In this work, the nonlinear BUCKLING and post-BUCKLING behavior of shallow arches made of Shape Memory Alloy (SMA) is investigated. Arches are susceptible to large deflections, due to their slenderness, especially when the external load exceeds the serviceability limit point. Beyond this, loss of stability may occur, the famous snap-through BUCKLING. For this reason, curved beams can be used in passive vibration control devices for seismic response mitigation, and the geometrically nonlinear analysis is needed for the accurate prediction of their response. Thus, in this research effort, the assumptions of the Euler-Bernoulli beam theory are considered, and the Von Karman strain field is employed to account for large deflections. The formulation of the problem is displacement-based regarding the axial (tangential) and transverse (normal) displacements, while the two governing equations are coupled and nonlinear. In order to introduce the SMA constitutive law, the stress-strain experimental curves described in the literature are employed together with a fiber approach at specific control cross-sections along the beam. The numerical solution of the longitudinal problem is achieved using the Analog Equation Method (AEM), a Boundary Element Method (BEM) based technique, and the iterative procedure is based on a Newton-Raphson scheme by using a displacement control algorithm to trace the fully nonlinear equilibrium path and overcome the limit points. Several representative examples are studied, not only to validate the proposed model but also to investigate the nonlinear BUCKLING and post-BUCKLING of SMA shallow arches.

Purpose: To assess the efficacy of minimal surgery scleral BUCKLING in patients who were referred to Labbafinejad medical center in a 5 year period.Material and methods: Records of all patients with retinal detachment who had undergone minimal surgery between 1995 and 2000 and were followed up for at least 6 months were retrospectively reviewed. The records were evaluated with respect to clinical features and disease characteristics and the success rate was determined according to anatomic reattachment and visual acuity of better than 20/200. All intraoperative and postoperative complications were reported. Roles of factors such as extent and duration of retinal detachment, macular status, proliferative vitreoretinopathy, evidence of long standing retinal detachment, type of break, myopia, lens status, intra-operative complications, and cryotheraply on success rate were determined. Regression analysis was used to identify the factors which played the main role in success.Results: Seventy patients (72% male, 25% female) underwent minimal surgery scleral BUCKLING. Mean age (SD) was 44 (17.6) years. Oveall operations were successful (92.9%) and 58 patients have good or useful visual outcome (89.2%). Macular detachment significantly increased the failure rate (P<0.04). Regression analysis showed that the extent of retinal detachment had significant correlation with success rate.Conclusion: The success rate of minimal surgery and final visual acuity in this series were acceptable and similar to other experiences. A controlled clinical trial with a longer period of follow up is recomended to determine role of factors such as duration of retinal detachment and pre-operative visual acuity on anatomic and functional results.

The paper presents an investigation on the behavior of a plate with variable thickness and simple boundaries under in plane compressive loads using energy, finite differences, and finite elements methods. The more important parameters affecting such behavior, are the spatial location of the corrosion patch, the corroded surface and thickness at corroded place. These are studied through changing them at practical ranges, and the more critical cases are indicated. At first the critical load of plate is calculated using energy and finite differences methods which is a basic parameter in all such studies. To consider the effect of mid plane variation due to corrosion, FEM is employed via ALGOR software. The geometric and material non-linearity are taken into account and the effect of progressive corrosion on gradual strength reduction is traced.

In this paper the behaviour of steel frames is investigated under an applicable range of initial rotational geometric imperfection in joints, which are mostly created during the manufacturing process. A nonlinear analysis is applied in both geometry and material behaviour of steel frames. The results show considerable reduction in BUCKLING and ultimate load carrying capacity of portal frames, when they are affected by a rotational imperfection.