SAP2000 Nonlinear Analysis Setup for Steel Design: Notial loads

[juandavidguzman]

I’m using SAP2000 v26 to design steel structures based on AISC 360-10, and I'm configuring a nonlinear analysis for the structure. I use the Direct Analysis Method and apply a process where each load case starts with the structure deformed under dead load (state D). Additionally, I adopt K=1 for all elements and have set Tau-B Variable for stiffness reductions.

Is it still necessary to apply notional loads if I’m already considering a nonlinear analysis with deformations? If yes, how should I configure these notional loads in SAP2000?

 

[JoshPlumSE]

It's probably still required to have the notional loads. The point of the loads is to de-stabilize the compression members. Gravity loads are not usually sufficient to do this.

Look at a simple braced frame. Unless you're gravity loads are already displacing the columns laterally at each floor level, then your gravity deflections are NOT sufficiently inducing the deflections that are required for the the Direct Analysis Method.

The normal way to do this is just what it says in the code.... Look at the loads applied at each floor level and apply 0.2% of this load laterally. Just like wind or Seismic, you will have two different Load Combinations for this, one for each lateral direction (assuming a 3D structural analysis).

 

[STpipe]

Definitely need to include the notional loads. The non-linear analysis (along with stiffness reduction) is what allows you to use K = 1 for the design of members, but you still need to account for destabilizing loads.

With SAP2000, there should be an option to automatically generate the notional loads under load patterns. You would set notional load, and under the option "Auto Generated Loads", you would select the applicable standard that's used for generating these loads.