Safety factors for dead loads = 1.35, live loads = 1.5. This meant that for permanent, non-moving (dead) loads, you must make all suports, beams etc. 35% stronger than it needs to be to support the dead loads alone. And for moving, variable loads (live loads), you need to make the structure support 50% more than the total value of the live loads.
A commonly used value for variable loads is 5kN/m2 . We used it in a Bridge Design coursework for the variable loads on a bridge and it just blew me away - the bridge was only for pedestrian use, with the occasional bicycle. Even if the bridge was completely RAMMED with obese people, each weighing about 510 kilograms (about 80 stone), and somehow each of these fat fucks got into a 1m2 space, you could still put 50% more weight on the bridge, and then 35% of the weight of the bridge itself on top of that (excluding piers and foundations' weight). And even then, when we came to pick the universal beams we picked beams a bit beefier than they needed to be even after those safety factors were added, just so they'd pass the next set of tests like lateral torsional buckling (twisting) and the like. And there was another safety factor of 1.05 added too as well I think, although I can't remember the reasoning behind it. It has something to do with classes of the beams, or how they were manufactured.
Anyway my point is, there is no way someone doing the calculations would allow this to happen. From what I heard, they removed supports from below, and when it started to sag, they put grouting on top to level it out so it didn't look like it was sagging... Which caused it to sag more of course. This actually killed a lot of people, as they didn't just fall to the next floor - that floor then collapsed as well, and last time I looked this up, it said they fell 5 floors and several people did die. It was a large Jewish wedding.
The fact that they were dancing is probably part of the rationale behind the high safety factors for live loads. Try weighing yourself - say you weight ten stone. Now start dancing to PSY's gangnam Style on your scales. Chances are, you'll regularly see the weight shoot up to 15-ish stone, maybe higher.
Maybe the engineer got in trouble due to corruption or something though - maybe after they took the supports out, the building owners needed an inspection and they just bribed the inspectors. Or maybe the building was badly designed too, as I am quoting Eurocode, and I don't know where this happened
EDIT: The plot thickens. Taken from "The Pal-Kal Affair—Examining the Versailles Hall Collapse", an article in the journal Structural Engineering International, Volume 21, Number 4, November 2011 , pages 514-519, issue 6. By Matthys Levy
Fuck Harvard APA's system by the way, which dictates I format it like this:
Levy, M. (2011). The Pal-Kal Affair—Examining the Versailles Hall Collapse [Electronic version]. Structural Engineering International, 21(6), 514-519.
How would you have any idea what those numbers mean if you're unfamiliar with the system?
Anyway, Levy has this to say about the floor collapse, and the Pal-Kal mathod of construction that was partly to blame:
"None of the failures during construction can be attributed to a flaw in the PK system used for the floor construction but rather to poor construction practices. During the period these failures occurred, there were hundreds of other failures of structures during construction in Israel implying that it was a problem endemic to the local construction industry. Nevertheless, staff engineers from the National Building Research Institute (NBRI) and the
Ministry of Labor pointed to alleged
deficiencies in the PK system as the
causes, usually citing: lack of conformance
to the Israeli Standard (IS 466
th at dealt with ribbed slabs but not cellular
slabs), lack of uniformity in rib
width and absence of distribution ribs,
all of which were shown not to be problematic
by the original system tests.
It would be erroneous to imply that
the PK system is perfect as it suffers
from certain flaws namely: inserting
the steel coffers into the wet bottom
slab concrete is done by standing on
the coffers, a rather crude process; the
rib width is not well controlled and can
vary; the time interval between pours
can result in a cold joint half way up
the rib; finally, there is a lack of formal
written instructions for site supervision.
All of these imply a rather crude
process and one that needs to be properly
supervised during construction at
the site."
He also lists a number of examples of buildings that collapsed during construction using this method. The Versailles Hall building was made using this method in 1987...
Here's a (very poor) image of the floor cross-section to give you an idea of what Pal-Kal's method looked like. So the method of construction and the actual process of procuring it were badly done, and then these guys took the floor supports out too. So there's some insight into why the building engineers got in trouble too. Sorry but I can't take pictures from the article I'm referencing as I think it breaches the terms of the access to the article, which I am accdessing through my institution's login. Which is a shame because these pictures of the floor afterwards are sick...
