• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.714-719
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• 2000

The analysis of structures may be classified into three categories: theoretical, numerical, and experimental approaches. The numerical and experimental methods are very useful when the structures to be analyzed have complicated shapes or geometry because theoretical methods are restricted to simple and special cases. However, the theoretical methods are very important analysis in the viewpoint that they can give basic insight for the structural behavior. Among them the modal model method is widely used because of the powerful propertiy of eigenfunctions(mode shapes), or orthogonality. In this paper, the modal model method was reviewed and studied for various models for structures: string, beam, membrane, and plate. Governing equations and solution methods were compared and a structural-acoustic coupling system was used for an application.

• Steel and Composite Structures
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• v.8 no.6
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• pp.457-473
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• 2008

Yielding of the internal steel reinforcement is an important mechanism that influences the Intermediate Crack-induced debonding (IC debonding) behavior in FRP-strengthened RC members since the FRP is required to carry additional forces beyond the condition of steel yielding. However, rational design practice dictates an appropriate limit state is defined when steel yielding is assured prior to FRP debonding. This paper proposes a criterion which correlates the occurrence of IC debonding to the formulation of a critical steel yielding length. Once this length is exceeded the average bond stress in the FRP/concrete interface exceeds its threshold value, which proves to correlate with the average bond resistance in an FRP/concrete joint under simple shear loading. This proposed IC debonding concept is based on traditional sections analysis which is conventionally applied in design practice. Hence complex bond stress-slip analyses are avoided. Furthermore, the proposed model incorporates not only the bond properties of FRP/concrete interface but also the beam geometry, and properties of steel and FRP reinforcement in the analysis of IC debonding strength. Based upon a solid database, the validity of the proposed simple IC debonding criterion is demonstrated.

• Smart Structures and Systems
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• v.4 no.5
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• pp.605-628
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• 2008

In bridge structures, damage may induce an additional deflection which may naturally contain essential information about the damage. However, inverse mapping from the damage-induced deflection to the actual damage location and severity is generally complex, particularly for statically indeterminate systems. In this paper, a new load concept, called the positive-bending-inspection-load (PBIL) is proposed to construct a simple inverse mapping from the damage-induced deflection to the actual damage location. A PBIL for an inspection region is defined as a load or a system of loads which guarantees the bending moment to be positive in the inspection region. From the theoretical investigations, it was proven that the damage-induced chord-wise deflection (DI-CD) has the maximum value with the abrupt change in its slope at the damage location under a PBIL. Hence, a novel damage localization method is proposed based on the DI-CD under a PBIL. The procedure may be summarized as: (1) identification of the modal flexibility matrices from acceleration measurements, (2) design for a PBIL for an inspection region of interest in a structure, (3) calculation of the chord-wise deflections for the PBIL using the modal flexibility matrices, and (4) damage localization by finding the location with the maximum DI-CD with the abrupt change in its slope within the inspection region. Procedures from (2)-(4) can be repeated for several inspection regions to cover the whole structure complementarily. Numerical verification studies were carried out on a simply supported beam and a three-span continuous beam model. Experimental verification study was also carried out on a two-span continuous beam structure with a steel box-girder. It was found that the proposed method can identify the damage existence and damage location for small damage cases with narrow cuts at the bottom flange.

• Steel and Composite Structures
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• v.39 no.2
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• pp.215-228
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• 2021

This paper investigates the effect of micromechanical models on the bending behavior of bidirectional functionally graded (BDFG) beams subjected to different mechanical loading. The material properties of the beam are considered to be graded in both axial and thickness directions according to a power law. The beam's behavior is modeled by the mean of quasi 3D displacement field that contain undetermined integral terms and involves a reduced unknown functions. Navier's method is employed to determine and compute the displacements and stress for a simply supported beam. Different homogenization schemes such as Voigt, Reus, and Mori-Tanaka are employed to analyze the response of the BDFG beam subjected to linear, uniform, exponential and sinusoidal distributed loading. The results obtained by the present method are compared with available results in the literature and a good agreement was found. Several numerical results are presented in tabular form and in figures to examine the effects of the material gradation, micromechanical models and types of loading on the bending response of BDFG beams. It can be concluded that the present theory is not only accurate but also simple in predicting the bending response of BDFG beam subjected to different static loads.

