Sidesway Web Buckling Question 2

[LobstaEata]

A question came up recently whether sidesway web buckling for wide flange beams being used for temporary needle beam shoring (laterally unbraced) could be satisfied by wedging in hardwood blocking on both sides of the web between the top and bottom flanges at the bearing (jacking) points rather than welding stiffener plates.

Requirements for web crippling and local web yielding for this case has been satisfied.

 

[LobstaEata]

I've attached a sketch in an attempt to clarify the question. The contractor (building mover) would like to avoid having to weld in steel stiffeners into his beams only to have to grind them out after the job is done.

Does anyone have an opinion regarding the use of wood blocking to satisfy Sidesway web buckling for this temporary condition?

 

[BAretired]

I think I would like to see a couple of through bolts holding the two blocks together. Otherwise, the friction may let go.

Best regards,

BA

 

[LobstaEata]

BAretired

Good point. Thanks.

Perhaps the hardwood blocking could be clamped tight against the web to avoid drilling the web.

 

[BAretired]

LobstaEata,

Yes, a couple of C-clamps might just do the trick.

Best regards,

BA

 

[beton1]

Can you weld a couple of small clips that can hold the wood in? This would be less intrusive and easily removed
compared to stiffeners.

 

[beton1]

The reason I mention this is that I have seen temporary clamps hit and dislodged. Just a thought.

 

[271828]

I don't know if the blocks can, in reality, provide enough bracing, but I know for sure that there's no way to back up the idea. I personally would not use the wood blocks in this way unless I had a very lightly loaded situation, but the load wouldn't be big enough to cause problems then anyway.

For one thing, make sure that SSWB is the right limit state. Take a look at Fig. C-J10.1 and the accompanying description of hte limit state. I think it's counter-intuitive.

 

[kslee1000]

It is quite difficult to fit wood blocks into spaces shown. I agree with 271828, the SSWB will occur under substantial load because the lack of restraining forces at the wood-steel interfaces. The provided detail will help to a certain point, then sudden failure could occur. As a mininum, I suggest you shoud provide details as BA's original idea, but to account for the loss of section in your analysis.

 

[LobstaEata]

Thank you for all your comments.

For the time being, the contractor was told that steel stiffener plates will be required. This type of shoring work will be ongoing with this contractor for other projects in the future though, so I thought I'd throw the question out there.

The flexural load of the needle beams approaches the working load (yes...I'm an old ASD guy), but web crippling and web yielding don't appear to be a concern. SSWB however is exceeded by 10%.

Normally, with this small of an overage, I'd just watch the beams closely during the jacking process, but on this project, I won't be on site. I figure Murphy's law could end up ruling and over-jacking (higher reaction loads) could occur, so I figured steel stiffeners would be the appropriate solution for this project.

I am interested in whether we can find a way to get a timber blocking solution to work though and that it will satisfy the intent of the code for SSWB.

Again, thanks for all your comments and suggestions.

 

[swearingen]

You seemed to be amenable to bolted blocks (drilling holes through the beam web) - how about bolted steel stiffeners? If they were thick, hammered in, and bolted with a clip to the web, I'll bet they'd go a lot farther than the wooden ones to preventing SSWB. The best part is that they could be reused later...


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[LobstaEata]

Not so amenable to drilling holes in the Contractor's rolled shape stock, as mentioned before. I know he isn't too keen on that himself. That's why I'm trying to determine whether hardwood blocking (clamped not bolted) will satisfy SSWB criteria.

I did talk to the contractor before about bolting angles to the web, but given the two stel stiffener choices he had, he preferred welding. Welds can be ground flush. Holes are forever.

I understand this might be a question that tests the limits of what the code will permit, but considering the high wattage of the crew on this forum, I'm confident the subject is able to be brightly illuminated.