Cold-formed Steel Framing Research Articles

New nonlinear lateral-vertical coupled shear element model for use in finite element structural analysis applications

In nonlinear structural analysis, shear walls within whole-system models are often modeled using a spring model with a single degree of freedom where the lateral stiffness of the shear wall is modeled as a nonlinear spring. The stiffness of the spring is often described by the hysteretic relationship between the lateral restoring force and shear wall lateral deformation. In this study, a new shear element is introduced, which couples the lateral and vertical stiffness of the shear wall. This new shear element is able to better describe the behavior of shear walls in mid-rise and tall buildings. An illustrative example is presented to help explain the application of the new shear element in finite element modeling. In the examples, the new shear element is used to calculate displacement and internal forces for cold-formed steel frames. The results show that without including vertical wall stiffness, the lateral displacement is significantly underestimated. The difference increases with the height of the building and for a ten-story frame the new model demonstrates an increased lateral displacement at roof level of 64.1% when compared with current typical shear element model (lateral stiffness only).

Seismic behavior of cold-formed steel frame shear walls sheathed with ply-bamboo panels

This paper presents an experimental study on the monotonic and cyclic lateral loading behavior of cold-formed steel (CFS) shear walls sheathed with glued laminated bamboo (glubam ply-bamboo) panels. A total of 16 model shear wall specimens with two types of aspect ratios were tested using ASTM loading protocols. The observed phenomena and the effects of different cyclic loading regimes are discussed. The shear capacity and deformability of ply-bamboo sheathed CFS shear walls are evaluated and compared with wood sheathing panel (WSP) sheathed CFS shear walls through four seismic equivalency parameters recommended by American Iron and Steel Institute (AISI) in 2010 (AISI-RP10-4 2010). The load distribution of the screws along the vertical edges of the panels and the forces in the shear anchors are discussed. The results obtained in this study can further promote the application of bamboo-based material in CFS structures, as potential options for eco-friendly and cost-effective construction.

Dynamic and cyclic response of a full-scale 2-storey cold-formed steel structure with and without infill materials

Cold-Formed Steel (CFS) has become more and more popular in recent years as an alternative construction material. Short construction time and very high strength to weight ratio under lateral forces made cold-formed steel an attractive option in earthquake prone countries such as Japan, New Zealand and the US. These structures are formed of CFS frames with either boards and sheatings attached to the frames or infill materials sprayed to the frames on-site. This paper presents the results of dynamic and cyclic experiments conducted on two different 3-D and 2-storey models. The first model was CFS frame system without infill material and the second one was with infill material. In order to identify the actual dynamic characteristics of models such as modal frequencies and damping ratios, large-scale tests are conducted instead of 2-D panel tests. Ambient vibration tests were carried out to determine modal frequencies of the models at different damage states and forced vibration tests were carried out to determine modal damping ratios at high vibration levels. In addition to ambient and forced vibration tests, cyclic tests were performed to obtain the hysteretic behavior of the model. It was observed that with the application of infill material, lateral load resisting capacity increased by 3.5 times, ductility of the model increased from 2.58 to 3.96 and damping ratio increased from 6.7 to 9.0%. In addition to identification of dynamic characteristics, the main motivation of this study is to investigate the possible use of ambient vibration surveys in the determination of damage level. Results showed that ambient vibration surveys can be used as a damage detection tool after an earthquake or any other hazard.

Investigation on flexural strength of cold-formed thin-walled steel beams with built-up box section

Built-up sections are widely used in cold-formed thin-walled steel frames. This paper mainly investigates the in-plane behaviour of built-up box beams with nested C section and U section under pure bending about strong and weak axis. The four-point bending test was conducted on a total of 7 groups of specimens, including built-up box sections (CU) and individual sections (C, U). A finite element model is developed and verified by the test results for further parametric analysis. The stress distribution at mid-span cross-section shows that the components in built-up beams can resist the bending moment together. For built-up box beams bending about strong axis, the reasonability of the capacity superposition method and equivalent method is assessed by the discussion on test results and numerical analysis results. The equivalent box section is suggested to calculate the flexural strength of built-up box beams bending about weak axis. Finally, the comparison between predicted and actual flexural strength indicates that this simplification of the proposed method can slightly under-estimate the flexural strength.

