Cold-formed Steel Framing Research Articles

Experimental study of fire resistant board configurations under standard fire conditions

Cold-formed Light gauge Steel Frame (LSF) floor-ceiling systems are commonly made with non-combustible fire protective membrane to protect the steel floor joists in fire. Thermal improvements to the fire protective membrane delay the heat transfer to structural elements and provide enhanced fire resistance level. Hence, this study addresses the thermal performance of different fire resistant board configurations under standard fire conditions to compare and propose improvements to conventional systems. Small-scale fire tests were conducted for a range of configurations of gypsum plasterboard, calcium silicate board and magnesium oxide board with the inclusion of thin steel sheathing. Fire test results showed that gypsum plasterboard and calcium silicate board performed very similar in regards to insulation criterion based failure times, while magnesium oxide board performed considerably worse. In all cases steel sheathing provided improved failure times. Improvements of 48%, 33% and 47% were obtained for gypsum plasterboard, calcium silicate board and magnesium oxide board when steel sheathing was used. This paper presents the details of the small-scale fire tests of different fire resistant board configurations and the results of time-temperature profiles. Based on these results, optimum fire resistant board configurations are recommended to achieve higher fire resistance levels for LSF floor-ceiling systems.

Recommendations for design of sheathing bracing systems for slender cold-formed steel structural members

The use of sheathing material as a structural component in the Cold-formed steel (CFS) construction holds great potential for stability of the structure and savings in the construction cost. However, there is no robust design method to account the structural contribution of sheathing boards. This paper presents the experimental results of 107 (including unsheathed and sheathed) CFS wall frame studs subjected to out-of-plane loading to study the feasibility of using gypsum board as a structural bracing sheathing material. The test parameters include various shapes and slendernesses of the CFS frame stud, thickness of the sheathing board and spacing between the sheathing bracing connections. The out-of-plane loading is applied as it causes lateral torsional buckling in the CFS structural members thereby creates pull-through failure at the sheathing bracing connections. Moreover, the suitability of the current AISI and Eurocode specification for the design of sheathing braced CFS structural member is studied. The experimental results indicate that the lateral buckling of the symmetric shaped (against the loading axis) CFS wall frame studs can be inhibited by gypsum sheathing. Whereas most of the singly symmetric and point symmetric CFS studs exhibit lateral torsional buckling and biaxial bending, respectively, due to the inadequate bracing effect of gypsum sheathing resulting in pull-through failure at the sheathing bracing connections. Therefore, a set of limitations for the use of gypsum sheathing as a structural bracing is suggested in the form of a generalized design parameter. Finally, the experimental results indicates that the design strength of the CFS wall frame stud can be increased in the range of 39% to 595% based on the shape and slenderness.

Numerical Study of Bolted Moment Connections in Cold-Formed Steel Frames

Bolted moment connections for cold-formed steel frames are considered very important and complicated items which need in depth studies. This paper studies the behaviour and strength of eave connections for members that consist of back to back cold-formed double channels in portal (right angle) steel frames. Relatively new configuration is suggested to facilitate the construction and reduce the cost of this type of connections. The connection is comprised of two stubs (welded built-up I shape) connected with two head plates, each stub is welded to its head plate, keeping in mind that the rafter stub is tapered I-shape. The web and flanges of cold-formed members are connected to the connection accessories by bolts. Numerical study is carried out using a finite element software package (ANSYS). The analysis accounts for geometric and material nonlinearities, large deformation and Elastic-plastic behaviour. Different parameters such as width to depth ratios and, width to thickness ratios of web and flange for the connection accessories and the cold-formed channels are considered. Different failure modes, including local yielding, flexural-distortional buckling, bearing failure as well as combined local yielding and bearing failures are observed. Moreover, moment-rotation relationships for this type of connection are deduced. The rigidity of this connection type is compared with EC3 classifications and generally it can be classified as a semi-rigid connection

Seismic collapse assessment of K-shaped bracings in cold-formed steel frames

K-shaped bracing is one of the lateral load resisting systems used in Cold-Formed Steel structures. Recently, some researches have been conducted to obtain further information about the seismic performance of the CFS using K-shaped bracings under monotonic and cyclic loads. In this research, the seismic performance factor of this structural system is under study. To determine the proper value of this factor, a non-linear finite element model of this structural system is developed using OpenSees software, and the cyclic behavior of this model is verified with previous experimental results. Several structures designed in accordance with Iranian seismic code were modeled using the verified model, and incremental dynamic analysis is performed on these structures. The analysis was performed according to FEMA P695 procedures using a ground motion set consisting of 22 earthquake records. Eventually, the studies showed that the seismic performance factor of 2 is a proper value for the cold-formed steel frames with K-shaped bracings. Also, as another result, the increase in the number of stories and the site’s seismic risk will increase the structure’s collapse probability. Furthermore, the height limitation proposed by seismic codes for this system seems to be somewhat conservative and it can be concluded that usage of the K-shaped bracing system is possible for taller structures in zones with low seismicity risk. Finally, it can be concluded that the K-shaped bracings might not have a suitable performance due to ductility issues.

