Iron frame

[5] With its high compression strength, the cast iron is well-suited for columns.

[3] Relative tensile weakness made the cast iron not the best choice for the beams and girders, this was compensated by making the bottom flange of an I-beam (the one experiencing the tension) much wider than the top, compressed, one and varying the beam profile to be wider at the middle, where the stress was higher.

[6] The first all-wrought iron roof was apparently installed in 1837 at the Euston railway station in London.

[7] Beams and girders were made of wrought iron with I-beam cross-section.

A less-known precursor to the modern steel frame construction, the four-storey Boat Store ("Shed 78", 1858–1860), has its rigid frame constructed also from cast iron columns and wrought iron girders.