Local and distortional buckling of perforated steel wall studs

The local and distortional buckling behaviour of flange and web-stiffened compression members was investigated. In particular, the behaviour of web-perforated sections was investigated both numerically and experimentally. Perforation reduces the perpendicular flexural stiffness of the web and thus particularly reduces the distortional buckling strength of the section. The main task of the research was to develop a design method for estimating the compression capacity of a perforated steel wall-stud under centric loading. The influence of the gypsum sheathing on the distortional buckling strength is also taken into account. It was shown that the method given in Eurocode 3 is quite rough and sometimes gives inaccurate results for estimating the elastic distortional buckling stress of both C-sections and intermediate stiffened plates. In the case of C-sections, the method developed by Lau and Hancock and the method developed by Schafer and Peköz correlate better with the results defined numerically. The Finite Strip Method (FSM) and Generalized Beam Theory (GBT) provided particularly good tools with which to analyze local and distortional buckling modes. It was also shown that interaction between different distortional buckling modes should be taken into account when analysing sections having both web and flange stiffeners. Distortional buckling stress of the web-perforated C-section with or without web stiffeners can be determined by replacing the perforated web part with an equivalent plain plate corresponding to the same perpendicular bending stiffness. Distortional buckling stress may be determined by some numerical method such as FSM or GBT. For the web-perforated C-section, an analytical method for the distortional buckling is also presented. Gypsum sheathing connections give rotational restraint to the wall–stud, thus improving distortional buckling strength. Some practical guidelines are given for calculating the rotational restraint. Buckling analysis showed that relatively small restraint may double the distortional buckling stress of the web-perforated section. Buckling analysis and experimental research showed that screw pitch also has a considerable effect on the distortional buckling stress. Using restraint values given by the connection tests, the predicted values for the gypsum board braced columns are in good accordance with the test results. In practical design, utilizing the gypsum board in the determination of the distortional buckling stress requires that the sheathing retains its capacity and stiffness for the expected service life of the structure. Furthermore, the connection characteristics should be carefully examined. Based on the results of the experimental and theoretical studies, design proposals were made for the design of compressed web-perforated steel wall studs. Some practical guidelines were also given for taking into account the gypsum sheathing. These design proposals are also valid for solid steel wall studs, especially for slender sections, which are sensitive to distortional buckling.reviewe

Optimum Design of Cold-formed Steel Z-shape Purlins Using a Genetic Algorithm

In this paper, a genetic algorithm is applied to optimize the dimensions of cold-formed Z-shape purlins continuous over two spans under gravity load. The optimization criterion is to maximize the load resistance per cross-section and the design variables are chosen from the discrete values based on the manufacturing requirements. Purlins are designed in accordance with Eurocode 3, Part 1.3. In addition, the modified Eurocode 3 method, in which the elastic local buckling stress and distortional buckling stress calculated using Finite Strip Method (FSM) are integrated into the design process, is used to determine the effective section properties. The results are compared with those obtained using Eurocode 3 method

Study on Light-gauge Steel Roof Trusses with Rosette Connections

This paper describes the Rosette-joining system and its possibilities in roof-truss structures in the span range of 8 to 12 meters (26 to 39 ft). The test programme that was carried out to verify the behaviour of the Rosette-joint and the thin-walled sections is described. The test results are given and analysed where they currently exist. The results are compared with values calculated according to the 1996 U.S. (AISI) [3] code supported by a distortional buckling analysis according to the Australian / New Zealand Standard (AS) [4] and FE Analysis results

Measured and simulated energy performance of OLK NZEB with heat pump and energy piles in Hämeenlinna

In this work, measured energy use of the building space heating, ventilation supply air heating, appliances and lighting is compared against simulated energy use modelled in IDA ICE. As built energy need and detailed measured input data is applied in building model calibration procedure. Calibrated building model energy performance is studied in both measured and test reference year climate conditions. Previously modelled as built plant automation and implemented control logics are compared against measured. Geothermal plant in this study consists of heat pump, solar collectors, boreholes and energy piles. Heat pump SCOP estimated by post processing according to heat pump manufacturer's performance map is compared against measured SCOP on the monthly basis. Opinion on actual plant operation is given and energy performance improvement potential is quantified. Important parameters for successful building model calibration are presented. Building compliance with Finland NZEB requirements are assessed. The results show good match with measured energy use after the model calibration.Peer reviewe

Heat Recovery from Exhaust Air as a Thermal Storage Energy Source for Geothermal Energy Piles

In pursuit of EU directive 2010/31/EU energy performance targets towards design of nearly zero-energy buildings consideration of renewable energy sources in the design is expected. Application of ground-source heat pump (GSHP) and energy piles in cold climate conditions for utilization of renewable geothermal energy may results in GSHP plant high seasonal coefficient of performance (SCOP) as long as source of thermal storage is considered in plant design. This numerical study investigates exhaust air of air handling unit (AHU) as a source of thermal storage for geothermal plant with energy piles, that can be utilized via air-to-liquid heat exchanger installed at the exhaust side of AHU after the rotor heat exchanger and exhaust fan. Modelling is performed in dynamic whole year simulation environment Equa IDA-ICE, where reference commercial hall-type building model is coupled with detailed custom heat pump plant. Exhaust air thermal storage capacity in multiple energy piles field configurations with varying soil conditions, distance between piles and pile lengths is analyzed. Results revealed that exhaust air thermal storage appears to be highly cost effective solution. Graphical figures presented in this paper can be further applied for preliminary exhaust air thermal storage capacity assessment in buildings with energy piles.Peer reviewe