Steel Structures Optimization of Members is not increasing member sizes to make them pass, using Indian code IS 800-2007 LSD

Question

Steel_Design_Optimizing_M_Intermediate_1_AISC_360-16.STD Steel_Design_Optimizing_M_Intermediate_1._IS800-2007 LSD.STD 
 
 Why I am getting "Fail" results after using optimization process of commands?; even selecting Ratio 0.9 initially, e.g look into a member no. 17, which is still showing Fail with Utilization Ratio =1.57 ! 
 
 I had followed COMMAND STRUCTURE: Performed Initial Analysis, Perform the Optimization using select command, Grouped the Members during Optimization, Re-Performed the Analysis, lastly Performed a Code Check . Used Is 800-2007 LSD. Used ISMB200 initially, assigned FYLD, DMAX, DMIN, profile ISMB, ration 0.9. 
 
 Also If I change just Design code in this very same file to AISC-360--2016, changing 1) Beam section from ISMB to W12x22, Profile to W12, under optimization command structures, above members pass (e.g no 17) with even decreasing beam size as W12x14 . 
 
 Thus my question remains while implementing with using IS: 800-2007, if I had made some error? or something else? 
 
 Screenshots, Staad.pro file both (IS )and AISC attached, used Staad Pro connect edition Version 22.03.00.28

Surojit Ghosh · Answer

I have noticed a problem related to member selection (SELECT command) in STAAD.Pro CONNECT Edition (including latest version - build 22.04.00.40) and this is related to IS800 code only. Though you have provided correct inputs, program is unable to select proper section when the critical condition is slenderness as well as interaction. Program supposed to perform iterative analysis to compute optimum section and member will be reported as fail only if highest section is not sufficient to resist the force. This is not happening now due to some internal problem and if you perform member selection, fail member will be reported. I have already reported this to the development team and hopefully this problem will be fixed soon. 
 There is no alternative, rather than manually changing the section size. You can use SELECT command, but if the member fails in slenderness or interaction, you need to change the section manually.