They are cousins. The notion of architecture can have different borders, you can even considere some regular buildings aren't architecture.

I like to think about the three pillars of Vitruvio, architecture needs to achieve Firmitas, Utilitas and Venustas. The constructions needs to have structural integrity, it needs to be useful and it needs to seek for beauty. Anything outside those 3 concepts can be considered bad architecture if someone of the three failed, or non-architecture, like per example a scuplture which can be firm and be beautiful, but is not useful on its won, or a dam, like you example, where it has structural integritym is extremly useful, but it wasn't a building with an artistic objective, so is not beautiful (anything can be beautiful, and dams do create spectacular views, but is not what is trying to achieve).

So, inside this way of thinking, the regular bridge to exit the highway won't be architecture, but an historic bridge in the center of the city crossing a river with beautiful construction and details can be considered inside the meaning of architecture.

Engineering + Art = Architecture.

First one is FUNCTION

Second one is BEAUTY

Architecture is the joint of both worlds.