Tendon Blowouts and Eruptions, Causes and Repairs Convention... · 2009 PTI Technical Conference TENDON BLOWOUTS AND ERUPTIONS CAUSES AND REPAIRS Douglas ... pockets in concrete ...

PTI 2009 Technical Conference & Exhibit – Portland, OR

TENDON BLOWOUTS AND ERUPTIONS CAUSES AND REPAIRS

by

Douglas Sarkkinen, PE, SE

Principal

Kramer Gehlen & Associates, Inc.

Vancouver, WA

2009 PTI Technical Conference TENDON BLOWOUTS AND ERUPTIONS CAUSES AND REPAIRS Douglas Sarkkinen, PE, SE

© Copyright Post-Tensioning Institute all rights reserved. Page 1 of 35


KGA projects




OVERVIEW

• Post – Tension Flat Plate Structures – Unbonded Monostrand

• Robust Structural System

• Millions of square feet of construction each year

• Problems can occur – during and after construction is completed

• Repairs can be done

• Designers/Contractors can learn from past problems




Presentation Covers:

• 4 types of Problems

• Examples – Case studies

• Causes

• Repairs




PROBLEM TYPES

Type 1 ‐ Anchorage Zone Blowouts

Type 2 ‐ Internal Slab Blowouts

Type 3 ‐ Tendon Eruption

Type 4 ‐ Surface Spalls at Tendons




Type 1 ANCHORAGE ZONE BLOWOUT
















Possible Causes

‐ Lack of bursting reinforcing steel‐ Bursting reinforcing steel misplaced(laying on the side or

too far away)‐ Low strength concrete‐ Voids or rock pockets in concrete‐ Offset anchorages allowing a head in the anchorage zone

of another.‐ Inadequate confining steel in thin slabs‐ Tendons located at a slab corner without adequate

confining reinforcing




REPAIRS

• Safety ‐ detensioning

• Investigation

• Evaluation

• Cleaning – chipping away to sound concrete

• New anchorage heads

• Adequate Confinement

• Replace concrete and restress




Type 2 ‐ INTERNAL SLAB BLOWOUTS













Causes

• Sharp tendon sweeps/near surface

• Inadequate confinement

• Stage Stressing not done




Repairs:

• Investigation ‐ Evaluation

• Situation Specific

• Repair in‐place or completely rebuild

• Extent of tendon damage




Type 3 – Tendon Eruption










Causes

• Anchorage slip

• Corrosion – tendon breakage

• Saw cutting or drilling




Repairs

• Investigation – Evaluation

• Often is neglected if only (1) tendon

• Replace tendon with 3/8” diameter tendons

• Patch Concrete

• Mitigate penetration of water




Type 4 – Surface Spalls



















Causes

• During construction – reverse curvature

• Possible voids

• Sometimes unknown

• Post‐Construction ‐ water




Repairs

• Investigation – Evaluation

• Corrosion

• Mitigate water Problem

• Clean and patch










Summary

• Robust system – but problems can occur

• Most causes are identifiable, but not always

• Repairs can be made

• Details, Details, Details.




Thank You!



Tendon Blowouts and Eruptions, Causes and Repairs Convention... · 2009 PTI Technical Conference TENDON BLOWOUTS AND ERUPTIONS CAUSES AND REPAIRS Douglas ... pockets in concrete ...

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