1. Selection of Material and Shape
Case Studies
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2. Floor Joists: Wood or Steel?
Aim: Light, stiff and strong joist for supporting floors in buildings
Traditionally, wood with rectangular section of aspect ratio 2:1 is used; steel I-beam with 15Be25 could be used instead
Which one is better?
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3. Floor Joists: Wood or Steel?
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4. Floor Joists: Wood or Steel?
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5. Floor Joists: Wood or Steel?
While M1 are more or less the same, M3 of pine wood is much better than that of steel
The cellular structure is the nature’s answer to bending! But steel can be standardized.
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6. Forks for a Racing Bicycle
Aim: light strong frame
Loading on frame is not obvious, but that on the fork is predominantly bending.
First maximize f2/3/, regardless of shape
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7. Forks for a Racing Bicycle
Six materials are singled out and shown in the next page
All except wood can be made into tubes
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8. Forks for a Racing Bicycle
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9. Efficient Spring Consider a leaf spring, the stored energy
The bending stiffness
The force F is limited by yielding
Substituting F and SB into the equation for U
For torsion bars or helical springs
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