• Earthquakes and Structures
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• 제18권3호
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• pp.285-296
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• 2020

Dams are important structures for management of water supply for irrigation or drinking, flood control, and electricity generation. In seismic regions, the structural safety of concrete gravity dams is important due to the high potential of life and economic loss if they fail. Therefore, the seismic analysis of existing dams in seismically active regions is crucial for predicting responses of dams to ground motions. In this paper, earthquake response of concrete gravity dams is investigated using the finite element (FE) method. The FE model accounts for dam-water-foundation rock interaction by considering compressible water, flexible foundation effects, and absorptive reservoir bottom materials. Several uncertainties regarding structural attributes of the dam and external actions are considered to obtain the fragility curves of the dam-water-foundation rock system. The structural uncertainties are sampled using the Latin Hypercube Sampling method. The Pine Flat Dam in the Central Valley of Fresno County, California, is selected to demonstrate the methodology for several limit states. The fragility curves for base sliding, and excessive deformation limit states are obtained by performing non-linear time history analyses. Tensile cracking including the complex state of stress that occurs in dams was also considered. Normal, Log-Normal and Weibull distribution types are considered as possible fits for fragility curves. It was found that the effect of the minimum principal stress on tensile strength is insignificant. It is also found that the probability of failure of tensile cracking is higher than that for base sliding of the dam. Furthermore, the loss of reservoir control is unlikely for a moderate earthquake.

• Structural Engineering and Mechanics
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• 제51권4호
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• pp.663-683
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• 2014

In order to study the dynamic failure mechanism and aseismic measure for high concrete gravity dam under earthquake, the comparative models experiment on the shaking table was conducted to investigate the dynamic damage response of concrete gravity dam with and without the presence of reinforcement and evaluate the effectiveness of the strengthening measure. A new model concrete was proposed and applied for maintaining similitude with the prototype. A kind of extra fine wires as a substitute for rebar was embedded in four-points bending specimens of the model concrete to make of reinforced model concrete. The simulation of reinforcement concrete of the weak zones of high dam by the reinforced model concrete meets the similitude requirements. A tank filled with water is mounted at the upstream of the dam models to simulate the reservoir. The Peak Ground Acceleration (PGA) that induces the first tensile crack at the head of dam is applied as the basic index for estimating the overload capacity of high concrete dams. For the two model dams with and without strengthening tested, vulnerable parts of them are the necks near the crests. The results also indicate that the reinforcement is beneficial for improving the seismic-resistant capacity of the gravity dam.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.133-144
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• 2020

This investigation is to study the effect of gravitational field and diffusion on a microstretch thermoelastic medium heating by a non-Gaussian laser beam. The problem was studied in the context of the dual-phase-lag model. The normal mode analysis is used to solve the problem to obtain the exact expressions for the non-dimensional displacement components, the micro-rotation, the stresses, and the temperature distribution. The effect of time parameter, heat flux parameter and gravity response of three theories of thermoelasticity i.e. dual-phase-lag model (DPL), Lord and Shulman theory (L-S) and coupled theory (CT) on these quantities have been depicted graphically for a particular model.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.425-434
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• 2020

The present paper is concerned at investigating the effect of hydrostatic initial stress, gravity and magnetic field in fiber-reinforced thermoelastic solid, with variable thermal conductivity. The formulation of the problem applied in the context of the three-phase-lag model, Green-Naghdi theory with energy dissipation, as well as coupled theory. The exact expressions of the considered variables by using state-space approaches are obtained. Comparisons are performed in the absence and presence of the magnetic field as well as gravity. Also, a comparison was made in the three theories in the absence and presence of variable thermal conductivity as well as hydrostatic initial stress. The study finds applications in composite engineering, geology, seismology, control system and acoustics, exploration of valuable materials beneath the earth's surface.

