• Earthquakes and Structures
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• 제25권2호
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• pp.125-134
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• 2023

In the present work, a new global damage index is proposed for the seismic performance and failure analysis of concrete gravity dams. Unlike the existing indices of concrete structures, this index doesn't need scaling with an ultimate or an upper value. For this purpose, the Beni-Haroun dam in north-eastern Algeria, is considered as a case study, for which an average seismic capacity curve is first evaluated by performing several incremental dynamic analyses. The seismic performance point of the dam is then determined using the N2 method, considering multiple modes and taking into account the stiffness degradation. The seismic demand is obtained from the design spectrum of the Algerian seismic regulations. A series of recorded and artificial accelerograms are used as dynamic loads to evaluate the nonlinear responses of the dam. The nonlinear behaviour of the concrete mass is modelled by using continuum damage mechanics, where material damage is represented by a scalar field damage variable. This modelling, which is suitable for cyclic loading, uses only a single damage parameter to describe the stiffness degradation of the concrete. The hydrodynamic and the sediment pressures are included in the analyses. The obtained results show that the proposed damage index faithfully describes the successive brittle failures of the dam which increase with increasing applied ground accelerations. It is found that minor damage can occur for ground accelerations less than 0.3 g, and complete failure can be caused by accelerations greater than 0.45 g.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.451-462
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• 2023

Lumped Damage Mechanics (LDM) is a theory proposed in the late eighties, which assumes that structural collapse may be analyzed as a two-phase phenomenon. In the first (pre-localization) stage, energy dissipation is a continuous process and it may be modelled by means of the classic versions of the theory of plasticity or Continuum Damage Mechanics (CDM). The second, post-localization, phase can be modelled assuming that energy dissipation is lumped in zones of zero volume: inelastic hinges, hinge lines or localization surfaces. This paper proposes a new LDM formulation for cracking in concrete structures in tension. It also describes its numerical implementation in conventional finite element programs. The results of three numerical simulations of experimental tests reported in the literature are presented. They correspond to plain and fiber-reinforced concrete specimens. A fourth simulation describes also the experimental results of a new test using the digital image correlation technique. These numerical simulations are also compared with the ones obtained using conventional Cohesive Fracture Mechanics (CFM). It is then shown that LDM conserves the advantages of both, CDM and CFM, while overcoming their drawbacks.

• Coupled systems mechanics
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• 제12권2호
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• pp.183-197
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• 2023

Scarce research has been published on crack propagation fracture of flywheels manufactured with carbon fiber-reinforced polymers. The present work deals with a calculation method to determine the conditions for which a crack propagates in the axial direction of the flywheel. The assumptions are: flywheels made with just a single thick ply or ply clustering laminates, oriented following the hoop direction; a single crack is analyzed in the plane defined by the hoop and axial directions; the crack starts close to one of the free edges; its axial length is initially large enough so that its tip is far away from that free edge, and the crack expands the entire circumferential perimeter and keeps its concentric position. The developed method provides information for a good design of flywheels. It is concluded that a fracture-based crack propagation criterion generally occurs at a lower speed than a stress-based criterion. Also, that the evolution of failure with thickness using the fracture criterion is exponential, demonstrating that thin flywheels are relatively not sensitive to crack propagation, whereas thick ones are very prone.

• Structural Engineering and Mechanics
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• 제90권2호
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• pp.209-218
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• 2024

The present paper is focused on the study of the propagation of plane waves in thermoelastic media under a modified Green-Lindsay (MG-L) model having the influence of non-local and two temperature. The problem is formulated for the considered model in dimensionless form and is explained by using the reflection phenomenon. The plane wave solution of these equations indicates the existence of three waves namely Longitudinal waves (LD-Wave), Thermal waves (T-wave), and Shear waves (SV-wave) from a stress-free surface. The variation of amplitude ratios is computed analytically and depicted graphically against the angle of incidence to elaborate the impact of non-local, two temperature, and different theories of thermoelasticity. Some particular cases of interest are also deduced from the present investigation. The present study finds applications in a wide range of problems in engineering and sciences, control theory, vibration mechanics, and continuum mechanics.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1586-1596
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• 2005

In this paper, a structural damage identification method (SDIM) is developed to identify the line crack-like directional damages generated within a cylindrical shell. First, the equations of motion for a damaged cylindrical shell are derived. Based on a theory of continuum damage mechanics, a small material volume containing a directional damage is represented by the effective orthotropic elastic stiffness, which is dependent of the size and the orientation of the damage with respect to the global coordinates. The present SDIM is then derived from the frequency response function (FRF) directly solved from the equations of motion of a damaged shell. In contrast with most existing SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM may require only the FRF-data measured at damaged state. By virtue of utilizing FRF-data, one may choose as many sets of excitation frequency and FRF measurement point as needed to acquire a sufficient number of equations for damage identification analysis. The numerically simulated damage identification tests are conducted to study the feasibility of the present SDIM.

