7.1 Graphically determine the magnitude and type of member in the framework shown in FIGURE 7.1 below - NSC Mechanical Technology Welding and Metalwork - Question 7 - 2019 - Paper 1
Question 7
7.1 Graphically determine the magnitude and type of member in the framework shown in FIGURE 7.1 below. Members: AE, BF, CF, DE and EF.
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Worked Solution & Example Answer:7.1 Graphically determine the magnitude and type of member in the framework shown in FIGURE 7.1 below - NSC Mechanical Technology Welding and Metalwork - Question 7 - 2019 - Paper 1
Step 1
7.2.1 Calculate the reactions at supports RL and RR.
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Answer
To calculate the reactions at supports RL and RR, we apply the principles of static equilibrium. We can sum the vertical forces and moments around one of the supports.
Given the total loads acting on the beam: 4 N, 5 N, and 3 N, locate their positions relative to RL or RR. Then, apply the following equations:
Sum of vertical forces:
RL+RR−(4+5+3)=0
Sum of moments about RL (select RL to eliminate RL):
−RRimes6+4imes1.5+5imes3+3imes4.5=0
Solving these equations yields:
RL=6.25 N
RR=5.75 N
Step 2
7.2.2 Calculate the bending moments at point B, C and D.
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To find the bending moments at points B, C, and D, we consider the equilibrium of sections of the beam:
At Point B:
MB=RLimes3−4imes1.5
=6.25imes3−4imes1.5=18.75extN.m
At Point C:
MC=RLimes6−5imes3−4imes1.5
=6.25imes6−5imes3−4imes1.5=25.5extN.m
At Point D:
MD=RLimes9−5imes6−4imes1.5−3imes6.5
=6.25imes9−5imes6−4imes1.5−3imes6.5=17.25extN.m
Step 3
7.2.3 Draw a bending-moment diagram.
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Answer
The bending moment diagram can be represented graphically by plotting the bending moments calculated at points A, B, C, D, and E.
At A (0): MA=0 N.m
At B: MB=18.75 N.m
At C: MC=25.5 N.m
At D: MD=17.25 N.m
At E (support): ME=0 N.m
The diagram will have lines connecting these points, showing the bending moment distribution, with negative moments between supports and positive peaks near the applied loads.