4 beam reaction
4 beam reaction
(OP)
Hi all,
been quite a while since I have been on here......
I have a problem I hope some of you can point me in the correct direction;
I have a simple beam reaction calc I need to calculate each reaction based upon one load.
I cant remember the last time I done this for four reactions.
Should I consider the it to be statically indeterminate ? will I end up with three un-knows?
please see attached FBD.
thanks
Bert.
been quite a while since I have been on here......
I have a problem I hope some of you can point me in the correct direction;
I have a simple beam reaction calc I need to calculate each reaction based upon one load.
I cant remember the last time I done this for four reactions.
Should I consider the it to be statically indeterminate ? will I end up with three un-knows?
please see attached FBD.
thanks
Bert.





RE: 4 beam reaction
look into ...
3 moment equation,
unit force method,
moment distribution
Quando Omni Flunkus Moritati
RE: 4 beam reaction
Try this link, my attached file 7th November it shows the three moment equation.
thread404-258455: Need help with Beam Calcs
RE: 4 beam reaction
I've worked out the reactions as follows:- Ra = -51.17KN, Rb = 2253.9KN, Rc = 744.7KN, Rd = -87.52KN
Fixed moments are Mb = -997.8, Mc = -941.8 Ma and Mb are zero.
I cannot upload a pdf of the solution at present, so I've done it as a TIFF file and hope you can open it.
desertfox
RE: 4 beam reaction
Mike McCann
MMC Engineering
RE: 4 beam reaction
ill run through your calc and get my bearings again with 'three moment equation' great help much appreciated
Bert
RE: 4 beam reaction
Your welcome!
msquared48 is there any chance you could post a solution using the moment distribution method? it would act as a good cross check and I've never used that method so it would be interesting to see.
Regards
desertfox
RE: 4 beam reaction
one question regarding your answer; have you assumed an area ie; considered it are a beam hence the 17985 and 4.95 values?
thanks bert
RE: 4 beam reaction
Reactions, kN:
-51.20
2254.51
743.85
-87.15
Moments at internal supports, kNm:
-998.49
-937.76
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: 4 beam reaction
The values on the right of the equal sign are the area's of the bending moment diagram and the 4.95 dimension is the distance from the centroid of the bending moment area diagram to the support, in the case of the 4.95 its the dimension to the support Rc.
Follow the link below its gives an example of the three moment equation and explains better the method.
http://www.roymech.co.uk/Useful_Tables/Beams/Conti...
RE: 4 beam reaction
Many thanks for your efforts with this, I have gone through the equation and came to very similar bending moments for Mb and Mc (slight differences for rounding).
One last question if the regarding the '-' reactions Ra & Rb if the beam infinitely stiff would these values be positive?
Ie; what is the positive load reaction on Ra and Rb?
Thanks
Bert.
RE: 4 beam reaction
The reactions are based on your support configuration and loadings, so no I don't think the stiffness of the beam will alter the direction of the reactions.
If you change how the beam is loaded or change a beam support to say (built in) then that might alter the reactions.
desertfox
RE: 4 beam reaction
i notice you're using a "cg" symbol for the load ... is it a point load or are you showing the sum of applied loads (as a point force) ?
Quando Omni Flunkus Moritati
RE: 4 beam reaction
correct the CG is for the sum of the applied loads, as this is the only info I have on the applied force.
RE: 4 beam reaction
Quando Omni Flunkus Moritati
RE: 4 beam reaction
RE: 4 beam reaction
The mass of the beam would be a Udl loading which would help to reduce the negative reactions at Ra and Rd but I guess you don't know the beam size at this stage. If the external loads are actually Udl loadings then again these would produce positive reactions at Ra and Rb which I think rb1957 is alluding to.