steel construction - need some validation/opinion

[greznik91]

Hi, just yesterday I posted a thread about what do you guys usually do when your expectations dont meet analysis results. In this case I was expecting larger dimensions of steel beam (HEB 240). Its a barn construction (Wolf system) but instead of glulam roof beams I have to make it all in steel. I cant get a second opinion in my company about this at the moment so I hope you guys can help me with some opinions on this.

Barn construction: 10 steel frames in transverse direction that are aprox. 5 m apart. Bases of all columns pinned. Moment connections between top of outer columns and beam and in the ridge.

Loads on a single frame:
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1513151791/tips/loads_rsqkeg.pdf[/url]

Envelope of bending moments:

I was comparing a stiffnes of standard glulam (GL28h) beam used by Wolf system - cross section dimensions of 14/48 cm with a steel beam and I have figured that stiffnes of steel beam is higher so based on that it should be allright.

Esteel = 21000 kN/cm2
Etimber = 1260 kN/cm2
Isteel (HEB 240) = 11260 cm4
Itimber (14/48 cm) = 129024 cm4
Esteel x Isteel = 21000 kN/cm2 x 11260 cm4 = 236460000 kNcm2
Etimber x Itimber = 1260 kN/cm2 x 129024 cm4 = 162570240 kNcm2


Still Id like to hear some opinions on this.

 

[jayrod12]

Check lateral drift.

I'm also not a giant fan of only a 240 deep beam spanning the 8.43m, that's an L/d of 35. A little higher than I would typically go. I'd be looking at something in the 350 deep range.

 

[greznik91]

Well the beam (HEB 240) has less than 50% utilization (of the cross section) and is in 'elastic area' in every point.

I have checked drift. In a model I have taken into account that outer columns are fixed with 20% fixity of column stiffnes. I have also modeled haunch that is 2 m in lenght from the face of a column.

Drift for load combinations without earthquake:

Drift for earthquake load combinations:

The bending moments, shear and axial forces arent that big... as I said... the beam is not even close to be at max utilization...

But still I feel uneasy with a beam being only 240 mm.

id like to see more opinions.

thanks

 

[greznik91]

Also... for this spans Wolf system use timber glulam beams 14/48 cm instead of HEB 240 beams.

When I was comparing stiffnes of timber beam to steel beam I found that the steel beam is even stiffer at a hight of just 240 mm.

REPOST:
Esteel = 21000 kN/cm2
Etimber = 1260 kN/cm2
Isteel (HEB 240) = 11260 cm4
Itimber (14/48 cm) = 129024 cm4
Esteel x Isteel = 21000 kN/cm2 x 11260 cm4 = 236460000 kNcm2
Etimber x Itimber = 1260 kN/cm2 x 129024 cm4 = 162570240 kNcm2

Have I missed something?

ALSO, if I choose IPE 330 that has similar moment of inertia (Iy = 11770 cm4 ) as HEB 240 (Iy =11260 cm4) I get better L/d ratio but as far as stiffnes go its pretty much the same... So if Id change a section Id use IPE 330 instead of HEB 240 but I dont really see a reason to do so?! What do you think?

 

[jayrod12]

I'm not overly familiar with Euro shapes, but if the 330 and 240 have the same stiffness, then I assume the 240 is heavier than the 330, perhaps significantly heavier. There's a cost savings, to a point, with going deeper.

 

[greznik91]

HEB 240 weight per meter is: 83,20 kg/m
IPE 330: 49,10 kg/m

Its cheaper - you got that right!
But as far as stiffnes goes Its pretty much the same.
looks like Id change it to IPE.

 

[jike]

Does the IPE 330 require more lateral bracing than the HEB 240 to achieve required allowable stresses? How do the width-thickness ratios (web and flanges) of those sections compare? Does that reduce allowable stresses below what is needed?

 

[BAretired]

HEB 240 has a flange width of 240 and a depth of 240, so it is a very stocky shape. A deeper shape would likely have a narrower flange and be more likely to buckle when the bottom flange is in compression. If buckling is not problem, it should be okay to substitute a deeper, lighter shape but if the EI values are the same, deflections will be identical for each of the two beam selections.

BA

 

[DETstru]

What are the drift values? As in the lateral displacement due to wind/seismic loads?

 

[greznik91]

DETstru - I posted drift values in my 2nd post in this thread. Its around 18 mm at the top of columns for load combinations without earthquake. In a case of an earthquake the drift at the top of outer column is approx. 27 mm.

Its strange since calculations shows that a steel beam with height of just 240 mm is sufficient (HEB 240), but it kinda doesnt feel right for a span like that. But if I substitute it with beam that has height of 330 mm (IPE 330) I have pretty much the same stiffnes but it looks much better. IPE 330 is also much lighter so thats a plus, but I have to check buckling first.