How to convert stress into moments in slabs? 1

[sepultura]

I want to modelate solid slab of concrete, and the program give me streess (kg/cm2), and I want to design it with moments (kg-cm). how to realize that convertion?

 

[DENSAL55]

Go to Display >> Show Member Force/stress diagram >> Shell Stesses/Forces if we select Forces we have All Forces M11 M22 which are out of plane moment in kg-cm/cm of lenght.

 

[sepultura]

Thans DENSAL55, but my questin is: How I could do it manually, if I have not the option of M11 or M22?
The stress (kg/cm2) I want to convert to moment (kg/m), manually. (in flexural design).

 

[Diquan]

Simple:

S=(M*c)/I

S = Stress
M = Moment
c = distance from the outer fiber to the center of the member
I = inertia of the section

=======================================
Diquan
diquan@yahoo.com

 

[Diquan]

... ou i forgot, when calculating the inertia in the equation:

I=b*h^3/12

"b" is 100cm or if you use inches "b" equal to 12in (1feet)

so, when calculating the amount of steel is going to give you "cm^2" for every "cm" - (cm^2/cm or in^2/in)

=======================================
Diquan
diquan@yahoo.com

 

[DENSAL55]

in the case of slab it is not so simple, because we have many type of stress
S11=F11/th-(12*M11/thb^3)*x3.
S22=F22/th-(12*M22/thb^3)*x3.
S12=F12/th-(12*M12/thb^3)*x3 etc...

x3 represente the variation of thickness of slab.

to obtain M11,M22 etc...
we must integrate the stress s11,s22,s12 along the thickness of the slab.
see "Internal Force and Stress Output Page 144 in the sap reference manual "
The Shell element internal forces (also called stress resultants) are the forces and moments that result from in tegrating the stresses over the ele ment thick ness. These
internal forces are etc...

 

[DENSAL55]

- x3 represente the variation of thickness of slab from midplan of slab to the point where the stress is calculated .

 

[stressed]

For designing the slab, don't forget about drawing section cuts to obtain resultant forces and moments for design. If you can get a copy of SAFE, you can export the slab from ETABS to SAFE for design of reinforcement and punching shear checks