Contour Enthusiasts Group Archives Forums General Common Interests Engineers... need help with Bridge project

I'm taking an autocad/solidworks summer course. We have been given a simple project to do in solidworks. Basically we build a "bridge" with a span of 100mm, to which we will apply a vertical-only load directly in the center of the span, on a 10mm x 10mm section. We will use the COSMOSXpress feature in solidworks to analyze the strength of the bridge/member, and knowing the factor of safety and the bridge weight, we will be graded on the ratio of (max vertical force it can withstand)/(total weight of the bridge). We are to select "Alloy Steel" in COSMOSXpress.

This does not have to be complex like a traditional bridge at all. It only has to resist vertical loading, and there are no requirements other than it spans 100mm and has a 10x10 mm "pad" in the center to apply the force to. For example, you could make an I-Beam as your entire bridge, and put a 10 x 10 pad in the middle and call that your bridge. Maximum vertical load with the least total weight possible is the only goal.

I'm looking for some kind of rule of thumb on the most efficient way to have a member that stretches a span, support a vertical only load. For example, if an I-Beam is most efficient, I'm wondering what the ratios of the respective sizes of the different parts of the I-Beams should be, etc.

I have been very busy with this class and one other one, so I'm really trying to do as well as possible on this to make up some homework points, and we don't have much time at all to do this. I'm hoping some Civil Engineers on the board or other engineers might be able to offer some guidance.

Thanks for any help!


Below is the official verbiage of the assignment:

Virtual bridge competition

You are to design a model bridge. The bridge will be analyzed using COSMOSXpress to determine the breaking point of the bridge (factor of safety times force).

Span Description: The bridge is to span between two level flat tables of equal height spaced 100mm apart.

Supporting the bridge: The bridge may only be supported (restrained in COSMOSXpress) by surfaces resting on the table (meaning no support for a stretch of 100mm and that the supports are all in the same plane). The bridge may be assumed to be glued down (meaning any faces touching the tables may be restrained in COSMOSXpress.

Applying the force: The force to the bridge must be applied midway between the tables (50mm from either side) and in the downward direction. The force will be applied to a 10mm X 10mm flat surface which must be incorporated into the design.

Material to be Used: Select alloy steel in COSMOSXpress

Scoring of the competition: The competition will be scored by a simple formula. (force at breaking point in Newtons ) / (weight of bridge in kg)

What to turn in: Part file for the final bridge design. HTML file of the COSMOS analysis with your score included in conclusion (as stated above).

Grading: This project will count for 5 percent of the total class grade replacing the quiz category on the syllabus.

2- Percent based on the performance of the bridge.
3- Percent based on completion and following directions
1 st place - 10 extra credit points toward home work grade
2 nd place - 5 extra credit points toward home work grade

I did a very similar project for my Foundations of Engineering class (easiest class i'll ever take ).

I used a program called west point bridge designer. It was made for a contest but your entry was optional. I'm not much of a civil engineer, but search for the program and see if it helps you any more. It has a load test and three or four different metal to use in several different sizes. Thats all I can help you with. Good luck.

or even simpler! BRIDGE BUILDER! Too much fun!

http://www.bridgebuilder-game.com/

I was gonna say that you could make some huge bridge that could hold up anything until I saw their creative scoring formula which determines your score based on the weight of your bridge.

I'm gonna say that since you can assume that any surface facing the table is also restrained, that an arch bridge is your definite best bet. Instead of just having 2 contact points with the table you can increase that to however many you want by using downward vertical supports on the end of the bridge that are restrained by the table. This is the traditional design that railroads have used for supporting massive loads at minimal cost (which would equate to weight in your test). But it will only work if the deck of the table is deep enough, otherwise the legs of your arches won't have a solid surface to push against.

If that might be bending the rules a bit, and you want to stick with something conventional and only 2 contact points with the table, I'd go with a Whipple truss design, also very popular with the railroads for high load capability.

Thanks for the info! I will look into the whipple truss design. Unfortunately, we can only use the table top horizontal surfaces as restraints.

Thanks again!