Drilling into a post-tensioned slab Another popular myth with post- tensioned slabs is that it is very difficult to drill into an existing slab because of the unknown location of the tendons and anchors. But as long the tendons and the concrete in front of the anchors are not damaged, drilling into a post- tensioned slab is a fairly routine issue.
Can you cut into a post tension slab?
What happens if you cut a post tension slab? Once the concrete is poured and sets, the cables are tensioned. Once tensioned, the cables cannot be de-tensioned. The hazard exists when workers cut into the slab and rupture the tensioned cable. Do NOT cut into a post tensioned slab if there is a chance you will rupture a cable.
Can I drill into a post tension slab?
Yes, you can drill into a PT slab. However, you want to make sure you know where the cables are located. I design PT slabs and repairs. It is rare for a tendon to break out of the slab on a residential house. It will shoot out the plugs around the slab edge. If it hit someone it could break a leg.
How long should I wait before drilling into concrete footing?
Only show this user. Concrete generally takes 28 days to cure out, you could drill without trouble after 7 and tighten your bolts after 14 without taking too much risk, A good mix design will be at 50%+ after 3 days and about 90% after 7.
How do you cut post- tension concrete slabs?
Test your knowledge – answer these questions:
- What is Post Tension Slab ?
- What are the advantages ?
- What is the “Post Tension” sign about ?
- When did we start using Post Tension
- What are other types of slab reinforcement
What happens if you drill a post tension slab?
Post-tension slab drilling, cutting, and coring can be incredibly dangerous. Not only is there a risk of structural collapse, but you also risk severe injury and death.
Can you bolt a safe to a post tension slab?
Post tension concrete slabs should not be used as a foundation for a gun safe. They have steel cables running through them. These cables are under thousands of pounds of pressure and are high-strength steel.
Does post tension slab crack?
Cracks more often occur during curing because the concrete generates heat and expands during the chemical process and shrinks as it cools. Because there is not yet tension on the tendon cables there is no reinforcement to hold the foundation together and cracks often occur during this period of time.
What happens if you cut a post tension cable?
Cutting a tensioned cable, or tendon, can endanger the contractor and compromise the structural integrity of the slab. Building professionals frequently use ground-penetrating radar (GPR) to locate cables within concrete slabs and reinforce the slab during and after cutting operations.
How far down are the cables in post-tension slab?
The plan maps show the rebar at 3" depth, and the post-tension cables at 8" depth. Discerning a post-tension cable from rebar generally requires scanning a larger area to properly understand the layout of structural elements in a slab. When in doubt, mark it out and avoid it!
How deep are post-tension cables in slab?
8 inches thickA residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed.
How long does a post tension slab last?
about 15-20 yearsConventional concrete & rebar foundations last about 20-30 years before failure begins to occur. Post-tension slabs are lasting about 15-20 years and are failing at a much higher rate. Post-tension slabs are created with concrete trenches around the perimeter of the house where the external walls will be placed.
Are post-tensioned slabs good?
First off, one could argue that post-tensioning is superior to conventionally reinforced concrete in a pure engineering sense. The reason is because post-tensioning is a method of pre-compression, which means the concrete is put into a state of compression, which allows the concrete to take on flexure without cracking.
What is the purpose of a post tension slab?
A post tension slab is a concrete slab with steel cables running through it that have been placed under 33,000 +/- pounds of tension. This tension makes the concrete slab and foundation much stronger than concrete without reinforcement and helps reduce cracking.
How do you remove a post tension slab?
After the structure has been gutted, each floor slab is typically removed by skid steer loaders using hydraulic and impact hammers. The tension from the cables is released and can be cut with hydraulic shears or torches.
How do you find the cable in a post tension slab?
0:481:24Post Tension Cable Locating with Ground Penetrating Radar - YouTubeYouTubeStart of suggested clipEnd of suggested clipThey need to know where the tension cables are we can find those in beams columns walls floors. WeMoreThey need to know where the tension cables are we can find those in beams columns walls floors. We can scan from the underside.
Can you cut prestressed concrete?
