Study of the nonlinear behavior of large bridge supports under earthquake solicitations

Abstract

For very large bridges it is important to efficiently manage displacements and deformation during earthquakes and under the passage of vehicles to avoid damage and collapse of the structure. Classic solutions consist in implementing spring type shock absorbers, which convert the kinetic energy into heat energy, helping in dissipating it. A very effective and rather simple solution which is often adopted for large bridges and other sensitive structures is to implement pendular bearings, characterized by a curved geometry: they have the dual role of vertical support and of horizontal elastic support, the stiffness of which is proportional to the vertical reaction divided by the radius of curvature (called “pendulum effect of the support”). Between the moving parts of the support device, the sliding surfaces may have some roughness: in this case, the frictional force must be defeated before any displacement can take place. Whenever a force which would cause the structure to undergo a horizontal movement is applied: • the deck is horizontally stationary if the horizontal force is smaller than the frictional force; • the deck moves if the horizontal force is greater than the frictional force; • if there is movement, the deck will undergo both horizontal and vertical displacement. The behaviour is therefore, by definition, nonlinear. During the study of the Third Bosphorus Bridge in Turkey all phenomena were considered for the passage of a train; for the earthquake, on the other hand, only the pendulum effect was taken into account, while friction has been neglected. The present Master Thesis consists of studying and modelling the entire behavior, with both pendulum effect and friction, under earthquake solicitations, analyzing a real case, specifically the Third Bosphorus Bridge, and evaluating the dynamic response in time.