Stepped spillways and chutes provide an effective means of dissipating energy in the release of flood water from impoundments. Their performance depends on whether flow is of the nappe or skimming type, and on the step geometry. Prediction of the flow type and energy dissipation performance is based on experimental results from model and prototype tests. This paper presents the results of an experimental investigation of the transition between nappe and skimming flow and energy dissipation for a wide range of flow conditions and step geometries. Previously proposed methods for predicting the transition conditions and nappe flow energy dissipation are shown to be inadequate for some conditions, and provisional new formulations are presented.
It is increasingly important in plastic analysis of structures to assess the required plastic hinge rotations implicit in ensuring a ductile mode of failure. The displacements of a frame at the onset of plastic collapse also provide a useful limit in second-order, inelastic, stability analysis. A method is descriptionbed for systematically applying the principle of virtual work to the calculation of notional plastic hinge rotations and deflections during the development of a collapse mechanism. Approaches to combining independent mechanisms of collapse, assessing the first and last hinges to form and calculating indeterminate moments in partial collapse mechanisms are also descriptionbed based on flexibility-based analysis.
Bentonite is becoming increasingly popular in South Africa in its application as an impervious liner either pure or mixed with soil. The local deposits of bentonite are of a quality equal to well-known international products. This paper summarizes the results of a laboratory investigation of selected engineering properties of the South African bentonites, including swell and permeability, and provides a deeper understanding of the chemical and geotechnical properties of bentonite.
Criteria that govern the failure mechanisms, variability and strength of rubble masonry concrete (RMC) are explored with reference to the behaviour of analogous particulate composites. Contiguous particle interaction and the potential for anisotropy are noted as two distinguishing characteristics that may account for much of this material's unique behaviour. Failure appeared to be initiated by deboning of the stone-mortar interface parallel to the principal stress long before the specimens attained their maximum stress. Variability of mechanical properties was found to be a function of anisotropy and heterogeneity.
The highly dynamic South African coastal zone is subject to a complex interaction of physical processes such as waves, winds, tides and sediment transport. Responsible coastal engineering design and environmental assessments require an adequate quantification of such processes. Mathematical modelling is increasingly being recognized as a powerful tool for quantifying coastal processes. This paper outlined a number of such models and discussed practical application to three case studies.