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Increasing Reaction Capacity
4

Increasing Reaction Capacity

Increasing Reaction Capacity

(OP)
I'm checking the connection design. I have an existing project that was reinforced by adding new composite construction. This has increased the required end reaction resistance required. The most simple solution would be to increase the existing fillet welds.
  • If the original connections were welded, is it possible to re-weld them using a larger fillet weld to increase the reaction capacity?
  • Are there any concerns about effects on the existing welds? ...on the metallurgy of the welds? The materials and the existing welds are common grades of steel/welds.
  • Is there anything that should be 'looked out for'? or that I should be concerned/aware of?
  • Do the old fillet welds have to be ground out?
  • By re-welding is the strength compromised during the welding process? There is little or no live load on the work at the time of welding.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

Dik:
Yes, you can usually increase the size of a fillet weld by adding few more passes. You should obviously use compatible filler metal and welding process. You should know something about the existing materials to make that compatibility determination. Is the (a specific) weld the limiting (cap’y. controlling) part of the connection, and the rest of the connection is still o.k. with the new loads? You should check the whole connection with the new weld size, as if a new connection. Example: say you have 1/4" fillet and your new calcs. show you need a 3/8th or 7/16th fillet. You need (the welder needs) to add several more passes, just as they would have, in the shop, in the first place, to increase the weld size. I would shore the beam, a/several posts and bottle jacks, to take most of the load off the connection.

RE: Increasing Reaction Capacity

(OP)
Thanks... that's what I was hoping... need to confirm the materials, but I'm pretty sure they are OK. The EOR has specified that the new reactions for the composite sections is half the web shear capacity. The original design likely used half the UDL that develops the section. The original bolts don't work. If the welding can do the trick it may be an easy 'work around'.

I didn't know if there were any issues about welding to existing welding... I think the electrodes are compatible, but will check. Rolled sections are compatible, for sure.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

Technically, no worries about the welding part considering all of this is more than likely mild steel. Make sure the steel is clean (to bare metal!) and hot (a bit of preheat doesn't hurt!) before welding, and you're good to go.

I hope you'll find a contractor that is willing to do this - this is a nightmare from responsibility point of view.

RE: Increasing Reaction Capacity

Hi dik

Obviously you know the situation better than I do however a couple of things to mention is just increasing the weld is not always the answer, usually the weld filler metal has higher strength properties than that of the base material so the weld itself might not be the weakest link and in addition the more heat you put into the joint, the more likely to have increased distortion.

Here is an extract from a site I found:-
7.6 DESIGN OF WELDED JOINTS SUBJECTED TO AXIAL LOAD
The complete penetration butt weld does not require design calculations. In case of incomplete penetration butt weld, effective throat thickness of the weld is computed and welding is done up to the required length. In case of fillet weld, size of the weld is fixed keeping in view the  minimum size of the weld as per IS:816-1969 recommends that when filet weld is applied to the square edge of member, the maximum size of weld should be less than the edge thickness by at least 1.5 mm as shown in Fig. 7.17. This avoids the washing down of edges of weld. When fillet weld is applied to the round toe of rolled steel sections, the maximum size of the weld should not exceed ¾ of the thickness of the section at the toe. When fillet weld is used for lap joint, then overlap of the members connected as shown in Fig. 7.17, should not be less than five times thickness of thinner part.

I couldn’t copy and paste the diagrams but you can see them if you follow this link:-


http://ecoursesonline.iasri.res.in/mod/page/view.p...




“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Increasing Reaction Capacity

(OP)
Thanks, king... I hadn't thought about pre-heating. I don't have a solution yet; I'm just looking at options. I don't know what the connections are or if they are the same for all locations. From photos it appears to have a beam seat with a stiffener and two bolts. I suspect these were for erection purposes, some connections appear to be bolted and some connections are currently obscure.

Thanks, fox... I'm just trying to find out possible solutions so I know how to proceed, and what possible options I have. Welding appeared to be viable. The beams have been reinforced compositely and cut back from the columns. The existing connection appears to be deficient, and it will be a matter of reinforcing it. This is part of an eMail I sent last night to indicate some of the connection issues:

VB5
This is the connection where there is a beam seat angle interfering with the gusset plate. There are three solutions:
• The gusset plate above can be installed; alternatively a small temporary gusset can be installed to accommodate the existing beam reaction. The beam seat can then be removed. This small gusset can be removed after the gusset below is installed;
• The proposed repair of adding stiffeners on each side of the seat angle, removing the existing stiffener, and fitting the new gusset plate to fit the beam-column connection and including the seat angle; or
• Provide temporary shoring to support the existing beam and remove the seat angle completely. This shoring would have to be approved by the EOR and would likely extend down two or three floors.

The gusset plate in this case is part of new X-bracing and can carry loads of up to 150K. I'm working for the steel supplier.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

(OP)
fox... forgot to note... that's a good link.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

More information: wall thickness and fillet weld dimension.
Be careful with distortions after preheat and adding welds.
Actual fillet weld should be 100% inspected. Then 100% after adding weld.

Regards

RE: Increasing Reaction Capacity

Concerns about cooling rate, microstructure, hydrogen cracking, ... are moot when talking modern, mild steel. And moderate preheat solves any remaining concerns.

RE: Increasing Reaction Capacity

(OP)
Thanks, fox...

The existing structure consists of conventional rolled sections... constructed about 25 years back with G40.21-44W steel and likely E60xx series electrodes. The building has been increased in height and the existing roof reinforced to become a new floor level. There are a bunch of weird conditions to be accommodated and new ones being found daily. Not one of my more boring projects...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

(OP)
Thanks, king... as noted, I hadn't even considered pre-heating. I've not dealt with increasing weld strength before. I was concerned about there being some effect on the metallurgy of the existing welds and am glad to know that they can safely be 'welded over' and increased if necessary.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Increasing Reaction Capacity

Before someone kills me about the overgeneralisation of my previous post, I'll add that you should seek a competent welding engineer to look over the details that you haven't shared here.

If you're talking 25 yr old steel, and significant thicknesses (let's say 25 mmn and more), My greatest concern would be lamellar tearing of not-perfectly killed steel or with high S content.
This would be more dangerous than the other dangers listed before.

RE: Increasing Reaction Capacity

(OP)
Thanks, king... The guy I work for is one... and any concerns would be addressed. This is for my own information so I don't suggest something 'silly'. Structural steel is not normally a problem.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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