carl425
....This "girder" is going to be the front edge of a 26" deep grid that will support a section of the upper deck of my layout. The back will be attached to the wall with 3-1/2" #10 screws into the studs. Cross members are every 16". My desire is that it be as small as possible so that it doesn't intrude on the lower deck.
While the photo below shows the 1/8" fascia in place, the front members are 1"x4"s, mainly to allow drilling-out holes large enough to accommodate switches to control track power without weakening their strength. The cross members are 1"x2"s, except at the ends of the two grid sections (necessitated by the steel post holding up the house which keeps the rain and snow off the layout). The wood used to "hide" the post does perform duty as a support.
The spans are about 5.5' and 7', and the grid about 21" deep. The rear member of the grid is 1"x2", screwed to the wall studs.
The grid used here on the upper level is of similar construction and in multiple sections to facilitate handling during installation.
Total span is about 16', with additional support provided by custom-welded brackets lag-bolted to the wall studs. Individual 1"x2" crossmembers of the grid sit atop each bracket.
The deep fascia hides the fluorescent fixtures used to light the lower level, and also controls the view for operators (the lower level is meant to be operated from rolling office-type chairs).
The brackets, four on the 16' section, effectively cut the span requirements to 4'. The top on all areas shown is 5/8 t&g plywood, which also contributes to the overall strength. It was applied in a manner that places the joints not directly over the joints in the grid-type framework. Layout depth here is about 32".
The area across the end of the aisle was built in a similar fashion, but with the end 1"x4" crossmembers attached to the wall studs where they meet the adjacent walls. The rear 1"x2" member of the grid is also screwed to the wall studs and rests on a 2"x4" bolted in place when the room was constructed. (My original plan was to use it to support engineered floor trusses for the front of the 16' section shown previously, and a similar one on the other side of the aisle, but that would have put the total length at almost 20', requiring a much deeper construction and a post at the opposite end.)
The layout here is 38" deep and uses no support backets, so the span of the front 1"x4" is 104". The plywood top, screwed in place, effectively turns the 1"x4" into a 104" long angle member (albeit a lopsided one). This portion of the upper level will support my full weight (under 200lbs.) a fact which I discovered when I found it impossible to paint the back side of the rails, even when standing on a step ladder.
So, to finally answer your question about that 105" span, a 1"x4" front member will definitely be strong enough if the ends of it are fully supported: either by end-crossmembers firmly attached to abutting walls or solidly supported by shelf brackets, posts, or blocking. The cross members (and plywood top, if applied) will add lateral strength.
Wayne
