ICE - Institution of Civil Engineers - Virtual Library

Sometimes it is difficult to measure the deflections of structure directly when investigating its behaviour. Thisis particularly true when the measurements are to be made on a structure in service. In such cases it may be much easier to measure the strains that develop in the structure under load and to infer the deflections of the structure from these measurements. The analytical procedures for doing this are given in the paper: they are a relatively straightforward extension of well-known structural theory, but they do not seem to have been published before. In this paper, attention is focused on two-dimensional beams and frames. Two methods for calculating the deflections are described: method 1 is a simplified, version which is effective for a particular class of beam/frame, whereas method 2 can be applied to any frame. The results obtained also serve as a check on the accuracy of the strain measurements, and on whether the structure is behaving as expected. The proposed methods are applied to problems for which the strains are known, and it is shown that both methods predict the exact deflected shape of thestructure. The effect of errors in the strain measurements is also considered. The way the procedure could be used in a real situation is considered in the final example. The extension of method 2 to three-dimensional frames is straightforward. It is believed that the proposed methods would be useful both to research workers and to engineers involved in structural assessment.

This paper presents a three-dimensional model of a helical two-stage gear system. Excitation is induced by periodic variation of the mesh stiffness. This case describes the real working of the gearing. The mesh phasing variation is related to the number of teeth and also to the location of the gears. First, dynamic response is calculated using Newmark's step-by-step time integration method. The numerical results are presented in both the frequency and time domains. The dynamic behaviour of a defect-free gear system and a defective one are compared in both the time domain and frequency domain. Two types of defect are considered: a cracked tooth and misalignment. The cracked tooth produces an amplitude modulation with the mesh frequency and its first harmonics on the dynamic response. An amplitude modulation also occurs when a misalignment is introduced. The Wigner–Ville distribution method is used to show the dynamic behaviour in the joint time–frequency domain and to localise the cracked teeth.

Details are given in this paper of the development of a numerical model for describing the bacterial transport processes in estuarine and coastal waters. The transport of enteric bacteria is influenced by many physical, chemical and biological factors, including both the suspended and bed sediments. In recent years, an increasing number of studies have shown that generally the sediments contain much higher bacterial population levels than previously assumed. The aim of this study has been to develop a numerical modelling tool for predicting the sediment-linked bacterial concentration levels in coastal and estuarine waters. This paper outlines the theoretical background of an enteric bacterial water quality numerical model. A conceptual model has been established for representing the transport of bacteria due to sediment movement, including deposition and suspension. Details are given of the solute and mass transport equations used to simulate the flow and transport of suspended sediments and enteric bacterial indicators. The enteric bacteria transport equation includes enhanced source and sink terms to represent bacterial kinetic transformation and disappearance or reappearance due to sediment deposition or resuspension. The model has been applied to the turbid water environment in the Bristol Channel and Severn estuary, UK, with initial results from the modelling study being presented.

In this paper an extended finite-element method (X-FEM) that is fully compatible with standard FE program has been formulated based on a virtual node technique. A cohesive crack model that is appropriate for concrete fracture under mixed-mode loading has been integrated into the formulation. The proposed method was implemented into a commercial FE program as a user subroutine, and two benchmark experimental tests were successfully modelled. The numerical robustness and predictive power of the proposed method have been demonstrated by its excellent predictions on arbitrary crack evolution and the associated load–displacement curves. Detailed numerical investigation of the crack wake shielding effects on the fracture loading curves showed that: (a) crack wake shear shielding has little effect on the peak fracture load and its immediate neighbouring softening phase; (b) the initial shear cohesive stiffness has a significant influence on the descending slope of the softening part of the load–CMSD curve; and (c) the shear cohesive strength appears to make the softening phase more stable and to delay the abrupt fracture point.