoplastic finite element model to evaluate the propagation and distribution of heat during bone drilling and assess the thermally affected zone (TAZ) that may lead to thermal necrosis. This model investigates the parameters influencing bone temperature during bone drilling, including drill diameter, rotational speed, feed force, and predrilled hole. The results indicate that our FE model is sufficiently accurate in predicting the temperature rise effect during bone drilling. The maximum temperature decreases exponentially with radial distance. When the feed forces are 40 and 60 N, the maximum temperature does not exceed 45 °C. However, with feed forces of 10 and 20 N, both the maximum temperatures exceed 45 °C within a radial distance of 0.2 mm, indicating a high-risk zone for potential thermal osteonecrosis. With the two-stage drilling procedure, where a 2.5 mm pilot hole is predrilled, the maximum temperature can be reduced by 14 °C. This suggests that higher feed force and rotational speed and/or using a two-stage drilling process could mitigate bone temperature elevation and reduce the risk of thermal osteonecrosis during bone drilling.

Buckling resistance of axially loaded cold-formed steel built-up stiffened box sections through experimental testing and finite element analysis

The use of cold-formed steel (CFS) built-up sections in engineering practice is widely gaining popularity due to their ability to provide sustainable solutions and optimised section design opportunities. This paper presents an experimental and numerical investigation conducted on CFS built-up stiffened box section columns under axial compression. A total of 13 new experimental tests were conducted with specimens having an overall web depth up to 550 mm. Detailed nonlinear elasto-plastic finite element (FE) models were then developed and verified against the test results. Upon verification, a parametric study involving 144 FE models was carried out to investigate the effects of section thickness, column length, and screw spacing on the buckling resistance of CFS built-up stiffened box sections. The test and finite element analysis (FEA) results were compared with the buckling resistances determined by the American Iron and Steel Institute (AISI S100) and Australian and New Zealand Standards (AS/NZS 4600). It was found that the buckling resistances determined by the AISI S100 and AS/NZS 4600 for CFS built-up stiffened box sections were conservative by 9.3% on average, compared to experimental and FEA results. Modified Direct Strength Method (DSM) design equations for predicting the buckling resistances of CFS built-up stiffened box sections were then proposed, and a reliability analysis was conducted to assess the feasibility of the proposed equations.

Overall flexural-shear buckling strength design of built-up radially battened columns

The built-up radially battened columns (RBCs) have a promising prospect in public building engineering due to their aesthetical form and good load-bearing capacity. However, their design methods are not covered in the current design specifications because of their distinctive appearance. This paper aims to present the flexural-shear buckling behavior of built-up RBCs and propose its corresponding strength design recommendations. At first, the finite element model (FEM) of the RBC is established, and a lot of examples are calculated in eigenvalue buckling analysis and elastoplastic analysis by using this FEM. Three kinds of possible first-order buckling modes are observed in the elastic buckling analysis, which are flexural-shear buckling, torsional buckling, and local buckling respectively. Only flexural-shear buckling is involved in this study, and torsional buckling will be investigated in a companion paper. Local buckling (of the chord tube wall) can be prevented by a radius-to-thickness ratio limit. It has been proven that shear deformation plays an essential role in determining the flexural-shear buckling of built-up members, thereby a unit shear angle model is established to study the shear stiffness of RBCs when they buckle overall. Then, the prediction equations for elastic flexural-shear buckling load and its corresponding normalized slenderness ratio are derived. The design curves for the ultimate load-bearing capacity of built-up RBCs are also proposed based on the numerous results from elastoplastic FEMs by changing normalized slenderness ratios. Furthermore, the compound buckling of RBCs is considered by employing a FEM that exerted the individual chord initial imperfection (FEM-c), and accordingly, a strength reduction factor caused by compound buckling is proposed. Finally, the design methods for the individual chords and radial-shaped battens are studied. The internal forces in chords and batten plates are derived and the analysis of the local buckling of batten plates is conducted. It is recommended that chords should be regarded as a member under combined compression and bending, and batten plates can be guaranteed to not lose their stability before the RBC reaches their ultimate load-bearing capacity by adopting the ‘isostable criterion’. In conclusion, these results provide a method for accurately and conservatively predicting the strength of RBCs when overall flexural or compound buckling occurs, which will expand the application of RBCs in engineering and make our public buildings more pleasing.

