Anti thermal strip for full corner joint welding

[Pixy]

We need to put side baseplates right below the main baseplates. Both are 16mm thick (5/8 inch). It need to be full open corner joint like the above illustration and not flush or half open joint. The welder is an expert. But this configuration is not common. So I need to ask something here:

I read

"In contrast to this slow spalling process, explosive spalling occurs when concrete is exposed to high temperatures, and water in the concrete vaporizes quicker than it can escape. This situation results in a rising vapor pressure that ultimately causes the concrete to explode."

By welding the full open corner joint. What thin insulation can or do you put in the boundary between the full open corner joint so the concrete edge (shown in red label in illustration above) won't be exposed to the welding high temperature and the edge corner concrete getting so hot and spall quickly. Only SMAC (Shielded Metal Arc Welding) machine is available and will be used by the welder. Thanks.

 

[dvd]

Remove the concrete and install a curb angle, then repair the concrete.

 

[Pixy]

The concrete can't be removed because the top baseplate was already installed years ago with anchor bolts at the four corners. Imagine an old baseplate and concrete pedestal (with the top baseplate covering the entire top to the edge) The baseplate to be put at side is new. So I'm thinking what materials are best insulation against heat that we can put at the boundary so the welding flame won't reach the concrete edge directly.

 

[TugboatEng]

Concrete is a good insulator. Can you tolerate damage in the immediate vicinity of the weld?

 

[Pixy]

No problem for 1 or 2mm of the edge gone but the problem is during explosive spalling of heated concrete, the debris can hit the welder body like grenade.

What material (list) has the most heat resistance (can't conduct much heat of the Shield Metal Arc Welding machine)?

Something that can be made into strip too.

 

[centondollar]

Why do you need a full-penetration joint (or the side plate) in the first place? Is it supposed to encase the concrete and prevent concrete anchor-induced shear failure or pull-out failure? I have never seen this type of reparation detail before.

To answer your question: I know of no material can prevent the arc heat from entering into the concrete at these thicknesses. Presumably, you also need pre-heat for the joint, which may or may not damage the concrete pedestal.

 

[Pixy]

Yes to encase the top of each column (first photo) with 4 pieces of 400mm (16") depth 5/8" thick baseplates at all sides (4 plates shown at 2nd photo) and welding all around and to the top of the original baseplate forming an iron cap (imagine 5 baseplates total in one concrete pedestral). To prevent concrete anchor-induced shear failure as retrofit because we didn't know how strong they made the original anchor bolts at the top. There is only one anchor bolt per side 1 foot away from the breakout cones of the top bolts so there is no breakout cones overlap as the designer made it. The side bolts are to avoid uplift of the entire cap simultaneously.

So the full-penetration corner joints will also occur at all the corners of the 4 baseplates and on top (total of 8 corners).

Did you mean the arc heat would only occur at the boundary gap of the corner joint or would the entire sides become molten affecting not just the gap??

 

[centondollar]

The extent of the HAZ can be estimated with simple formulas. For the weld thickness and extent (I assume you mean to weld all joints fully) proposed, the heat input would be massive and the plates would definitely become distorted - more without preheat, of course.

I would not be concerned with plate rupture at the joint. Just calculate the force exerted upon the concrete edges due to shear failure, and then design the welds for that load and a small safety factor. The weld thickness will most certainly not be the hypotenuse of a full open-corner joint with 16mm plate thickness. My guess is that a minimum throat thickness (<5mm), half-open corner joint and intermittent (stitch) welding will suffice to resist the transverse bursting of the column. Less heat, less plate distortion and sufficient strength - that is what you will need.

You can drill a hole in the plate and hang it on the threaded rod sticking out of the column, and then seal it by welding the rod (probably cheaper than trying to attach a nut) to the plate; this will prevent the plates from moving vertically.

 

[Pixy]

The extent of the HAZ can be estimated with simple formulas. For the weld thickness and extent (I assume you mean to weld all joints fully) proposed, the heat input would be massive and the plates would definitely become distorted - more without preheat, of course.

I would not be concerned with plate rupture at the joint. Just calculate the force exerted upon the concrete edges due to shear failure, and then design the welds for that load and a small safety factor. The weld thickness will most certainly not be the hypotenuse of a full open-corner joint with 16mm plate thickness. My guess is that a minimum throat thickness (<5mm), half-open corner joint and intermittent (stitch) welding will suffice to resist the transverse bursting of the column. Less heat, less plate distortion and sufficient strength - that is what you will need.

All the 16 pcs of baseplates have already been cut months ago. 4 sides for each column. So the half-open corner joint (your minimum throat thickness (<5mm) can only be done in between the top original baseplate and the top of the 4 sides. It can't be done for all the corners because the side baseplates were cut to the exact side dimension (that is 500x500mm). No extra length for any half-open corner joint idea. So the corners are only full open corner joints. Illustration here (top view of the 4 side plates).

How much of the corner concrete can spall for full penetration open corner weld? 2mm of corner concrete or 5mm of corner concrete blown off? What is your estimate?

 

[Pixy]

The welder put the shear retrofit in place (see photo above). He said he will put them first in all columns before doing full weld on the corners and top plates.

The top plate corner joints use half-open corner joint as centordollar suggested. But the corners at sides can't be done that way (see illustration in last message). The welder just put rebars at the fully open corner joints because I told him to avoid welding on the concrete as it may explode.

But still, is it not the welding can turn the corner joint area molten? Can the full weld spall the concrete at the corners? Or should intermittent stitch welding work (to save the concrete in the corner)?

We are not required for any Welding Procedure Specification anywhere. Welder can decide to do what they want. So please give me tips. Full weld or intermittent stich weld at the full corner?

Only one anchor bolt was used because this Hilti 5.8 M16 has capacity of 47 Kn or 10 kips shear and it is just to avoid uplift of the entire column up and down.

 

[Pixy]

Here is the Shear Retrofit (above) update:

Full welding (but with rebar inserted) done at the full-open corner joints.

The welders use entirely 1/8" 6013 welding rod. It's supposed to be used on metal sheet only. What happened when it's use for full weld on a full-open corner joints?

Can the degree of spalling inside the corner depend on the welding rod used? How deep estimate for a 1/8" 6013?

Baseplate thickness (in all sides of the iron cap): 5/8" size 500x400mm.

Thanks.