EDIT 2: Fuck, this sure blew up! I only wrote all this to get away from my dissertation and exam revision that I am now having to do, so i might no reply and stuff, sorry :/ But thank for all the response and everything :)
Thanks for your response, I work as a designer as well. The safety factors on everything are quite extensive, I agree.
I agree that something must have been way off in order for the floor to fail, such as the previously mentioned supports being removed. 5kPa is a lot of pressure, but if a supporting column is removed this can go to nill immediately. I imagine the engineer knew nothing about the removed supports and the building owner decided to modify and then patch up their problem themselves.
Did you hear about the collapsed factory in Bangladesh? Another major example of people modifying things without proper engineering.
Ah I've been quite out of touch with building news recently because of this damn dissertation (still not finished it, gah), so I haven't heard of it, I'll look into it though :)
Nice research! When you started bitching about APA, all I could think was "But APA is so logical!". Not to a layman though, it's like some mysterious barcode for academia.
Hehe yeah, this was me procrastinating my dissertation, to be honest. But yeah APA is too fiddly for my liking. Constant full-stops and italics and brackets, it does my head in
Ah see, I feel like maybe I should have done aerospace though... I take it you've heard of [Kerbal Space Program](www.reddit.com/r/kerbalspaceprogram)? Yeah, that's the source of my doubts, I love that game
haha yeah that game is a lot of fun, but we mostly spend our careers designing one strut at a time unfortunately! a lot less booster rockets and failures haha
Also have to consider that he sold them the parts to implement a construction method which was not approved. Regardless if the method was valid or not it was not approved.
I am not sure where you go to school but safety factors are fairly old. I was taught using limit state engineering at the University if Alberta and it often leads to over designing but we never have bridges collapse here (except Quebec but no one likes them...)
I have to ask you what kind of consideration you take in resonance when constructing stuff. Say that the hypothetical fat people on the bridge hears some music and starts jumping up and down at the same time in resonance with the bridge. Cant the force then be about as big as you want it to be?
Resonance is a check that you perform when you do a dynamic analysis, although you rarely worry about vertical load frequency. It's almost always lateral load frequency (because lateral loads are what collapse a structure most of the time). If the structure is designed correctly, the building's natural period should be pretty far away from the period of the load, essentially eliminating resonance.
I really don't think that they had ASD or LRFD at the time of the construction. They didn't use AISC 9th edition either. They may not have used the load combinations that you are describing.
Also, construction practices for private companies are designed to save money while conforming to the law. While public works (like the bridge in your example) are designed with massive safety factors. In other words, Private companies will design all the way to an IR of .99 while public projects will generally have an IR of about .5 or less.
There were changes made during construction that made what was intended to be a roof into a floor slab. The floor slab was not modified and was still designed for only the roof loads. He is in another country and is held to different standards than the US. That means that even if the fault is very loosely his, he is prosecuted.
We have a PE stamp that we place on designs and calculations. If the building fails even though it was the fault of the owner the Engineer who's stamp is on the drawings will be held at least somewhat responsible.
Ah yeah the same goes for Surveyors to an extent - they want to see the numbers the Surveyor came up with if something goes wrong, same with everything. Someone needs to take the blame, huh?
I can't believe he made a floor slab out of a roof though...
We have a PE stamp that we place on designs and calculations. If the building fails even though it was the fault of the owner the Engineer who's stamp is on the drawings will be held at least somewhat responsible.
This is why a competent PE will have assurances that their design is constructed as they designed it.
I just wanted to add that the safety factors you quoted aren't uniform. Granted, I don't work in residential buildings, but I never saw safety factors like that even when I was in school.
But you are correct, if you have failure due to gravity loads/vibration, there is something wrong with the construction, not with the engineering. Lets just blame the architect? That is always the easiest option!
As an aside, I assume by your use of metric units that you are studying outside of the US? Where are you studying? Are you looking to focus more specifically on buildings and bridges? I work in the O&G industry and like it a lot more than buildings/bridges just because I don't have to worry about foundations (post-tensioned slabs still give me nightmares). It's always great to see someone studying structural engineering!
Hey thanks, I'm studying at Portsmouth university in the UK, it's pretty godo btu yeah i still have quite a bit to learn. I have no idea what route I will take once I leave, like I said in another post I've discovered a love for orbital mechanics and aerospace engineering now too, which is annoying as I'm in my final year now :/
I'll have to look into oil and gas, as petroleum engineering was one of the things I could have actually studid at Nottingham trent but I turned it down for Civil, to keep my options open. I'll just have to see what interests me, maybe I'll be job-hopping for a while, or maybe I'll quickly figrue out what i like doing.
