I'm building storage lofts in a supply room. What weight can a 2x4 free-standing post safely support?

Question

Each loft has 4 of 2x4 fir posts, with 2 of 2x2 fir posts straddling the middles to control sagging. Floor is interior-finished concrete. Lofts are based upon 4Fx8F sheets of OSB. The large loft has 3 shelves built from 2x4 frame which OSB covers. The 2 half-lofts are based upon these sheets ripped in half (hence 2Fx8F), otherwise are the same (3 shelves). Each shelf supported onto 2x4 and 2x2 posts via a small piece of 2x4 using screws, and then lag bolts sent into the frame and post itself. I'm worried that loading up these lofts with telephones and wiring equipment and parts will start to make the 2x4 posts crack at the bottom where they sit flat upon the finished concrete. Once those posts start cracking like that, they could fail.

Answer 1

It depends on the species and to what degree the load is perpendicular to the load.  Using machine stress rated lumber, you can check the perpendicular load vs the grade.

Answer 2

I'm not sure what they're called, but they sell a thing at Lowe's that you put on the bottom of the piece of wood and it has a foot which rests on the concrete.  It is basically a metal bracket, and you s***w one side into the wood and bolt the other side down into the concrete.  It will keep the wood from moving where you don't want it to.  

Also remember that OSB can be pretty heavy, so even with nothing on the shelf yet, you already have a lot of weight.  To minimize buckling of the 2x4's you can connect them (about halfway down the 2x4) with a horizontal 2x4.  Also, adding diagonal 2x4's will add strength to the structure.

Answer 3

A 2x4 post will buckle under minimal load.  For a post, you will want to use a minimum of 4x4.  2x4's have way too much flex.  You can use the 2x4's for rails for the shelves as long as you have them vertically.  Hope this helps.