Polish Roof Collapse Kills at Least 12

[Lutfi]

This is very tagfic event. Read at Yahoo:

http://news.yahoo.com/news?tmpl=story&cid=514&e=4&u=/ap/20060128/ap_on_re_eu/poland_roof_collapse_16

This is the second roof collapse in Europe in less than one month.

Regards,
Lutfi

 

[JAE]

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?

 

[JStephen]

Maybe sawing through metal, which can also be done, perhaps preferable to torch cutting where there is a fire hazard.

 

[JAE]

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 members for the roof) didn't have any redundancy along with a weak link somewhere in the load path.

 

[HgTX]

Fatigue from cold?

Hg

Eng-Tips policies: faq731-376

 

[Ussuri]

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.

 

[corus]

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

 

[Yavoran]

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)

 

[JAE]

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.

 

[JAE]

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.

 

[Tomfh]

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...

 

[Ussuri]

JAE

Your figures are correct. 70 (0.69kN/m2) to 80 (0.78kN/m2) kg/sq.m is about 14 to 16 psf.

The UK loading code gives a minimum snow load of 0.6kN/m2. The snow load on the ground around Aberdeen-Inverness (North Scotland)is 1.0kN/m2. This will increase as the altitude increases.

From what I can gather from the eurocodes, which dont cover Poland and only go as far as Germany, the snow load at sea level is 1.2 kN/m2 (about 25psf). Again this will increase with altitude.

So based on that I would say those figures you quote are very low.

 

[IJR]

For those who want to have a look at the other side, here are a few points to think over:

1)this is the third I know,happened some 2 years ago, one happened in Moscow and killed at least 50(The Moscow water park,heavy dome). It was a reinforced concrete roof(ribbed membrane kind), resting on slender columns, Long span. Failure started by the movement of heavy snow-it was a buckling problem mainly(as seen by us), and the effect of chloride from the swimming pool(as reported by Russian engineers) on the durability of concrete.

2)All failures so far, have involved long spans and heavy snow loading.

Analysis after failure,most of the time, concentrate on heavy loading and ignores such issues as durability and stability.

best regards pals

 

[bushel3]

I agree that durability can play a role in failures. I read in one of the previous posts that the building was only seven years old. Is that old enough that durability should be a concern? In my mind a building that fails within seven years had a more severe problem than durability.

 

[SlideRuleEra]

I have preformed some "data mining" and come up with this link that may help give some insight thread507-86706

http://www.SlideRuleEra.net

 

[JAE]

Durability - in terms of fatigue - should not be an issue. Thermal swings just don't cause tensile fatigue unless the detail was extremely poor in design to begin with. And even then I'd doubt fatigue would be the issue. I still think that snow overload coupled with ponding or poor connections will be the ultimate cause...but we're all just speculating at this time.

 

[JAE]

Slide...your link indicates some posters believe the design snow load was in the range of 80 kg/m^2. Compared with the 14 stated in the article...I wonder if this is just a huge design error. Also - how do you convert from kg/m^2 to kN/m^2? I've always struggled with the SI force vs. mass thing.

 

[UcfSE]

Converting kg to kN should be a matter of multiplying kg, mass, by g, gravtitational acceleration (F=ma). In SI units, g is around 9.81m/s².

 

[civilperson]

The cause of extreme winters in North Europe could be global warming, which affects the Gulf stream coming from the tropics. Ground snow load in Albany, New York is forty pounds per square foot and roof loads in Tahoe, Nevada can reach 200 pounds per square foot. The cited loads for Europe seem extremely low.

 

[miecz]

JAE

I struggle with this as well. I think the confusion arises because multiplying by g converts to Newtons, not kN, as one would expect. 1kg weighs 9.81N. To get from kg/m^2 to kN/m^2 multiply by .00981. To get from kg/m^2 to psf, multiply by .2048161.