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ALL ABOUT STEEL

1. Light gauge steel products are known to offer a range of construction related benefits most notably; speed of construction, cost-effectiveness and safety. They are also popular due to the products’ unique lightweight characteristic, which makes them easy and safe to handle both during fabrication and construction.

2. A very wide range of lightweight structural sections are produced by cold forming thin gauge strip material to specific section profiles. These are often termed light gauge or cold formed steel sections. In most cases, galvanized steel strip material is used. The cold rolling process begins with coils of galvanized strip steel that are uncoiled, slit into appropriate widths and then cold roll-formed into the final product form. Profile shapes and section sizes do vary but most sections use lips at free edges and indented profiles to provide stiffness and avoid premature failure by local buckling. Thicknesses for load bearing products typically vary from 0.8 mm to 2 mm.

3. Infill walling is the generic name given to a panel that is built in between the floors of the primary structural frame of a building and provides support for the cladding system. Infill walls are considered to be non-load bearing, but they resist wind loads applied to the façade and also support their own weight and that of the cladding. Light steel walls using C-sections are increasingly used as infill walling within both steel and concrete framed buildings, and have largely replaced masonry or timber alternatives.

An important feature of light steel infill walls is that the size and thickness of the light steel C-sections can be varied depending on the height of the façade wall and the wind loads acting on it. Large windows, parapets and other architectural features are made possible. Infill walls are generally installed on site as individual elements that are pre-cut to length but they can be pre-fabricated as large panels with the cladding already attached. The same components may be used for internal separating walls, but here the main issues are fire resistance and acoustic insulation rather than resistance to loading. A nominal internal pressure is used in the design of internal separating walls.

4. Various forms of construction can be employed to create infill walls that span between floors in steel or concrete buildings. Traditionally, infill walls used masonry or timber, but the modern form of construction uses light steel C-sections that span between the floors and around openings. The C-sections are placed at a regular spacing depending on the external façade materials, and at spacing, which is also compatible with standard plasterboard and sheathing board sizes.

5. In multi-story framed construction, it is now common practice to use light steel infill walls to create a rapid dry envelope to support the external cladding. The same form of construction may be used as separating or compartment walls between different parts of the building. The use of light steel infill walls may be applied to steel or concrete framed construction. Lightweight, speed and ease of installation are important constructional benefits that have led to the rapid increase in use of this form of construction.

The light steel components used in infill walls consists of C sections and U sections of 75 to 200 mm depth that are cold roll-formed from galvanized steel strip of 0.8 to 2.0 mm thickness specified to BS EN 10346[1]. The galvanizing (zinc layer) provides excellent durability. The C-sections are placed at 400 or 600mm spacing and pairs of C-sections may be used next to large openings.

Wall panels can be pre-fabricated as story-high units or, more often, are site assembled from C-sections that are delivered cut-to-length. The second approach is often the only solution in renovation applications where tolerances in the original construction have to be accommodated.

Infill walls consist of a bottom ‘track’ attached to the floor and a top ‘track’ attached to the underside of the floor above. The top track is a U section and allows for sliding of the vertical studs and height adjustment. This movement is essential in concrete frames, where 2 to 3 mm shortening of the concrete structure per floor can occur over time as well as normal structural movements.

The vertical C-sections are designed to span 2.4 to 5m between floors, and to resist wind loads or other loads in bending. The horizontal C-sections above and below the windows transfer loads back to the vertical C-sections. One or two layers of ‘fire-resistant’ plasterboard (conforming to BS EN 520[2], Type F) to the internal face provide for up to 90 minutes fire resistance to the light steel infill wall.

6. Light steel separating walls use similar components to light steel infill walls and are used to provide acoustic separation and fire compartmentation between occupancies or distinct parts of the building. For both of these functions, double layers walls are generally specified in order to achieve the required acoustic attenuation between occupancies.

The structural loading for internal walls is relatively low and is generally considered to correspond to an internal pressure of 0.5 kN/m². The C-sections are generally much thinner than in external walls (typically 0.9mm thick) and gain some benefit of the stiffness of the plasterboard fixed on the outside. Because these walls are non-loading bearing, two layers of plasterboard would generally achieve the required acoustic insulation and 90 minutes fire resistance.

Partitions are not required to have acoustic or fire functions and so are single leaf walls comprising C sections of 55 to 90mm depth, depending on the wall height, with single layers of plasterboard on each side.