We get daily temperature variations up to 40 degrees F and loud noises due to expansions and contractions are a regular occurence, even in fairly old buildings.

Cheers

Greg Locock

I used to live in a house with a flat roof, in the winter you'd hear the occasional bangs, sounded similar to a shotgun. What we finally figured out was the ice on the roof was cracking as it expanded and contracted, it would scare the s**t out of someone that wasn't used to it. After awhile you didn't even hear it....Mike

Are there any expansion/contraction joints in your building?

Mike - I'm buying the ice theory. It makes sense as today was freezing again but the sun was beating on the roof during daylight, no popping/banging. Come 3:30 and after when the sun stopped hitting the room, the bangs came back, intensifying up until about 5:30.

I'll go up there tomorrow and re-post what I see.

Watermelon, I'm not sure. I only see joints in sheetrock in long corridors. Roof is membraned over, exterior is stucco'd. If I had to bet, probably not sufficiently, if at all!

Thanks for your inputs! -CB

Could there be the equivalent of finger clickers in the roof, i.e., shells that are dimpled in one direction and forced to deform into the other?  That would make a nice pop or bang.

TTFN

Hi ChasBean1:

Good idea to check the roof load and not make any assumption.  The old adage comes to my mind: when I ASS-U-ME, I make an ASS out of U and ME.

My understanding of expansion/contraction joints is they should be added when buildings approach 120 feet.  I will probably be shot down on this site for saying that, but oh well.  Your building measures approx 175 x 175, so one might expect to see a joint.

Next, they are easy to I.D.  You should see joints in the exterior, in the floors and maybe columns very close together at the joint.  If you had them, you'd know.

It sounds to me like there is some kind of movement taking place as a result of temperature changes.  Maybe some joists that are not welded down.

My only concern is this: (and I don't want to ring any alarm bells)  When a weld snaps suddenly, it makes a sound like a gun being fired.

Best you grab a flashlight, remove some ceiling tiles and have a look-see.  Due diligence.  Get the snow off the roof first.  And don't stockpile it on the roof.

A common cause of banging in steel buildings is bolted connections.  More likely to occur than the failure occurance of the weld, this occurs when the bolt overcomes the friction force of the nut and the bolt slides into contact with the side of the hole thus banging and becoming a bearing condition.

I experienced this peculiar phenomenon a few years back from my house. Repeated violent bangs coming from the roof (typical sloped wood trusses and plywood construction) that woke us from our sleep and it was scary. No damage to the roof. Later that evening, it was on the news, so it was fairly widespread in our area. If I recall the explanation was "Ice snapping/breaking off the roof surface"

I have not experienced such "bangs" since.

With regard to bolt slipping, I have witnessed several full scale transmission tower tests. These towers are loaded until they collapse. Loud noises are normal and they come from bolts slipping into bearing. However, they are different from the "roof bangs" Also, we start hearing "bolt bangs" when loading is beyond 75%. I don't think buildings are ever loaded beyond 75% of their structural capacity.

No doubt, an interesting topic.

AISC has a lot of information on the banging bolt phenomenon.  This may or may not be germaine to your case since it may be temperature and not load dependent and the banging bolts can only occur once per connection after the slip into bearing.  An interesting way to check this phenomenon is to loosen a bolt in the top row of a beam connection and listen to the sound.  The company I used to work for investigated this about fifteen years ago and that proved to the then skeptical AISC that this can sporadically occur with TC bolts due to the high initial pretension.  Here's a link from AISC on the subject of banging bolts: http://www.aisc.org/Template.cfm?Section=Search&template=/Search/SearchDisplay.cfm