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The manufacturing process of cold-formed thin-walled steel columns induces cold work in them and significantly affects their behaviour. This effect has traditionally been assessed using idealised residual stress distributions based on limited laboratory measurements in conjunction with the specification of different mechanical properties for the flat portions and the corner regions. This conventional approach is highly empirical and often does not accurately reflect the effect of cold work on column behaviour. This paper presents an advanced numerical approach for modelling the full-range structural behaviour of press-braked thin-walled steel columns, in which the effect of cold work is accurately and explicitly represented. In the proposed approach, the amount of cold work is quantified using residual stresses and the equivalent plastic strains predicted by a closed-form analytical solution for the cold-forming process and these analytical predictions are directly included in a finite element model for nonlinear buckling analysis. Using results obtained from this advanced numerical column model, the effect of cold work on column behaviour is examined for both carbon and stainless steel sections. The numerical results also explain why both the residual stresses and the column behaviour of cold-formed steel sections may differ considerably among nominally identical sections. The proposed method has the potential to replace laboratory tests to a large extent and can thus be deployed in future research to minimise the need for expensive laboratory testing.

The manufacturing process of cold-formed thin-walled steel members induces cold work which can be characterized by the co-existent residual stresses and equivalent plastic strains and has a significant effect on their structural behaviour and strength. The present paper and the companion paper are concerned with the prediction of residual stresses and co-existent equivalent plastic strains in stainless steel sections formed by the press-braking method. This manufacturing process consists of the following two distinct stages: (i) coiling and uncoiling of the sheets, and (ii) press-braking operations. This paper presents an analytical solution for the residual stresses and co-existent equivalent plastic strains that arise from the first stage. In the analytical solution, the coiling–uncoiling stage is modelled as an inelastic plane strain pure bending problem; the stainless steel sheets are assumed to obey Hill’s anisotropic yield criterion with isotropic hardening to account for the effects of material anisotropy and nonlinear stress–strain behaviour. The accuracy of the solution is demonstrated by comparing its predictions with those obtained from a finite element analysis. The present analytical solution and the corresponding analytical solution for press-braking operations presented in the companion paper form an integrated analytical model for predicting residual stresses and equivalent plastic strains in press-braked stainless steel sections.

The manufacturing process of cold-formed thin-walled steel members induces cold work which can be characterized by the co-existent residual stresses and equivalent plastic strains and has a significant effect on their structural behaviour and strength. The present paper and the companion paper are concerned with the prediction of residual stresses and co-existent equivalent plastic strains in stainless steel sections formed by the press-braking method. This manufacturing process consists of the following two distinct stages: (i) coiling and uncoiling of the sheets, and (ii) press-braking operations. This paper first presents an analytical solution for the residual stresses and the co-existent equivalent plastic strains that arise from the second stage while a corresponding analytical solution for the first stage is presented in the companion paper. In both solutions, plane strain pure bending is assumed and the effect of material anisotropy is taken into account. On the basis of these two analytical solutions, an analytical model is presented to predict residual stresses and equivalent plastic strains in press-braked stainless sections. The predictions of the analytical model are shown to be in close agreement with results from a finite element-based method, demonstrating the validity and accuracy of the analytical model. The analytical model provides a much simpler method for the accurate prediction of residual stresses and equivalent plastic strains in different parts of a press-braked stainless steel section than a finite element-based method.

