Steel Bowstring Truss Design
Steel Bowstring Truss Design
(OP)
Greetings,
I'm getting ready to design a couple of different steel bowstring trusses. Length to depth ratios will be about 6 to 1. I will be using HSS sections. Configuration will be radiused top chord, and suspended bottom chord (top chord bearing), sort of in the Vulcraft frame of thinking. Max length will be 77-feet. Full-contact (no gussets) welded joints.
These are the biggest I've ever designed, so naturally I'm a little wary. I'll be using Risa-3D, and IBC 2003.
Oh, and over a pool, so corrosion issues are present.
Any hints, tips, or known pitfalls I should be on the lookout for? Or, can anyone recommend any good publications?
Thanks x 10^6
I'm getting ready to design a couple of different steel bowstring trusses. Length to depth ratios will be about 6 to 1. I will be using HSS sections. Configuration will be radiused top chord, and suspended bottom chord (top chord bearing), sort of in the Vulcraft frame of thinking. Max length will be 77-feet. Full-contact (no gussets) welded joints.
These are the biggest I've ever designed, so naturally I'm a little wary. I'll be using Risa-3D, and IBC 2003.
Oh, and over a pool, so corrosion issues are present.
Any hints, tips, or known pitfalls I should be on the lookout for? Or, can anyone recommend any good publications?
Thanks x 10^6






RE: Steel Bowstring Truss Design
RE: Steel Bowstring Truss Design
Thanks for the response. Good point. On that subject, I'm wondering if we need to specify some "TLC" when transporting, storing and erecting these fairly flimsly elements.
Thanks!
RE: Steel Bowstring Truss Design
Then be sure to add that means, methods, and safety are the contractor's responsibility.
RE: Steel Bowstring Truss Design
One book I have, is "Simplified Truss Design" by Michele Melaragno copywrite 1981. I wouldn't buy it, but if you can find it in a library it might be worth looking at. However, it is on a pretty basic level. You might also look into some old wood design books since bowstring timber trusses were common in the past.
I don't think you will have a problem with a span to depth ratio of 6 and a total span of 70'. Forty years ago it was not uncommon to see timber bowstring trusses span 150' or more.
If I was designing a steel bowstring truss, the part I would be unsure of is how to design the welds.
RE: Steel Bowstring Truss Design
RE: Steel Bowstring Truss Design
JAE's input is right on target. Bracing is critical so is lifting and handling.
You may want to consider cambering the truss. I would require camber that would neutralize the dead load deflection to start with.
I would use 2-D modeling. I do not see much value added for doing 3-D modeling.
The jitter bugs will go away. This is normal. Good luck.
RE: Steel Bowstring Truss Design
Thanks. I was wondering about the camber issue - I didn't know whether truss manufacturers did it for bowstrings. My preliminary swipe at it resulted in about 1/4 to 1/2" DL deflection, and I was wondering what that might look like. I'm thinking that cambering might be in order. Even a tad of overcamber would help to mitigate the eye's natural tendency to see deflection in level objects. Also, a tad of visual camber gives you that sort of psychological warm-fuzzy that deflection doesn't.
Thanks
RE: Steel Bowstring Truss Design
I have however, designed 200 ft span trusses for a hangar, where the depth/span ratio was about 12. I had, if I remember correctly, about 6"-7" of camber called out for these trusses, maybe a little more.
As for weld design, if you don't already have it, I would get a copy of AISC HSS Design Manual. It is a very good reference on design of welded tube connections. And also a book called "Handbook of Structural Steel Connection Design and Details". Also a great reference for connection design. Here is the link to the latter book at amazon:
http://www
There is another book which you might find helpful, called "Design of Building Trusses" by Ambrose. It is a bit simplified but might have some tips or lessons learned for bowstring trusses. It is generally a good reference book for ideas, but does not go into great detail on calculations.
Hope this helps.
RE: Steel Bowstring Truss Design
RE: Steel Bowstring Truss Design
RE: Steel Bowstring Truss Design
Wow, that's cool. Thanks a ton! We'll be doing fully-welded also. To complicate life, the architect has decided he wants full-width skylights in every other bay. So, now I have very little roof diaphragm, and I will be desigining horizontal X-bracing in the skylight bays to resist diaphragm forces and out-of plane wall loads (tilt-up with brick veneer).
Good times ahead!