Direct Analysis Method for Steel Buildings using RISA 3D

This video illustrates the process for conducting the Direct Analysis Method for steel structures per the 15th Edition of the AISC Steel Construction Manual (AISC 360-16, Specifications for Structural Steel Buildings, Chapter C). This video performs design according to LRFD, though the ASD procedure is similar.
The primary benefit of performing structural analysis per the Direct Analysis Procedure is that the effective length factors K for all columns can be assumed equal to 1. Thus, the effective column length is equal to the unbraced length.
The necessary features for the Direct Analysis Method are:
1) Stiffness Reductions: apply 80% stiffness to all stiffnesses that contribute to the stability of the structure, plus an additional reduction to flexural stiffness of members with high compressive loads.
2) Second-Order Analysis: consider both P-Delta (capital Delta, accounting for deflections at column ends) and P-delta (lowercase delta, accounting for deflections along the lengths of columns) effects.
3) Notional Loads: lateral loads that account for structural imperfections, equal to 0.002 times the factored gravity loads on each story.

[@g.sunilnaikg.sunilnai7996]

Its soo usefull for me as a civil engineer sir thank you soo much love from India 🙏

[@StructuresProfH]

You are most welcome!

[@chrisaprile813]

Nice video presentation. Thanks.

[@StructuresProfH]

You are welcome!

[@2718rm]

I believe risa will perform p little delta analysis is you select the geometric nonlinear analysis approach

[@StructuresProfH]

Yep. Good catch! Geometric Nonlinear Stiffness analysis was just added in RISA v20, which was released about a month ago. I'm still working on v19, which does not have this feature. For those interested, here is a link with more details: risa.com/post/p-delta-analysis-using-geometric-nonlinear-stiffness-in-risa-3d

[@2718rm]

@@StructuresProfH thanks for the video!

[@chrisaprile813]

@@StructuresProfH I would add that you still have to use the nodal shear method when adding any special 'user inputs' for member end connections, for example adding custom releases to mimic partial fixity.

[@amrmasoud5580]

I have noticed that Risa 3D is more famous and well distributed than Etabs in USA, is that right?

[@amrmasoud5580]

why you used RISA 3D ? what its advantages versus staad or etabs? besides, I know that RFEM has a large capabilities in analysis.

[@chrisaprile813]

Mainly user interface - RISA3D is very simple to learn regardless of how long you have been in engineering. RISA3D is also very compatible with spreadsheets, which if your company has already uses for design analysis (steel, wood, or concrete), then the outputs from RISA3D can easily be adapted to what you already have in house.

[@amrmasoud5580]

Can Risa do pushover analysis?

[@amrmasoud5580]

please , give me tutorial for how to model 3D tall concrete by RISA 3D?

[@structureexpert7985]

can use direct analysis for concrete structure?

[@StructuresProfH]

You can analyze concrete structures in RISA, but the procedure is not quite the same as the direct analysis method for steel structures. RISA allows you to switch your governing code document in the options, so many of these things may be automated in the program - check out the RISA documentation for details on whatever code you use.
As for the differences: Assuming you are designing your concrete structure according to ACI 318-19, there is no notional load. Instead, the axial-moment interaction diagram for column capacity has a "minimum eccentricity limit" defined in Section 22.4.2.1. Also, the stiffness reduction for concrete is different from steel. Concrete needs to account for cracking and creep; Section 6.6.3.1 in ACI 318-19 has reduced moments of inertia for factored load analysis.
As for the similarities: Both steel and concrete structures can be analyzed using second-order effects (P-Delta or P-delta). These work the same way. To get the P-delta effects (that is, deflections along the length of the column), you should define nodes along the length of the members, just like for steel. When you use second-order analysis for concrete structures, you don't need to do the moment magnification procedures for nonsway or sway systems (Sections 6.6.4.5 and 6.6.4.6); the second-order analysis already magnifies your design moments.

[@structureexpert7985]

@@StructuresProfH thank you for explanation. Does software can calculate small p delta directly? Yes to include small p delta we have to mesh column, Example mesh length= width of column B. for most of software can calculate accurate small delta for single curvature like a single cantilever column. How about double curvature?

[@gopidurgapu4558]

Sir I am studying mtech in civil engineering,I have doubts in Ansys,how to contact u sir.

[@gopidurgapu4558]

Reply sir