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Seismic performance of light-gauge steel framed houses

Final Activity Report Summary - SEISTEELHOUSE (Seismic Performance of Light-Gauge Steel Framed Houses)

Earthquakes are responsible for extensive material damage and loss of life. Typically, when people without first-hand experience face with low probability and high consequence risks, they tend to perceive them as very remote. Therefore, individuals, as well as decision makers, tend to adopt risk-seeking instead of risk-averse approaches when it comes to earthquake. However, in the field of building design, long term planning is essential as the building stock of a geographical region is developed and remains functional for decades.

This research project addressed the problem of seismic performance of light-gauge steel framed houses. Traditional construction techniques for private houses are less and less sustainable in Europe because of their large labour requirements. One alternative solution, with the potential to reduce labour on site, is represented by prefabricated light-gauge steel houses. These types of structures gained significant market share in the United Kingdom and the Nordic countries, and they gradually become more popular in the entire Europe. As the presence of light-gauge steel houses on the markets of earthquake prone countries in Europe was still moderate the objectives o this project were very much 'foresight' objectives.

Given that no specific regulations exist in the current European standards concerning earthquake performance of light-gauge steel houses, the study focussed on several relevant aspects. Some of the research specific objectives were to:
1. better understand the loading side;
2. develop analytical methods for the evaluation of the resistance side of the design;
3. assess if the current detailing practice of light-gauge steel houses satisfied earthquake requirements and propose improvements;
4. participate in the development of design guidelines for the earthquake design of light-gauge steel houses.

Both experimental and analytical methods were used in the study. The main results and conclusions of the research were:
1. a proposal for the evaluation of the earthquake load reduction factor q for the case of light-gauge steel houses. Buildings were designed to withstand very strong earthquakes with damage but without collapse. The aim was to totally avoid damage only in case of 'q times' smaller earthquakes. Existing proposals of q were based on the observation that the earthquake resisting walls in a light-gauge steel house were very ductile. According to the results of this study q was more limited because the houses were rigid and could not fully exploit the advantages of the ductile behaviour.
2. an analytical procedure was developed for the evaluation of the resistance and rigidity of light-gauge steel shear walls sheathed with thin flat steel plates. Flat steel plates were used as sheathing without taking into account their strengthening effect, especially because the evaluation of the resistance and rigidity was possible only through testing. The method that was developed in this project was refined up to the point that it would be easily usable by a designer.
3. a design guide was partly developed within the framework of this project. A summary of parts of the Eurocodes was presented within it and could be used for the earthquake design of light-gauge steel houses. Several new proposals were added to cover this specific field. The design guide contained a proposal for the standardised testing and result interpretation methods for shear walls of steel houses. This proposed testing method was one of the outcomes of this project and was based on the experience gained from an extensive testing program.

The outcomes of the research led to proposals to improve the seismic design of the light-gauge steel houses. On the loading side an improved way to evaluate the q factor was proposed. On the resistance side an analytical proposal was developed for the particular configuration of walls sheathed with flat steel. Results, conclusions, experimental experience and opinions that were developed as part of this project contributed to the shaping of the 'Seismic design guide of light gauge steel framed buildings'.