In this work, a new 3D thermomechanically coupled phenomenological model is proposed for SMAs. SMA behavior is described through several strain mechanisms, each associated with its proper internal variables. Forward and reverse transformation are allowed to take place simultaneously with martensite variants reorientation. This model is built to capture the particular behavior of SMAs when subjected to complex loading, namely non-proportional thermomechanical loading. The effect of thermomechanical coupling, related to dissipation and latent heat is examined by means of conducting simulations under various thermal conditions. The validity of the model is demonstrated by approaching experimental results of complex thermomechanical loading paths of SMA structures.