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Polish Roof Collapse Kills at Least 12

Polish Roof Collapse Kills at Least 12

RE: Polish Roof Collapse Kills at Least 12

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?

RE: Polish Roof Collapse Kills at Least 12

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

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

Fatigue from cold?

Hg

Eng-Tips policies:  FAQ731-376

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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

RE: Polish Roof Collapse Kills at Least 12

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)

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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...

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.

RE: Polish Roof Collapse Kills at Least 12

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.  

RE: Polish Roof Collapse Kills at Least 12

Units...I must admit I find the US way of doing things complicated, (kips, k-ft, psi, psf etc).  I guess its what you are used to .

I did a little more digging in the Eurocode to see what it would have suggested for a snow load.  I have never used it so, if I have got it wrong, please dont shoot me.

Katowice is in the south of Poland at an altitude of 284m.  BS EN 1991-1-3:2003 Figure C.13 gives the snow map of Poland and from what I can gather the town is on the border of Zone 2 and Zone 3.  The snow load on the ground sk=0.9 kN/m2 for Zone 2, and sk=(0.006*284)-0.6 but not less than 1.2kN/m2 for Zone 3.

There is also a requirement for an exceptional snow load, sad=2.0*sk=2.4kN/m2.

The corresponding snow load on roof (I have had to guess as I dont know roof pitch, GA etc) s=mu*Ce*Ct*sk or sad
giving s=0.8*1.0*1.0*2.4= 1.92kN/m2 (40psf)  or 0.96kN/m2 (20psf).

Sounds like these ae still substantially lower than you apply in the US.

200psf = 9.6kN/m2 is very high.  That is well in excess of the floor loading we use for say a plant or boiler room (at 7.5kN/m2), including weight of machinery.

RE: Polish Roof Collapse Kills at Least 12

That 200 PSF is in a ski area, with exceptional snowfall, not very many places in the US would be designed for that.

As to the US units being complicated...all through school & college, we are taught the SI system- then find in the real world, people are using kgf/cm^2 and other oddball units.  And even the SI system has its oddities- why is the fundamental unit a KILOgram, and not a gram?

RE: Polish Roof Collapse Kills at Least 12

Good question, I have absolutely no idea.  

I guess when they were picking the seven base units for the SI system someone had an off day, because length is in metres as opposed to KILOmetres.

RE: Polish Roof Collapse Kills at Least 12

Most of the snow loads in the US vary from 0 in the southern half (using roof live load = 20 psf) to around 20 to 30 psf in the mid states to 60 psf in the far north (I think Maine has 100 psf ground snow in the far north regions).

Out west, with a drier climate in the mountains, the snow load drops except in the higher altitudes of the mountains such as JStephens pointed out.

In my area (midwest - Nebraska/Iowa) the roof snow usually comes out at about 17 to 21 psf.

RE: Polish Roof Collapse Kills at Least 12

This was printed in the New Civil Engineer Yesterday.

Quote:

Published 02 February 2006 at 08:00  
 
Outdated loading codes triggered Polish collapse  
 
 
 
Outdates snow loading requirements in Polish building codes have emerged as the key contributing factor to Saturday’s collapse of the flat roof of an exhibition hall in Katowice.
More than 60 people died in the tragedy and the search for bodies was still continuing as NCE went to press.
Around 500 visitors were attending a racing pigeon exhibition in the Katowice Trade Hall when the collapse occurred.

The seven year old, 100,000m2 building was experiencing the worst winter by far since it opened. It is reported to have had more than 500mm of compacted snow and ice on its roof at the moment of collapse.

The roof of the steel framed building is reported to have been designed to take up to 800mm of normal snow, then in line with the local codes.

But a recent analysis of Polish snowfall records over the last 50 years has found that in some areas the design snow loading should be up to 70% higher.

Recent prolonged sub-zero temperatures could also have increased the chances overloading from snow and ice.

“Under those conditions heat leaking through the roof can melt the lower layers of snow, which refreeze as ice when the heating is off,” said Steel Construction Institute director Graham Owen. “Over time the density of the ‘snow’ will approach that of water.”

Owen added: “The roof trusses were more than 10m above floor level. At that height any excessive deflection would have been very hard to spot.”

Dave Parker

 

RE: Polish Roof Collapse Kills at Least 12

Speaking of SI, how normal is it to say "500 mm" rather than "50 cm" or even "half a meter" in that context?  It's not like they knew the depth of the snow even to the nearest 5 mm.

Hg

Eng-Tips policies:  FAQ731-376

RE: Polish Roof Collapse Kills at Least 12

Generally speaking, in my experience, millimetres are used for all measurements, up to say 100 metres.   But I guess it will depend on industry and application (eg roads).

For instance we rarely use centimetres, and I have never come across decimetres.


RE: Polish Roof Collapse Kills at Least 12

Huh.  In Israel the centimeter is the standard conversational unit, used in very much the same situations where we in the US use "inch".

Hg

Eng-Tips policies:  FAQ731-376

RE: Polish Roof Collapse Kills at Least 12

Hg

Units used by the general public in the UK can be anything.  I was taught centimetres at school, my family use feet and inches, miles etc. In day to day things (non-engineering) I will use a hotch-potch of units, metres, miles, gallons, pints, stone.  I only use feet and inches when giving my height though.

At work however, its only millimetres for lengths and metres for levels.

Its all a bit of mess really, and I think as long as everyone is clear what unit is being used it doesn't make much difference.

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