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Post Tension - FAQ
What Does Post-Tensioning Mean for Residential and Commercial
Foundations?
Simply put, Post-Tensioning is a method of reinforcing concrete, masonry,
and other structural elements by prestressing the structural element during
the construction phase for the purpose of counteracting the anticipated
external loads that it will encounter during its lifecycle.
What are the two methods of prestressing?
1) Pre-tensioning -- This method consists of stressing the reinforcing inside
of large steel buttresses, and then casting the concrete around the
reinforcing. This method can only be done at a precast manufacturing facility
and requires the completed prestressed concrete members to be trucked out
to the job site and then assembled.
2) Post-tensioning -- Reinforcing is simply installed on the job site after the
contractor forms up the slabs or constructs the walls. The reinforcing steel
is housed in a sheathing or duct that prevents the steel from bonding to the
concrete so that it can be stressed after the concrete cures (hardens).
Using the posttensioning method enables a builder to get all the advantages
of prestressed concrete or masonry (described below) while still enabling the
freedom to construct the member (slab, wall, column, etc.) on the job site.
Why Does Concrete and Masonry Need to be Reinforced?
Concrete, masonry, and most cement based products are very strong in
compression. However, concrete is relatively weak in tension. Conversely,
steel is very strong in tension. Combining reinforcing steel with concrete or
masonry results in a product that can resist both compressive and tensile
forces. Also, compressing the concrete increased the tensile bending
strength of the concrete so that a designer can achieve longer spans with
thinner concrete sections. Compressing the concrete also helps resist the
development of shrinkage cracks.
What Kind of Materials are Used in Post-Tensioning?
Post-tensioned reinforcing consists of high strength steel strands or bars.
Typically, strands are used in horizontal applications like foundations, slabs,
beams, and bridges. Bars are used in vertical applications like walls and
columns. A typical strand has a tensile strength of 270,000 psi and a typical
bar has a tensile strength of 60,000 psi. Strands typically have a diameter of
1/2 inch and are stressed to a force of 33,000 pounds using a hydraulic jack.
What are the uses and advantages of using post-tensioning?
Post-tensioned reinforcing has been used for many decades in bridges,
elevated slabs (parking garages and residential or commercial buildings),
residential foundations, walls, and columns. The use of post-tensioned
reinforcing can result in thinner concrete sections, longer spans between
supports, stiffer walls to resist lateral loads, and stiffer foundations to resist
the effect of shrinking and swelling soils. The additional advantage of putting
the concrete into compression can be used to construct slabs and walls that
have fewer visible cracks that can allow the passage of moisture and
termites.
What Does Post-Tensioning Mean for Residential and Commercial
Foundations?
- Eliminates contraction joints
- Minimizes the size an number of expansion cracks
- Eliminates cracked and uneven floors and walls.
- Far superior foundation to traditional floating slabs.
Simply put, Post-Tensioning is a method of reinforcing concrete, masonry,
and other structural elements by prestressing the structural element during
the construction phase for the purpose of counteracting the anticipated
external loads that it will encounter during its lifecycle.
What are the two methods of prestressing?
1) Pre-tensioning -- This method consists of stressing the reinforcing inside
of large steel buttresses, and then casting the concrete around the
reinforcing. This method can only be done at a precast manufacturing facility
and requires the completed prestressed concrete members to be trucked out
to the job site and then assembled.
2) Post-tensioning -- Reinforcing is simply installed on the job site after the
contractor forms up the slabs or constructs the walls. The reinforcing steel
is housed in a sheathing or duct that prevents the steel from bonding to the
concrete so that it can be stressed after the concrete cures (hardens).
Using the posttensioning method enables a builder to get all the advantages
of prestressed concrete or masonry (described below) while still enabling the
freedom to construct the member (slab, wall, column, etc.) on the job site.
Why Does Concrete and Masonry Need to be Reinforced?
Concrete, masonry, and most cement based products are very strong in
compression. However, concrete is relatively weak in tension. Conversely,
steel is very strong in tension. Combining reinforcing steel with concrete or
masonry results in a product that can resist both compressive and tensile
forces. Also, compressing the concrete increased the tensile bending
strength of the concrete so that a designer can achieve longer spans with
thinner concrete sections. Compressing the concrete also helps resist the
development of shrinkage cracks.
What Kind of Materials are Used in Post-Tensioning?
Post-tensioned reinforcing consists of high strength steel strands or bars.
Typically, strands are used in horizontal applications like foundations, slabs,
beams, and bridges. Bars are used in vertical applications like walls and
columns. A typical strand has a tensile strength of 270,000 psi and a typical
bar has a tensile strength of 60,000 psi. Strands typically have a diameter of
1/2 inch and are stressed to a force of 33,000 pounds using a hydraulic jack.
What are the uses and advantages of using post-tensioning?
Post-tensioned reinforcing has been used for many decades in bridges,
elevated slabs (parking garages and residential or commercial buildings),
residential foundations, walls, and columns. The use of post-tensioned
reinforcing can result in thinner concrete sections, longer spans between
supports, stiffer walls to resist lateral loads, and stiffer foundations to resist
the effect of shrinking and swelling soils. The additional advantage of putting
the concrete into compression can be used to construct slabs and walls that
have fewer visible cracks that can allow the passage of moisture and
termites.
Morris Engineering began
offering post-tensioning
services to Oklahoma in
2004. We have made a
strong investment to learn
and develop post-tensioning
techniques from other states
where this innovative
technique is already being
put to wide-spread use.
We will provide you with a
foundation that is specifically
engineered to provide
efficiency, strength, and
durability for the life of your
floor.
For more information,
contact
Ross Morris
Morris Engineering
(405) 912-2775
| 617 N.W. 27th Street - Moore, OK 73160 (405) 912-2775 Phone (405) 912-2322 Fax |
