SLIP CRITICAL COLUMN SPLICE

[Veer007]

I have to done slip critical column splice connection with different seriel of column profile, is there any limits for max shim plate size? can anyone assist me?

 

[KootK]

I believe that the limit is 1/4" before the shims need to be welded to one of the connected parts.

 

[Veer007]

Thank you @Kootk, attched is the connection i have currently, there is a 1" shim, Either i have to provide butt plate (ifso it will not act as bearing type?)or is this accpetable to provide 1" shim for slip critical? i thought no issue since force will be transferred via faying surface of connection plates, Am i wrong?, advise

 

[sbisteel]

AISC allows for thick shims to be used in slip critical connections without limitations on thickness, check out J5.2 in the manual. The 1/4" limit applies to bearing bolts, but even then you are allowed a reduction in bolt strength once you get over that 1/4" thickness. Shims must have the same surface prep as the rest of the faying surfaces.

 

[KootK]

I agree with sbisteel. I got discombobulated between the Canadian & US codes. In Canada, SC bolts have to be bearing for ULS.

Code adherence aside, something about a gapped, ULS SC bolted column splice makes me a bit uncomfortable. Based on your sketch, it seems that the goal is really size transitioning rather than tolerance provision. Perhaps you could just shop weld the 1" shim (or 3/4") onto the narrow member in the shop and then have the ability to use bolts in bearing as a backup.

With regard to the SC bolting, I would expect that a thicker plate might actually improve the connection. I believe that a longer stretch length on the bolts makes the tensioning to a particular value easier to achieve / more reliable.

 

[BridgeSmith]

In AASHTO, slip resistance is not affected by the presence of shims, so long as the surface condition coefficient used is the lowest for any of the faying surfaces. For the ultimate capacity in shear, AASHTO allows you to either reduce the shear capacity of the bolts (by a factor corresponding to the total thickness of the shims) or extend the shim and add additional bolts to secure it.

 

[Veer007]

Thank you all, i have to follow CISC (code of practice), going to use Class B (blast cleaning)surface preparation , connection to be under service capacity noted on CISC

Agree @sbisteel to use 1" shim and same surface preparation

@KootK, is this fine to have the same connection with shim plate shop welded to narrow column? yeah the connection will be okay under factored load for bearing capapcity of bolts(to be checked for CISC), Also does the shim plate need to be welded on the columns with same connection force?

I have provided 1/8" as erection clearence (unavoidable situation), is this ok for SC connection?, advise, Also used load conversion factor as 1.4 for service capacity and factored capacity, is this correct?

Agree @HotRod10, i have to provide additional bolts to enhance connection capacity as i have thicker shim, is this ok?

Let me know your concerns,



Thanks all!!

 

[BridgeSmith]

I'd have to look at how to calculate the number of extra bolts required; I've never actually used that option. We always just use the shear capacity reduction for the bolts and calculate the number of bolts required passing through all 3 plates.

 

[Veer007]

@HotRod10, attached is i found this on web, i have grip length as 70mm, i'm going to use 25mmØ A490 bolts, still i need to calculate reduction factor?

Thanks all!!

 

[KootK]

@KootK, is this fine to have the same connection with shim plate shop welded to narrow column?

Sure, it just becomes part of the column, right?

Also does the shim plate need to be welded on the columns with same connection force?

I would think so, yes.

I have provided 1/8" as erection clearence (unavoidable situation), is this ok for SC connection?

Sure. As has been mentioned, up to 1/4" you're good for bearing and slip critical without reduction. In this application the 1/8" shim is your only shim.

Also used load conversion factor as 1.4 for service capacity and factored capacity, is this correct?

It's reasonable. Only the EOR can tell you if it's correct.

 

[Veer007]

Yes you are right, i can't proivde more then one faying surface as this also will need to pass in bearing type

Thanks all!!

