Industrial Stairs, Tubes of Angles?

[pinoymaker]

This is my first post in this forum.

I am currently designing and detailing a steel stair for an industrial project. From a strength point of view, I can use an L5x5x3/8 for the columns. I thought this would make a nice clean connection to the channels supporting the walking surface. However, my supervisor would rather have tubes as columns. Is there any particular reason to have tubes instead of angles? Even though strength wise, the angle is sufficient. I thought the tubes is more for an architectural decision than engineering.

thank you

 

[structSU10]

The eccentricity of the connection could become an issue with angle columns, as you induce a bending moment in two directions. Tubes are a much more forgiving section for unbalanced or eccentric loads.

 

[pinoymaker]

Thank you for the reply. I do not think ecc. would be a problem since I would be attaching the channel to each legs at the same plane. I would also have diagonal bracings below the landing/walkway. I checked lateral loading from seismic, and they are ok. I do think this is one of those cases that "its always been done this way, we do it this way."

 

[MikeHalloran]

It would be nice to know your supervisor's reason for preferring tubes, but existence of the preference is pretty much the end of the discussion.
... right?




Mike Halloran
Pembroke Pines, FL, USA

 

[pinoymaker]

It's only the end if I can't find a good argument, thus the reason for being in this forum.

 

[UcfSE]

Did you check the actual effects of the eccentricities, and the angle bending about the principal axes?

 

[pinoymaker]

I checked bending on the geometric axis. I still can't see how there will be ecc. coming from the platform. Thank you everyone. I think its pretty much a lost cause. But would still like to know if there are other reason.

 

[IFRs]

Closed shapes are subject to invisible corrosion and are not allowed by some owners. With angles "what you see is what you get"

 

[pinoymaker]

With angles "what you see is what you get", thank you.

 

[BAretired]

For an industrial stair, I would prefer angle over HSS because of ease of connection. Light mechanical supports are often made up using angles for the same reason and the stress is normally quite low. Do you really need L5x5x3/8? I'm guessing you could get away with a lighter angle.

BA

 

[MikeHalloran]

Yep, angles don't corrode where you can't see it.
Tubes, too, if you plug and seal weld the ends. Some folks just don't trust the seal welds. ... for good reason, but that's specific to particular places, e.g. where the welders are not very good.

Angles as columns tend to be a little "wiggly", even if they're nominally stiff enough to carry the load.

Mike Halloran
Pembroke Pines, FL, USA

 

[pinoymaker]

With an L4x4x3/8, Im about 2% over stress. Using the L5x5x3/8, I'm down to 62% stress. My highest landing is about 16ft off the ground. My loading is 100psf live load. The ease of connection is my original argument against HSS. I will be bracing the columns regardless of shape, so I dont think they will be wiggly. Thanks again everyone.

 

[WARose]

May want to check your code (wherever this project is happening)…….throwing strength consideration aside: I got my hand slapped (on a project in Florida) over using angle hand rails because (according to the building code official) they are no longer considered graspable. So we were forced to switch to tubes/HSS for that reason.

 

[delagina]

i dont know where you are. i do industrial, petrochem structures, pipes and hss are rarely used as columns because they are "expensive".

 

[Ron]

As long as the angles are properly braced, there is not an issue. Keep in mind that stairs are designed as static structures but often perform as dynamic structures according to the way they are loaded. In particular, lateral movement of stairs is sometimes an issue.

 

[dvd]

How big of a forktruck are you planning on not hitting this with? Tube may perform a little more robustly when reacting to contingencies.

 

[IsaacStructural]

I was just going to write what dvd wrote. If they are driving forklifts around this all day, the column is bound to get hit. I've seen the flanges of fairly heavy w sections bent to hell from impacts. An angle column would be bent. A warehouse with dozens of forklifts buzzing around all the time is a lot different than a massive petrochemical facility.

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[BAretired]

I examined a warehouse building a few years ago with HSS columns and forklift trucks running over the floor at considerable speed. Several of the columns had been penetrated completely by the forks and some were nearly on the point of collapse. The columns were repaired and further protected by reinforced concrete pedestals from floor level to a height of about three feet. So far as I am aware, there have been no further incidents of a similar kind.

If forklift trucks are being used in the vicinity of the columns, a similar treatment may be prudent.

BA

 

[pinoymaker]

Thank you all for the reply. As for the forklift, it would be highly improbably to have a forklift hit this particular stair. It would be outside, immediately next to dirt. Large entrances are on a different side of the building. There are large vessels beyond the dirt, that would block future developments of anything that would resemble an access road. I also checked for earthquake loading, and lateral is not a problem.

 

[kingnero]

I believe you underestimate forklift drivers.

FWIW, in your particular case and for as far as I know the circumstances, I'd also choose angle profiles. boss's the one who pays you, though...