FE Exam Statics - Force Members On A Truss

[@Genieprep]

Hello guys, so there was a typo at the end, make sure you correct it. F(AD) should be equal to √(34^2+34^2), which still equals to 48 K 😊

[@Mohamed_Khalaf]

enGENIEer noticed that 😅 You’re doing really great efforts Keep it up

[@oneloveafrica8860]

Ok ...you are doing good

[@juzoe4749]

Thank you for spending the time to make these videos

[@balkish.9679]

Do you have the solution to the truss problem at the end of your video?

[@mugdhathote]

Hello there. Thanks for the great help. I have questions for you. 1) Did you find any question based on Virtual work or Influence line? 2) One of the videos you mentioned about solving practice exams and you added you have solved 2 practice exams. I know we can order that from NCEES website. If we order two exams (for a same discipline) then will it be two different exams? Thank you in advance!!

[@Genieprep]

Hello, I did get a question on virtual work and influence line but they were both really simple, straight forward, I will share those problems sometime in the future. So the NCEES website sell only one of the practice exams for each discipline. The other practice exam, I came up with the questions using my college books and the FE Civil practice problem book by Linderburg. I hope this helps and good luck!

[@mugdhathote]

@@Genieprep Thanks for the quick reply. Definitely would like to see problems on VW an IL. Would like to ask you more questions related to fluid / Hydrology. Should I ask you here or is there any other forum I need to post or send you directly?

[@Genieprep]

@@mugdhathote No problem and you can email me your questions at [e-mail].

[@semisikaufusi2467]

Happy New Year...a very good practical application of various methods to solve this problem. Excellent.

[@alexisziegler1903]

Can you do a video on Control System problems?

[@rushabhshah6815]

we can also find resultant force AD once we get FyAD(which is 34) by using Fy= Fcos(theta) where theta need to be calculated, comes to 45

[@ThePhanttasm]

The way you determined TvsC sorta goes against my intuition. In my mind, if the forces are pulling away from a member, it causes tension. But I would have kept the arrows pointing towards the joints, and negative numbers would determine compression.

[@han34han34]

It is a very useful video. Thank you a lot.

[@alexandereppert7204]

For all other members you used the internal forces (green numbers) except for member AD. Why isn't F(AD) = √(34^2+34^2) ?

[@Genieprep]

Yes, you are right, F(AD) = √(34^2+34^2) = 48k . Thank you for catching that! That was a typo.

[@alexandereppert7204]

@@Genieprep phew! I was worried I was missing something. Thanks!

[@Genieprep]

@@alexandereppert7204 I apologize about that! No totally a typo, also if you use the 28k instead of 34, it would not add up to 48k.

[@khaderdiri9755]

I didn't understand the head, head arrow. And why do we have two unknowns for x? We also have two unknowns for y... Would you please let me know 🌹

[@hjjjhh5774]

Thank you so much for your helpful videos 🙂

[@Genieprep]

Hey! I’m glad you found them helpful. Thank you for watching!

[@keannadakwa1210]

Hello, I am trying to solve another truss probelm using this method, but I cannot apply it the same way you did. Do you have an email where I can ask for help with this FE Exam question?

[@Genieprep]

Hi Keanna! Thank you for watching. You can contact us at [e-mail] and we will help you.

[@pinchinacherenfant6908]

Thank you for everything. I am a civil engineer, and plan to take my FE next 2021. I wanted to find those practice problems, how could i find them, please?

[@Genieprep]

Hello Pinchina, thank you for watching, to get the practice problems, you just need to sign in at www.engenieer.com

[@loveaboveall2382]

You are a genius. Thanks!

[@ahulse78]

When you were solving for moments around A, why is it 28k times 20 feet? Shouldn't the length be AD? Since that is member that is acting on point A? (Just like when you figured out the first piece and it was 35 (20+15)By)

[@carultch]

Moments are a cross product. When you have a horizontal force applied to a diagonal lever, it produces the same moment as if you had a shorter lever that were purely vertical. By multiplying it only by the perpendicular component of the member length, that accounts for the sine term in the cross product.

