Pel Stadium Seating Limited had the idea of taking stadium seating to a new level of style and economy by creating the world’s first all-plastic stadium seat. The company asked the Radar design consultancy for their input and Radar responded by providing a futuristic design with contoured plastic stanchions, which replaced the boxy metal stanchions that have been used on nearly every seat up to now. Next, Radar turned to Optima Design Services and asked them to make the seat tough enough to stand up in the stadium environment.

With Pro/E, Optima Design was able to design a durable, all-plastic seat that could withstand the stress of football hooligans jumping on it.

Radar provided Optima with a number of different structural requirements for the Eventa seat. The most difficult challenge was for the seat to withstand large football hooligans jumping in the air and landing on it in an attempt to break it off. This challenge proved particularly difficult for an all-plastic seat because dynamic loads applied by so-called ‘fan’ are all directed toward the small plastic mechanism that connects the seat with the stanchion.

This mechanism was primarily designed for raising or lowering the seat, making it easy for fans to pass by when the seat is not occupied.

From clay to surface model

Radar supplied Optima engineers with point cloud data generated by scanning the clay model they created while developing the conceptual design. Using conventional methods, engineers would have had to go through the tedious process of manually defining splines and surfaces by eye to match the point cloud data. Not only is this time consuming, but it requires a considerable amount of judgment on the part of engineers, running the risk of compromising the design intent.

In this case, however, Optima engineers took advantage of the Scantools functionality of Pro/Engineer Interactive Surface Design Extension (ISDX) to automatically fit surfaces to point cloud data. The surfaces that were generated by Scantools represented the design intent so well that only a few manual tweaks were needed. “The new automated approach saved 60 to 70% of the time that would have been required with the conventional methods,” says Darren Forrest, Director, Optima Design Services. “This helped to substantially reduce the cost of completing the project.”

Mechanical design concept

The next step was to design the mechanism in the stanchion that allows the seat to swivel up and down. The stanchion is designed as a space frame with ribs strategically located to distribute stresses efficiently through the structure. The stanchion part of the mechanism, which consists of two male slots shaped like pie slices with a small cylinder between them, is designed to mate with the seat.

" The use of Pro/E Structural and Thermal simulation enabled the evaluation of more iterations, resulting in a better quality product designed in less time and at less cost. "

The seat part of the mechanism incorporates two female pie-slice-shaped pieces with space between them to provide room for the cylinder. A bolt that passes through the centre of this mechanism provides the physical connection. The male and female pie-slices interface with each other to provide positive stops that limit rotation and deliver strength to resist bending moments applied to the seat.

The backrest is fixed to the stanchion, and the seat is weighted by a metal bar, so it automatically flips up when it is not in use. The use of gas injection moulding makes it possible to use hollow sections in the seat, which is gas injected and improves the seat to backrest strength-to weight ratio. The seat and backrest are made of polypropylene while, the stanchion and other components are made of 30% glass-filled nylon.

Software prototyping

In the past, after defining the initial design concept, Optima engineers would build and break a series of prototypes in order to detect and correct structural deficiencies. Five or six prototypes would generally be required to get a design of this complexity right - a process that would take nearly a year. Engineers estimated that this design would have taken 18 months without Pro/Engineer; using Pro/Engineer it took only nine months of work from concept to manufacture, and reduced prototyping expenses substantially. Even better, with the integration between Pro/Engineer and Pro/Engineer Structural and Thermal Simulation, Optima has been able to replace its old process with a new, much faster process based on software prototyping.

On the Eventa project, Optima engineers worked in the familiar Pro/Engineer environment to define the additional information required to convert it to a virtual prototype. Engineers first applied shell elements to the surface model because shells can be analysed very quickly. After running through enough design iterations to get the design close to finalised, they converted the surface model to a solid model to achieve the highest possible analysis accuracy.

Pro/E graphic showing the amount of stress in the seat when simulating a person jumping on the end of the seat.

Checking the displacement (movement) of the seat by simulating someone sitting on the seat using Pro/Engineer simulation tools.

This analysis shows the seat under compression whilst simulating a person jumping on the end. The values here can be higher as the material is under compression.

The Pro/Engineer Mechanism Design Option was also used to define the mechanism, primarily by defining joints and contact points that come into play as the mechanism operates. A variety of load cases were also defined, such as applying a downward force to the seat to represent a person jumping on it.

Integrated analysis

With the mechanism conditions and boundary conditions complete, Optima engineers simply pushed a button to perform the analysis in Pro/Engineer Structural and Thermal Simulation. And because this simulation software is completely integrated with Pro/Engineer, engineers never had to leave Pro/Engineer to conduct the analysis.

“It is essential to have an integrated solution for CAD/CAE,” Forrest said. “It allows for better collaboration, higher quality products, and a faster design process.” Within a few hours of starting the process, the engineers received their first results.

As expected, the analysis results highlighted a number of weaknesses in the initial design. The results showed high stresses in the male and female pie-slice-shaped segments, so engineers reinforced the areas highlighted by the analysis. The analysis also showed weaknesses in the body of the stanchions, seat, and backrest that were addressed by adding and re-positioning ribs. On the other hand, the analysis showed that some areas of these components faced very low stresses, so, in these areas, material was removed in order to reduce manufacturing costs. The use of Pro/Engineer Structural and Thermal simulation enabled Optima to evaluate more design iterations, which resulted in a better quality product designed in less time and at less cost.

The optimised design

Optima engineers performed 15 design iterations on the mechanism, and nearly five more on each of the major components. Their goal was to optimise the design by meeting all of the client’s mechanical requirements, while minimizing material costs. Engineers showed their customer the final design, which required only a few tweaks.

" The very first prototype passed all the demanding physical tests required of a stadium seat, including first and foremost the 'football hooligan' test "

At about this time, the materials suppliers said they couldn’t meet the original ultimate tensile strength specification, so Optima engineers went back to the Pro/Engineer model, entered the new material specifications, and made a few tweaks to get it working with the new material specifications. In the past, this would have required at least one, possibly two iterations of building and testing prototypes, which would have taken much longer. Not only was it easy to rerun the analysis, but the associative nature of Pro/Engineer made it extremely easy to implement the engineering changes. After making the modifications to the design, all downstream deliverables were updated automatically, saving time and reducing errors.

Right first time

The very first prototype passed all the demanding physical tests required of a stadium seat, including first and foremost the ‘football hooligan’ test described above. Getting the design right the first time made it possible to complete the design process in only six months, half the time of conventional design methods. Without Pro/Engineer, such a design would have required at least four or five physical prototypes, which are not only time consuming, but also expensive.

Ultimately, Optima engineers created a better-performing design than was possible in the past because the speed of the virtual prototyping process - enabled by the integration between Pro/Engineer and Pro/Engineer Structural and Thermal Simulation - made it possible to consider more than twice as many iterations.

The new seat is already being used in the UK at Lord’s cricket ground and Sheffield Arena, and is being installed at the 90,000 seat national football stadium. “Our customer was very impressed that we were able to meet their demanding specifications with the very first prototype,” Forrest concluded.