New design theory of second-order direct analysis for high-strength steel columns

Use of columns fabricated from high-strength steel (HSS) plates with design strength larger than 460 MPa is becoming popular in congested cities like New York, Hong Kong and Shanghai and so on. The column sizes using high strength material can be considerably reduced, so the usable floor area is increased. Also, load from structural weight at construction stage is reduced because of smaller member size. However, the stability consideration of slender columns is more crucial in design, because of their higher design strength relative to Young’s modulus of elasticity. Currently, the linearbased design method associated with the effective length assumptions is common for buckling checks of steel columns. When using this method, large numbers of member tests are required for generation of the buckling curves for different material grades of sections, and these tests are expensive and time-consuming resulting in an unfavourable condition for promotion of HSS columns in practice. To this, a new theory of secondorder direct analysis is introduced in this chapter for the design and buckling check of HSS columns with the separated considerations of geometric imperfection due to initial member crookedness and material imperfection from residual stress (RS). Therefore, only a limited number of small-scale and simple measurements of RS of the HSS sections are required for identifying the RS patterns and magnitude for input parameters of the analysis model. This chapter reviews the experimental investigations on the residual stress of HSS sections, and the buckling behaviours of HSS columns under compression. The modern design theory and the numerical procedure are discussed. Finally, several examples are provided to confirm the validity of the proposed analysis and design method.