MCEER HIGHWAY PROJECT
Task D2-3: Energy Dissipation and Intelligent Devices for Bridges with Steel Superstructures
Earthquake Protective Systems
|Principal Investigator(s) and Institution(s)
Michael A. Riley and Fahim Sadek, National Institute of Standards and Technology
Recent earthquakes have clearly demonstrated the seismic vulnerability of bridges constructed with steel superstructures. The relative flexibility of these bridges, especially in the transverse direction, may result in overstressing or even failure of components; particularly, the end-diaphragms that experience large deformations and may buckle or suffer brittle fracture during seismic excitations. Innovative techniques such as passive energy dissipation and semi-active devices are viable options to enhance the ductility and energy dissipation capacities of the diaphragms, thereby increasing the safety and reliability of steel bridges.
The objective of this research task is to develop experimentally validated methodologies for improving the seismic performance of bridges with steel superstructures, through the use of embedded energy dissipators and intelligent semi-active control devices in the end-diaphragms. The results will enable the development of guidelines for use in the design of new bridges and the retrofit of existing bridges using control devices to optimize structural performance and safety.
The scope of this task will include the development of a detailed numerical model for the scale model bridge that will be tested at the University of Nevada, Reno (UNR). This model will be designed to allow simulations with a variety of response control schemes. In addition, simplified models will be developed to closely capture the response of the bridge. The models will simulate the nonlinear response of the bridge (including material and geometrical nonlinearities) under dynamic loading and the model response will be verified against the experimental results. In the first year of this task, the effort will focus on investigating the performance of various passive energy dissipation devices for improving the seismic response of the bridge. Those devices can be included in either the bracing system or the connections of the end diaphragms to provide enhanced ductility and energy dissipation capacity. For that purpose, various devices including metallic yielding dampers, slotted bolted connections, friction devices, and fluid viscous dampers will be compared. The models will be used to identify which system will most effectively improve the performance of the bridge under moderate and severe earthquakes, including near-source ground motions. The bridge will be tested with the selected device(s) at UNR in a subsequent year for verification and implementation.
A second year of this task will address the use of intelligent semi-active devices in reducing the seismic response of the bridge. Semi-active systems that will be considered include variable damping (variable fluid orifice, variable friction, and magnetorheological dampers) and variable stiffness devices. Available control algorithms will be considered and new ones will be developed. Control algorithms that will be considered include linear quadratic regulator, sliding mode, bang-bang, and control. Of particular interest are nonlinear algorithms that take advantage of the nonlinear response of the control devices. To determine the best systems, this task will compare the seismic response of the modeled bridge with a variety of combinations of devices and control algorithms. Comparisons with passive control devices will also be conducted to assess the relative effectiveness of the intelligent systems. During the third year, experiments will be conducted on the UNR model bridge with the selected device(s) and algorithms. The experiments will be a collaboration effort between NIST and UNR.
Future years, if funded, will focus on conducting comparative studies between the analytical and experimental results for verification and model improvement, as well as the development of design procedures based on the results of the first two years.
Development of improved end diaphragm designs that include passive or semi-active control devices. Selection and placement of passive and semi-active control devices' configurations for optimum performance.
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