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Researchers investigate best practice with steel frames

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An increasing interest in the use of cold section or lightweight steel section structures has highlighted a number of technical problems

In an effort to resolve some of the technical problems associated with the use of cold section or lightweight steel section structures, Hanson Brick formed a working group in conjunction with Oxford Brookes University and Corus Framing. The group comprised specialists in masonry, steel and structural engineering who addressed matters including:

A continuous brickwork outer leaf and the differential movement characteristics of steel frame and masonry cladding

Current building practice is generally to provide support to the brickwork outer leaf at every three storeys, often by incorporating stainless-steel shelf angles. This may lead to significant increases in cost. These increases are most likely to occur when one is considering the additional cost of the steelwork, the horizontal movement-joint material and the special-shaped pistol stretcher bricks required to cloak the angle.

Tests on the TF2000 brick-clad timberframed building at BRE Cardington - where six storeys of continuous masonry were constructed - have been promising. This research investigated the implications of incorporating several storeys of continuous masonry and the effects on detailing. Very little monitoring of differential movement in real buildings has been carried out. With little practical evidence available, an assessment may be made relating to the expansion rate of various types of clay brick.

Movement (namely global expansion) is defined in categories 'low', 'medium', 'high', and 'very high' based on a standard test measurement.

Investigation into reduction in the number of wall ties

The brick outer leaf to light steel framing is typically tied back to the vertical steel studs that provide resistance to wind loading. This is a slightly conservative approach as the masonry has significant resistance to wind load and the cost of wall ties is significant.

The research investigated the possibilities of reducing the number of wall ties and the implications of this for the steel frame. The material saving in terms of wall-tie channels results in a cost saving of around £60 for the gable walls of a typical house. However, the requirement for additional ties around the windows and doors may not result in such a saving to the front and rear elevations. In fact, because it is important to standardise site components, the wall-tie channels to front and rear elevations would also require additional holes and fixings. It was estimated that the typical saving for a small detached house would be approximately £50.

Brickwork infill at roof level between dwellings

Brickwork is often required at roof level at the division between residential properties, due to the change in level. This is a concern with light steel framing because there is a possibility that condensation will occur. The infill detail has often been substituted by an alternative form of cladding. The research addressed the condensation issue and looked at the type of support required for the masonry.

Parapet design

The stability of end parapets, with their associated high wind loads, is often difficult to resolve structurally. The stability of masonry parapets using light steel framing was therefore investigated with consideration given to the use of cantilevered rolled hollow sections. However, this method of construction is rather cumbersome and, as an alternative, further investigation was carried out to ascertain whether it would be possible to cantilever the parapets out horizontally by providing bed-joint reinforcement.

Hanson Brick has produced a series of information sheets that highlight design guidelines

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