Hong Ping Zhu

A New Solution Method for Vibration Analysis of Circular Cylindrical Thin Shells with a Circumferential Surface Crack

In this paper, a new solution method is proposed for determining the natural frequency of a given mode for a finite-length circular cylindrical thin shell with a circumferential part-through crack. The governing equation of the cracked cylindrical shell is derived by integrating the line-spring model with the classical thin shell theory. The proposed method calculates the natural frequency from an initial trial to satisfy both the governing equations and appropriate boundary conditions through an optimization process. The initial trial is proposed to satisfy the governing equations by using the beam modal function to determine the modal wavenumbers and mode shapes of cylindrical shells in the axial direction, assuming the flexural mode shapes of cylindrical shells in the axial direction to be of the same form as that of a flexural vibration beam with the same boundary conditions. Four representative sets of boundary conditions are considered: simply supported (SS-SS), clamped-clamped (C-C), clamped-simply supported (C-SS), and clamped-free (C-F). Compared with the finite element (FE) method, the proposed solution method is verified to provide an accurate and efficient way to calculate the dynamic characteristics of both intact and cracked cylindrical shells.

Optimum Design of Passive Control Devices for Reducing the Seismic Response of Twin-Tower-Connected Structures

ABSTRACT Based on the 3-single-degree-of-freedom (SDOF) model of twin-tower structures linked by the sky-bridge and passive control devices, the frequency functions and the vibration energy expressions of the structures are derived by using the stationary white noise as the seismic excitation. The analytical formulas for determining the connecting optimum parameters of viscoelastic damper (VED) represented by the Kelvin model and the viscous fluid damper (VFD) represented by Maxwell model are proposed using the principle of minimizing the average vibration energy of either the single tower or the twin tower. Three pairs of representative numerical examples of twin-tower-connected structures are used to verify the correctness of the theoretical approach. The optimum parametric analysis demonstrates that the control performance is not sensitive to damper damping ratio of VED and relaxation time of VFD. The effectiveness of the proposed control strategies based on the 3-SDOF models is also proved to be applicable to multi-degree-of-freedom systems. The theoretical analysis and numerical results indicate that the seismic response and vibration energy of the twin-tower-connected structures are mitigated greatly under the two types of dampers. The presented control strategies of VED and VFD can help engineers in application of coupled structures.

Seismic Response Analysis of Reinforced Concrete Frame Structures Considering the Variation of Parameters

The orthogonal polynomial expansion method expression of stochastic structure was deduced. Then, based on orthogonal polynomial expansion method, taking a 20-storey reinforced concrete frame structure as an example, the impact of the randomness of structural parameters on time history response was researched. Meanwhile, in order to verify the correctness of analysis program, the calculation results of orthogonal polynomial expansion method were compared with the Monte-Carlo method which based on Newmark integral. The results show that it can get relatively accurate results when the number of terms of the orthogonal polynomial is 5. Structural mass and stiffness have a greater impact on the structural dynamic response. And the greater number of random parameters, the greater the impact on structural dynamic response.

Optimal Sensor Configuration for Bridge Structures Following a Probabilistic Approach

In this paper, a statistical methodology is introduced for identifying the most effective way to install a limited number of sensors on a typical distributed-parameter system, i.e., a three-span continuous bridge model with two elastic supports to extract as much information as possible. This is performed by minimizing the uncertainties associated with the identified bridge modeling parameters. In the proposed methodology, the information entropy is employed as a measure to quantify the uncertainty of the identified structural modeling parameters. The problem of optimal sensor placement is then formulated as a continuous optimization problem, in which the information entropy is minimized, with the sensor configurations as the minimization variables. The generally used discrete-coordinate systems modeled by the finite element (FE) method can only approximate their actual dynamic behavior, which would in turn influence the sensor configuration results, and the sensors are confined to be only put on discrete nodes related to the coarse mesh scheme usually employed. For structures such as bridges belonging to typical distributed-parameter systems, it’s more reasonable and convenient to be modeled as continues-coordinate system with analytical formulation. It’s the main purpose of this paper to develop a sensor placement method for continues-coordinate systems following the Bayesian theorem and the information entropy method, with the binary-encoded genetic algorithm (GA) employed as the optimization technique.

