Let us look at an interesting example of a huge drawbridge that failed due to dry-friction.

Figure 4.4 : Schematic diagram of a Draw-bridge

Figure 4.4 schematically shows one-half of this drawbridge where the deck used to be positioned by moving the four-bar parallelogram linkage O₂ABO₄. After about a year, one of the bridge towers failed by fatigue. An experiment with the other half revealed that the whole bridge vibrated violently at a rather low frequency each time the deck was raised. The answer was found in the bearing at B. This bearing carried the huge load of the counterweight. As a result, the grease originally present in the bearing got squeezed out and the bearing was running dry. This dry friction gave rise to chatter which was violent enough to ultimately cause the failure by fatigue. The simple remedy to this vibration problem consisted in providing proper grease cups at B and keeping them under regular inspection.