Strength prediction of built-up radially battened columns in torsional buckling

The built-up radially battened column (RBC) has found its promising application in public buildings due to its aesthetical form and good load-bearing capacity. Like the X-shaped column, torsional buckling may be the major failure mode of the RBC under axial compression. However, current specifications lack rational design methods for the torsional buckling strength prediction of this innovative column. This paper will focus on the torsional buckling behaviour of the RBC and propose its corresponding strength design formulas. At first, the key sectional properties of the radially continuous-web tube columns (RCTC) are derived theoretically and are proven to be consistent with the numerical calculation result. Then, a finite element model (FEM) using the shell element of RCTC is established, accordingly, the elastic torsional buckling behaviour of RCTCs is investigated, and an expression for accurately estimating the elastic torsional buckling load of RCTCs is proposed. Afterward, the FEM of built-up RBCs is established to conduct the elastic buckling analysis and elastoplastic bearing capacity prediction. The elastic torsional buckling load of built-up RBCs is predicted by modifying the expression for RCTCs via the number of battens and the proportion of the area of battens. A key design parameter, the normalized slenderness ratio, is also obtained. Finally, the strength design recommendation of the RBCs for torsional buckling is presented on the ground of numerous elastoplastic FEM results by changing the normalized slenderness ratio, and a limit RBCs’ dimension that can prevent the built-up RBC from the torsion buckling is further proposed. These results are expected to guide the design of the RBC and promote its application in engineering.

Web crippling resistance of cold-formed steel built-up box sections through experimental testing, numerical simulation and deep learning

This study proposes a deep-learning framework, namely a deep belief network (DBN), for investigating the web crippling resistance of cold-formed steel (CFS) built-up stiffened box sections. A total of 12 new web crippling tests are presented initially, which were carried out under interior-two-flange (ITF) and end-two-flange (ETF) loading conditions. In the experimental tests, two cross-section dimensions were considered, and the overall web depth varied from 290 mm to 550 mm. The yield strength of the specimens varied from 371.7 MPa to 643.6 MPa. The specimens were characterised by different screw spacing, varying between 50 mm and 300 mm. An elasto-plastic finite element (FE) model was developed and validated against the test results. Subsequently, a total of 1,356 data points for training the DBN were generated based on the validated FE model. When a comparison was made against the test results, the absolute percentage error of the DBN predictions was found to be around 10%. Using the DBN predictions which were based on the validated FE model, a comprehensive parametric study was undertaken to investigate the effects of section thickness, yield strength, bearing length and screw spacing on the web crippling resistance of CFS built-up stiffened box sections. New design equations for predicting the ITF and ETF web crippling resistances of CFS built-up stiffened box sections were then proposed, and a reliability analysis was undertaken to assess the feasibility of the proposed equations.

Understanding the regulation ability of roll bending on strip shape in a CVC-6 tandem cold mill using a 3D multiple stand FE model

Roll bending is a common technique to regulate the strip shape in tandem cold rolling (TCR), but its regulation ability at each stand is poorly understood at present. In this study, based on a 3D multiple stand elasto-plastic finite element (EPFE) model, the effects of work roll bending (WRB) and intermediate roll bending (IRB) on the strip crown, strip flatness and elastic deformation of work roll (WR) were quantitatively studied at each stand in the TCR. Results show that the regulation abilities of WRB and IRB on the strip crown both show a downward tendency from Stand 1 (S1) to Stand 5 (S5), which both depend on the strip plastic rigidity. Moreover, under various WRBs and IRBs, the strip shape is mainly determined by the elastic deflection of WR in the upstream stand, while it is determined combinedly by the elastic deflection and flattening deformation of WR in the downstream stand. Furthermore, the regulation ability of WRB on the strip crown and quadratic flatness is at least 2.5 times larger than that of IRB. The experimental results show that the developed multiple stand EPFE model can well predict the trend of the quadratic and quartic flatness between coils. These findings help understand the influence mechanism of the roll bending on the strip shape and improve the strip shape by optimising the roll bending in the TCR.

