I'm adding this, it's one of my favorite, I show it occasionally to new users of sap or etabs:
The same very simple model is analyzed in etabs or sap. The results are different because of end length offsets and moment release assignment.
All 3 share the same geometry and load and sections, a 0.5x0.5 rectangular section with default material STEEL I've picked kN-m units, although not important.
The load is uniform q=20 in this case kN/m.
In etabs end offsets are enabled by default which is good and bad, it depends.
In sap end offsets are disabled by default and the same applies.
If one would model the same, without touching end length offsets results will be like A in etabs and like C in sap.
For A, the beam is pinned, when end releases are applied software assumes the beam span is between column interior faces L=6-0.5=5.5 and so
M=q*L^2/8=20*5.5^2/8=75.625 (etabs shows 75 because the default number of output stations is 3, an number of 11 will do the trick)
For B, the columns are pinned, at top, from the statics point of view A and B are identical, but because of end length offsets the release is under the beam, statics look way more difficult to solve by hand.
For C, end length offsets are removed, M=q*L^2/8=20*6^2/8=90, doesn't matter if you assign releases to column or beam.
Between A and C the design moment error percent is:
6^2 vs 5.5^2; 36 vs 30.25; 36/30.25=19% ; default output stations 90/75=20%
For span=20 and columns 1x1: 20^2 vs 19^2; 400 vs 361; 400/361 = 10%
For span=6 and columns of 1x1 36/25 = 44% difference
Now doing the same let's say supermarket precast concrete model with columns having fork top pinned connection to beams in sap vs etabs with default will yield different results. Because the pinned connection is centered on column and beam (a typical detail in some regions for these structures) the etabs user will underestimate the bending moment in beams in etabs with default.
The same goes for other if the model doesn't follow the construction details and the software and user makes wrong assumptions.
So license or not, in the two software made by the same company, with almost identical interface, results can be different although input is apparently identical.
see also:
The same very simple model is analyzed in etabs or sap. The results are different because of end length offsets and moment release assignment.
All 3 share the same geometry and load and sections, a 0.5x0.5 rectangular section with default material STEEL I've picked kN-m units, although not important.
The load is uniform q=20 in this case kN/m.
In etabs end offsets are enabled by default which is good and bad, it depends.
In sap end offsets are disabled by default and the same applies.
If one would model the same, without touching end length offsets results will be like A in etabs and like C in sap.
For A, the beam is pinned, when end releases are applied software assumes the beam span is between column interior faces L=6-0.5=5.5 and so
M=q*L^2/8=20*5.5^2/8=75.625 (etabs shows 75 because the default number of output stations is 3, an number of 11 will do the trick)
For B, the columns are pinned, at top, from the statics point of view A and B are identical, but because of end length offsets the release is under the beam, statics look way more difficult to solve by hand.
For C, end length offsets are removed, M=q*L^2/8=20*6^2/8=90, doesn't matter if you assign releases to column or beam.
Between A and C the design moment error percent is:
6^2 vs 5.5^2; 36 vs 30.25; 36/30.25=19% ; default output stations 90/75=20%
For span=20 and columns 1x1: 20^2 vs 19^2; 400 vs 361; 400/361 = 10%
For span=6 and columns of 1x1 36/25 = 44% difference
Now doing the same let's say supermarket precast concrete model with columns having fork top pinned connection to beams in sap vs etabs with default will yield different results. Because the pinned connection is centered on column and beam (a typical detail in some regions for these structures) the etabs user will underestimate the bending moment in beams in etabs with default.
The same goes for other if the model doesn't follow the construction details and the software and user makes wrong assumptions.
So license or not, in the two software made by the same company, with almost identical interface, results can be different although input is apparently identical.
see also:
Code:
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