International Journal of Structural Stability and Dynamics

Thin-walled cylindrical structures have been found to display three distinctly different stability failure modes under wind loading, depending on their geometric and material properties. In low cylinders the radial compression at the meridian facing the wind causes a buckling mode similar to that for cylinders under constant radial compression, while very long cylinders display a failure mode characterized by buckling in the lower third of the structure at the side which faces away from the wind. The failure of medium height cylinders is characterized by a number of horizontal, ripple-like buckles in an area around the upper half of the meridian which faces the wind. In an ongoing experimental study, a series of small-scale specimens with a wide range of geometric parameters is being tested in a wind tunnel. To the knowledge of the authors, this is the first time that the particular buckling mode for medium height cylinders has been documented in an experiment. The present paper gives a summary of the results gained from this study so far and compares them qualitatively to those of a previous numerical study.

The potential of continuous wavelet transforms for damage assessment of existing bridges is investigated herein. Different types of continuous wavelet transforms have been under investigation and the most effective ones have been introduced in a toolbox to automate the damage assessment procedure. In this paper, the performance of the wavelet approach and the influence of different parameters in the damage assessment procedures are studied through two examples: a simply supported beam and a three-span concrete bridge. Applying the wavelet transforms to a structure's static and/or dynamic response showed promising results with regard to localization of structural modification or damage. This paper underlines the high sensitivity of the wavelet analysis to damage intensity and its ability to be applied directly to the damaged data. These key characteristics could lead to this approach becoming one of the best for structural health monitoring of existing bridges in the near future.

This paper deals with the determination of free vibration characteristics and instability conditions of flexible spinning cylinders partially filled with fluid. Using the linearized Navier–Stokes equations for the incompressible, inviscid flow, a 2D model is developed for fluid motion at each section of the cylinder. The forces exerted on the cylinder wall as a result of the fluid motion are calculated as functions of lateral acceleration of the cylinder axis in the Laplace domain. Applying the Hamilton principle, the governing equations of flexural motion of the cylinder are derived and then combined with the equations describing the fluid forces to obtain the coupled field equations of the structural motion and the liquid sloshing dynamics. Using the obtained model, the free vibration and the stability conditions of the cylinder as well as the effect of material viscoelasticity on the stability boundaries are examined. The results of the stability analysis are presented for a number of examples, and some conclusions are outlined.

In this work, a one-dimensional beam model for buckling analysis of framed structures under large displacement creep regimes is presented. The equilibrium equations of a prismatic and straight spatial beam element are formulated in the framework of corotational description, using the virtual work principle. Although the translations and rotations of the element are allowed to be large, the strains are assumed to be small. The material of a framed structure is assumed to be homogenous and isotropic. The bilinear elastic–plastic model with isotropic hardening and the power creep law are adopted for describing the inelastic behavior of the material. The numerical algorithm is implemented in a computer program called BMCA and its reliability is validated through test examples.

The experimental and analytical behavior of 400 kV S/C portal-type guyed towers under different loading conditions is presented. The portal-type tower essentially consists of two masts extending outward in the transverse direction from the beam level to the ground. In addition, two sets of guys connected at the ground level project outward along the longitudinal axes and converge in the transverse axes. The experimental behavior of the guyed tower is compared with the results of finite element analysis. The 400 kV portal-type guyed towers with III and IVI type insulator strings are analyzed using finite element software. Full scale tower test results are verified through comparison with the results of the finite element analysis. The initial prestress in the guys is allowed to vary from 5% to 15% in the finite element modeling. The effect of prestress variation of the guys on the tower behavior is also studied.

A study on the influence of meridional curvature on the buckling and postbuckling behavior of cross-ply laminated shells of revolution subjected to thermal and mechanical loads is carried out using the semianalytical finite element method. The nonlinear equations are solved using the Newton–Raphson iterative technique. The adaptive displacement control method is employed to trace the equilibrium path. Examined herein are the effects of positive and negative meridional curvature, the number of layers and the number of circumferential waves on the buckling/postbuckling behavior of cross-ply laminated, simply supported shells under thermal, external pressure, torsional and axial loadings. It is found that the critical load increases with the increase in the rise-to-radius ratio of positive meridional curvature shells for the loading cases considered. The critical temperature, torsional, axial loads decrease and the critical external pressure increases with increasing magnitude of the rise-to-radius ratio of negative meridional curvature shells. The postbuckling response of shells exposed to a uniform temperature rise is of a hardening nature for both positive and negative meridional curvature cases. Shells subjected to external pressure show a softening type of initial postbuckling response for positive meridional curvature, and a hardening type of postbuckling response for negative meridional curvature. The qualitative nature of postbuckling characteristics for torsional and axial loading cases may be softening, hardening or initially softening and later hardening, depending upon the combined influence of the rise-to-radius ratio, the number of circumferential waves and the number of layers.

Active multiple tuned mass dampers (AMTMDs) consisting of several active tuned mass dampers (ATMDs) with uniform distribution of natural frequencies have been proposed for vibration mitigation of structures under wind loads. In this regard, the optimum parameter criterion is defined as the minimization of the root-mean-square (RMS) displacement and acceleration responses of the structure with the AMTMD. Meanwhile, the effectiveness criterion is defined as the ratio of the minimum RMS displacement and RMS acceleration of the structure with the AMTMD to those without the devices, respectively referred to as the displacement and acceleration reduction factors (DRF and ARF). With these two criteria, the influences of the selective parameters on the effectiveness and robustness of the devices for vibration control under wind loads are studied. In addition, the stroke of the AMTMD is examined by quantitatively assessing the RMS displacement of each ATMD. Results indicate that in comparison with a single ATMD, the AMTMD can cause more reduction in the displacement and acceleration responses of the structure under wind loads. The stroke of the AMTMD is greater based on the ARF than the DRF criterion. In particular, the simulation results in the time domain confirm that by resorting to the AMTMD, a large control force can indeed be decentralized into many smaller control forces without losing the level of response reduction.

Research and development of seismic response control devices has gained prime importance recently, due to an increased number of devastating earthquakes. Passive control systems are now accepted all over the world and hence research in this area is continuing to develop reliable, efficient and cost effective devices along with constitutive modeling. This paper begins with qualitative description and comparison of passive, active and semiactive control systems. Further, it mentions advantages of passive control systems over the others. A detailed literature review of passive devices is then provided which includes the historical development of the devices, their dynamic behavior, testing of these devices incorporated in the structural models and their analytical formulations. The pros and cons of these devices in retrofitting of structures and their first and recent applications in a wide variety of structures are also discussed. The passive response control systems that are discussed include viscoelastic dampers, yielding dampers, viscous dampers, friction dampers, tuned mass dampers, tuned liquid dampers, tuned liquid column dampers, superelastic dampers, like shape memory alloy dampers and base isolators.

A thin circular plate with a free or movable boundary, and weakened along an internal concentric circle, is considered. The frequencies of the circular plate varying with the radius of the weakened circle and the extent of the weakening represented by an elastic rotational restraint are determined. The results for the first four modes are tabulated. For the free plate, the internal weakening only slightly decreases the fundamental frequency of the plate, which is advantageous. For the plate with a movable edge, the internal weakening greatly decreases the fundamental frequency, especially for the purely hinged case.