IS1893 2016 Clause 6.4.3 calls for a reduction of moment of inertia values by 0.35 for beams and 0.7 for columns of concrete members only while analyzing the structure for static seismic and response spectrum/linear dynamic analysis. STAAD.Pro now includes a code-specific option for reduced section properties of concrete members which will automatically generate a separate stiffness matrix for these IS1893 2016 load cases. For all other load cases, the analysis will be performed using the unreduced stiffness matrix.

You may use this feature by either selecting the new Code Specific option and then selecting IS1893 2016 as the code in the Member Specification dialog Property Reduction Factors tab. You can manually enter the command using the MEMBER CRACKED CODE IS1893 2016 command.

Using the code-specific member reduction properties helps by automating the analysis for when reduced section properties are required by the IS1893 2016 code. A separate stiffness matrix is produced using the reduced stiffness values for use with load cases containing IS1893 2016 static seismic and response spectrum loads. The unreduced stiffness matrix is then used for all other load cases.

The prime advantage of this feature is that this analysis is completely automated once the reduction factors are defined. Previously, in order to comply with the IS1893 2016 Clause 6.4.3 provision, you would have to specify reduced section properties for members, analyze the structure for only the IS1893 2016 seismic load cases, then use a CHANGE command to reset the stiffness reduction factors back to unity, and then re-analyze the structure for the remaining load cases. Care had to be taken that only concrete members had the reduction factor applied, as the global MEMBER CRACKED command can be applied to any member. For large models with hundreds and thousands of members and hundreds of load cases, the implementation of clause 6.4.3 using the previous reduction command would be very cumbersome.

Use of the code-specific reduction factors automates the analysis procedure. These reduction factors are only applied to concrete members with the member list or member groups (non-concrete members are ignored for this command). The separate stiffness matrix is automatically created using these reduction factors for use with IS1893 2016 seismic loads only while the unreduced stiffness matrix is used for all other load cases. No re-analysis or change commands are required.