Doesn't work that way. The sea is far too deep. The crust of earth shift. Rogue waves tear solid steel apart. It is an impossible thing to anchor concrete pillars. Into the deep black water. The oil rigs, the deepest fixed ones go about 500 meters. That is nothing.
To build a bridge that long, you must stay on solid land.
They built a rail viaduct over rivers and paddies. China.
One hundred and sixty kilometers. To reach a thousand, you simply keep building across a wide, flat plain.
They would connect two major landlocked cities. Join Paris to Berlin. Pour thick concrete. Drive the heavy pylons into hard dirt, never the sea. The heavy steel tracks would then be laid.
But it's too expensive. Weak nations get ruined. Good men die in the mud.
The weight is held by earth. It is the master. The deep sea forgives nothing.