huangyhg

polish roof collapse kills at least 12
this is very tagfic event. read at yahoo:
looks like heavy snow overcame the roof. curious that they talked about "sawing" out debris to get to people yet they later described the "metal" roof. maybe a wood structure with metal roofing?
maybe sawing through metal, which can also be done, perhaps preferable to torch cutting where there is a fire hazard.
there was a video link over at foxnews.com and it was definitely a steel structure. in fact, i saw some very unique steel members (multiple pipe columns tied together into a single column assembly) and the reporter on the scene stated that there were some type of rods or suspension ties holding the roof up (stay cable system?).
they also said that it had been very cold lately and the reporter pondered whether there was metal fatigue from the cold (never heard of that in a building with cold winters...). the building was about 7 years old.
i wonder if there was simply a too heavy snow, and the original design (with tension
fatigue from cold?
hg
last night the bbc reported two initial possible failure modes:
1] the weight of snow collapsed the roof. there was a quote from the owners/managers? stating they regularly cleared the roof from snow.
2] the intense cold caused the connections to fail because of environmental stress/strains.
one in germany and now one in poland. both caused in part by the extreme cold weather. no global warming here then.
it is doubtful that the weight of snow caused the failure as the snow had been cleaned off. the likely cause of failure is the ineadquacy of building/strcutural codes/engineers to consider thermal loads. presumably in a heated building with extreme cold outside there will be large temperature differenctials in the roof structure and walls. the restraint offered at the connections may well have caused excessive stresses and subsequent failure maybe by thermal ratchetting over the years. just a guess.
global warming, incidentally, is associated with extreme weather conditions, ie. cold/heat/hurricanes etc. and not with a general increase in temperature as such.
corus
jae may be rigth.
the problem in europe in the last few years is the dramatical change in the weather conditions.
the snowfalls are 2 times greater than usual. or at least from what is regarded as usual in the codes)
also the temperatures falling down to -35 for weeks ( every year!!!!).
this may be the reason why so many roofs colapsed lately.
so.
europe needs new codes reagrding the snow and wind loads.
this is for sure.
y
(to get it right assume you are wrong)
more data gathered from news sources:
1. there were attempts to remove snow build-up from the roof (according to the building owners) but they keep referring to rescuers removing snow from the collapsed roof to get the debris moved...which suggests that there was still considerable snow there.
2. one report stated that the structure was wood beams with concrete slabs.
3. someone else stated that the heated building may have started melting the snow in contact with the roof. in which case, ponding may have played a part.
i recall a roof collapse in san antonio, texas, some years ago after san antonio received 13 inches of snow (yes, i know it doesn't snow in south texas but that year it did). the roof collapsed due to melting snow and the water couldn't get to the roof drains at the back of the roof area due to ponding.
enr reports the building's designer stated that the design was based upon 70 to 80 kg/sq. m. is my math right or does this convert to 14.4 psf? just checking. compared to the midwest us - that's low. we usually see snow loads of 17 to 21 psf for flat roofs...more if rain-on-snow is included.
i don't live in a snow area. is it common to require owners to regularly clear roofs of snow? that seems like a recipe for disaster to me. i have always despised solutions that require people doing things. people are lazy...

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