Lightweight Steel Framing Research Articles

Analytical Methods to Estimate the Thermal Transmittance of LSF Walls: Calculation Procedures Review and Accuracy Comparison

An accurate evaluation of the thermal transmittance ( U -value) of building envelope elements is fundamental for a reliable assessment of their thermal behaviour and energy efficiency. Simplified analytical methods to estimate the U -value of building elements could be very useful to designers. However, the analytical methods applied to lightweight steel framed (LSF) elements have some specific features, being more challenging to use and to obtain a reliable accurate U -value with. In this work, the main analytical methods available in the literature were identified, the calculation procedures were reviewed and their accuracy was evaluated and compared. With this goal, six analytical methods were used to estimate the U -values of 80 different LSF wall models. The obtained analytical U -values were compared with those provided by numerical simulations, which were used as reference U -values. The numerical simulations were performed using a 2D steady-state finite element method (FEM)-based software, THERM. The reliability of these numerical models was ensured by comparison with benchmark values and by an experimental validation. All the evaluated analytical methods showed a quite good accuracy performance, the worst accuracy being found in cold frame walls. The best and worst precisions were found in the Modified Zone Method and in the Gorgolewski Method 2, respectively. Very surprisingly, the ISO 6946 Combined Method showed a better average precision than other two methods, which were specifically developed for LSF elements.

Composite floor system with cold‐formed trussed beams and prefabricated concrete slab

AbstractSteel‐concrete composite floor systems represent a common solution for buildings, leading to reduced material consumption and improving the structural strength and flexural stiffness. Lightweight steel frame construction systems, based on the combination of thin‐walled cold‐formed steel members (CFS) and panels (e.g. wood, cementitious, gypsum plaster), may also benefit from the composite behaviour in the case of concrete slabs. In this context, full‐scale experimental tests were conducted to evaluate the structural behaviour of a floor system conceived with 0.95 mm thick CFS trussed beams and prefabricated concrete slabs. An innovative solution for shear connectors was designed and tested in order to ensure full interaction between the CFS trussed beam and the concrete slab. The thin‐walled channel (TWC) connector is based on a lipped channel CFS attached to the top chord of the truss by standard self‐drilling screws. Experimental results indicate efficient behaviour of the TWC shear connectors with improved bending capacity of the floor system.

FINITE ELEMENT ANALYSIS OF THE SEISMIC BEHAVIOR OF THE ASSEMBLED LIGHT STEEL FRAME- LIGHT WALL STRUCTURES

In order to meet the needs of the development of low-rise assembly structure in rural areas, a fabricated light-weight steel frame-composite light wall structure is proposed in this paper. The light-weight steel frames are used to bear the vertical loads. The single-row-reinforced recycled concrete wall-boards are used as lateral members to resist most of the horizontal earthquake loads. The wall-board, EPS (Expanded Polystyrene) insulation modules, and fly ash blocks form the thermally insulated wall. Four fabricated lightweight steel frame-composite light wall structures and one light-weight steel frame (FRA) structure were tested under the low cyclic loads. The influence of wall reinforcement spacing and structural form (be it fly ash block or not) on the seismic performance of this new structure was analysed and the damage process of the specimen was simulated using the ABAQUS® software. The results show that the light steel frames and the single-row-reinforced recycled concrete wall-board can work well together. Furthermore, the structure has two clear seismic lines. Due to the use of EPS insulation modules and fly ash blocks, the structure has good anti-seismic and thermal insulation abilities. Reducing the spacing of bars or compositing fly ash blocks can significantly improve the seismic performance of the structure. The finite element method (FEM) calculations agreed well with the experimental results, which validates the proposed model.

Prefabricated hybrid steel wall panels for mid-rise construction in seismic regions

Light steel framing systems are increasingly used in a variety of low-rise buildings, while are gradually penetrating to the mid-rise residential construction. The increased demand for mid-rise light weight steel frames in recent years has resulted in various research activities being undertaken in order to enhance the performance of these systems in compliance with the increased demands of mid-rise construction. This paper investigates the performance of a hybrid wall panel system (HWPS) made of a hot-rolled steel panel and a cold-formed steel panel in seismic regions. The hot-rolled steel panel resists the shear force, while the gravity load is distributed proportionally between the hot-rolled and cold-formed panels. The research employs the results of an experimental program to investigate the performance of the proposed hybrid panel, and a numerical study on the seismic performance of a 4-storey building made by HWPS. A practical design procedure is suggested for the system according to relevant specifications, and the results are compared with those obtained from employing a fully hot-rolled steel frame (moment resisting frame) and then a fully CFS frame system. The structural performance and the construction cost of two systems are then compared.

