I have a steel structure sitting on top of concrete columns and beams. I would like to analyze and design the steel using Direct Analysis and AISC 360 code. At the same time I want to analyze & design the concrete portion using Pdelta analysis and ACI 318 code. Each design should have it’s own set of load combinations. How can I do it ?

You can define two different sets of load combinations for steel and concrete design ( actually these combinations should be defined as REPEAT LOADS as opposed to LOAD COMBINATIONs ). After specifying a set of REPEAT LOADs corresponding to steel analysis/design, you can add the PERFORM DIRECT ANALYSIS and CHANGE commands and follow it up by the REPEAT LOADs corresponding to concrete analysis/design. Finally add the PDELTA ANALYSIS and CHANGE commands. These will be followed by two sets of design namely steel design as per AISC 360 and concrete design as per ACI 318. To ensure that each design considers the appropriate load cases, you can use the LOAD LIST ENV command before the steel design and LOAD LIST command before the concrete design.

An example is attached to demonstrate how to set up the analysis/design correctly for this type of problem.

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