These pictures are from a real Beam Upgrading Job. (Click on the thumbnail to enlarge).
Barn - Roof Tie Beams
The central two beams were bending and beginning to crack around knot holes. The beams support the purlins above via short struts, but are not connected to the wall plates. This design allows movement of the timber framed walls outwards and of the tiled roof structure downwards.
|To Upgrade the beam it is first supported with scaffolding and propped through to ground. A slot is then cut into the top of the beam (so that cosmetically the repair is easily hidden). This slot can be cut using a chainsaw, chain morticer or a combination auger stitching and routing.
|The slot is cleaned out and the rebar is trial fitted. A number of lengths of bar are used, according to Structural Engineering Calculations.
|The bars are laid one above another using small spacers to maintain the calculated positions. Normally the majority are placed as low down within the beam as possible, with perhaps one or two bars near the top of the beam to prevent twisting and 'hogging'.
|Once the bars are correctly placed an epoxy grout is mixed, which will form a permanent composite structure.
|The epoxy grout must cover the upper bar completely, but if a cosmetic finish is required to the upper surface the slot void above the grout can be filled with a stainable product, or with a timber fillet. The epoxy grout should meet the fire resistance standards for the timber. An Upgrade of this type is likely to increase the overall load capacity of the beam by approximately 100%.
There are several major benefits of using
a Modified Resin Flitch compared with a conventional bolted Flitch;
1. Flitch plates are in a single piece, so often require mechanical handling (because of their weight) and alteration of the building in order to place them (because of their length).
2. Flitch Plates require a very accurate slot to be cut.
3. Flitch plates require a large number of holes to be drilled on Site through steel. These holes also weaken the timber and provide locations for cracking to originate.
4. Flitch Plates are supplied either 'bright', in grease, or in 'mill finish' - in both cases extensive cleaning can be required before use.
5. High Tensile Re-bar or Allthread Bar are low cost, bendy in long lengths, light in weight, so can usually be carried by two men around corners and up stairs, with no mechanical handling or building alterations.
6. Re-bar and Allthread will bend over a length enough to follow any existing beam deflection - a Flitch Plate will not adapt to the deflection.
7. Resin around the bars and spacers bonds all of the existing timber and its defects. There are no holes to weaken the timber, no bolts, nuts and washers to cause long term chemical erosion of the timber.
8. The resin/bar composite moves with the timber as a complete unit - a Flitch Plate form a solid, rigid central spine.
9. A Flitch Plate and its fixings are prone to condensation and interstitial condensation. The resin/bar composite has no air spaces and no external metal fixings to act as 'cold spots'.
10. In awkward installations rebar and Allthread can be placed in shorter lengths and coupled in-situ.