Stress-laminated timber bridge decks made of glulam beams are advantageous when it comes to their strength, production and construction costs. The thickness of a deck with a specified span and width is typically determined by considering requirements relating to strength and stiffness stipulated in a design code and specifically in Europe the Eurocode 5. Linear stress calculations do not have inherent potential to simulate slip or gaps between beams, but experience from finite element (FE) simulations and full-scale tests shows that these nonlinear effects from slip and gaps between glulam beams exist. In this paper, comparisons between linear and non-linear FE results for two bridge decks with different spans, widths and thicknesses are made. Separate comparisons are made in the ultimate limit state (ULS) and the serviceability limit state (SLS). It is shown that non-linear effects may be important and should be considered, especially in the case of thin decks.Keywords: prestressed, stress laminated, timber bridge deck, finite element, FEM