how to model a 2" gap between cap and the pipe pile in Pushover

[engidude]

As shown in the attached sketch. The steel pipe pile stops 2" below the cap while the reinforced concrete core continue into the cap.
The intention of such detailing is to force the plastic hinge to be formed underneath the cap and prevent damage to the concrete of the cap.

My question is how to model the 2" gap in PUSHOVER. To capture the behavior of the system a 2" column element needs to be defined. But the hinge length of the element should be much linger than the element length. Should I assign just the 2" as hinge length or assign the calculated hinge length as the hinge length? I'm leaning toward to use the the calculated hinge length though it is much longer than the element length.

 

[JasonMcKee71]

I would use the calculated one. The hinge is not concentrated at one point and additionally the rebars, as they are placed, can resist a moment by themselves.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
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Interaction Diagrams
Reifnorcement Design etc.

 

[stressed]

It's not so much a "gap" as it is a change of section properties requiring that you define and model different sections - one section composite steel pipe filled with reinforce concrete, and another frame/column element which is reinforced concrete only (without pipe) going into the pipe cap. You will need to use Section Designer to define the composite steel pipe section with reinforced concrete.

I am unclear why the hinge length must be 2". As you probably already know, you can assign multiple hinges to each beam/frame element.