Using molecular dynamics simulations, we study the plane shear flow of an assembly of slightly polydisperse disks, at controlled pressure and shear rate, without gravity. We use biperiodic boundary conditions to avoid wall perturbations. We add to the usual interaction term (elasticity, friction and dissipation) a cohesive force of the Van der Waals type. The properties of this system depend on two dimensionless numbers. The first one is related to the shear state imposed to the material. The second one characterizes the intensity of the cohesion. In steady homogeneous shear flows, we measure the variations of the solid fraction and of the effective friction as a function of those two numbers, from which we deduce a viscoplastic constitutive law. Moreover, the grains agglomerates in transient clusters when the cohesion number increases. The analysis of the space and time correlations shows a structural transition when the cohesion force becomes larger than the confinement force.