An arched passage contains industrial equipment used for hydroelectric turbines and generators. This passage is underground below the main turbine hall.

Thrust Deck Support Nov 23, 2006

We're on the thrust deck, one floor beneath the Power House.

The large vertical pipe you see is the shaft that is being spun by the turbine blades below. This is connected above to the rotor inside the alternator, which would be spinning around 250 RPM. All that equipment above—the alternator—weighs about 90 tons.1 The bell-shaped item surrounding the pipe is the thrust bearing.

The other thing to notice here is the stone arch. That massive arch is supporting those 90 tons of rotating equipment. It takes that load and distributes it out to the sides. There is one of these for each of the 11 generators on the floor above in the power house.

Archival photo 1904 showing construction of the stone arch below ground that supports the weight of the alternators in the Power House. The stone arch is in mid-construction, and supported by a timber frame below to provide the arch shape.
Thrust deck under construction: This archival photo from 1904 shows one of the thrust deck stone arches being built. The timber supports below provide a frame while the arch is built up, before the key stone can be set in place (to allow the arch to be self-supporting).

Thrust bearings absorb the axial load from a rotating shaft. If you use the example of a drill, this is what takes the load from you pressing against the drill. The alternators are large spinning pieces (like the drill bit), and the housing of copper and steel weighing down on the floor is the same as the force of you pressing on the drill. Again, 90 tons of it.

  1. Ball, N. R. (2005). The Canadian Niagara Power Company Story. Erin, Ont.: Boston Mills Press in association with FortisOntario.