National Building Group
Foundations & Piers
Most companies in the steel building industry don't spend near enough time with the "Bottom
Support" of their buildings. Each building will require an engineered foundation for the
bottom support of it. Every structure is analysed to the specific criteria required to
support it and therefore it is necessary to review the plausible foundation methods which
are best suited for the particular building. With this in mind let's review these 4 types
of foundations.
T-Type Foundation
The "T" shaped foundation has served as one of the most commonly used foundations and has
served the test of time. It is used to support a structure in areas where the ground will
freeze. The footing is placed below the frost line and the walls are added on top of it. The
footing is wider than the wall, providing extra support at the base of the foundation. This
foundation can be designed to support point loads from steel walls anchored to it.
|
|
Slab-On-Grade Foundation (Single Pour)
Correct to its term as slab floor is poured as one single layer several inches thick. The
edges or outer perimeter is thicker and contains reinforcing re-bar to strengthen this outer
portion of the slab which forms an integral footing for the building. This is all poured in
one pour and Anchor Bolts are positioned into the wet concrete. The slab normally rests on a
bed of crushed gravel to improve drainage. Casting a wire mesh in the concrete reduces the
chance of cracking. A slab on grade is primarily used in areas where the ground doesn't freeze,
however where insulation is properly utilized it can be engineered to resist frost heaves.
|
|
Frost Protected - Slab-On-Grade Foundation
This method only works with a heated structure. It requires 2 sheets of rigid polystyrene
insulation. One is placed on the outside of the foundation wall and the other laid flat on a bed
of gravel at the base of the wall. At the base of the wall the insulation holds heat from the
structure in the ground under the footings which prevents heat loss from the edge of the slab.
This heat keeps the ground temperature around the footings above freezing. Concrete is poured
in one operation as opposed to 3 pours when doing a T-shaped foundation.
|
|
Pier Foundations
The pier foundation is the most commonly used method for supporting a structure in areas where the
ground will freeze. The concrete pier is begun below the frost line and anchor bolt is set into the
top of it. The concrete of the pier will be either placed in a tube where sandy soils are present or
straight in the hole if in clay. The diameter of the pier will be determined by the engineer and may
require a reinforcement cage where necessary.
|
|
Summary: The above information serves to provide our clients with some basic
information concerning the foundations which can be used for their particular project. This has proved
very helpful as a reference page and does not replace engineered drawings.
