The state-of-the-art of progress of structural engineering over the last 50 years is examined in three areas: (1) The spatial idealization of structural elements in the form of kinematical assumptions; (2) The constitutive idealization of materials in the form of generalized stresses and generalized strains relations; and (3) The computational implications of solution strategy in the form of closed form, approximate, and numerical procedures on the structural level.

Abstract:As an alternative to the prescriptive design based on individual member capacity check, performancebased design by direct simulation of structural system behaviour under ultimate loads is developed, both in concept and in computer implementation. The method has been proposed as an alternative design against the conventional prescriptive design using equations in codes with somewhat unreliable assumptions. This paper discusses the implementation of the method to ultimate design of a benchmark plane frame and a stadium constructed for the East Asian Game 2005 in Macau. The results show the advantages of the method in efficiency, economy and safety. The approach represents a new design practice for engineers in the 21 st century.This practical advanced analysis will result in a more uniform reliability and safety for the designed frames such that redundant members will not be over-designed and key members under-designed. Research along the line of more accurate simulation should be carried out in future rather than refining the prescriptive member-based design formulae. Although general purpose finite element packages developed decades ago are, in principle, able to design steel structures by non-linear analysis using beam-column and shell elements, their daily application to civil engineering structures is impractical as many design code requirements cannot be simulated directly and automatically.Keywords: Second-order analysis, advanced analysis, P-Δ−δ effects, elastic analysis, plastic analysis and design. INTRODUCTIONIn the conventional structural design, the effective length and bending moment are assumed and determined and then used with the prescriptive design rules. The error connected with the assumption of effective length factor (L e /L) can be very large and the method is limited to types of structures such as those with elastic critical load factor greater than 3 for Eurocode-3 [1], 4 in BS5950 [2] and 5 in AS4100 [3].Buckling is an interactive member and system behaviour that the buckling strength of a member relies on the member and system stiffness. For example, a wind-cross in a portal frame in Figure 1 assists the whole structure as well as every member against buckling. This characteristic is different from stress computation by a linear analysis where the stress in a column is not much affected by the stress of another member far from this column and the St. Venant principle holds.Elastic and elastic-plastic analysis of steel frames have been carried out extensively by many researchers. Chen and his co-workers [4,5]