×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*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.

# Beam and cable problem. HELP!2

## Beam and cable problem. HELP!

(OP)
There is a cantilever beam. One end is Fixed and other end is supported by an Inclined cable.
.
Loading is vertically downward at the Tip of beam, denoted as P. Beam and cable are not considered Rigid. So they are considered to be deformed.
.
So due to P, Flexure stress will govern and bend the beam.
.
And wire will be elongated so tension will govern. For very little deformation this horizontal component of Tension causes pure Compression on beam. And vertical component reduces the moment due to P.
.
The more the beam gets deformed the Compression stress turns into flexure stress on beam.
.
So there are two dependent Phenomena. And undoubtedly the condition is statically indeterminate for sure! And I cant find a way to solve it analytically!
.
Is there is a way to attack this type of problem? Or is it possible to govern an equation? Has it been done? Please help.

### RE: Beam and cable problem. HELP!

(OP)
Ok.
No. For my thesis work.
Thanks.

### RE: Beam and cable problem. HELP!

yes, singly redundant ... i'd apply unit force method.

this'd directly solve the vertical component of the cable load, which'd be good enough for a professional result, but maybe not if a school problem ... if so, don't ask here.

strain energy method would give you the correct result.

### RE: Beam and cable problem. HELP!

Depending on the relative stiffness of beam vs. cable, could the compression load induced at the beam tip induce buckling-type instability?

(OP)
Thanks.

### RE: Beam and cable problem. HELP!

(OP)
Should not. Actually Im using this type of configuration for an aircraft structural member. In that member a Aluminium frame is considered to be installed at the Tip. So there should not be any buckling.

Thanks.

### RE: Beam and cable problem. HELP!

there will be compression in the beam (and bending) from the cable. it might be small (if the cable isn't pretensioned), but under load it'll increase, and it could be a factor.

buckling and crippling and possibly beam-column effects.

"In that member a Aluminium frame is considered to be installed at the Tip." ... what does this mean ? your sketch showed a cable-stayed cantilever; is the more structure at the tip ??

### RE: Beam and cable problem. HELP!

(OP)
In this picture I didnt show it and hence I assumed that there is no local buckling. In fact there will be a stabilizer. For stabilizer attachment a aluminuim frame will be installed.
Thanks.

### RE: Beam and cable problem. HELP!

do you mean a doubly cantilevered beam ?? (with a redundant cable brace ?)

or do yo mean at the fixed end of the cantilever ??

### RE: Beam and cable problem. HELP!

(OP)
No. I have made a CAD with approximated estimated value. This picture is attached. You can have an idea of the system from it.

The aluminium frame and How and where the wires will be connected is not considered actually. It can be with Stabilizer beams through frame holes. It will be designed later by me according to the results with the assumption of local buckling is not present.

Thanks

### RE: Beam and cable problem. HELP!

this is SO different to your original sketch !

i think this is so redundant that FEA is the only way ... unless you can rationalise a very simple structure/loading.

### RE: Beam and cable problem. HELP!

(OP)
Thanks. Ill go for FEA then

### RE: Beam and cable problem. HELP!

NOTE. I have seen a design manual for cable supported structures... just can't remember "where". Will scratch my brain... see if anything surfaces.

CAUTION.

The devil is in details, such as cluster-joint load-centers, collum eccentricities and torque, collum symmetry/stability, thermal expansion/contraction [including variations within wires/wire-groups/collums, etc], individual wire* stiffness, etc

*"WIRE" Note: do You intend to use solid wire [round or 'shaped' cross-section], conventional wire rope, anti-rotation wire-rope, etc? Steel, CRES, HRA, fiber filaments or rod, etc?

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

### RE: Beam and cable problem. HELP!

(OP)
Thank you very much

Im going through the article!

First of all I have very poor idea about wires!
I use solid Round Wires. Wire ropes in market are too thick as much as I have seen! So wires like GI wires, binding wires is what I have chosen though these have a large elongation!
My chosen wires will be only tension members. Wont take any compression and torsion generally. So are not Anti rotation and rods.

They will not be pretensioned like spokes in wheel. So I have to let the Beam resist bending moment initially with a very low loadings and almost no deformation. But wires will be in operation when Loadings are getting larger in value and deformation is not negligible!

Thanks

### RE: Beam and cable problem. HELP!

are the wires purely structural ? why no pretension ? (that's quite odd for cable stayed structures.)

what size of wire are you thinking ? i'm thinking a/c control cables are 3/16" dia, i'm sure you can get them 1/8" maybe 1/16".

personally i'd let the wires react all the bending, they'd be very efficient to doing this, and use the "beam" as a "king-pin" to react the compression due to the pre-tension.

### RE: Beam and cable problem. HELP!

Integrator62...

Suggest you consider using [in-practice or in-theory] CRES spring-wire per ASTM A313 Standard Specification for Stainless Steel Spring Wire.

NOTE.
This spec lists several alloys/strain-hardened variations for ~small diameter wire. In general, though, these various wires are hardened to roughly the same extreme-high-strength-stiffness/diameter and are made to very exacting standards of quality [metallurgy, surface finish, tolerances, etc].

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

### RE: Beam and cable problem. HELP!

(OP)
I cant say how to Thank you rb1957

Yes purely structural. Dont want to make it pretensioned because of the complex design. I have shown a CAD design in the link below.

But Right now I am thinking of making it a little more complex and pretensioned. Hope It will work better.

### RE: Beam and cable problem. HELP!

(OP)
Thanks, I am going for it wktaylor

### RE: Beam and cable problem. HELP!

"I cant say how to Thank you" ... yes, you can ... "Like this post? Star it!" ... what we call LPS (Little Purple Star) ...

#### 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.

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!