Why is etabs giving me lesser moment than manual design

[oloksy]

Good day, I started learning Etabs lately and I noticed most tutors on youtube saying that we should use shell thin for the solid slab. Now my question is why does shell thin produce lower moment than that of the membrane ( which matches that with the manual calculation)

 

[Enhineyero]

Your post is a bit ambiguous. Is it a slab supported by walls? columns? beams? idealised support?

Different plate elements have different 'releases' and should be used for the appropriate member type. Best refer to the ETABS manual. In my experience, results from a well-modelled structure in ETABS shouldn't differ with hand calculations by more than 10%.

 

[oloksy]

Enhineyero, the solid slab is supported by beams around its four edges

 

[klaus.]

start with a simple beam instead of slab .....

 

[Agent666]

The issue is shell elements act like a flange carrying some portion of the beam axial forces from flexure. If you review the beam axial load with the shell you will see what I mean. Then change to a membrane and notice the difference.

https://www.eng-tips.com/viewthread.cfm?qid=471033

This post covered the same issue. Have a read and post back with any unanswered questions.

 

[271828]

start with a simple beam instead of slab .....

Agreed. Start with a problem for which you know the exact solution.

Also, bravo for digging in and figuring out the program.