Optimization of large-scale rigidified inflatable structures for housing using physical programming

This paper makes important initial steps in the application of large-scale structural optimization to Rigidified Inflatable Structures (RIS) for cost competitive residential construction, and does so within the realistic framework of multiobjective optimization using the effective physical programming approach. Over the past two decades, structural optimization has proved to be an invaluable tool in numerous arenas. Its faint beginnings in civil engineering have given way to important applications in the aerospace industry, and more recently, in the automotive industry and many other areas. Importantly, structural optimization has given way to the broader field of Multidisciplinary Design Optimization (MDO). Within this context, this paper explores the feasibility of RIS design for residential construction with respect to cost, structural integrity (e.g., buckling, deformation), and other practical issues. A cylindrical structure is considered, and is subjected to code-specified snow and wind loads. Within a multiobjective framework, a physical-programming-based optimization approach is developed to examine the behavior and feasibility of reinforced and non-reinforced polymers as primary RIS materials. Using a finite element model of approximately 72000 degrees of freedom, we illustrate how the physical programming method effectively addresses the multiobjective and multiscale nature of the problem. Initial results indicate favorable feasibility of RIS use in housing. Further studies of broader scope are suggested

Study of a honeycomb-type rigidified inflatable structure for housing

This paper presents a parametric study aimed at uncovering general design principles that govern the structural performance of honeycomb-type rigidified inflatable structures (RIS) as load-bearing wall systems for use in residential housing. This study involves the use of finite element modeling and optimization. A series of honeycomb-type RIS wall systems, each comprising different honeycomb cell sizes, are examined. The problem at hand is stated in the form of minimizing material volume subject to: permissible stress, maximum allowable deflection, and membrane thickness. The optimization results help identify optimal design configurations for given sets of loading conditions and material properties. The effects of various design parameters, such as cell size, material properties, and membrane thicknesses, are discussed. The performance of honeycomb-type RIS wall systems is compared with that of rectilinear-type RIS wall systems, which were studied previously. The work presented makes a significant step in establishing the feasibility of RIS for housing applications

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline