Why there are initial moment and shear forces?

[semon]

Hi everyone,

I am working on seismic analysis of a bridge. After adding contact element 3D to represent abutment model, the bridge moves in 10 seconds when I put zero in all the Earthquake loading that I applied to all the foundation and abutments. While the bridge model does not respond like the bridge model with contact element when I apply Earthquake loading with zero values.

This gives me initial (when earthquake loading is zero) moment, shear and displacement.
What could be the problem?

Please help me.

Thank you

[vesna]

Could you please reformulate your question. It is hard to understand.

[mhscott]

Do you have gravity loads?

[semon]

@mhscott yes I do have gravity loads.

[semon]

@Veshna

I am using contact element to represent bridge abutment-deck interaction and interaction at adjacent decks in expansion joint. When I apply displacement time history with zero values in all the locations where earthquake loading should be applied to bridge, it gives me constant initial forces (moment and shear forces) and suddenly shear forces and moment increases and decreases.

My question is,

since the initial constant forces are due to the masses on decks and piers, then why does it suddenly changes after sometime even I dont apply any external forces?

Thank you