The reasons for prestressed concrete lintels being so durable and practical are also the reasons why it is hard to cut. However, they can be cut, preferably by concrete cutting professionals using the right tools and equipment.
How to strengthen a slab?
Some common methods to strengthen the slab include adding new intermediate supports, increasing slab depth, adding concrete beams, creating a composite section by applying externally bonded steel or fiber-reinforced polymer, or adding external post-tensioning.
What is post tension cable?
Post-tension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Once the slab cures, qualified personnel apply tension and grout the cables. Contractors sometimes need to drill or cut into a post-tensioned slab for repair or renovation work. Cutting a tensioned cable, or tendon, can endanger ...
Do you need post tension tendons for stairwells?
Large openings for stairwells or large duct shafts between floors often require cutting post-tensioned tendons. Determine potential locations for the new opening into the slab. These should avoid major structural members such as beams and bands of post-tension tendons.
An Enhanced Throwback Story: Post-Tension Slab Drilling and 130 Cores
Post-tension slab drilling, cutting, and coring can be incredibly dangerous. Not only is there a risk of structural collapse, but you also risk severe injury and death. It’s definitely NOT something you want to play around with.
The Job Site
Before the recession, a company bought three lots on one road. They built condos on the center lot with a parking garage underneath. Just as they finished pouring slabs on the parking garage of the two remaining lots, the recession hit.
The Project: Scanning Ahead of 130 Coring Locations
Using our 1.6 GHz GPR antenna, we scanned every proposed coring location. This customer didn’t care about cutting embedded conduits — avoiding a PT cable hit was their only concern.
The Results of Post-Tension Slab Coring x 130 Cores
Of course, when it’s time to actually do the post-tension slab coring, everyone gets (understandably) nervous because hitting a PT cable could be a matter of life or death. But there was no need to fret. In the end, not one single cable was cut or even nicked!
How does a Post Tensioned Concrete Slab Work?
When a beam or slab bends downwards, the top portion of the slab goes into compression, and the bottom portion goes into tension. This is usually taught in Engineering 101 taken during the first year of University.
Components of a Post Tensioned Concrete Slab
In simple terms, the components which make up a post tensioned slab include:
How is a Post Tensioned Concrete Slab Constructed
The construction sequencing for a post tensioned concrete slab differs from a conventionally reinforced slab. Below is a step-by-step sequence of the construction methodology of a PT slab (similarities with a conventional RC slab highlighted in Green ):
What is the Benefit of a Post Tension Slab?
PT Slabs have several benefits compared to reinforced slabs. Due to the concrete being utilised to its strengths (compression), this allows longer spans and thinner slabs.
How to Identify a Post Tension Slab
A post tensioned slab can be identified by the grouting of the live stressing end of the cables. Once the cables are tensioned and grouted, the live ends where the jack applies the stressing is also grouted. The grouting is usually a different mix to the concrete slab itself so usually has a different colour.
Can I Drill into a Post Tension Slab?
This depends on the type of post-tensioning used. In Australia the most common form of post tensioning used in concrete slabs is bonded post tensioning. Bonded post tensioning simply means that after stressing of the cables has occurred, the PT ducts are fully grouted, this allows for a progressive transfer of the force from the cables to the slab.
What are the Design Considerations of a Post Tensioned Concrete Slab
To design a post tensioned slab effectively the full benefits of the compressive force needs to be exploited. This means that an adequate quantity of post tensioned needs to be provided within the slab to reduce the conventional rebar requirement as much as possible.
Can you cut holes in concrete?
Often it is necessary to cut holes in concrete floor slabs . For slabs reinforced with rebar or wire mesh, this is considered fairly routine. However, for post-tensioned (PT) slabs, this can be mistakenly regarded as difficult, expensive, and dangerous.
Can a PT tendon be cut?
Cutting openings in PT slabs does require care and caution because of the possibility a PT tendon may get cut. Tendons carry a high amount of force, usually around 27,000 pounds for a 1/2-inch-diameter strand, and must be detensioned in a controlled manner to assure performance and safety.
