I was having a debate with someone today, and I'm pretty sure I've got this right. Basically we have an exposed floor of wooden joists, and need to prop something up above them ( a wall). We will put a spreader plate in the form of a piece of timber below. My colleague said the longer the spreader plate, the more the load is spread. I said I agreed with him, but only if we used several pieces of timber making it sufficiently stiff. If we used one piece of timeber, it would flex enough that it would put most of the force on the immediate joists either side of the prop.
The long and short of it is, would a sufficiently stiff beam (several wooden plates) spread a point load (the prop) equally over several joists, with a longer beam spreading the load even more i.e. 10 joists would carry 1/10 of the load??
I'm attaching a diagram
In essence yes. This is something you'll see happening building sites quite regularly. There is a limit on how far a load can be spread tho; if you were to analyse the spreader modelling each joist as a support, you'll see that there comes a point where the load has worked it's self out which can leave you with some redundant material. The other thing you need to be careful of is that the EUDL the spreader provides doesn't exceed the design limits of the joists.
There are lots of methods to analyse bearing areas but as a bolt and braces solution, this is usually ok.