Pittsburg Convention Center failure
Pittsburg Convention Center failure
(OP)
This article on ENR is about a failed section of floor at the Pittsburg DLL Convention Center. I note the following statement from the article:
The structural-steel slip connection of a girder at the X-9 expansion joint that runs in the short direction of the David L. Lawrence Convention Center in Pittsburgh is a detail that at least some structural engineers don’t favor, a source told ENR.
htt p://www.en r.com/news /buildings /archives/ 070222.asp
I guess I’m surprised that anyone would design a thermal slip connection in framing where the slip occurs via bolts sliding in horizontal slots. What they describe happened was that the bolts eventually gouged out the hole and reduced the ability of the connection to slip.
I’ve for years never used this detail (not that I’m all that smart) but because I was taught that you use either double support beam/column arrangements or Teflon seats (which apparently is the resulting repair).
Is this expansion joint via slotted hole detail used that much? I’m just surprised it was used on a project of this magnitude.
The structural-steel slip connection of a girder at the X-9 expansion joint that runs in the short direction of the David L. Lawrence Convention Center in Pittsburgh is a detail that at least some structural engineers don’t favor, a source told ENR.
htt
I guess I’m surprised that anyone would design a thermal slip connection in framing where the slip occurs via bolts sliding in horizontal slots. What they describe happened was that the bolts eventually gouged out the hole and reduced the ability of the connection to slip.
I’ve for years never used this detail (not that I’m all that smart) but because I was taught that you use either double support beam/column arrangements or Teflon seats (which apparently is the resulting repair).
Is this expansion joint via slotted hole detail used that much? I’m just surprised it was used on a project of this magnitude.






RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
I've also used a seat (similar to what the article suggests was the repair concept) where the beam sits atop a steel seat with a teflon pad connected to the beam which rests upon another pad (either teflon or stainless) which is bonded to a steel backer plate. The whole teflon arrangement usually has some slotted holes to allow bolts to restrict any ultimate sliding-off that might occur. The bolts are vertical and connect the seat to the bottom flanges of the beam, but only loosely torqued to still allow the slip. Many times the lower pad is bonded to a neoprene or other elastomeric pad to allow slight rotation at the beam end without gouging the teflon.
Here's a couple of links:
h
http://www.sepbearings.com/fluorogold.pdf
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
Dik
RE: Pittsburg Convention Center failure
DaveAtkins
RE: Pittsburg Convention Center failure
I usually do the double framing out of a simplistic and lazy desire to not detail a connection able to accomodate thermal movement. This is by far the best way to go for the engineer and contractor. I have seen both seated connections with a teflon bearing or elostmeric pads and I have also seen horizontal long slotted holes in the various firms I have been with.
Another thing that I did not consider obvious until recently is that a teflon slide bearing is NOT that frictionless. The coefficient of static friction for a teflon bearing is on the order of 0.15 to 0.18 or so. These things have low kinetic friction, but it has to first move to mobilize it. On the cryongenic vessel I was supporting, the static frictional force imposed a larger shear at the slide bearing than the seismic shear imposed at the restrained end. This was a big surprise to me at the time.
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
I thought that they only "fixed" the single failed girder connection back in 05. I'm not sure if the threads were included in the slots or not. However, I wouldn't think that it would have mattered. In my messing around with old bridges, I find that every steel on steel movable connection is frozen. I think that the biggest problem with this connection in any use is the hassle of inspecting it. During construction, the temptation the torque down the bolts is overwhelming.
vincentpa, could you post your pdf to mytempdir.com?
RE: Pittsburg Convention Center failure
The original article stated that "some engineers" question its use and I was wondering how many engineers out there actually use it. I was taught that it was a poor connection design.
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
The article wasn't real clear, but I read that by fixing that adjacent girder, they may have limited this girder from sliding, - but then the article went on to blame the gauging for preventing the sliding too. I'm sure we'll hear more research on it with time. The slide connection pictured isn't great, and definitely isn't appropriate for nasty bridge environments, but I would still be willing to use it in certain circumstances.
RE: Pittsburg Convention Center failure
http://www.mytempdir.com/1233866
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
I'm afraid that the inner workings of a "simple" end connection are not all that "simple" and we need to be careful when we piggy-back a new twist on to a tried and true detail.
RE: Pittsburg Convention Center failure
Best regards - Al
RE: Pittsburg Convention Center failure
The connection is what I thought it was.
I absolutely don't think that simple slotted holes can serve as an adequate expansion joint in a beam to beam connection.
The "fix" that is shown on the last slide is what I think ought to have been there from the start.
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure
A hardened bolt sliding on soft steel will gaul the surfaces, and in bridges that will lead to rust and seize the connection. For me, I do stadium steel work quite a bit and I get the luxury of using large linear journal bearings or mechanical hinged linkages at bearing seats to allow constant quite movement. Though our travel demand is often (+/-) 12" or more.
RE: Pittsburg Convention Center failure
http://en
RE: Pittsburg Convention Center failure
RE: Pittsburg Convention Center failure