Weichung Yeih

Applications of dual MRM for determining the natural frequencies and natural modes of an Euler–Bernoulli beam using the singular value decomposition method

In this paper, a dual multiple reciprocity method (MRM) is employed to solve the natural frequencies and natural modes for an Euler‐ Bernoulli beam. It is found that the conventional MRM using an essential integral equation results in spurious eigenvalues and modes. By using the natural integral equation of dual MRM, the spurious eigendata can be filtered out. Four numerical examples are given to verify the validity of the present formulation. In one of these four examples, fixed‐fixed supported beam, it is found that the boundary eigenvector cannot be determined by either the essential or natural integral equation alone since the rank of the corresponding leading coefficient matrix is insufficient. The singular value decomposition method is then used to solve the eigenproblem after combining the essential and natural integral equations. This method can avoid the spurious eigenvalue problem and possible indeterminancy of boundary eigenvectors at the same time. q 1999 Elsevier Science Ltd. All rights reserved.

Detection of the corrosion damage in reinforced concrete members by ultrasonic testing

In this study, the amplitude attenuation method in ultrasonic testing was used to evaluate the corrosion damage of reinforced concrete members. It is found that the amplitude attenuation method has good performance in corrosion detection for reinforced concrete members. There exists a consistent relationship between the average amplitude attenuation and the electrochemical parameters such as open circuit potential values, the instantaneous corrosion rate, and thickness loss.

Generalized finite difference method for solving two-dimensional inverse Cauchy problems

In this paper, a meshless numerical scheme is adopted for solving two-dimensional inverse Cauchy problems which are governed by second-order linear partial differential equations. In Cauchy problems, over-specified boundary conditions are imposed on portions of the boundary while on parts of boundary no boundary conditions are imposed. The application of conventional numerical methods to Cauchy problems yields highly ill-conditioned matrices. Hence, small noise added in the boundary conditions will tremendously enlarge the computational errors. The generalized finite difference method (GFDM), which is a newly developed domain-type meshless method, is adopted to solve in a stable manner the two-dimensional Cauchy problems. The GFDM can overcome time-consuming mesh generation and numerical quadrature. Besides, Cauchy problems can be solved stably and accurately by the GFDM. We present three numerical examples to validate the accuracy and the simplicity of the meshless scheme. In addition, different levels of noise are added into the boundary conditions to verify the stability of the proposed method.

Dual boundary element analysis for cracked bars under torsion

A dual integral formulation for a cracked bar under torsion is derived, and a dual boundary element method is implemented. It is shown that as the thickness of the crack becomes thinner, the ill‐posedness for the linear algebraic matrix becomes more serious if the conventional BEM is used. Numerical experiments for solution instability due to ill‐posedness are shown. To deal with this difficulty, the hypersingular equation of the dual boundary integral formulation is employed to obtain an independent constraint equation for the boundary unknowns. For the sake of computational efficiency, the area integral for the torsion rigidity is transformed into two boundary integrals by using Green’s second identity and divergence theorem. Finally, the torsion rigidities for cracks with different lengths and orientations are solved by using the dual BEM, and the results compare well with the analytical solutions and FEM results.

A pullout test for determining interface properties between rebar and concrete

In this study, the rebar-concrete interface properties were investigated by conducting the single rebar pullout test. Using a combination of the stress approach and fracture mechanical theory, the corresponding material parameters were obtained and the model was verified as being suitable for reinforced concrete composite material. Advanced Cement Based Materials 1997, 5, 57–65.

Applications of dual MRM for determining the natural frequencies and natural modes of a rod using the singular value decomposition method

Abstract In this article, the dual multiple reciprocity method is employed to solve the natural frequencies and natural modes for a rod. The conventional approach using dual MRM is not qualified as a systematic method because of the following two reasons: (1) it needs to distinguish the spurious eigenvalue only after the corresponding eigenmode is obtained; (2) the possible indeterminancy of eigenvector may be encountered when the constraint equations chosen are highly dependent such that the rank of the leading coefficient matrix is insufficient. To construct a systematic way, we propose to consider all constraint equations together instead of using the singular or hypersingular equation alone as the conventional MRM uses. The singular value decomposition method is, then, used to solve the eigenproblem after combining the singular and hypersingular equations. This method can avoid the spurious eigenvalue problem and the possible indeterminancy of boundary eigenvectors at the same time. Three numerical examples are given to verify the validity of the present method.

Applications of the direct Trefftz boundary element method to the free-vibration problem of a membrane

In this paper, the direct Trefftz method is applied to solve the free-vibration problem of a membrane. In the direct Trefftz method, there exists no spurious eigenvalue. However, an ill-posed nature of numerical instability encountered in the direct Trefftz method requires some treatments. The Tikhonovs regularization method and generalized singular-value decomposition method are used to deal with such an ill-posed problem. Numerical results show the validity of the current approach.

Enhancement of bond strength for epoxy-coated rebar using river sand

Abstract In this paper, improvement of bond strength for epoxy-coated rebars is studied. Although the epoxy-coated rebar is well accepted as an alternative corrosion prevention method in engineering practice, it still suffers from its poor bond performance, which requires modification of design parameters such as development length and splice length. Following our previous study [Proceedings of the Third Structure Engineering Conference (1996) 651–659], it is proposed to mix the river sand in the epoxy to improve the bond strength of epoxy-coated rebar. Specimens of several sizes of river sand and sand/epoxy weight ratios were studied. The single-rebar pullout test was performed to examine the bond strength. The open circuit potential method and the linear DC polarization method were conducted for corrosion rate measurements to ensure for keeping the merit of epoxy-coated rebar, i.e. the ability of corrosion. Experimental results show that the proposed method is very promising.

MECHANICAL PROPERTIES OF CARBONATED CONCRETE

Abstract In this paper, mechanical properties of carbonated concrete were studied. Com‐pressive strength, splitting tensile strength, elastic modulus, bond strength and hardness for carbonated concrete subjected to various carbonation conditions were evaluated. Experimental results indicated that all these mechanical properties showed a higher value after carbonation. Especially the bond strength for fully carbonated concrete was about 1.7 that for uncarbonated concrete. Hardness experiments showed that concrete 0.5 cm deeper than the carbonation depth, measured by the method of RILEM CPC‐18, had a hardening effect due to carbonation products. It was found that enhancement of compressive strength was more significant if the carbonation and the loading directions were orthogonal. SEM photos showed that limestone was formed after carbonation, which is the main reason for changes in mechanical properties.

The Influence of Aggregate Size and Binder Material on the Properties of Pervious Concrete

Specimens were prepared by altering parameters such as aggregate sizes, binder materials, and the amounts of binder used and were subsequently tested by using permeability, porosity, mechanical strength, and soundness tests. The results indicated that the water permeability coefficient and connected porosity decreased as the amount of binder used increased and increased with increasing aggregate size. In the mechanical strength test, the compressive, splitting tensile, and flexural strengths increased as the amount of binder used increased and decreased with the increase of aggregate size. Highly viscous binder enhanced compressive strength, water permeability, and the resistance to sulfate attacks. In the mechanics and sulfate soundness tests, the mix proportion of alkali-activated slag paste used in this study exhibited a superior performance than the Portland cement pervious concrete (the control) did, but the difference in water permeability between the two types of concrete was insignificant. The mix proportions of cement paste containing 20% and 30% silica fume exhibited less mechanical strength than the control did. Moreover, compared with the control, the cement paste containing silica fume demonstrated poor resistance to sulfate attacks, and the difference in the water permeability between such specimen and the control was not noticeable.