×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Roof top structure with flat roof

Roof top structure with flat roof

Roof top structure with flat roof

(OP)
I am designing an awning that is going on top of a 2nd story roof. I used section 29.5.1 to determine my roof top structure horizontal MWFRS and uplift loads. Section 29.6 Parapets refers you to section 27.4.5 for the effect of parapets on the MWFRS of structures. I don't have an actual parapet on the awning, but this is an open structure and section 27.4.3 states that if the roof angle is less than 5 degrees and there are fascia panels present that the fascia panels must be considered an inverted parapet. Typically when I do these awnings the only portion of the awning that receives any wind pressures is the fascia panel so normally I would calculate the MWFRS wind pressure on the fascia panels according to 27.4.5 and my positive and negative pressures on the roof according to to section 27.4.3 for open buildings. In this case the fact that section 29.6 in the roof top structure section refers me to section 27.4.5 for parapets, it makes it seem like I should calculate my MWFRS loads with section 29.5.1 but then do I have to add my parapet loads from 27.4.5? Once again, I don't have an actual parapet, only the requirement in 27.4.3 that for open buildings with roof slopes less than 5 degrees that the fascia panel be treated as an inverted parapet. My mean roof height of the existing building is 34'-8" and the transverse direction building width is 115'-0". The awning is 13'-0" tall and the fascia is 8" tall so its total height is 13'-8". Vertical area, Af = 15 psf. So Af < 0.1Bh so GCr = 1.9. qh = 30 psf. Rooftop structure Fh = 55 psf. If I have to parapet pressures according to section 27.4.5 (44 psf) for the "effect of the parapet on MWFRS" then my MWFRS pressures are 99 psf. Is this correct? I am unsure on this one as it is an open, rooftop structure. Chapter 29 doesn't discern between open or enclosed structures, just roof top structures but does refer me to 27.4.5 for parapets. Chapter 27 doesn't discern between structures on grade and structures on a roof. On one hand since chapter 29 does not discuss open structures, the requirement to treat the fascia panels as an inverted parapet does not apply. But on the other hand this IS an open structure it is just also a rooftop structure. Do I:
1. Add the forces together = 99 psf or
2. Use the MWFRS loads determined by chapter 29, 55 psf?

RE: Roof top structure with flat roof

I'm away from ASCE 7 right now but I don't think your option 1 is correct. You don't add parapet pressures and MWFRS pressures to the same area.

Not sure about the 55 psf though - would have to calculate it out.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Roof top structure with flat roof

(OP)
JAE,
I don't think option is is correct either. Chapter 29 doesn't differentiate between open and enclosed structures so I am leaning towards using the worst case of chapter 27 and 29 which is controlled by chapter 29.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close