 

[BridgeSmith]

From the AASHTO Bridge Design spec:

When bolts carrying loads pass through fillers 0.25 in. or more in thickness in axially loaded connections, including girder flange splices, either:

The fillers shall be extended beyond the gusset or splice material, and the filler extension shall be secured by enough additional bolts to distribute the total stress in the member uniformly over the combined section of the member and the filler or,

As an alternative, the fillers need not be extended and developed provided that the factored resistance of the bolts in shear at the strength limit state,specified in Article 6.13.2.2, is reduced by the following factor:

R = (1+gamma)/(1+2*gamma) (Eq. 6.13.6.1.4-1)

where gamma = Af/Ap

Af = sum of the area of the fillers on both sides of the connected plate (in^2)

Ap = smaller of either the connected plate area or the sum of the splice plate areas on both sides of the connected plate (in^2)

As I said, I always use the 'alternative' option, applying the reduction factor.

 

[Veer007]

As i told earlier i have to provide extended shim that have been welded with above narrow column, so this will pass in bearing type also, is this ok? Do you refer me any detail were shown in CISC handbook for the shim thickness or reduction factor?

Advise the reduction factor shall also need to consider even where grip length doesn't exceed 5*bolt dia? As i noted above..

if Comments towards For canadian standard would be greatful for me..My project is residential core slab building..

Thanks all!!

 

[BridgeSmith]

I don't know if I can help you with a welded shim on a bolted connection. We never mix connection types, and the AASHTO spec doesn't cover it. I couldn't say for sure, but there's probably a reason for that. I'd speculate that there could be some strain compatibility issues. There's certainly a difference in the fatigue stress limits.

I'm not understanding why you would want to anchor the shim by welding when you're bolting the remainder of the connection. On the rare occasion where we need to transition the thickness of a flange within a girder piece, we would taper the thickness of the thicker flange down to match the thinner flange and specify a full penetration butt weld. Most of the time, we just do a bolted field splice between girder pieces, with fillers where required, designing the connection using the reduced shear capacity for the bolts.

 

[Veer007]

As per CISC spec, i need to check the connection will pass in bearing type under factored load even its slip critical, if i didn't weld them with column will make more eccentricity at bearing type connection, then only i need to make single faying surface for a connection,

Also i can't able to taper flange to suit as this will reduce column section and Can't do without getting proper approval from EOR

I never used reduction factor for shear in the past jobs i done, so only i dont know how can i get into myself to acheive enough strutural requirements to this connection by using CISC.

Thanks in advance!!

 

[BridgeSmith]

"As per CISC spec, i need to check the connection will pass in bearing type under factored load even its slip critical,"

It's the same in AASHTO. The reduction in shear capacity of the bolts is only for the ultimate shear capacity of the connection under design loading. The check for slipping under service load is unaffected by the presence of shims or fillers, assuming the surface condition of all faying surfaces is the same, or the check for slippage uses the lowest coefficient of friction of a faying surface within the bolted plies.

I'm not familiar with the CISC, so if that's the spec you're designing to, you'll have to design using the provisions in that spec. I was just showing what the options in the AASHTO spec are and how the design of the connections is done for it. I can't comment on the web reference; I have no idea where it came from or what it's applicable for.

 

[Veer007]

oh, sounds good..presence of shims doesn't affect slip critical conn, aslo i'm using blast cleaning surface preparation for both column and shims, but have to make single faying surface

And the main theme of welding of shim (1 inch thick) with column would need to reduce eccentricity in bearing type, thats all..can u refer me spec page shown in AISC handbook for reduction factor, Just for ref. Is there any sample calculations would be nice..

Thanks in advance!!

 

[BridgeSmith]

Yes, you have to check for slip on a single slip plane, if you don't have splice plates on both sides of the flange (or web) being spliced.

I can't help you with the reduction factor out of the AISC; I haven't seen it or used it.

 

[sbisteel]

AISC J5.2a, page 16.2-130 in the 14th edition.

 

[Veer007]

thanks

yes, i have splice plates after then shim plate which placed near flanges of narrow column..


thank you