Brief History of Composite Steel Construction
In multi-story buildings, the framing system is a load-bearing structure giving the building stability and structural integrity. Typically, the framing system of a tall building combines stacked vertical columns with interconnected horizontal beams. Generally, the vertical columns and horizontal beams are fabricated from steel, precast concrete, or formed-in-place concrete. The horizontal beams usually support flooring sections that are also made of steel, precast concrete, formed-in-place concrete, or metal. The three most common methods of erecting framing systems are: 1) pouring concrete in place using forms to produce vertical columns, horizontal beams and floor sections; 2) assembling precast concrete columns, beams and floor sections, and; 3) assembling steel columns and beams with steel or concrete floor sections. None of these framing systems offer a structure that is highly rigid and fire resistant while at the same time being easy to assemble.
Tall buildings would be impossible without advances in technology. The composite steel frame skeleton was nothing short of a structural revolution when it was developed in Chicago in the late nineteenth century, and it has been evolving ever since. Early tall buildings constructed with cast-iron framing were susceptible to fire and it was discovered that encasing the iron in concrete increased the material’s resistance to fire. Composite beams are structural members composed of steel and concrete joined together to act as a single unit. An example is a composite beam with a steel flange (I or W shape) attached to a concrete floor slab. There are two primary advantages: the system that results from joining the two materials is stronger, and composite action maximizes the properties of each material. The compressive strength of the concrete combined with the tensile strength of the steel yields a significantly stronger system. Initially, iron and/or steel frames replaced conventional load-bearing masonry walls to minimize the depth and width of structural members, allowing larger openings in the facades of buildings. The outer skin or curtain wall - now a non-structural element - could be thinner and filled with glass while the iron/steel skeletons were clad in materials such as terra cotta or brick. The benefits of the new construction method included reduced wall thickness, increased valuable floor space, allowed more daylight to reach into the building’s interior, and reduced weight, all of which allowed substantial increases in height. Structural steel has led the market for framing systems for commercial building construction for the past 50 years.