Even though the LVL beam constructed in the previous post is very strong, the span is just too long so support is required under the beam. The plans call for 2 columns - steel jack posts - set at 11 feet intervals.
Jack posts have 6 components:
1) two metal plates
- a bottom plate which is secured to the concrete footing so that the jack post does not move, and
- a top plate which is secured to the underside of the beam. This plate has a special hole in to which the an end of the threaded bar fits.
2) two metal tubes, one of fits inside the other. The smaller diameter tube has a number of holes in it.
3) A short 4" solid metal bar which fits into the holes in the smaller diameter tube. The two tubes are adjusted in length to fit the distance from the footing to the beam, and the length secured by placing the short bar in one set of holes.
4) a plate with a threaded bar in it. The plate fits over the top of the small diameter tube, and the other end of the threaded bar fits into the top plate secured to the bottom of the beam.
The height of the jack post is adjusted in 2 ways. Gross adjustment is done with the 2 metal tubes, securing the length by placing the short bar in holes in the small diameter tube. Fine adjustment is made by turning the threaded bar using a wrench.
The idea is to adjust the jack post so it is just supporting the beam.
This picture illustrates the top plate and the threaded bar. The top plate is secured to the bottom of the LVL beam, and the threaded bar is inserted into a hole in the top plate. A smaller plate rests on the top of the smaller diameter tube.
There are 'bumps' on the bottom of the smaller plate into which the tube fits.
This picture illustrates how the bottom plate is secured to the concrete footing and the larger diameter tube is placed on top of the bottom plate.
There are 'bumps' on the bottom plate over which the tube fits to hold it in place.
When the concrete floor is eventually poured the bottom 4" or more of the post will be embedded in the concrete floor, and hence permanently secure the post.