Premium? No need. I made my L girders out of furring strip 1x4 and 1x2. Sold in strapped together bundles to hide how bad some were warped. The slightly warped ones straigthened out really well once assembled into the L shape. The really bad ones were turned into kindling for the fire pit. Honestly didn’t have many I couldn’t use. I even had to join some together to make longer than the 8’ legths they come in. Following Westcott’s instructions, I’m able to climb my 165 pounds up on my layout anywhere, including the middle of span of these joined together girders with legs spaced 10’ apart. It’s solid.
As construction progresses, the longest span of 1x3 L girder should be about 66 inches. One track spanning a river with a bridge. I expect it to work fine.
Why only 66", when every one here seem to think that a 3" web L-girder can have a span that easily exceeds 8ft.? I may, for safe keeping, still put a leg at the half-way point in the span anyway. I am, however trying to maximize the space for storage under the layout, as well as an area to put my work bench, which will also go under the layout.
On another note, I correct myself AGAIN; I do not have a 4", but a 3" web L-girder. I looked in my storage unit yesterday to inventory the salvagable benchwork I have and the existing L-girders have a 3" web
A good rule of thumb is a span of 20 times the beam depth. With a 1x2 on top of the 1x3 the depth is 3.25 inches. That’s a span of 65 inches. You can stretch that a bit, but you’ll get more deflection and potentially some lateral sway, particularly with the unbalanced “L” rather than a symetrical “T”.
Ray
The L piece makes it no longer a simple beam and imparts much additional strength. The twisting - yes, when you just have the basic structure with the only joists being at the legs. Once you put joists on, every 16" or so, there will be very little ability for the L girder to twist. Linn Westcott tested this all out, he didn;t pull the numbers in that chart out of his hat. And we’re talking about static loading, there is for all intents and purpsoes no liv eload in a model railroad - the weight of the locos and cars is insignificant compared to scenery back in the day which was almost exclusively plaster based. Modern lightweight methods reduce the load even more. And those spans are rated to carry human weight and higher, so if you want to climb all over your layout then yes, you want to use more supports.
–Randy
Good point Randy. As I recall, my old layout had an unsupported span of about 84". And, no, I don’t intend to climb onto the layout at any time. The major concern here, of course, is regarding sag. I made the mistake on my old layout of using 3/8" CDX and I did have significant variations in height, but I think that it was probably due to warping of the CDX, rather than sag. That was the intent of my original question - - at what distance between legs can I expect sag? I do believe the question has been answered, but I wanted to make sure I was on the right track (no pun intended!). Thank you all.