###### Abstract
[PERSON] and [PERSON] [32] used FEM to perform a 3D nonlinear transient heat transfer analysis for subsurface delamination detection in bridge elements. Their 6-month analyses were performed and simulated using a large vertical concrete block, investigating the effects of the environmental conditions on the thermal gradient detection. [PERSON] and [PERSON] [33] investigated the favorable time window for passive IRT inspections of one reinforced concrete bridge deck during one day using only numerical modeling. [PERSON] et al. [23,34] investigated experimentally and numerically the preferable conditions for thermographic analysis in concrete bridge decks during a 24 h timespan. The researchers [24,35] also studied the effect of depth, shape, and thickness of delamination on bridge decks, as well as ambient temperature and solar radiation conditions (one typical day in each different season), for subsurface damage detection using thermographic cameras. Those studies have shown that FEM is a potential tool to support passive IRT inspections in concrete bridge components. However, there is no study exploring the use of FEM for the simulation of continuous and extended periods of passive ITR inspections of concrete components. In addition, most of the countries still do not have standards that regulate the use of IRT for inspection of infrastructure components, with a lack of studies [36] that orientate the planning of inspections for a long period in different locations and weather conditions. In this way, this research presents a computational model that can be useful to find windows of opportunity for planning inspections with the potential to detect subsurface damages in existing concrete bridges. Construction of test samples that represent bridge elements with diverse damage levels and environmental conditions is difficult, as the specimens normally have a large size and the monitoring of the IRT performance in a wide range of meteorological scenarios takes a considerable amount of time [24; 32]. Therefore, if the integration of IRT and FEM is used, different structure locations and weather conditions can be added to the model to estimate the thermal gradient expected for target defects in the simulated concrete components. The modeling in the long term can be useful to identify periods during the day and/or during different seasons when the thermographic inspection technique would have acceptable performance in damage detection, with a possible reduction of the cost and time spent in field tests. Therefore, the main contribution of this study is the development of a FEM model to support long-term inspection plans in concrete bridges using solar loading thermography. A thermal camera was used to inspect a sample of concrete bridge slab with artificial subsurface delamination during different seasons and weather conditions. A numerical model was developed to simulate the experimental concrete specimen, radiation source, and IRT inspection. To validate the model, a comparison between the experimental and numerical surface temperatures and thermal gradients was performed. Then, the calibrated model was used to predict the most favorable periods to detect the subsurface delamination in a concrete structure during one year of inspection.