Creep Theory Research Articles

Numerical modeling of delayed damage and failure of concrete structures under sustained loading

The combination of subcritical damage growth and creep deformation can cause delayed failure of concrete materials. Such a time-dependent failure behavior adds a new consideration in design of concrete structures. To investigate this behavior, a time-dependent constitutive model for concrete is proposed. The model is anchored by integration of the continuum damage mechanics and nonlinear creep theory. It captures several essential mechanisms responsible for delayed failure behavior of concrete, which include instantaneous softening damage, plasticity, subcritical damage growth, and nonlinear creep. The model is calibrated by the creep experiments on concrete specimens under uniaxial compression and three-point bending. It is shown that the model can well capture the time-dependent deformation and failure of concrete structures under a wide range of loading levels. The contributions of different individual mechanisms to the overall structural response are investigated. The calibrated model is then used to simulate the response of a reinforced concrete frame under sustained loading. The simulation yields the stress-life curve, which is an essential metric describing the delayed failure behavior of concrete structures.

Experimental study of creep Poisson ratio of hydraulic concrete under multi-age loading-unloading conditions

Elastic creep theory, which is widely used in concrete dam engineering, assumes that the elastic Poisson ratio and the creep Poisson ratio equal the effective creep Poisson ratio. However, differences in creep test conditions and stress state make this assumption controversial. To accurately clarify the Poisson effect of hydraulic concrete, uniaxial compression creep tests with four loading ages (3d, 14d, 28d, and 60d) and conventional triaxial compression creep tests with three loading ages (14d, 28d, and 60d) are conducted under unified test conditions. And high-precision creep data of transverse and longitudinal for multi-age loading and unloading are obtained. We then denoise the creep data by using a Savitzky-Golay filter. Furthermore, based on the denoised creep data, we calculate the Poisson ratio at each stage for uniaxial compression and conventional triaxial compression. Finally, we compare and analyze the Poisson ratio of each stage in different stress states. The results show that the creep tests have the same noise when conducted under the same test conditions, and the optimal denoising by the Savitzky-Golay filter is obtained with parameters W (window width) = 9 and N (polynomial order) = 6. Under different stress states, the elastic Poisson ratio, creep Poisson ratio and effective creep Poisson ratio are not equal to each other, and the elastic Poisson ratio is greater than the creep Poisson ratio. In addition, under the conventional triaxial stress state, the effective creep (creep recovery) Poisson ratio in each direction is different, which indicates that the creep (creep recovery) in each direction is dependent under multi-axial stress state.

Safety evaluation of a vehicle\u2013bridge interaction system using the pseudo-excitation method

A method for analysing the vehicle–bridge interaction system with enhanced objectivity is proposed in the paper, which considers the time-variant and random characteristics and allows finding the power spectral densities (PSDs) of the system responses directly from the PSD of track irregularity. The pseudo-excitation method is adopted in the proposed framework, where the vehicle is modelled as a rigid body and the bridge is modelled using the finite element method. The vertical and lateral wheel–rail pseudo-excitations are established assuming the wheel and rail have the same displacement and using the simplified Kalker creep theory, respectively. The power spectrum function of vehicle and bridge responses is calculated by history integral. Based on the dynamic responses from the deterministic and random analyses of the interaction system, and the probability density functions for three safety factors (derailment coefficient, wheel unloading rate, and lateral wheel axle force) are obtained, and the probabilities of the safety factors exceeding the given limits are calculated. The proposed method is validated by Monte Carlo simulations using a case study of a high-speed train running over a bridge with five simply supported spans and four piers.

Difference in anisotropic vortex pinning in pristine and proton-irradiated (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 single crystals

We measured the in-plane electrical resistivity of pristine and irradiated (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 single crystals in B//c and B//ab up to B = 13 T to study the difference between in-plane and out-of-plane vortex pinning and the effect of proton irradiation on these pinning. The crystal structure analyzed by the selected area electron diffraction was monoclinic in these two samples. Protons incident along the c-axis caused an expansion of the lattice constants a and b. The expansion of the lattice constants significantly increased the c-axis coherence length ξc. The vortex pinning in B//ab is well understood by an intrinsic pinning mechanism, which was attenuated by proton irradiation. On the other hand, the vortex pinning in B//c is well understood by the plastic creep theory due to point defects that are enhanced by proton irradiation.

