An underground parking garage collapsed and killed seven Swiss firefighters fighting a vehicle fire. How could this happen? Reinforced concrete is a composite material in which concrete provides the compressive strength and steel provides the tensile strength. Failure of the bond between the two destroys the composite and collapse results. See the picture of reinforcing steel rods added to a concrete bridge after it opened on p 331 of BCFS3.
Possibilities for Collapse
The concrete slab was post tensioned concrete. After it was in place it was decided that additional tensile strength was necessary or water leakage had corroded tendons and additional tendons were provided outside the beam without the protection the concrete provides to the tendons from the 800ºF heat(less than a self cleaning) required to cause the tendons to fail. The fire could have provided the heat and concrete may have spalled off, exposing the tendons
The concrete may have been inadequate to insulate the tendons. Apart from the fire, tendon corrosion from water may have weakened the tendons. This happened at an autorace track in the Carolinas. As I recall, a mandril was inserted in a precast concrete pedestrian bridge beam to position the tendons in the right locations. Concrete was placed in the form around the mandril. When the mandril was removed, concrete was placed in the void. The plug was not watertight and seepage corroded the tendon(s). Collapse resulted. Apart from the tendons, if the structure was precast concrete, metal connectors could have failed because of corrosion. The investigation will tell us what happened.
