Section Studs Research Articles

Fire performance of superabsorbent polymers protected full-scale cold-formed steel wall lined with plasterboards

Superabsorbent polymers (SAPs) have shown promise in enhancing the fire resistance of steel structures because of their exceptional absorbency and water retention capabilities. This study innovatively applies SAP insulation to cold-formed steel (CFS) walls with gypsum (GP) boards to improve fire performance. One full-scale CFS wall underwent axial compression testing at ambient temperature, and four full-scale fire experiments were conducted on CFS walls with load ratios of 0.27 and 0.85. All specimens were sheathed with double layers of GP boards, and rock wool served as the cavity insulation, with SAP insulation material applied to the cavity of wall studs. Additionally, a novel finite element model was developed to simulate the fluid-heat interaction within a furnace-CFS wall. The simulation results showed that SAP insulation material significantly changes the fire-induced failure mode in wall studs at a 0.27 load ratio, transitioning from hot flange (HF) local buckling to local buckling of the whole stud section. The inclusion of SAP insulation material absorbs heat, effectively delaying the rise in wall stud temperature. This property significantly enhances the structural performance of CFS walls during fire exposure. With SAP insulation material, the fire resistance time of the CFS walls increased by over 66 min compared to non-SAP insulation material counterparts. Moreover, increasing the stud web depth and reducing the HF width-to-thickness ratio can enhance the fire performance of CFS walls. The HF critical failure temperature of specimen S2 with an HF width-to-thickness ratio of 80 was 783 °C, 150 °C higher than that of specimen P2 with an HF width-to-thickness ratio of 67. Additionally, the adverse effect of screws on the fire performance of the CFS wall was localized. After 120 min of fire exposure, the temperature on the ambient side, which was severely influenced by the screws, was 360 to 370 °C.

Fire performance of gypsum-sheathed cold-formed steel walls with rectangular section studs

This study conducted axial compression experiment of one full-scale CFS wall at ambient temperature and four full-scale fire experiments of CFS walls with two initial load ratios of 0.27 and 0.85. Specimens were sheathed with double layers of gypsum plasterboard, rock wool was the cavity insulation and the wall studs had rectangular cross sections. A finite element model was used to optimize the arrangement of rock wool cavity insulation for the CFS walls. The results showed that the failure mode changed from local buckling of the hot flange under a load ratio of 0.27 to local buckling of the whole stud section under a load ratio of 0.85. The fire resistance time of the specimen without rock wool insulation in the stud cavity was 7 min longer than that of the specimen with rock wool insulation. This was attributed to the thermal radiation effect of the stud cavities, which delayed the increase in hot flange temperature and improved the fire resistance time of the CFS walls. Thus, for CFS walls with rock wool-insulated cavities, the stud cavity configuration was more reasonable without than with rock wool insulation. When the axial thermal expansion load was considered, the load on the wall studs increased by a maximum of 43.3 kN per stud. In addition, for CFS walls with low load ratios of 0.27, the wall studs near the face-layer board joints tended to buckle first.

Design of Short Wall Timber Formworks Using New Formulas

The construction of reinforced concrete requires formwork, whether from timber, steel, or any other material. Generally, formwork accounts for 20% to 25% of a project's cost. This research aims to come up with new formulas that can guide the engineer in designing timber formwork in a safe, easy, and economical manner. By using the statistical analysis program in this study, we calculated the spacings of studs, wales, and ties in a faster manner than the traditional method by analysing the results of bending, shear, deflection, crushing, etc. The results of the study involve the effects of placement rate, concrete temperature, sheathing thickness, pressure values, and stud and wale sections on the spacing of components of the formwork. There are seven equations built to calculate the spacings of individual components.

Push-out test of headed stud connectors subjected to freeze-thaw cycles and artificial corrosion

To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel–concrete composite structures under the influence of freeze–thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.

