beams by computer analysis 2

[flyby911]

hello

do you trust the moment values resulting from sap , Etabs...etc analysis?? even if it differs from values resulting from manual load distribution and solving beams?

another thing for flat slabs
how do you handle the huge values of shells -ve momnets at column joints? and what are the actual design values you use?

 

[csd72]

The stiffness of flat slabs is influenced to a certain extent by the prescence of reinforcement. The slab therefore has a tendency to behave the way that you design it.

The code clauses rely on this to work, whereas the computer analyses tend to treat it as an elastic medium and figure out the moments based on this assumption.

It is important to remember that reinforced concrete is not an elastic medium, so any elastic analysis is still only an approximation.

csd

 

[ahmedhegazi]

Results you get from Software differ from one by hand because of many factors some of them are as follows:

1-Size of plate element and mesh size
2-Torsional stiffness for a beam is considered so some of stresses are transferred as torsion
3-axial deformation of column supports

Using software results need always engineering judgment

For flat slab you will always have high values at support and lower value for positive moments than hand calculations , to avoid this I generally design for the moment around my column and add around 20% extra reinforcement for positive moment.

 

[NS4U]

Shear deformation is another one that can throw you're hand calculated values off.

I'm not sure about other programs but in SAP under section properties you can set the shear area equal to zero... thus the software will only consider bending deformation.