Study on the Influence of the Thickness of Column on Axial Compression Behavior of Cold-Formed Steel Composite Wall

By changing the thickness of the column, the axial compression behavior of the one-side sheathed wall and the both-sides sheathed wall can be altered at different levels. Simulation and inspection of cold-formed thin-walled steel frame wall had been finished by using a finite element simulation software called ABAQUS, which was applied by test data from relevant literature. The axial carrying capacity of the sheathed wall was superior than the unsheathed wall, therefore, all models had been built and studied based on the one-side sheathed wall and both-sides similar sheathed wall. The analysis results proved that the axial compression behavior of the one-side sheathed wall and the both-sides sheathed wall could be increased substantially by adding the thickness of studs, and this change was more sensitive to the influence of the wall with one-side sheathed wall especially.

Study on Bolted and Blind-Bolted Single Shear Connections of Cold-Formed Steel Members

Abstract The paper presents the results of tests on single shear bolted connections of cold-formed steel sections with a wall thickness of 4 mm made with standard fully threaded M16 grade 8.8 bolts. The tests were performed for connections with washers and without washers. The obtained results were referred to earlier studies of analogous connections using blind fasteners Huck BOM R16. The failure mode was identified, the load capacity and stiffness were compared, and a method to determine the non-linear load-displacement characteristics of such connections was proposed. The effect of stiffness of joints on structural response of exemplary cold-formed steel frame was shown.

Seismic Behavior of Cold-Formed Steel Frames with Bolted Moment Connections

AbstractThis paper investigates the seismic behavior of the cold-formed steel (CFS) frame with bolted moment connections by quasi-static loading tests and numerical analysis. The quasi-static loadi...

Effect of Joint stiffness on Elastoplastic behavior of Cold-formed thin-walled Steel frames

In this paper, the first-order elastic analysis and second-order elastic analysis of cold-formed thin-wall steel frame (shelf) in practical engineering are carried out by using ANSYS and SAP2000 modeling analysis software, and the influence of semi-rigidity and second-order effect of joints on its overall performance is analyzed. At the same time, on this basis, the static elastic-plastic analysis of the shelf is carried out, and through the comparative analysis of the structural influence coefficient and displacement magnification coefficient of the shelf, the seismic performance of three kinds of beam-column connections (rigid connection, semi-rigid connection, hinged joint) is evaluated. And the structural influence coefficient of the shelf is put forward innovatively.

Elevated temperature thermal properties of carbon steels used in cold-formed light gauge steel frame systems

Fire design of cold-formed Light gauge Steel Frame (LSF) systems requires an accurate assessment of the thermal properties of each component at elevated temperatures. Heat transfer models based on these properties are implemented in order to accurately simulate the thermal behaviour of LSF systems in fire. For all carbon steel components, thermal properties are presented in Eurocode 3 Part 1.2. To verify the accuracy of thermal properties in Eurocode 3 Part 1.2 for the cold-formed steel components used in LSF construction, a series of thermal property tests was conducted based on the ASTM standard test methods. Thermal property tests were conducted to determine the specific heat at constant pressure, relative density, thermal conductivity and thermal diffusivity of three types of carbon steels, namely Grade 500 steel, Grade 300 steel and Grade 140 steel, due to their use in LSF construction. Test results showed the differences between the Eurocode 3 Part 1.2 model for carbon steels and the measured thermal property data for both specific heat and thermal conductivity of all three types of carbon steels due to chemical composition and the influence of carbon content. Hence, new equations were developed for specific heat and thermal conductivity for the selected carbon steels. To verify the effect of the measured thermal property results, 3-D heat transfer models of LSF floor-ceiling systems were developed and analysed. New thermal properties of carbon steels were used as inputs and comparisons made against fire test results for validation purposes. This paper presents the thermal properties of three selected carbon steels, which are commonly used in cold-formed LSF systems and the results.