Behavior and Design of Thin-Walled Cold-Formed Steel Clip Angles Subjected to Shear Load

AbstractThin-walled cold-formed steel (CFS) clip angles are commonly used to connect CFS framing members or attach CFS members to the main building structure. The design provisions for CFS clip angle connectors have not been included in the AISI design specifications and standards. This paper presents a research project aimed at developing a design method for the thin-walled cold-formed steel load bearing clip angles subjected to shear forces. An extensive test program was conducted to investigate the behavior and shear capacity of clip angles with various dimensions and thicknesses. It was found that the local buckling and the distortional buckling could dominate the failure mechanism dependent on the plate slenderness ratio. Based on the test results, two design methods were developed for determining the nominal shear strength of load bearing clip angles with and without consideration of the clip deformation, respectively. The ASD safety factors and the LRFD resistance factor were also produced to suppo...

Issues of alternating load in design of cold-formed steel frames with lap joints

Issues of alternating load in design of cold-formed steel frames with lap joints

Buckling and Vibration Analysis of Cold-Formed Steel CHS Members and Frames Using Generalized Beam Theory

This paper reports the results of an investigation on the use of Generalized Beam Theory (GBT) to assess the buckling and vibration behaviors of thin-walled members and frames built from cold-formed steel circular hollow section (CHS) profiles. Initially, the concepts and procedures involved in performing GBT buckling and vibration analyses are presented, paying particular attention to the derivation of the mass tensors that account for the influence of the inertia forces. Then, the formulation, numerical implementation and validation of a GBT-based beam finite element for isolated members are described. Next, the determination of the frame linear stiffness, geometric stiffness and mass matrices, which incorporate the influence of the frame joints, is addressed. Finally, in order to illustrate the application and capabilities of the proposed GBT finite element formulation, numerical results are presented and discussed — they concern the buckling and vibration behaviors of an "L-shaped" frame. For validation purposes, most GBT-based results are compared with values yielded by shell finite element analyses carried out in the code ANSYS.

Cyclic flexural response and energy dissipation of cold-formed steel framing members

This manuscript summarizes an experimental program investigating the cyclic flexural behavior and energy dissipation of C-shaped cold-formed steel structural framing members experiencing global, distortional or local buckling. Understanding the cyclic flexural moment-rotation (M–θ) response of individual members is essential in developing analytical models that can facilitate analysis-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). A cyclic loading protocol was adapted from FEMA 461 with targets based on elastic buckling properties. Abrupt drops in flexural strength after peak moment were observed with subsequent stiffness degradation and pinching of the moment-rotation response associated with straightening of buckling deformations during loading direction reversals. Members experiencing local and distortional buckling accumulated damage at the compressed web and flanges within the leading buckled half-wave that spread throughout the cross-section forming flexural hinges after several cycles. In members experiencing lateral-torsional buckling, damage localized at the C-section flange-stiffening lip but distinct flexural hinges were not observed. Energy dissipation per cycle in members undergoing lateral-torsional buckling remained constant through large flexural rotations because the failure mechanism involved mid-span cross-section rigid body motion without plastic deformations spreading across the cross section. Local and distortional buckling specimens resulted in more dissipated energy per cycle compared to global buckling specimens, but the energy dissipation rapidly decreased as applied displacements increased. Energy dissipation within the damaged half-wave(s) is higher for lower cross-sectional slenderness and increasing section modulus, key trends that will be useful for generally defining cyclic hysteretic response of thin-walled cold-formed steel members in planned future work.

Performance of cold-formed-steel-framed shear walls sprayed with lightweight mortar under reversed cyclic loading

Sheathing with sprayed lightweight mortar (SLM) is proposed to enhance the performance of shear walls framed with cold-formed steel (CFS). Full-scale specimens were tested to assess the failure mode, strength, stiffness, ductility, and energy absorption achieved. Slippage between the CFS framing and the SLM significantly increased the walls’ strength and stiffness and restricted crack propagation. The failure mode typically involves local buckling of the end studs. Specimens with SLM on the front and calcium silicate boards (CSBs) on the back were weaker than specimens with SLM sheathing on both sides. Joint-strengthened knee elements or X-shaped steel-strap bracings increased the load-bearing capacity and reduced the ductility of the specimens.

