[en] The analysis of tubesheet assemblies is presently almost exclusively carried out by neglecting the effect of the solid separation(s) between the different perforated zones (e.g. diametral lane). The problem is thus transformed into an axisymmetric one and equivalent elastic constants are used for the perforated zone. The above approximation is necessarily conservative since it does not take into account the following two possible effects: (1) increased local rigidity due to the presence of a lane of unperforated material with resulting high levels of local stresses. (2) non-axisymmetric displacements of the tubesheet periphery which may induce local loss of contact at the gasket and result in a leaky joint. The purpose of the paper is to report on an experimental investigation carried out with an epoxy resin model of a tubesheet with two passes and a wide diametral lane. Various thermal loading configurations both symmetric and non-symmetric have been applied and, in addition, the effect of rate of temperature increase has been studied. (Auth.)