The problem of cleaning structural monitoring data from thermal effects has been studied since the pioneering developments in this area. The first attempts approached the problem in a statistical way, in terms of time history correlations. The availability of powerful numerical tools able to solve the thermo-mechanical stress-strain analysis suggests pursuing a dynamic modeling approach. However, defining boundary conditions and assigning the initial conditions can be problematic. Some aspects of such an analysis are discussed in this paper and a proposed procedure is exemplified with reference to an existing railway bridge.