Advanced analysis and design of steel structures with tapered members

Abstract

Tapered members can make full use of materials with a high load-carrying capacity. The reduction in the structural self-weight can further facilitate the construction, maintenance and decrease the life-cycle costs. Today, the tapered members have been increasingly adopted in the practical structures due to their structural efficiency and low fabrication costs benefited from the extensive use of building information modelling (BIM) technology and automatic welding robots. Designers do not consider the tapered members primarily because the analysis of this kind of structures is cumbersome and unconvincing. The current analysis methods and stability checking equations based on the finite element and the linear-analysis methods are tedious and inaccurate. The analysis methods without considering the initial imperfections usually provide inaccurate deformations and internal forces, which lead to uncertain evaluation on the member performance. Moreover, most design equations are only suitable for simple tapered scenarios with idealized boundary conditions, such as the simply-supported web-tapered-I members. For the design of space structures, the conventional approaches are incapable to predict the critical members. Therefore, this research intends to propose a new practical method for the design of tapered members in line with the direct analysis method (DM). In this thesis, a comprehensive advanced analysis and design approach for structures with tapered members are developed. The beam-column elements with high efficiency for eight common section types are derived for the conventional analysis methods. The consistent mass matrices, equivalent nodal forces and eccentricity matrices for elastic static and dynamic analysis are derived. For DM, the general geometric imperfection shape, which can be used to simulate the worst initial configuration for both prismatic and tapered members, is proposed. An advanced tapered element incorporating the effects of the initial imperfections and the arbitrarily located internal hinge is developed. Further, a new efficient element allowing for shear deformation is proposed in the mixed-field form. Based on the numerical method proposed for DM, the study presents the section capacity evaluation equation and the buckling curves for tapered columns with different tapering ratios. The correction factors used to revise the prescriptive equations in the AISC360-16 are derived for checking the flexural buckling strength of tapered members. A batch of examples is used to illustrate the accuracy and efficiency of the proposed design methods. This work is essential for the practical design of steel structures with tapered sections.