At approximately 5:45 am on 16 May 1968, resident Ivy Hodge went into her kitchen in flat 90, a corner flat on the 18th floor of the building, and lit a match to light the gas stove for a cup of tea. The match sparked a gas explosion that blew out the load-bearing flank walls, which had been supporting the four flats above. It is believed that the weaknesses were in the joints connecting the vertical walls to the floor slabs. The flank walls fell away, leaving the floors above unsupported and causing the progressive collapse of the south-east corner of the building. Source
One issue with pre-cast concrete slab construction involves the joining of one slab to its neighbors. Robust construction requires that surrounding structure be integrated enough that the load carried by one element can be carried by its neighbors in the event one of them fail. Poor integration means that load cannot be diverted to the neighboring structural elements.
Incidentally, John D. McDonald wrote a superb book titled Condominium. Yep, the condo building collapsed in the story with a little bit of help from a hurricane. One of the contributing factors was that the pilings were not a continuous pour as required by code and best practice. Frequent downpours resulted in silt washing into the borehole covering the exposed surface from the interrupted pour which then prevented the next pour from adhering to it
I suspect good old John D (famous for his Travis McGee series) did research and asked construction guys "What are the most glaring examples of bad practice you see in the construction of Florida condos?"
When everybody is building it is difficult for suppliers to meet the demand and interrupted pours happen.
I was wondering when someone was going to bring up John D. McDonald. Not only is "Condominium" prescient it's a real good read and you can probably grab a copy used for almost nothing. Fair warning: The "Travis McGee" series is highly addictive.
ReplyDeleteI am sure there was some "Payola" to the building Inspectors to look the other way. There always is, besides cops, Planning and Building Inspection Departments that are bent three ways to Mondays. Always follow the money. The clincher? The pilings were not a continuous pour...
ReplyDeleteIf there's more than a 30 minute interruption in the middle of a concrete pour, you will get a "cold joint."
ReplyDeleteIn a house foundation with continuous rebar, it's not going to matter much more than being a minor inconvenience.
In a commercial high rise, a "cold joint" can present major problems. We had one in a Post Tension Cable slab pour one time. 480 yards of concrete and the two closest batch plants went down with maintenance issues. So not only was the concrete coming from another plant from across town in a major metro area, we were getting "hot loads" of mud, which is just as bad as a "cold joint."
Not just Florida. Obviously. Less obvious, not just condominiums or high rise structures.
ReplyDeleteI was a home builder for several decades. The ability to pour a monolithic structure was always paramount. My solution was to hold off the pour until every element was in place and ready. I understand on larger projects there is not that level of 'float' allowed in the schedule. But it is no less paramount. When they cut that corner, someone pays.
I did work on a high rise in Seattle. The inability to make a monolithic pour ended up delaying the project for 4 months, then again for some indeterminate time. I left the project at that point.
Mike Guenther mentions an important point of 'hot loads'. Batch plants will sometimes alter the mix to allow extended travel time. The crew at the jobsite must be aware of this and be prepared to reject a truck. I have rejected trucks precisely for that reason. Be prepared to stand firm against the raised tempers at that point.
Any good construction management university program should have a materials lab to demonstrate these concerns.
Thanks for commenting.
DeleteAll these 'senseless, nit-picking' rules in construction are written in blood and treasure, but every few generations we have to learn them again. Kipling's "Gods of the Copybook Headings" and "Hymn of Breaking Strain" should be required reading in engineering school.
ReplyDelete