The standard way of fixing a beam cover to a steel beam is to cut tapered noggins to a precise size from 3” x 2” timber and then hammer them into the steel beam itself so that they finish flush with the top and bottom edge.
Secondly the beam cover should be pre-drilled (using a combination of a 10mm and a 4mm drill bit) in preparation so that it can be screwed to the noggins. Start this by measuring the position of the noggins in the steel beam and then transferring these measurements onto the beam cover. (Rather than mark the beam cover with a pencil these positions could be indicated using a small piece of low tack masking tape).
With the 10mm drill bit drill two holes (approx. 10mm deep) into the beam cover to correspond with the position of each noggin. Next drill the hole completely through using the 4mm drill bit.
Then, with the beam cover lifted tightly into position against the ceiling (probably with a suitable number of strong helpers) screw through the beam cover and into the noggins using 50mm x 4mm screws.
The 10mm holes are then filled using 10mm cross grain pegs (included) with a tiny smear of PVA glue to secure them. The pegs should then be shaved back taking exceptional care not to mark the surface of the beam cover itself. A small pot of touch-up stain is also included to colour the end of the pegs but they will not match the beam cover exactly. See fig 1.
If the beam is to be fireproofed then the fire resistant plasterboard would be fixed to the noggins first and the beam cover fitted over the plasterboard. Remember to factor in the thickness of the plasterboard when calculating the internal measurements of the beam cover. See fig 2.
If a beam cover is just purely for decorative purposes (in other words there is no steel beam to cover) then a simpler method of fixing is appropriate. This involves fixing a pine panel securely and directly to the ceiling, positioning the decorative beam over it and screwing through it into the pine panel. Ceiling spars are also fitted this way. Needless to say that both decorative beams and spars come ready supplied with the correct pine fixing panels. See fig 3.