Manager Says Keep the Restraints — I Think They’re Unnecessary. Who’s Right?

[ALphaSpace]

I’m working on a project where the architect has asked us to revisit the column and beam arrangement supporting an internal staircase. Image 1 shows the current set-up and image 2 is what i have said we can achieve:

• The column is an SHS 200x200x16, total height 10.8m to roof.
• It supports only a steel stair, no slabs or significant floor structure
• Axial load ≈ 150kN
• The column is currently laterally restrained at 3.6m and 7.2m, and again at roof level

The column sits in a 3-storey atrium space within a school, and the architect is concerned about the risk of pupils climbing on the restraint beams from the stairs. They have asked for these beams to be removed.

To accommodate this, I proposed that the column be cut back and terminated at Level 2 half landing (7.2m), which is where the stair ties in and is the final level it needs support. I checked the column assuming it’s unrestrained in the other axis, using buckling length factor of 2.0. The utilization came out at just 0.38, well within capacity.

I told the architect that, the restraints could be removed and the column could stop at Level 2 half landing.

However, my manager has now taken the opposite view and insists that the column must be restrained every 3.6m and extend up to the roof, regardless of the actual structural demand. He has already communicated this to the wider design team and has asked me to go back and tell them that the restraint beams are required, essentially reversing what I previously said.

While I initially agreed to do so, the more I think about it, the more uncomfortable I am. From a structural point of view, I don’t believe the restraints are necessary, and my calculations support that which i have shown my manager. It feels wrong to go back and push for a detail that I don’t believe is justified, particularly when it’s been requested to be removed for genuine safety reasons.

I would appreciate any thoughts? Opinions?

 

[RenHen]

That seems worth re-opening the discussion on & your last paragraph is a compelling summary of why. If you're right that the bracing the architect has safety concerns about is not required on paper and your manager is overriding that after you informed the architect, he should be explaining why that is, both for your own professional development and so that you can speak intelligently to the issue when the architect asks why you changed your mind. And if you’re missing something and the bracing really is required, your manager should definitely be explaining that to you as well!


I'll add I think the Architects concern is reasonable. I was one of those no good kids climbing around steel atrium framing to hang lights for student events and such. I work for the company that designed the big atrium at my school and the engineer was not thrilled to see old photos of a younger and dumber me 20' off the ground in his column bracing.

 

[ALphaSpace]

That seems worth re-opening the discussion on & your last paragraph is a compelling summary of why. If you're right that the bracing the architect has safety concerns about is not required on paper and your manager is overriding that after you informed the architect, he should be explaining why that is, both for your own professional development and so that you can speak intelligently to the issue when the architect asks why you changed your mind. And if you’re missing something and the bracing really is required, your manager should definitely be explaining that to you as well!


I'll add I think the Architects concern is reasonable. I was one of those no good kids climbing around steel atrium framing to hang lights for student events and such. I work for the company that designed the big atrium at my school and the engineer was not thrilled to see old photos of a younger and dumber me 20' off the ground in his column bracing.

Thanks for the response.

So his comments back to me after I said it was a safety concern was if the students wanted to hang off the balustrade they could. A beam there isn’t going to make a difference.

In regards to the actual design he said given kids running up and down the stairs how stable isn’t going to be. It seemed to be very much a finger in the air judgment then actual reasoning but he was very adamant.

 

[duckhawk]

In my opinion there is a big difference between hanging off a railing and hanging off a railing with somewhere to put your feet below it.

As long as image 2 has anchorage and a foundation designed to take moment, i don't see an issue with it. There are structural analysis softwares that allow you to test the structure for vibration.

However, following the order of roles within any team is a big factor in getting anything done, as long as the manager doesn't compromise what is right.

 

[Greenalleycat]

It looks like the axial load is applied quite eccentrically to the column?
Is that factored into your assessment

 

[ChorasDen]

I don't understand the purpose of these restraints, can anyone enlighten me? They appear to be long and relatively slender in the render, are they preventing the development of a buckling shape within the column by acting as tension/compression elements to restrain the column?

