If You have high steel structures or towers exposed to wind, how shall the displacements of the steel structure and vessels be handled. Some rules in germany allow the evaluation of this stresses against the figures of thermal expansion. This seams senceful at first sight, because the stresses out of displacement are self limiting as the stresses for thermal expansion. Nevertheless, if the steel structure is modelled as beam in the model, standard practice is the evaluation of the pipe stress as occasional load. What is the right procedure acc. to B 31.3?