Elon Musk indicated that the SpaceX Super Heavy Booster will use welded, internal, longitudinal hat stringers [to support its structure when unpressurized]. To the degree it may need hoop stiffness (probably not), combine with slosh baffles.
Elon provided a general description of the internal structure of the SpaceX Super Heavy Booster.
Below are pictures of what hat stringer supports look like in airplane and rocket structures. Stringers were used in the wing of the Space Shuttle.
There are several pictures from a presentation that was uploaded to slideshare called Skin Stringers in Aircraft from work for a Masters in Engineering. (by Attaullah Khan, Muhammad Subhan, Wajahat Ali)
In aircraft construction, a stringer is a thin strip of material to which the skin of the aircraft is fastened. In the fuselage, stringers are attached to formers (also called frames) and run in the longitudinal direction of the aircraft. They are primarily responsible for transferring the aerodynamic loads acting on the skin onto the frames and formers.
Elon was answering a question from the Everyday Astronaut.
How will the booster support its own (and Starship’s) weight when it’s unfueled? It won’t have a chest-plate of sweaty 310S like the Starship will, right? Will it need some kind of back bone or internal structure to remain structurally stable when unpressurized?
Welded, internal, longitudinal hat stringers. To the degree it may need hoop stiffness (prob not), combine with slosh baffles.
— Elon Musk (@elonmusk) February 7, 2019
Slosh Baffles are Ribs in Fuel Tanks