 

[Greenalleycat]

Choras, it looks to me that the column is used to support the 2 flights of stairs and has beams welded off to take the load
These will prevent buckling in that direction
In the other direction there is no restraint therefore the design has two 'restraint beams' at each level - these are the ones that OP wants to delete
These are presumably to reduce the compression buckling length
This would leave the original buckling length unchanged towards the stairs, but would increase the buckling length in the other direction significantly as, not only is the restraint deleted, but it goes from being a restrained column to a cantilever column so the buckling length goes way up

What isn't clear to me in OP's calcs is whether there is allowance in the column design for what appears to be the eccentric load from the stairs
The lower one possibly has a colum at the other end of the beam? But the upper level appears to be a straight cantilever beam off the side of the column

 

[ChorasDen]

@Greenalleycat
Ah, I did not realize the column was tube steel, I assume it was a wide flange similar to the restraint beam. I do very little (otherwise known as none) steel design, how are the restraint beams actually restraining the column here? They look like they may be 20ft clear, with who knows how they are fixed at ends, I'm trying to wrap my head around the theory here for the purpose of the restraint beams themselves. I agree the eccentricity is quite high on this member, particularly if you include the moment at the attachment of the fixed cantilever that you alluded to in your response, good catch.

 

[ALphaSpace]

Choras, it looks to me that the column is used to support the 2 flights of stairs and has beams welded off to take the load
These will prevent buckling in that direction
In the other direction there is no restraint therefore the design has two 'restraint beams' at each level - these are the ones that OP wants to delete
These are presumably to reduce the compression buckling length
This would leave the original buckling length unchanged towards the stairs, but would increase the buckling length in the other direction significantly as, not only is the restraint deleted, but it goes from being a restrained column to a cantilever column so the buckling length goes way up

What isn't clear to me in OP's calcs is whether there is allowance in the column design for what appears to be the eccentric load from the stairs
The lower one possibly has a colum at the other end of the beam? But the upper level appears to be a straight cantilever beam off the side of the column

Just to clarify the upper landing beam is spanning between two columns the photo doesn’t show the second column on the other side of the landing. So the upper beam isn’t a cantilever but rather a simply supported beam.

Regarding the eccentricity I have allowed for this and applied moments to the column as well.

And yes by removing the restraints the buckling length in theory increases 4x. However even still with this increased buckling length. The section capacity is only at a 0.38 utilisation ratio.

 

[ALphaSpace]

@Greenalleycat
Ah, I did not realize the column was tube steel, I assume it was a wide flange similar to the restraint beam. I do very little (otherwise known as none) steel design, how are the restraint beams actually restraining the column here? They look like they may be 20ft clear, with who knows how they are fixed at ends, I'm trying to wrap my head around the theory here for the purpose of the restraint beams themselves. I agree the eccentricity is quite high on this member, particularly if you include the moment at the attachment of the fixed cantilever that you alluded to in your response, good catch.

Those restraint beams are spanning about 7.2m. They provide lateral restraints and reduce the buckling length of the column. The essentially behave as a tension and or a compressive member stopping the column from displacing laterally.

So by removing the restraints the buckling length is then increased by a factor of two, and now because there is no end restraint and is a cantilever column your restraint factor is 2, creating a total increase in buckling length of 4x.

 

[ALphaSpace]

In my opinion there is a big difference between hanging off a railing and hanging off a railing with somewhere to put your feet below it.

As long as image 2 has anchorage and a foundation designed to take moment, i don't see an issue with it. There are structural analysis softwares that allow you to test the structure for vibration.

However, following the order of roles within any team is a big factor in getting anything done, as long as the manager doesn't compromise what is right.

Do you believe vibration would be an issue? I could ulander stand for the sake of restraint beams to be kept if vibration issues are mitigated from the get go.

But not sure if a vibration would cause issue even without the restraints.

I just feel it’s way overkill.

 

[Greenalleycat]

@ALphaSpace if you've allowed for the moment and the axial load and the cantilever column effective length...why are you using a 200x16 SHS that is ~2.5x the strength it needs to be?
Surely you could adopt a more economic section

Considering that you have a column either side + welded beam and, I assume, a grunty baseplate that provides some moment/torsional capacity, your manager seems to be quite overly conservative

 

[ALphaSpace]

@ALphaSpace if you've allowed for the moment and the axial load and the cantilever column effective length...why are you using a 200x16 SHS that is ~2.5x the strength it needs to be?
Surely you could adopt a more economic section

Considering that you have a column either side + welded beam and, I assume, a grunty baseplate that provides some moment/torsional capacity, your manager seems to be quite overly conservative

Completely agree on the section size as well. It can be reduced. I don’t want to give him a heart attack lol.

I suppose the frustration I’m having is we have been asked for alternative solutions by the architect for a completely valid reason. I’ve provided that alternative solution through alternative design verification however he is adamant on not changing it.

I generally try to be helpful wherever I can.