In order to validate the principal assumptions inherent to plastic design of frames and continuous beams, it is necessary to predict the available rotation capacity at positions in the structure where plastic hinges are likely to form at collapse. The required rotation capacity is a function of the geometry of the structure and the loading and may be quantified within certain broad parameters. In order to predict to rotation capacity available at critical points in the structure, it is necessary to satisfy limit states criteria on a consistent basis. This paper deals with a proposed method of predicting the available rotation capacity and classifying members rather than sections. The available rotation capacity is predicted on the basis of two principal parameters and an interaction equation. The proposed prediction model is compared with experimental results.
The patterns of variation in total traffic with time of day, day of the week and hour of the year (in descending order) are will known as a result of numerous studies in this area. Very little is, however, known about the variation in heavy vehicle traffic over these periods. In this paper the total and heavy vehicle traffic patterns are compared for weekly and annual variation. Also, a method is developed according to which the percentage of heavy vehicles can be determined for any of the 1 000 highest hours of total traffic. This is especially useful for calculating the percentage of heavy vehicles in the design hour.
The paper describes a study carried out to investigate the use of South African condensed silica fume as a Portland cement replacement material in structural concrete. Aspects dealt with in the paper are fresh properties, strength development and the development of a mix design method. Results indicated a significant effect by condensed silica fume on all concrete properties. Concrete workability was found to reduce dramatically with increasing dosages of condensed silica fume. However, rates of workability decrease were found to be test-dependent. Reduced quantities of bleeding were recorded for concrete with increasing condensed silica fume replacement, and concrete strength development was greatly improved. A unique mix design method, capable of proportioning concrete with a range of condensed silica fume replacements for chosen values of 28-day strength and taking into account the water/binder ratio and dosage of condensed silica fume used, is proposed. Consideration is given to the practical implications of the work for concrete specifiers and producers.
Problems attributed to the bracing of timber roofs have necessitated a fresh look at the bracing criterion given in the timber design code, SABS 0163 (1994). The difference between bracing provided for stability of the overall structure and bracing that is used to reduce the effective length of compression members is discussed. The differences between bracing at discrete intervals and bracing by means of a continuous elastic diaphragm are shown. Revised design rules are proposed, which, if implemented, should solve the problems currently being experienced with timber roofs.