sacs API 4F design of stability direct analysis method

Question

API 4F 5th add the "design for the stability"about the "drilling and well servicing structures" . The direct analysis method of AISC 360 is the first way to solve the "design for the stability" . We should think about the following: 
 1,all member deformations. 
 2,second order effects. 
 3,geometic imperfection. 
 4,stiffness reducetion due to inelasticity. 
 5,uncertainly in strength and stiffness. 
 I want to know how to Set up them in &rdquo;SACS&rdquo;（especially the member geometic imperfection. there are a lot of member in the rig derrick ）? 
 Thanks . 
 my email: haoshanbo@163.com

Geoff McDonald · Answer

Currently the direct analysis is not possible as there is no way to reduce the modulus of elasticity of the structure for the stiffness matrix formulation while retaining the original stiffness for the code check calculations. I recommend that you use the effective length method described in Appendix 7 of AISC 360-15 instead as that does not require any stiffness reduction. 
 Regards, 
 Geoff