Assessment and Repair of Precast Parking Deck with Construction Defects

Speaker Introduction

• Kyle Standish from Klein and Hoffman, Chicago.
• Acknowledges co-author Dan Moser and team members Bill and Diego.

Overview of Presentation

• Focus on specific project assessing and repairing a precast parking structure.
• Utilizes techniques from the 364 document.

Project Details

• Structure Information:
  • Precast parking structure, approximately 7 years old.
  • Supported two levels, three bays wide, accommodating 150-200 cars.
  • Constructed with top double tees, central bay as the ramp.
• Condition:
  • No expected deterioration due to chlorides or corrosion.
  • Notable crack found in a double tee stem.

Identification of Problem

• Crack Characteristics:
  • Severe crack, dimensions varied from 1/4 to 3/8 inch wide.
• Initiated investigation to determine the cause of cracking.

Assessment Procedure

Document Review

• Accessed comprehensive documentation:
  • Architectural, structural, and precast shop drawings.
  • Design calculations available, allowing for thorough review.
• Key Comparison:
  • Identified discrepancy: 0.6 diameter tendons in calculations vs. 0.5 diameter tendons in shop drawings.
  • Eureka moment: Smaller tendons would not provide adequate structural support.

Field Investigation

• Crack Documentation:
  • Detailed observations of the primary crack and other potential cracks in the structure.
• Conducted visual examinations of the entire structure to identify other issues.
• Tendon Inspection:
  • Exposed a tendon to confirm size, which was indeed 0.5 inches as per shop drawings.

Testing Procedures

• Structural Testing:
  • Conducted compressive strength tests and bond pull-off tests.
  • GPR (Ground Penetrating Radar) confirmed tendon positions and sizes.
• No significant deterioration or corrosion found during tests.

Evaluation and Reporting

• Evaluated structural integrity based on gathered data.
• Comparison of applied loads and design capacities:
  • Confirmed 0.6 diameter tendons met code requirements; 0.5 diameter did not.
• Communication: Created a comprehensive report detailing findings and recommendations.

Repair Strategy

• FRP (Fiber Reinforced Polymer) Strengthening:
  • External post-tensioning to reinforce the affected double tee.
  • Injected cracks to prevent ongoing issues before applying FRP.
• Final Implementation:
  • Careful monitoring and quality control to ensure effectiveness of repairs.

Conclusion

• Emphasis on the need for a thorough assessment process:
  • Document review, field investigation, testing, evaluation, and effective communication.
• Ensured repairs addressed both structural and durability concerns.

Questions and Discussion

• Clarified causes of cracks, concluding it was due to overstraining in tendons.
• Discussed the possibility and limitations of load testing in this scenario, confirming that repairs were necessary regardless of load test outcomes.