Wind Load Calculations for a 50ft x 14ft Patio Cover at a 6 Degree Pitch

Click For Summary

Discussion Overview

The discussion revolves around calculating wind loads for a patio cover measuring 50ft by 14ft with a 6-degree pitch. Participants explore various methods and considerations for determining the appropriate wind load calculations, particularly in relation to building codes and the unique geometry of the structure.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes the need to calculate wind load at 90mph and questions which airfoil equations to use, considering the patio cover's low angle and elevation.
  • Another suggests writing a program to calculate net forces based on pressure coefficients over the geometry, arguing this would yield better results than using airfoil assumptions.
  • A participant expresses skepticism about the applicability of the UBC equation for vertical walls, suggesting that the wind vectors acting on the flat cover may not be entirely vertical.
  • One reply proposes that a conservative estimate could be made by assuming maximum possible forces, although this approach is not universally accepted.
  • Another participant raises uncertainty about whether the UBC calculation for vertical walls would yield greater forces than those from wind gusts moving over the roof.
  • There is a mention of the necessity to adhere to national building codes, which require structures to withstand specific wind speeds, and the importance of consulting local regulations.
  • Discussion includes the distinction between downforce and uplift, with emphasis on how these forces relate to air pressure dynamics under the cover.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to calculate wind loads, with no consensus on the most appropriate method or the applicability of existing equations. The discussion remains unresolved regarding the best practices for this specific scenario.

Contextual Notes

Participants acknowledge limitations in their calculations, including assumptions about wind vector directions and the specific conditions under which the patio cover will be subjected to wind forces. There is also mention of the need for further clarification from local building authorities regarding code requirements.

Physics_Kid
Messages
172
Reaction score
11
this falls into civil engineering, but as we all know everything boils back to physics. and, i couldn't find any good civil forums to join.

so, i have a basic Q but need help understanding some things.

1) i am building patio cover approx 50ft long x 14ft off the house. it has a pitch around 6 degrees.
2) i need to submit design loads. wind load is my last piece. i need to calc at 90mph. but at this low angle and low elevation (~8ft) its more like a airfoil, a very flat airfoil. what airfoil equations to use? i initially though i would calc max downforce or uplift by considering the area as a vertical plane using the UBC '97 equation force=A*Ce*Cq*Qs, but this may yield way more force than i need to account for.

any ideas here?
 
Engineering news on Phys.org
How far in depth do you want to go? You could write a program to calculate the net up/down force that results from flow over geometry that you input. This method basically calculates the pressure coefficient at each geometry point and integrates it over the surface to determine a net force value. This is how I've done it before and would give much better results than assuming it's an airfoil.

I'd be more concerned about the force exerted on it by the air due to the surface area of the cover.
 
the UBC equation is the force on the complete area @ 90MPH, but UBC is for vertical walls. i don't think my small flat cover will see wind vectors that are completely vertical on either top or bottom side (although a 90mph downward micro-burst is possible but not likely).

its a open cover so i don't expect to see large pressure diffs between top and bottom areas. the wind load #'s are never likely to be seen, but town code says it must be included in the design, etc.
 
Why not just assume it's possible and state that it's a very conservative estimate? That's what I would do.
 
i am not 100% that the std UBC calc for a vertical wall yields greater force than say a 90mph wind gust where the air moves rapidly down the roof and over the cover. this would fall into airfoil arena, no?

i'll ask my town folks what they expect for a wind calc.
 
You do have a national building code, no?
I believe structures in the USA have to withstand a 90mph wind.
You could design it as an open roof or as an overhang with the guidlines from the code, but it takes some time to figure out the formulas and designations.
Ask your townfolk what is the latest edition applicable to your structure, and there might be a copy in the library for you to peruse.
The code bases a design on downforce and uplift.

2005 version of wind loads:
http://www.ce.udel.edu/courses/CIEG407/CIEG_407_Protected/Chapter%206%20Wind%20Loads.pdf
 
Last edited by a moderator:
yes, downforce and uplift is what we design to, but those are vector summations. an uplift is most likely due to air pressure under the cover (like a strong ground wind coming low and pressurizing the air under the open cover, would need a lot of this to get significant pressure diff), and air pressure due to the cover acting like an airfoil.

the other std force i have is UBC calculation for basic plate that is subject to a wind at 90 degrees.

pic of how i might see a force from acting like an airfoil.
http://img221.imageshack.us/img221/8441/67599143.png
 

Similar threads

Lawn/Garden Wind Speed required to topple Patio Screen Support
  • · Replies 10 ·
Replies
10
Views
3K
Wind Load Calculator: Gable Roof Envelope Procedure
  • · Replies 4 ·
Replies
4
Views
10K
Wind loading due to gusts; resultant torque on a 6' parabolic dish
  • · Replies 4 ·
Replies
4
Views
3K
Design Large Sign for Wind Loads
  • · Replies 12 ·
Replies
12
Views
10K
Aerodynamic Forces on 6' x 3' plate at 45 degrees - 70 MPH?
  • · Replies 6 ·
Replies
6
Views
3K