My guess is it was due to substandard materials that were tested beyond their capacity, lead to load failure and collapse.
A high quality bridge should have been able to withstand the stress test and perform to rated limits and beyond.
I don’t think it was an accident; it was a feature.
The bridge’s superstructure was something Verrastro said he’s not seen in 42 years of designing bridges. Rather than using steel trusses, it employed heavier concrete trusses. The bridge also had a concrete roof, adding even more weight.
“This was a very long span and then they used very heavy material,” he said. “The majority of pedestrian bridges are steel.” Steel bridges are about one-tenth the weight of concrete, he said.