English - Truss Analysis Using Method of Joints Part 1 of 2

Analyzing a simple truss using the method of joints

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[mxlwmtiam]

I don't understand why every truss or beam design video always show pin and roller on each end, is it all the real bridges and buildings have the same thing. I thought they are bolting very tight both ends. Please tell me, I would very much appreciate.

Thanks,

[CTSCIVIL]

@mxlwmtiam

I asked this question many years ago:

It is recommended that triangulated trusses are designed with simple, pin-jointed members, even when the truss connections are welded.

This practice has been successfully followed for decades, and is enshrined in design Standards. which states that for the purpose of calculating the forces in

members the connections may be assumed to be pinned. Assuming pinned connections is obviously ideal for hand analysis.

[CTSCIVIL]

@mxlwmtiam

Analyzing trusses with fully rigid joints is not generally recommended, as the transfer of moments at the joints makes the connection design much more involved. It may be that the consideration of the joint capacity inspires a slight adjustment of the setting out, to provide a gap or overlap joint, which introduces some modest eccentricity. This is generally taken in the chord members.

[mtsaygo1723]

T^T my professor taught us the when the rotation is clockwise.. it'll be positive...? :(( i'm confused... well definitely counterclockwise is negative.. ohemgee..

[CTSCIVIL]

@mtsaygo1723 it does not make any difference. the choice of positive and negative rotation depends on you and on the problem you are solving. looking at different text books will clearly show you that it is all YOU.

thanks for stopping by

[southpawking1]

Hi I am an engineering student from UK, London.

Can you please tell me how you get 3/5AB at 5:59 in your video.

[CTSCIVIL]

in order to get 3/5 AB you need to resolve the force in member AB

if you have angles, you usually use sines and cosines to resolve forces into components but in out example we use lengths of members instead. lets say that we have an angle "theta" between members AB and AC, the horizontal component of AB will be (AB cos "theta") and the vertical component will be (AB sin "theta") look closely at the vertical component and you will see it is the same as 3/5 AB using the triangle ( 3 4 5 ) above.

[CTSCIVIL]

@drzai

show me your good grades and that will be enough. :)

[gematt7]

thank you so much! :)

[staranjela]

love the video man

[oelpalsiit]

You should put the direction of the force if you are assuming, whether if it is ( + ) or ( - ) , just like what you did in finding the Fy, direction of the force should be vertical not horizontal, more confusing... anyway thanks:)

[mxlwmtiam]

Thank you so very much, for taking the time to answer me.

I am still learning how things or buildings stand up tall.

[Anip92syn]

@mtsaygo1723 yeah..hes ASSUMING direction counterclockwise is +ve...

[Gazzawey]

Thnx doctor I thought I will never going to understand this u r gifted