• Coupled systems mechanics
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• 제2권4호
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• pp.375-387
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• 2013

Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot's basic theory of dynamics of saturated porous media with u-P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor-Zienkiewicz-Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.

• Smart Structures and Systems
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• 제21권1호
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• pp.65-74
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• 2018

In this article, an analytic non-classical model for the free vibrations of nanobeams accounting for surface stress effects is developed. The classical continuum mechanics fails to capture the surface energy effects and hence is not directly applicable at nanoscale. A general beam model based on Gurtin-Murdoch continuum surface elasticity theory is developed for the analysis of thin and thick beams. Thus, surface energy has a significant effect on the response of nanoscale structures, and is associated with their size-dependent behavior. To check the validity of the present analytic solution, the numerical results are compared with those obtained in the scientific literature. The influences of beam thickness, surface density, surface residual stress and surface elastic constants on the natural frequencies of nanobeams are also investigated. It is indicated that the effect of surface stress on the vibrational response of a nanobeam is dependent on its aspect ratio and thickness.

• Structural Engineering and Mechanics
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• 제30권2호
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• pp.135-146
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• 2008

This study utilizes the fine-tuning and small-digit characteristics of the successive zooming genetic algorithm (SZGA) to propose a method of structural damage detection in a continuum structure, where the differences in the natural frequencies of a structure obtained by experiment and FEM are compared and minimized using an assumed location and extent of structural damage. The final methodology applied to the structural damage detection is a kind of pseudo-discrete-variable-algorithm that counts the soundness variables as one (perfectly sound) if they are above a certain standard, such as 0.99. This methodology is based on the fact that most well-designed structures exhibit failures at some critical point due to manufacturing error, while the remaining region is free of damage. Thus, damage of 1% (depending on the given standard) or less can be neglected, and the search concentrated on finding more serious failures. It is shown that the proposed method can find out the exact structural damage of the monitored structure and reduce the time and amount of computation.

• 터널과지하공간
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• 제16권5호
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• pp.394-404
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• 2006

암반구조물의 동적 거동은 구조물이 위치하는 동적 물성과 입력지진파의 특성에 따라 크게 다르며, 절리군이 발달한 암반은 블록의 역학적인 특성과 함께 불연속면의 구조적, 역학적 특성에 따라 다르다. 본 연구에서는 불연속체 해석 기법인 UDEC을 이용하여 지하구조물 주변에 발달한 불연속체의 구조적인 특징에 따라 변화하는 암반의 동적 거동을 평가하고, 이를 연속체 해석 기법인 $FLAC^{2D}$의 결과와 비교를 통해 절리 암반의 지진에 대한 동적 거동의 타당성을 비교 검토하였다. 그 결과, 불연속체가 고려된 해석 결과는 절리의 거동에 의한 영향으로 구조적인 형상에 따른 변화가 나타났으며, 연속체 해석 결과는 불연속체 해석 결과에 비해 과다 평가되는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.939-957
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• 2015

In this paper, a new approach based on the continuum model is proposed to estimate the main cable tension force of suspension bridges from measured natural frequencies. This approach considered the vertical vibration of a main cable hinged at both towers and supported by an elastic girder and hangers along its entire length. The equation reflected the relationship between vibration frequency and horizontal tension force of a main cable was derived. To avoid to generate the additional cable tension force by sag-extensibility, the analytical solution of characteristic equation for anti-symmetrical vibration mode of the main cable was calculated. Then, the estimation of main cable tension force was carried out by anti-symmetric characteristic frequency vector. The errors of estimation due to characteristic frequency deviations were investigated through numerical analysis of the main cable of Taizhou Bridge. A field experiment was conducted to verify the proposed approach. Through measuring and analyzing the responses of a main cable of Taizhou Bridge under ambient excitation, the horizontal tension force of the main cable was identified from the first three odd frequencies. It is shown that the estimated results agree well with the designed values. The proposed approach can be used to conduct the long-term health monitoring of suspension bridges.