The cracking of screw connections at the corners of wallboards is a typical failure mode for cold-formed steel (CFS) shear walls, resulting in premature performance degradation of CFS structures. A ...toughening method with carbon fiber reinforced polymer (CFRP) sheets at screw connection locations is proposed for strengthening the CFS shear walls. Totally 6 full-scale CFS shear walls with or without CFRP-toughened connections were tested, and the parameters of the lamination scheme, wallboard type and screw distance were investigated. A numerical model is developed for simulating the seismic behaviour of the tested specimens, and a theoretical model for predicting their shear strength is proposed. Results showed that the shear strength and lateral stiffness of the CFS walls with CFRP-toughened screw connections increased by more than 30 %, and the continuous lamination scheme provided greater strength. The fastener-based numerical model could effectively be used for predicting the hysteretic performance of toughened CFS shear walls well; both the pinch behaviour and ultimate strength are predicted well, and it can be used as an effective tool for the seismic design of toughened CFS shear walls with a theoretical model.
•Novel CFS composite shear wall with CFRP-toughened screw connections was proposed.•Influence of the lamination scheme, wallboard types and distance of screws were considered.•Experimental investigation, numerical simulation and theoretical calculation of the toughened wall were performed.•The generation and expansion of cracking at the corners of wallboards were inhibited.•The shear wall with CFRP-toughened had good seismic behavior.
Higher strength steel makes it possible to reduce the weight of members without changing the cross-sectional shape. To apply high-strength steel to light-gauge steel structures, it is necessary to ...quantify the strength of screw connections. In this study, single plane shear tests of screw connections using high-strength steel were conducted, and an evaluation formula for the strength of the connections was proposed. It was shown that the evaluation formula was able to properly evaluate the strength of the screw connections.
Current design rules for timber joints with dowel-type fasteners require input parameters such as yield moment and withdrawal capacity, which are determined within the European framework of ...certification testing. Databases containing these data were assembled. A large scatter was observed. Bespoke series may deliver clear trends. If representative data is considered, these clear trends vanish. Globally valid regression equations are conservative leading to incorrect prediction of failure modes.
The current cold-formed steel (CFS) design standards have not yet provided adequate design methods for built-up nested CFS channel compression members, which may fail by either local or distortional ...buckling, despite several research studies in recent times. These research studies have proposed improved DSM based design methods that led to capacity predictions with varying accuracy. Besides, there were some contradicting observations regarding the effects of screw connections on their compression behaviour and capacities. Hence, this research study investigated the behaviour and capacity of nested CFS channel compression members. It included experimental tests of short single channel and nested channel compression members failing by local-distortional interaction and local buckling, respectively, development and validation of suitable finite element models of nested channel compression members and finally a parametric study to (1) show that distortional buckling is not the critical failure mode of nested channel members, and (2) examine the effects of screw characteristics and spacing on their behaviour and capacities. Importantly, the accuracy of currently available design equations in the CFS design standards and recently published research papers was investigated and a simple DSM based design method is recommended. This paper presents the details of this research study, its results and findings.
Display omitted
•Investigated the behaviour of short screw-fixed built-up nested channel (NC) compression members.•NC members fail by local buckling although single channels are dominated by distortional buckling.•For single members dominated by distortional buckling, NC member capacities are more than the sum of individual capacities.•For single members dominated by local buckling, NC member capacities are equal to the sum of individual member capacities.•Proposed a simplified and reliable design method based on the current DSM equations.
•The five full-scale experiment on LFTST columns subjected to eccentric compression.•The FE approaches to model the eccentric compression performance of LFTST columns and validated by the ...experimental results.•The calculation formula of stable bearing capacity of LFTST columns subjected to eccentric compression.
In this study, a new L-shaped column fabricated by thin-walled square steel tubes (LFTST columns) based on self-drilling screw connections is proposed. The LFTST columns consisted of square steel tubes, U-shaped parts, angle parts, gusset plates, and self-drilling screw connections. LFTST columns possess several advantages including easy transportation, rapid assembly, and eco-friendliness. Consequently, they are suitable for low-rise buildings, such as village-building, low-rise dormitories, and low-rise office buildings. However, the compression behavior of LFTST columns remains silent. Five full-scale LFTST column specimens were subjected to eccentric compression tests. The variables under consideration included eccentricity (with values of 0 mm, 40 mm, and 80 mm), thickness (2 mm and 4 mm), and the number of gusset plates (0, 1, and 3). The failure modes, bearing capacity, load–displacement response, and strain development of the LFTST specimens were obtained. Subsequently, finite element (FE) models of LFTST columns were established and used to analyze the eccentric compression behavior of LFTST columns. The FE modeling results agreed well with the experimental results. A detailed parameter analysis was conducted to evaluate the effects of various factors. These factors included the thickness of the plates (2 mm, 3 mm, and 4 mm), the width of the gusset plates (100 mm, 150 mm, and 200 mm), limb spacing values (0 mm, 150 mm, and 300 mm), and eccentricity (0 mm, 20 mm, 40 mm, 60 mm, and 80 mm). In addition, the calculation formula for estimating the ultimate bearing capacity of the LFTST columns was derived employing the double coefficient product method. The proposed formula was validated by experimental and FE results.
