.Calculating Reaction Forces and Moments for 3 Pin Frame ABCDE

[thebest99]

A 3 pin frame ABCDE is supported at A and E. it supports vertical loads of 60 kN at B 80 kN at c and 100 kN at D as well as a horizontal UDL of 50kNm along DE. Calculate the reaction forces.

I have REV = 124 kN and RAV = 116 kN. REH = 115.3kN and RAH = 215.3 kN.

Are these correct

Next it is asking for bending moments.

BA @ A =0kN
BA @ B =-1076.5kNM
BA @ C =0kN
BA @ D =-826.5kNM
BA @ E =0Kn

Then asking for shear forces:

Worked some out but could someone help. Plus is the above correct. Thanks for the help

 

[pongo38]

Sorry. We need a sketch or dimensions and angles. Between the hinges, any shape could happen. And which way is the horizontal load acting?

 

[thebest99]

i have now attached what i have to do. have to complete all of task 2. i have done a lot off work on this. if can help me get the correct results be great thank you

 

[pongo38]

dimensions please. If you show your working, I can tell you how to check it yourself.

 

[thebest99]

hi pongo thanks for your time on this, we are given no dimensions, i have attached what i have done. when i go through it it just doesn't seem right. if could you could have a look be much appreciated

 

[pongo38]

There is no point in going beyond reactions if they are not correct. You did include the two 8 m dimensions in your working drawing, and I could easily conclude that AB = DE = 5m, from your loading. However, the height of C above BD is not clear. In your working, where you take moments about C for CDE, you have REH * 6m, but 100 * 3 m. Those two dimensions are inconsistent. You have however, got the point of self checking. For the vertical loads, you used moments to find the vertical reactions and then checked vertical equilibrium. Correct, allowing for rounding errors. You should do the same for the horizontal loading. Moments about C for CDE (done correctly) will give you REH. Moments about C for ABC will give you RAH. Then check if horizontal equilibrium is satisfied. You are nearly there. Just make a few corrections, and then, when you are satisfied that the reactions are definitely in equilibrium, proceed with shear force and bending moments. If you want a final check on reactions, you could take moments about any point not so far used. That would uncover any untoward calculation error, although it would not be an independent equation.

 

[nvn]

thebest99: This does not seem to make sense yet; or am I missing something? You said no dimensions were given. Then you stated 8 m dimensions in one attached file; but no vertical dimensions. Also, you do not show any constraints. And you do not state which joints are pinned, and which joints are welded. How can the problem be solved with no constraints nor joint information?

 

[thebest99]

i am still confused, and not quite there yet

 

[thebest99]

hi folks, found out the dimensions, A to D is 5m and B to C is 1m. what we was given is attached, and i drew it up. and the angle B C 7.12 degress as shown in my working attached, hope this is clear

 

[thebest99]

the height of B to C is 1m not the length to clarify. hope you can help. sorry i drew my 3 pin frame out a bit shoddy

 

[thebest99]

attached is a better drawing. on this i have put my calcualtions for REH etc.

 

[nvn]

thebest99: You still did not show or state the joint constraints, and you still did not show or state where the pins are located. Which joints are pinned, and which joints are welded?

 

[thebest99]

pinned support at bottom of legs A and E. and also C

i do not believe there are any joint constraints. Sorry

 

[nvn]

thebest99: As mentioned by pongo38 in post 6, your calculation for REh is currently incorrect. Try again. Also, do not round your intermediate calculations. You are rounding numbers too much. Also, you did not clearly draw RAh and REh on your free-body diagram. As pongo38 pointed out, first ensure all reaction forces are correct, before you proceed with determining shear forces and bending moments.

 

[thebest99]

i seem to calc 8.66 =REH, is this correct or coukd you help mne get the correct answer

 

[pongo38]

You must show your working. As I said before, everything that is statically determinate can be obtained in two different ways and is therefore self-checking. For example, you obtained REH by declaring that the bending moment to the right of C must be zero. However, you made a mistake in the dimensions in doing that calc. You then used horizontal equilibrium to calculate RAH. If you had checked it by taking the bending moment to the left of C, you would have then found that there was an error somewhere. So you do have the capability to check your own REH. This self-checking principle continues to be valid when you calculate your bending moments. For example the moment at B can be obtained in two ways - by summing the moments from AB, or from summing the moments from BCDE. Please let us know when the penny has dropped. It's a really powerful tool. The same will be true for shear force, or axial force. In the case of shear force, you have the additional check using V=dM/dx. [incidentally, your units for bending moment in your calcs are incorrect. Can you see why that is obvious? What is the definition of bending moment that you are using?]

 

[nvn]

thebest99: No, 8.66 kN for REh is incorrect. Try again.