4.2.1.2. Equilibrium Equations

Try these first

1. 1.

   What is the sum of vertical forces in a static truss?

   Hint

   Think about forces acting up versus acting down.

2. 2.

   Define static determinacy.

   Hint

   How many equations do we use?

3. 3.

   What does the equation ∑F_x = 0 represent in truss analysis?

   • Sum of all vertical forces
   • Sum of all horizontal forces
   • Sum of all moments

   Hint

   Think about which forces are acting in the horizontal direction.

4. 4.

   A truss is statically indeterminate if:

   • True
   • False

   Hint

   Review the conditions for determinate vs. indeterminate.

5. 5.

   A truss has 8 members, 4 joints, and 3 reactions. Is it stable? Justify your answer using the appropriate relationship.

   Hint

   Apply the m + R < 2j condition.

6. 6.

   In a truss analysis, if the internal force in a member returns negative, what does it imply? Provide an example.

   Hint

   Think back to the sign convention!