Presenting a Suitable Quick Construction Pattern Using Prefabricated Components in Critical Conditions

Abstract Every year, many people in the world lose their homes due to natural disasters such as earthquakes, floods and so on. In critical situations, the use of prefabricated parts in the buildings has many technical and economic advantages. Hence, today, this technology is widely used in the industrialized societies. The purpose of this research is to provide an appropriate model for speeding up the process of constructing buildings using prefabricated parts in critical conditions. To do this, Analytic Network Process (ANP) approach has been used to select the best option for speeding up construction projects using prefabricated parts and in critical situations. In this study, the intended criteria are quality, time, cost, and strength. The options that we should compare and the best option among them, according to the criteria mentioned, are Lightweight Steel Frame (LSF) parts, steel parts and concrete parts. In order to find this prioritization, the viewpoints of civil engineers and construction experts have been used. It should also be noted that for the ANP method, the Super Decisions software has been used.

Thermal transmittance of lightweight steel framed walls: Experimental versus numerical and analytical approaches

Given the great influence of the thermal transmittance of the building envelope on the overall thermal performance and energy efficiency of the building, it is essential to accurately determine the U-value of the main building envelope elements. Due to the great heterogeneity of the thermal conductivity of the elements presented in a lightweight steel-framed (LSF) wall, and to the geometric complexity of some steel framed structures, a reliable estimation of the thermal transmittance of LSF elements is even more challenging. Indeed, thermal bridging originated by steel studs must be considered in the assessment of the thermal transmittance of LSF walls. In this work, the thermal transmittance (U-value) of three LSF walls with different configurations will be investigated based on four different approaches: experimental laboratorial measurements based on the Heat Flow Meter (HFM) method; 3D finite element method (FEM) simulations using ANSYS CFX® software; 2D FEM-based simulations using THERM software; analytical estimations based on the ISO 6946 procedure for building components with inhomogeneous layers. Several verification procedures were performed to ensure the reliability of the results. It was found that a secondary wood stud can mitigate the thermal bridging effect of the steel frame and improve the LSF thermal performance, which is more noticeable when there is no thermal insulation. Furthermore, a good agreement was found between the results of the 2D FEM and the analytical ISO 6946 approaches for the LSF wall with only vertical steel studs.

Experimental study on seismic performance of a low-energy consumption composite wall structure of a pre-fabricated lightweight steel frame.

This study developed a low-energy consumption composite wall structure constructed with a pre-fabricated lightweight steel frame that is suitable for houses in villages and towns and evaluated its anti-seismic performance. A low-reversed cyclic-loading test was conducted on four full-scale pre-fabricated structure specimens, including a lightweight, concrete-filled steel tube (CFST) column frame specimen (abbreviated as SFCF), a lightweight CFST column frame composite wall specimen (abbreviated as SFCFW), an H-steel column frame specimen (abbreviated as HSCF) and an H-steel column frame composite wall specimen (abbreviated as HSCFW). The failure characteristics, hysteretic behaviour, strength, rigidity, ductility and energy dissipation capacity of each specimen were compared and analysed. The results demonstrated that the pre-fabricated, double L-shaped beam–column joint with a stiffener rib which was proposed in this study worked reliably and exhibited good anti-seismic performance. The yield, ultimate and frame yield loads of the specimen SFCFW were 1.72, 1.80 and 2.03 times higher than those of specimen SFCF. The yield load, ultimate load and frame yield loads of specimen HSCFW were 1.27, 1.68 and 1.82 times higher than those of specimen HSCF. This indicates that the embedded composite wall contributed significantly to the horizontal bearing capacities of the SFCF and HSCF specimens. The embedded composite wall was divided into multiple strip-shaped composite panels during failure and achieved a stable support for the frame in the later stages of elastoplastic deformation. The horizontal strips of the tongue-and-groove connection between the strip-shaped composite panels produced reciprocating bite displacements, and ultimately improved the structure's energy dissipation capacity significantly.

