Direct Analysis Method

RE: Direct Analysis Method

Biswatosh — Tue, 17 Jun 2014 07:36:23 GMT

The AISC code suggests the Direct Analysis to be performed by either magnifying the moments reported by the first order analysis (B1 - B2 method ) or by performing the rigorous iterative second order analysis( P-Delta Analysis).

The first approach is an approximate method, whereas the second one is an exact method based on second order iterative process. So, one can expect certain degree of deviation of the results generated by both methods.

Secondly, you have mentioned that you are trying to see the statics check result for the combination case.

But, it is not suggested to use the "Load Combination" for any non-linear analysis, so for the Direct analysis.

Instead of Load combination, try using the "Repeat Load" case.

Regarding the second part of your query, the idea is to manually reduce the the axial and flexural stiffness to account for the material non-linearity as specified by the DAM. So, you can either use the cracked section factor to reduce the A and I value or reduce the E value while performing the P-Delta analysis. But, there is no such way available in Staad to use one value of E for analysts and another E value for design operation.

For more detail on Direct Analysis Method, please refer to the following link

communities.bentley.com/.../10606.direct-analysis-and-its-implentation-in-staad-pro.aspx

RE: Direct Analysis Method

Biswatosh — Tue, 17 Jun 2014 07:35:27 GMT

Secondly, you have mentioned that you are trying to see the statics check result for the combination case.

But, it is not suggested to use the "Load Combination" for any non-linear analysis, so for the Direct analysis.

Instead of Load combination, try using the "Repeat Load" case.

For more detail on Direct Analysis Method, please refer to the following link

communities.bentley.com/.../10606.direct-analysis-and-its-implentation-in-staad-pro.aspx