algorithmic modeling for Rhino

Help for newbee Kangroo cable definitions

Hello Everybody


First of all I must express my feelings about Grasshopper and kangaroo : Amazing work that will change the shape of design architecture and engineering.


As for my need of help. After many times of trial and error I am afraid  I will not be able to master kangaroo without good knowledge of civil engineering. So I am asking for help.


I am on to a concept drawing of a factory shed which I like to design with a suspended cable system. But I cant define any suspended cable system no matter hard I try. Does anyone has any pre-defined grasshopper definition. I can do the rest. I need to define shape of the wire rop, so I can be sure to have neccesary clearance from the ground. here is my pre-design.


Thank for any help

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Comment by Steve Lewis on June 25, 2011 at 4:51am

JJsolly is correct for a single curvature span you can estimate loads and geometry assuming a catenary profile.


If you have a 2-way spanning cable net with or without double curvature you cannot use a catenary defintion and you will have to form-find it using a suitable iterative numerical approach that accurately models the form with the requiried equilibrium required.


Comment by tonguc salgar on June 22, 2011 at 5:11am

thanks alot for the reply. I will in to what you mention right a way. The reason I want to use kangaroo is to get fast feedback from when I made design changes. The above basic design tends to change when I get better understanding of Kangaroo and grasshopper. But to bigin with I need to solve this basic system. But You gave me new directions to follow thanks alot.


Comment by jjsolly on June 22, 2011 at 4:44am

The sag of the cable will form a catenary under uniform loading (which it looks like you have)..


The final sag of this catenary can be chosen by you - this then determines the tension in the cable and hence it's thickness and the requirements on the surrounding structure.


You do not need to use Kangaroo to form-find the cables in this roof for scheme design - they will be VERY close to catenarys.


If i've misunderstood the question then I would recommend looking at the USS Wire Rope Engineering Handbook which has simple equations for the shape of cables under a whole variety of situations...

Comment by jjsolly on June 22, 2011 at 4:41am

The sag of a wire rope can be set at any value you please. Under uniform loading (which it looks like you have) the cable will form a catenary - and the mathematics for a catenary curve are easily available - in fact there is a function in GH to draw one.


Essentially the smaller the sag the greater the cable tension and this then defines the thickness of the cable and the load applied to the rest of the supporting structure. The extension of the cable can be factored into the construction sequence so you will achieve the deflection you are looking for.




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