Replacing Existing Bolts in a Brace

[swearingen]

In AISC's Design Guide 15 for retrofit of existing structures, it states, "In all types of riveted and bolted connections, old rivets or common (A307) bolts can be removed and replaced with A325 or A490 bolts."

My question is whether anyone has a problem with doing this "hot," i.e. replacing the bolts one by one without unloading the connection. This is a chevron brace in an industrial structure with a large piece of equipment near the top of the chevron - essentially these braces are currently loaded as columns.


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

 

[hokie66]

I wouldn't want to replace the bolts while equipment is in operation. And replacing them without temporary shoring would depend on the loads taken by the bolts and the quantity of bolts in a connection. For instance, with 6 bolts, I would not worry about replacing them one at a time. With 4 or less, I would want to be sure of the loads.

 

[JStructsteel]

Hokie66, I dont understand your logic...if 6 bolts are loaded to 95% you would replace 1 at a time, but if 4 bolts are loaded to 95% you wouldnt? Is this beacause of load sharing?

 

[jike]

He is limiting the potential overstress in the existing bolts during replacement.

1 out of 6 = 17%
1 out of 4 = 25%

 

[JStructsteel]

ok, thats a good point. thanks

 

[swearingen]

There's 16 bolts per connection (the brace is a wide flange w/claw angles), so I'm not worried about overstress. The biggest issue is that we wouldn't do it in a hurricane, which is what this connection was designed for in addition to the vessel.

I was just curious to see if anybody had seen some research on hot-swapping bolts like this. I know they hot-swap bolts on piping flanges all the time, but structurally speaking this is a different loading condition.


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

 

[hokie66]

swearingen,

I don't recall ever seeing any guidance for replacing bolts. In your situation, I think it just comes down to judgment, and with 16 bolts per connection, I would just do it. But I still believe your question is a good one.

 

[PEinVA]

If it was me, I'd require an inspection company to be present during the "hot-swapping" to witness that a single bolt is removed and replaced at a time.

You could get an antsy contractor who wants to move quicker and end up giving you problems.....just my thoughts.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[csd72]

Dont do it, props are cheap insurance.

 

[kelowna]

swearingen,

I have replaced rivets by bolts on an old bridge. As some other people has said, done carefully, and if enough rivets are left in place to ensure the stability of the members, no extra precautions are required, and this bridge was in (heavy) use during the operation.

As also said, control is critical. Replace as many rivets as you feel confortable doing and not more. Not less neither, the more onerous of a condition to the work the harder the workers will try to short cut it.

 

[swearingen]

Another question popped up: what order would you replace them? Our general thinking was to start from the center of the connection and alternate bolts out to each extent of the connection.

Also, these are chevrons with a 345k point load on the beam above at the point of the chevron. It is clear that the members will not go into tension for any load case, but due to "bubbling" in the large process unit, the whole structure bumps and shakes a good bit. We'll be fully pre-tensioning the bolts because of this...


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm