Window Support Beam - Simple Calc

[SoFloJoe]

Hi All,

I understand that I maybe grasping at straws here, trying to make something work that on paper does not.

My client is a window installer and has an opening roughly of 15ft. It has a standard 96" in high sliding doors at the bottom and on top is a 70"high fixed window setup. In between the windows requires a support beam to provide a structural connection for both the sliders below and fixed above. Attached is a photo

I am doing a simple beam calc and focusing on wind loads, currently at the max which is the -37psf (with 0.6 ASD Load combo already applied). Tributary height about 85".

Doing a simple beam calc I am getting an overall moment of 950 kip-in and my Sx requirement w/ 0.65 SF applied to a 50ksi yield strength is +/-30 in3 (the beam would be rotated 90 deg in the direction of the wind). I am not worried about moment of inertia since there should not be any deflection here due to windows below and above the beam.

BUT, with such a high section modulus my beam dimension is too large I need to stay within +/-6"x4". I feel like I might be going too conservative with my calcs. Is there a reduction allowance or different method of approach to make the Sx go down?

Thanks for your help!

 

[MIStructE_IRE]

Does lateral wind deflection not govern your design here?

Are you assuming that the beam is unrestrained in terms of buckling? Could you gain restraint from the vertical mullions?

 

[SoFloJoe]

Yes, deflection does not. The beam will be restrained from deflection by connection to the windows and mullions below and above.

 

[wannabeSE]

Have you double checked your calcs
With 83" tributary to the beam and 37 psf, the load is 256 plf
With a 15' span, I get 7200 lbs-ft or 86.4 kip-in

 

[JLNJ]

If you have sliding doors at the bottom, wouldn't you want to minimize the vertical deflection so that the doors don't bind? That big panel of glass must have some real weight to it.

You will want to limit the horizontal deflection as well, though the limits might not be as tight as the vertical deflection. Maybe you design so the "typical" wind deflections govern, but let the hurricane wind deflection go somewhat over.

In the end, if your numbers check, you can only do what you can do. Just because the architect or owner wants a small beam, you can't suspend physics or the effects of the mechanics of materials.

 

[SoFloJoe]

Thanks wannabeSE.. you are right!! I did double check but glossed over my rounding from lbs to kips . Now this makes sense!

Yes I am going to check also the weight on top but my main concern was that I was way out of the ballpark.

Thanks everyone!