Q.S. Li

Full scale measurements of wind effects on tall buildings

This paper describes the results obtained from the measurements of wind effects on two tall buildings with 70-storeys and 30-storeys, respectively. The field data presented are wind velocity and acceleration response measured at the top of the tall buildings over the last two years. The damping characteristics which were obtained by using the random decrement technique are demonstrated and discussed.

An experimental investigation of the effects of free-stream turbulence on streamwise surface pressures in separated and reattaching flows

An experimental investigation was conducted to study the effects of free-stream turbulence on surface pressures on a flat plate with rectangular leading-edge geometry using turbulence-producing grids. The measured mean, standard deviation and peak pressure coefficients as well as lateral cross-correlation of fluctuating pressures are presented and discussed.

Dynamic Behavior of Taipei 101 Tower: Field Measurement and Numerical Analysis

This paper presents selected results measured from a monitoring system with 30 accelerometers installed at six floor levels in 508-m high Taipei 101 Tower located in Taipei City, Taiwan where earthquakes and strong typhoons are common occurrences. Emphasis is placed on analyzing the data recorded during three typhoons (Matsa, Talim, and Krosa) and a seismic event (Wenchuan earthquake occurred on May 12, 2008 in Shichuan, China) to investigate the effects of wind and seismic on the supertall building. Dynamic characteristics of the tall building such as natural frequencies, mode shapes, and damping ratios determined from the measured data are presented and compared with those calculated from the finite-element model of the high-rise structure. The seismic performance of this supertall building to a long distance earthquake (Wenchuan earthquake) is assessed based on the field measurements and numerical analysis. The findings of this study are expected to be of considerable interest and practical use to prof...

Combinatorial optimal design of number and positions of actuators in actively controlled structures using genetic algorithms

In this paper, the optimal design of the numbers and positions of actuators in actively controlled structures is formulated as a three-level optimal design problem. Features of this design problem such as discreteness, multi-modality and hierarchical structure are discussed. A two-level genetic algorithm (TLGA) is proposed for solving this problem. The concept, principle and solution process of the TLGA are described. A case study is presented, in which a building is subjected to earthquake excitation and controlled by active tendon actuators. The results of this study show that: (1) the design problem for optimizing number and configuration of actuators simultaneously in actively controlled structures has the features of non-linearity, mixed-discreteness and multi-modality; (2) a three-level design model can give a reasonable description for this kind of design problem; (3) TLGA is an effective algorithm for solving the combinatorial optimization problem.

Buckling of multi-step non-uniform beams with elastically restrained boundary conditions

Abstract In this paper, the governing differential equation for buckling of a multi-step non-uniform beam under several concentrated axial forces is established. The special solutions of bending moment for buckling are found first for eight types of non-uniform beams, then the recurrence formula method and the transfer matrix method for determining the critical buckling force of a multi-step non-uniform beam are proposed. In the recurrence formula method, the two fundamental solutions of bending moment and the recurrence formulas developed in this paper are used to determine the critical buckling forces for a multi-step non-uniform beam without spring supports, and the four fundamental solutions of displacement and the recurrence formulas are adopted for buckling analysis of such a beam with rotational and translational springs at the ends and intermediate points. With this proposed procedure, the eigenvalue equation for a multi-step non-uniform beam with any kinds of the two end supports and any number of rotational and translational springs at the ends and intermediate points can be conveniently determined from a second order determinant. By using the transfer matrix method, the eigenvalue equation for the title problem can be established from a fourth order determinant. The numerical examples show: (1) the results calculated by the present methods are in good agreement with those obtained by FEM, (2) one of the advantages of the present methods is that the total number of the segments required by the proposed methods could be much less than that normally used in finite element method, (3) the two procedures proposed in this paper are exact and efficient methods.

