- Project Type: Evaluation
The Vital Structure:
The owner of a parking garage contacted Vital Structures to evaluate the garage steel framing due to corrosion. The structure consisted of a cast-in-place concrete parking deck with traffic coating, supported by painted steel framing with an elevated asphalt-paved parking area below the structure.
The client was concerned about apparent corrosion of the structural steel support columns and beams which support the upper level of the parking structure. Prior limited concrete patch repairs and re-coating attempts had not been successful as a long-term resolve, and resulted in accelerating the concrete and steel deterioration. Drainage of the parking structure was partially restricted. The garage had suffered from years of deferred maintenance and substandard prior repair attempts.
The evaluation approach included:
- Performed concrete coring of the parking deck to collect samples for petrographic examination, chloride ion content and carbonation testing.
- Performed destructive test cuts of the concrete parking deck to review cause of spalls, condition of reinforcing steel, and extent of deterioration.
- Mechanically ground structural steel framing members to achieve measurements of remaining solid steel, and to determine the extent of corrosion for options between repair or replacement.
- Performed a representative gravity load analysis of the parking deck, in an effort to determine the remaining structural load capacity of the upper garage parking deck.
The evaluation found the following conditions:
- Parking deck traffic coating had failed in various locations. Leaks were noted around internal drains and various perimeter locations.
- Several steel beams had substantial section loss due to run-off and leaks from the upper parking deck.
- Bases of steel columns were buried in asphalt/earth with no protective coating or concrete elevated piers. Several areas of substantial section loss were noted at the column bases.
- The upper parking deck had regularly been treated with corrosive de-icing chemicals.
We prepared an evaluation report with general recommendations, including temporary shoring, structural member replacement and protective coatings. Due to the high degree of soluble salts and chloride ion content, and with prior substandard repairs causing an accelerated deterioration due to entrapped contaminants, we determined that several sections of metal deck, concrete slab, structural steel beams and column bases would require replacement in lieu of repair.
Steel framing members which resulted with less contamination catalyst content and a higher degree of remaining steel section could be salvaged and reinforced with steel plate and angle welded reinforcement.
Since the original paint and galvanize coating had long been depleted at much of the garage area, recommendations for complete surface preparation, including treatment of chloride ions and soluble salts, with application of a high performance rust inhibitive paint system was given. Additionally, low-level parking regrading was necessary due to the steel column bases being embedded below grade, and elevated concrete pier supports were submitted as an option. As the client’s budget was constrained, we provided a phased repair approach including requirements for limited parking use and temporary shoring.
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