Key Construction Monitoring Technology for Long-Span Continuous Girder Bridge

This paper integrates a monitoring practice for the construction of a long-span continuous girder bridge to explore strain measurement and geometric shape control technology. In doing so, the actual stress of the bridge in the cantilever-construction stage is identified, and the influence of ambient temperature on the geometric shape control of the main girder is eliminated. According to linear creep theory, a strain correction method based on the superposition principle is proposed to remove the strain induced by concrete shrinkage and creep. By identifying the pattern of the solar thermal effect on the main girder geometry, a double in-situ measurement interpolation method is proposed to predict the adjusted value of formwork erection elevation. The results show that the deviation between the measured and corrected stress values on the root section of the main girder under the maximum cantilever state of the main girder is 16%–23%, which verifies the necessity of strain correction. The corrected values of measured stress on each controlled section are essentially identical to the calculated values, and both have consistent change patterns throughout the construction process, which verifies the validity of the strain correction method. During the cantilever-construction stage, the vertical deformation of the main girder owing to the solar thermal effect is parabolic and significant; hence, the main girder geometry should be measured prior to sunrise. The double in-situ measurement interpolation method can effectively eliminate the adverse effects of solar thermal when lofting the vertical formwork elevation in a non-ideal period.

Creep tide model for the three-body problem

We present a tidal model for treating the rotational evolution in the general three-body problem with arbitrary viscosities, in which all the masses are considered to be extended and all the tidal interactions between pairs are taken into account. Based on the creep tide theory, we present a set of differential equations that describes the rotational evolution of each body, in a formalism that is easily extensible to the N tidally interacting body problem. We apply our model to the case of a circumbinary planet and use a Kepler-38 like binary system as a working example. We find that, in this low planetary eccentricity case, the most likely final stationary rotation state is the 1:1 spin–orbit resonance, considering an arbitrary planetary viscosity inside the estimated range for the Solar System planets. The timescales for reaching the equilibrium state are expected to be approximately millions of years for stiff bodies but can be longer than the age of the system for planets with a large gaseous component. We derive analytical expressions for the mean rotational stationary state, based on high-order power series of the ratio of the semimajor axes a1∕a2 and low-order expansions of the eccentricities. These are found to very accurately reproduce the mean behaviour of the low-eccentric numerical integrations for arbitrary planetary relaxation factors, and up to a1∕a2 ~ 0.4. Our analytical model is used to predict the stationary rotation of the Kepler circumbinary planets and we find that most of them are probably rotating in a subsynchronous state, although the synchrony shift is much less important than our previous estimations. We present a comparison of our results with those obtained with the Constant Time Lag and find that, as opposed to the assumptions in our previous works, the cross torques have a non-negligible net secular contribution, and must be taken into account when computing the tides over each body in an N-extended-body system from an arbitrary reference frame. These torques are naturally taken into account in the creep theory. In addition to this, the latter formalism considers more realistic rheology that proved to reduce to the Constant Time Lag model in the gaseous limit and also allows several additional relevant physical phenomena to be studied.

Structural Analysis Using Applied Element Method: A Review

This paper presents a review on a displacement-based method of structural analysis. In Applied Element Method (AEM), the structure is simulated as an assembly of elements formed by dividing the structure virtually. These elements are connected in both normal and tangential directions by springs. AEM can be used to analyze structural behavior from the initial loading until total collapse. It combines between the advantages of Finite Element Method (FEM) and Discrete Element Method (DEM). In this paper, the differences between AEM and the other numerical methods are discussed. Next, basic introduction to AEM and its assumptions are presented. The element formulation and the effect of number of the connecting springs between elements in addition to the element size are illustrated. Finally, applications of AEM such as cyclic loading condition, dynamic small and large deformation range, creep theory, functionally graded material, masonry building and fiber reinforced polymer and polypropylene composite are explained.

Analysis of belt transmissions capabilities using the brush model

The mechanics of power transmission is usually modeled by two different theories: the creep theory and the shear theory. Recently, the authors introduced an alternative theory based on the brush model, which allows to compute the tangential stress distribution along the winding arc of pulleys. The brush model is able to predict the speed loss along the driving and driven pulley as a function of the transmission parameters (e.g. pre-load, friction, pulley radii etc.) and the operating parameters (i.e. angular speed and resistant torque). In addition, the energy efficiency of the system is obtained by knowing the speed loss and the energy dissipation; this contribution can be subdivided into energy loss due to friction and energy loss due to the non-recoverable elastic deformation of the bristle.In the present paper, using the previously developed model, a sensitivity analysis aimed at mapping the transmission capabilities as a function of geometry and operating parameters is proposed. These results, given as look-up table (or contour plot), are very important in mechanical systems simulation (e.g. real-time systems, hardware in the loop systems) since they allow to introduce the phenomenological behavior of the pulley-belt transmission without introducing complex models in the simulation.