Dynamic Property of a New Type of Postearthquake Temporary Prefabricated Lightweight Steel Structure

For a new type of postearthquake temporary prefabricated lightweight steel structure proposed in this paper, mainly composed of steel frame, prefabricated hanger slabs, prefabricated hanger columns, reinforced concrete superposed slabs, etc., parameters of dynamic property for the structure, including natural frequency, vibration mode, damping ratio, etc., are determined by the test method. For prefabricated hanger columns and prefabricated hanger slabs, they are all produced with construction waste in factory and assembled on‐site, which can form exterior walls. The united method, based on forced vibration method and ambient random vibration method, can quickly obtain accurate natural frequencies of the full‐scale two‐story experimental model. In this paper, damping oscillatory method is used to obtain damping ratio which can be determined only by the test method. In order to analyse the modal of the experimental model, a finite element model for the full‐scale two‐story experimental model is established, where the weight of prefabricated hanger slabs is assumed to be supported by prefabricated hanger columns, and the stiffness of prefabricated hanger columns is also increased. In addition, the connections between lightweight steel frame and prefabricated hanger columns are regarded as flexible connection. Comparing natural frequencies obtained from the finite element method with that obtained from the test method, magnification factor of stiffness for prefabricated hanger column is determined. In the analysis of modal for the full‐scale two‐story experimental model, the results show that the experimental model satisfies the requirement of design for seismic performance.

Thermal and sound insulation of lightweight steel-framed façade walls

Lightweight steel-framed (LSF) construction has the potential to reach high standards regarding the functional performance of buildings. Despite the benefits of this construction system, the effect of thermal bridges caused by the high thermal conductivity of the steel structure can be a disadvantage. Furthermore, because LSF buildings have low mass and the connections between the outer and the inner sheathing of the walls are usually rigid, provided by steel studs, some acoustic performance drawbacks are also possible. Excessive heat loss or poor sound insulation are related to the external envelope behavior of buildings. Although several studies can be found regarding the influence of the steel frame on the thermal or sound insulation performance of LSF façade walls, the study of this influence from both perspectives at the same time is not widespread. In this work, the influence of the steel frame on both the thermal and sound insulation performance of LSF façade walls is studied. The thermal behavior and sound insulation are assessed using specialized software, namely THERM and INSUL, respectively. With this work it is intended to provide guidelines which can contribute to an effective design of LSF façade walls, considering both functional performances.

Low reversed cyclic loading tests for integrated precast structure of lightweight wall with single-row reinforcement under a lightweight steel frame.

Given the development of precast structures for low-rise residential buildings, this study explores a new structure—namely, an integrated precast structure of lightweight recycled concrete wall with single-row reinforcement—under a lightweight steel frame filled with recycled concrete (integrated precast structure for short). The lightweight steel frame and lightweight wall cooperate to bear the forces. The applied concealed bracing, either a rebar bracing or a steel plate bracing, increases the shear resistance of the wall. The lightweight steel frame is designed to bear the vertical loading, whereas the seismic load in the horizontal direction is jointly borne by the frame and wall. This study presents the results of low reversed cyclic loading tests on nine specimens of integrated precast structures. An analysis is then carried out to investigate the mechanical properties of the specimens; based on these results, a formula for the force-bearing performance of the inclined section is developed. The results show satisfactory performance as an integrated piece; the proposed structure has two seismic lines of defence, with the lightweight wall restraint by the side frame being the first line and the steel frame being the second line. Because the failure of the wall can be categorized as shear failure, the restraint of the lightweight steel frame significantly reduces the potential damage of the wall. As the beams and columns of the steel frame tend to bend against failure, the wall filling helps resist sliding. Therefore, the reinforced joints of the connecting beams and columns show no visible signs of damage, indicating that the connection between the beams and columns is reliable. The narrow spacing of rebars and the setting of concealed bracing contribute to the increase in ductility and energy efficiency of the integrated structure and the evident reduction in the failure process. Furthermore, the recycled concrete increases the seismic resistance of the structure.

