Dallas City Hall Plaza Parking Garage – Repair of Bonded Post-Tensioned Slab System

Dallas City Hall and Plaza are recognized by many due to the opening scenes of Dallas, the television show. What is less known is that the structure is a significant early example of bonded post-tensioned concrete which was utilized throughout the superstructure and two-story parking garage constructed beneath the plaza. Opened in 1977, the parking garage is a two-way bonded post-tensioned concrete slab with unreinforced drop panels supported by flared circular concrete columns. The garage covers two city blocks, extends under two adjacent multi-lane streets, and supports mature landscaping, pool, fountain, and up to 11’-0” of soil. In 2017, several square feet of a drop panel fell from the structure and subsequent observations found multiple locations of drop panel and column capital failures. A structural investigation including destructive and non-destructive testing, and analysis of the existing structure was undertaken to determine the cause of the failures. Structural repairs were then developed to address the failures as well as the root cause of the failures. Constructability and value engineering reviews were incorporated into the process to maximize benefit while reducing risk and costs.

Learning Objectives:

1. Attendees will learn of about early bonded post-tensioned systems and lessons learned regarding the design and construction of these systems
2. Attendees will learn of new design and data acquisition tools available to the design professional.
3. Attendees will learn to creatively and thoughtfully evaluate the use of technology and material advances and how to blend these advances with proven practical approaches.
4. Attendees will learn the importance of constructability reviews and value engineering which maintains quality while reducing risk and costs.