The two are not equivalent. A patent application is something a patent attorney will make hundreds of in a career. A bridge that can survive the big one is something a team of engineers would do a few times in their career (treating it as a unit). There are multiple orders of magnitude in difference between the two.

I can tell you from witnessed experience that a "car engineer" can custom design a house, do most of the code-related work himself, and pass all relevant inspections on the first try (with flying colors and compliments from the inspector), which seems much closer in scope.

Seems to me he could almost certainly design a bridge with resistance to failure due to an earthquake. The material and principles involved in designing earthquake resistant structures are well understood and publicly available. The primary constraints on such structures are the cost and time to build them.

As for surviving "the big one"... it depends on how big? I'm not sure humanity in general knows how to build a bridge that could survive a dozen meters of shift between its piers. But that is a possibility in the largest conceivable earthquakes.

Don't know about the bridge but he can definitely build the next Facebook.

Because of the internet - information is much more readily available. Nowadays a layman can just search all the information and perform similarly.

Maybe? A wooden pedestrian bridge with seismic shift absorbers like pagodas have seems feasible for a 1-man job, given enough time.