×
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!
• Students Click Here

*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

Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

 Forum Search FAQs Links MVPs

Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

(OP)
Below is what I am trying to build

H=7.5' W=8' L=10'
There is an option to reinforce the structure like in the picture below. The blue line cables should be optional

Can this be build of wood?

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

You have artificially created a LOT of tension in those lines by requiring the verticals to e that short. Increase the height by 12-15 more inches. That tension will resolve itself into much higher stress in the long horizontal beam, and very little support (vertical) lifting force to resist wind, gravity, and cyclical (flapping) canopy loads.
How will you resist the corners from lifting as one side gets hit by local up/down forces not on the other corner? This will twist the two horizontal beams significantly.

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

Those outriggers need to be deeper. They look spindly. Base of columns need to be rigidly connected to base to resist rotation. Good pressure treatment and embedded in concrete works well. Raising the columns to reduce tension in the cables is needed, but that doesn't take care of uplift from wind. I would take care of it by raising the columns as racookpe1978 mentioned, but also deepen the outriggers and create a rigid connection between the outrigger and column.

That above will get you a stable structure. There will still be issues with deflections and racking, but maybe you can live with that flexibility.

-Mac

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

What material is used for the "ceiling"? If it is fabric, you should take a look at how much it will sag, as it will accumulate rain, leaves, etc and create a ponding effect. If it is framed with wood or other material, that could add considerable weight and add to your overturning problem. Lastly, give adequate consideration to how the posts are supported or embedded into the ground. Can it be built of wood?....absolutely, if designed and detailed correctly.

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

If you want to eliminate the cables, then look at relatively heavy steel Tee connections. Simpson has a line of these.

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

(OP)
thanks guys!
I had a similar post asking about how to calculate the above structure when it is made of metal
racookpe who posted here reported that as duplicate and it was deleted. Good work buddy !

The shade is made of fabric and it is retractable
I will use cables for that and that should reinforce the structure. The cables will run along the long side of the shade

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

Quote (mjr6550)

If you want to eliminate the cables, then look at relatively heavy steel Tee connections. Simpson has a line of these.

There is no way you could get rigid strong-tie connections to work for gravity loads in this situation. Between the cantilever and reduction in connection rigidity from fastener slip, etc. that is not a good idea.

-Mac

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

OK, try this.

Cables run from left vertical (about midway) to the back of the right vertical, then across to the front of the left horizontal. That gives one half of two different tension braces. The second runs from right mis-point vertical, across to left top vertical, then back to right horizontal to complate the two tension crosses. Verticals still need to bw a bit higher than what is drawn in the sketch.

Verticals and horizontals will not easily swing back and forth. The canopy run from a high cross member down over the two crossing x's (to eliminate the debris/leaves/water ponding) down to the front.

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

Mac, With a retractable awning I don't see why there is a large gravity load. Awnings like this are routinely attached to wood framing with lag screws in brackets with a spacing of about 6" for a moment arm. I don't think fastener slip is much of a concern either. I do think the horizontal members look too small.

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

I hear you, mjr. I missed the retractable awning part. I still don't like the idea of relying only on strong-tie connections for a cantilever. Thermal and moisture changes in the wood will cause the cantilever connection to lose rotational stiffness. You will have a saggy cantilever in the matter of a few years. I would leave the cables and add the strong-tie connections to stabilize in uplift.

-Mac

RE: Need help with calculating the size of a retractable shade cantilever pergola (woodl frame)

(OP)
Guys ..this is the shade type that I have in mind

no awing there

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!

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.