Moment Distribution Discrepancy
Moment Distribution Discrepancy
(OP)
I have been running continuous beam models in SAP2000 and trying to verify those results using hand calculations. The models consist of twenty equal spans with cantilever end spans and a uniform load across the entire beam. The hand method I am most familiar with is moment distribution and the results are not matching within a reasonable percentage for the spans closest to the cantilevered ends. I have had three other fellow engineers check the hand calcs to see if any errors were made in calculating K's, DF's, the use of the COF's and for random sign errors, no errors were found. At first I thought I was making an error in the inputs for SAP so I checked moment distribution examples from my text book versus results produced by SAP. The examples were all two or three span continuous and the results matched fine. It seems the more spans the further off the results get for the spans adjacent to the cantilevers. The moments calculated using the moment distribution method for the first interior support are significantly lower than the SAP results. I am puzzled, any helpful tips?
RE: Moment Distribution Discrepancy
RE: Moment Distribution Discrepancy
When I have compared moment distribution with the stiffness matrix method, I have experienced some cases off by as much as 10%. The differences between the methods have to do with axial or shear deformations which are not taken into account with the moment distribution method.
What you might want to do with your SAP model is to input very large cross sectional areas, so that those deformations do not have any influence and your SAP results should approach the results obtained by moment distribution.
RE: Moment Distribution Discrepancy
RE: Moment Distribution Discrepancy
RE: Moment Distribution Discrepancy
RE: Moment Distribution Discrepancy
It doesn't sound like you know what your doing, particularly since the extent of your library is an introductory structural analysis book.