What was identified as the primary issue on the I-35W Bridge according to the provided notes?

What was identified as the primary issue on the I-35W Bridge according to the provided notes?

• A. Overloaded gusset plates
• B. T1 steel butt weld failure
• C. Impact damage
• D. Rivet hole filled with wellment started a crack

Answer: (A)

The key idea is how the joints in a truss bridge transfer all the forces. Gusset plates are the connections that tie multiple members together and carry the combined reactions from those members. If those plates don’t have enough strength or thickness for the actual loads, they become overloaded, yielding or cracking and undermining the load path through the structure. That failure at the plate level can cascade, causing the entire bridge section to lose support and collapse. The notes point to this plate capacity issue as the primary problem, not a single weld defect, external impact, or a rivet-hole crack. So the correct concept is that the gusset plates were overloaded.

The key idea is how the joints in a truss bridge transfer all the forces. Gusset plates are the connections that tie multiple members together and carry the combined reactions from those members. If those plates don’t have enough strength or thickness for the actual loads, they become overloaded, yielding or cracking and undermining the load path through the structure. That failure at the plate level can cascade, causing the entire bridge section to lose support and collapse.

The notes point to this plate capacity issue as the primary problem, not a single weld defect, external impact, or a rivet-hole crack. So the correct concept is that the gusset plates were overloaded.