Seismic damage control of nonlinear continuous reinforced concrete bridges under extreme earthquakes using MR dampers

Abstract

Under extreme earthquakes, a continuous bridge tends to fail because of the damage to the bearing or the pier. A strong connection between the girder and the pier decreases the bearing displacement, but the increased inertia force of the girder to the base of the pier leads to pier damage. Conversely, a weak connection while protecting the pier causes bearing damage. In many cases, the bridge loses its function due to the damages concentrated on local members, while the rest of the members remain undamaged. To simultaneously protect both the bearing and pier during earthquakes with an evenly distributed damage pattern, a new real-time semi-active control algorithm based on the damage of bridge members (RTSD) using magneto-rheological (MR) dampers is proposed. Two displacement indices are established to represent the damage status of the bearing and pier and are used as control signals for the MR damper forces. A typical three-span continuous reinforced concrete bridge modeled by nonlinear fiber damage elements is used for the demonstration of the proposed method. Passive controls using viscous dampers (PVD) and MR dampers with a constant current (PMR) are also adopted for comparisons. Numerical simulation results show that the proposed method is more effective in protecting the bearing and pier than the passive controls. With the RTSD control, the damages to the bearing and pier are balanced and the limited damages to each pier can be evenly developed within the allowable range. Moreover, the initial damper force can be set in a wide range for the RTSD control to protect both the bearing and pier under various earthquakes. In contrast, it is impossible to select a proper damper force by passive controls. The RTSD control can also control the pier damage within different prescribed targets under extreme earthquakes.