(i) In long bridges, choosing an abutment pier as the fixed pier can be advantageous when dealing with significant longitudinal earthquake loads. Since fixed piers absorb these forces, they tend to be large and bulky. However, abutments, being typically shorter, can accommodate this size increase while minimizing the induced bending moment due to their lower height. This design choice can also enhance the bridge’s aesthetics by integrating the substantial pier into the abutment structure.
(ii) Designating the central pier as fixed allows the bridge deck to move from that point towards the ends. Conversely, fixing the abutment necessitates greater movement allowances in each bearing to accommodate temperature variations and shrinkage. This leads to larger movement joints. By selecting the central pier as fixed, the required movement per bearing is reduced, resulting in smaller, more efficient joint designs.