Search

This paper presents a new and accurate finite element contact-modeling approach, to predict the axial compressive behaviour of bare cold-formed steel (CFS) lipped-channel sections (studs) set in tracks under concentric, static axial compressive loading. Detailed finite element analysis (FEA) models of the stud-track assemblies are developed using the ABAQUS software. The new modeling approach is validated against test results and captures stud-to-track gap and contact normal behaviour, which significantly influences studs' axial compressive performance. Hard contact (HC) has been used widely in literature for its simplicity, although it overestimates axial structural stiffness. Two softened pressure-overclosure relationships, with linear (LSC) and piecewise linear (PLSC) functions, were investigated for the first time in axially loaded bare CFS studs. PLSC best-replicated studs' axial-compressive behaviour, post-peak response, and failure mechanism under track boundary conditions. PLSC slightly overestimated the axial stiffness by 1 %, underestimating axial shortening and ultimate capacity by 3 % and 6 %, respectively. HC significantly overestimated the axial stiffness by a factor of 3, with a 5 % overestimation of ultimate capacity. LSC failed to predict the accurate failure mechanism for studs having gauge thicknesses less than 3 mm. PLSC scale factors were established and were found to be closely correlated with studs' non-dimensional slenderness (λ), following bilinear relationships. New predictive equations were developed to determine the PLSC scale factors for λ ranging between 0.49 and 1.2 to enable designers to use accurately calibrated models to capture bare studs' complex axial compressive behaviour in the elastic and inelastic range. • Axial compressive contact modeling of bare cold-formed steel studs set in track. • Studied two softened pressure overclosure relations: Linear (LSC) and Piecewise linear (PLSC). • Compared softened contact results with hard contact (HC) and forty-two test data. • PLSC captured the most accurate peak load, axial stiffness, and failure mechanism. • Proposed novel bilinear equations to determine accurate PLSC scale factors. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic performance of a single storey moment resisting cold‐formed steel (CFS) portal frame through cyclic testing. Six monotonic and six cyclic tests were performed on three different section sizes of CFS portal frames. The portal frames were 3.2m long x 2.2m high and the CFS sections bolted with either perfect‐fit tolerance bolt holes (PTBH) or normal tolerance bolt holes (NTBH) connections. Connections with NTBH are standard in CFS, but connections with PTBH are often only used for short‐spanning frames. Results from the tests demonstrated that both PTBH and NTBH connections had stable hysteresis and good hysteretic energy dissipation capacity and ductility. On average, the NTBH connections performed better under cyclic loading in comparison to the PTBH connections (5.4% larger ductility and 22.3% increased energy dissipation). Strain gauge results show failure due to combined bending and bi‐moment stresses, of which the bi‐moment stress component accounted for 41% of the total longitudinal stresses at the section web. It should be noted that bi‐moment stresses are often incorrectly ignored by practitioners; the experimental test results thus show that by doing so the sections would fail at 59% of the design moment. [ABSTRACT FROM AUTHOR]

Highlights • Cyclic testing of cold-formed steel portal frames. • Perfect-fit and normal tolerance bolt hole connection types investigated. • Good seismic performance through ductility and energy dissipation capacity. • Normal tolerance bolt hole connection has greater ductility and energy dissipation capacity. • Bi-moment should be considered by designers as it is the second largest stress after major axis bending. Abstract This paper investigates the seismic performance of a single storey moment resisting cold-formed steel (CFS) portal frame through cyclic testing. Six monotonic and six cyclic tests were performed on three different section sizes of CFS. The portal frames were 3.2 m long × 2.2 m high and the CFS sections bolted with either perfect-fit tolerance bolt holes (PTBH) or normal tolerance bolt holes (NTBH) connections. Connections with NTBH are standard in CFS, but connections with PTBH are often only used for short-spanning frames. Results from the tests demonstrated that both PTBH and NTBH connections had stable hysteresis and good hysteretic energy dissipation capacity and ductility. On average, the NTBH connections performed better under cyclic loading in comparison to the PTBH connections (5.4% larger ductility and 22.3% increased energy dissipation). Strain gauge results show failure due to combined bending and bi-moment stresses, of which the bi-moment stress component accounted for 41% of the total longitudinal stresses at the section web. It should be noted that bi-moment stresses are often incorrectly ignored by practitioners; the experimental test results thus show that by doing so the sections would fail at 59% of the design moment. Initial failure was localised at the top of the column sections in the form of local buckling at the web-to-flange junction under compressive stresses. Several load cycles past the initial buckling stage led to a further reduction of steel ductility due to strain hardening and strain ageing leading to fracture of the steel in the section corners. The buckling/tearing failure in the columns would result in a reduced axial load carrying capacity. [ABSTRACT FROM AUTHOR]

