The deformation kept accumulating when applying temperature load

[Sunicetk]

Hi I want to ask a question about the deformation simulation in Abaqus.
I am now doing a case that I appply temperature load onto different parts of a truss bridge and then obtain the deformation of the bridge. The data of temperature load I use is the real data I measured in 36hours(measurement interval was 1 minute). Therefore, the deflection(U3) should change following the trend of the temperature change, which should be up in the daytime and down in the nighttime. However, although the deflection followed the trend of temperature, it also kept decreascing all the time. Is there any option or setting that I can change to correct this kind of error?

 

[FEA way]

What were the boundary conditions, initial conditions and interactions in this simulation ? Which kind of analysis step was used ? Can you share some screenshots showing the model ?

 

[Sunicetk]

Thank you very much for your reply.

The model is a truss bridge with concrete deck as shown in the figure.
For boundary conditions, the type is displacement/rotation. Two ends are fixed and the other two are moveable at u1 and ur1.
The initial condition is temperature predefined field all 20 degrees all over the structure.
Interactions are tie(between crossbeams and concrete deck).
The analysis step is static,general.