Three routes (I-980, I-880, and I-24) come together in Oakland, California as 'The Stack.' During the Loma Prieta Earthquake this interchange, which looks like a big 'X' from the air, had similar damage to the four ends: crumbled interior diaphragms from too many cable restrainers holding the superstructures together at the hinges.
The concrete barrier rail had to be isolated from the columns to prevent a smaller effective column length and subsequently larger shear forces. I wonder if those knee joints have to carry the column plastic moment? Probably the columns are pinned to the bent caps, which became standard policy after Loma Prieta.
We'll continue looking at urban interchanges over the next week to see if we can learn anything important through the process.
California Bridges - The Oakland Stack by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.