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Construction & Maintenanceof
Post‐Tensioned Slab‐on‐GroundFoundations
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Why use PT Slab‐on‐Ground Foundations
• Better Performance
• Quicker to Construct
• More Economical (concrete savings)
• Easy to Install
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Why are PT Slabs Easy to Install?
• Less pieces of reinforcing to handle
• Can fit irregular shapes easily
• Tendons and anchorages can be moved to avoid blockouts, penetrations, and recesses.
• But, MUST FOLLOW DETAILS!
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PT Slab‐on‐Ground Foundations
• Construction• Site Preparation• Foundation Construction
• Maintenance• End‐Users Responsibilities
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Site Preparation• It’s a Slab‐on‐GROUND – you have to know
what you are building on.• They are designed to meet a specific set of
soil “parameters”. • The performance of ANY foundation is
dependent up on obtaining accurate soil information about the site.
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Site InvestigationLook for Site Anomalies
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Site Investigation
Look for Site Anomalies
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Site PreparationInspect the site to look for unusual conditionsTrees can influence soil moisture & should be removed, including the root system
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Site PreparationInspect the site to look for unusual conditions
• Trees can influence soil moisture & should be removed, including the root system
• Anything that appears “out of the ordinary”• Contact the geotechnical and structural engineer for recommendations
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Site Preparation• READ the General Notes sheet prepared by
the structural engineer. This sheet may contain special instructions about specific site preparation requirements.
• Contact the structural engineer should anything be unclear or in question.
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Site Preparation• The site should be initially stripped of all surface vegetation and other deleterious material.
• The exposed subgrade should be scarified and recompacted.
• Proof roll the site to identify any loose soil• Grade the lot for positive drainage away fromthe foundation during and after construction.
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Site Preparation
Grade the lot for positive drainage away fromthe foundation during and after construction.
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Preparing for Concrete Placement
• Adequately brace forms• CHECK THE FORM LAYOUT. Make sure that it is correct, level, and square.
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Preparing for Concrete Placement
• Adequately brace forms• CHECK THE FORM LAYOUT. Make sure that it is correct, level, and square.
• Check all plumbing locations before the PT is installed and the concrete is placed.
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Under‐Slab Systems
Correcting mistakes in PT applications is difficult ………. and expensive.
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Under‐Slab SystemsRight‐Way
Wrong Way
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Preparing for Concrete Placement
• Adequately brace forms• CHECK THE FORM LAYOUT. Make sure that it is correct, level, and square.
• Check all plumbing locations before the PT is installed and the concrete is placed.
• Do Not install screeds until after the PT is installed
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Foundation Make‐Up
• Clean the bottom of the stiffening ribs and footings
• Check all stiffening ribs and footing sizes and locations
• Check the slab thickness• Provide a smooth and level subgrade
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Specification for Unbonded Tendonsfor SOG Applications
New Publication by PTI:
Stand‐alone Specification of PT Materials for SOG
Contact:Post‐Tensioning Institute atwww.post‐tensioning.org
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Specification for Unbonded Tendonsfor SOG Applications
• Resource for Architects, Engineers, Contractors, Inspectors and governing agencies to insure quality PT materials.
• In addition to detailed requirements for PT materials, specification contains requirements for:– Fabrication, handling, delivery and storage– Tendon Installation– Stressing– Elongation Measurement & Recording– Tendon Finishing
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“Standard” PT System Anchorage Assembly
Corrosion Protection "Grease"
High Density Polyethylene Sheathing
P-T Coating
7 wire Steel Strand
Anchor
2‐pc Wedge
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PT Installation Details• Exposed Strand behind Stressing Anchors
• Increases friction ‐ concrete forms into the interstices of the strand
• Dangerous – causes jack to suddenly rotate when force is released
• Damages the jack
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PT Installation Details• Exposed Strand behind Stressing Anchors
• Replace Sheathing• Tape• 1 inch Rule
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PT Installation Details• Easy to Install ‐‐‐‐‐‐ but MUST follow simple details.
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PT Installation Details• Easy to Install ‐‐‐‐‐‐ but MUST follow simple details.
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PT Installation Details• Easy to Install ‐‐‐‐‐‐ but MUST follow simple details.
Initial curing tensile stresses build‐up at reentrant (inside) corners causing cracking to occur. Rebar is typically installed at these locations.
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Concrete Placement
Do Not stand on Tendons
Cold Joints
Consolidation
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Tendon Finishing
1. Cut tendon tail after stressing is approved.2. Fill stressing pocket recess.
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Fixed‐End Installation
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Foundation MaintenanceThe property owner is responsible for site maintenance, but they must be educated on
what this mean as it relates to a SOG foundation.
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Foundation MaintenanceThe long‐term performance of a slab‐on‐
ground foundation is dependent upon good drainage and a moisture maintenance program
by the property owner.• Do not alter the drainage
pattern of the site• Provide a minimum of
3%‐5% of slope away from the foundation with the first 5 feet
• Roof drains should not discharge water at the perimeter of the foundation
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Construction & Maintenance of PT SOG Foundations
For more information concerning the construction & maintenance of post‐tensioned slabs‐on‐ground,Contact the Post‐Tensioning Institute atwww.post‐tensioning.org
Also Available in Pocket‐Size Version