Reidar Bjorhovde

Development and use of high performance steel

Abstract Structural steel has been used in construction in the United States for more than 100 years, starting with the Eads Bridge in St. Louis (1867–1874). The material and its many products have undergone significant changes since the initial applications. Some of these were prompted by demands for higher strength and improved economies of construction, and many were caused by developments in joining techniques and fabrication. Increasingly complicated and demanding service and other environmental conditions have also been important. A brief review of some early steel developments is presented, but the major focus of the paper is today’s requirements for high performance steels, including the properties of tensile strength and stiffness, ductility, toughness, weldability and corrosion resistance.

Experimental study of single angle columns

Abstract The paper presents the results of an experimental investigation of the buckling response of single angle columns. Equal- and unequal-legged angles were used with a range of maximum principal slenderness ratios that aimed at determining elastic and inelastic failure characteristics, including flexural and flexural-torsional effects and the influence of the width-to-thickness ratios of the legs. Verifying previous theoretical calculations and being generally in good agreement with the results of other studies, where such were available, the findings emphasize the importance of the flexural-torsional buckling mode, especially in the inelastic range of behavior. Tentative design recommendations are made, but it is also noted that further research is needed to amplify the data. In particular, the influence of the width-to-thickness ratio of the angle legs needs to be examined systematically.

Limit states design considerations for gusset plates

Abstract In spite of the extensive use of gusset plates as connecting elements in a variety of structures over the years, current design criteria are essentially based on very limited research work, and primarily of elastic analytical background. For example, North American design practice uses the results of the elastic model studies of Whitmore, obtained through research that was completed in 1952. With these things in mind, the paper discusses the design considerations that must be made when designing for ultimate strength, specifically, utilizing the limit states design formulation. Thus, limit states design models are described for tension and compression applications of gusset plates, although it is noted that much more research is needed before the criteria for compression can be considered as complete. Of particular interest are the second-order deformation effects in gusset plates; these are recent findings in experimental studies. It is demonstrated how load application and direction as well as type and orientation of the boundary connections have a major influence on the strength and behavior of these plates. A final summary itemizes the design checks that should be made.

The strength of heavy columns

Abstract The paper presents the results of a study on the maximum strength and behavior of wide-flange steel columns of large cross-sectional dimensions. Thus, hot-rolled and welded built-up shapes of flange thickness up to 150 mm and web thickness up to 75 mm were examined, using a variety of steel grades and manufacturing methods. It was found that there is a clear correlation between the relative maximum strength and the flange thickness for heavy hot-rolled wide-flange shapes. Specifically, the capacity drops by as much as 10 to 15% as the flange thickness goes from 25 to about 75 mm. As the thickness increases further, the relative maximum strength goes up, and it regains its full value when the flange is 125 to 150 mm thick. The effect is a function of the slenderness ratio of the column; it is most pronounced in the intermediate range. Welded built-up shapes appear to be less heavily influenced by the flange thickness variation, especially for short and long members. However, the welded shape database was limited, and further studies need to be conducted to verify the findings for these shapes. The results are currently being evaluated for design code recommendations.

Behavior of composite frames during construction

Abstract Composite construction has been widely used for building structures over the past 25 years. Initially developed for beams and girders in buildings and bridges, composite elements now also include columns and shear walls, and are frequently utilized in high-rise structures, owing to their axial load capacity and stiffness. The last few years have seen the development of the complete composite frame, where the advantages of steel and concrete are combined to provide structural systems of great strength and stiffness. The complexities of the design and construction of these frames are legion, however; in particular because the designer must consider the construction method very carefully to ensure satisfactory performance. The paper discusses the unique design considerations that must be made, including the effects of construction sequence on the overall stability and strength, and makes recommendations for design procedures.