Manufacturing strains and subsequent residual stresses are key elements in the behavior of thin-walled structures, as they induce buckling, warping, and failure. This work proposes a combined experimental and numerical analysis of these features by investigating the additive manufacturing of a thin-walled structure using directed energy deposition. In-situ measurements of temperature and in plan displacement fields during fabrication are identified over the entire part and all along the process by using infrared and optical cameras. One novelty of this work is to determine the displacement field without stopping fabrication unlike most of the existing approaches, which significantly simplifies the monitoring of the process. In addition, a numerical modeling of the process has been developed to investigate the formation of residual stresses. One novelty of the proposed approach is to reach reasonably short computation time, by decoupling thermal and mechanical problems, which is interesting for parametric studies. Results are relevant, as the computed temperature and displacement fields are in good agreement with the in-situ measurements. A complementary buckling analysis also shows the ability of the model to predict when fabrication has to be stopped due to excessive out of plan deflection. The presented model can therefore be used as a tool to select suitable process parameters for a given part.