Behavior of CFS shear walls infilled with lightweight ceramsite concrete under cyclic loading

To meet the lateral resistance requirement for cold-formed steel (CFS) shear walls in multistory buildings, a novel CFS shear wall filled with lightweight ceramsite concrete is proposed in this paper. Three full-scale specimens were conducted under cyclic loading to evaluate their failure mode, bearing capacity, lateral stiffness, ductility, and energy dissipation. The experimental results showed that the main failures of the walls were bond-slip cracks between the CFS framing and fillers, cracking of sheathings, and compression failure at the corners of the fillers. The bearing capacity and energy dissipation of the infilled walls were superior to that of unfilled wall. Increasing the stud section area could improve the lateral behavior of the wall. Finite element (FE) models were introduced to simulate the shear performance of the test specimens. The numerical simulation results were in good agreement with the experimental results; hence, the FE models for simulating CFS shear walls were validated. Subsequently, a parametric study was performed by varying the parameters, including the ceramsite concrete strength, wall thickness, aspect ratio, steel strength, and sheathing material. Furthermore, a calculation method was proposed to determine the bearing capacity of the CFS shear walls. The calculated results agree well with the experimental results. A comparison between the proposed CFS shear walls and existing CFS shear walls showed that the lateral performance of the proposed walls was higher than that of CFS shear walls.

Experimental and numerical investigations of LSF walls subject to distortional buckling

Light gauge Steel Frame (LSF) wall systems are increasingly replacing the conventional concrete and heavy steel structural systems due to the many advantages they offer. Web stiffeners are often included in the wall stud sections to improve their local buckling capacities and thus most of these studs are prone to buckle distortionally. Unlike for other buckling modes, the composite behaviour of wall studs sheathed with gypsum plasterboard is complicated for distortional buckling. This paper presents the details and results of experimental and numerical investigations into the structural behaviour of LSF walls subject to distortional buckling. Eight LSF wall assemblies were tested with varying parameters such as stud geometry, plasterboard thickness, number of plasterboard layers, sheathing arrangements and screw spacing. A high-fidelity finite element model capable of simulating the behaviour of LSF walls was developed and validated using the experimental results. The developed numerical models included geometric and material nonlinearities, initial geometric imperfections, contact interactions between stud, track and plasterboard sheathing, and most importantly the non-linear in-plane and pull-through screw connection behaviour. The validated numerical model was also used to further investigate the distortional buckling behaviour of LSF walls and the effects of some of the key modelling parameters. The analyses showed that stud-to-sheathing screw connections have a significant effect on the load-bearing capacity of LSF walls subject to distortional buckling, which can be enhanced by reducing the screw spacing and increasing the sheathing thickness and the number of sheathing layers.

Enhancing static resistance of steel stud wall systems for blast design using new section geometries

Steel Stud Wall Systems (SSWSs) have been attractive structural alternative due to its merits. This research is mainly focused on enhancing static resistance of SSWSs to resist moderate blast events. Resistance function is considered an important item of data in calculating dynamic response of a system using Single Degree of Freedom model. Resistance function can be obtained by quasi-static experimental loading. Or alternatively, using FE modelling for finding the non-linear static response of a system. This research shows how combinations of the various in-lack parameters can be arranged to maximize efficiency of the system for performance as blast proof structures. This is performed by analyzing different section geometries from traditional ones with aids of FE software (ABAQUS 16). The solution is under quasi-static loading and the obtained toughness is used to hold comparison between the new geometries and the traditional stud section. Two validation models followed by a comprehensive parametric study are performed to investigate back-to-back cold formed sections efficiency in comparison to traditional system from blast point of view. For this purpose, two new introduced factors Material Utilization Factor (M.U.F) and (EF) are used to relate the various design variables and outputs to the amount of material used in the sections. The paper shows how using the new sections and changing parameters may maximize the system efficiency to raise toughness and elastic load limit up to 3.94 times and 3.78 respectively from the traditional system. Finally, important conclusions are withdrawn about the efficiency of the new sections. Withdrawn conclusions are emphasizing that using back-to-back cold formed sections with a certain arrangement is much beneficious than traditional used sections.

