THEORY AND METHODS FOR EVALUATION OF …（评价理论和方法u2026）.pdf

III THEORY AND METHODS FOR EVALUATION OF ELASTIC CRITICAL BUCKLING LOAD 3.1 Introduction The codes of practice tackle the stability of steel structures by determining the effective buckling length of the structural members. Therefore, the problem of stability is very important. Underestimation of this effect may lead to disastrous results or unj ustified factors of safety. Consequently, the Steel Construction Institute (SCI) suggested the previous approach for estimating the effective length factor presented BS 449: part 2: (1969) should be modified by recommending three methods for evaluating this factor. The first, termed extended simple design, also described in the previous chapter, starts by evaluating the relative stiffness coefficients of the surrounding columns and beams of the column under consideration. Then, using these stiffnesses, the effective length factor can be estimated from charts based on the study carried out by Wood (1974a). The second method, termed the amplified sway method, states that the bending moments due to horizontal loading should be amplified by a factor, as discussed in chapter 2. The third, a more accurate method, is to determine the elastic critical load factor λf from cr Theory and Methods f or Evaluation of Elastic Critical Buckling Load 73 which the effective length ratios of individual members may be determined. The critical load factor λf is defined as the ratio by which each of the factored loads would have to cr be proportionally increased to cause elastic instability. If this parameter is known, the axial load in every compression member Pi at instability is known as