The shear behaviour of self-drilling screw connections between thin steel sheets is investigated via experimental testing, numerical and analytical modelling in this paper. A total of nineteen sets ...of single-lap joint specimens with self-drilling screw connections were tested to failure under shear. The full force versus deformation curves were recorded, and three typical failure modes were obtained and were shown to be closely related to the ratio of the screw diameter to the sheet thickness. Prior to testing, constitutive responses of the employed thin steel sheets were acquired from tensile coupon tests, and were further represented by a three-stage model including an elastic branch, a plastic branch described by the Ludwik equations, and a damage branch defined by the Johnson–Cook model and the linear accumulation damage evolution law. Advanced finite element (FE) models of the screw connections were developed and validated against the obtained shear test results, and a parametric study on the influences of the sheet thickness and the screw diameter was carried out afterwards. Based on the obtained test and FE results, a new prediction model for the shear deformation behaviour of self-drilling screw connections was proposed and calibrated. The newly proposed prediction model was further introduced into the numerical models of the cold-formed box girders fabricated by self-drilling screws, the applicability of which was verified by the close agreement with the available experimental evidence.
•Nineteen sets of single-lap screw connections were tested to failure under shear.•Constitutive responses of steel sheets were acquired and represented by a three-stage model.•Advanced FE models of the screw connections were developed and validated.•New prediction model for shear behaviour of self-drilling screw connections was proposed.•Applicability of the model was verified by test results of box girders fabricated by screws.
A small-scale experimental study was carried out to investigate the pull-through failure of the C-shaped Cold-Formed Steel (CFS) roof purlin sections subjected to wind uplift force. The parameters ...investigated to comprehend the pull-through behavior of roof purlin are thickness, web depth, flange width of the CFS purlin section, and size of the screw head diameter. The test specimens experienced two different modes of pull-through failure (rupture and bearing) along with the prying effect. It was observed that the pull-through failure mode transitions from rupture of the purlin section around the screw fastener in 1 mm thickness to bearing type in 2 mm and 3 mm thicknesses. The test results were compared with existing design limits and previous studies from the literature which concluded that the existing elastic design approach for the service limit state is unconservative. Hence, a suitable design limit to predict the critical pull-through capacity of C-shaped roof purlins under high wind load is proposed. Additionally, reliability studies were carried out to determine the resistance and safety factors for the proposed design equations. The suggested design specifications are applicable and conservative for the material strength in the range of 350 MPa.
Display omitted
•The pull-through capacity of a C-shaped CFS roof purlin section is investigated using small-scale tests.•Test result indicates that the thickness of the section and the diameter of the screw head are important parameters.•The change in the purlin thickness led to the failure mode transition from rupture to bearing.•Suitable design limit is proposed for the C-shaped section.
An experimental study was conducted to explore the strength contribution of plywood sheathing boards that are regularly used in the cold-formed steel (CFS) wall panel construction. A series of ...material tests and 4-point bending full-scale tests were carried out. The testing program includes various key design factors such as sheathing board thicknesses, screw spacings and slenderness of the CFS studs. The test results indicate that the plywood sheathing thickness of 12 mm is sufficient for restraining the lateral torsional buckling (LTB) of the slender CFS studs, which also increased the ultimate moment capacity of the CFS wall panel by a maximum of 150%. However, the improvement in flexural strength varies depending on the local and global slenderness of the CFS wall stud. The spacing between the sheathing-screw connection also significantly influenced the structural contribution of plywood-sheathing. The design calculations were carried out as per the AISI design provisions and latest improvements suggested by the previous research works. The design calculations indicate that the design moment capacity of the CFS wall panel can be increased by a maximum of 48%, and most of the design results are conservative compared to the experimental results. Although, it was found that the modified design provisions of AISI are reliable for the strength predictions, the failure modes predicted greatly varied compared to the experimental results. Therefore, a series of individual sheathing screw connection tests were carried out to discover the key factors that influence the bracing effect of sheathings. On the basis of the results obtained from individual sheathing connection tests, the preliminary modifications that are required for the accurate failure mode predictions are suggested.
•The bracing effect of plywood sheathing is explored through experimental investigation.•The plywood sheathing was able to restrain the lateral torsional buckling of the Cold-formed Steel wall studs.•The predicted failure modes based on AISI provisions were varying compare to the experimental results.•The preliminary modifications that are required for the accurate failure mode predictions are suggested.
In order to study shear-slip constitutive model of screw connections between cold-formed steel (CFS) profiles and its application in numerical analysis of CFS built-up columns, a total of 225 ...steel-to-steel screw-fastened connections were investigated under monotonic loads. The thicknesses of C-section steels and diameters of self-drilling screws were varied to study their effect on shear performance of connections. The experimental results show that the failure modes can be divided into three types, which include bearing failure of screw holes, shear failure of screws and pull-out of screws. Furthermore, the shear-slip constitutive model of screw-fastened connections was developed and then the methods for estimating stiffness parameters, strength parameters and displacement parameters were derived. In addition, the numerical models were put forward by applying the shear-slip constitutive model on basis of previous built-up back-to-back CFS columns tests. The results of numerical simulation are consistent with the previous test results by comparisons. The proposed shear-slip constitutive model can effectively simulate the shear-slip behavior of screws used in built-up back-to-back CFS columns.
•Monotonic loading tests of steel-to-steel screw-fastened connections were carried out.•Bearing failure of screw holes, shear failure of screws and pull-out of screws are the three types of failure modes.•A shear-slip constitutive model of screw connections was developed.•A numerical model applying the model was developed to simulate built-up back-to-back CFS columns.
