Splices of column longitudinal reinforcement are not allowed when the required length of longitudinal reinforcement is less than the conventional mill length of (typically 60-feet). Splicing of longitudinal reinforcement shall be outside the plastic hinge regions. But in SDC A, splices need only be located a minimum of 1.5 times the column diameter from the top and bottom of the column. The bridge plans shall clearly identify the limits of the permissible splice zone.
For bridges in SDC’s A and B, no lap splices shall be used for #14 or #18 bars. Either lap or mechanical splices may be used for #11 bars and smaller. Lap splices shall be detailed as Class B splices. The smaller bars in the splice determine the length of lap splice required. When space is limited, #11 bars and smaller can use welded splices, an approved mechanical butt splice, or the upper bars can be bent inward (deformed by double bending) to lie inside and parallel to the lower bars. The spacing of the transverse reinforcement over the length of a lap splice shall not exceed 4-inches or one-quarter of the minimum member dimension.
For bridge in SDC’s C and D, bars shall be spliced using mechanical splices meeting the requirements of Section 6-02.3(24)F. Splices shall be staggered. The distance between centers of splices of adjacent bars shall be greater than the maximum of 20 bar diameters or 24-inches.
Development of longitudinal reinforcement shall be in accordance with the AASHTO Seismic Section 8.8.4 and 8.8.8 requirements for SDCs C and D. Column longitudinal reinforcement shall be extended into crossbeams as close as practically possible to the opposite face of the crossbeam (below the bridge deck reinforcement).
Headed bars may be used for longitudinal reinforcement at the bottom of columns. The head shall be placed at least 3-inches below the footing bottom mat reinforcement. This may require the footing to be locally thickened in the region of the column to provide cover for the bottom of the headed bars.
Columns in SDCs A and B may use spirals, circular hoops, or rectangular hoops and crossties. Spirals are the preferred confinement reinforcement and shall be used whenever a #6 spiral is sufficient to satisfy demands. When demands require reinforcement bars greater than #6, circular hoops of #7 through #9 may be used. Bundled spirals shall not be used for columns or shafts. Also, mixing of spirals and hoops within the same column is not permitted by the AASHTO Seismic Specifications. Figure 7.4.5-1 and 7.4.5-2 show transverse reinforcement details for rectangular columns in high and low seismic zones, respectively.
Columns in SDCs C and D shall use circular hoop reinforcement where possible, although rectangular hoops with ties may be used when large, odd shaped column sections are required.
The revised BDM Section 7.4 and Figure 7.4.3-1 & 2 are attached FYI.
This memorandum revises WSDOT column reinforcement in accordance with AASHTO LRFD SGS requirements, and in accordance with knowledge acquired from the January 2014 NHI Seismic Training course in Washington.