• Structural Engineering and Mechanics
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• 제89권4호
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• pp.375-381
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• 2024

In this paper, Eringen's nonlocal thermoelasticity is constructed to study wave propagation in a rotating two-temperature thermoelastic half-space. The problem is applied in the context of the dual-phase-lag (Dual) model, coupled theory (CD), and Lord-Shulman (L-S) theory. Using suitable non-dimensional fields, the harmonic wave analysis is used to solve the problem. Comparisons are carried with the numerical values predicted in the absence and presence of the gravity field, a nonlocal parameter as well as rotation. The present study is valuable for the analysis of nonlocal thermoelastic problems under the influence of the gravity field, mechanical force, and rotation.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.481-497
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• 2010

The shaking table tests were conducted on two small-scale models (Model 1 and Model 2) to examine the earthquake-induced damage of a concrete gravity dam, which has been planned for the construction with the recommendation of the peak ground acceleration of the maximum credible earthquake of 0.42 g. This study deals with the numerical simulation of shaking table tests for two smallscale dam models. The plastic damage constitutive model is used to simulate the crack/damage behavior of the bentonite-concrete mixture material. The numerical results of the maximum failure acceleration and the crack/damage propagation are compared with experimental results. Numerical results of Model 1 showed similar crack/damage propagation pattern with experimental results, while for Model 2 the similar pattern was obtained by considering the modulus of elasticity of the first and second natural frequencies. The crack/damage initiated at the changing point in the downstream side and then propagated toward the upstream side. Crack/damage accumulation occurred in the neck area at acceleration amplitudes of around 0.55 g~0.60 g and 0.65 g~0.675 g for Model 1 and Model 2, respectively.

• Structural Engineering and Mechanics
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• 제35권3호
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• pp.365-377
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• 2010

In the present article, effect of non-uniform excitation due to spatially variation of seismic input on nonlinear response of concrete gravity dams is considered. The reservoir is assumed compressible. Isotropic damage mechanics approach is used to model static and dynamic nonlinear behavior of mass concrete in 2D space. The validity of utilized nonlinear model is considered using available theoretical results under static and dynamic conditions. The tallest monolith of Pine Flat dam is selected as a case study. Two cases are analyzed for considering the effect of limited wave propagation velocity on seismic behavior of the dam-reservoir system in which travelling velocities are chosen as 2000 m/s and infinity. It is found that tensile damage in neck and toe regions and also, in the vicinity of the base increase when the system is excited non-uniformly.

• Structural Engineering and Mechanics
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• 제48권1호
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• pp.17-39
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• 2013

In the present paper, a coaxial rotating smeared crack model is proposed for mass concrete in three-dimensional space. The model is capable of applying both the constant and variable shear transfer coefficients in the cracking process. The model considers an advanced yield function for concrete failure under both static and dynamic loadings and calculates cracking or crushing of concrete taking into account the fracture energy effects. The model was utilized on Koyna Dam using finite element technique. Dam-water and dam-foundation interactions were considered in dynamic analysis. The behavior of dam was studied for different shear transfer coefficients considering/neglecting fracture energy effects. The results were extracted at crest displacement and crack profile within the dam body. The results show the importance of both shear transfer coefficient and the fracture energy in seismic analysis of concrete dams under high hydrostatic pressure.

• Structural Engineering and Mechanics
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• 제21권2호
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• pp.137-150
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• 2005

Dynamic analysis of dam-reservoir-foundation system is usually carried out by employing a simplified and approximate one-dimensional model to account for fluid-foundation interaction. The approximation introduced on this basis is examined thoroughly in this paper by comparing the method with the rigorous approach. It is concluded that the errors due to approximate method could be very significant both for horizontal and vertical ground motions.

• Structural Engineering and Mechanics
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• 제56권2호
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• pp.169-188
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• 2015

There are two types of nonlinear analysis methods for building frameworks depending on the method of modeling the plastification of members including lumped plasticity and distributed plasticity. The lumped plasticity method assumes that plasticity is concentrated at a zero-length plastic hinge section at the ends of the elements. The distributed plasticity method discretizes the structural members into many line segments, and further subdivides the cross-section of each segment into a number of finite elements. When a reinforced concrete member experiences inelastic deformations, cracks tend to spread form the joint interface resulting in a curvature distribution. The program IDARC includes a spread plasticity formulation to capture the variation of the section flexibility, and combine them to determine the element stiffness matrix. In this formulation, the flexibility distribution in the structural elements is assumed to be the linear. The main objective of this study is to evaluate the accuracy of linear flexibility distribution assumed in the spread inelasticity model. For this purpose, nonlinear analysis of two reinforced concrete frames is carried out and the linear flexibility models used in the elements are compared with the real ones. It is shown that the linear flexibility distribution is incorrect assumption in cases of significant gravity load effects and can be lead to incorrect nonlinear responses in some situations.