2-force member

60o

100 lb10" 10"

200 lb

C

Normal Forces

pins in slots

STATICS REVIEWFREE-BODY DIAGRAM

SYSTEMS

Find forces Ax and Ay and A total

Find shear stress in pin A

Find the amount of normal stress in rod BC (diameter 0.5 in) and the shear stress in the pin at A (diameter 0.25 in) in single shear.

60o

100 lb

10" 10"

200 lb

C

200 lb

BC

Ax

Ay100 lb

90o

Find distance AC

Find force BC

Find Normal stress in BC

637 psi

125 lb 60o

30o

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3 kN

Member AC is made of 1040 hot rolled steel with a cross-section 10mm thick and 30mm wide and the 3 kN load is repeated. The hole for pin C is 12 mm in diameter. Find the force in member AC (hint, treat it as a truss at pin C). Will member AC fail at the hole?

3kN

AC

DC

4

3

5

Pages 714 and 721

Pg 727 curve B

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20o

150mm50mm

1kN

A

B

C

D

75mm

Find the stress in the 10 mm diameter connecting rod.If the rod is made of AISI 1020 steel with repeated loading, is it safe?

AyBC

20o

1kN

Annealed 393Hot rolled 448Cold drawn 517

Page 714 use annealed, Su = 393 MPa Sy = 296 MPa

It is safe

C

Cutting reaction

Surface normal force

Ax BC

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Example of roller normal forces

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Fixed end and internal forces

300 lb

500 lb

P

VM300 lb

500 lb

Ax

Ay

Ma

a

P, V, M positive sign conventionStatics Sign Conventions

Positive Forces1st Quadrant

Positive MomentCounterclockwise

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Treat all joints at pinned1. Find support reaction A and F

2. Use special case pin D to find force BD

3. Draw free-body of pin A 4. ΣFx = 0 and ΣFy = 0 to find AB and AD

6. Draw free-body of pin B. Find forces BC and BE.

7. Draw free-body of pin C. Find force CE. Find stress in CE.

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5. Draw free-body of pin F. Find forces EF and CF. Find stress in EF and CF

Find the normal stress in bar BD. Show the free-body diagram and all work. Hint: the vertical force on pin E from the roller on the floor is zero because the frame has no y forces.

2800 lb

AP

Ay = 0Ax 2800 lb

N = 0

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Static tip-over

BfBn

h

0.4m0.4m

Tip-over condition

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Friction

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