Development of Structural Metal Energy-Dissipation Techniques for Seismic Disaster Mitigation of Buildings in China

Buildings in seismic zones are required to provide proper stiffness and load-bearing capacity to resist frequent earthquakes, and possess proper ductility and energy-dissipating capacity to prevent collapse under rare earthquakes. To meet these requirements, the concept of structural energy-dissipation techniques for the bi-functions of load-bearing and energy dissipating are proposed. A number of structural metal energy-dissipation elements, such as buckling-restrained steel plate shear walls, non-buckling corrugated steel plate shear walls, two-level yielding steel coupling beams and energy-dissipative columns, have been developed. They are designed to provide stiffness/strength to guarantee the operation of buildings under frequent earthquakes, but also dissipate energy to reduce seismic effects to a considerable extent for collapse-prevention of buildings. The experimental and theoretical studies on these structural metal energy-dissipating dampers are presented. The efficiency of these structural dampers for disaster mitigation of buildings against earthquakes are also presented to provide a reference for their practical application.

Theoretical Study on Vibration Control of Symmetric Structure with Shape Memory Alloy (SMA)-Friction Damper

The paper proposed an innovative shape memory alloy (SMA)-friction damper. The damper consisted of the superelastic SMA wire and the friction element in series. According to the working mechanism of the damper, the paper set up the mechanical model of the damper. Seismic elastic-plastic time history response analysis program and energy analysis program of the damped structure were designed. The numerical calculations of the vibration control of a threestory shear-type symmetric structure with the damper were carried out. The results indicated that the damper can decrease the displacement and the inter-story displacement of the structure effectively, but increase the acceleration of the structure comparing with uncontrolled structure. The SMA-friction damper can not only adjust the working status of the energy dissipation elements automatically according to the seismic responses of the structure, but also has some advantages as simple configuration and economical application.

Experimental investigation of dissipation-element statistics in scalar fields of a jet flow

We present a detailed experimental investigation of conditional statistics obtained from dissipation elements based on the passive scalar field$\theta $and its instantaneous scalar dissipation rate$\chi $. Using high-frequency planar Rayleigh scattering measurements of propane discharging as a round turbulent jet into coflowing carbon dioxide, we acquire with Taylor’s hypothesis a highly resolved three-dimensional field of the propane mass fraction$\theta $. The Reynolds number (based on nozzle diameter and jet exit velocity) varies between 3000 and 8600. The experimental results for the joint probability density of the scalar difference$ \mathrm{\Delta} \theta $and the length$l$of dissipation elements resembles those previously obtained from direct numerical simulations of Wang & Peters (J. Fluid Mech., vol. 554, 2006, pp. 457–475). In addition, the normalized marginal probability density function$\tilde {P} (\tilde {l} )$of the length of dissipation elements follows closely the theoretical model derived by Wang & Peters (J. Fluid Mech., vol. 608, 2008, pp. 113–138). We also find that the mean linear distance${l}_{m} $between two extreme points of an element is of the order of the scalar Taylor microscale${\lambda }_{u} $. Furthermore, the conditional mean$\langle \mathrm{\Delta} \theta \vert l\rangle $scales with Kolmogorov’s$1/ 3$power law. The investigation of the orientation of long dissipation elements in the jet flow reveals a preferential alignment, perpendicular to the streamwise direction for long elements, while the orientation of short elements is close to isotropic. Following an approach proposed by Kholmyansky & Tsinober (Phys. Lett. A, vol. 373, 2009, pp. 2364–2367), we finally investigate the probability density function of the scalar increment$\delta \theta $in the streamwise direction, when strong dissipative events are either retained in or excluded from the measurement volume. In the present study, however, these events are related to maximum points of the scalar dissipation rate$\chi $together with their local extent. When these regions are excluded from the scalar field, we observe a tendency of the probability density function$P(\delta \theta (r))$towards a Gaussian bell-shaped curve.

A new view of flow topology and conditional statistics in turbulence

By partitioning a turbulent flow field into relative simple units, the original complex system may be better understood from studying decomposed structures. In this paper, some general principles for identifying geometrical decomposition are discussed. Logically, to make analysis more objective and quantitative, the decomposed units need to be non-arbitrarily defined and space filling. Following this vein, we introduced two topological approaches satisfying these prerequisites and the relevant work is reviewed. For a given scalar variable, dissipation elements are defined as the spatial regions that the gradient trajectories of this scalar can share the same pair of scalar extremums (one maximum and one minimum), whereas for the general vector variables, vector tube segments are the part of vector tubes bounded by adjacent extremums of the magnitude of the given vector. Both structures can be characterized by representative shape parameters: the length scale and the extremum difference. On the basis of direct numerical simulation data, the statistics of the shape parameters have been studied. Physically, those structures reveal the ‘nature’ topology of turbulence, and thus their characteristic parameters reflect the flow properties. For instance, when the vector tube segment approach is applied to the velocity case, the negative skewness of the velocity derivative can be explained by the asymmetry of the joint probability density function of the shape parameters of streamtube segments. Conditional statistics based on these newly defined structures identify finer flow physics and are believed helpful for modelling improvement. Application examples illustrate that, in principle, these methods can generally be applied to different flow cases under different situations.