Local buckling of the flanges and webs of I-sections are two of the most significant factors causing strain-weakening behaviour of plastically-designed steel structures. In the new South African code for steel design, SABS 0162:1984, the provisions for web buckling in particular appear to be over-conservative. The background theory to these requirements Is discussed and a new theoretical model proposed. The requirements of the code and the theoretical predictions are compared to the results of a series of tests in which the negative Influence of coincident axial force is apparent.
Study of 17-year old concrete by means of conventional petrographic thin sections has shown that milled granulated blastfurnace slag particles in the concrete are not characterized by advanced hydration or reaction effects. In carbonated concrete the slag particles are as susceptible to carbonate replacement as are other concrete constituents.
The prediction of the elastic modulus of concrete for design is complicated by the variety of factors affecting this parameter. The influences of aggregate stiffness and concrete strength are incorporated in a new design approach which is being included in the new BS 0000 (originally CP 110). The application of this approach to South African conditions was discussed in the paper with specific reference to local aggregates and cements. Aggregates were grouped according to their elastic properties so that designers could make better estimates of concrete modulus than might have previously been possible. The ideal approach to elastic modulus prediction by means of the concept of two-phase models was also introduced.