Replace Item 3 & 4 with the following and change Item 5 (Other Criteria) to "Item 4"

Superstructure Widening by Adding Column(s) and Substructure

Use the AASHTO/BDM seismic design criteria with appropriate R factors to design and detail the new columns and footing for the maximum required capacity.

            Analyze the widening and the existing structures as a combined unit.

            If the existing structures is supported by single column piers, and is located in SPC B or C (LRFD Seismic Zone 2, 3, or 4), the existing columns shall be retrofitted unless the existing column has adequate ductility to              meet current standards.

            If the existing structure is supported by multiple column piers, the need to retrofit the existing columns as part of the widening shall be determined as follows.

a. For existing bridges in SPC B or C (LRFD, Zone 2, 3, or 4) that are widened with additional columns and substructure, existing columns should be considered for retrofitting unless calculations or column details indicate that the existing columns have adequate ductility. Non-ductile existing columns will likely not be able to carry vertical load if they experience the inelastic deflection that a new (ductile) column can tolerate.

b. Only the columns should be retrofitted. Retrofitting the foundations supporting existing columns is generally too expensive to consider for a widening project. Experience in the past EQ in California has shown that bridges with columns (only) retrofitted have performed quite well.

d. Approval for retrofitting existing multiple columns piers is subject to available funding and approval of the Bridge Design Engineer.

Add the following to Item 4., Other Criteria

Care shall be taken when modifications are made near or on the existing bridge to isolate any added potential stiffening elements (such as traffic barrier against columns)

The relative stiffness of the new columns compared to the existing columns should be considered in the combined analysis. The typical column retrofit will be steel jacketing with grouted annular space (between the existing column and the steel jacket.

When strutted columns (horizontal strut between existing columns) are encountered, the strut should be removed and the existing columns analyzed for the new unbraced length and retrofitted, if necessary. Refer to WSDOT Research Report of Strutted Columns (nearing completion as of this date).