RAM Concept's "K Factors"

From what I understand in RAM Concept language...

R axis = X axis

S axis = Y axis

Slight clarification; the direction of the slab objects is defined by the user with the R axis. The default of 0 degrees for the R axis corresponds to the positive global X axis, but slab objects can be rotated (counter-clockwise) in plan.

KMr is a stiffness variable for moments about the R axis. Section 17.20 Slab area properties explains best.

Note, throughout the program we use R and S when referring to the local axis of an object (slab, beam, wall, column) and X and Y for reference to the global axis.

Slight clarification; the direction of the slab objects is defined by the user with the R axis. The default of 0 degrees for the R axis corresponds to the positive global X axis, but slab objects can be rotated (counter-clockwise) in plan.

KMr is a stiffness variable for moments about the R axis. Section 17.20 Slab area properties explains best.

Note, throughout the program we use R and S when referring to the local axis of an object (slab, beam, wall, column) and X and Y for reference to the global axis.

Hi Seth,

I checked on the Manual but I couldn't find a thorough explanation of the theoretical formulation of the K parameters.

Could you please confirm if the following is correct?

kMr - affects the bending stiffness about the R axis

kMs - affects the bending stiffness about the S axis

kMrs - affects the torsional stiffness (I presume just the Jourawski stiffness - 1st order)

kFr - affects the axial stiffness along R axis and the bending stiffness about S axis

kFs - affects the axial stiffness along S axis and the bending stiffness about R axis

kVrs - affects the in-plane shear stiffness (is it just for diaphragm action?)

Could you also please provide the above k parameters for the 3 listed options?

Two way slabs

One way slab

No torsion two way slab

thanks

Davide

I think you have it correct. Take note of section 53.3.1. You can select one-way slabs or no-torsion beams in the behavior tab and check the various K values yourself. Two-way slabs are all 1.0 values. 

Hi Seth, I am back on this topic just because I noticed that the orthotropic parameters can be set higher than 1. In the specific I am reviewing a model where the engineer adopted kMr and kMs = 10.

I would expect the orthotropic factors to be limited between 0.001 and 1.

Could you please clarify?

Thanks 

Sometimes people want something extra stiff, e.g. to simulate a rigid end zone. We added a tool for this in Ram Concept 8.2 by the way, see: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/53257/rigid-support-zones-in-ram-concept 

By the way, Karl Gullerud and I are giving a Webinar next week "Take Your Concrete Floor Designs to the Next Level Using RAM Concept" and this is one of the topics.