Numerical study of LSF walls made of cold-formed steel hollow section studs in fire

Cold-formed steel square and rectangular hollow section (SHS/RHS) studs are often used to replace the conventional lipped channel section studs in light gauge steel frame (LSF) wall systems to meet the required high load demand. To ensure adequate structural fire resistance of SHS/RHS stud walls, four full-scale fire tests were previously completed under standard fire conditions. However, the full-scale fire tests are expensive and time-consuming, while the complex fire performance cannot be adequately explained through test observations and results alone. Hence, a numerical study was undertaken by developing simplified and sheathed stud finite element (FE) models of tested walls. This paper provides the details of the developed models of LSF walls made of SHS/RHS studs at both ambient and elevated temperatures and a comparison with experimental results. The validated models were used to highlight the advantage of using SHS/RHS studs in cavity insulated stud walls and further understand the factors that may affect the fire resistance of LSF walls, such as steel grade and stud depth. In addition to the simplified stud model, advanced modelling techniques were used to explore the effects of sheathing and localised plasterboard fall-off on the wall behaviour in fire. Overall, this paper presents a numerical study of SHS/RHS stud walls and the simplified stud model developed in this paper can be used to predict the fire performance of other SHS/RHS stud walls with similar wall configurations.

Influencing factors analysis on shear capacity of cold-formed steel light frame shear walls

The Cold-formed steel (CFS) light frame shear wall is the most important lateral force-resisting element in CFS building systems. Extensive researches have been completed on the shear performance of CFS shear walls with various kinds of panels. It’s found that the shear capacity of the CFS shear walls is affected by many aspects. Therefore, this paper consolidates a large number of test results world-wide and establishes a database on the lateral strength of CFS light frame shear walls. The influencing factors of the shear wall’s shear capacity are analyzed systematically, which includes material properties, stud sections and spacing, framing thickness, sheathing thickness, aspect ratios, openings, screw types and spacing, loading methods, etc. The logic behind these factors is found out through the analyses of the test data and design suggestions are made accordingly.

SHOULD CALIFORNIA'S PUBLIC POLICY ON JUDICIAL NON-JURISDICTION OVER GAMBLING DEBTS BE REVISITED? BREAKING DOWN THE KELLY AND POSTLE DECISIONS

SHOULD CALIFORNIA'S PUBLIC POLICY ON JUDICIAL NON-JURISDICTION OVER GAMBLING DEBTS BE REVISITED? BREAKING DOWN THE <i>KELLY</i> AND <i>POSTLE</i> DECISIONS

Fire tests of cold-formed steel walls made of hollow section studs

Light gauge steel frame (LSF) walls as primary load-bearing components have been increasingly used in the construction of cold-formed steel (CFS) buildings. Their fire safety has thus become an important consideration for designers. Currently, LSF walls made of lipped channel section (LCS) studs are commonly used in low-rise buildings, but with the expansion of CFS applications to mid-rise buildings, cold-formed steel square and rectangular hollow section (SHS/RHS) studs are being used to meet the higher load capacity demands. However, the fire resistance of LSF walls made of SHS/RHS studs has not been investigated yet, so their fire resistance levels (FRLs) are unknown, restricting their use in mid-rise buildings. Four full-scale load-bearing standard fire tests were therefore conducted to investigate the performance of cold-formed steel SHS/RHS stud walls exposed to fire. The test results showed that CFS SHS/RHS stud walls achieved a higher FRL due to the superior elevated temperature mechanical properties of CFS SHS/RHS, while the temperature development exhibited good similarity with uninsulated LCS stud walls of the same wall configuration. However, a different thermal behaviour was observed when SHS/RHS studs were used in cavity insulated walls, as the hollow cavity reduced the temperature difference between the stud hot and cold flanges. This eliminated the fire resistance reduction caused by thermal bowing deformations and provided an improved fire performance than cavity insulated LCS stud walls. This paper presents the details of the fire tests and the results.