Connections used for cold-formed steel frame shear walls sheathed with engineered bamboo panels

This paper presents experimental research on the load-bearing behaviors of self-drilling screw connections in cold-formed steel (CFS) frame shear walls sheathed with engineered bamboo panels. In total, 105 specimens were tested using monotonic and cyclic loading protocols. The performance of the CFS–bamboo connections was studied under various conditions with respect to differently engineered bamboo sheathing panels, screw features, end distances, and loading rates. The failure modes and performance parameters are discussed. The test results obtained in this study indicate that engineered bamboo panels can be used as efficient sheathing panels for CFS structures with good mechanical performances. Based on the connection test information, fast modeling was carried out on the lightweight CFS–bamboo shear walls.

Framework for construction system selection based on life cycle cost and sustainability assessment

Abstract The objective of this study is to develop a framework for the selection of construction systems of low and medium rise buildings used in residential, office and commercial applications. The construction systems considered are reinforced concrete framing (RC), structural steel framing (SS) and cold-formed steel framing (CFS). The framework is developed in accordance with the relevant guidelines for life cycle analysis and sustainability and is intended to support decision making in the design stage. The system boundary for the study is from cradle-to-grave, including all cost components from construction stage, use stage and disposal stage in addition to possible recycling/reuse options. The developed framework integrates building information modeling, energy simulation modeling and end of life scenarios to calculate and compare life cycle costs and sustainability advantages of construction system alternatives. All future costs are discounted to their present value using the appropriate interest rates. Uncertainties in the input parameters are modeled using realistic probability distributions and then used in a Monte Carlo sensitivity analysis to investigate the impact of changes in the input parameters on the result. Application of the developed system to a university building revealed the following results. The total life cycle cost is nearly the same for RC framing system and CFS framing system, while the life cycle cost of SS framing system is 13.4% more. When the system is credited for possible revenues resulting from early operation and recycling/reuse, the total life cycle cost of the RC framing system and the SS framing system become nearly the same while the life cycle cost of the CFS framing system becomes 22% less. Sensitivity analysis of the results shows that the discount rate has the most effect on the estimated mean cost followed by the inflation rate and the construction cost. The sustainability assessment focuses on calculating the LEED points associated with material recycling/reuse potentials and waste management.

Bending performance of cold formed steel structural member with perforated section in housing framing system

The study shows a numerical analysis on bending behavior of cold-formed steel framing system and the effective cost reduction between perforated and non-perforated steel section in steel framing system. The results are presented in the form of displacement and yield moment. Using finite element analysis software, a total of 26 set of nonlinear analysis were executed to determine the effects of opening spacing, edge distance and thickness of section on bending behavior. The result shows that the increasing of the opening spacing and edge distance would increase the bending capacity. C-channel steel section showed better moment resistance in thicker section. The result was then compared to the C-channel steel section without perforation. From the analysis, it was observed that C-channel steel section without perforation had higher bending capacity than C-channel steel section with perforation in major axis. However, there is a small difference in terms of yield moment when comparing C- channel section with 0.4D of square opening and 0.3L edge opening as well as 0.1L opening space with C-channel section without perforation while reducing the volumes up to 7.28%. Thus, C-channel section with 0.4D of square opening, 0.3L edge opening and 0.1L opening space give a very effective cost reduction.

Diaphragm performance of cold-formed steel floors with steel form-deck and gypsum-based self-leveling underlayment

Cold-formed steel composite floor systems are being widely used in cold-formed steel framing for mid-rise building construction, primarily because of their structural and economic efficiency. This study investigated the diaphragm performance of cold-formed steel composite floors through cyclic load testing and numerical simulation. The composite floors consist of cold-formed steel C-shaped joists and a subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. The test results indicated that the primary failure mode of the specimens was shear failure of the self-drilling screws that connected the steel form-deck and end joists. A finite element model was developed and validated with the test results in terms of hysteretic curves, failure modes, and seismic performance indices such as the ultimate load-bearing capacity and stiffness degradation. Moreover, extensive parametric studies were conducted using the proposed models. The results of analyses showed that the spacing of the screws connecting the steel form-deck to the joists at the floor perimeter and as well as the floor aspect ratio have significant impacts on the diaphragm performance. By contrast, the thickness of the gypsum-based self-leveling underlayment, joist depth, and web perforations exert only a minor influence on the diaphragm performance. Finally, a simplified method was proposed to calculate the central displacement of composite floors based on theoretical analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors in engineering practice.

