Pre-fab construction can save a lot of time and money when it comes to relatively simple structures like parking garages, but sometimes the piper comes to collect. Last October, a big chunk of a five-story, pre-fab parking garage at Miami Dade College’s west campus collapsed, killing four workers.
Not only did the collapse kill the workers, it also forced a three-month closure of the campus and spawned a flurry of lawsuits against the builder, Ajax Buildings Corp.
The investigation into the collapse is on-going, but it is focused on three possibilities: A construction error; a flaw in one or more of the pre-fab pieces; and possible damage from a crane that struck the structure days before the catastrophe.
Pre-fab garages are common. Crafting the giant slabs off-site and bolting them together at the final location is much more economical than building the garage from scratch. But, like the popular wooden blocks game called Jenga, the whole thing can come crashing down if key pieces are not properly placed. Until the whole garage is up and the pieces are bolted and welded together, the semi-finished garage is unstable.
The floor slabs of one section of the garage all crashed down in one direction, and remained attached to the wall. This has led engineers to speculate that construction error is to blame, rather than design. Perhaps the pieces were not placed in precisely the correct order, or perhaps the connecting bolts and welds were not added correctly. When one part of the floor began falling, it knocked the rest down in that section like an accordion folding onto itself.
“I would look at erection procedures — that’s probably the one question to ask first,’’ said Mark Santos, a Miami structural engineer, in an article in the Bradenton Herald.
While construction error seems to be the most likely reason for the collapse, another possibility being raised is that there was some flaw in one or more of the prefab pieces.
Pre-fab concrete pieces are generally considered to have a smaller likelihood of flaws, because they are cast in controlled factory conditions. Nevertheless, flaws – often internal, and thus difficult to observe – have been found in pre-fab garage pieces lately. An article in the January 2011 issue of Journal, a publication from Hoffmann Architects, Inc., about flaws in pre-fab garages, notes:
“[T]here has been a spate of precast concrete parking garage failures in recent years. While some have been catastrophic and highly publicized, the vast majority of failures don’t make the headlines. Nonetheless, if ignored, even inconspicuous defects can lead to dangerous conditions. The average motorist would be shocked to learn that upwards of tens of thousands of precast concrete structures exhibit some degree of structural distress.” (To read the whole article, click here)
Finally, the possibility exists that the structure was damaged by a crane that struck a column on the outer portion of the building two days before the collapse. The crane and column were inspected after the accident and work was allowed to continue, but the possibility that some invisible damage was caused exists.
Investigators hope to have answers to what caused the collapse later this spring. The bottom line is that an error somewhere along the line – either at the pre-fab plant or at the construction site – caused a catastrophe that cost four lives.