For practical reasons, it is typical for different types of sheathings (referred to as dissimilar) to be connected at both flanges of the stud (lipped channel-section) in cold-formed steel (CFS) panelized construction (e.g. one side has interior sheathing and the other exterior sheathing). However, limited studies are available on the axial behaviour of CFS studs with different combinations of sheathings present at both-flanges of a stud. This novel experimental study investigates the structural behaviour of nineteen (19) CFS panels with sheathing on one side only and different sheathing on both flanges of the wall panel using combinations of eight (8) different sheathing board types [fibre-cement boards (FCB) (8 mm/10 mm/12 mm thick); calcium silicate boards (12 mm thick); orient strand board (12.5 mm thick); and heavy duty FCB (6 mm/9 mm/12 mm thick)]. Also, first time an attempt is made to study the effect of dissimilar configuration using eight (8) different sheathing board types on axial strength of CFS panels in India. Experimentally tested single stud wall panel specimens consist of; one bare single-stud; eight (8) specimens sheathed with different types of sheathing boards on one flange only; and ten (10) specimens with combinations of different sheathing boards on both-flanges. Average test results are obtained by performing two (02) tests for each specimen. The strength enhancement of a bare single-stud from the sheathing boards has been investigated by testing specimens with a single layer of sheathing at one-flange and combinations of different sheathing boards on both-flanges. The ultimate axial compressive strength, load–deformation behaviour and failure patterns are the parameters compared. A new analytical and semi-analytical design methodologies namely; Rayleigh–Ritz (R-R) method and finite-strip method based on direct strength method (DSM) are adopted for evaluating the axial compressive strength of the CFS wall panels with dissimilar sheathing. Limited studies are available to verify the efficacy of R-R method and DSM to estimate the axial compressive strength of CFS wall panels with dissimilar sheathing on both flanges. Results establish that DSM may be used efficiently rather than the R-R method for axial compressive strength prediction of dissimilar sheathed CFS wall panels. The predicted values show good agreement with the experimental test results, and therefore, demonstrate that the semi-analytical method may be applied efficiently in design. • First time an attempt is made to study the axial compressive behaviour of CFS panels with dissimilar sheathing in India. • A total of 19 axial compressions tests were carried out on single-studded CFS wall panels with dissimilar sheathing. • Bare stud, one-flanged and both-flanged specimens using 8 different sheathing boards were considered for testing. • Tests were carried out on sheathing boards to evaluate the modulus of elasticity and peak deformation at failure. • Performance assessment of the Rayleigh–Ritz and Direct Strength Method is carried out using the experimental results. [ABSTRACT FROM AUTHOR]

Studs are the primary load-bearing components in cold-formed steel (CFS) wall panels, connected to tracks at both ends with self-tapping screws, forming a semirigid boundary condition (BCT). Most existing tests on the axial compressive behaviour of bare CFS studs are based on either theoretically-hinged (BCH) or fully-fixed boundary conditions. Previous researchers have employed BCT only on sheathed stud-wall panels. However, practicing engineers and current design codes, e.g., Eurocode 3, follow an all-steel design. Therefore, this research experimentally investigated bare-CFS-studs' axial compressive behaviour with BCT, considering, for the first time, the combined effect of the tracks' warping rigidity, stud-to-track gap, non-linear connection stiffness, and bare studs' various cross-sectional slenderness. Forty-two industry-standard lipped channel sections (studs) of five thicknesses (1.2-3 mm), three depths (75–125 mm), and two heights (1.2 & 1.5 m) were tested under static-concentric axial compressive loading with BCT. Another fourteen studs were tested with BCH, a comparator to BCT. Results demonstrated that the studs' global failure mechanisms were flexural-torsional in BCT instead of flexural in BCH. Studs' axial stiffness was two-phased in BCT due to the stud-to-track gap, compared to single-phased stiffness in BCH. >1.8 mm stud-to-track gap caused stud-to-track connections' failure and studs' sudden capacity reduction during gap closure. Studs achieved 1.22 times higher axial-compressive strength, 2.3 times more axial-shortening, 0.7 times lower axial stiffness, and 58% lower axial-compressive strain at the web-midheight under BCT-PhaseII than BCH. Tested strengths were compared with EC3 design strength, and an effective-length-factor of 0.65 was suggested for efficient design of studs with BCT. • Experimental comparison of bare CFS studs' axial compressive performance. • Investigated two boundary conditions: semirigid track (BC1), ideal hinged (BC2). • Stud-to-track gap, semirigid connections caused two-phased axial stiffness in BC1. • Tracks' warping rigidity causes studs' higher axial strength and axial shortening. • Improved EC3 design rule for bare CFS studs' design under axial compression in BC1. [ABSTRACT FROM AUTHOR]