Seismic Connection Force for SPC A Bridges

[TTK]

Section 5.2 of AASHTO Division I-A requires the fixed line of bearings to resist a seismic force equal to 20% of the TOTAL superstructure weight not just the fixed bearing reactions.

For long multispan bridges this design force becomes extremely large and creates problems in the fixed bearing designs.

The same bridge designed in an SPC B zone would have much lower design forces since the actual acceleration coefficient could be used instead of the more stringent 20% criteria.

Has anyone else run into this problem and if so, how did you accomodate this large force?

 

[bridgebuster]

You could use two lines of fixed bearings. Or, discuss using SPC B criteria with your client.

The 20% rule is a quick, down and dirty method. In screening bridges for seismic vulnerability, I've used 20% times dead load as a quick check of anchor rod capacity.