ARC281 Lecture 4 Notes

Lecture 4 - Method of Sections -
Trusses
Type Lecture

Date @September 28, 2023

Materials https://www.youtube.com/watch?v=Yt4XvWFdei0&t=1s

Reviewed

Trusses/Frames - Axial
Beams/Bending Elements - Shear, Bending Moment



Some FBD Symbols

Method of Sections

MoS for solving trusses

MoS for solving beams

Force Diagrams

Typical Force Diagrams

Bonus Examples


Last Week:
We want things to stay still

If there are still they are in equilibrium

If they are in equilibrium they aren’t moving in any of the 6 degrees of freedom

We often break the problem into a 2D problem, with 3 degrees of freedom

Which means we want ΣFx = 0 and ΣFy = 0 and ΣMz = 0




Lecture 4 - Method of Sections - Trusses 1

, We can use these equations to solve for the Reactions of the system that keep it in
Static Equilibrium



But what happens INSIDE the elements?


FBD - Implied (Partial) FBD)
Implied at Joint - or what is happening at
the dot

If an arrow is pointing toward the joint
it means it is in compression

If an arrow is pointing away it is in
tension




Implied in Members - or what is
happening at the dot




Truss 01 - FBD
Solve for the reactions




Lecture 4 - Method of Sections - Trusses 2