Simple Wire Barrier Deflection

[bucknast]

I'm review materials to be used for a mesh barrier with a cable or wire border that will handle most of the loading, it must span 96", be fixed at both ends at an equal height, and be able to resist deflecting more than 4" at midspan by a force acting there of 20 lbfs perpenticular to the wire. I'd like to evaluate the possibility of preloading the wire to help with this 4" deflection requirement. I'm using the change in wire length (dL), assuming the loaded system is approximately two right triangles, at maximum deflection to give a wire tensile force (P) at this condition: P=dL*E*A/Lo. I'm then using this force to calculate the component that resists the perpindicular loading, and also the stress in the wire to evaluate if it would break/deform. I'm not sure where to include the term for preloading in this scenario. Can I simply add it to my P result to get a value for preload tension + tension from deformation? Is there anything else I'm missing here? Thanks for your help.

 

[Compositepro]

If I understand your problem correctly, preloading (or tensioning) your wire will not reduce deflection because the deflection will be determined by the tensile modulus of the wire. Basically the change in length of the wire is proportional to the change in load. Preloading does not change this relationship.

 

[GregLocock]

Tensioning a wire certainly does reduce the deflection!

OP draw an FBD and all will be revealed.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[chicopee]

When you preload the wire, you will get a reduction in the cross sectional area of the wire. Then deflecting the center of the preloaded wire by 4", you can calculate the tension in the wire by using the reduced cross sectional area in your formula. In turn, you'll have a further reduction in the cross sectional area based in the tension of the wire; I would then average the two calculated cross sectional area and repeated the above calculation. You should be able to calculate the first reduced cross section area using poisson's ratio. There will be a bit of trial and error to get the value that you need.