ENGR1304: FEA & Bridges

FEM Finite Element Method:

Breaks large complex geometries into small connected elements in order to analyze things like strength properties.

Connect nodes with springs:

Simple linear spring force:

Simple Stress Strain diagram:

Materials behave like simple linear springs within their elastic region.

Some example problems relating Young's Modulus to spring forces:
https://notendur.hi.is/eme1/skoli/edl_h05/masteringphysics/11/youngsModulus.htm

Failure Criteria:

von Mises criterion
- reasonable estimation of fatigue failure, especially in cases of repeated tensile and tensile-shear loading
States that failure occurs when the energy of distortion reaches the same energy for yield/failure in uniaxial tension. Mathematically, this is expressed as,

principle stresses:

http://demonstrations.wolfram.com/MohrsCircleAndFailureCriterionForPlanarStressStates/

Review Mechanics of Materials notes:
http://engr1304.blogspot.com/2014/03/mechanics-of-materials.html

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Bridges!

Create a bridge in Inventor (or import it from CAD into Inventor)
**Make this as one single part rather than an assembly. We will do more with constraints on our next project.

Create a loading blocks where forces can be applied:

Environment → Stress analysis

Assign a material to your bridge:

Apply fixed constraints:

Apply a load:

Add mesh
Play around with the mesh settings, create a tighter mesh in high stress areas. Update the mesh by right clicking on the red lightning bolt in your files.

Do the stress analysis!
Generate a report
Experiment with the probes
Investigate different directions of stress and strain

Civil ENGR & materials design unit

Bridge Project:
* Create Bridge (30 points)
* Apply three different loads (30 points)
* Re-design Bridge to better support above loads (30 points)
* Compare 3 different building materials. (10 points)

Bridge Report and Presentation:
*Present your bridge to the class (30 points)
*Create a report detailing the above comparisons (70 points)

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1. Choose a large bridge to re-create and do a stress analysis on.
- your recreation will not be exact, but you should use the general form & dimensions of an existing bridge.

____/30 points for bridge

2. Apply 3 different loading conditions
(____/ 30 points)

Loading Condition #1:
Assume the average person weighs about 150 pounds and occupies ~ 2.5 square feet in a crowd...

Loading Condition #2:

Approximate wind loads with this simple formula:

Wind pressure (Psf) = .00256 x V^2
V = wind speed in mph (use a worst case scenario of 112 mph → 32 lbs/sq ft)

Wind Load (Force) = Area * wind pressure * drag coefficient
Drag coefficient estimates:
1.2 for long cylinder tubes
.8 for short cylinders,
2.0 for long flat plates
1.4 for shorter flat plates

http://www.wikihow.com/Calculate-Wind-Load

http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29BE.1943-5592.0000316?journalCode=jbenf2

Apply the wind force horizontally to your bridge.

Loading Condition #3
Choose the worst-case scenerio road train, get weights/lengths off of the wiki article:
http://en.wikipedia.org/wiki/Road_train