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$6–41.$ Determine the force developed in members $FE$, $EB$, and $BC$ of the truss and state if these members are in tension or compression

$6–41.$ Determine the force developed in members $FE$, $EB$, and $BC$ of the truss and state if these members are in tension or compression

$6–41.$ Determine the force developed in members $FE$, $EB$, and $BC$ of the truss and state if these members are in tension or compression

6–41. Determine the force developed in members FE, EB, and BC of the truss and state if these members are in tension or compression

​$ \text{Step by Step Solution​} $

$ \text{Step 1: Given Data} $

We are tasked with determining the forces in members $FE$, $EB$, and $BC$ of the truss and identifying whether these forces are in tension (T) or compression (C).

\begin{array}{c}
\text{Forces:} \\
F_1 = 11\,\text{kN} \\
F_2 = 22\,\text{kN}
\end{array}

$ \text{Step 2: Free Body Diagram} $

The free body diagram of the truss is shown below, illustrating all applied forces and support reactions.

Free Body Diagram

$ \text{Step 3: Horizontal Reaction at A} $

The horizontal reaction at support A is determined by equilibrium of forces in the x-direction:

\begin{array}{c}
R_{Ax} = 0
\end{array}

$ \text{Step 4: Vertical Reactions} $

The vertical reactions are related by the equilibrium condition:

\begin{array}{c}
R_{Ay} + R_D = F_1 + F_2 \quad \text{(1)}
\end{array}

$ \text{Step 5: Moment About Point A} $

Taking moments about point A to solve for $R_D$:

\begin{array}{c}
R_D \times (5.5\,\text{m}) = F_1 \times (2\,\text{m}) + F_2 \times (3.5\,\text{m}) \\
R_D = \frac{F_1 \times 2 + F_2 \times 3.5}{5.5}
\end{array}

$ \text{Step 6: Calculate $R_D$} $

Substituting the given values:

\begin{array}{c}
R_D = \frac{11 \times 2 + 22 \times 3.5}{5.5} \\
= \frac{22 + 77}{5.5} \\
= 18.0\,\text{kN}
\end{array}

$ \text{Step 7: Calculate $R_{Ay}$} $

Using equation (1) to find $R_{Ay}$:

\begin{array}{c}
R_{Ay} = F_1 + F_2 – R_D \\
= 11 + 22 – 18 \\
= 15\,\text{kN}
\end{array}

$ \text{Step 8: Method of Sections} $

We apply the method of sections by cutting through members $FE$, $EB$, and $BC$.
method of section and cut the members

$ \text{Step 9: Force in Member BC} $

Taking moments about point E to find $F_{BC}$:

\begin{array}{c}
F_{BC} \times (2\,\text{m}) = R_D \times (2\,\text{m}) \\
F_{BC} = R_D \\
= 18.0\,\text{kN (T)}
\end{array}

The positive value confirms member BC is in tension.

$ \text{Step 10: Force in Member FE} $

Taking moments about point B to find $F_{FE}$:

\begin{array}{c}
F_{FE} \times (2\,\text{m}) = R_D \times (3.5\,\text{m}) – F_2 \times (1.5\,\text{m}) \\
F_{FE} = \frac{18 \times 3.5 – 22 \times 1.5}{2} \\
= \frac{63 – 33}{2} \\
= 15.0\,\text{kN (C)}
\end{array}

The positive value confirms member FE is in compression.

$ \text{Step 11: Force in Member EB} $

Summing forces in the y-direction to find $F_{EB}$:

\begin{array}{c}
F_{EB} \times \left(\frac{4}{5}\right) + R_D – F_2 = 0 \\
F_{EB} = (F_2 – R_D) \times \left(\frac{5}{4}\right) \\
= (22 – 18) \times 1.25 \\
= 5.0\,\text{kN (C)}
\end{array}

The positive value confirms member EB is in compression.

$ \text{Conclusion} $

\begin{array}{ll}
\text{Member FE:} & 15.0\,\text{kN in compression (C)} \\
\text{Member EB:} & 5.0\,\text{kN in compression (C)} \\
\text{Member BC:} & 18.0\,\text{kN in tension (T)}
\end{array}

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