Frames: Multi-Force Members

disassemble pins: each 2-D pin has R_{x}, R_{y} equal-and-opposite

Frames contain at least one multi-force member. Take members apart, draw free-body diagrams, and enforce equal-and-opposite pin forces. Do not treat a loaded beam-column as a truss bar.

$R x, R y$: Pin components

Step-by-step solved example

Two-bar frame: vertical post pinned at A, beam AC with a midspan load, pin at C on the post. How to start?

Dismember the frame; pins carry two components, not two-force bars.

1. FBDs
Separate beam and post. Load stays on the beam. Pin C: C_x, C_y on beam, reversed on post.
2. Solve
Beam: ΣM about one pin finds the far pin component. Then post with those knowns plus support A.

Answer: Disassemble; solve the loaded beam first, then the post

10 practice questions

0/10 correct

1.A truss bar is modeled as

2.Putting a joint load at mid-panel of a truss

3.Machines (pulleys, pliers) are solved as

4.Internal pin force on two adjoining members

5.A rigid, welded joint transmits

6.Statically determinate 2-D frame needs

7.Smooth pulley pin force equals

8.Start with the member that

9.A two-force member inside a frame can still be used to

10.If ΣM of a whole assembled frame is not zero