II. It is not clear from your description what kind of supports are applied in reality - please send sketches/photos along with a description.

III. If I understand correctly, the bolts pass through the concrete - connecting the support plate with some other plate(s) on the other concrete surface. If so, I don't understand how you planned to represent the bolt with a spring support?
The simplest and most common modelling of such a bolt is a 1-D reinforcement bar.

Regards.

I am modelling reinforced concrete slab supported at four-corners on steel plates (200x200 mm). Steel plate is connected with the slab through M20 bolt. To connect the bolt a special assembly has been placed inside concrete during casting.

I modeled the bolt using vertical spring at joint (at exact location of bolt) with z-direction fixed. I have applied boundary conditions on the steel plate with x and y-directions fixed.

The model ran, but I found the deflection is too low and slab failed much before the yielding of tensile steel.

My understanding, I could not model the bolt connections.

My questions:

1. Do I need to build a physical bolt as a macro element (ABAQUS has this option)? If yes, how and what should be its material model?
2. Instead of using physical bolt what other options I have?

I can send the model for your review.

Regards
Ahsan