Concept explainers
8.9 through 8.14 Each of the following problems refers to a rolled-steel shape selected in a problem of Chap. 5 to support a given loading at a minimal cost while satisfying the requirement σm ≤ σall. For the selected design, determine (a) the actual value of σm in the beam, (b) the maximum value of the principal stress σmax at the junction of a flange and the web.
8.10 Loading of Prob. 5.74 and selected W250 × 28.4 shape.
Fig. P5.74
(a)
The actual value of
Answer to Problem 10P
The actual value of
Explanation of Solution
Given information:
Refer to problem 5.74 in chapter 5 in the textbook.
The rolled steel section is
Calculation:
Show the free-body diagram of the beam as in Figure 1.
Determine the vertical reaction at point B by taking moment at point D.
Determine the vertical reaction at point D by resolving the vertical component of forces.
Shear force:
Show the calculation of shear force as follows;
Show the calculated shear force values as in Table 1.
Location (x) m | Shear force (V) kN |
A | 0 |
B (Left) | –40 |
B (Right) | 80 |
C | –40 |
D | –40 |
Plot the shear force diagram as in Figure 2.
Location of the maximum bending moment:
The maximum bending moment occurs where the shear force changes sign.
Refer to Figure 2;
Use the method of similar triangle.
The maximum bending moment occurs at a distance 2.4 m from the left end of the beam.
Bending moment:
Show the calculation of the bending moment as follows;
Show the calculated bending moment values as in Table 2.
Location (x) m | Bending moment (M) kN-m |
A | 0 |
B | –16 |
Max BM | 48 |
C | 32 |
D | 0 |
Plot the bending moment diagram as in Figure 3.
Refer to the Figure 3;
The maximum bending moment in the beam is
Write the section a property for a
Dimension | Unit( |
d | 259 mm |
102 mm | |
10.0 mm | |
I | |
Here, d is depth of the section,
Find the value of C using the relation:
Substitute
Find the maximum value of normal stress
Here,
Substitute
Thus, the actual value of
(b)
The maximum value of principal stress
Answer to Problem 10P
The maximum value of principal stress
Explanation of Solution
Calculation:
Find the value
Here, c is the centroid and
Substitute
Find the area of flange
Here,
Substitute
Find the centroid of flange
Substitute
Find the first moment about neutral axis
Here,
Substitute
At midspan the value of
Find the maximum value of principal stress
Here, actual value of normal stress
Substitute
Find the shear stress
At midspan the value of
Therefore, the shear stress
At section C,
The shear force at point C is
The bending moment about C is
Find the value of
Substitute
Find the shear stress at b
Substitute
Find the maximum shearing stress (R) using the relation:
Here,
Substitute
Determine the maximum value of the principle stress using the relation:
Here, R is the maximum shearing stress and
Substitute
Based on results,
Select the maximum value of principal stress
Thus, the maximum value of principal stress
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Chapter 8 Solutions
Mechanics of Materials, 7th Edition
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