Terms & Conditions

Data Security

We are committed to ensuring that your information is secure. In order to prevent unauthorised access or disclosure we have put in place suitable physical, electronic and managerial procedures to safeguard and secure the information we collect.

All data is stored in secure electronic systems accessible only to Oasys staff with both valid network login credentials and specific authorisation to access the system.  Our systems further limit data access by role to ensure data is available only to those who have a specific need to see it.

If at any point you suspect or receive a suspicious communication from someone suggesting they work for Oasys or a website claiming to be affiliated with Oasys, please forward the communication to us or report the incident by email to [email protected] or in writing to Oasys, 8 Fitzroy Street, London, UK, W1T 4BJ as soon as possible.

Data Security Notice Updated 27th February 2020

top ]


Website Terms and Conditions

The contents of this web site are protected by copyright and other intellectual property rights under international conventions. No copying of any words, images, graphic representations or other information contained in this web site is permitted without the prior written permission of the webmaster for this site.

Oasys accepts no responsibility for the content of any external site that links to or from this site.

top ]



Software Licensing Terms

Terms and Conditions of Purchase

The full conditions of purchase and maintenance for all Oasys desktop software are set out in the Oasys Software Licence and Support Agreement.

The full conditions of purchase and maintenance for Oasys Gofer and Oasys Giraphe are set out in the Gofer SaaS Agreement  and the Giraphe SaaS agreement.

All prices are subject to TAX at the current rate.

Prices and specifications are subject to change without notice – please ask for a written quotation.

Although every care has been taken to ensure the accuracy of all information contained herein, the contents do not form or constitute a representation, warranty, or part of any contract.

Superseded Versions of Terms and Conditions

Oasys keeps copies of all superseded versions of its terms and conditions.

Maintenance & Support Services

Support and maintenance is included with all subscription licences for their full duration.

Annual maintenance contracts are available for software under a perpetual licence, prices are based on a percentage of the most recent list price.

This service includes:


top ]



Cookies Policies

View available cookies policies below:


top ]


Form-finding asymmetric bridges

Authored by Peter Debney

I am often asked about form finding tension structures but the other day I was asked how to do one that I have not done before: an asymmetric bridge.

Form-finding is a method that determines the geometrically optimal structure to resist a set of tension forces. This may be a fabric surface or a net of cables, but the end result is a structure that has the minimum inherent energy yet has all the forces in balance.

Compression structures are different though. The minimum energy form for an arch, for example, is a pile of rubble. While tension forces stiffen, compression buckles. This means that to form-find an arch you need to cheat. Thankfully engineers of the past realised that ideal arches are mirror images of ideal catenaries: to form find an arch you simply need to turn it upside down. This means that to form find a compression structure you need to reverse the loads and put it all into tension.

So, to the bridge. I wasn’t initially given a form to work to, so I decided to make a tied arch bridge with a deck that snakes like an S in plan. Constructing the deck’s form was a simple matter of using the flex command from within GSA; likewise I flexed the arch (coincident bar and spacer elements) into a parabolic arch of a suitable rise.   Manually added ties completed the basic geometry.

As discussed above, to form find the arch I need to put it into tension, but I could not reverse the load on the ties as that would put them into compression, and neither could I simply apply point loads for the hangers as the force direction must change as the arch moves. I decided I needed to make mirror image copies of the ties above the arch to pull it into shape.

While GSA can mirror elements and nodes through a plane, I needed to mirror about a parabola. The easiest way I could think of was to copy the node coordinates into Excel and use the functions there to create the new locations, having first reordered the node numbers along a vector using the Manage Data command. I then copied the new nodes back into GSA and added the extra ties.

The last step before form finding was to ensure that the deck and real hangers would not interfere, so I created a Stage containing just the arch and upper hangers. I also created a similar one for the “real” geometry for the subsequent static analyses.

Having set the form finding soap film target prestresses, I could then form find the analysis stage to determine the arch geometry and prestress.

That completed, I just needed to reverse the arch prestress loads in the loads table using the function command, copy the tie prestress into the “real” hangers, and change the arch Bars into Beams to produce the result you can download below.

Is this the final form? Well, no. For one thing such a form find tends to be an iterative process and so some elements of the above exercise will need repeating; for another I didn’t include all the necessary forces.

What have I left out and how should you deal with it? I look forward to hearing your suggestions.

Here is the GSA arch model. Note that it is in 8.7 format, so you will need that version or higher to open it.

Require more information?

  • This field is for validation purposes and should be left unchanged.

Newsletter Sign up

Please fill out your details below to receive the latest oasys news.

  • This field is for validation purposes and should be left unchanged.