# Truss problem Timoshenko

• Engineering
newbie1127
Homework Statement:
Hello everyone,
i am new to the forum and this is my first message, please go easy on me if i break any rules/make mistakes

i recently started reading Strength of Material by Timoshenko and in the first chapter encountered a problem in one of the solved examples (attached screenshot)

The problem is of a truss with point load,
i dont understand the second figure(b) particularly how it was calculated, i tried using method of joints, but i am getting different results.
Relevant Equations:
xyz
xyz

#### Attachments

Mentor
Homework Statement:: Hello everyone,
i am new to the forum and this is my first message, please go easy on me if i break any rules/make mistakes

i recently started reading Strength of Material by Timoshenko and in the first chapter encountered a problem in one of the solved examples (attached screenshot)

The problem is of a truss with point load,
i don't understand the second figure(b) particularly how it was calculated, i tried using method of joints, but i am getting different results.
Relevant Equations:: xyz

xyz
Welcome to PF. Can you show your work so far? It's best if you can post the math equations using the "LaTeX Guide" link in the footer. Thanks.

newbie1127
Welcome to PF. Can you show your work so far? It's best if you can post the math equations using the "LaTeX Guide" link in the footer. Thanks.

i don't know where to begin, i skipped the question for now
i only have used method of joints where i did:

assumed equilibrium conditions and hence did,
1) sum of all horizontal forces = 0
2) sum of all vertical forces = 0
3) all moment about a point = 0 and calculated the force values

problem is i start the problem with another value
for example:
i take initial force of 27000 lb to calculate value of AB
whereas, the author starts with 18000 lb and hence, i get different result

my values for AB : 27000 lb - initial force ; and get 54000 lb - as tension force on AB
author's values for AB : 18000 lb - initial force ; and gets 36000 lb - as tension force for AB

i think i am missing some concept that has to be applied before appling the method of joint or some other method. i just don't know what it is

newbie1127
I got the answer, thanks to someone named NRG99

solution i found: using the triangle law of forces as suggested by NRP99

Now that i think on it, i was too concerned about why it was that 18000 and 9000 were written seperately and if they had any physics significance turns out it was just a mathematical by-product of solving the problem and doesn't represent anything

also, i want to end this by giving credit to the author,
while calculating the solution i came across the number 1053
i wouldn't have thought anything of it if i didn't know the answer 9000√13
i wouldn't have thought 13 was a factor of 1053
i know he is a super smart guy, i just thought it was interesting to mention.

• Lnewqban
Homework Helper
Gold Member
Welcome!
I hope you bring more questions to us.
Timoshenko is an excellent book (I and II).

• newbie1127