Probabilistic characteristics of pressure fluctuations in separated and reattaching flows for various free-stream turbulence

Abstract The statistical characteristics of the fluctuating pressures acting on bluff bodies in the region of flow separation are investigated in this paper. Probability density functions of the pressure fluctuations have shown a significant non-Gaussian behaviour. The lognormal density function is found to be in close agreement with the obtained experimental data. A probability distribution for the maximum magnitude of peak pressures expected during a period is proposed and the agreement between the experimental data and predicted results are good. The effects of free-stream turbulence intensity and integral scale on the statistical nature of pressure fluctuations are presented and discussed. The second part of this paper concerns the action of fluctuating wind pressure on building cladding. The effect of free-stream turbulence intensity and integral scale in model test on equivalent constant pressures for the purpose of cladding design is investigated, making use of direct integration of measured pressure data in the wind tunnels.

An exact approach for free vibration analysis of rectangular plates with line-concentrated mass and elastic line-support

An exact approach for free vibration of an isotropic rectangular plate carrying a line-concentrated mass and with a line-translational spring support or carrying a line-spring-mass system is presented in this paper. The mode shape function of vibration of such a plate is expressed in terms of the four fundamental solutions derived in this paper. The main advantage of the proposed method is that the resulted frequency equation for such a rectangular plate can be conveniently obtained from a second-order determinant. The proposed method is thus computationally efficient due to the significant decrease in the determinant order as compared with previously developed procedures which usually led to an eighth-order determinant for solving the title problem. Two numerical examples are given to illustrate the efficiency of the proposed method and to investigate the effects of the location and the magnitude of a line-concentrated mass and elastic line-support as well as the influence of the aspect ratio on the natural frequencies of a rectangular plate.

Failure probability prediction of concrete components

In order to predict the probability of failure for brittle fracture of concrete components under multiaxial stress states, the imperfections of concrete components are modeled as cracks with different shapes in this paper. A new probability distribution function for evaluating the failure probability of concrete components is proposed. A simplified measurement method for determining the parameters of the governing Weibull distribution, using the three-point bending test, is presented and discussed. The experimental results of the combined bending/torsion failure tests of concrete components verify that the proposed crack model is more reasonable than the Batdorfs crack model and the proposed prediction formula can evaluate the failure probability of concrete components accurately.

Decoupling control law for structural control implementation

Abstract Multi-story buildings, subjected to wind or earthquake excitation, can be modeled as multi-degree of freedom (MDOF) systems defined by a set of coupled second order ordinary differential equations. In this paper, the dynamic coupling characteristics of multi-story building are examined, and it is found that the coupled property in a system can be described as a positive feedback from the control theory point of view. This positive feedback property of a MDOF system may intensify structural vibration. For the structural control implementation, open-loop and closed-loop decoupling control laws are proposed. All coupled “channels” of the system are “broken off” when the vibration control design is based on the proposed control laws. A complex MDOF structural system, therefore, is equivalent to a set of single degree of freedom (SDOF) systems, and the control design can be carried out independently for any specific degree of freedom. Thus, the proposed control laws provide an efficient tool by which the vibration of a selected floor can be suppressed without any effect on its neighboring floors because the control is one to one. Meanwhile, the computational procedure of the control design can be significantly simplified because all analyses and design are conducted based on SDOF systems.

A computational approach for free vibration of non-uniform flexural–shear plates

Abstract The concept and an analytical model of a flexural–shear plate are proposed in this paper. The governing differential equation for vibration of such a plate with variably distributed mass and stiffness considering the effects of damping and axial forces is established. Using appropriate transformations, the equation is reduced to a Bessels equation or an Eulers equation or a differential equation with constant coefficients by selecting suitable expressions, such as power functions and exponential functions, for the distribution of mass and stiffness along the height of the plate. The exact solutions of one-step non-uniform flexural–shear plates are derived and used to obtain the frequency equations of multi-step non-uniform flexural–shear plates. The new exact approach which combines the transfer matrix method and closed form solutions of one-step flexural–shear plates are proposed for free vibration analysis of multi-step non-uniform flexural–shear plates. The new transfer matrix and the resulting frequency equations are presented. Numerical examples demonstrate that the calculated natural frequencies and mode shapes of tall buildings with narrow rectangular plane configuration which are treated as flexural–shear plates for vibration analysis are in good agreement with the corresponding experimental data.