Moment-capacity of bolted side-plates for apex joint of nested tapered box beam portal frames

This paper is concerned with the apex joint of a novel cold-formed steel (CFS) nested tapered box beam (NTBB) portal frame. The NTBB section comprises two G-sections welded together, and its novelty lies in that it can be tapered, leading to material savings. At the apex joint, the NTBB sections are connected through bolted side-plates, whose strength is the focus of this paper. A non-linear elastoplastic finite element model is described herein, and a parametric study undertaken covering 340 finite element models. A sensitivity analysis has been conducted to identify key parameters for the study. In the parametric study, the thickness, the pitch of the frame and the size of the bolted side-plate are varied. Both opening and closing moments have been considered. Using the results of the parametric study, a design recommendation is proposed for the minimum thickness of the bolted side-plates.

Dynamic stability analysis of metro tunnel in layered weathered sandstone

In this study a coupled-eulerian–lagrangian (CEL) approach has been applied to assess the internal blast loading conditions, for the tunnel built in three layers of sandstone rock. The three weathered stages of sandstone have been considered in this study i.e., slightly, medium and also highly weathered sandstone in three different layers. The sandstone rock weathering increases as we move towards the ground surface from deep subsurface. The elastoplastic finite element model with varied overburden depth with dimensions of 60 m (L × B × H) each to incorporate different parametric cases. An explosive is assumed at the center of the tunnel, with the capacity of hundred kg of trinitrotoluene (TNT), the explosive is assumed to be hanging in the air inside the tunnel opening with equal distance from all sides. The TNT sphere and air that is inside the rock tunnel has been modelled through CEL technique to simulate actual in-situ condition. Through Mohr-Coulomb, Concrete Damage Plasticity, and Johnson-Cook constructive material model the elastoplastic behaviour of different materials like rock, steel bars and concrete has been simulated respectively. The cage of steel bars has been embedded through interaction constraint in concrete liner to produce reinforced concrete liner. In the initial stages of simulation with 5 m of overburden depth the tunnel has been placed in the upper layer of sandstone. For further analysis, the position of the tunnel has been changed for overburden depth of fifteen, twenty-five and thirty-five meter. In accordance with the result of the simulation, for rock in terms of acceleration, velocity, and dis-placement, the depth of the overburden and the displacement of the crown are inversely related. No damage in terms of compression is seen in this simulation, but in all instances, a small damage owing to tensile failure has been noted.

Test and direct strength method on slotted perforated cold-formed steel channels subjected to eccentric compression

This paper aims to investigate the buckling behaviors of cold-formed steel (CFS) channels with slotted web holes determined by the Steel Stud Manufacturers Association (SSMA) under eccentric compression, and propose the simplified direct strength method (DSM) formulas for engineering practicing. An experimental study on 20 specimens was conducted, including 18 slotted perforated specimens with nine eccentricities increasing from −20 mm to 20 mm and 2 unperforated specimens subjected to axial compression. Two kinds of nominal lip lengths for cross sections were selected as 15 mm and 20 mm. The experimental results indicated that the failure modes of slotted perforated specimens subjected to eccentric compression depended on the position of the eccentricity. Compared with the slotted perforated specimens subjected to pure axial compression, the ultimate loads of specimens subjected to positive eccentric compression decreased by 21.70 % on average, while they decreased by 16.38 % on average for those subjected to negative eccentric compression. Moreover, a nonlinear elasto-plastic finite element model (FEM) was developed and validated against the experimental results. Furthermore, combined with the experimental results, extensive FE parametric analyses were conducted to predict the eccentricity impact coefficient formulas. Finally, based on DSM of unperforated CFS members subjected to pure axial compression in AISI S100-16 and the eccentricity impact coefficient formulas, the suitable DSM design formulas for slotted perforated CFS channels determined by the SSMA under eccentric compression were proposed, without the need to calculate the elastic buckling critical stress for slotted perforated CFS channels.

