Cosmos/M bridges the gap

Finite Element Analysis was almost made for bridge design and its use in this field is nothing particularly new. But design engineers at Mabey & Johnson turned to COSMOS/M, supplied by CentiDesktop, for its excelent ease and speed of use. The design team has now parameterised their design configurations and a series of FEA models can be analysed automatically -- based on the answers to a few simple questions. The result is a much more rapid solution to the increasingly difficult and unusual problems thrown at Mabey & Johnson.

It has been said that the majority of design work is simply the development of an existing idea or product. While this may be true it is often interesting to see how far a design idea can progress with the help of computer tools. Desktop Engineering recently worked with a company that has brought an old idea up to date using finite element analysis.

Donald Bailey developed the Bailey bridge during the Second World War to provide an inexpensive and easily constructed bridge system that could be taken anywhere in the world and built with the minimum of equipment as speedily as possible.
A combination of experience and engineering know-how enables the engineers to predict likely structural responses to most situations. However more accurate validation can only be achieved by testing a model. As Peter Tomlinson, Mabey & Johnson’s senior designer commented "Physical testing of a design can take several weeks and soak up considerable expense. And it doesn’t allow different configurations to be tested. We really needed a way to analyse our designs more efficiently."

While the use of FEA in bridge design is not unique. Mabey & Johnson have taken the application one stage further than most. By using the parametric capabilities of COSMOS, Peter Tomlinson’s team have parameterised their design configurations. For a particular customer query, a series of FEA models can now be created and analysed automatically, simply by answering a few basic questions. Such capability makes thorough assessment of a range of solutions very simple, with minimal manual input.

This essentially simple system has been developed by Mabey & Johnson over the past 50 years into a complete range of structures, which are far removed from those originally devised. Today’s Bailey bridges are exported worldwide to meet the enormous global demand for temporary and easily assembled spans. Its applications range from a permanent road bridge in New York to a temporary structure replacing a bridge lost to mountain floods in Nepal Finite Element Analysis (FEA) was the answer and COSMOS/M running on a PC was the chosen solution.

It is diversity of applications that presents Mabey & Johnson’s engineering team with such an interesting challenge. They are constantly being called upon to apply their bridging expertise to unusual, often difficult, situations, many with tight deadlines. It is vital for engineers to quickly determine how their bridge designs will perform under varying conditions if design integrity is to be assured.

Explains Peter, " we can now model a design in a matter of hours and get results for different loading conditions in a similar timescale. The system flexibility allows us to change and study a whole range of models and for each, rapidly simulate the traffic on the bridge and its behavior. We can also check for resonance problems by calculating the natural frequencies of the structure. Reassuringly, results from the software correlate well with physical test results.

"More often than not we are confirming what experience suggests is the solution, but that validation is vital today," says Peter. "It also gives an immediate and clear picture when things aren’t quite right. As a result we can present, with justification, the most appropriate solution for the customer. This solution is based on information derived in a fraction of the time and cost it would take to generate using traditional means, which gives us a strong technical edge."

Most recently the company has been looking more closely at key elements within their bridge structure, particularly the hinge joint that connects two sections of a bridge and the behavior of its securing pin. Since the contact and resulting behavior of the pin within the joint changes as a load is applied, non-linear analysis is required.
Peter has modelled the joint structure and, using Cosmos/M’s non-linear module, examined what happens to the pin and surrounding area when load is applied. By being able to look inside the material and at the contact area (difficult to undertake physically) a clear behavioral picture is derived particularly after the material has yielded – the main cause of bridge failure. It is anticipated that this information will enable the hinge design to be further developed to increase strength and safety.
The company’s adoption of FEA and COSMOS/M has improved the efficiency and productivity of the bridge design process, and provided a quality of information that enables the ideal solution to be presented and justified to the customer.