Cough is an important defensive reflex of the respiratory tract needed to clear and protect the upper airways; however, it may become exaggerated and interfere with quality of life. Although chronic cough may be successfully treated when associated with the common causes such as asthma and eosinophilic bronchitis, gastrooesophageal reflux disease and post-nasal drip syndrome or rhinosinusitis, increasingly, idiopathic cough or cough with no associated cause is recognised. Chronic cough is often associated with an increased response to tussive agents such as capsaicin, used as an index of the cough reflex. Some airway receptors mediate or influence cough through activation of vagal afferent pathways which converge on brain stem respiratory networks and of supramedullary centres. Plastic changes in intrinsic and synaptic excitability at the brain stem, spinal or ganglionic level may be the mechanism by which the cough reflex is enhanced in chronic cough. Subjective and objective measurements of cough in the clinic are now available but a major unmet need in chronic cough is the availability of effective antitussives. Future directions in chronic cough include the pathophysiological mechanisms of the enhanced cough reflex, and the discovery of effective antitussives that can successfully alleviate chronic cough. Chronic Respiratory Disease 2007; 4: 159—165

Residual stresses in cold-formed sections may play a significant role in determining their behaviour and strength. Laboratory measurements of residual stresses by destructive methods are not only time-consuming but also of limited accuracy. This paper presents a finite element-based method for predicting residual stresses in press-braked thin-walled sections, which overcomes these difficulties. In this method, the effects of coiling and uncoiling are accounted for analytically, with the resulting residual stresses specified as the initial stresses in a subsequent finite element simulation of cold bending. The method provides residual stress distributions over the cross-section as well as across the thickness. Numerical results from this method are shown to agree closely with laboratory measurements, demonstrating the validity and accuracy of the method. Numerical results presented in the paper show that the maximum residual stresses in a press-braked section generally occur in the corner region and away from the surfaces, and their values can be much higher than those at the surfaces. This means that the conventional method of measuring the surface residual stresses in the laboratory and assuming a linear variation across the plate thickness may greatly underestimate the real residual stresses. The results also explain why residual stresses may differ considerably in otherwise identical sections. The method offers a powerful tool for exploring the effect of different forming parameters on the magnitude and distribution of residual stresses so that these forming parameters can be optimised.

Residual stresses in cold-formed members may play a significant role in determining their behaviour and strength, and have traditionally been obtained by laboratory measurements. This paper presents the results of research which forms part of a larger study on the theoretical predictions of residual stresses in cold-formed sections. The paper is concerned with residual stresses that arise from the coiling and uncoiling process experienced by steel sheets before they are cold formed into sections. In this paper, a closed-form solution is presented for these residual stresses, in which the coiling and uncoiling process is modelled as an elastic–plastic plane strain pure bending problem with the steel assumed to obey the von Mises yield criterion and the Prandtl–Reuss flow rule. To facilitate its application in subsequent finite element simulation of the cold-forming process, the prediction of equivalent plastic strains is also addressed in this solution. The accuracy of the solution is demonstrated by comparing its predictions with those from a finite element simulation. Numerical results from the analytical solution are also presented to illustrate the development process of residual stresses and the effects of coiling curvature and yield stress on the final residual stresses.

Interleukin-8 (IL-8) is a neutrophil chemotactic factor expressed in many cell types, including human airway epithelial cells (HAEC). Inhaled corticosteroids are now used increasingly early in the treatment of airway inflammation such as in asthma, and directly interact with HAEC at relatively high concentrations. We have investigated the effect of dexamethasone on IL-8 expression in primary cultured HAEC obtained from transplantation donors. Northern blot analysis was used to measure IL-8 mRNA levels in HAEC, and radioimmunoassay was used to measure IL-8 protein in culture supernatant fluids. We demonstrated that IL-8 was expressed by primary cultured HAEC and that this was enhanced by IL-1 beta and tumour necrosis factor-alpha stimulation, but not by IL-6 or lipopolysaccharide. Dexamethasone suppressed IL-8 mRNA expression and protein synthesis dose-dependently in both resting and stimulated HAEC. The half-life of IL-8 mRNA determined in the presence of actinomycin D was less than 1 hr, and dexamethasone preincubation had no effect on mRNA stability. These results support the view that HAEC may play an important role in the pathogenesis of airway inflammatory diseases, and that glucocorticosteroids may exert their anti-inflammatory effects by blocking IL-8 gene expression and generation in these cells.