Statics: Lesson 50 – Trusses, How to Find a Zero Force Member, Method of Joints

Statics: Lesson 50 – Trusses, How to Find a Zero Force Member, Method of Joints

Look at this massive 21-member truss—looks absolutely terrifying, right? Don’t panic! In Lesson 50 of engineering mechanics, I am showing you how to shrink this complex exam problem into a simple structure in just a few seconds using the ultimate secret weapon: Zero Force Members!

Before writing equations, I’m sharing my two golden rules to spot zero force members instantly using the Method of Joints (the T-Joint and L-Joint rules). We will also look at how to take advantage of structural symmetry to calculate support reactions in just 5 seconds! Once we delete the zero force members, we’ll use a clean Free Body Diagram (FBD) and equilibrium equations ($\Sigma F_x=0, \Sigma F_y=0$) to solve the remaining joints. Grab your calculator, and let’s crush this roof truss together!

Timestamps:

00:15 – The secret to solving a massive 21-member truss

00:53 – Explaining Symmetry: Finding support reactions in 5 seconds

01:55 – Rule 1: The ‘T-Joint’ trick for Zero Force Members

03:24 – Rule 2: The ‘L-Joint’ trick for dual zero members

04:39 – Live Action: Deleting zero force members and shrinking the truss

05:58 – Finding internal forces for members with direct external loads

07:41 – Joint A Solution: Finding AL & AB using a $45^\circ$ angle

12:56 – Joint K Solution: Finding the $63.44^\circ$ angle using inverse tan

15:55 – Calculator Trick: Using the Equation System Solver for fast answers

19:01 – Joint J Solution: Solving for the final member (JD) and wrapping up

𝐌𝐲 𝐄𝐧𝐠𝐢𝐧𝐞𝐞𝐫𝐢𝐧𝐠 𝐍𝐨𝐭𝐞𝐛𝐨𝐨𝐤 for notes! Has graph paper, study tips, and Some Sudoku puzzles or downtime between classes! https://amzn.to/3pTSZXw
𝐄𝐧𝐠𝐢𝐧𝐞𝐞𝐫𝐬 𝐏𝐮𝐳𝐳𝐥𝐞 𝐁𝐨𝐨𝐤 Sodoku, Mazes, Word Search, Word Scramble – 400 puzzles and solutions – Perfect Gift! https://amzn.to/3KxtS3L
𝐂𝐚𝐩𝐬𝐭𝐨𝐧𝐞 𝐃𝐞𝐬𝐢𝐠𝐧 𝐉𝐨𝐮𝐫𝐧𝐚𝐥 For your senior design project documentation! 100 pages of numbered graph papers. https://amzn.to/3OtZJ6z
𝐅𝐄 𝐑𝐞𝐯𝐢𝐞𝐰 𝐉𝐨𝐮𝐫𝐧𝐚𝐥 For you notes and work while preparing for the FE Exam. 100 pages of graph paper! https://amzn.to/3ONRILn
𝐏𝐄 𝐉𝐨𝐮𝐫𝐧𝐚𝐥 𝐒𝐓𝐀𝐑 𝐋𝐨𝐠 Record your projects in preparation of your PE application or for your annual review at work…(Situation, Task, Analysis, Results) https://amzn.to/3rjyAMp
𝐇𝐨𝐰 𝐭𝐨 𝐀𝐜𝐞 𝐒𝐭𝐚𝐭𝐢𝐜𝐬 Great book to review or have on your shelf to make sure you never forget Statics! https://amzn.to/455QRKM

Top 15 Items Every Engineering Student Should Have!

1) TI 36X Pro Calculator https://amzn.to/2SRJWkQ
2) Circle/Angle Maker https://amzn.to/2SVIOwB
3) Engineering Paper https://amzn.to/2K7vYbP
4) Mechanical Pencils 40pk https://amzn.to/2GGRG4y
5) Desk/Bed Clamp Reading Light https://amzn.to/2YzN5qG
6) Stainless Steel Rulers https://amzn.to/31aqMcP
7) Small Stapler https://amzn.to/2ynDOrk
8) Post it Tabs for Page Markers https://amzn.to/2SSIP4q
9) Noise Canceling Wireless Headphones https://amzn.to/3aMLbdY
10) Wireless Mouse https://amzn.to/2ROkY5Y
11) Multicolor Pen/Pencil https://amzn.to/3331AXy
12) Portable Charger https://amzn.to/2RsitHG
13) Backpack Rain Cover https://amzn.to/2Gq4ATM
14) Amazon Dot https://amzn.to/2Gs42g4
15) Portable Bluetooth Speaker https://amzn.to/3aIMZV0

This video is NOT sponsored. Some product links are affiliate links which mean if you buy something we’ll receive a small commission.

Follow me on Instagram https://instagram.com/jeff_hanson_phd

Please consider supporting the channel by subscribing, commenting, and liking each video. This moves these videos up the search list and helps me greatly. Thank you for watching.

My Patreon: https://www.patreon.com/Jeff_Hanson Please help keep the free videos coming by donating. Thank you for the many blessings.

This video is copyrighted by the Jeff Hanson for the private use of our audience. Any other use of this video or any pictures, descriptions, or accounts of the video without written consent from Jeff Hanson is strictly prohibited.

#statics #jeffhanson #engineeringmechanics #trusses #zeroforcemember