Having the concrete backfill stop nearly 2′ below grade protects the concrete from rapid drying and shrinkage. If the pressure treated timbers are entirely saturated at time of encasement, and are allowed to dry to below 19% moisture content in service they will shrink enough so as the combination of factors will create a force great enough to overcome the bonding of the two elements. Most hand mixed concrete, has excess water, which contributes to the shrinkage. Shrinkage can be increased by filling a hole to the top with concrete, where it is exposed to rapid drying from temperature and humidity changes. I did my own research, to determine why it is you have experienced the issues you describe.Ĭoncrete does shrink. These two gentleman are not only Registered Design Professionals, but have also been responsible (either directly or through their students) for a significant percentage of the wood structural research performed in the U.S. In this text, they cite the value for the bond strength between concrete and wood. (former Professor of Agricultural Engineering at Virginia Tech) authored the highly regarded textbook, “Wood Technology in the Design of Structures”. (former Professor of Structural Engineering at Washington State University) and Dr. The bonding of any pole barn post in concrete will provide the uplift resistance needed to keep your building…where you intended it to be. They won’t hurt anything, but it does seem to be a waste of both time and materials. Neither of these solutions offers the same amount of vertical resistance, as what is naturally provided.

As well, I’ve seen holes drilled through the same area, and short pieces of rebar placed through the holes. Ignoring totally the bond strength between wood and concrete, I’ve seen cases where either numerous large nails have been driven into the column (in the collar area) before the concrete encasement has been poured. Keep in mind, the top of the 18 inch thick encasement is 22 inches below grade, which makes it unlikely surface forces will influence any possible column shrinkage.

There are some who would believe the column is going to somehow shrink away from the concrete encasement. One of the forces which a pole building column must be able to resist is uplift – the columns literally being sucked out of the ground by the wind.

Applying the 30 psi wood-to-concrete bond strength from Hoyle and Woeste, the union of the two materials results in the ability to resist 5400 pounds of force! Obviously bonding of a pole barn post in concrete is nothing to discount. With 10 inches of concrete in contact with the sides of the column, the total surface area of the column, in contact with the surrounding concrete, is 180 square inches. The distance around the 4×6 is 18 inches. This poured concrete is known as a bottom collar. Placed suspended into a 40 inch deep hole, so the bottom of the column is eight inches above the bottom of the hole, an 18 inch thickness of redi-mix concrete is poured around it. Let’s take a look at a very small pole building column, a nominally sized 4 x 6 (3-1/2 inch by 5-1/2 inch surfaced). Now what does this mean in plain language? “Concrete encasement of the post in the ground contact area enlarges the friction surface and can generally be credit with a wood-to-concrete bond strength of 30 psi.” and Frank Woeste’s 1989 textbook “Wood Technology in the Design of Structures”, in Chapter 21 (Post-Frame Building Design) on is the following: Need help deciding how many clamps you need? The Ellis MFG Column Form Designer can help.In Robert J. All prices are by the set (two scissors).The units are identical, no right or left, up or down.

Clamps are made of high carbon steel with malleable iron castings to promote long life and many reuses.

Only a hammer, nails, and lumber are needed to erect form.

All parts are connected to make single units with no loose parts to get lost.

Column forms should be built using 3/4' or 5/8' Plywood and 2x4 or 2圆 vertical wallers (laying flat).

' Net Concrete Dimensions' indicates the finished concrete column size.

To dismantle, simply tap the wedge up to loosen the scissor clamp bars from the wood form. Slot spacing in bars and castings have been designed to eliminate dead spaces and insure you are always able to clamp tight to your wood form. Hammer down each wedge to seat bars tight against the wood forms. Simply slide each red castings along the bar up to the adjacent bar, drop the wedge through a slots in the in the casting and matching slot in the bar. Steel bars clamp quickly snug to your wood forms. Ellis Scissor Clamps provide a fast, easy, accurate and affordable way to build concrete column forms for pouring your concrete columns.

Concrete forms to go around columns