Improved fire resistance of cold-formed steel walls by using super absorbent polymers

Fire resistance is an important concern in the design of steel structures. The fire protection mechanism of traditional methods is to cover the external surface of steel members and delay fire-induced heat transfer. This paper develops an innovative solution to improve the structural fire resistance using super absorbent polymers (SAPs) with an experimental study to successfully demonstrate the effect of SAPs on cold-formed steel (CFS) walls. The SAP insulation material was filled in the cavity of CFS walls to provide thermal insulation and absorb heat. Six 1.1 m × 1.1 m CFS walls with SAP insulation materials inside were prepared and subjected to the ISO 834 time-temperature curve. During the experiments, a large amount of water vapor was observed from the SAP insulation materials, effectively removing heat and providing fire protection. The effects of various combinations of SAP insulation materials and steel studs and different configurations of CFS walls on the fire resistance are discussed. The results show that increasing the stud web depth, using autoclaved lightweight concrete (ALC) boards and SAP insulation materials can substantially improve the fire resistance of CFS walls. An optimal configuration of CFS walls with ALC boards as the face-layer sheathing and SAP insulation materials in the cavity of the rectangle hollow section studs was proposed and showed high heat consumption and low damage during fire exposure, which was supported by the maximum temperature of the steel studs being less than 150 °C after exposure to ISO 834 fire for 2 h. Finally, a possible application scenario for the SAP material was proposed for the fire protection of steel structures.

Thermal behavior of external-insulated cold-formed steel non-load-bearing walls exposed to different fire conditions

An external-insulated cold-formed steel (CFS) wall is a potential configuration that overcomes the disadvantage of cavity insulation in the fire performance of such walls and can meet the sound and thermal insulation requirements for building structures by increasing the thickness of insulation material. This paper conducted eight mid-scale non-load-bearing fire experiments on external-insulated wall specimens. Four different fire conditions were tested, including ISO 834 fire, external fire, hydrocarbon fire and a typical realistic design fire. A quasi-steady heat transfer state was identified at the final stage of external fire exposure. The effect of substituting the cavity insulation with external insulation on the fire performance is discussed by comparison with the previous fire experiments on cavity-insulated CFS walls. The results show that external insulation is a more reasonable configuration than cavity insulation for improving the fire resistance of CFS walls. In addition, two types of stud buckling, which include the local buckling of the whole stud section and local buckling of stud hot flange and adjacent web, were identified for non-load-bearing walls in fire, and the corresponding cause and conditions were described. In addition, to achieve high efficiency in the thermal performance modeling of CFS walls in fire, a quick and simplified calculation method was developed to get the temperature profile of steel frame based on a one-dimensional finite difference method. Moreover, an unexposed surface temperature of 900 °C was recommended as the criterion to predict the falling-off of the fire-side face-layer gypsum plasterboards of CFS walls in the heat transfer modeling.

Full-scale fire resistance tests of steel and plasterboard sheathed web-stiffened stud walls

Light gauge steel-framed (LSF) walls, commonly made with lipped channel studs and gypsum plasterboard sheathing, are increasingly being used in low to mid-rise buildings. Improvements have been made with respect to fire, wind/seismic and energy performance of LSF walls with the use of improved stud sections, wall configurations, different sheathing members, and insulation materials. Although the provision of sheet steel as sheathing has been found to improve the in-plane shear capacity of LSF walls, its effects on the fire performance of load bearing walls remain unknown. Three full-scale ISO 834 standard fire tests were conducted in this study to investigate the fire performance of axially loaded gypsum plasterboard and steel sheathed LSF walls made with web-stiffened studs. The results revealed that compared to the commonly used lipped channel stud, the web-stiffened stud is capable of withstanding a 57% greater axial compression load, yet yield the same fire resistance level (FRL), when sheathed only with two layers of gypsum plasterboard. Under the selected load ratio, the addition of steel sheathing caused only marginal improvements in the stud temperature development, resulting in minor improvements to the FRL of load bearing walls. However, the axial load bearing capacity improvement caused by the inclusion of steel sheathing allowed the web-stiffened stud to withstand a 10% greater axial compression load compared to the plasterboard only wall.

