Find the zero force members in a truss: example #1

[@orianx]

Why isn't the joint you're point at, at 4:17 a zero force member? There are two collinear forces meeting said member.

[@Engineer4Free]

Good eye! I just made up this problem and missed that one. You are correct, that is also a zero force member under this loading condition. Thanks for pointing it out, I'll will take this video down and repost it (and the next one because it carries through) with the correction.

[@orianx]

Engineer4Free Glad I could help 😊

[@vatsaakhil]

Yes exactly

[@garret1930]

You don't have to remove the videos, just add an annotation and comment in the description

[@yuriykovalov2936]

just had the same question, thank you. Still a little unclear though. So the one at 4:17 is a zero force member, what about it's opposing brother?

[@collegeguy1325]

none of my proffs have been able to explain the zero member force concept so clearly like you! Thank you for taking time to explain with examples in a clear, coherent way!

[@philsmitherson]

I was about to comment but read the description haha. I was really confused for a while though so I came from your website to see if anyone commented on KZbin. if you add an annotation I think it will help people who don't know it's wrong. Great videos though, they helped a lot and I finally understand it!

[@散华-l9m]

Cool ! I have watched the previous 2-3 videos about trusses, and then I can handle the question in this video on my own

[@gregwarner3753]

I would say the vertical members are there to limit the length of the beams supporting the longinitudal beams of the roadway. Other uses of 'zero force's members to provide adequate stiffness for compression members that may be longer than 40 times their thickness.

[@Engineer4Free]

Yes, zfms serve a such a purpose. And also, not that as the load changes, the internal force will change in each member, including which ones are zfms. In real life, the situation won't be so simple as this too

[@altontorres9676]

at 6:26 i dont get why its zero force memebr but on your next video with two forces its just on the opposite side and it counts as a force member? what am i missing?

[@niranjanwagh5767]

What two zero force members you missed? I only recognized the one at 4:17 . Which one is second?

[@pestifygaminghacks4713]

Thanks sir

[@belissegiovanni]

thank you

[@timyassa4343]

at 7:20, why isn't the member that goes from the very top of the truss system to the bottom right now a zero force member?

[@Engineer4Free]

Hey Tim, thanks for pointing that one out as others have, I missed it while making the video. I just added in a note of it into the description now. Sorry about that but good job for noticing!

[@timyassa4343]

Engineer4Free no problem! thanks for the reply. great video btw

[@lunapotter5593]

At 7:10 the final diagram, Are they both zero the ones attached to the top and the one attached to the purple force is not zero right?

[@irfanmehmood1772]

Won't there be one more zero force member in this example? Kindly Reply and please upload videos of Dynamics also?

[@Engineer4Free]

Yes, good eye and thanks for pointing it out. There is a note in the description of this video explaining the ZFM that I missed: "I missed two ZFMs in this video on the right hand side of the truss. They are the ones where my cursor is at 4:17. By the end of the video, you can see that I should have identified them as ZFMs because otherwise they would throw off the equilibrium at the joint that is on the bottom of the truss about 1/3 of the way from the right hand side. Sorry about that, and thanks to those who pointed it out!!!"

[@irfanmehmood1772]

Engineer4Free Also post complete course of Dynamics

[@Engineer4Free]

I plan to upload a full course on Dynamics within the next few months :)

[@sikolu5580]

@@Engineer4Free when are the dynamics videos out? this was really helpful

[@Engineer4Free]

Hey, sorry for the wait. I am just working now to finish up the series on Linear Algebra and Differential Equations first. I'm just one person trying to do many things -_-

[@anematix7178]

I'm so confused, how come at 3:51 that force would have a perpendicular component causing it to be a 0 force member. Why would it have to have a perpendicular component??? :(

[@Engineer4Free]

The joint has 3 members attached to it. Two of those members are in line with each other, and if they had internal forces, then those internal forces would share the same line of action. If the the third member that is not one of the two co-linear members has an internal force, then that internal force will not be in line with the other two, it will be at some angle. An angled force can also be represented as the sum of two forces, in which one force is parallel to the reference line that the angle is taken from, and one force is perpendicular to that same line. It's no different than talking about the "x component" or "y component" of a force that's on an angle taken from the x or y axis. So IF there was an internal force in the third non-co-linear member that's on an angle compared to them, then it would be applying some amount of force to the joint that is perpendicular to the lines of action of those other two co-linear forces. If that were the case, then the joint would not be in static equilibrium, as there is no 4th member available to provide an equal and opposite force that is perpendicular to the line that we keep referring to. Because this truss IS in static equilibrium, then every individual part (member, joint) must also be in static equilibrium. This means that this joint in question must be in static equilibrium, and that can only be true if there is no unbalanced force that is perpendicular to the line that we keep talking about. Therefore, the internal force in the third non-colinear member must be equal to zero for that joint to be in equilibrium. Hence the member is a zero force member. Does that clear it up?

[@anematix7178]

Blessed

[@tallamanish8271]

Thank you!!

[@Engineer4Free]

You're welcome Tallam!!

[@mohammedlasmi649]

Members zero force. It means that we can remove this members from trusts? Lose of materials. Thanks

[@Engineer4Free]

Theoretically yes. Practically no. They carry no internal force when the structure is loaded in this exact way, but when the loading changes, the ZFMs will change too. Plus considerations for stability and rigidity.

[@shivbratyadav2601]

i think there is one more 0 force member

[@Engineer4Free]

Yeah sorry I brainfarted. There is an explanation in the description of the video.

[@EnergyTransformation-DS]

Still two more zero force members

[@halobaby0331]

i still dont get it

[@Engineer4Free]

Watch this video first that explains the concept: www.engineer4free.com/4/how-to-identify-zero-force-members-in-trusses