[@sylvesterj95]

Does this triangular method work for any 2 component truss member as long as we have the respective dimensions?

[@Genieprep]

That 's right! It is cool method, is not it 😂🤣

[@oleopathic]

Why is this method superior to the method of sections?

[@Genieprep]

Hi TA, so you have to make sure you know when to use the method of section and method of joint. When we're trying to find one force member, it's better and faster to use the method of section. But let's say, you have to find the deflection of a truss at reaction A, to use the virtual work method (aka unit load method), you have to find all the force members on the truss, and that's where we should use the method of joint because it would be faster to find all the members. I hope this helps and good luck with your PE!

[@oleopathic]

@@Genieprep thank you. Certainly finding forces in all members of a truss would be too intense for an PE's AM section. For PE's PM structural it seems plausible. So seems that for AM section method dominates. Thank you for response.

[@carultch]

@@oleopathic There are some cases where you have an advantage in using both methods together. The method of sections has the advantage of getting 3 member forces with the same group of equations, while the method of joints is more limited in the number of member forces it can give you at once, but has the advantage of getting member forces that aren't within the same section of 3 members. You can always use the method of joints to brute force your way through any truss, but it is easier if you can strategically simplify it. It also helps to use zero force members, and symmetry to reduce the problem as much as you can by inspection. If you have a 12 member truss, and you identify 3 zero force members, and 4 pairs of member forces that are equal by symmetry, you can reduce this down to one installment of the method of sections, and one or two installments of the method of joints.

[@koashaygyi]

Thank you

[@ali1993sarah]

The sqrt(34^2 +28^2) = 44.05 and not the 48.08! I believe its wrong!

[@ali1993sarah]

34=Ay, and 28=Ax, but to take the sqrt we have to add the internal force (6) to 28 which =34. Then, sqrt(34^2+34^2)=48.08 thnx

[@user-zf4rz2mn6y]

Based on Joint method member AD supposed to be 42* sqrt2=59.4, and member Ac =14, I do not agree with your results in those 2 members, the rest is accurate. Thanks

[@graysongrzybowski943]

This concept is very simple to follow, however it does not make sense. how can you have 34 kip going downward at and angel and it still be exactly equal to 34 at the joint at A. does not make any sense

[@Genieprep]

Hi Grayson, thank you for watching. That's a great point, so the member AD is diagonal, and that's why we have to break it down into 2 components x and y, so we will have FADx and FADy. After that, if we do the summation of the forces on the y, we are going to have FADy and the reaction Ay. These two forces have to be equal and opposite to each other to reach equilibrium at joint A. I hope this makes more sense and good luck with your studies 😊

[@hey1989able]

thank you!!

[@rxqueen333]

This was incredibly confusing. I would go to Gregory Michaelson for structures problems.

[@Genieprep]

Selina, using fast method of joint can be tricky to understand at first, it is easier to understand just method of joint but in this video, it is more about how to solve a whole truss under 2 min and it is only important to know if you're using unit load method to solve for deflection in truss, otherwise, you just need to know method of section, kzbin.info/www/bejne/pX-4cop5gcyVZ7s. I hope this helps and good luck with your studying 😊

[@Traveler360d]

This problem will take more than 3 minutes in the exam.

[@Genieprep]

This method should be used only if you need to find all forces on the truss, so you can calculate the displacement at a given point using the unit load method (see page 158 on the reference handbook). If you practice a lot, it should not take you more than 1 minute. Also if you try to use the method of joint or method of section to solve all force members that will take you longer. On the other hand, if you are asked to solve only one force member on a given truss, you should use the method of section. Good luck!

[@Digitalbeexxjaxy]

I have a few questions

[@landonkandon]

your outro song is cancer. otherwise great videos