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BRIDGE DESIGN PROJECTMe 35a
Fall 2008
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
Load Existing Design
Load the file me_35a_bridge_design (downloaded from the course website)
STEP 2
Once uploaded the construction site can be seen
Now step 2 is to place joints and members to build your bridge.
Given Construction Site
Design Tools
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.
Select to draw a joint
A joint is being placed by clicking here at the desired point
Select to draw a member
The joints that were created
Truss members drawn
Shows total construction cost – Objective is to minimize this
Shows status of bridge – If working – Green, If under construction – yellow, If the bridge fails when load is applied - Red
Apply the load on the bridge to check if it works
Red – Oops..!! OUR BRIDGE FAILED..!!
Red colour indicates the members that are failing – Now we need to modify the members
STEP 3: MODIFYING 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
Material Properties of the material used – Shows the maximum tension and compression the member can withstand
Material of the Bar – Default is carbon steel. One can choose a superior material for higher strengths but it would be costly
C/S of the Bar – Solid or Hollow. Hint – Use Hollow c/s for members under compression & Solid for members under tension
Diameter of the Bar
Increase diameter of the Bar
Decrease diameter of the Bar
Arrow tool to select elements
Selected Elements – Lets now change their parameters as we have seen earlier
Diameter of these members have been increased now
STEP 4: CHECK 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
Yahoo.. The members seem to be working well – they aren’t failing
Status is green – bridge is working fine – Excellent! Good job
However the cost seems to be high still
Check the load test report and see what you can change for each member
STEP 5: CONTINUE 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
SUBMISSION
Once you finish save the file as “Last_name(s).bdc” and mail to [email protected]
Further instructions for submission are in the instruction sheet that is available on the website
CRITICAL 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