Collapsed Parking Garage

Partially collapsed garage

A single-level, double tee Condominium parking garage located in Denver, CO partially collapsed during the winter of 2014. Five double tee stems fell, crushing and trapping several cars below. No injuries were sustained during the event. Emergency shoring was installed shortly after the incident.

The atypical construction of the garage included precast double tee stems supported on conventional steel beams and columns. The steel columns extended below the slab a couple of feet on grade concrete and were supported by concrete piers.

Damage to cars in collapsed portion of garage

A combination of factors led to the collapse of the garage:

  1. A high water table caused corrosion of the steel column supports. Damage extended into non-collapsed areas.
  2. There was no lateral bracing in the garage to prevent rolling of the steel beams.

Column and baseplate removed from collapsed portion of the garage

Corrosion of structural column steel below the slab on grade concrete

This particular location was found in an area where the collapse did not occur.

One of the double tee stems was damaged beyond repair. The other four stems were found to be salvageable with minor concrete repairs. The original construction plan called for jacking of the salvageable double tees to the proper elevation and repairing the steel supports below.  Restruction Corporation value- engineered the complete removal of the salvageable double tee stems and stored them offsite for reinstallation, following completion of repairs to the steel structure. The shorter tee stems were shored and jacked in place, as they did not collapse.

Removal of precast double tees: The largest hydraulic crane in Denver was required for removal due to the loads and pick distance.

The repairs to the steel support structure consisted of installing all new concrete pier caps, hot-dipped galvanized steel columns, W-beam steel supports, and lateral support bracing.

New concrete pier cap and hot-dipped galvanized steel column

The four salvaged double tee stems and one new double tee stem were then reinstalled. New hot-applied waterproofing was used on the top of the stems and additional bi-level drains were installed.  Finally, a new concrete topping slab returned the garage to its original pre-collapse state.

Resetting of double tee stems

Bottom level of garage after repairs

Top level of garage after repairs

Removal of precast double tees – tees were stored off-site for reinstallation.

Newly installed steel columns and beams

New lateral bracing of steel beams

New lateral bracing of steel beams

Hot-applied waterproofing used on the top of the double tee stems