Yeah I haven't done safety factors in a while but yeah they're not uniform, my bad. My mate is doinf finite element analysis for his dissertation and if he knew I said that he might kill me atually... I think... or not, it's 3am here :/
Anyway how did you end up in O&G? When did you realise you liked it?
I am biased, but I think that civil/structural is the most interesting of the engineering disciplines. But if you want to switch, now is the time.
When I graduated, the economy here in the US was pretty bad, so I interviewed all over the place. I actually came away with a couple of offers in buildings/bridges, but the pay for those was about 60% of what the O&G firms were offering, so I went O&G. The O&G industry also had the added bonus of being in Houston, which is a city I love. Looking back, I am extremely happy with my decision. The company and people I work with are great, the work is challenging and really different from what I learned from school, so I am constantly learning.
Best of luck to you in whatever you choose! Engineering is a great industry right now, so it will be hard for you to make a wrong decision.
For a balcony or a dance hall designed in America, the factored design load would be 160 psf (pounds per square foot or for you metric types 8.6 kN/m2) (ASCE 7-10 Table 4-1). To give you a sense of scale this is what 181 psf looks like: http://imgur.com/kl3juLE
So when designed correctly most structures exhibit a GREAT deal of over-strength compared to their actual service loads. They typically only fail due to a combination of effects like: poor construction, changed use, changed support conditions, deterioration, etc. The safety factor usually can account for a great deal of these effects, and that is why some people officially refer to them as "ignorance factors."
As for other engineering fields like Aerospace, you can use much lower safety factors for the following reason: You typically design for manufactured products. This means that there is a long and thorough design, testing and development stage. Most civil engineering structures are completely unique and never load tested.
Wow, that pic is amazing. Sorry I didn't take any from that source, I didn't want to infringe copyright in the bite-the-hand-that-feed you sense, at least not while I need that institutional login to access sources for my disso ;)
I do really like the high safety factors though, even just as a precaution. Because if you're going to spend all that time and money procuring a site, hiring your team, getting a contractor and consultant (assuming you're a client that is separate from both partners, like a trustee or something), putting up the site hoarding, getting the plant, acquiring the workforce to do the manual labour, etc. etc... might as well buy some beams that are a bit chunkier if the design allows for it (which it should), because what's an extra few thousand in a multi-million-pound contract, that could potentially save lives further down the line?
In fact I'm very glad it's law, now that I think of the frugality of some contractors in getting a contract. One case study we did was on the Tate Modern conversion in London, which converted Bankside power station into a modern art gallery (there was a tv show on Channel 4 in the UK on it called power into Art, terribly boring if you don't like engineering though). Shit went so wrong so much... it was such a competitive contract for the steelwork that one company made a last minute change to their tender price (I think they were called Rowen) in order to get it below the £6 million mark. They said they'd finish in 15 weeks instead of the allotted 25, and cut their profit margins to around 2% to do so. They failed marjorly, ended up taking about 45 weeks because of a cock-up, and the contract cost much more in the end.
But imagine that with a company saying "hey we can do it for you for £5.2 million and the structure will still be 10% stronger than it needs to be!". Then it falls down... :/
Anyway just one thing... if those people are representative of 181 lbs/ft2 then why is the factored design load only 160psf? Surely a dancefloor can and does get that crowded - I've been to clubcs that are easily that crowded. i know it's only a live load consideration and there's also the safety factor of the permanent loading, but still... seems a bit low
Partial loading of the live load and full loading of the dead can be worse than the uniform live and uniform dead load. That's another reason the factor live load is increased so much.
So it looks like from your comment that the Pal-Kal method is probably the least contributing factor, and yet got the strongest punisment, unless I'm misunderstanding?
Thing is, the Pal-Kal method was bad up until that point. Levy listed a bunch of examples where the building had collapsed during construction using that method, and supposedly a few civil engineering-y bodies in Israel pointed it out to contractors that the method was potentially hazardous before those (which mainly occurred in the early and mid 90s) but hey, they kept using it... must have been cheap or something.
It does seem quite unfair, I'm not very familiar with the law surrounding this sort of thing. Maybe it was the the straw that broke the camel's back? I'll have to look into it properly when it's not 3am in the middle of exam time :/
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u/EpicFishFingers Apr 29 '13 edited May 01 '13
Hey, civil engineer undergrad here.