Fire design rules for load bearing cold-formed steel frame walls exposed to realistic design fire curves

Light gauge Steel Frame (LSF) walls are extensively used in the building industry due to the many advantages they provide over other wall systems. Although LSF walls have been used widely, fire design of LSF walls is based on approximate prescriptive methods based on limited fire tests. Also these fire tests were conducted using the standard fire curve (ISO 834-1, 1999 [1]) and the applicability of available design rules to realistic design fire curves has not been verified. This paper investigates the accuracy of existing fire design rules in the current cold-formed steel standards and the modifications proposed by previous researchers. Of these the recently developed design rules by Gunalan and Mahendran (2013) [2] based on Eurocode 3 Part 1.3 (EN 1993-1-3, 2006 [3]) and AS/NZS 4600 (Standards Australia (SA), 2005 [4]) for standard fire exposure (ISO 834-1, 1999 [1]) were investigated in detail to determine their applicability to predict the axial compression strengths and fire resistance ratings of LSF walls exposed to realistic design fire curves. This paper also presents the fire performance results of LSF walls exposed to a range of realistic fire curves obtained using a finite element analysis based parametric study. The results from the parametric study were used to develop a simplified design method based on the critical hot flange temperature to predict the fire resistance ratings of LSF walls exposed to realistic fire curves. Finally, the stud failure times (fire resistance rating) obtained from the fire design rules and the simplified design method were compared with parametric study results for LSF walls lined with single and double plasterboards, and externally insulated with rock fibres under realistic fire curves.

Numerical evaluation: AISI S400 steel-sheathed CFS framed shear wall seismic design method

Seismic design provisions for steel-sheathed cold-formed steel framed shear walls, specific to Canada, are not provided in the existing AISI S213 Standard “North American Standard for Cold-Formed Steel Framing – Lateral Design”. A multi-phase approach was adopted in order to develop appropriate seismic design provisions for inclusion in the new AISI S400 Standard “North American Standard for Seismic Design of Cold-Formed Steel Structural Systems”. The approach included the extensive displacement based testing and dynamic testing of shear walls, the analysis of the test data results, the development and calibration of dynamic numerical models in OpenSees, and lastly, the dynamic response history analyses of twelve archetype buildings designed for the seismic hazard in three cities; Halifax (low seismic), Montreal (medium seismic) and Vancouver (high seismic). It is this last phase of the study that is documented herein. Fragility curves were developed from the buildings' response to 44 scaled ground motion records following a method adapted from the FEMA P695 analysis methodology. The results showed that the design method is appropriate, including the seismic force modification factors of Rd=2 and Ro=1.3. Improvement to the predicted seismic response of CFS framed buildings could be forthcoming if one were to account for the contribution of the non-structural gypsum wall panels.

Flexural Behaviour of Reinforced Slab Panel System with Embedded Cold-formed Steel Frames as Reinforcement

This paper presents the experimental investigation on flexural characteristic of slab panels with embedded cold-formed steel frame as reinforcement. Perforated cold-formed steel channel sections are formed into steel frames as replacement to the conventional reinforcement bars inside precast concrete slab panels. A series of six experimental specimens for precast slab panels were tested. The specimens with 3 configurations namely control sample (CS) with conventional reinforcement bars, single horizontal C-channel section (SH) and double horizontal C-channel sections (DH) formed into rectangular hollow section. Results show that the tested slab specimens failed at the flexural crack at mid-span, under loading point and shear at the support. Tearing of shear connector in the cold-formed steel section was found to be the main factor for the structural failure. SH specimens achieved the highest ultimate load capacity, with average value of 138.5 kN, followed by DH specimens, 116.5 kN, and the control samples, 59.0 kN. The results showed that the proposed reinforced slab panel with embedded cold-formed steel frame was more effective compared to conventional reinforced slab.