Modeling of Sand Triaxial Specimens under Compression: Introducing an Elasto-Plastic Finite Element Model to Capture the Impact of Specimens’ Heterogeneity

This paper follows up on a series of reference papers that inspired MDPI’s Topic “Stochastic Geomechanics: From Experimentation to Forward Modeling”, where global and local deformation effects on sand specimens are fully described from high-resolution boundary displacement fields, as supported by a comprehensive experimental database (which includes varying degrees of specimen’s heterogeneity) that is available to the scientific community for further study. This paper presents an elasto-plastic comparative analysis of different finite element models reproducing different sand specimen heterogeneity configurations as follows: loose, dense, and half-dense half-loose specimens. The experimental conditions for these specimens’ heterogeneity configurations were simulated with an axisymmetric finite element model. To characterize the stress-strain response obtained from the experiments, an elasto-plastic constitutive model with strain-hardening and softening laws was adopted to reproduce the sand specimens’ mechanistic response. An expert-based calibration of the numerical models accounted for both global and local effects by making use of global observations captured by the triaxial point sensors (i.e., axial force and displacement) and by local observations captured by 3D digital image correlation analysis (i.e., 3D boundary displacement fields). Results show that predictions of the proposed numerical models are in good agreement with the experimental observations, both global and local responses. The combined use of global and local observations to calibrate sand triaxial specimens sets the basis for a more comprehensive parameterization process. For the first model set, three experiments were assumed with homogeneous materials. While both dense and loose models showed good agreement with the experiments, the displacement field prediction of the half-dense half-loose layered model identified limitations in reproducing heterogeneous configurations. Afterward, the second set compared and analyzed the half-dense half-loose layered models by implementing a heterogeneous model, showing significantly better model predictions (i.e., after the implementation of the heterogeneous model, which accounts for a transition zone between the upper and lower segments).

Structural behaviour of cold-formed steel T-Stub connections with HRC and screws subjected to tension force

Cold-formed steel (CFS) T-Stub connections are widely used in single-story buildings, and their use is increasing in multi-story and long-span buildings. Recently, an innovative CFS T-Stub connection was developed using self-drilling screws and the Howick Rivet Connector (HRC), and such a newly-developed connection demonstrated excellent structural performance in the building industry. In this paper, a comprehensive experimental and numerical investigation was conducted to investigate the failure mechanism and structural behaviour of CFS T-Stub connections with a combination of HRC and screws under tension force, considering the effects of screw numbers. Firstly, a total of 15 new experimental tests were conducted on the CFS T-Stub connections with various numbers of screws. From the experiments, it was observed that the HRC was subjected to shear failures, while screws failed primarily due to tilting and bearing failures in all investigated specimens. Then, a non-linear elasto-plastic finite element (FE) model was developed and validated against the experimental results in terms of connection strength and failure modes. Finally, the design strengths obtained from the American Iron and Steel Institute (AISI 2016) & Australia/New Zealand standards (AS/NZS 2018) and Ahmadi et al. (2016) were compared with the test and FEA results, showing that the ultimate design strength of CFS T-Stub connections was overestimated by 16% and 14%, respectively. However, for T-Stub connections with HRC alone and with HRC and one screw, these design guidelines were unconservative by 5%.

Study on Damage Evolution of Tunnel Lining under Strike-Slip Fault Movements

For the purpose of investigating the damage mechanism and failure characteristics of tunnel lining under the strike-slip fault movements, a three-dimensional elastoplastic finite element model was established in the present study including a railway tunnel across an active strike-slip fault. With the assistance of this numerical model, the tensile and compressive damage, plastic strain development process, and shear failure of the secondary lining at different fault plane positions were analyzed, and further, the damage laws of the secondary lining at different fault displacement and tunnel-fault intersection angles were summarized. The simulation results showed that when the maximum imposed fault displacement is 30 cm, the most unfavorable fault plane appears at the junction between the moving block and the fracture zone, and serious tensile cracks and shear failures occur on each fault rupture plane. Besides, the maximum plastic strain and compressive damage are distributed in the vault and invert. In addition, with the increase of the fault displacement, the axial strain of the secondary lining increases as well, of which the main part shows the tensile strain. Interestingly, with the decrease of the crossing angle, the axial strain gradually changes from the tensile strain to the compressive strain, which is consistent with the direction of the fault angle. Furthermore, the tensile and compressive damage of the secondary lining increases with the increase of movement distance. At the same time, the tensile damage along the tunnel ring develops, and the compressive damage propagates mainly in tunnel vault and invert. With the decrease of the crossing angle, the degree of the tensile damage in the lining reduces, as well as its range. The compressive damage area of the lining develops from the vault and inverted arch to the tunnel wall on both sides, which has a trend of penetrating the side walls on both sides. The distribution area and maximum value of the overall lining damage indices in tensile (OLDT) and overall lining damage indices in compressive (OLDC) increase with the increase of fault movement distance. With the decrease of the crossing angle, the distribution range and maximum value of OLDT decrease, and the distribution range of OLDC increases, while the maximum value basically remains the same. The research results of the present work can provide reference for the antidislocation design of railway tunnels crossing strike-slip faults.

