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    Bridge Designing (Mech/civil engrs)

    Here is a very unusual question

    here is a bridge I am trying to design. Just cant get it right. The final text well be a train crossing the bridge.

    http://www2.paklinks.com/gupshup/gallery3/brgTP.gif

    The beam labelled B fails when I try to cross the train . Somehow I have to disperse the compressive force on it. Anyway Ideas?... I dont have much material left, I think i can add 3-4 more links.

    [This message has been edited by who---me (edited June 16, 2001).]

    #2
    heres how a previous design kept failing....

    http://www.users.bigpond.net.au/fuee/brg.gif

    :-/

    ------------------
    Guy with the Urdu Custom Title :~P

    [This message has been edited by who---me (edited June 16, 2001).]

    Comment


      #3
      Not a Mech/Civil Eng ... sorry

      But just wanted to ask you ... what computer software are you using? Look cool!
      I know that you believe that you understood what you think I said, but I am not sure you realize that what you heard is not what I meant.
      - Robert McCloskey

      Comment


        #4
        you need to change the design of the structure..

        the load is not being transferred properly from the structure to the abutments. if you look at the colours the load is not transferring from the bridge to the rock face.

        Comment


          #5
          Ahmadjee its called BridgeBuilder :-P how original. :~D

          Originally posted by blackzero:
          you need to change the design of the structure..

          the load is not being transferred properly from the structure to the abutments. if you look at the colours the load is not transferring from the bridge to the rock face.

          Well thats what I am trying to do.....But run put of funds.
          Any idea on how to do it some other way.



          ------------------
          Guy with the Urdu Custom Title :~P

          Comment


            #6
            Now the truss doesnt fail the actual path does
            :-\

            http://www2.paklinks.com/gupshup/gallery3/BRG2.gif

            back to the design board

            Comment


              #7
              couple of questions..

              1. are you at uni.
              2. what level class is this?

              just wanted to check how to phrase the response.

              here are a few bridge design ideas.. which work well.
              http://www.pre-engineering.com/resources/trusses.htm
              http://www.pre-engineering.com/resources/trusses2.htm


              anyways
              what is the span of the bridge and the weight of the train? maybe i can look something up..

              also try alt.engineering.civil newsgroups... they can be quite helpful..

              I am though an engineer.. i have not designed truss structures in six years since graduation... water's mah baby.

              [This message has been edited by blackzero (edited June 17, 2001).]

              Comment


                #8
                ah done it...... Just calculating the forces in the members now. Thanks for the help anyway...

                http://www.users.bigpond.net.au/fuee/finbrg.gif

                and it was a very small "Mechanics of Structures" assignment at uni..second year engineering.

                Todays lesson..... Bridges dont have to be always pretty to work

                Comment


                  #9
                  doent that look pretty!!.....

                  BTW......I aint a civil engineer... This is a cross faculty course

                  .....The trusses in the links are single point on the either side trusses. My material is aparently too weak and I didnt have a lot of it. But then I have 2 contact points at the abutments

                  [This message has been edited by who---me (edited June 17, 2001).]

                  Comment


                    #10
                    http://www3.pak.org/gupshup/smilies/smile.gif It brings back my memory of first year design class. Well, my bridge using balsa wood was the best in my group. Let me remember what I had done and who had the best/worst design. http://www3.pak.org/gupshup/smilies/ahaa.gif


                    I didn't do civil engg. but can give you some advice from experience. I hope it might be of any help. http://www3.pak.org/gupshup/smilies/smile.gif

                    I assume you are restricted with the amount of material due to cost etc. but can you use wires to support the structure.

                    The worst design that was tested had a lot of beams like u have in the last pic. Try to avoid extra structures above the main bridge. It really doesn't do much for the strenth of the bridge.

                    In my design all the beams were directed in the centre point coz weigt was to be suspended in the centre. It had a hut (an inverted V type of) shape.

                    Comment


                      #11
                      yaar its all theoretical.... and the top part is VERY important... You cant even remove one member from there without colapsing the whole thing. Just look at the color changes when the train passes.

                      Waisay last year we had a paper bridge competition. Had to make it out of 1 A4 sheet and it had to span 20 cm. One bridge weighed 18gm and went up to 47Kgs...BLOODY HELL!!!...
                      mine failed at 16 :-(

                      ------------------
                      Guy with the Urdu Custom Title :~P

                      [This message has been edited by who---me (edited June 17, 2001).]

                      Comment


                        #12
                        hehe...

                        my groups bridge won the award.

                        we had to span 12 inches using only balsa wood, glue and string.

                        I used curved bridge structure as it transfers all the force to the abutments.. as long as the material itself doesn't split.

                        Comment


                          #13
                          well that structure does look really weak,...

                          I am guessing building towers to do a cantiliver design is out of the question cause of cost. How about using prestressed cables as part of the structure? like a prestressed bridge span might make it easier to support with a truss?or putting the bridge span on top so that the truss is in compression -- that way it can carry a lot more load...

                          Also how about using a curved truss from one end to the other?

                          By the way this bridge builder program... is that just a simple statics calculator of sorts?


                          black zero... that sounds like a familiar nick.,.. any connection to fraudia?.... by the way what do you do in water? lets exchange notes... since I am in the same area as well.

                          Comment


                            #14
                            The program is just a Game which my uni uses for practice (this is level 8 of the actual game I think). This one just allowes 4 pins. I cant have a cantilever. No cables allowed either. The red shows force just below the safety factor. So we are safe. All then ones I have seen, have red somewhere.
                            And I dont have anymore pieces left.
                            Anyway I have given it where I needed to give it.

                            Black zero how much weight did yur bridge take?
                            Originally posted by hmcq:
                            well that structure does look really weak,...

                            I am guessing building towers to do a cantiliver design is out of the question cause of cost. How about using prestressed cables as part of the structure? like a prestressed bridge span might make it easier to support with a truss?or putting the bridge span on top so that the truss is in compression -- that way it can carry a lot more load...

                            Also how about using a curved truss from one end to the other?

                            By the way this bridge builder program... is that just a simple statics calculator of sorts?


                            black zero... that sounds like a familiar nick.,.. any connection to fraudia?.... by the way what do you do in water? lets exchange notes... since I am in the same area as well.

                            Comment


                              #15
                              hmcq.. guilty as charged.. younger sibling to fraudmeister..

                              would be glad to share notes.. will drop you a note with the email.

                              bridge.. i did not give it enough movement gap at the cantilever (in this case a table) so it failed at that point.. ours was the only team which did not get the engineer assigned to help us out.. (he fell ill.. 200 miles away no less)

                              the bridge should have taken a lot more.. but ended with a few kilos.. cant remember how much exactly.. it was either 4 or 8 kilos. someone had thought it would take 20... and it should have.. if for that oversight... that is the moment i decided not to concentrate on structures.. http://www3.pak.org/gupshup/smilies/smile.gif

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