I used shell elements to model concrete slab of 160mx20m. Some openings in the slab are available. The slab thickness is not uniform through 160m, ranging from 1.2m to 1.8m and back to 1.5m. The boundary conditions on 20m span are simply supported.
However, at the joints shared by 1.2m and 1.8m shell elements, I found the vertical reaction force (due to slab selfweight)is much much larger than that in other joints. When I changed the slab thickness to uniform value, there was no same occurance.
I suspect SAP2000 can't model this problem using shell elements.
Can anybody give some help? Thanks.