Prediction of the in-plane mid-span displacement of cold-formed steel floor with steel form-deck and gypsum-based self-leveling underlayment

Cold-formed steel composite floor systems have been widely used in cold-formed steel framing for mid-rise building construction, primarily owing to its structural and economic efficiency. The composite floors consist of cold-formed steel C-shape joists and subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. This paper presents a theoretical method, an experimental investigation, and a simplified model analysis on the in-plane displacement of cold-formed steel composite floors under horizontal loads. Based on the design method of timber floors, the calculation methodology of the mid-span in-plane displacement of cold-formed steel floor with steel form-deck and gypsum-based self-leveling underlayment is proposed. Subsequently, cyclic shear tests of two full-scale floors with and without gypsum-based self-leveling underlayment were executed to investigate the failure mode, load bearing capacity, and in-plane displacement. The test results indicated that the primary failure mode of the specimens was the shear failure of self-drilling screws that connected the steel form-deck and end joists. Furthermore, the in-plane displacement of the test results agreed well with that of the proposed method. Finally, referring to the deformation results of floors under different loading stages, the composite floor analysis model was simplified to a nonlinear diagonal spring model according to the method of equivalent in-plane stiffness, and it was verified through ABAQUS finite element analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors.

Fire experiments of cold-formed steel non-load-bearing composite assemblies lined with different boards

At present, fire-resistant boards have become the most common fire protection productions in cold-formed steel (CFS) structures. In this paper, a fire experimental investigation of 12 CFS composite assemblies is carried out and the effects of different boards and insulation material are discussed. For non-load-bearing CFS composite assemblies lined with only GP board on the fire side, significant flexural deflection of CFS frame towards the furnace and local buckling of steel web is observed, due to the thermal bowing and fall off of fire-side GP board. Compared to the GP board, the low-bulk-density calcium-silicate (CS) board is not prone to fall off during the fire exposure. Replacing the fire-side base-layer GP board with CS board generates an effective fire protection on the cavity and ambient-side of assemblies. Therefore, the buckling of steel frame becomes insignificant and the testing fire resistance time of insulation failure is extended by 9 min to 46 min. The thermal insulation performance of aluminum silicate wool is obviously superior to that of rock wool in fire. For the present assemblies using aluminum silicate wool as external insulation instead of rock wool, the fire resistance time of insulation failure is extended by 18 min. Meanwhile, the composite panel and autoclaved lightweight concrete (ALC) board display excellent thermal insulation performance. For the CFS assemblies using aluminum silicate wool as external insulation, GP and CS boards as fire-side composite panel and ALC board as ambient-side base-layer sheathing, the fire resistance time of insulation failure becomes more than 171 min.

Seismic performance of cold-formed steel bolted moment connections with bolting friction-slip mechanism

Typical cold-formed steel (CFS) moment-resisting connections generally have relatively low ductility and energy dissipation capacity as a result of low local/distortional buckling resistance of thin-walled CFS elements, and therefore, may not be suitable for seismic applications. To address this issue, a comprehensive analytical study is presented on the seismic performance of CFS bolted beam-to-column connections with fiction-slip mechanism aiming to obtain more efficient design solutions suitable for CFS frames in seismic regions. Experimentally validated finite element (FE) models in ABAQUS are used to predict the hysteretic behaviour and failure of a range of CFS connections by taking into account the characteristics of the bolting system as well as nonlinear material properties and geometrical imperfections. The developed models are then used to investigate the effects of CFS beam cross-sectional shape and classification, bolt configuration, and slip resistance on the seismic performance of the connections. It is shown that using bolting friction-slip mechanism can significantly increase (up to 200%) the ductility, energy dissipation capacity and damping coefficient of the connections especially for CFS beams with thinner plates (class 3 and 4). Based on the results, the best design configurations are identified to improve the cyclic response of the CFS connections under strong earthquakes. While conventional bolted moment connections with class 3 and 4 beam cross-sections generally do not satisfy the AISC requirements for intermediate and special moment frames, it is shown that optimum designed connections with bolting friction-slip mechanism can be efficiently used in high seismic regions.

Research on in-plane lateral performance of a new-type composite timber wall panel with cold-formed steel frames

A series of researches on the behaviour of a new structural system, composite timber wall panel with cold-formed steel frames, are investigated under monotonic and reversed cyclic loading. In order to improve the in-plane lateral performance of the composite timber panels, sixteen different optimized composite timber panels were proposed and tested, including increasing the thickness of the sheathings, improvement with steel X-bracings, filling with straw and advance of connection between sheathing and wood framing. The main objective of the investigation is to explore the pervasive mode of failure, determine the quantification of the improvement in lateral performance of these optimized composite timber wall panels and evaluate the benefits of each optimization during the process of failure.

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base (Part 1) Basic Seismic Response of Three-Story Frame

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base (Part 1) Basic Seismic Response of Three-Story Frame

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base

Shake Table Test of Light-gauge Cold-formed Steel Frame with Friction / Viscous Damper and Sliding Base