1. B RIDGE D ESIGN P ROJECT Me 35a Fall 2008

2. STEP – 1 The required file and the instruction sheet is uploaded on the course website http://www.its.caltech.edu/~me35a Download the file and the instruction sheet. The instruction sheet has the information to download and install the software. Once the software is install Using the software open the file me_35a_bridge_design.bdc downloaded from the course website to load the required construction site to build the bridge

3. Load Existing Design

4. Load the file me_35a_bridge_design (downloaded from the course website)

5. STEP 2 Once uploaded the construction site can be seen Now step 2 is to place joints and members to build your bridge.

6. Given Construction Site Design Tools

7. GOAL OF THE PROJECT At the above given construction site – build a truss bridge at the lowest possible cost. The necessary instructions on the project can be found in the instruction sheet on the website Working of the software and building a bridge is briefly explained in this file.

8. Select to draw a joint

9. A joint is being placed by clicking here at the desired point

10. Select to draw a member The joints that were created

11. Truss members drawn

12. Shows total construction cost – Objective is to minimize this

13. Shows status of bridge – If working – Green, If under construction – yellow, If the bridge fails when load is applied - Red

14. Apply the load on the bridge to check if it works

15. Red – Oops..!! OUR BRIDGE FAILED..!! Red colour indicates the members that are failing – Now we need to modify the members

16. STEP 3: M ODIFYING THE MEMBER PROPERTIES We can change the following properties of the member: Material of the member Diameter of the member Cross-section of the member – Hollow or Solid cross- section

17. Material Properties of the material used – Shows the maximum tension and compression the member can withstand

18. Material of the Bar – Default is carbon steel. One can choose a superior material for higher strengths but it would be costly

19. C/S of the Bar – Solid or Hollow. Hint – Use Hollow c/s for members under compression & Solid for members under tension

20. Diameter of the Bar

21. Increase diameter of the Bar Decrease diameter of the Bar

22. Arrow tool to select elements Selected Elements – Lets now change their parameters as we have seen earlier

23. Diameter of these members have been increased now

24. STEP 4: C HECK BY LOADING THE BRIDGE We have now changed some property of the member and we would like to check if the bridge is stable now Lets apply the loading again as done earlier

25. Yahoo.. The members seem to be working well – they arent failing

26. Status is green – bridge is working fine – Excellent! Good job

27. However the cost seems to be high still

28. Check the load test report and see what you can change for each member

29. STEP 5: C ONTINUE THE ITERATE ON THE PROPERTIES OF ALL MEMBERS Now continue to check if you can change the properties of each member and the bridge still being stable. Do it on every member and see what is the lowest cost you can get up to

30. S UBMISSION Once you finish save the file as Last_name(s).bdc and mail to bhajay@caltech.edubhajay@caltech.edu Further instructions for submission are in the instruction sheet that is available on the website

31. C RITICAL HINTS Load Test Report tells you if the member is in compression or tension. If subjected to: Tension – Use Solid Bars Compression – Use Hollow Bars Try to take advantage of symmetry. Many times taking 2 bars of same properties can be cheaper than using two of much inferior but different properties