Determination of the Contact Condition

In time history analysis , the contact condition changes as loads and ground excitation change. Determination of the contact condition is based on the law of friction, the previous contact condition and the current material overlap. The contact condition decision is made as follows

If the previous iteration condition was tension release then
If there is a penetration then
The new condition is sticking  contact
Else
The new condition is tension release
End if
Else
If the force Fn is tension then
The new condition is tension release
Else
Set the new condition to be the same as the previous condition
If the previous condition was sticking  contact then
If 
then  the new condition is sliding contact
Else
If 
then  the new condition is sticking contact
End if
End if
If it is the first iteration then
Set the new condition to be sticking contact
End if
End if