• Structural Engineering and Mechanics
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• v.40 no.1
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• pp.29-48
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• 2011

Under large storm loads sections of a long pipeline on the seabed can be uplifted. Numerically this loss of contact is extremely difficult to simulate, but accounting for uplift and any subsequent recontact behaviour is a critical component in pipeline on-bottom stability analysis. A simple method numerically accounting for this uplift and reattachment, while utilising efficient force-resultant models, is provided in this paper. While force-resultant models use a plasticity framework to directly relate the resultant forces on a segment of pipe to the corresponding displacement, their historical development has concentrated on precisely modelling increasing capacity with penetration. In this paper, the emphasis is placed on the description of loss of penetration during uplifting, modelled by 'strain-softening' of the force-resultant yield surface. The proposed method employs uplift and reattachment criteria to determine the pipe uplift and recontact. The pipe node is allowed to become free, and therefore, the resistance to the applied hydrodynamic loads to be redistributed along the pipeline. Without these criteria, a localised failure will be produced and the numerical program will terminate due to singular stiffness matrix. The proposed approach is verified with geotechnical centrifuge results. To further demonstrate the practicability of the proposed method, a computational example of a 1245 m long pipeline subjected to a large storm in conditions typical of offshore North-West Australia is discussed.

• Earthquakes and Structures
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• v.16 no.1
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• pp.41-54
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• 2019

Reinforced Concrete (RC) shear walls are widely used in Nuclear power plants as effective lateral force resisting elements of the structure and these may experience nonlinear behavior for higher earthquake demand. Short shear walls of aspect ratio less than 1.5 generally experience combined shear flexure interaction. This paper presents the results of the displacement-controlled experiments performed on six RC short shear walls with varying aspect ratios (1, 1.25 and 1.5) for monotonic and reversed quasi-static cyclic loading. Simulation of the shear walls is then carried out by Finite element modeling and also by macro modeling considering the coupled shear and flexure behaviour. The shear response is estimated by softened truss theory using the concrete model given by Vecchio and Collins (1994) with a modification in softening part of the model and flexure response is estimated using moment curvature relationship. The accuracy of modeling is validated by comparing the simulated response with experimental one. Moreover, based on the experimental work a multi-linear hysteretic model is proposed for short shear walls. Finally ultimate load, drift, ductility, stiffness reduction and failure pattern of the shear walls are studied in details and hysteretic energy dissipation along with damage index are evaluated.

• Steel and Composite Structures
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• v.48 no.3
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• pp.335-351
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• 2023

This research studies the primary resonance and nonlinear vibratory responses of multilayer functionally graded shallow (MFGS) shells under external excitations. The shells considered with functionally graded porous (FGP) core and resting on two types of nonlinear viscoelastic foundations (NVEF) governed by either a linear model with two parameters of Winkler and Pasternak foundations or a nonlinear model of hardening/softening cubic stiffness augmented by a Kelvin-Voigt viscoelastic model. The shells considered have three layers, sandwiched by functionally graded (FG), FGP, and FG materials. To investigate the influence of various porosity distributions, two types of FGP middle layer cores are considered. With the first-order shear deformation theory (FSDT), Hooke's law, and von-Kármán equation, the stress-strain relations for the MFGS shells with FGP core are developed. The governing equations of the shells are consequently derived. For the sake of higher accuracy and reliability, the P-T method is implemented in numerically analyzing the vibration, and the method of multiple scales (MMS) as one of the perturbation methods is used to investigate the primary resonance. The results of the present research are verified with the results available in the literature. The analytical results are compared with the P-T method. The influences of material, geometry, and nonlinear viscoelastic foundation parameters on the responses of the shells are illustrated.

• Advances in nano research
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• v.16 no.2
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• pp.187-200
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• 2024

This study focuses on wave propagation analysis in the curved nanobeam exposed to different thermal loadings based on the Nonlocal Strain Gradient Theory (NSGT). Mechanical properties of the constitutive materials are assumed to be temperature-dependent and functionally graded. For modeling, the governing equations are derived using Hamilton's principle. Using the proposed model, the effects of small-scale, geometrical, and thermo-mechanical parameters on the dynamic behavior of the curved nanobeam are studied. A small-scale parameter, Z, is taken into account that collectively represents the strain gradient and the nonlocal parameters. When Z<1 or Z>1, the phase velocity decreases/increases, and the stiffness-softening/hardening phenomenon occurs in the curved nanobeam. Accordingly, the phase velocity depends more on the strain gradient parameter rather than the nonlocal parameter. As the arc angle increases, more variations in the phase velocity emerge in small wavenumbers. Furthermore, an increase of ∆T causes a decrease in the phase velocity, mostly in the case of uniform temperature rise rather than heat conduction. For verification, the results are compared with those available for the straight nanobeam in the previous studies. It is believed that the findings will be helpful for different applications of curved nanostructures used in nano-devices.

