Sorry to be so slow in responding, but it's looks like y'all got it all right without me. In Portland a right angle Strong-back is referred to as a
Hog Trough, don't know why, just is. In school I learned that a
Hog trough was three pieces, as gafftapegreenia, suggested. There are also T-Backs which are Hog Troughs with the right angle piece in the center. I've seen T-backs and Strong backs used quite often as stiffeners behind flats for both Movie and Theatrical sets.
They make very effective legs but I don't like to load them very heavily. Can I give you and exact load
rating ? No. But, look at it this way. When using
Hog-trough as a
leg the structural integrity comes from a variety of different mechanisms.
#1 The screws going through the two pieces of 1x, and into the framing of the
platform. By taking advantage of the inherent properties of the
leg, those being the fact that it consists of two
flat planes both of which can be secured to perpendicular framing members, you
gain a lot of horizontal integrity, they resist side-to-side movement very well.
#2 The fact that you can screw through both faces into framing also means you have more mechanical fastening then you would have with a standard, single 2x4
leg.
#3 The manner in which a
Hog-trough leg in manufactured increases the structural integrity of the material by a huge factor. The simple fact that you are adding a "back" onto the 1x4 means that both pieces are keeping each other from flexing longitudinally which translates to greater compression strength.
Now the drawbacks to
Hog-trough legs are also multi faceted;
#1 While the compression strength is great most of the down-force support is accomplished by the fact that the top of the
leg is resting against the bottom of the
platform covering. Yes, some load is carried by mechanical fastening
system, ie screws, nails., but the majority of the load is carried by the covering material itself. This can lead to issues of Plywood "peeling away from" the framing, especially in the corners, when the
platform is loaded heavily.
#2 Most shops 1x
stock is of low quality. The major issue here being that when Joe Shcmoe
Wood Butcher goes to
leg up a
platform he starts slamming the screw in and splits the wood of the
leg. Since you are very close to the end of the wood this can lead to splitting and cracking and there goes you shear force resistance.
#3 The footprint. Since you have an L shaped "
foot" when using
Hog Trough legs you have a very large surface area. This is good, in the sense that it spreads the load, bad in that it opens you up to a greater chance of encountering inconsistencies in the flooring. In other words you run a bigger chance of hitting a high spot in the floor. A good way to counter this is to
chamfer the outside corners of the
leg with a 15-30 degree angle after cutting it to length.
The Best Legging
System I have ever seen? Well, outside of using a Knee Wall or
Apple Box set up Like I use with
Triscuits, a combination
Compression leg Hog trough would be it.
Sorry to be long winded. Who Knew
Hog Trough could be so facinating ?