Steel & Concrete Load Combinations & Analysis

Jeremy :

You can definitely have two different sets of load combinations for steel and concrete design ( actually should be defined as REPEAT LOADS as opposed to LOAD COMBINATIONs ). You can use the LOAD LIST ENV … command before the steel design and LOAD LIST … command before the concrete design to instruct the program to design the steel and concrete against the appropriate combos. All of these can be handled in a single file.

The fact that the two materials demand a separate analysis type, makes the matter little complicated and my first thought is, you should use two separate models. Both models will have both the steel and concrete members. In one model you can have the concrete cases, PDelta analysis and design as per ACI. In the other file you can have the steel cases, Direct analysis and design as per AISC. This is going to work for sure.

Jeremy :

You can definitely have two different sets of load combinations for steel and concrete design ( actually should be defined as REPEAT LOADS as opposed to LOAD COMBINATIONs ). You can use the LOAD LIST ENV … command before the steel design and LOAD LIST … command before the concrete design to instruct the program to design the steel and concrete against the appropriate combos. All of these can be handled in a single file.

The fact that the two materials demand a separate analysis type, makes the matter little complicated and my first thought is, you should use two separate models. Both models will have both the steel and concrete members. In one model you can have the concrete cases, PDelta analysis and design as per ACI. In the other file you can have the steel cases, Direct analysis and design as per AISC. This is going to work for sure.

I also spoke with the technical support from Bentley. Here is their response below:

"You will need to create two sets of load combinations to do so. So, for example, let us suppose that load combinations 100 to 199 are for steel and 200 to 299 are for concrete. You would first ensure that load cases 100 to 199 have notional loads and 200 to 299 do not. Then, you can set up your design commands: AISC code check for steel members and ACI design for concrete members. The trick is to use the LOAD LIST command to specify which load cases pertain to each. You would add the command LOAD LIST 100 TO 199 before the AISC code check, and the command load list 200 to 299 before the ACI design. In this way you can ensure that the proper loading conditions are used for design.
Finally, let me point out that if you wish to implement different analysis commands for the steel and concrete members you can do that as well. Say you wanted to use a PERFORM DIRECT ANALYSIS command for the steel members and a PDELTA ANALYSIS command for he concrete ones. You would input the commands PERFORM DIRECT ANALYSIS and CHANGE after load case 199 (but before load case 200) and then put the command PDELTA ANALYSIS after load case 299."

Thanks.

I agree with most of it except the fact that you should use LOAD LIST ENV and not LOAD LIST for the AISC 360-10 code check part. The reason for that that is explained in the following wiki

communities.bentley.com/.../20793.strengthserviceability-check-in-design

Having both analysis in the same file should work as suggested by technical support but I would like to do a small test at my end before I confirm that. Having separate models would always work and that is why I suggested going that route. Anyway I will do a quick test at my end and revert back on that part.

Sye,

Thanks. Please let me know what you find out.

Using the two analysis types as part of the same analysis model should be fine. I verified it with the attached example.

Direct_Analysis_Steel_and_Concrete_Model.std

A wiki is now added on the same topic

communities.bentley.com/.../31334.analyzing-designing-a-structure-made-of-steel-and-concrete