Inelastic behavior of cold-formed braced walls under monotonic and cyclic loading

The ever-increasing need for housing generated the search for new and innovative building methods to increase speed and efficiency and enhance quality. One method is the use of light thin steel profiles as load-bearing elements having different solutions for interior and exterior cladding. Due to the increase in CFS construction in low-rise residential structures in the modern construction industry, there is an increased demand for performance inelastic analysis of CFS walls. In this study, the nonlinear behavior of cold-formed steel frames with various bracing arrangements including cross, chevron and k-shape straps was evaluated under cyclic and monotonic loading and using nonlinear finite element analysis methods. In total, 68 frames with different bracing arrangements and different ratios of dimensions were studied. Also, seismic parameters including resistance reduction factor, ductility and force reduction factor due to ductility were evaluated for all samples. On the other hand, the seismic response modification factor was calculated for these systems. It was concluded that the highest response modification factor would be obtained for walls with bilateral cross bracing systems with a value of 3.14. In all samples, on increasing the distance of straps from each other, shear strength increased and shear strength of the wall with bilateral bracing system was 60 % greater than that with lateral bracing system.

Computationally efficient fastener-based models of cold-formed steel shear walls with wood sheathing

The lateral behavior of sheathed, cold-formed steel (CFS) framed shear walls depends considerably on the complex behavior that occurs at each fastener location. Screw fasteners attach the sheathing material to the CFS framing, but relative motion of these components creates local damage, resulting in non-linearity at the scale of the entire shear wall. A computational model of a CFS shear wall is developed in which each fastener is represented by a non-linear, radially-symmetric spring element. The material parameters of the fastener element are determined from physical tests of sheathing-to-stud connections with small numbers of fasteners. The fastener material model includes a softening backbone curve, pinching, and loading and unloading parameters. The remainder of the model employs rigid sheathing panels, beam–column elements for framing, semi-rigid rotational springs for stud-to-track connections, and springs for hold-downs. The models are subjected to lateral cyclic displacement histories using the OpenSees structural analysis software. Thirteen full-scale shear wall tests of two different widths are modeled with various construction details related to the ledger track, gypsum board, vertical and horizontal seams, and number and thickness of field studs. The computational analyses are compared to the full-scale physical tests based on load–displacement behavior, lateral strength, drift at failure, initial stiffness, and energy dissipation, and are compared to specification-based strengths and displacements. The computational models provide detailed information on forces in the framing members and interaction forces at individual fasteners. This fastener-based computational approach is able to efficiently reproduce key aspects of the lateral behavior of CFS shear walls.

Thermal Performance of Load Bearing Cold-formed Steel Walls under Fire Conditions using Numerical Studies

Cold-formed Light gauge Steel Frame (LSF) wall systems are increasingly used in low-rise and multi-storey buildings and hence their fire safety has become important in the design of buildings. A composite LSF wall panel system was developed recently, where a thin insulation was sandwiched between two plasterboards to improve the fire performance of LSF walls. Many experimental and numerical studies have been undertaken to investigate the fire performance of non-load bearing LSF wall under standard conditions. However, only limited research has been undertaken to investigate the fire performance of load bearing LSF walls under standard and realistic design fire conditions. Therefore in this research, finite element thermal models of both the conventional load bearing LSF wall panels with cavity insulation and the innovative LSF composite wall panel were developed to simulate their thermal behaviour under standard and realistic design fire conditions. Suitable thermal properties were proposed for plasterboards and insulations based on laboratory tests and available literature. The developed models were then validated by comparing their results with available fire test results of load bearing LSF wall. This paper presents the details of the developed finite element models of load bearing LSF wall panels and the thermal analysis results. It shows that finite element models can be used to simulate the thermal behaviour of load bearing LSF walls with varying configurations of insulations and plasterboards. Failure times of load bearing LSF walls were also predicted based on the results from finite element thermal analyses. Finite element analysis results show that the use of cavity insulation was detrimental to the fire rating of LSF walls while the use of external insulation offered superior thermal protection to them. Effects of realistic design fire conditions are also presented in this paper.

