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An analytical procedure, which retains the influence of finite deflections, is developed herein for the dynamic behaviour of rectangular shaped rigid-plastic beams. In the general formulation of the problem deformation is assumed to proceed under two distinct mechanisms depending on the extent to which the value of the peak pressure exceeds the static collapse pressure of the beam. These mechanisms are described by kinernatically admissible velocity fields that satisfy the appropriate continuity conditions. The governing equations of motion are derived from a variational statement consisting of the principle of virtual work and D'Alembert's principle. The conventional parabolic yield surface (which describes the coupling action between axial forces and bending moments at yield) and its associated flow rule are adopted to describe the plastic behaviour of the beam material. The kinematic small but finite deflection analysis, in which the membrane forces and bending moments interact, generally leads to basic equations which are of nonlinear character. These resulting equations are solved analytically and closed form expressions are developed for the prediction of maximum permanent deformation of the beam. A dynamic membrane analysis is carried out in those cases when the input energy is sufficiently high that the beam undergoes moderately large deformation (i.e. deflections of the order of beam thickness). Finally the dependence of the permanent deflection on the applied pressure and impulse is obtained for a family of rectangular pulses. This relationship is represented by an isoresponse curve in a form convenient for direct engineering use. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Introduction Humans have several different types of hair, classified into eight different groups, of which types VII and VIII predominate in South Africa. The scalp with its abundance of hair is often used as a preferential donor site for small burns. Major reasons cited are that the donor site is hidden from view (covered by hair), rapidly epithelializes with minimal scarring and provides a relatively large surface area. The author postulates that the type of hair will have an influence on the healing of scalp donor sites, complications and aesthetic outcome. Contrary to international consensus, the Red Cross War Memorial Children’s Hospital (RCWMCH) experience indicated that the use of the scalp as donor area is not ideal due to the frequent complications seen amongst paediatric patients e.g. visible scars, recurrent folliculitis, patchy alopecia, hypertrophic scarring and areas of de- and hyperpigmentation. Objective This study reviewed the complications encountered with the use of the scalp as primary donor area in children of mostly black African origin (type VI-VIII hair). Methodology A retrospective folder review of patients admitted to RCWMCH between 2003 and 2015 with major burns (>30% total body surface area) was conducted. A total of 179 patient folders were reviewed. Only children (n=25) with unburned scalp donor areas were included in this study. Both short- long-term complications were identified. The patient age range was six months - 12 years, while the mean patient follow-up period was 580 days and mean burn TBSA was 44.92% (range 4 – 85%). Results Patient demographics: black African 60% descent (hair types VI-VIII), 32% mixed race (hair types III-V) and 4% Caucasian (hair types II-III). In the group of black African children 60% had short-term and 46.7% long-term complications, whereas in the mixed race children 37.5% had short-term and 25% long-term complications. No complications were encountered in the Caucasian group. Eleven (48%) of patients in total had short-term complications (88.9% folliculitis, 22.2% delayed healing) and seven (28%) had long-term complications (57,1% non-healing wounds, 42.8% recurrent folliculitis, 57.1% alopecia, 42.9% depigmented scars, 28.6% visible scars, 28.6% hypertrophic scars). The first procurement in 11 children resulted in a 91% complication rate (54.5% short-term and 36.4% long-term). Ten children had two procurements resulting in an 80% complication rate (40% short-term and 40% long-term complications). In four children with three scalp procurements an acute 25% complication rate, with no subsequent long-term complications, was encountered. Discussion Hair type has an influence on outcome and donor sites should be carefully selected. Hair types VI-VIII has a higher propensity for complications and these usually follow the first procurement procedure. Complications did not increase with multiple procurements. Significant complications with long-term sequelae are not uncommon when the scalp is used as donor site and these complications are difficult to treat. Although the sample size is small, it does reflect a significant complication rate. Conclusion Contrary to international consensus, the use of the scalp as donor site in South African children with hair types VI-VIII with large burns should not be the preferential site and should only be used as a last resort.