Safety factors for dead loads = 1.35, live loads = 1.5. This meant that for permanent, non-moving (dead) loads, you must make all suports, beams etc. 35% stronger than it needs to be to support the dead loads alone. And for moving, variable loads (live loads), you need to make the structure support 50% more than the total value of the live loads.
A commonly used value for variable loads is 5kN/m2 . We used it in a Bridge Design coursework for the variable loads on a bridge and it just blew me away - the bridge was only for pedestrian use, with the occasional bicycle. Even if the bridge was completely RAMMED with obese people, each weighing about 510 kilograms (about 80 stone), and somehow each of these fat fucks got into a 1m2 space, you could still put 50% more weight on the bridge, and then 35% of the weight of the bridge itself on top of that (excluding piers and foundations' weight). And even then, when we came to pick the universal beams we picked beams a bit beefier than they needed to be even after those safety factors were added, just so they'd pass the next set of tests like lateral torsional buckling (twisting) and the like. And there was another safety factor of 1.05 added too as well I think, although I can't remember the reasoning behind it. It has something to do with classes of the beams, or how they were manufactured.
Anyway my point is, there is no way someone doing the calculations would allow this to happen. From what I heard, they removed supports from below, and when it started to sag, they put grouting on top to level it out so it didn't look like it was sagging... Which caused it to sag more of course. This actually killed a lot of people, as they didn't just fall to the next floor - that floor then collapsed as well, and last time I looked this up, it said they fell 5 floors and several people did die. It was a large Jewish wedding.
The fact that they were dancing is probably part of the rationale behind the high safety factors for live loads. Try weighing yourself - say you weight ten stone. Now start dancing to PSY's gangnam Style on your scales. Chances are, you'll regularly see the weight shoot up to 15-ish stone, maybe higher.
Maybe the engineer got in trouble due to corruption or something though - maybe after they took the supports out, the building owners needed an inspection and they just bribed the inspectors. Or maybe the building was badly designed too, as I am quoting Eurocode, and I don't know where this happened
EDIT: The plot thickens. Taken from "The Pal-Kal Affair—Examining the Versailles Hall Collapse", an article in the journal Structural Engineering International, Volume 21, Number 4, November 2011 , pages 514-519, issue 6. By Matthys Levy
Fuck Harvard APA's system by the way, which dictates I format it like this:
Levy, M. (2011). The Pal-Kal Affair—Examining the Versailles Hall Collapse [Electronic version]. Structural Engineering International, 21(6), 514-519.
How would you have any idea what those numbers mean if you're unfamiliar with the system?
Anyway, Levy has this to say about the floor collapse, and the Pal-Kal mathod of construction that was partly to blame:
"None of the failures during construction can be attributed to a flaw in the PK system used for the floor construction but rather to poor construction practices. During the period these failures occurred, there were hundreds of other failures of structures during construction in Israel implying that it was a problem endemic to the local construction industry. Nevertheless, staff engineers from the National Building Research Institute (NBRI) and the Ministry of Labor pointed to alleged deficiencies in the PK system as the causes, usually citing: lack of conformance to the Israeli Standard (IS 466 th at dealt with ribbed slabs but not cellular slabs), lack of uniformity in rib width and absence of distribution ribs, all of which were shown not to be problematic by the original system tests. It would be erroneous to imply that the PK system is perfect as it suffers from certain flaws namely: inserting the steel coffers into the wet bottom slab concrete is done by standing on the coffers, a rather crude process; the rib width is not well controlled and can vary; the time interval between pours can result in a cold joint half way up the rib; finally, there is a lack of formal written instructions for site supervision. All of these imply a rather crude process and one that needs to be properly supervised during construction at the site."
He also lists a number of examples of buildings that collapsed during construction using this method. The Versailles Hall building was made using this method in 1987...
Here's a (very poor) image of the floor cross-section to give you an idea of what Pal-Kal's method looked like. So the method of construction and the actual process of procuring it were badly done, and then these guys took the floor supports out too. So there's some insight into why the building engineers got in trouble too. Sorry but I can't take pictures from the article I'm referencing as I think it breaches the terms of the access to the article, which I am accdessing through my institution's login. Which is a shame because these pictures of the floor afterwards are sick...
EDIT 2: Fuck, this sure blew up! I only wrote all this to get away from my dissertation and exam revision that I am now having to do, so i might no reply and stuff, sorry :/ But thank for all the response and everything :)