concrete column under impact load

[Amna Alhassany]

Hello everyone,
I am working on an LS-DYNA numerical simulation of a reinforced concrete column subjected to lateral impact using an impactor .

My issue

In the experimental research paper that I am trying to validate, the impact force-time history shows two peaks (double peak response).
However, in my LS-DYNA model I always obtain only one peak (single peak), even though the impactor hits only once and then separates.

Model description

• Units: mm – ms 

• Column: solid elements (concrete + reinforcement)

• Base: fixed support

• Top: slab + additional mass tied between them

• Impactor: deformable body with initial velocity V = 0.46 mm/ms in the impact direction (Y direction).

• Contact: *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE 

• I am extracting impact force from the contact resultant force

• the blue curve is the experimental test