Long-slotted holes as expansion joint
Long-slotted holes as expansion joint
(OP)
What is your opinion on the use of long-slotted holes to accommodate thermal/wind induced movements (not temporary but as a permanent expansion joint)? The long slot is in the horizontal direction; gravity load is normal to the direction of the slot. I'm looking for references that advise against this practice.






RE: Long-slotted holes as expansion joint
See attached article.
RE: Long-slotted holes as expansion joint
RE: Long-slotted holes as expansion joint
Are there any codes, design guides etc that doesn't allow the use of long-slotted holes for this purpose? As far as I can tell the AISC manual and the AISC high strength bolt design guide doesn't say anything about accommodating movement along the slot; just that the loads should be close to normal to the direction of the slot.
RE: Long-slotted holes as expansion joint
I've always thought these connections violate the specification anyway. The spec doesn't make allowance for shear being tranferred through bolts in a joint that are not at least snug tight. These bolts are only finger tight, and they are being used to transfer shear load.
RE: Long-slotted holes as expansion joint
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Long-slotted holes as expansion joint
For example: Rust (or dirt, slime, paint, barnacles (?) and biologic trash like pigeon poop or the like) in the joint, slot, and between the bolts and the supposedly sliding part of the three pieces. Galvanic corrosion, flooding or roof leaks, new insulation in ten years, new paint, sand-blast residue not removed, grit and sweeping from later renovations will foul the supposedly "open" slots and prevent movement. (Each part ( the bolt, the beam, and the supported/supporting steel) have to remain free for the life of the building - and that's very hard to guarantee in the real world for even four to ten years.
Assume your design is perfect and will be kept perfect over the life of the building. But this means the mechanical parts of your assumed design need to be verified, then re-inspected regularly during construction of every joint. Unfortunately, without very, very diligent inspections, today's installers won't do it themselves, nor will they always ensure their newbies and apprentices will do the assembly with the care and attention to exact detail that your drawing must assume will be followed. Too much day labor, temp labor, and unskilled labor is used today to avoid precautions that - in year's past - could be taken for granted.
It is hard enough to even get all the bolts, washers, and nuts mounted in conventional steel joints even made up when they are all identical, much less fully torqued properly. And here you are demanding that some bolts are snug, some torques tightly, some with backing nuts ......
The mechanical details above are good. They are proper for designing such a flexible joint in the building. But if you can avoid using them - all the better.
RE: Long-slotted holes as expansion joint
Mike McCann
MMC Engineering
RE: Long-slotted holes as expansion joint
what is this spec you are referring to?
RE: Long-slotted holes as expansion joint
RE: Long-slotted holes as expansion joint
I have read the paper and it like the joint was not the proper one and was not carefully designed.
The sloted hole is normally used on seated beam to void unseated. So the bolts are locked with two nuts and the suface is the one that takes vertical forces. This is a tipical detail on expansion joints on buildings.
I think the way it is said on several reports "the failure of structures is 50% by poor detailing, the other 50% are other reasons".
RE: Long-slotted holes as expansion joint
Mike...some of the frozen joints I've seen could have used a little peanut butter...and I prefer grape jam.
RE: Long-slotted holes as expansion joint
Long slots used in the stability angle of a seat connection is intended to avoid rigidity in the connection. The bolts are not in bearing, which can resist slippage. The connection shear is taken in the bearing seat connection only. With the addition of slide bearing pads, you have an expansion joint.
I have reviewed the forensic report on the Pittsburg Convention Center, and several factors contributed to the poor movement in the knife connections that failed. The actual failures were in the welds of the knife angles to the columns. The lack of slippage in the angles induced large axial loads and prying in the welds of the outstanding angle legs. As a practical connection it is impossible to determine the effects of surface prep, bolt plowing, and connection eccentricity on the expansion/contraction movement require by the connection.
http://www.FerrellEngineering.com
RE: Long-slotted holes as expansion joint
http://www.FerrellEngineering.com
RE: Long-slotted holes as expansion joint
RE: Long-slotted holes as expansion joint
I never never never use slotted holes for expansion. Some old book I can not find anymore suggested not to use these when vertical reaction exceeds 12 tons metric(26kips).
Next I wouldnt use anything that is not likely to pull itself back gracefully when the expansion is gone.
If my boss forces me to use them(he is a proponent), then I would put a plate with rounded top at contact, to cut down friction and sticking, or wait until he doesnt watch and go on with PTFE or elastomer
respects
ijr
RE: Long-slotted holes as expansion joint
Now I need to find code references, provisions etc to back this up. Has anyone seen something to this effect anywhere?
RE: Long-slotted holes as expansion joint
Because some have used it successfully means absolutely nothing to me.
I have recently done some investigation into thermal effects on connections in some industrial buildings. The thermal effects are very hard to quantify.
IMO, if you cannot accurately determine the effects of thermal and wind on your connection, you have to eliminate that force....best way is a double column row.
I agree with JAE's description.
How can one depended on a direct bearing shear connection to slide?
How do you determine the force at which the connection will slide?
This detail screams of fatigue problems.
RE: Long-slotted holes as expansion joint
zoparrat, there is no code reference to back not using this detail, its just good engineering judgement. The code cannot specifically exclude every poor detail anyone can dream up.
RE: Long-slotted holes as expansion joint
Agree with that. The codes identify good practice. Not too many sections of codes and specs spend time identifying bad practices.
RE: Long-slotted holes as expansion joint
Your best spec argument may be that there is no spec allowing it either. RCSC/AISC does not allow the use of finger tight bolts in a structural bearing connection. They also do not allow the use of a non-steel filler, which eliminates the use of Teflon between the plies. Thirdly, snug-tight, the least restrictive installation pretension, requires that all plies be pulled into firm contact.
It will be difficult to find a spec that specifically addresses the use of long slotted bearing connection as expansion joints. Especially when many of the parameters are already specifically rejected.
http://www.FerrellEngineering.com
RE: Long-slotted holes as expansion joint
The 2004 RCSC bolt specification (referenced by the AISC specification), section 4, says that joints with fasteners loaded in shear shall be snug-tightened, pretensioned, or slip critical. "Finger-tight" does not fall within any of these categories.
Not only is this detail a bad idea, it also violates the applicable specifications.
RE: Long-slotted holes as expansion joint
RE: Long-slotted holes as expansion joint
6.1.2. Slotted Hole: When a slotted hole occurs in an outer ply, an ASTM F436 washer or 5/16 in. thick common plate washer shall be used as required to completely cover the hole.
Can't a common plate washer be made of any type of material?
RE: Long-slotted holes as expansion joint
RE: Long-slotted holes as expansion joint
You don't need washers between inner plies of a bolted joint.
RE: Long-slotted holes as expansion joint
All connected plies that are within the grip of the bolt and any material that are used under the head or nut shall be steel...
http://www.FerrellEngineering.com
RE: Long-slotted holes as expansion joint
http://www.FerrellEngineering.com
RE: Long-slotted holes as expansion joint
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