Repair of Structural Timber Using Steel
In many cases, we might not be able to repair timber with timber alone. For over 200 years, the use of metals for strengthening and mending structural timber has been in use. Engineers and researchers have begun to use steel plates in the retrofitting of historic timber structures as a result. Also, the use of steel and epoxy (to be used very carefully) in timber conservation will avoid the dismantling of a structure. In this way, we will keep the maximum of the original material as many timber members which are in sound condition get damaged in the process. This article outlines ways of repairing damaged timber members using steel components.
List of Contents
1. Different Methods of Timber Conservation Using Steel Plates
1.1 Use Of Flitch Plates
In this case, the decayed portion of the timber is removed and replaced by new timber which is butted to the old. A steel plate is inserted between (See Fig 1) in a central slot and is carried back at least three times its own depth on either side of the junction. The plate is secured by rows of staggered bolts whose heads are countersunk below the timber surface. In the case of a beam end, the steel plate will require stiffening with side angles bearing on the pad stone or wall plate. The advice of a structural engineer should be sought with regards to the number, thickness, length etc., of the steel plates to be used in the repair.
1.2 Use Of Side Plates
In circumstances where the repairs are not apparent, the side plates should be used. Steel plates are bolted horizontally on both sides of the timber beam (see Fig 2). Side plates should not be fastened to uneven surfaces because the voids behind them provide excellent insect breeding grounds.
1.3 Use of Top And Bottom Plates
In this method, metal plates can be placed at the bottom and top of the weakened timber beam and bolted vertically. The steel plates take the position of the top and bottom flanges of an I section, and the timber acts as the web. (See Fig 3)
The bolting of the plate to the beam must be a rigid joint spread over a wide area to reduce the splitting of timber. The bolt holes must be staggered to avoid weakening the timber beam. The bolting of the plate to a joint must be flexible through slotted holes and should not be filled with any glue or grout to allow for seasonal movements. (See Fig 4)
1.4 Repair Of Rotten Ends
When the end of a beam is rotten due to a fungal attack, the method of repair can be illustrated in Fig 5.
2. To Conclude
Degradation of structural timber can occur as a result of decay, over-loading, or faulty design and renovations in the past. Steel can be used to reinforce and connect timber constructions in a cost-effective and long-lasting manner. The majority of these solutions have been around since the 1980s and 1990s. This will not only save money on conservation but will also help to preserve the historical integrity of the building. The steel used to repair the timber beams must be so placed to be concealed when the work is completed. The steel plates must be cleaned and applied with an anti-corrosive coating.
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