Practical advanced analysis for steel frame design

This dissertation presents three practical advanced analysis methods for a two-dimensional steel frame design: (1) an explicit imperfection modeling methods; (2) an equivalent notional load method; and (3) a further reduced tangent modulus method. The methods can be used to assess realistically both strength and behavior of a structural system and its individual members in a direct manner. As a result, the methods can be used for design without tedious separate member capacity checks, including the calculations of K-factor. Key factors influencing steel frame behavior are described including: material, geometric, and connection nonlinearity, and simple procedures to enable designers to assess this behavior are provided. The procedures incorporate the refined plastic-hinge concept for spread of plasticity together with practical modeling for geometric imperfections. The magnitudes of geometric imperfections for braced and unbraced frames are proposed. The strengths predicted by the proposed procedures are compared well with those predicted by the exact plastic-zone analysis as well as by the conventional LRFD procedure. The displacement predictions are also compared well with the plastic-zone solutions. Analysis and design principles in using the proposed methods are given in detail, and comparative case studies are made to compare the practical advanced analysis with the LRFD design procedures. The case studies cover various braced, unbraced, and semi-rigid frames. Member sizes determined by the proposed methods are compared with those determined by the LRFD method, and a good agreement is generally observed. The proposed methods have been developed and refined to achieve both simplicity in use and, as far as possible, a realistic representation of actual behavior and strength of members as defined by the LRFD member capacity formulas. It is concluded that the proposed procedures are suitable for adoption in practice