Statics: Exam 3 Review Problem 1; Truss Combo Method

Top 15 Items Every Engineering Student Should Have!

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

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.

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.

[kirkdoloroso]

Angle DF is not equal to the Angle ADE based on the given dimensions of the truss.
Using the slope method and trigonometry, the Angle ADE should be 57.99 degrees. Same goes for Angle AED.

Therefore:
EFx = 0
21.875 kips - AB(cos(21.8)) + AD(cos(57.99)) = 0 <--- equation 1

EFy = 0
2.5 kips - AB(sin(21.8)) + AD(sin(57.99)) = 0 <--- equation 2

Using a system solver calculator, AB = 29.17 kips (compression) and AD = 9.83 kips (tension).

Proceeding to the Joint B (to solve BD):
EFx = 0
15 kips - 29.17(cos(21.8)) + BD(cos(38.7)) = 0
BD = 15.48 kips (tension)

The truss is actually symmetrical by inspecting it in Joint A. But with the presence of the loads in B and E, the forces become different.
Therefore, solving Joint A:

EFx = 0
29.17(cos(21.8)) - 9.83(cos(57.99)) - AC(cos(21.8)) + AE(cos(57.99)) = 0 <--- equation 1

EFy = 0
29.17(sin(21.8)) - 9.83(sin(57.99)) + AC(sin(21.8)) - AE(sin(57.99)) = 0 <--- equation 2

Using a system solver calculator, AC = 33.65 kips (compression) and AE = 17.68 kips (tension).

Hope it helps.

[RK-txxb]

Hello Jeff, you marked "DE" instead of "AE".

[maheshdabholkar]

Gy = 37.5 kips
Fx = 15 kips
Fy = 2.5 kips
BA = 29.17 kips (C)
DA = 9.83 kips (T)
DE = 21.875 kips (T)
FD = 23.43 kips (T)
FB = 20.5 kips (C)
BD = 15.47 kips (T)
EG = 0 kips
CG = 37.5 kips (C)
EC = 40.02 kips (T)
AC = 33.65 kips (C)
AE = 17.69 kips (T)

[manuboker]

Wonderful Statics lessons!! really taking the time to explain the problems along with a good sense of humor :))

[andrewerhard]

Hi Professor Hanson! Your statics videos were tremendously helpful to me, and now I am taking thermodynamics! Do you have any plans to finish your thermodynamics series?

[waichingwong]

I think that the angle between the AD and DE is 57.99 not 50.2. Thank you.

[georgesadler]

DR. Hanson, this a powerful Review of The Truss Combo Method, however you marked DE instead of AE. These lectures continues to be awesome.

[dormin]

Can we do a moment about point F? Then doing some methods of joints to find the BD and AE ???

[cruzruiz]

I think you named your tittle wrong, "exam 3" on youtube and "exam 2" on white board!

[osakweolorchukwu.i]

I took moment about point D to start with, and I got a different answer for BA; 29.17kips. I've analyzed closely and I'm not able to find the mistake in either my solution or yours. Someone please help out😖