Part A $-$ Determining the forces in three specified members of the truss

Learning Goal:

If a truss is in equilibrium then every member in the truss must also be in equilibrium. This principle is used in analyzing a truss using the method of sections. To apply the method of sections, we use an imaginary cut through members of the truss to expose the forces in those members as extemal forces.

$($Eigure $1)$

If the free$-$body diagram of the joint on either side of the cut is known, we can apply the equations of equilibrium to that part of the member to determine the forces at the cut section. Since only three equilibrium equations $,{\displaystyle \underset{?}{\overset{?}{}}}{F}_y=0,$ and ${\displaystyle \underset{?}{\overset{?}{}}}{M}_O=0)$ can be applied to the freebody diagram of any segment, we should try to select a cut that passes through no more than three members of the truss in which the forces are unknown. Note that the moment equation can be written multiple times, but there are still only $3$ independent equilibrium equations available.

For the Howe bridge truss shown, $d=11ft,F_1=3150lb,F_2=1750lb,F_3=2350lb,$ and $F_4=4450lb.$

$($Eigure $2)$

Figure

$2$ of $2$

$2$ of $2$

Express the magnitudes of the forces in pounds to three significant figures. Separate your answers with commas.

View Available Hint$($s$)$

$A$

Determine the forces in members $CD,DH,$ and $GH$

Express the magnitudes of the forces in pounds to three significant figures. Separate your answers with commas.

View Available Hint$($s$)$

$F_{CD}=,F_{DH}=,F_{GH}=$

$lb,lb,lb$

Part B $-$ The Sense of the Forces

State if the members considered in part A are in tension or compression

Complete each sentence by dragging the appropriate word into the blank. The words can be used more than once.

Member $CD$ is in

Member $DH$ is in

Member $GH$ is in

Part $C-$ Determining the forces in three members on the left$-$hand side of the truss

Determine the forces in members $HI,BH,$ and $BC$

$F_{BC}=,F_{HI}=,F_{BH}=$