Do you need a soils
report for your steel building foundation?
You can have a foundation for your steel building
by calling the Salsa Steel Corporation.
Give them a call - they can also help you with
your foundation questions.
P.O. Box 396
Chowchilla, CA 93610
Do I need to have a soils report?
How thick should I pour my slab foundation?
Some basic tips for a solid slab foundation
Concrete cracks, is it normal?
Three primary purposes for reinforcing slabs
How Thick Should My Slab Be?
Your slab must be at least 4" thick. It can be thicker and should be
thicker depending on the use of your building and slab. For instance if
you are working on large heavy equipment a thicker slab and high
concrete strength would be more suitable. And likewise, a storage
building or studio would only need a 4" thick 2,500 psi foundation.
Slab thickness must be determined by a foundation engineer or your local
officials. For ballpark estimating purposes, slabs in the southern half
of the U.S.A. tend to be 4 inches while the thickness can exceed 8
inches in northern climates.
Tips for a Successful Foundation
WWR when installed properly provides adequate reinforcement, it is
imperative that supports are used. Do not let your concrete contractor
“pull?the wires up. For beginner/novice concrete crews we recommend
using rebar as your choice of reinforcement.
Cut your foundation control joints in within the first 12 hours.
Properly placed and cut control joints will hide and control the
cracking of the slab due to shrinkage.
Avoid using a concrete sill notch. This adds unnecessary concrete to
your foundation. Ask your Metal Building Supplier to provide you with a
formed base angle.
Common Foundation Problems
Welded Wire Reinforcement
Below is a picture of a 4 1/2" concrete slab with welded wire
reinforcing (WWR). As you can see the WWR is on the bottom of the slab
penetrating only about a 1/4". The WWR should be located between the
center of the slab and the top 2 inches. This is a very typical
scenario. This slab failed under normal loading conditions and had to be
Not all Foundations Are Created Equal!
A good alternative would be to use a heavier gauge wire reinforcement
with supports. A better solution for beginner/novice crew would be to
use a rebar reinforcement, for example a #3 bar @ 18?o.c. It should be
noted that WWR when installed correctly is a great reinforcement
material. However, it takes a very skilled crew to place it properly.
Perfect concrete without cracks is nearly impossible to find much less
achieve. The very nature of concrete is to crack somewhere, it is a
mixture of concrete, aggregate, and water. Cracks are generally caused
by the rapid evaporation of the water. Most cracks (hairline to pencil
lead) are aesthetic at best and present no load failure. However
improperly placed reinforcing and control joints are the leading factors
to major cracking (3/8" and greater) in which case need to be treated.
There are three primary purposes for reinforcing slabs-on-grade and they
Shrinkage control is the greatest design concern with slabs-on-grade.
Steel reinforcing along with joint spacing offer two primary elements
that can be effective in controlling shrinkage cracks. The most common
mistake among designers and engineers is not providing enough of steel
reinforcing for a slab-on-grade.
Concrete is brittle ?it is very susceptible to additional cracking and
fracturing by dramatic changes in weather. The change in temperature is
commonly referred to as Temperature Gradient. Steel reinforcing offers
the best assistance because it essentially has the same coefficient of
thermal expansion, thereby expanding and contracting at the same rate as
Slabs-on-grade design procedures usually provide a designer with the
slab thickness. The thickness of the slab is a function of loading,
subgrade, modulus of rupture for concrete, and slab stiffness.
As you can there are three primary design considerations for a every
Joint Spacing (Crack Control lines)
Having a firm understanding of each and their relationship is key to any
Types of Reinforcement
There are 3 types of reinforcement that we utilize in our foundation
Rebar is a steel deformed bar ranging in size from #3 (3/8") to #18 (2
1/4") diameter. These bars come in two grades. Grade 40 and Grade 60
Typically all bars over #5 are specified as grade 60 and like wise #4
and #3's are grade 40. Grade refers to the yield strength of the bar.
Your only concern here is, that when placing your order your specify the
WWR (Welded Wire Reinforcement) is a smooth or deformed welded wire
reinforcement that is available in mats or rolls. With its cost
efficiency, WWR is frequently the reinforcing steel of choice for
slabs-on-grade. However, WWR’s full benefits of controlling cracking and
reducing maintenance can only be realized when it is positioned
accurately and properly placed on supports. One of the primary causes of
under-performing slabs-on-grade is the inadequate positioning or
complete absence of supports(1).
Supports are imperative to the accurate use and design of WWR in any
slab. This firm will not specify/design nor sponsor the use of rolled
wire reinforcement in any of our foundation designs. It is the opinion
of our principals in charge that rolled wire reinforcement is the most
difficult reinforcement to place properly. It is also our opinion that
properly placed (Rolled) WWR happens less than 5 out of every 100 slabs
poured. See Foundation Problems for more information.
Mesh Fiber is a synthetic or steel (hair like) fiber reinforcement that
is mixed into the concrete at the mixing plant. It offers great
reinforcement against (shrinkage) cracking in the concrete. However, a
common mistake many make is to eliminate steel reinforcing all together.
While this may be acceptable in some scenarios (slab portion), steel is
still a must in the footings. The mesh typically cannot handle the heavy
service loads alone. A better solution is to use mesh along with WWR and
Rebar. Mesh fiber adds about $7-$15 per cu yard of concrete. Mesh is
typically used in high performance specs.
(1)Tech Fact 702-R-03, Wire Reinforcement Institute
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