Truss

[Alex786]

hi guys,
kindly find attached a sketch which shows a eccentric truss with knee bracing for the column. This is designed for the huge lateral forces from the wind load.kindly put your reviews for the attached design.

 

[Ron]

Alex786...I could not get your attachment to show.
Besides, that's not quite the way the forums are intended to work. To ask for a blanket review of a design will probably get you no constructive answers. No one has the time to review your design for adequacy or even comment unless you ask specific questions. This is not a free engineering review service. In order to review a design, all of your assumptions have to be laid out, all of your design parameters would have to be given, your location and code would have to be given, and material specifications provided. That's way too much to expect from a forum.

Please re-state your issue with specific questions that you might have. Give your location and code. Perhaps then you will get some beneficial response.

 

[msquared48]

Didn't work for me either.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MikeHalloran]

The provided link points to a file that exists only on Alex786's computer.



Mike Halloran
Pembroke Pines, FL, USA

 

[Alex786]

Dear Ron,
truss has a specific geometry to withstand loading's, so i just asked your opinion. Sharing ideas and opinions is what this forum is about , correct ?
Please find attached the truss design , This is originally modeled in SAP 2000 v 15 ultimate , this is a roof canopy structure, 115 meters x 90 m . there is a huge lateral load for wind . Any details will be provided.
Thanks
Alex

 

[hokie66]

You will have to ask your question better than that. What about the truss is eccentric? What kind of roof framing do you have? What form do the columns take? Is the lateral wind loading resisted just by column bending?

 

[Alex786]

The truss is eccentric , the knee brace is from the column to the lower chord of truss .The bracing is of eccentric type. Roof framing is cladding aluco bond 4 mm thick . columns are pipe sections dia 610 mm x 40 mm

 

[hokie66]

The truss is eccentric about what? Cladding is not framing. If you can't explain your problem, we don't have much hope of helping.

 

[Archie264]

A couple of comments:

From just looking at the proportions or the diagram the knee brace looks small. But it might be large enough to do so weird things to the column. And strictly speaking, since the horizontal chords are carrying moment near the columns that isn't actually a truss but is, rather, a frame. I think the distinction is important since, as shown, there will likely be some large moments transferred around and through the truss/column interaction as well including in that horizontal bottom chord adjoining the column. Also, it is worth asking whether that knee brace will provide enough lateral stability to the system.

Without knowing anything about the system other than what's shown on the sketch I would suggest you consider whether it would be better to design the trusses as pure trusses, pin them to the columns, and provide the lateral stability to the system through something that is more robust than just those braces (i.e. full frame bracing, shear walls, etc.) That is simply my opinion based on a limited understanding of the situation and actual condition may vary significantly, of course. In other words, that's just my two cents (rubles, lira, rupees, etc.) worth.

 

[woodman88]

It is a truss, if you look at it in plane and removed the column above the lower chord and the upper chord from the column to the "eccentric brace" you have a triangular configuration. Extending the column and upper chord out to meet, braces the column so it can be pinned at the bottom. It does not look IMHO like a good design. But may work. More importantly, is why it would have been be done this way.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

Usually a "Knee Brace" extends a large distance below the bottom chord connection to the column, like 25% to 33% of the column height, to be effective enough to lower the required size of the column.

This is not the case here, and I would hardly call this a knee braced condition.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

If the nodes represented by small circles are intended to be hinges, the system is unstable as drawn.

If the columns are continuous from ground to the top chord, knee braces would not be required and the structure would be capable of resisting substantial wind load without knee braces. If the columns are terminated at the bottom chord, the structure has negligible resistance to lateral load and is not helped much by knee braces.

BA

 

[Ron]

Agree with Mike....if to scale, your "knee braces" are woefully insufficient. Agree also with BAretired that if the columns extend to the top of the truss, there is no need for knee braces.

You could also eliminate the knee braces by embedding the columns and creating a fixed condition at the base of the columns.

 

[msquared48]

But, if the columns extend to the top chord of the truss, then the first diagonal of the truss becomes a knee brace and would have to be designed as such.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

And to comment further, the truss would have to be able to take a moment at the column, since the knee brace is part of the truss.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

I would not call the first diagonal a knee brace as it is required for stability, but I agree that the trusses would be continuous and therefore indeterminate to some degree. I am not sure why the columns are hinged at the bottom as they would assist in carrying lateral loads to a much greater degree if the baseplate was restrained against rotation.

BA

 

[msquared48]

BA...

You are correct. I would not call it a knee brace either, but it, in effect, it is helping the top and bottom chords of the truss to create the same resisting moment to help the column and structure laterally.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com