The issue you are facing stems from the small gap between the steel pipe and the rebar and the challenges in defining the correct interaction in ABAQUS. Below is a step-by-step guide and explanation to resolve this problem:

1. Understanding the Problem

• Tiny Gap Issue: When you zoom in, the small gap (which is likely due to mesh discretization or geometry definition) prevents the tie constraint from effectively linking the steel pipe and the rebar.

• Warnings: These indicate that no nodes were adjusted to create the tie constraint, meaning ABAQUS could not establish the required interaction due to the tiny or nonexistent overlap.

2. Corrective Steps

Geometry Preparation

1. Ensure Perfect Contact:

• In the Part section, align the rebar’s position so that it touches the steel pipe precisely. Use datum points or reference geometry to ensure the rebar is positioned correctly.

• Avoid manual adjustments by ensuring the pipe and rebar geometry aligns during part creation.

2. Use Boolean Operations (Optional):

• Instead of relying on tie constraints for separate parts, you can use Boolean operations to merge the pipe and rebar into a single part (if suitable for your analysis).

Interaction - Tie Constraint

1. Modify the Tie Constraint Settings:

• Set a position tolerance in the tie constraint interaction. The default tolerance may be too small.

• Try increasing the position tolerance slightly beyond the gap size (e.g., start with 0.01 or 0.1 depending on your model units).

2. Use Adjustments:

• Enable the “Adjust Slave Surface” option to allow ABAQUS to slightly move the nodes of the rebar or pipe to bridge the gap.

3. Switch Master-Slave Roles:

• Set the steel pipe surface as the master and the rebar as the slave. This ensures that the larger element (pipe) controls the interaction.

Alternative Interaction (General Contact)

• If the tie constraint fails:

• Use “General Contact” in the Interaction module:

• Define a contact interaction with frictionless or small sliding properties.

• This can simulate a welded connection without needing precise alignment.

Mesh Refinement

• A coarse mesh might exaggerate small gaps. Refine the mesh near the pipe and rebar to improve the node alignment.

3. Simulation Workflow

1. Rebuild Geometry:

• Re-check the alignment and ensure the rebar and pipe surfaces are precisely touching.

2. Define Interaction:

• Use a Tie Constraint with a higher position tolerance or enable node adjustment.

3. Verify Connection:

• Run a preliminary simulation to confirm the interaction is working. Check the interaction outputs in the .dat file or visualization.

4. Solutions to Avoid This Issue in the Future

1. Use Reference Geometry for Alignment:

• Ensure exact positioning during the part creation phase.

2. Simplify Geometry:

• Where possible, use a single part for welded components.

3. Improve Meshing:

• Use finer meshes near interaction zones to reduce gaps.

5. Summary

The best solution for your case would be to:

1. Align the rebar and pipe accurately in the geometry setup phase.

2. Use a Tie Constraint with adjusted settings (increased position tolerance, adjust slave surface).

3. Refine the mesh near the rebar-pipe interface.

If the Tie Constraint still doesn’t work, try General Contact with appropriate settings.