×
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

Jobs

ASCE 10-97 triangulated hip bracing

ASCE 10-97 triangulated hip bracing

ASCE 10-97 triangulated hip bracing

(OP)
Good morning,
I have been searching old posts on the subject, but I couldn't find any answer.

I am trying to fully understand the requirements of ASCE 19-97 with reference to the need or advantage of triangulation of hip members.
My concern derives from the possibility to reduce leg slenderness in case of X and K bracing patterns when redundant members are added without having hip members or not triangulated hip bracings.

In the event of a square section tower, and wind at 45deg, both diagonals and legs are in compression.
To me, using non triangulated redundant to reduce leg slenderness is therefore allowing compressed members (diagonals) to brace another compressed element (leg) without the needed rigidity in the perpendicular plane.
it seems that TNX Tower software is also highlighting the issue, see below the comments from its User Manual

"Secondary Horizontal Braces Leg. Secondary horizontals ordinarily are not considered to be able to brace leg members. When the secondary horizontals are sufficiently triangulated to have this capability, then you may check this box"

Additionally , other software like MStower is requesting additional care in case of not fully triangulated structures (plan + hip bracing)
I found some documentation on the subject, referring to power transmission tower collapse and the effect of triangulation, but nothing that really gives clear guidelines on the subject.

Paolo

RE: ASCE 10-97 triangulated hip bracing

Well, if not one else response I'm willing to give it a partial response.

AISC requirements for bracing and tower requirements will be a certainly bit different from what you get with the tower codes. Different industries, different assumptions. The AISC requirements will (I believe) be a more stringent. That's because they're primarily aimed at building type structures.

For communication towers or such, the industries tend to be a bit more liberal. They're looking at towers with a history of successful performance and trying to justify that they should be allowed under the newer codes.

Plus, we know that if you triangular the bracing then it should provide SOME stability to the member. Is it fully braced at that point.... I'm not sure that it is. But, is that okay? If they're requiring you to do a geometrically non-linear analysis does that allow them to get away with less conservatism with their unbraced lengths?

If I wanted to really research the issue, I'd go through the code and commentaries (both ASCE and AISC) and see what technical papers they are referencing on this subject. Then I'd start collecting these papers and reading through them in detail.

RE: ASCE 10-97 triangulated hip bracing

Quote (OP)

To me, using non triangulated redundant to reduce leg slenderness is therefore allowing compressed members (diagonals) to brace another compressed element (leg) without the needed rigidity in the perpendicular plane.

This is going to be difficult to explain but I'll give it a go anyhow:

1) A compressed member can definitely brace another compressed member. In buildings, this happens all the time. A vertical braced frame, in compression, will brace the tops of all the gravity columns which are also in compression. The trick to it is to ensure that the thing doing the bracing is stiff and strong enough that it can share it's stiffness with the members that it is providing bracing to.

2) With your tower, it is not the diagonals that are bracing the tower legs. Rather, it is the vertical trusses formed by the diagonals, the legs, and the web members that are bracing the tower legs. And while the diagonals on their own may be too close to buckling themselves to provide bracing to the legs, the trusses just mentioned will be nowhere close to buckling in plane.

3) From what I can see, all of the horizontals connected to the legs of your tower are in fact triangulated in the planes shared by the legs and the diagonals. Thus, I believe that all of those horizontals can be counted as bracing.

This is the same principle that allows us to assume that building truss compression chords are braced in the plan of the truss at each panel point. Even in tension, the opposite truss chord would be nowhere near stiff enough to provide bracing to the compression chord on its own.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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


Resources

White Paper - The Criticality of the E/E Architecture
Modern vehicles are highly sophisticated systems incorporating electrical, electronic, software and mechanical components. Mechanical systems are giving way to advanced software and electronic devices, driving automakers to innovate and differentiate their vehicles via the electric and electronic (E/E) architecture. As the pace of change accelerates, automotive companies need to evolve their development processes to deliver and maximize the value of these architectures. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
Modern cars, trucks, and other vehicles feature an ever-increasing number of sophisticated electrical and electronic features, placing a larger burden on the wiring harness that enables these new features. As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - Modeling and Optimizing Wire Harness Costs for Variation Complexity
This paper will focus on the quantification of the complexity related costs in harness variations in order to model them, allowing automated algorithms to optimize for these costs. A number of real world examples will be provided as well. Since no two businesses are alike, it is the aim of this paper to provide the foundational knowledge and methodology so the reader can assess their own business to model how variation complexity costs affect their business. Download Now

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