St-Laurent Residential Parking

Comprehensive investigation and forensic analysis of the causes leading to major structural collapse

On November 26^th 2008, the South-East section of the underground parking structure of the apartment building, located at 135 Deguire Boulevard in Montreal, collapsed, killing one man. The owner of the apartment building, Canadian Apartment Properties Real Estate Investment Trust (CAPREIT), hired a group of experts to establish the technical causes of the collapse and submit any recommendations deemed appropriate for the effective maintenance of similar parking structures.

To perform the investigation, CAPREIT hired Dr. Jacques Marchand, President of SIMCO and expert in concrete durability engineering to coordinate site operations and cover all aspects of the investigation related to materials analyses and Dr. Denis Mitchell, President of Denis Mitchell Consulting inc., to take charge of structural analyses.

The investigation conducted on the two parking garages on Deguire Boulevard in Ville Saint-Laurent confirmed that the combination of construction defects and material degradation (for instance corrosion of reinforcement) can have very unfortunate consequences on the safety of reinforced concrete structures. For structures, such as buildings and bridges, these two phenomena, and their consequences, typically remain hidden for decades, and can only be detected using specialized (and often invasive) techniques.

The results of the investigation also emphasized the fact that parking garages are exposed to very aggressive environmental conditions, hence, they are susceptible to a wide range of degradation phenomena, among which reinforcing steel corrosion remains the most prevalent. This is particularly the case for indoor parking garages as de-icing salt penetration and steel corrosion is a temperature-sensitive phenomena.

While maintenance operations (such as deck washing) can contribute to extend the useful life of relatively new parking structures, they have little beneficial influence on the behavior of old and heavily chloride-contaminated structures. Once the corrosion reaction has been initiated, the only practical solution to extend the service life and maintain the safety of the structure is to rely on state-of-the-art repair techniques.

A comprehensive condition assessment of the two parking structures was performed using a wide range of different techniques to evaluate the quality of construction, characterize the in-situ concrete, determine the extent of damage and identify the factors at the origin of the collapse.