Grout filled steel hollow section 3

[Bodgy Engineer]

Hi all,

Was wondering if there was any resources on grout filled hollow section?

I have a high consequance of failure, steel power pole that was impacted by a vehicle causing a visible deformation. A buckling analysis indicates a capcity reduction of at least 25%.

The reduction in capcity comes from the deformation inducing sudden changes in the section/stress concentrations, as well as flattening out the stiffners and reducing the section diameter.

Was hoping to grout fill the pole, more to prevent the section buckling rather then any composite action. Would like any understanding of the methodology behind this methodology.

 

[GeorgeTheCivilEngineer]

Well that certainly is a bodge.

Why not cut out and replace the damaged section, or reinforce with additional steel or concrete surround?

I mean... I guess it would stop buckling from normal design forces, but I'm not sure I could rely on grouting it to prevent failure in the event of another impact. So you could grout if other vehicle protection measures are also put in place.

 

[Bodgy Engineer]

GeorgeTheCivilEngineer the vehicle hit just above the ground line, the damage continues below the ground line. This would need to be exposed, which would reduce the footing capcity, which would then require propping, which will be difficult, given the site. Otherwise, it would work.

Yeah, traffic barrier would likely be installed.

One thought I did have is the grout breaking up under load, as the section is quite large (800mm diameter), and the section will not be fully grouted (I.e. grout will be from foundation to 1.5m above ground line). I do not think this will be am issue.

 

[XR250]

Will the grout keep the sides of the tube from buckling outwards?

 

[MotorCity]

Instead of filling in with grout, why not embed the pole in sacrificial concrete bollard?

 

[CrabbyT]

Pics please?

 

[KootK]

My read on this is that the pole has been bashed inwards. As such:

1) The pole is kind of "pre-buckled" in it's current state.

2) Buckling outwards is likely much less of an issue than is further buckling inwards.

3) No bollard or protection setup is likely to address the reduced capacity accruing from the pre-buckling.

I don't feel that the concrete infill is a great strategy for this. Where the pole is pre-buckled, you'll have the potential for some wicked P-Delta action locally tending to further buckle the pre-buckled areas. And, even in tact, I could see the concrete potentially crushing behind those local areas. Or, at the least, proving that the concrete wouldn't crush sounds like an odious undertaking.

The concrete filling of undamaged members to prevent buckling is a different animal in my opinion. There, the geometry of this is still such that it take very little restraining stiffness to get the job done. That kind of goes out the window once you have large deformations backed into the cake.

For me, I think that this would be an exercise of:

4) Reinforcing the area with metal and;

5) Adding protection barrier elements if this incidence can reasonably be expected to recur.

 

[azcats]

Is the foundation reinforced concrete or plain?

I had a similar question a decade ago here: Damaged Large Pipe Column Repair

Mine was alleged to have been hit by a truck.

 

[phamENG]

azcats - loving the tread marks. They didn't even flinch....

OP - I think KootK covered it well. If you have space to somehow cut this thing open and pump grout in, surely there's some way to shore it up enough to cut out the damaged section and weld in a repair? Or, if it's a straight section (no taper), is there a size up that would 'nest' with the original size? If so, could you cut a piece from some of that stock and fit it around your damaged area and weld it in place, effectively bypassing the damaged section?

 

[dhengr]

PhamENG:
“They didn't even flinch...?” They were actually intent on missing the bushes, so they didn’t hurt them, and didn’t even see the steel sign post.

 

[Bodgy Engineer]

azcats
Your pole will likely be a lot thicker. This pole is probably about 5mm (not entirely sure), where as your pole is approx 10mm.

Footing type is direct buried. Encased in plain concrete for durability reasons.


KootK - 2) Buckling outwards is likely much less of an issue than is further buckling inwards.

I doubt it could buckle outwards as well. It would increase it's own section properties to do so, so not very likely to happen. There's negligible axial load, so it will be a flexural failure.

KootK - 4) Reinforcing the area with metal and;

Difficult to do, given the shape and the 75mm or so of displacement. Well difficult to do, and actually provide the adequate support.

Additionally the damage continues past the ground line (still dispalced about 35mm at ground line).

phamENG - I think KootK covered it well. If you have space to somehow cut this thing open and pump grout in, surely there's some way to shore it up enough to cut out the damaged section and weld in a repair? Or, if it's a straight section (no taper), is there a size up that would 'nest' with the original size? If so, could you cut a piece from some of that stock and fit it around your damaged area and weld it in place, effectively bypassing the damaged section?

Cutting out the damage would require propping the pole. The site constraints (in regards to propping) make this onerous (and essentially not viable).

 

[Agent666]

One thing to remember these things are designed to crumple when a vehicle hits them limiting the damage to occupants of a vehicle. Filling it with concrete would potentially damage future vehicle occupants who should chance upon the pole at speed.

Replace the pole if there is a concern, they are meant to be replaced if they are taken out.

https://engineervsheep.com

 

[HTURKAK]

Mr. Bodgy Engineer ,

Grout Filling the pole at least will not worsen the situation however , the contribution of grout will not be countable..

The pictures you have posted implies the wall thk. of the pipe should be around 1/4 in.

I will suggest you , the use of split sleeve reinforcement after fixing the pole . The split sleeve may be made from plate or pipe using the same material.

One of the pictures i have found at web search for SPLIT SLEEVE REINFORCEMENT ,

Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[dauwerda]

One thing to remember these things are designed to crumple when a vehicle hits them limiting the damage to occupants of a vehicle.

I disagree with this (at least in the US). Precast concrete poles and wood poles are often used in addition to the tapered tube steel pole that is being addressed here. The ability to crumple and absorb energy might be an added bonus for the steel poles, but it is definitely not a design consideration.

I wouldn't be completely opposed to this as a band-aid until a more robust fix or replacement could be done. (If you hadn't said high consequence of failure, and your pole could tolerate a fair bit of deflection, I might even let it turn into a more permanent type solution).

One other thought on making the proposed solution calc out:
How are you getting the grout inside the pole? Is there any chance you could get vertical rebar inside as well? If so, you could extend the grout up at least 1.5 times the diameter of the pole above the damage, and essentially ignore the strength of the steel below this (other than being used for confining the grout) and instead use the strength of the reinforced concrete/grout. The moment/loads are transferred through the 1.5 lap distance, which is standard design for this type of pole. Essentially you would be turning the design into something like this:

https://www.valmontutility.com/products-solutions/transmission-poles/hybrid-poles

 

[azcats]

Is it really necessary to shore the pole to temporarily remove the foundation in the damaged area? Unless it's a dead end or direction change pole, it's probably not significantly loaded unless the wind is blowing.

My quick & dirty fix would involve nelson studs to and a RC shell above and below the damage that could handle the flexural forces. Lots of unstated caveats to consider here though and I'd more likely push hard for replacement.

Out of curiosity, how did you determine the capacity reduction of 25%? The local P-delta forces that KootK mentioned would seem difficult to quantify.