Challenges and Technologies for Affordable Housing System

Housing affordability and provision of an adequate shelter are the challenges faced by the government in the developing countries. When the phenomenal rise in population, it resulted in shortage of dwelling units of housing especially for the low and middle income group earner. This paper aims to highlight the challenges in providing affordable houses for all. The literature analysis conducted highlighted the challenges which include high cost of construction materials and technologies, constraints on available land and high land cost, large population at the urban centers and financial constraints. The paper identifies the potential technology as a solution to deliver an affordable housing system. The finding shows that there were affordable technologies which can contribute to low cost housing which are interlocking and compressed earth block, thermal insulating technology, lightweight steel framing and bamboo reinforced wall panel. As a conclusion, the planning authorities and developers should monitor and solve the issues and challenges in providing affordable house. Using the locally available raw materials will help to reduce the construction cost. The affordable house technology may reduce the building construction costs and plays the vital role in increasing the house ownership.

Two new methods for the in-situ measurement of the overall thermal transmittance of cold frame lightweight steel-framed walls

The in-situ measurement of the overall thermal transmittance (Uoverall) of lightweight steel-framed (LSF) walls, including the effect of thermal bridges due to metal structure, is a challenge for designers, engineers and energy audits. The present study introduces two methods for the in-situ measurement of the overall thermal transmittance of cold frame lightweight steel-framed walls. The two methods, Representative Points Method (RPM) and Weighted Area Method (WAM), focus on the fast and accurate in-situ measurement of the Uoverall at the central part of an existing LSF wall. The methods combine the analysis of the examined wall using thermal images with the recording and processing of indoor/outdoor air temperature and heat flux. The requirements and the procedure for the employment of the methods on an existing wall are extensively described. The methods concern cold frame LSF walls, however numerical analysis shows that the methods can also be employed on hybrid frame LSF walls. The methods were experimentally validated on a well-known cold frame LSF wall. The results of the in-situ measurements were in a good agreement with the theoretical values, determined in accordance with the international standard ISO 10211 ensuring the validity of methods.

An integrated energy performance-driven generative design methodology to foster modular lightweight steel framed dwellings in hot climates

This paper presents a study on the application of lightweight steel framed (LSF) construction systems in hot climate. A generative design method created 6010 houses, with random geometry and random roof and exterior wall types with different insulation levels, and EnergyPlus was used to evaluate the energy consumption for air-conditioning of each building. The main goals were to determine which geometric variables correlate with the energy performance, and to provide some guidelines to foster efficient LSF buildings in hot climates. By correlating six geometry-based indexes with the energy consumption for each construction element type group, it was verified that roofs do not show significant correlation, while exterior walls presented weak to moderate positive correlation with the building volume, very weak to weak negative correlation with the relative compactness, no correlation with the shape coefficient, moderate to strong negative correlation with the window-to-floor, window-to-wall, and window-to-exterior surface ratios. The results also show that buildings with larger windows and greater level of insulation have better energy performance. No significant difference of energy performance was found between different LSF construction systems with equivalent thermal resistance.

Literature Review of Shear Performance of Light-weight Steel Framing Wall Panels

In this paper, a comprehensive review of light-weight steel framing wall panels was carried out. The structure and force characteristics of light-weight steel framing wall panels were introduced. The testing and theoretical research results on the shear behaviour of light-weight steel framing wall panels were summarized in the domestic and foreign. And combined with the existing standards in China, the author's views and ideas are put forward to the problems in the research field of this kind of structural system.

Fragility assessment of the connection used in small-scale residential steel house subjected to lateral wind loads

Typhoon disasters risk assessment is needed for small-scale residential houses with less than two stories or less than 500 square meters, since they accounted for about 55% of total buildings in Korea. Therefore, this study was focused on the evaluation of wind fragility for this small-scale lightweight steel frame structure when subjected to lateral wind loads. For this purpose, Monte Carlo Simulation technique was used to derive wind fragility based on random wind load parameters and experimental data of resistance capacity of the connection in this type of structure. Finally, the structural safety of a small-scale lightweight steel house was evaluated, and the fragility was derived. Results show that wind direction parallel to long dimension of structure was the most critical condition. Additionally, the median probability of failure occurs at a very high wind speed. Further research should focus on study with detail structural analysis to narrow down the uncertainty in this study.

