Advanced Analysis as a New Dimension for Structural Steel Design

Abstract

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]

Equivalent bow imperfections for use in design by second order inelastic analysis

“…Hence, both safer, more consistent and more efficient design can result from design by advanced inelastic analysis with imperfections or GMNIA. With improvements in computational power and software, design by GMNIA is becoming more widespread in practice and is receiving a growing level of attention in research [8][9][10][11][12][13][14]. Suitable equivalent bow imperfections for use in design by advanced inelastic analysis are therefore urgently needed.…”

Equivalent bow imperfections for design by second order inelastic analysis

“…Osgood formulation [16,17] , as given by Eqs. ( 7) and (8), where ε and σ are the strain and stress, respectively, fy is the yield (0.2% proof) stress, defined by Eq. ( 9), ε0.2 is the total strain at the 0.2% proof stress, equal to 0.002 + fy/E, εu is the ultimate strain, and n and m are the strain hardening exponents.…”

“…Hence, both safer, more consistent and more efficient design can result from design by advanced inelastic analysis with imperfections or GMNIA. With improvements in computational power and software, design by GMNIA is becoming more widespread in practice and is receiving a growing level of attention in research [7][8][9][10][11]. Suitable equivalent bow imperfections for use in design by advanced inelastic analysis are therefore urgently needed.…”