A cross-section of a beam is shown.
Which of the following is the maximum stress in the beam if the maximum bending moment is 200 kN m and \(I_{\text{xx}}\) is 168.75 × \(10^{-6} \text{ m}^4\)?
- 177.8 MPa
- 177.8 GPa
- 355.6 MPa
- 355.6 GPa
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A cross-section of a beam is shown.
Which of the following is the maximum stress in the beam if the maximum bending moment is 200 kN m and \(I_{\text{xx}}\) is 168.75 × \(10^{-6} \text{ m}^4\)?
\(A\)
\(M=200\ \text{kN m}\ = 200\ 000\ \text{N m}\)
\(y=\ \text{distance to neutral axis}\ = \dfrac{300}{2} = 150\ \text{mm}\ = 0.15\ \text{m} \)
\(\sigma = \dfrac{My}{I_{\text{XX}}} = \dfrac{200\ 000 \times 0.15}{168.75 \times 10^{-6}} = 177.8\ \text{MPa}\)
\(\Rightarrow A\)
An \(\text{I}\)-beam is loaded as shown.
The load is then increased.
Which increase in dimension would provide the most resistance to bending?
\(D\)
→ The most efficient way to increase bending resistance in an \(\text{I}\)-beam would be to increase the height/depth of the web \((D)\), since resistance to bending increases with the cube of the depth from neutral axis.
\(\Rightarrow D\)
The diagram shows a child with a mass of 45 kg hanging 2 metres from the left end of a structure, and an adult with a mass of 85 kg hanging 1 metre from the right end. \begin{array} {ll}
\text{R}_\text{L} = \text{............................... N} & \text{Direction ...............................} \\
& \\
\text{R}_\text{R} = \text{............................... N} & \text{Direction ...............................} \end{array}
i. \( \stackrel {\curvearrowright} {\sum{ \text{M}}{^{+}_\text{L}}}: \)
\(0\)
\(=(2 \times 450)+(4 \times 850)-(\text{R}_\text{R} \times 5) \)
\(5 \times \text{R}_\text{R}\)
\(=900 + 3400\)
\(\text{R}_\text{R}\)
\(=860\ \text{N} \uparrow \)
A pictorial sketch of a laminated timber beam used in a bus shelter is shown. This beam has a second moment area of `117 × 10^(-6)\ text{m}^(4)`. The maximum applied bending moment is 17 kNm.
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`18.2\ text{MPa}`
Second Moment of Area (`l`)`= 117 times 10^(-6)\ text{m}^(4)`
Maximum Bending Moment (`M`)`= 17 times 10^(3)\ text{N}`
Distance (Neutral axis → outside of beam) = 125 mm
`=> y = 0.125\ text{m}`
`:.\ text{Bending Stress}_text{max}` | `=(My)/l` | |
`=(0.125 times 17 times 10^(3))/(117 times 10^(-6)` | ||
`=18.2\ text{MPa}` |
The chassis for a motor vehicle could be made from a solid steel bar or hollow steel tube. Both the bar and the tube have the same mass and cost per metre.
Justify why a hollow tube would be used in preference to a solid bar to build the vehicle chassis. (3 marks)
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→ Hollow tube has a higher second moment of area and is therefore more rigid.
→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.
→ Stiffness is therefore a major design requirement.
→ The hollow tube also provides damage protection for any electrics cabling.
→ Hollow tube has a higher second moment of area and is therefore more rigid.
→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.
→ Stiffness is therefore a major design requirement.
→ The hollow tube also provides damage protection for any electrics cabling.
An engineering team has been contracted to design a multi-function lifting device for a coastal container wharf.
The table shows some of the engineering design elements for this lifting device.
Explain how the lifting device can be tested and evaluated to determine if the criteria for the listed engineering elements are met. (6 marks)
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A scooter deck, made from aluminium alloy, and its cross-section are shown.
The scooter's manufacturer is concerned that there is too much deflection along the length of the deck when a rider stands on it.
Describe ONE suitable design modification to give the deck greater rigidity without adding extra mass. Use a labelled sketch to support your answer. (3 marks)
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The diagram shows a beam.
The beam's second moment of area is 76.96 × 106 mm4. It is subjected to a maximum bending moment of 250 kN m.
What is the maximum bending stress of the beam?
`B`
`M=250\ text{kNm}\ = 250 xx10^(-3)\ text{Nm}`
`y=(200)/(2)\ text{mm}\ =100 xx10^(-3)\ text{m}`
`I=76.96 xx10^(6)\ text{mm}^(4)=76.96 xx10^(-6)\ text{m}^(4)`
`S_text{bending}` | `=(My)/I` | |
`=(250 xx10^(-3)xx100 xx10^(-3))/(76.96 xx10^(-6))` | ||
`=324.8440…\ text{MPa}` |
`=>B`