Dears,

I am trying to model reinforced concrete slab column connection under displacement control (1mm/min) Fig1. using concrete damaged plasticity (CDP) in ABAQUS. The material parameters that I used are the following.( from Fig 2 to Fig 7)

I used static analysis with the time period= 1 and an initial increment size=0.01

However, I used steel bars as a wire section with 210,000Mpa for elastic modulus and 0.3 as passion ratio, the yield stress and the ultimate stress and plastic strains are the following (275Mpa, 482Mpa and 0.002)

An embedded interaction between the concrete and the steel reinforcement is defined.

Tie constrain is defined for the interaction between column and slab.

The connection is sit on steel support modeled as Deformable section with only elastic properties (E=210,000Mpa and passion =0.3) frame having dimensions of width 4cm depth 8cm. The Coulombic friction model is chosen to model the interaction between slab and support considering tangential (A constant friction coefficient of 0.2) and normal behavior at the interface (hard contact)

The results are measured on a reference point set just above the center of column stub and linked with the top surface of the column with coupling constraint.

I am obtaining the ultimate load (28 KN) on a very small displacement (0.7 mm) which indicates that the results do not match with experimental data since the ultimate load for this connection was about 50KN at 10mm displacement.

However, changing the time period strongly affects the ultimate load.

For example, at Time period =0.25, the ultimate load= 52KN at 1.7mm displacement.

My questions are:

Why changing the time period strongly ultimate load

How can I get less stiff curve (initial stiffness) (i.e. increasing the displacement at failure).

Fig7 ( Load Vs Displacement curve connection model without steel reinforcement)

Fig 8 ( Load Vs Displacement curve connection model with steel reinforcement)