I know some of you guys will remember my truss thread from not to long ago and alot of people wanted to know how it went. Well I managed to get first place, the goal of the project was to build a truss that would fail at exactly 750lbs. Ours failed closest to the goal, failing at 828lbs. While failing at 750 was the goal failing over the 750lbs was more desirable then failing under the mark. Also, I should mention our truss was the only truss that failed exactly were we expected it to fail. On to the pic's:

VIDEO: The video isnt the best, it starts half way through.
View My Video

 

Nice job.

How was it loaded? Also, it that top joint?

 

Both ends were rested on pins and it was loaded in the center with an extensometer.

 

hey I notice you went with the lap joints .....i misunderstood you though, I thought it had to hold at least 750lb, not fail at 750lb...what kind of glue did you use? are the square blocks just to reinforce the joints?

 

Just elmers wood glue.

 

How did you calculate the breaking point? Or was it trial and error? Wild guess?

 

Congrats on winning.

I'm kinda surprised though, I would have expected the wood glue to fail long before 750 lbs.

 

once wood glue is dry it is far stronger than the wood....if you look closely you can see the wood broke at the joint, not the glue

 

Congrats!

 

We had to calculate the force, stress and shear stress for each member. We just went by that and clearly there is an obvious area of higher stress. I updated the post and added a video of the testing session

 

Is this a first year project?

How did you know the max. sheer and bending moment the wood could take?
Did you do a test on a single piece?

 

All hand calculations or did you use FEA?

 

All hand calculations because we had to do it manually to turn in with our report. It was alot of work ,but there was 3 of us in the group so it wasent that bad. Plus we found a program called wintruss, that you can basically draw any 2d truss you would like and add forces and it will calculate the force and stress in each member. We used that just to compare our numbers vs the programs and it was dead on. I just thought it was pretty cool we won. I really am starting to love engineering, it is a hell of alot of work but I think it will be all worth it.

 

I'm assuming the teacher told you an adhesive that would fail well after the wood? If that is the case, that makes this project very simple to design. If you had to figure in joint failure, that adds a decent bit more calculations. I'd imagine where most of your classmates failed was with actually building what they designed. If not, I'd be kind of scared. This is pretty basic 3rd year engineering stuff.

 

I was suprised on how many groups actually didnt know what the hell they were doing( it was kinda scary). It was more or less designed to be a learning experience, its kinda scary in genral how many engineering students can do book work but dont have a clue when it actually comes time to do something hands on. I know this isnt the greatest project in the world I just figured I would share.

 

x19384834839!!!

this is sooo true in my school.(manhattan college 4th year mech. eng student) I feel that is where someone like you and i have an advantage over them, we are very good with hands on and can put our ideas not only on paper, but produce them as well.

 

Just wait until you get into real engineering world. It is great to see those people that had 4.0s in college struggle with the simplest things....a little common sense anyone? lol.

That is a cool project. At Cal state they have a huge bridge competition where they build a larger scale bridge for a civil engineering project. I can't get over the people that suck when it comes to actually applying things you learn in lecture/books.

 

Our final project was to design a bridge to span 12 feet using no fasteners (no nails, screws, glue, etc) and with no power tools, and with 8 feet members as the maximum length. The goal was to be the lightest possible. Our bridge was 56 lbs, the next lightest was 98 lbs, and one group even came in at over 200 lbs. It was absurd. One group's bridge was a "self-supporting suspension bridge" which didn't even pass a simple free body diagram.

Most people just built something that would work, and did no calculations to the strength of the bridge. It was pretty sad. Our group won by a long shot, and even though it just had to support our 290 lb professor, we all climbed on for a picture.

As an added bonus, we built a 2 foot deep pool of water under the gap the bridges had to cross. Given that we tested these in December, in Pittsburgh, and there was ice on the water earlier in the morning, a failure would have been unfortunate.

After about 75 man hours. 14 feet long and balances perfectly on the 3.5" wide center section.







What kind of engineering are you studying?

 

Cool project kookz, I am studying mechanical engineering.

 

i suck at book work . but i built a 4oz balsa wood bridge that supported 101lbs. the kid that beat me cheated and made a damn I-beam and called it a bridge .

i weight 126lbs. and was able to stand on one foot on top of my bridge but thats a different subject .

congrats. was there any weight requirement to contructing your bridge and what wood was used

 

nice project....how are you holding the decking to the main span...you said no fastners...i see the joints using the dowels...did you just use dowels to hold it from sliding?

and i cant stand the 4.0 people who can run calcs for days on end...but when i comes to actaully doing something other that given problem they are all lost out in the blue.

 

thats the difference between go getters and book worms. it's annoying how much stress is placed on going to a good college. I live 40min from NASA and 30min from Lockheed Martin and most the people i know at both locations aren't 4.0 or 5.0 honor students, they are regular run of the mill guys who understand concepts and how to make them wok better . i have yet to meet an employee from MIT or CalTech at NASA

 

Yeah, we drilled holes 1/2" deep. Split the end of the dowel with a chisel, and made tiny wedges out of oak. Put the wedges just barely in the dowel, and then when we hammered them into the hole the wedge was driven in. It was pretty slick if I do say so myself, we did the same thing for the top, so those planks were secure.