Strain Hardening Ultra High Performance Fiber Reinforced Concretes (SH-UHPFRC) have a high elastic limit (around 10 MPa) and high tensile strength (upto 20 MPa) and exhibit significant strain hardening (1 to 4 %) under tensile loads. These appealing features make them extremely effective materials for strengthening and improving the durability of existing structures. However, their cast on site application induces significant eigenstresses due to restraint conditions. In this paper, the effects of various restraint conditions on the tensile viscous response of SH-UHPFRC was determined experimentally using a Temperature Stress Testing Machine and was modelled. Tests were done at partial and full restraint conditions to study the eigenstresses development. The ageing linear viscoelastic response of the material was modeled using an ageing generalized Maxwell model, fitted on the experimental data of eigenstresses. The influence of the scatter of free shrinkage measurements on the model prediction was studied through a sensitivity analysis.