Extreme Wind Fragility Assessment for Window System Failure in Lightweight Steel Frame Structure in Korea

In this research, we concentrate on defining the initial step in the framework of probability risk assessment of wind loads by developing wind fragility on small-scale residential facilities in South Korea, i.e., the window system installed in a lightweight steel frame house. The study was to develop a fragility model using random variables according to the wind loads parameters and the resistance capacity of the window system. Design- and material-based experimental results in typical residential facilities in South Korea provided capacity parameters, i.e., resistance capacity of the window system, which allow us to obtain the failure probability of the window system under various limit conditions and consequently be used to evaluate the vulnerability of windows in this small residential steel house. The study has successfully proved that the most vulnerable are the leeward windows, i.e., opposite to the wind direction. Usage of this methodology could lead to a more predictable structure performance and facilitate the introduction of performance-based design guidelines for this component of building. Fragilities such as those presented here also can be convolved with wind hazard curves to develop a risk assessment tool, which can evaluate the potential impact of a natural hazard in public planning and mitigate the consequent economic losses and social disruption.

Cyclic Loading Tests for Cold-Formed Steel Wall Frames with Lightweight Concrete

Lightweight steel framing is a method in housing and construction that have been widely used in lightweight steel construction. In this method, the structure is built by cold formed steel elements. They are cost-effective, light, and easy to assemble. However, the performance of lateral load resisting systems in cold-formed steel structures specially the behavior of cold-formed steel shear walls filled with lightweight structural concrete under seismic loads has not been studied in detail. In this study, an experimental investigation on cold-formed steel frames filled with lightweight structural concrete has been conducted and the results are presented. Six full-scale cold-formed steel frames filled with lightweight structural concrete with two different configurations were studied. The test was performed under a standard cyclic loading regime. This study is focused on the ultimate lateral load capacity and seismic response modification factor of cold-formed steel walls filled with lightweight concrete subjected to cyclic loads. Based on the test observation, detailed discussions on the failure modes of cold-formed steel wall specimens are given. Finally, shear load resistance, seismic response modification factor, failure modes, energy dissipation and stiffness of tested shear walls are proposed and discussed. The results show that although lower height to width ratio leads to a greater shear load resistant, energy dissipation, and stiffness for shear wall filled with lightweight concrete, its seismic modification factor is lower than those shear walls, which have higher height to width ratio.

The Effectiveness of Thermal Insulation in Lightweight Steel-Framed Walls with Respect to Its Position

Lightweight steel-framed (LSF) construction, given its advantages, has the potential to reach high standards in energy and environmental performance of buildings, such as nearly zero-energy buildings (nZEB). When compared with traditional construction, LSF system offers distinct benefits in such fields as sustainability, cost-effectiveness, constructive process, and safety at work. Despite the benefits of this constructive system, the effect of thermal bridges in LSF elements, caused by the high thermal conductivity of the steel structure, can be a disadvantage. The excessive heat losses or gains through these thermal bridges are more relevant in buildings’ exterior envelope, such as facade walls. These building components’ thermal performance is crucial in the buildings’ overall energetic behaviour, with a direct impact on energy consumption and resulting monetary costs during their operational stage. In this work the influence of the thermal insulation position on its effectiveness is evaluated in LSF facade walls. For this purpose, several LSF wall types are assessed, namely cold, warm, and hybrid construction. The influence of thermal bridges instigated by the steel studs in the LSF walls’ overall thermal performance is evaluated as well. The computations are performed using specialized finite element software (THERM).

天井下地を経由しない慣性力伝達経路を持つ天井の開発

When we used a conventional method about the “specific ceiling” because it is necessary to secure a performance established in Ministry of Land, Infrastructure and Transport technical standard, it was necessary to attach many braces. Therefore the conventional method was very difficult to plan the building equipment. The coauthor developed the new earthquake-resistant technique of the “specific ceiling” using a light weight steel frame established in Japanese Industrial Standards. It is the system which we named “Linear brace” and can secure very high rigidity and strength. It was recognized that the earthquake-resistant performance of the ceiling was largely improved.

Numerical thermal analysis of the vertical external partition made as the frame thin-walled steel structure

The article presents numerical thermal analysis of the vertical external partitions made in the lightweight steel framing technology. Steel posts that perform the structural role lead to the formation of linear thermal bridges and have a negative effect on the level of thermal transmittance U . Therefore, optimal solutions are being explored for such technologies. One of the solutions is to use perforated Thermo sections. The effect of perforated Thermo sections on energy loss was verified through comparison to the wall made of solid sections. Furthermore, the calculations analysed the effect of linear thermal bridges that are formed on wall connections in the corner. Computer simulation was employed to emphasize the significant differences in the temperature distribution in both analysed wall structures that resulted from constructional solutions.