ASTM A24542T refers to the “Tentative Specifications for Light Gauge Structural Quality Flat Hot-Rolled Carbon Steel,” a standard published by the american-society-for-testing-materials (ASTM).
In the context of the 1935-miami-dade-building-code, this specification was adopted to define the material requirements for cellular steel floors. Ordinance No. 3334 (1947) mandated that steel used in manufacturing steel floor units must meet the requirements of Grades A, B, or C of ASTM A24542T (p. 331). This ensured that the structural integrity of cellular-steel-floor-standards met specific quality benchmarks for hot-rolled carbon steel.