Structural Vulnerability Analysis Based on Beta Distribution

The research of structural vulnerability analysis is mostly based on the Cornell theory. Using other methods to do seismic fragility analysis is relatively rare. In this paper, beta probability density function is used to continuously fit the probability distribution of damage levels for a frame structure under given seismic intensities. It gets the probability density distribution of the structure under different intensities. The results show that, based on beta probability density function, it can get comparatively accurate solution for structural seismic vulnerability analysis. This method is not only simple and fast, but also the damage state is expressed by continuous damage parameter. The research provides the reference for future earthquake damage prediction and the elaborate calculation about economic loss of earthquake insurance.

The Settlement Analysis and Reinforcement of a Cast-In Situ Concrete Floor

After form a removal concrete cross ribbed beam floor in a commercial plaza, the vertical cracks are discovered, and the settlement analysis and reinforcement of a Cast-in-situ concrete floor are performed. The detection of the maximum crack is 0.3mm,and the Maximum settlement of cross ribbed beam is 48mm. By theoretical analysis, improper form removal during construction stage makes the actual floor force inconsistent with the design of a load transfer, which is the main reason of the excessive settlement in the cross ribbed beam. Through the economy, ease of handling in construction and other aspects of comparative analyses, the close beam side by epoxy grout and paste the carbon fiber under the beam to reinforce the cross ribbed beam. After reinforcement, no defect is discovered in the project so far.

An Improved Contact Model for Pounding Simulation of Base-isolated Highway Bridge

A modified Hertz model with nonlinear damping (Hertz damp model) is proposed for capturing the seismic pounding response of adjacent structures. Relevant parameters in the model are theoretically derived and numerically verified. Then, this model is used to simulate pounding response of a base-isolated highway bridge subjected to near fault ground motions. At the same time, nonlinear viscous dampers are installed between bridge decks for pounding prevention. The appropriate damping coefficient of the dampers can be found by parametric studies. It is shown that nonlinear viscous dampers are effective in reducing the relative displacement between bridge decks. At last, the hysteresis curve, the maximal damper force and stroke are used to demonstrate the behavior of nonlinear viscous dampers. The results indicate that satisfied viscous dampers can be produced to eliminate pounding according to the current manufacturing skills.

Experimental Research on Influence of Temperature on PZT-Based Health Monitoring for Smart Aggregates

Since piezoelectric materials exhibit strong temperature dependency. The change of temperature results in marked variation of the PZT transducer’s electric impedance signals, which may lead to misjudgment of the structural health condition. A experiment was implemented on smart aggregates with embedded PZT transducers under 35°C, 45°C and 55°C three working conditions, and found that the temperature had significant influence on the electric admittance signals of embedded PZT transducers. The peak magnitudes of the admittance curves changed and the curves shifted leftward. Then a temperature compensation technique was used to minimize the temperature effects.

Detection of Small Damage of Beam Structures Based on the Slope of Proper Orthogonal Mode

In recent two decades, the issues on structural damage detection and health monitoring have been paid considerable attention in mechanical and civil engineering communities. A lot of researchers have developed many methods to try to resolve the problems. To this day, detection of the small damage of structures, however, has still been a difficulty. The correlation theories of proper orthogonal decomposition (POD) and the basic principle of a new structural damage detection method based on the slope of POD are introduced in this paper. Numerical study on beam structures for small damage detection based on the proposed method is implemented. From the study results one can find that the method based on the slope of the difference of proper orthogonal modes (POMs) has the abilities to localize the small damage of beam structures.

Damage detection on the joint of steel frame through high-frequency admittance signals

The basic idea of a piezoelectric admittance (reciprocal of impedance) technique for structural health monitoring is presented in this paper. An experimental study on damage detection of a steel frame structure is operated by the use of the high-frequency piezoelectric admittance signals. In this experiment, three PZT active sensors are bonded to three different components around a joint of the steel frame separately, and the looseness of bolts is identified by monitoring the variations of piezoelectric admittance measurements. From the experimental results it is found that the PZT active sensors hold the ability to detect structural local damage, i.e. they are insensitive to the damage in far fields. Subsequently, two damage indexes, the covariance and the cross correlation coefficient between two real admittance data sets are defined respectively, by which the extent of damage of the frame structure is evaluated. It is found that the cross correlation coefficient index can correctly reflect the damage extent of the frame structure qualitatively in different frequency ranges, but the covariance index can not.