Development of cold-formed steel section portal frames

A series of column, beam, and connection tests for portal frames, which consisted of closed cold-formed steel columns and rafters, were carried out to develop a new portal frame system. First, the compressive and flexural strength of the sections were investigated and second, the structural behavior of the connections including the moment-rotation relation, the yield and ultimate moment capacity of the connections were studied. The connection test specimens consisted of column-base, column-rafter, and rafter-rafter connections. The main factors of the connection test were the thickness and the shape of mild steel connecting elements, which were important for the unique attachment system of wall panels. The connection test results were compared with those achieved by using advanced analysis procedures. The semi-rigid connection concept was considered for the analysis of the portal frame using the secant stiffness of the connections, which were estimated from the moment-rotation curve of the connections tested. Simple formulas for the ultimate shear strength of the screw fastener connections were also proposed and compared with the test results.

Developments in light steel and modular construction in Europe

The use of light steel framing as a method of house construction has increased significantly throughout Europe in recent years.The steel industry has supported an intensive technical development, and housing systems are now available from several European companies.For example, in the UK, the market share for steel has reached approximately 5% of current house and apartment building.This paper describes the general forms of construction that have been adopted, and the levels of performance that are achieved.Recent developments associated with the use of light steel modules and steel frames in medium-rise residential buildings are also presented.

Design of scaffolds of cold-formed steel tubes by second-order analysis to pr-Eurocode 3

A computer procedure for the second-order structural design of scaffolds made of cold-formed tubes is proposed. The semi-analytical stability function is used for the determination of buckling resistance of scaffolding units. The approach is based on the rigorous second-order analysis allowing for the P- and P- effects and the uncertain assumption of effective length is not required. For simulation of imperfection, the present method uses an elastic buckling mode with 0.5 % scaffold height as system imperfection and buckling curve “c” for cold-formed sections in member imperfection. The method has been applied to design of hundreds of steel and bamboo scaffolds successfully and it is observed that properly engineered scaffolding systems with proposed design and acceptable standard of site workmanship are of adequate safety margin. It is expected that a proper design and fabrication procedure will reduce the high scaffold rate of collapse in different parts of the world, as reflected in Taiwanese experience in a considerable reduction of scaffold collapse since its introduction of rigorous design and fabrication procedure 3 years ago.

Development of a new cold-formed steel building system

This paper presents a new innovative cold-formed steel building system that has no conventional frames, purlins or girts. As this building uses a new structural system, the load paths and structural behaviour are unknown.Therefore a series of full scale tests of a 5.4 m x 5.4 m steel building was conducted under simulated wind uplift and racking loads. The test results showed that in its present state, this new building system needs to be modified for its intended purpose. The structural behaviour of the test building was also investigated using finite element analysis. This paper presents the details of the new cold-formed steel building system, full scale tests, finite element analyses, the results, and finally the details of an improved building system.

Effects of elevated temperatures on the mechanical properties of cold-formed steel

This paper describes the development of an expression for the complete stress-strain curve of cold-formed carbon steel at elevated temperatures that covers the full strain range. The stress-strain relationship of cold-formed steel material at elevated temperatures is necessary in the analysis and simulation of cold-formed steel structures under fire. However, most stress-strain curve models are based on hot-rolled steel and very few stress-strain curve models based on cold-formed steel have been reported. Therefore, a stress-strain curve model of cold-formed carbon steel material at elevated temperatures is developed. The cold-formed steel grade G550 and G500 with thicknesses of 1.0 and 1.9mm, respectively, have been investigated. The stress-strain curves at elevated temperatures predicted by the European Code and other researchers were compared with test results. It is shown that the predicted stress-strain curves do not compare well with the cold-formed steel test results. Hence, a full strain range expression up to the ultimate tensile strain for the stress-strain curves of cold-formed carbon steel at elevated temperatures is proposed in this paper.