Predicting the fire performance of LSF walls made of web stiffened channel sections

Fire performance of plasterboard lined Light-gauge Steel Framed (LSF) walls has been investigated using numerical and experimental studies in the past. However, past research has been limited to lipped channel sections (LCS) and welded hollow flange channel (HFC) sections. This paper investigates the fire performance of LSF walls made of a new web-Stiffened Channel Section (SCS) stud using numerical models, validated using available fire test results. The SCS succeeds in eliminating both local and distortional buckling when used as 3 m long LSF wall studs at ambient temperature. Ambient temperature compression capacity evaluations showed that the performance of the SCS is equivalent to the welded HFC, but is superior to the LCS. Fire performance of load bearing and non-load bearing LSF walls made with each of the three stud sections was assessed for three common wall configurations using thermal and structural finite element analyses. Extended FRL versus Load Ratio curves were developed using a combination of steady state and transient state coupled temperature-displacement analyses. The results showed that the effect of stud geometry on the fire performance of LSF wall configurations is minimal. Under the same load ratio, all three stud sections perform similarly in each of the wall configurations. Considering the ambient and fire performance results, the reduced cost and also the potential double connectivity to plasterboard via its lip elements, the SCS is recommended for use in LSF walls. This paper has also highlighted the susceptibility of non-load bearing LSF walls to fail in fire under structural inadequacy.

Fire design of LSF wall systems made of web-stiffened lipped channel studs

Cold-formed steel stud sections are commonly used as compression members in fire rated load-bearing light gauge steel frame (LSF) wall systems. Although conventional lipped channel section (LCS) studs are commonly used in LSF wall systems, there is a growing interest in developing innovative stud sections to increase the load carrying capacities when used in fire rated LSF wall systems. One such section is the web-stiffened section (WSS), which has increased load carrying capacities as well as enhanced acoustic properties. However, the applicability of the existing structural fire design rules has not been investigated for the WSS stud sections while the advantages of using such sections have not been demonstrated. Therefore, the structural behaviour of WSS stud sections was investigated under ambient and fire conditions using finite element analyses and their capacities were compared with those of conventional LCS studs. Three different LSF wall configurations and three stud thicknesses were considered for both stud sections. The applicability of existing structural fire design rules for LCS and WSS studs used in fire rated LSF wall systems was then investigated based on finite element analyses, effective width method and direct strength method. The results show that WSS studs have much higher load carrying capacities than LCS studs under ambient and fire conditions and that direct strength method based design rules are simpler to use than the effective width based design rules for the structural fire design of LSF wall systems made of both LCS and WSS studs. This paper presents the details of this investigation and the results.

Seismic performance of high-strength lightweight foamed concrete-filled cold-formed steel shear walls

To improve the seismic behavior of cold-formed steel (CFS) shear walls, cold-formed steel high-strength lightweight foamed concrete (CSHLFC) shear walls with straw boards are proposed. This study conducted tests of six full-scale shear wall specimens to investigate the failure mode, load-bearing capacity, ductility, stiffness characteristic and energy dissipation capacity. The test parameters included HLFC density grade, stud section area, wall thickness and vertical load. Test results indicated that HLFC has greater effect on seismic performance and failure mode of the shear walls. The failure modes were cracking and crushing of HLFC, cracking of straw boards, local buckling of studs, and relative slippage between HLFC and studs, which made the wall exhibit good ductility and energy dissipation capacity. Compressive bearing capacity of HLFC and restrictive effect of HLFC on steel frame increased the shear strength and stiffness. The most effective way of improving seismic performance was to increase wall thickness, followed by increasing HLFC density grade and stud section area, but increasing vertical load had an adverse effect on seismic performance. Based on experimental results and mechanism analysis of shear walls, a simplified design formula for predicting the shear strength was proposed base on strut-and-tie model. The calculated results obtained by the proposed formula showed better agreement with the experiment results compared with the results from ACI 318-14, EC8 and CNS 383-16 standards.

