Mechanical joints such as bolts and spot welds affect vibration damping of assembled structures. In this paper, we investigate the characteristics of damping due to friction in joints to increase damping of assembled structures. The structure considered consists of three steel plates (main long plate sandwiched in between two short plates) jointed with bolts. First, we evaluate the damping characteristics based on the mode shapes obtained from a linear FE model. Second, we evaluate the damping characteristics based on energy dissipation at the interfaces, being calculated from the contact information (contact pressure, contact area and sliding distance) obtained from a nonlinear FE model by static contact analysis. To validate the procedure, the estimated and measured modal damping ratios of the test structure are compared and the estimated change in modal damping ratio from 1st to 5th bending mode is in good agreement with the measured change. The primary conclusion is that the large energy dissipation occurs at the edge area of the shot plates and the energy dissipation and the vibration energy for each mode vary depending on mode shape (symmetric or asymmetric bending modes). This leads to the differences in the modal damping ratio for each mode.