Seismic Vulnerability of Strutted-Column Bridge Bents

Strutted-column bents represent a type of reinforced concrete bridge substructure found in some bridges built before the early 1970's. The bents were designed using steel detailing and confinement that is inappropriate for ductile behavior. These bents consist of two or more columns that are connected by horizontal beams/struts, at some location along the clear heights of the columns. The presence of the struts in these bents causes an increase in the number of locations that inelastic demands can occur relative to the number found in typical bents. These features coupled with the poor detailing and confinement cause uncertainty about the seismic performance of the strutted-column bents. The seismic vulnerability of strutted-column bents was assessed by: 1.) determining the characteristics and the construction details of the bents in an inventory of bridges with strutted-column bents, 2.) evaluating the bents to determine anticipated inelastic demands that they might experience and their potential to meet these demands, and by 3.) experimentally testing two subassemblages that were representative of the beam-column joint regions of those bents that were determined to be the most seismically vulnerable. The subassemblages exhibited poor hysteretic behavior after they attained their respective yield displacements because of the deterioration of strut bar anchorage in their B-C joints. The information that was obtained from the three phases of work was used to appraise the seismic performance potential of the bents and bridges. The bents and bridges should perform satisfactorily if the displacement ductility demands in the B-C joint regions of the bents, µ, are less than four. Large values of µ could jeopardize the performance of the bents, and hence the performance of the bridges as well.


Publication Date: 
Friday, December 1, 1995
Publication Number: 
WA-RD 361.1
Last modified: 
10/12/2016 - 15:42
Glen J. Pappas, M. Lee Marsh.
Washington State Transportation Center (TRAC)
Number of Pages: 
Beams, Bents, Bridge substructures, Columns, Earthquake resistant design, Hysteresis, Inelastic stress, Joints (Engineering), Reinforced concrete bridges, Seismicity, Struts.