Entering and Tightening Clearances

[EngTomPE]

AISC has published Entering and Tightening Clearances for bolts up to 1.5" dia.(Table 7-16 in the 13th edition Steel Manual). Does anyone know about clearances for larger bolts? In my case I have 2.5" A325 bolts. I need to keep things as tight as possible to minimize plate thicknesses. Any suggestions?

 

[connectegr]

2.5" A325? - is a minimized plate thickness possible?

is 2.5" the length or the diameter?

Does the connection require pre-tension? What installation method? The gun required for 2.5" diameter bolt pre-tension will be enormous and HEAVY. I would say, go with the thick plate and spare the iron worker some grief.

http://www.FerrellEngineering.com

 

[EngTomPE]

Yep, 2.5" diameter A325 bolts, pre-tensioned. I'm designing a bolt-on padeye to connect to a 9 foot diameter steel pipe flange (for a water intake). The bolt size/strength is over-sized, but the holes in the flange are 2.688" and they'll have them available for bolting up the pipes in final position. The padeye will be removed after placement for connecting the next section of pipe.

Yes, it's all heavy, but will be available on-site. The base plate on the padeye starts getting really thick really quick if I get too conservative in providing clearance.

I'm going to try and look up some wrench manufactures info. Any thoughts on alternate resource?

 

[connectegr]

I looked at the catalogs I have and 1 1/2" is the largest torch wrench I can find. I saw some larger bolts recently at the Bay Bridge site, but I did not observe the installation or the equipment they were using. Good luck.

http://www.FerrellEngineering.com

 

[gwynn]

Most of the pre-tensioned connections of that size I have seen are for use with Dywidag or Williams rods. Both can provide pre-tensioning, but from what I have seen it is generally through jacking - not using a wrench.

 

[dhengr]

TomP:

It seems the me the bolt spacing, etc. is already determined by the intake flange designer and you have to match it, so what clearance are you concerned about? He designed that pipe flange for one thing and I would check with him to confirm that you can lift on it the way you want to, and in the orientation you want. He may also have some concerns about any deformations of that flange. Will he allow you to use (abuse?) these bolts and then reuse them himself?

A few sketches, dimensions, weights, etc. would be helpful in explaining what you are trying to accomplish with your lifting system. You must need several lifting points on that intake and a spreader beam system to actually match the C.G. On bolts that size you may find a wrench, off someone’s shelf, but you also start thinking about making your own wrenches.

Without seeing what you really have, I’d look at a piece of heavy walled mech. tube that just fit in the flange holes; it would be 2 or 3" longer than the thickness of the flange and 1.25" side plates would fit over these mech. tubes (same dia. holes as in the flange) and be held in place with 3/4" bolts and washers through the mech. tube. These two side plates, with the mech. tube and 3/4" bolt in double shear, at the flange, would start to make up your lifting system. Maybe you need several shear pins for each pair of side plates. Maybe the existing 2.5" bolts would serve the same purpose as my mech. tube. I don’t see that the bolts have to be particularly tight for the lift, they just serve as shear pins.

 

[ajh1]

Per the ASTM standard, A325 bolts are only available up to 1.50" in diameter. Above that you are probably looking at an ASTM A354 Grade BC bolt. Note that head sizes may not be the same as would be expected in an A325 bolt.

 

[EngTomPE]

ajh1 - I noticed that about the bolt specification last night. I am going to contact the pipe designer and point that out, and make sure I'm checking for the correct spec. on the bolt strength.

Bolts are in tension only, I want them pre-tensioned for proof loading and to keep things tight during lift. There is a beam attached. A sketch is attached for reference.

 

[hawkaz]

This is going to be fun to install. I saw a project with 1 1/2" A325 several years ago- They put a 6' cheater bar on the torque wrench, and still couldn't get it torqued down enough.

Unfortunately, I don't recall how they finally got it torqued down.

 

[dhengr]

TomP:

I don’t see that you have to tighten those bolts down to some significant proof load value, just make sure they are good and tight. This isn’t a structural joint where proof load or preload has much meaning, except that you don’t want the joint to open up and allow the pipe flange to roll. Just make sure the bolts have sufficient tensile cap’y. with your (or some code) FS, which you are deigning to. I would be more concerned about deforming the flange and wall of the pipe, or the weld btwn. them, with those loads on such a small, concentrated area, you better take a look at that.

With the scheme you have now, do you have the W36-150 in stock or is that what’s needed? It’s essentially going to act like two sloped tension fields, through its web, btwn. the padeye and the two base pls. I’d move the outer stiff. pls. btwn. the base pl. and WF out, and make them one end pl. on the beam and the base pl., for cleaner fit-up and welding; .75" above the top of the WF and 2/3s of the way down on the base pl., and a single slope on the sides. The inside stiff. pls. should start at the inside edge of the base pl. and slope up to end somewhere near the end of the padeye, and then remove the middle web stiff. That’s the way the loads want to go. Cope these two stiffs. at the flg./web radius and at the flg. tip to the base pl. Now, take a look at the web stress immediately under the padeye and under the web/flg. radius, at the ‘k’ value.

But, you still have a nasty weld condition btwn. the padeye, through the flg, and into the WF web and the stiffs. This high trough flg. force at the flg./web juncture (core) can be problematic, and you tend to have hard spots btwn. the padeye and stiffs. which are kinda tough to rationalize. Finally, change the padeye to 1.5" and the two cheek pls. 1.25" doughnuts and weld all around; or maybe 1" and two doughnuts at 1.5". When the main pl. of the padeye is significantly larger than the WF web, the web will likely control your deign. The single stiff. pls. centered under the padeye are really hard spots, with a nasty stress picture.

Talk to your friendly rigger about smaller shackles and two slings to his hook. Maybe it would be cleaner to have a shackle and padeye immediately over each of your base pls. and a spreader beam btwn. the two padeyes holding them apart and preventing them from twisting to much. Maybe slot a HSS so it fits onto the padeyes, or a much smaller WF btwn. the base pls. and padeyes. You could machine some small doughnuts which fit the heads of the bolts, and weld them on top of your base pl., then use their wrench and tighten the nut from below.

 

[NS4U]

RCSC does not provide guidance/support for prequalification testing of bolt grades other than A325 and A490. Sure, you could use one of the methods outlined in there but I'm not sure it's applicable. Moreover, at 2.5" dia. you're probably looking at 300 kips or more of pretension.


If you are relying on pretension for strength, you'd need to go a bolt tensioner.

 

[NS4U]

Sorry just saw on the sketch that you are calling for 100 kips of pretesion. How do you plan to get 100 kips?

You'd need to do prequalifcaiton testing with a Skidmore which takes time and money. Might be better off just going with renting a bolt tensioner. However, with such a large diameter bolt you're probably looking at the pretty big one.