Investigators Develop New Design Methodology for Steel Truss Bridge Towers
MCEER investigators have developed a systematic design/retrofit procedure for steel truss bridges that allows controlled rocking and uplift at the base of bridge piers to protect the bridge tower from damage due to earthquakes. The procedure uses a capacity-based approach, and was validated by a series of shake table tests carried out at the University at Buffalo (UB).
The technique, which allows the bridge tower to rock in a controlled manner, has been implemented in some instances in the past, such as for the seismic retrofit of the north approach spans of the Lion’s Gate Bridge in Vancouver, British Columbia. However, to date, no systematic design procedure based on reliable test data has been available to engineers.
During the test program, a 20 ft. truss tower was subjected to ground motions simulating the 1994 Northridge, California earthquake. Testing was conducted both with and without passive energy dissipation devices, inserted at the pier base to control the dynamic rocking behavior. Tests were conducted with hysteretic dampers as well as with viscous dampers provided by Taylor Devices, Inc., a member of MCEER’s Strategic Partnerships Network. Results showed that satisfactory designs can be achieved both with and without the dampers, but the use of energy dissipation was effective in limiting the amplitude of uplift (reducing it by half in some of the examples tested) and in limiting the velocity of the impacting pier leg during the rocking motion.
The research was funded by the Federal Highway Administration as part of MCEER’s highway project and was carried out by Michel Bruneau, UB Professor of Civil, Structural and Environmental Engineering and MCEER Director, and Michael Pollino, a recent Ph.D. graduate of the UB Department of Civil, Structural and Environmental Engineering, currently employed at the Boston office of Simpson Gumpertz and Heger.
A technical report is in preparation and will be available in early 2008.