International Journal of Structural Stability and Dynamics

Tensegrity systems are statically and kinematically indeterminate systems. They typically contain a large number of cable elements and struts. However, there are a number of critical cable elements in tensegrity systems, with the sudden rupture of any of them, their forces are shed into the structure in a dynamic manner, leading to more severe damage. This paper presents a numerical and experimental investigation into the collapse behavior of tensegrity systems due to a cable rupture. The test results are served as a basis for the finite element modeling and furthermore for the development of a new approach to structural design of tensegrity systems. It was found that the most important factors, influencing the collapse behavior of the tensegrity systems due to a cable rupture, are the damping ratios and load level at which a cable element is suddenly ruptured.

In vibration-based structural damage detection, it is necessary to discriminate the variation of structural properties due to environmental changes from those caused by structural damages. The present paper aims to investigate the temperature effect on vibration-based structural damage detection in which the vibration data are measured under varying temperature conditions. A simply-supported slab was tested in laboratory to extract the vibration properties with modal testing. The slab was then damaged and the modal testing was conducted again, in which the temperature varied. The modal data measured under different temperature conditions were used to detect the damage with a two-stage model updating technique. Some damage was falsely detected if the temperature variation was not considered. Natural frequencies were then corrected to those under the same temperature conditions according to the relation between the temperature and material modulus. It is shown that all of the damaged elements can be accurately identified.

A cable-stayed bridge model was made based on the design drawings of Shandong Binzhou Yellow River Highway Bridge (BZB) and detailed model tests were conducted. In the tests, the cable damage effects on the loading behavior and dynamic performance of the bridge model were studied by considering different cable damages' locations, different numbers of damaged cables, and different damaged levels of cables etc. The experimental results revealed that the cable damages may significantly affect the internal forces of other cables and the stress distributions of the girders; however, they have less influence on the natural frequencies of the bridge model. In parallel with the model tests, a finite element model of the bridge structure has been established. Numerical analysis for the bridge model with cable damages was carried out to validate the experimental results and explain the phenomena observed in the model tests.

The interference effect between buildings has been a popular issue in structural wind engineering for a long time. Most researches about this issue have been focused mainly on high-rise buildings. For long-span bridges, the interference effects between structures are rarely discussed. In this paper, an aerodynamic elastic model test of a free-standing bridge pylon located adjacent to two large-scale cooling towers is presented. Through the mode analysis, the structure mode shapes are obtained. Then by the simulation of the two cooling towers in the boundary layer during the aeroelastic model test, the vibration responses of the bridge pylon in smooth and turbulence flows are obtained respectively. The study shows that the interference effect of the two huge-volume cooling towers on the wind induced vibration responses of the bridge pylon should not be neglected. In smooth flow, due to the regular shedding vortex from the upwind cooling towers, the interference effect is evident in that strong resonant responses are induced on the lower-order modes of the downwind bridge pylon. However, in turbulence flow, this kind of interference effect is greatly reduced. Moreover, more attention should be paid to the case when the cooling towers are located at the perfectly right upwind direction of the bridge pylon. Their interference effect will certainly cause great resonant vibrations in the longitudinal direction, which cannot be ignored for granted. Furthermore, the turbulence flow at the bridge pylon considering the interference effect is measured through a 1:500 flow experiment to discover the interference effect of the cooling towers. In the end, a dynamic magnification factor is proposed to take the interference effect into consideration, with a value of 2.25 suggested for the design of pylons.

In this work, the importance of the capability to capture dynamic loading for an integration method is emphasized. In a step-by-step integration procedure, amplitude distortions in the transient and steady-state responses depend on the step discretization error of dynamic loading for each time step. Correlations between amplitude distortion and step discretization error for dynamic loadings are analytically established for a specified integration method. These correlations may be considered as the basic numerical properties in evaluating a step-by-step integration method. As a result, the superiority of the previously published algorithm (PPA) [S. Y. Chang, Int. J. Numer. Meth. Eng.77(8) (2009) 1100–1120] over its modified form and the member of Newmark family method (MNM) with β = γ = 1/2 in capturing dynamic loading is analytically verified (even though the three algorithms have exactly the same characteristic equation).

This paper presents the snap-through and bifurcation elastic stability analysis of nano-arch type structures with the Winkler foundation under transverse loadings by the strain gradient and stress gradient (nonlocal) theories. The equations of equilibrium are derived by using the variational method and virtual displacement theorem of minimum total potential energy. In the elastic stability analysis, von Karman's nonlinear strain component is included, with the deformation represented by a series solution. It is concluded that in general, the strain gradient theory pushes the system away from instability as compared to the classical theory. However, the nonlocal theory does the reverse and causes the system to experience instability earlier than that of the classical theory. Moreover, theories with different small-size considerations change the mechanism of instability in different ways. For example, in similar conditions, the strain gradient theory causes the system to reach a snap-through point, while the nonlocal theory causes the system to stop at a bifurcation critical point.

In this paper, an active controller for buildings with bilinear hysteresis and time delay is studied. The bilinear hysteretic model is treated as a stiffness restoring force. By using specific transformation and augmentation of state parameters, the equation of motion of the system with an explicit time delay is transformed into a standard state space where there is no explicit time delay. A linear quadratic Gaussian control method is proposed for the controller design with time delay. The method is verified with numerical simulations of three-story and 20-story buildings. Comparison study of simulation results indicates that the control performance will deteriorate if the time delay is not taken into account in the control design. The proposed time-delay controller not only effectively compensate the time delay for better control effectiveness, but it also works well with both small and large time-delay problems.

The buckling of higher-order shear plates is studied in this paper with a unified formalism. It is shown that usual higher-order shear plate models can be classified as gradient elasticity Mindlin plate models, by augmenting the constitutive law with the shear strain gradient. These equivalences are useful for a hierarchical classification of usual plate theories comprising Kirchhoff plate theory, Mindlin plate theory and third-order shear plate theories. The same conclusions were derived by Challamel [Mech. Res. Commun.38 (2011) 388] for higher-order shear beam models. A consistent variational presentation is derived for all generic plate theories, leading to meaningful buckling solutions. In particular, the variationally-based boundary conditions are obtained for general loading configurations. The buckling of the isotropic or orthotropic composite plates is then investigated analytically for simply supported plates under uniaxial or hydrostatic in-plane loading. An analytical buckling formula is derived that is common to all higher-order shear plate models. It is shown that cubic-based interpolation models for the displacement field are kinematically equivalent, and lead to the same buckling load results. This conclusion concerns for instance the plate models of Reddy [J. Appl. Mech.51 (1984) 745] or the one of Shi [Int. J. Solids Struct.44 (2007) 4299] even though these models are statically distinct (leading to different stress calculations along the cross-section). Finally, a numerical sensitivity study is made.

This study examines how the vibration absorbers influence the stability of nonlinear flow-solid interaction systems. A novel approach is proposed for the analysis of dynamic stability of the two-dimensional nonlinear system using the internal resonance contour plot (IRCP) and flutter speed contour plot (FSCP). The system considered is a planar rigid-body with plunge and pitch vibrations. The two ends of the body are supported by cubic nonlinear springs with quadratic damping. The vibration absorber attached beneath is also considered as a rigid body, with the mass and position of the absorber adjusted for optimization of vibration reduction. The method of multiple scales (MOMS) is employed to obtain a fixed point solution. The P-method is also adopted to obtain the eigen plot and Poincaré Map for comparison. Finally, both the IRCP with FSCP are cross-referenced to provide guide-lines for identifying the optimal location for the absorber with regard to stability and vibration reduction without the need to alter the framework of the main body.