BUILDING ELEMENTS WITH LIGHTWEIGHT STEEL STUD STRUCTURAL FRAMES

Murat Aygün, Ph.D, Hülya Kuş, Ph.D.

Division of Building Construction, Department of Architecture

Istanbul Technical University

The earthquake of Kocaeli 1999 has brought about an increase in the employment of steel frames in some upmarket residential projects for high-income property buyers in Turkey.

These frames provide a lightweight structure with elastic behavour for earthquake safety. The structure comprising prefabricated steel panels enable short erection times to be achieved with simple assembly methods in comparison to in-situ reinforced concrete frames by obviating the need for formwork, curing and multiple work trades. Absence of cold bridges and low risk of condensation due to the inherent properties of steel contribute to the overall performance of these frames.

Adversely, fireproofing measures as supplementary layers or treatments are required for providing fire safety to the steel frame. Further restrictions are the limited openings and floor spans as well as the number of storeys that can be obtained, imposing constraints on architectural design and building function. Precautions are also required against woodpests and woodrot, mostly applied as chemical treatments.

The lightweight steel frame consists of various distinct components. Studs and braces with slender sections are coupled with sheathing boards such as OSB, plywood, fibre cement, on the outside as vertical structural members for walls. Studs are connected to rails at the top and bottom. Joists with the same sections provide support to floors in the horizontal plane. The bottom rail rests on the sole plate acting as the interface between the steel structure and the reinforced concrete foundations.

There are three main types of junctions between structural components of the frame: Single-rail, double-rail and baloon frame. The components are connected to each other by mechanical means, i.e. nails, screws, bolts, gang nails and gusset plates.

Thermal insulation is located at one or more of the three positions relative to the stud in the wall section, i.e. outside, inbetween or inside the studs. In the case of the insulation inbetween the studs, the space should be filled tightly with no gaps remaining, hence flexible or semi-rigid materials are selected, e.g. rockwool, glasswool, as opposed to the external and internal locations where rigid materials are preferred, e.g. polymers, glass foam, to resist compression by the subsequent layers. A breather membrane is laid outside the sheathing boards, for allowing vapour to escape outside while preventing penetration of moisture to inside.