Pullout Strength of Steel Pins in Cold-Formed Steel Framing

Steel pins are an attractive and efficient alternative technology to screws when connecting cold-formed steel or other materials to cold-formed steel members. However, unlike screws, pins remain an essentially proprietary connection technology based on manufacturer claims of special pin shank design. As such, current cold-formed steel design standards and specifications do not include provisions for their direct use and designers have no simple, rational means for making informed design decisions beyond information provided by manufacturers. This paper reviews the current design model for screws and examines the basic tension pullout/withdrawal limit state of helical knurled steel pin connections for cold-formed steel thicknesses common in residential construction. Included in this paper is a determination of material properties using a nondestructive test method as an alternative to traditional methods for estimation of steel base metal thickness. A simple lower bound friction model is proposed for helical steel pins and the model is calibrated using data from 32 physical pin tests. The calibrated model is shown to provide an acceptable degree of reliability and safety consistent with that of screws in current cold-formed steel design standards and specifications.

Effect of Panel Joints on the Performance of Cold-Formed-Steel Light-Frame Shear Walls

AbstractSome existing qualification/validation data for alternatives to code-compliant light-frame cold-formed steel (CFS) shear wall construction were developed before requirements for test specimens with 1∶1 aspect ratios and the inclusion of a vertical panel joint. These requirements were introduced on the notion/assumption that walls with an included panel joint and 1∶1 aspect ratio provide a lower bound estimate of wall performance (strength, displacement, and toughness). In this technical note, data from three independent experimental test programs were analyzed to shed light on panel joint and aspect ratio effects on cold-formed steel frame shear wall performance. The analysis showed that the performance of walls without a panel joint and with aspect ratios as high as 214∶1 provide reasonable lower bound measures of performance.

An experimental investigation on the seismic behavior of cold-formed steel walls sheathed by thin steel plates

The use of cold-formed steel (CFS) frames has grown extensively in recent years, particularly in the earthquake-prone regions. However, the behavior of lateral resisting systems in CFS structures under seismic loads has not been scrutinized in detail. Towards this, an experimental investigation has been conducted on cold formed steel frames sheathed by thin galvanized steel plates, the results of which are presented here. The experiments involve 24 full-scale steel plated walls tested under cyclic loading with different configurations of studs and screws. Of particular interest were the specimens׳ maximum lateral load capacity and the load-deformation behavior as well as a rational estimation of the seismic response modification factor, R. The study also evaluates the failure modes of the systems. The main factors contributing to the ductile response of these shear walls are also discussed in order to suggest improvements so that the walls respond plastically with a significant drift and without any risk of brittle failure.

Cyclic axial response and energy dissipation of cold-formed steel framing members

This paper summarizes results from an experimental program that investigated the cyclic axial behavior and energy dissipation of cold-formed steel C—sections structural framing members. Fully characterized cyclic axial load–deformation response of individual members is necessary to facilitate performance-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). The cyclic loading protocol was adapted from FEMA 461 with target displacements based on elastic buckling properties. Cyclic response showed large post-buckling deformations, pinching, strength and stiffness degradation. Damage accumulated within one half-wave after buckling. The total hysteretic energy dissipated within the damaged half-wave decreased with increasing cross-section slenderness. More energy dissipation comes at the cost of less cumulative axial deformation before tensile rupture.

Analytical Analysis of Seismic Behavior of Cold-Formed Steel Frames with Strap Brace and Sheathings Plates

Cold-formed steel frames (CFS) are popular all over the world. In this study, we have investigated 112 frames with different bracing arrangements and different dimensional ratios with different thicknesses of sheathing plates under cyclic and monotonic loading using Finite Element Nonlinear Analysis. We also evaluated seismic parameters including resistance reduction factor, ductility, and force reduction factor due to ductility for all specimens. On the other hand, we calculated the seismic response modification factor for these systems. The maximum modification factor among shear wall panels with sheathing plates related to GWB (gypsum wall board) specimen with thickness of 15 mm was 5.14; among bracing specimens in bilateral bracing mode related to B sample was 3.14. The maximum amount of resistance among the specimens with bilateral (2-side) bracing systems belongs to the specimen C (2-side double X-bracing) with the dimension ratio of 2 (4.8 m × 2.4 m) and resistance of 305.60 kN and also among the shear wall panels with sheathing plates, it belongs to DFP (douglas fir plywood) with a thickness of 20 mm and resistance of 371.34 kN.