how do you know it's reinforced concrete instead of steel encased in concrete?
because steel girders are not encased in concrete. except to protect them from impact. due to the dissimilar expansion and loading rates between the materials, concrete surrounding a steel beam would crack and fall off the steel. even if there were some form of pins to try and hold it on.
concrete is effective in compression, not tension. that's why there is steel rebar in the concrete, carrying the tension load. I doubt the concrete beams holding the coal bunker was built as a pre-stressed structural element on site. that requires controlled formwork to pre-tension the rebar. something normally done at the factory and shipped to the job site.
there is a large array of steel rebar running along the long axis of those beams, with crosswise ties to keep proper spacing during the pour. rebar is formed with a raised cross hatch pattern all over it to give the concrete something to grip to, and vice versa.
