Assessment and Restoration of Post-tensioned Waffle … Convention/Session... · Assessment and...
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Transcript of Assessment and Restoration of Post-tensioned Waffle … Convention/Session... · Assessment and...
Assessment and Restoration of
Post-tensioned Waffle Slabs in Parking
Ramp Structures
Gabriel A. Jimenez, Ph.D., P.E., S.E.
Principal/Managing Director
Walter P Moore
• Longer spans and/or heavier loads requires increasing the slab thickness in order to limit deflections
• Dead load becomes the major portion of the design load
• Economical reasons: rib the slab in both directions to provide greater stiffness with less weight
Motivation
• Rows of concrete ribs at right angles to each other with solid heads at the columns.
• Square pans or dome forms to create the void, or recess, between the ribs.
• Standard dome forms: 24-inch or 36-inch module with sloping sides forming a bevel of 1 ½-inch/ft from the vertical.
• Use: Office buildings, parking structures, warehouses
Waffle slabs
• Top of slab reinforcement: WWF or conventional reinforcement
• PT reinforcement started in the 1960s – Monostrand
Post-tensioned waffle slabs
Susceptible to corrosion
Courtesy of Adapt technical note
• Concrete deterioration generally signals the onset of accelerated distress
• Symptoms of concrete deterioration: – spalling, cracking, scaling, rust staining and abrasion
• Deterioration mechanisms primarily responsible: – Corrosion Related Distress – Cracking – Material Related Degradation – Others
Concrete deterioration
• Concrete is a naturally porous material
• Concrete pores have diameters ranging from 15 - 1,000 A (10 millionths of mm)
• Chloride ion diameter is less than 2 A
• All concrete is susceptible to chloride ion contamination by virtue of its natural porosity
Chloride contamination
MOISTURE AND
CHLORIDE ION
ROAD SALT
RUST BUILD-UP
CAUSING
PRESSURE
DELAMINATION
OR FRACTUREOPEN SPALL
SALT WATER
CONTINUOUS
CORROSION
• Corrosion - dynamic electro-chemical process & induces progressive deterioration
• Corrosion by-products (rust) - 5 to 8 times larger (volume) than the parent metal
Corrosion
MOISTURE AND
CHLORIDE ION
ROAD SALT
RUST BUILD-UP
CAUSING
PRESSURE
DELAMINATION
OR FRACTUREOPEN SPALL
SALT WATER
CONTINUOUS
CORROSION
Areas of vulnerability
Areas of vulnerability
Typical deterioration
Testing
Instrumental Testing Acoustic testing/hammer sounding Impact-echo Impulse response Covermeter Ground-penetrating radar Rebound hammer Corrosion potential testing Acoustic monitoring
Material Testing Compressive strength Petrographic examination Chloride content Carbonation Metallurgical and physical examination of the prestressing steel strand
Ground Penetrating Radar
Screwdriver penetration test
Exploratory openings
Exploratory openings
Core sampling and corrosion potential
Analysis
Repair strategies • No tendon repair
Insignificant strand deterioration no loss of prestressing force
• Selective abandonment Tendon is severely
deteriorated/damaged No repair needed based
on a design having greater design capacity than current code
• Repair Severe deterioration –
loss of prestressing force
• Tendon supplement/replacement
Existing tendons insufficient for current code/use
Requires installation new tendons
• Selective/Full structure replacement
Insufficient capacity or significant deterioration
• Stabilization/Strengthening
Restoration of structural capacity by external post-tensioning
Drawings and specifications
Repairs
Punching shear
Tendon splice repair
• Connects 2 sections
• Steel cylinder with spring-loaded wedges
Center stressing splice • Stressing/splicing from an intermediate location
• Sometimes in combination with splice coupler
• Cast metal with pre-molded wedges
Center stressing splice
Sheathing repair • All damaged sheathing must be repaired
• Sleeves/waterproofing tape/coatings suitable for PT applications
Drying and regreasing
Procedure developed for the push-through system
Dries annular space between tendon and sheathing
Drying and regreasing
Thank you for your attention
Gabriel A. Jimenez, Ph.D., P.E., S.E.
Walter P Moore
www.walterpmoore.com
713-630-7485 [email protected]