Modified Steel-Jacketed Columns for Combined Blast and Seismic Retrofit of Existing Bridge Columns

Steel jacketing has been used extensively in the United States to retrofit seismically deficient bridge columns. This procedure, which consists of encasing a RC column in a steel jacket, is effective in providing a ductile seismic response but does not enhance the blast resistance of the column. This is because a gap is typically left at the top and bottom of the jacket to prevent increased flexural strength, such as to avoid undesirable overload of the footing or cap beam. Blast tests have demonstrated that direct shear failure can develop at these gap locations. A modification to steel-jacketed columns is proposed here to provide an added blast resistance. It consists of structural steel collars placed around the gaps and tied to the adjacent elements with postinstalled anchors. Blast tests were conducted to investigate the effectiveness of this simple proposed detail. Experimental results indicated that the concept was effective in preventing direct shear failure. Severe blast load demands were applied to investigate the behavior of the retrofitted column under extreme ductility demands. All specimens exhibited satisfactory ductile behavior, except one, which uncharacteristically failed due to fracture of the tube's vertical weld seam.