Hi guys, i am a second year mechanical engineering student and as part of my major assessment, i have to complete a design project, of my own topic. As such, i have decided to design a utility tray to go on the back of my ute/truck. One requirement that the project must address is that it has to include calculations. Since, am 5 weeks into second year however, my facilitator isn't expecting 'full on' calculations of dynamic loading and stuff like that. He said to keep it simple through assumptions. From this, I am thinking I would to design the frame, by calculating the number and position of beams etc. to hold â€˜X-amountâ€™ of weight/load. As for assumptions, Iâ€™m thinking of cancelling out vibrations (have not learnt anything about this) and assuming that the load is evenly distributed, to make things easier. The problem I'm having is that I'm not to sure how to go about working out the number and position of beams the frame would need. Can you guys, give me suggestions and/or ideas how to do this? Cheers, Joel

Start with a sketch of the section of your UTE. Place your tray where you desire. Find someplace on the frame of the ute where you can attach your tray. Now you have to connect the dots :O I try to design structures like this as if they were a truss and not a beam. The elements of a truss are connected by pin joints and have tension or compression only. You don't have to use pin joints you can join them with a weld. But a design of triangles is very strong and rigid. Trusses were covered in my Statics and dynamics classes which were second year I believe. The acutal tray will be a beam and need to be analyzed as such. The rest can be tension or compression members. Try to design for a static load of 5 or 10 X the actual load on the tray. That should cover the dynamic loads you see on an off road vehicle.

What calculational methods for stress are you familiar with? Do you know about moments of inertia, simple beam stress calculation, strength of materials and free body diagrams? Once you know which tools are available, then you can start to simplify the model of the tray and generate some conservative calculations.

@JPfalt. so far this term we've learnt about free body diagrams, moment & couplings, truss analysis and using the conditions of equilibrium to solve as well as moment of inertia. Unfortunately however i missed the class of moment of interia and have not learnt about beam stresses; ill go through a few textbooks. Would i need to be familiar with these topics (moments of inertia, simple beam stress calculation, strength of materials and free body diagrams)?

thanks Erich, i wasnt sure how to make a start. not sure what you mean about solving it as a truss. not sure how i could do this.