Auto-parametric resonance of a continuous-beam-bridge model under two-point periodic excitation:an experimental investigation and stability analysis

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study.An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns.The parametric vibration equation is established for the test model using the finite-element method.The auto-parametric resonance stability of the structure is analyzed by using Newmark's method and the energy-growth exponent method.The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model.Compared with the experiment,the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena,and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones.For a continuous beam bridge,when the ratio of multipoint excitation frequency(applied to the columns)to natural frequency of the continuous girder is approximately equal to 2,the continuous beam may undergo a strong auto-parametric resonance.Combined with the present experiment and analysis,a hypothesis of Volgograd Bridge's serpentine vibration is discussed.

Assessment of composite failure and ultimate strength without experiment on composite

This paper attempts to estimate the ultimate strength of a laminated composite only based on its con- stituent properties measured independently. Three important issues involved have been systematically addressed, i.e., stress calculation for the constituent fiber and matrix materials, failure detection for the lamina and laminate upon the internal stresses in their constituents, and input data determination of the constituents from monolithic measurements. There are three important factors to influence the accuracy of the strength prediction. One is the stress concentration factor （SCF） in the matrix. Another is matrix plasticity. The third is thermal residual stresses in the constituents. It is these three factors, however, that have not been sufficiently well realized in the composite community. One can easily find out the elastic and strength parameters of a great many laminae and laminates in the current literature. Unfortunately, necessary information to determine the SCF, the matrix plasticity, and the thermal residual stresses of the composites is rare or incomplete. A useful design methodology is demonstrated in the paper.

BRIDGING TOUGHENING OF EPOXY RESINS BY DISPERSED THERMOPLASTICS

The particulate toughening behaviour of epoxy resins modified by ductile thermoplastics is elucidated here by various bridging models. The experimental data for three different epoxy/PSF sys- tems are presented to illustrate the trend of the toughening characteristics. The conventional continuous bridging model is shown to have underestimated the effect of the particulate toughening. A joint appli- cation of the discrete bridging model and the multiple bridging model, however, shows promising result for modified epoxy systems such as AG80/DDS/PSF and E51/DDS/PSF. These models also provide quantitative descriptions for the crack pinning phenomenon previously observed by Fu and Sun in AG80/DDS/PSF.

Prediction of three-dimensional elastic behavior of filament-wound composites based on the bridging model

This work provides a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle.In the meso-scale,a representative volume element(RVE)is defined and the bridging model is adopted to establish a theoretical predictive model for its three-dimensional equivalent elastic constants.The results obtained through this method for the previous experimental model are compared with the ones gained respectively by experiments and classical laminate theory to verify the reliability of this model.In addition,the effects of some winding parameters,such as winding angle,on the equivalent elastic behavior of the filament-wound composites are analyzed.The rules gained can provide a theoretical reference for the optimum design of filament-wound composites.

Self-contained eigenvector algorithm applied to the identification of aerodynamic derivatives of bridge model

On one hand, when the bridge stays in a windy environment, the aerodynamic power would reduce it to act as a non-classic system. Consequently, the transposition of the system’s right eigenmatrix will not equal its left eigenmatrix any longer. On the other hand, eigenmatrix plays an important role in model identification, which is the basis of the identification of aerodynamic derivatives. In this study, we follow Scanlan’s simple bridge model and utilize the information provided by the left and right eigenmatrixes to structure a self-contained eigenvector algorithm in the frequency domain. For the purpose of fitting more accurate transfer function, the study adopts the combined sine-wave stimulation method in the numerical simulation. And from the simulation results, we can conclude that the derivatives identified by the self-contained eigenvector algorithm are more dependable.

Finite element model validation of bridge based on structural health monitoring——Part Ⅱ:Uncertainty propagation and model validation

Because of uncertainties involved in modeling, construction, and measurement systems, the assessment of the FE model validation must be conducted based on stochastic mea- surements to provide designers with confidence for further applications. In this study, based on the updated model using response surface methodology, a practical model vali- dation methodology via uncertainty propagation is presented. Several criteria of testing/ analysis correlation are introduced, and the sources of model and testing uncertainties are also discussed. After that, Monte Carlo stochastic finite element （FE） method is employed to perform the uncertainty quantification and propagation. The proposed methodology is illustrated with the examination of the validity of a large-span prestressed concrete continuous rigid frame bridge monitored under operational conditions. It can be concluded that the calculated frequencies and vibration modes of the updated FE model of Xiabaishi Bridge are consistent with the measured ones. The relative errors of each frequency are all less than 3.7%. Meanwhile, the overlap ratio indexes of each frequency are all more than 75%; The MAC values of each calculated vibration frequency are all more than 90%. The model of Xiabaishi Bridge is valid in the whole operation space including experimental design space, and its confidence level is upper than 95%. The validated FE model of Xia- baishi Bridge can reflect the current condition of Xiabaishi Bridge, and also can be used as basis of bridge health monitoring, damage identification and safety assessment.

Analytical method of dynamic properties of FRP based on micromechanical level

Abstract A mathematic model is proposed for predicting the dynamic properties of fiber reinforced plastic composites （FRP） with interphase. Dynamic properties mainly include loss factors and elastic moduli. The results of elastic moduli fi＇om the present model are compared with other models. Elastic moduli Ell, E22, G12, G23 and loss factors ηll, η22, ηl2 and η23 of FRP are calculated and a study of the effect of elastic modulus Ej and loss factor rh ofinterphase on dynamic properties in FRP is carried out here. In this paper, E11 linearly increases with El, but the growth rate is slow. E22, G12, G23 increase rapidly for lower value of EI. The longitudinal loss factor E1 decreases with the increase of El in the case of rh 〈 0.0026. But η11 linearly increases with E1 in larger range of η1, η1 〉 0.0026. On the contrary, transverse loss factor η22, transverse shear loss factors r/23 and longitudinal shear loss factors η12 increase with increase of E1 in the case of lower value of η1, but decreases at larger value of ηl. And they also show insensitivity to E1 at higher value.

Damage Analysis of Superconducting Composite Wire with Bridging Model

The multi-filamentary Bi2Sr2CaCu2O8＋x （Bi-2212） round wires are made of super- conducting filaments, metal Ag and Ag alloy, which are typical composite structure. Since the filament is brittle, there are various defects and cracks in the Bi-2212 round wire after heat treat- ment. In this paper, we assume that the filaments in the wire are uniformly arranged. Adopting the bridging model which is often used in the fiber-reinforced composite, we calculate the ulti- mate strength of the round wire. The effects of the volume fraction, elastic modulus and interface shear strength are discussed in detail.