• Steel and Composite Structures
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• v.33 no.3
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• pp.463-472
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• 2019

Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

• Journal of the Korean Society of Safety
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• v.25 no.2
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• pp.47-54
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• 2010

This paper presents a simple and efficient two-dimensional rigid-body-spring network model able to accurately estimate the fractural behavior of civil fiber reinforced pavements. The proposed rigid-body-spring network model, denoted as RBSN model, considers civil fiber reinforcing materials using the beam elements and link spring elements. The RBSN method is able to model collapse due to asphalt crushing and civil fiber slip. The RBSN model is used to predict the applied load-midspan deflection response of civil fiber retrofitted asphalt specimen subjected to the three-point bending. Numerical simulations and experimental measurements are compared to based on tests available in the literature. The numerically simulated responses agree significantly with the corresponding experimental results until the maximum load. However, It should be mentioned that, in order to more accurately predict the postpeak flexural behavior of the civil fiber retrofitted asphalt pavement, development of the advanced model to simulate the slip relationship between civil fiber and asphalt is required.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.3
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• pp.292-298
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• 2015

A wiper is a safety device removing rain and debris from windshield and ensuring visibility of drivers. If contact pressure distribution between rubber of the blade and the windshield is unbalanced, unwanted noise, vibration, and abrasion of the blade can occur and sometimes fatal accidents could occur. To improve the safety of the wiper, there have been many researches on the contact pressure analysis of the wiper, but the analysis results were not converged or require much computational time due to material nonlinearity of the rubber and contact conditions between the blade rubber and the windshield. In this research, a simple model with 1D beam and 2D shell elements was used for the contact pressure analysis instead of the 3D blade model. The simplified model saved computational time of the analysis and resolved convergence problems. The accuracy of the analysis results was verified by comparing them with experimental results for different rail spring curvatures.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.499-508
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• 2002

A simple design method for rib-reinforced seismic steel moment connections has been recently proposed based on the equivalent strut model. An experimental program was implemented to verify the proposed design method, as well as develop the schemes that will prevent cracking at the rib tip where stress concentration was evident. All specimens designed using the proposed method were able to develop a satisfactory connection plastic rotation of 0.04 radian. In addition to rib reinforcement, slight beam flange trimming pushed the plastic hinging and local buckling of the beam away from the rip tip and effectively reduced cracking potential at the rib tip. Using strain gage readings, the strut action of the rib and resulting reverse shear in the beam web were also experimentally identified.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.149-162
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• 2011

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.291-309
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• 2023

This paper addresses the finite element modeling of functionally graded porous (FGP) beams for free vibration and buckling behaviour cases. The formulated finite element is based on simple and efficient higher order shear deformation theory. The key feature of this formulation is that it deals with Euler-Bernoulli beam theory with only three unknowns without requiring any shear correction factor. In fact, the presented two-noded beam element has three degrees of freedom per node, and the discrete model guarantees the interelement continuity by using both C⁰ and C¹ continuities for the displacement field and its first derivative shape functions, respectively. The weak form of the governing equations is obtained from the Hamilton principle of FGP beams to generate the elementary stiffness, geometric, and mass matrices. By deploying the isoparametric coordinate system, the derived elementary matrices are computed using the Gauss quadrature rule. To overcome the shear-locking phenomenon, the reduced integration technique is used for the shear strain energy. Furthermore, the effect of porosity distribution patterns on the free vibration and buckling behaviours of porous functionally graded beams in various parameters is investigated. The obtained results extend and improve those predicted previously by alternative existing theories, in which significant parameters such as material distribution, geometrical configuration, boundary conditions, and porosity distributions are considered and discussed in detailed numerical comparisons. Determining the impacts of these parameters on natural frequencies and critical buckling loads play an essential role in the manufacturing process of such materials and their related mechanical modeling in aerospace, nuclear, civil, and other structures.