Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 51 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Dynamic behaviour of damaged reinforced concrete beams and application of white noise analysis to crack detection</b>]]> Vibration monitoring is a useful and precise method for non-destructive evaluation of defective members. The fundamental concept underlying this method is that the dynamic properties and responses of the structure will change if any defect occurs. The aim of this paper is to investigate the responses of damaged reinforced concrete members to dynamic excitation and to identify the location of probable defects. A powerful multi-purpose finite element (FE) package, COSMOS/M, is used for the analysis of the damaged concrete cantilever beams studied in this paper. The mechanical and geometrical properties of all beams are the same, but the location and the depth of the cracks are changed in these members. The analysis process is performed in the frequency domain. Initially, a modal analysis is performed to determine and compare the natural frequencies and mode shapes of the various defective members. Each member is then excited by an individual vertical force, with the specifications of white noise located at the end of the member, and the responses are monitored at different locations along the member. These responses are used to investigate the dynamic properties of the defective members and to identify the crack location. <![CDATA[<b>Optimising structures using the principle of virtual work</b>]]> This paper presents a method for optimising structures with a given geometry and loading based on the principle of virtual work. The Virtual Work Optimisation Method, or VWOM, that was developed minimises the mass of the structure while meeting building code strength requirements, and flexibility (or deflection) criteria. The optimisation can be readily constrained by grouping together members with the same sectional properties. The VWOM automates most of the design process, obviating the requirement of experience and expertise in stiffening a structure. Three case studies were conducted using the VWOM: (i) the benchmark optimisation ten-member truss; (ii) a truss frame designed by professional engineers; and (iii) a 24-storey frame. The results of the VWOM were compared with published or available solutions. The VWOM produced structures that were 0,9 to 15,1% lighter than those produced by the methods used in the comparisons. If every member was allowed to have its own sectional properties, the VWOM found even lighter structures (by as much as 19,5%). The VWOM is less computationally expensive than the comparison methods, requiring two or three orders of magnitude fewer iterations to converge to the solution. <![CDATA[<b>Desiccation of soil by vegetation and potential interaction with buildings</b>: <b>a field study</b>]]> Desiccation of clay soil caused by vegetation - grass, bushes and trees - and its effects on the stability of slopes, buildings, roads and other structures has long been a topic of interest and concern to the geotechnical engineer. Several international symposia on the topic have been held during the past 60 years, and the literature on the subject is voluminous. A review of past studies of soil desiccation and its effects showed that, with few exceptions, investigations had been of a short-term nature and had not adequately considered the variable annual effects of atmospheric and hydrological causes of soil desiccation and rehydration. As a contribution to providing this longer-term information, it was decided to embark on an extended study of the effects of evapotranspiration by vegetation and atmospheric climate on the seasonal and year-to-year variation of soil water content. The study is now complete and this paper presents an overview of the investigation from 2000 to 2006, including the influence of annual weather variations on the desiccating effects of lines of trees and bushes, the potential effects of desiccation caused by single trees on adjacent buildings, and the portrayal of these effects by means of soil water content and storage profiles, and soil water balances.