Hi,
Here is an observation we have found recently which we were unaware of earlier, but could have some significant negative consequences for those that use this load case.

The MAX combination in Restraint Summary will not always give the MAX, but instead give a sum of two forces as shown below.

Take the following load case setup as an example:


L25 which is supposed to give the maximum Fy (saving the sign) between L4 to L11 does not do so in this particular case as seen below. It instead takes the sum of Fy found in L10 and L11. This only happens in some cases, but not others.




We contacted Intergraph who sent us the document in the link below:

MAX load combination in Restraint Summary

This states that is is a misunderstanding of the way caesar II calculates and reports the MAX value. What I got from this document is that we should never use MAX combination case as it is not reliable.


The CAESAR Help file states clearly that

MAX - Indicates a combination that reports the maximum displacement, the maximum force, and the maximum stress value of the cases combined. This method retains the original sign. Displacements are the displacements having the maximum absolute values of all the load cases included in the combination. Forces are the forces having the maximum absolute values of all the load cases included in the combination. Stresses are the stresses having the maximum absolute values of all the load cases included in the combination. This method is typically used to report the greatest restraint loads from among a selected set of load cases.


But since the bolded part is not always correct, it should perhaps be more clearly explained in the guide. A few companies use the MAX combination in the restraint loads to design supports.


My question now is, can this MAX combination be used reliably for stresses?

For example, using the above load case set up, is it correct if we say:

  • L29: L12, L13 (OCC) (MAX)
  • L30: L29+L4 (OCC) (Scalar)


in order to get the max occasional/accidental stress in the WIN1 direction (North/South)? Will this be always reliable?