Nope! They are completely solid.

How does it not move?

Hmm, not sure! The design looks very similar; it would be difficult to tell without being in the field.

We also built a similar staircase, using an I beam, and could not eliminate the movement.. We had to have the steel fabricator fill in a good part of the "I" to make it steady. The design looks gorgeous, but works better with a solid beam. I wonder if CG&S has some of their treads mounted to the wall- that makes them more steady. But on the runs that are floating, we found that it is impossible to avoid the movement.

i see your drawings of the stair design but there are no dimensions for the two C channels or the T shaped tread support. would you be able to share that information? do you have any additional drawings---side view?

I'm afraid that's about as detailed as we can get.

CG&S how did you get the color on the beam? Is it applied as a stain?

It was a solution designed to create a patina.

Unfortunately I was not able to trace down the exact patina solution used. I do know that it was applied with a cloth and buffed to achieve a nuanced, textured look.

I just installed similar design for an outdoor staircase. We have precast treads installed on top of treads steel plate. Each precast is around 110lb and it's vibrating when i tried walking on it. Any suggestion to avoid this vibration ?

someone suggested to anchor few of the concrete treads to the wall against it. I am worried it will spoil the clean look but safely is very important

Did you check the design with a structural engineer? They could help ensure that your stair has the right properties.