b ridge d esign p roject me 35a fall 2008. step – 1 the required file and the instruction sheet is...

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 bhajay@caltech.edu

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