2.1 Introduction

Steel has been used as a construction material for civil engineering systems since the late 19th century. Prior to about 1890, cast and wrought iron components were used as columns and other elements in some civil engineering structures, but these structural elements generally had variable resistance, somewhat unpredictable failures, and limited ductility when compared to modern steel structures. During the 1890s, cast and wrought iron columns disappeared from common usage, and structural steel became the construction material of choice. This occurred because of improvements in the Bessemer process that permitted economical production of large quantities of steel required for building and bridge construction. Structural steel provided high strength with great ductility and consistent material behavior. These properties resulted in increased usage of steel in construction, but initial development of these steel structures followed construction practices employed with cast iron and wrought iron elements. Standard codes and specifications were not available until the 1920s (AISC 1928, ICBO 1927, AASHO 1931), and so the early structures were designed by standard practice and observations of the performance of past construction.

Experienced structural engineers designed buildings and bridges based upon simple calculations and nominal stress levels that had evolved from cast and wrought iron elements (Schneider 1905). The cost of structural steel was relatively high, while the cost of labor was relatively low, and so steel was produced as plate, bars and angles, and most structural elements were built-up...