Local and global buckling prevention design of corrugated steel plate shear walls

Local buckling and global buckling may occur in corrugated steel plate shear walls (CSPSWs) under shear loads. In general, the seismic and even strength design of CSPSWs may require no local buckling occurrence in the folds (namely sub-panel elements) and no global buckling occurrence in CSPSWs if they are used as energy dissipating devices. Therefore, the width-to-thickness ratio limits of folds or sub-panels and the normalized slenderness ratio limits of CSPSWs are major concerns for preventing their local and global buckling in their seismic and strength design. This paper presents the local and global buckling behavior and load-bearing capacity of trapezoidally corrugated steel plate shear walls (T-CSPSWs) and sinusoidally corrugated steel plate shear walls (S-CSPSWs) under pure shear. Firstly, finite element models (FEMs), FEM-l and FEM-g, are established for analyzing the local and global buckling of CSPSWs separately. Based on extensive numerical results, the formulas for more accurately estimating elastic local and global buckling loads are proposed for T-CSPSWs and S-CSPSWs under shear loads, respectively. Accordingly, the normalized width-to-thickness ratios of flat folds or curved sub-panels and the normalized slenderness ratios of CSPSWs are conducted. Finally, the ultimate load-bearing capacity respectively subjected to local and global buckling of CSPSWs under shear loads is calculated by employing elastoplastic FEMs, and the width-to-thickness ratio limits and the normalized slenderness ratio limits are further obtained in terms of a design criterion that local and global buckling load resistance of CSPSWs is not less than fully sectional shear-yielding load.

Web crippling design of cold-formed stainless steel channels under interior-two-flange loading condition using deep belief network

This research presents a deep-learning framework, namely a deep belief network (DBN), for analyzing the interior-two-flange web crippling performance of cold-formed stainless steel channels with centered and offset web holes. An elastoplastic finite element (FE) model, validated using 101 experimental results which were previously reported in the literature, generates a total of 43,200 data points for training the DBN. When compared to a total of 54 experimental results published in the literature, the DBN predictions were shown to be approximately 10% more conservative. Using the same large training data, the developed DBN model outperformed the Backpropagation Neural Network (a typical shallow artificial neural network) and the PaddlePaddle-based linear regression model. A parametric analysis was then performed using the DBN predictions to explore the effect of section size, web holes and bearing length. Design equations for (reduced) web crippling strength are proposed for the cold-formed stainless steel perforated channels, and the feasibility of the proposed equations was assessed by the conducted reliability analysis.

The strength design of deeply buried circular corrugated steel arches with considering only soil radial restraining

Buried circular corrugated steel arches (BCCSAs) are often adopted in underground engineering. However, the current design specifications cannot accurately estimate the BCCSA’s load-bearing capacity due to the complicated interaction between the soil and the arch. This paper presents the strength design recommendations for deeply buried circular corrugated steel arches with various rise–span ratios under axial compression and under combined axial compression and bending moment respectively, with meeting a proposed width–thickness ratio limit of the BCCSA for local buckling prevention. At first, a finite element model (FEM) of sinusoidally corrugated steel plate (S-CSP) for analyzing its local plate buckling under axial compression (FEM-l) is established, and this FEM can eliminate other possible buckling modes except the local buckling mode by constraining the out-of-plane displacement at the crest and valley lines in S-CSPs. Through FEM-l, the local buckling behaviors of S-CSPs are studied and the width–thickness ratio limit of S-CSPs under axial compression for local buckling prevention is determined in terms of a design principle that local buckling of plate elements does not occur before fully sectional yielding. Then, a global arch-spring model of BCCSA is established for analyzing its elastic global buckling, with considering the interaction between the soil and arches by simplifying the radial restraint of soil as radial unidirectional springs around the arch. The normalized slenderness of BCCSA in the arch-spring model is obtained from its elastic global buckling load calculated by theoretical derivation with bidirectional spring assumption. Finally, the ultimate load-bearing capacity of BCCSAs is calculated by employing elastoplastic finite element models under axial compression and under combined axial compression and bending moment respectively. Based on extensive numerical results obtained in this study, the conservative strength design methods for BCCSAs are proposed in practical engineering applications.

