bridge collapse

huangyhg

bridge collapse
making the news the present time.
a bit more detail here:
we'll watch this unfold.  montreals bridges and overpasses are very complex, convoluted, and in various states of deterioration.  all built of reinforced concrete some 30 years ago and subjected to a very harsh environment of chloride based deicers.  the supreme court of canada ruled in the last several years that all construction in quebec must be unionized to avoid the 'problems' with the construction industry of the past.  we drive through montreal often and wonder about its infrastructure.  this problem will boil down to money and political will and lets hope finally will be put on the front burner.  five people dead.
connect2, are you familar with this kind of bridge?  it appears to be a vaulted abutment that reaches out toward the roadway and has the concrete slab (or girders) bearing atop the abutment seat.  it looks like a single span.  
from the pictures i couldn't tell if the superstructure is concrete slab or slab on girder.
i'm very interested in learning more about this type of bridge.
much thanks
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
it does not look good for the authority according to the following news.
five dead.
hmmm...seems like abrupt failure with no evidence of the impending collapse during a previous bridge inspection.....shear failure is abrupt.
from the fox news article in my first post.
"the incident occurred before 1 p.m. (1700 gmt) one witness told tva he noticed that the road sunk by 1 to 2 inches (2.5-5 centimeters) when the traveled over the overpass minutes earlier and called emergency dispatchers at 12:30 p.m. (1630 gmt)."
was this a warning unheeded?
a road crew cleaned up some pieces of concrete from the roadway below a couple of hours before the collapse.
the bridge does seem to have a cantilevered bearing seat which is common in the area.  i think it's a two span bridge with simple spans.  a quick glimpse i got from a video seemed to show that the bearing seat and a large portion of the abutment face sheared off diagonally.  some horizontal rebar are also seen extending from the top of the abutment indicating a possible lap/bond failure at the critical point.  the abutment would have been simply reinforced, not prestressed, so it would have cracked, perhaps at the back of the bearing seat, early on in order to mobilize the top horizontal steel.  this bridge would have also had an expansion joint directly above the bearing seat.  after 36 years (built around 1970) of deicing salt and a leaking joint seal (inevitable) any significant cracking at the top would have lead to likely corrosion of the top rebar.  a public inquiry has been called and it will interesting to see if an expanding crack at the back of the bearing seat and probably down the sides of the abutment have been overlooked during inspections over the years.
they've now closed a similar bridge and are looking at 45 more.  the quebec construction industry had problems with organized crime about the time of construction.  we'll see if that played a part.
a local professor said that since the bridge survived 36 years it meant that the design/construction was ok and that it must have been simply poor maintenance.  while it's true that poor maintenance is a likely contributing factor even a compromised design or construction mistakes/shortcuts  can survive for a while until it's luck runs out due to it's reduced safety index.
in a way it's good that this didn't happen during construction with private contractors involved.  legal suits involving private interests tend to result in publication bans on engineering reports as part of any settlement.  there have been many cases where the engineering profession can't learn from the failure due to these bans.
sorry for the long post.
i see a parallel between falling concrete and industry where a part keeps failing and is no problem as long as there is a spare in the parts bin. here the there is no problem until the cleanup crew doesn't have any concrete to cleanup.
some good pictures available at
looks like a fairly standard 'half-joint' (or 'halving joint') bridge.  britain has quite a few similar bridges on their older motorways that are 30-40 years old.