Large scale bridging in mode-I delamination of layered composites is an important toughening mechanism. While its extent depends on constituent materials, it is also influenced by specimen geometry. Here, an analytical approach is adopted to express the through the thickness longitudinal strains in a double cantilever beam (DCB) specimen with the applied load and bridging tractions. The expression for the strains is confronted with strain data from embedded Bragg grating sensors to obtain bridging tractions in specimens with different thicknesses. The results show that the maximum stress of traction-separation in the bridging zone and maximum crack opening displacement at the end of the bridging zone are independent of thickness. However, the form of the bridging traction depends on thickness and is not a material property. The identified bridging relations are appended in a cohesive zone model to simulate delamination. The proposed approach predicts fracture of DCB specimens with different thicknesses. (C) 2014 Elsevier Ltd. All rights reserved.