A novel hybrid model to design fiber-reinforced shotcrete for tunnel linings

This article proposes a workflow to design fiber-reinforced shotcrete (FRS) for tunnel linings. The workflow is divided into two major stages: artificial neural network (ANN) development for predicting the composite toughness, and tunnel lining design through numerical modeling. First, an artificial neural network was developed to predict FRS toughness from ASTM C1550 and EN 14488–5 panels, with concrete strength and fiber characteristics as input parameters. An extensive literature review was developed to build a database gathering the relevant FRS properties for this work. The second part of this research consisted of developing an elastoplastic finite element model to design a steel fiber-reinforced tunnel lining application. Parameters from a real case study of a circular tunnel were taken from the literature to calibrate the proposed computational model. The model results are compared to analytical solutions and indicate good agreement. In this sense, the workflow is an alternative for designing fiber-reinforced shotcrete for tunnel linings.

Axial strength of slotted perforated cold-formed steel channels under pinned-pinned boundary conditions

The use of cold-formed steel (CFS) channel sections is becoming popular as the load-carrying members in building structures, and such channel sections are often perforated for the ease of installation of services. However, limited experimental investigation has been reported in the literature for such channel sections under pinned-pinned boundary conditions. In this paper, a total of 16 CFS channel sections with and without slotted web holes were tested under pinned-pinned boundary conditions, and it was shown that all specimens with short lips failed by distortional-local buckling interaction controlled by distortional buckling and all specimens with long lips failed by local buckling. Moreover, the slotted web holes caused the axial capacities to decrease slightly by 2.4% on average for specimens failed mainly by distortional buckling and 6.4% on average for specimens failed by local buckling. A nonlinear elasto-plastic finite element (FE) model was also validated against the test results, a parametric study was conducted using the validated FE model. In addition, the results obtained from the tests and parametric study were compared against the results predicted by the current direct strength method (DSM) in AISI S100–16 for CFS channel sections with web holes. It indicates that the results predicted by the DSM are un-conservative for most CFS channel sections with web holes under pinned-pinned boundary conditions, especially un-conservative by 27.0% on average for CFS channel sections failed by local buckling. Therefore, new design formulas were developed based on the current DSM formulas for CFS channel sections with web holes.

Experimental and numerical study of a novel cold-formed steel T-Stub connection subjected to tension force

Cold-formed steel (CFS) is a popular form of construction in New Zealand and the developed world because it can be cost-effective, durable, sustainable, resilient to extreme environmental and seismic loads and easy to install. When used in domestic and medium-rise buildings, T-Stub connection between CFS channel sections is formed by using self-drilling screws which connect the flanges. In the literature, no prior investigation on the tension capacity of such connection has been reported. Therefore, this paper describes a novel test procedure for determining the tension capacity of such CFS T-Stub connection and the associated mechanism of failure. An experimental test program that comprises thirty experimental tests is reported in this paper. Three channel section thicknesses were examined: 0.55 mm, 0.75 mm, and 0.95 mm. All specimens failed as a result of tilting of the screws and bearing failure. Non-linear elasto-plastic finite element (FE) models were developed, and the predictions were validated against the experimental test results. It was adjudged that there was reasonable agreement in terms of connection strength and failure mode prediction. Finally, the design strengths derived from current design standards were compared with the experimental failure loads. It was found that the American Iron and Steel Institute (AISI 2016) and Australian and New Zealand Standard (AS/NZS 2018) are conservative by 6% and unconservative by 10% for the initial and final failure loads of T-Stub CFS connections, respectively.