• Structural Engineering and Mechanics
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• v.73 no.2
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• pp.191-207
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• 2020

This study aims at investigating the size-dependent free vibration of porous nanoplates when exposed to hygrothermal environment and rested on Kerr foundation. Based on the modified power-law model, material properties of porous functionally graded (FG) nanoplates are supposed to change continuously along the thickness direction. The generalized nonlocal strain gradient elasticity theory incorporating three scale factors (i.e. lower- and higher-order nonlocal parameters, strain gradient length scale parameter), is employed to expand the assumption of second shear deformation theory (SSDT) for considering the small size effect on plates. The governing equations are obtained based on Hamilton's principle and then the equations are solved using an analytical method. The elastic Kerr foundation, as a highly effected foundation type, is adopted to capture the foundation effects. Three different patterns of porosity (namely, even, uneven and logarithmic-uneven porosities) are also considered to fill some gaps of porosity impact. A comparative study is given by using various structural models to show the effect of material composition, porosity distribution, temperature and moisture differences, size dependency and elastic Kerr foundation on the size-dependent free vibration of porous nanoplates. Results show a significant change in higher-order frequencies due to small scale parameters, which could be due to the size effect mechanisms. Furthermore, Porosities inside of the material properties often present a stiffness softening effect on the vibration frequency of FG nanoplates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.2
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• pp.55-64
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• 1984

Presented is a nonlinear constitutive model for progressive tensile fracturing of concrete. The model is incremental, path-dependent, and tensorialy invariant. The total strain tensor is assumed to be a sum of a purely elastic component and an inelastic component. The material is considered to contain weak planes of all directions which characterize the planes of the microcracks. A one-to-one functional dependence is assumed between the normal stress and the normal strain across each of the weak planes. The tangential stiffness of concrete is then derived form the principle of virtual work. The present theory can be applied to loading histories which are nonproportional or during which the principal directions rotate. Good agreement with the available direct tensile test data which cover strain-softening is demonstrated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.4 s.70
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• pp.395-404
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• 2005

This paper presents a reliable numerical procedure for nonlinear time-history analysis of space steel frames subjected to dynamic loads. Geometric nonlinearities of member (P-$\delta$) and frame (P-$\Delta$) are taken into account by the use of stability functions in framed stiffness matrix formulation. The gradual yielding along the member length and over the cross section is included by using a tangent modulus concept and a softening plastic hinge model based on the New-Orbison yield surface. A computer program utilizing the average acceleration method for the integration scheme is developed to numerically solve the equation of motion of framed structure formulated in an incremental form. The results of several numerical examples are compared with those derived from using beam element model of ABAQUS program to illustrate the accuracy and the computational efficiency of the proposed procedure.

• Computers and Concrete
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• v.24 no.1
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• pp.73-83
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• 2019

Concrete reinforced with fiber reinforced polymer (FRP) bars (FRP-RC) has attracted a significant amount of research attention in the last three decades. A limited number of studies, however, have investigated the effect of bond slip on the performance of FRP-RC columns under eccentric loading. Based on previous experimental study, a finite-element model of eccentrically loaded FRP-RC columns was established in this study. The bondslip behavior was modeled by inserting spring elements between FRP bars and concrete. The improved Bertero-Popov-Eligehausen (BPE) bond slip model with the results of existing FRP-RC pullout tests was introduced. The effect of bond slip on the entire compression-bending process of FRP-RC columns was investigated parametrically. The results show that the initial stiffness of bond slip is the most sensitive parameter affecting the compression-bending performance of columns. The peak bond stress and the corresponding peak slip produce a small effect on the maximum loading capacity of columns. The bondslip softening has little effect on the compression-bending performance of columns. The sectional analysis revealed that, as the load eccentricity and the FRP bar diameter increase, the reducing effect of bond slip on the flexural capacity becomes more obvious. With regard to bond slip, the axial-force-bending-moment (P-M) interaction diagrams of columns with different FRP bar diameters show consistent trends. It can be concluded from this study that for columns reinforced with large diameter FRP bars, the flexural capacity of columns at low axial load levels will be seriously overestimated if the bond slip is not considered.

• Advances in nano research
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• v.10 no.2
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• pp.151-163
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• 2021

The main target of this study is to investigate nonlinear transient responses of moving polymer nano-size plates fortified by means of Graphene Platelets (GPLs) and resting on a Winkler-Pasternak foundation under a transverse pressure force and a temperature variation. Two graphene spreading forms dispersed through the plate thickness are studied, and the Halpin-Tsai micro-mechanics model is used to obtain the effective Young's modulus. Furthermore, the rule of mixture is employed to calculate the effective mass density and Poisson's ratio. In accordance with the first order shear deformation and von Karman theory for nonlinear systems, the kinematic equations are derived, and then nonlocal strain gradient scheme is used to reflect the effects of nonlocal and strain gradient parameters on small-size objects. Afterwards, a combined approach, kinetic dynamic relaxation method accompanied by Newmark technique, is hired for solving the time-varying equation sets, and Fortran program is developed to generate the numerical results. The accuracy of the current model is verified by comparative studies with available results in the literature. Finally, a parametric study is carried out to explore the effects of GPL's weight fractions and dispersion patterns, edge conditions, softening and hardening factors, the temperature change, the velocity of moving nanoplate and elastic foundation stiffness on the dynamic response of the structure. The result illustrates that the effects of nonlocality and strain gradient parameters are more remarkable in the higher magnitudes of the nanoplate speed.

• International Journal of Highway Engineering
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• v.4 no.1 s.11
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• pp.149-159
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• 2002

This study was performed to estimate the high-speed direct tensile strength(DTS1), low-speed direct tensile strength(DTS2) , indirect tensile strength(ITS) resilient modulus(MR) and stiffness index(SI) of sand asphalt mixture based on the absolute viscosity, kinematic viscosity, penetration, softening point and PG grade of binder. DTS2 showed higher correlation with the physical properties than other properties of mixture, and the next was DTS1, ITS, SI and MR in order. Among binder properties, PG grade showed the highest relation with DTS2. Therefore. it was found that the high DTS mixture could be made when the binder with a high PG grade was used. However, since the individual physical property showed a relatively low correlation, various properties were used together in regression analysis. The estimation models of DTS and ITS were over 0.99, respectively. R2 of MR and SI estimation models were over 0.91 and 0.93, respectively. It was concluded that mechanical properties could be estimated with a high coefficient of determination from those physical properties.