Seismic behavior of cold-formed steel high-strength foamed concrete shear walls with straw boards

To satisfy the requirements of thermal insulation property and load-bearing capacity of cold-formed steel (CFS) shear walls in mid-high buildings, a new type of CFS shear wall referred to as cold-formed steel high-strength foamed concrete (CSHFC) shear wall with straw boards on both sides is proposed in this study. Straw board is an one-way slab consisting of horizontally distributed natural straw fibers and has excellent thermal property. High-strength foamed concrete (HFC) is a new type of lightweight foamed concrete with high compressive strength. Seven full-scale specimens with different configurations were conducted under reversed cyclic loading to assess the failure mode, load-bearing capacity, ductility, lateral stiffness and energy dissipation. The test parameters include HFC strength grade, aspect ratio, stud section type and opening of the specimens. Compressive bearing capacity of the HFC and restrictive effect of the HFC on the studs and screw connections significantly improved the wall's shear strength and lateral stiffness. Together with bond-slip behavior between the HFC and the studs, HFC cracking and straw boards cracking, these makes the walls exhibit better ductility and energy absorption. The failure mode typically includes local buckling of the studs, inclined cracking of the HFC and straw boards and relative slippage between the stud webs and the HFC. Enhancing HFC strength grade and increasing studs' section area could effectively improve the seismic behavior, whereas increasing walls' length could improve shear capacity and lateral stiffness. Comparison of the results between CSHFC shear walls and traditional CFS shear walls shown that the seismic performance of the CSHFC shear walls was much higher than those of traditional CFS shear walls.

Residual capacity of fire exposed light gauge steel frame walls

Light gauge Steel Frame (LSF) walls made of cold-formed steel stud and track sections and lined with gypsum plasterboards are commonly used in buildings as load bearing members. During fire events, gypsum plasterboards act as a thermal barrier and delay the temperature rise in the steel studs. Fire usually occurs on one side of LSF walls during which a non-uniform temperature distribution is developed across the steel stud cross-section. This results in thermal bowing deformations and non-uniform distribution of strength and stiffness within the studs. In most situations, fires are extinguished well before excessive or permanent plastic deformations of studs and/or stud failures occur. Hence the LSF wall frames could be re-used provided their residual capacities after fire events are adequate. This paper presents a study aimed at determining the residual compression capacities of LSF wall studs following fire exposure. A full scale standard fire test of LSF wall panel was conducted first, followed by a series of short column tests of lipped channel studs obtained from the tested LSF wall panel. Finite element analyses of the tested studs were undertaken using the measured post-fire mechanical properties of cold-formed steels. The residual compression capacities of these fire exposed short columns were also predicted using the ambient temperature cold-formed steel design rules. A numerical parametric study was then undertaken for 3m long studs in LSF wall panels with varying wall configurations following an exposure to standard fire. This paper presents the details of these experimental and numerical studies of fire exposed LSF wall panels and the results. It demonstrates the potential of re-using LSF wall frames following fire exposures and provides appropriate limits for fire exposure time and stud hot flange temperature for three commonly used LSF wall configurations.

A Review of Parameters Influencing the Fire Performance of Light Gauge Steel Frame Walls

Load-bearing Light Gauge Steel Frame (LSF) walls are made of cold-formed steel frames and lined with fire-resistant gypsum plasterboards, and include cavity insulation based on energy performance requirements. Despite the importance of their fire performance, the current fire design methods rely mostly on a prescriptive approach, which relies on fire resistance ratings (FRR) provided by the wall manufacturers due to the lack of knowledge of the various parameters affecting the fire performance of LSF walls. This paper identifies the parameters affecting the fire performance of LSF walls, and presents a detailed review of the fire performance of LSF walls as a function of these parameters, based on recent research studies. It discusses the effects of elevated temperature thermal properties, plasterboard fall-off, cavity insulation, wall configuration, and stud section shapes on the thermal performance of LSF walls, and presents a detailed study of the temperature distribution patterns across the stud cross-sections. Negative effects of plasterboard joints are also demonstrated using fire test results. Elevated temperature mechanical properties of steel, time–temperature profiles of walls, stud section shapes and their sizes were found to be affecting the structural performance of LSF walls in fire, and their effects are discussed. The importance of using accurate elevated temperature mechanical properties in determining the FRR of LSF walls is also demonstrated. A good understanding of the identified parameters on the fire performance of LSF walls can lead to the use of a performance-based fire design method, and development of LSF walls with enhanced fire performance.