building 40 ()
Columns made of cast iron were introduced in the 1770s, the first building with multiple storeys using cast iron for both columns and beams is the
Ditherington Flax Mill in
Shrewsbury (1797). Columns were joined usually at the floor level and sometimes bolted together, the longer beams were made of sections that were also kept together by bolts. At first, the stiffness of the frame was achieved through the use of
masonry that filled the openings in the frame, but since 1844, a
rigid frame was used that was stable by itself (former fire station at the
Portsmouth Dockyard). With its high compression strength, the cast iron is well-suited for columns. At first, the
cruciform profile was used, later displaced by the hollow round shape and
H-beams. 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. Cast iron was rapidly replaced in the beams by the wrought iron in the mid-19th century, the process had accelerated after the
Dee Bridge disaster of 1847. == Wrought iron ==