Application of the hereditary creep theory in assessing the effect of temperature influence on the strength of carbon fibre plastics

One of the problems, which engineers face in using of carbon-reinforced composites, is the large scatter of the strength characteristics. To diminish scatter the method of the merger of tests results under varied climatic conditions might be applied. The aim of this merge is diminishing the scatter of the strength test results, and therefore improving the strength estimation accuracy. It is also in connection with the problem of the impact of climatic changes on the material properties. The climate impact is significantly larger in composites than in metals. To deal with those two problems the heredity mechanics developed earlier by Russian academician Ju. N. Rabotnov and his successors has been applied. The developed earlier modification of this theory, related to climate influence, has been applied to the problem of experimental data merger, obtained under varying temperatures, into one generalized set. For consideration of the orthotropy properties which are specific for reinforced composites, it was proposed the experimental investigation of the specimens cut in three different directions. The Rabotnov’s heredity equation should be written in tensor form. The property of viscoelasticity, which is inherent for carbo-plastics materials (especially under the elevated temperatures), is utilized in the decision of this problem. Experimental data and results of the model application are presented.

Calculation of eccentrically compressed reinforced concrete columns under various creep laws

The article proposes resolving equations for eccentrically compressed reinforced concrete short columns obtained on the viscoelastic model basis. Comparison of the results obtained according to the theory of heredity, theory of hardening, aging, flow, kinetic theory, as well as the nonlinear theory of concrete creep by Yu.A. Gurieva is presented.

Stress-strain state of the short eccentrically compressed reinforced concrete columns with nonlinear creep

The article presents the derivation of the resolving equations for calculating short eccentrically compressed reinforced concrete elements taking into account the creep of concrete. The case of symmetric reinforcement is considered. A viscoelastoplastic model of hereditary aging by A.G. Tamrazyan is used. Comparison of solutions based on linear and nonlinear creep theory is performed.

Long-term deflection prediction in steel-concrete composite beams

This paper aims to improve the current state-of-the-art in long-term deflection prediction in steel-concrete composite beams. The efficiency of a time-dependent finite element model based on linear creep theory is verified with available experimental data. A parametric numerical study is then carried out, which focuses on the effects of concrete creep and/or shrinkage, ultimate shrinkage strain and reinforcing bars in the slab. The study shows that the long-term deformations in composite beams are dominated by concrete shrinkage and that a higher area of reinforcing bars leads to lower long-term deformations and steel stresses. The AISC model appears to overestimate the shrinkage-induced deflection. A modified ACI equation is proposed to quantify time-dependent deflections in composite beams. In particular, a modified reduction factor reflecting the influence of reinforcing bars and a coefficient reflecting the influence of ultimate shrinkage are introduced in the proposed equation. The long-term deflections predicted by this equation and the results of extensive numerical analyses are found to be in good agreement.

A study on the prediction of displacement in the accelerated deformation stage of the creep bedding rock landslides

In view of the complexity, randomness, and uncertainty of landslide evolution, it causes substantial damage to the environment every year, in the absence of a mature model for landslide displacement prediction. Most of bedding landslides are characterized by creep, and its displacement in the accelerated deformation stage changes with time in line with the law extremely similar to that of rock creep. From the perspective of the rock creep theory, a nonlinear viscous component is proposed, and a model for predicting the displacement in the accelerated deformation stage regarding creep landslides is established by combining it with the plastic component. The cumulative displacement-time series data at the monitoring points is input as the parameters, and the model parameters are obtained via the nonlinear fitting of the model parameters, and thereafter the prediction of landslide displacement in the accelerated deformation stage is rendered possible. Taking the landslide on the South Slope of West Open-pit Mine in Fushun and the Jimingsi landslide as the research cases, the newly proposed displacement prediction model is employed to analyze and predict the cumulative displacement of landslides. By comparing the measured and predicted values at the selected prediction time points in the initial stage of accelerated deformation and in the pre-sliding stage, it is found that, in these two landslides, the maximum relative error (RE) at each monitoring point and each prediction time point in the initial stage and the pre-sliding stage of accelerated deformation is respectively less than 2% and less than 7%, and that the correlation coefficient of predicted and measured values of displacement in the phase of accelerated deformation is greater than 0.99, and the results show that the proposed model for predicting the displacement of creep bedding rock landslides has satisfactory accuracy and applicability, and can meet the demand of landslide displacement prediction and serve as an effective way to prevent the environmental risk posed by landslides.

Localizing gradient damage model coupled to extended microprestress-solidification theory for long-term nonlinear time-dependent behaviors of concrete structures

A nonlocal damage-based model is proposed to predict the nonlinear long-term deformation of concrete structures, which couples the localizing gradient-enhanced damage (LGED) model for crack nucleation and propagation to the extended microprestress-solidification (XMPS) theory for creep and shrinkage deformations. The proposed LGED-XMPS model circumvents damage localization by incorporating higher-order deformation gradients, and connects creep and shrinkage to inherent moisture transport and heat transfer processes. For creep part, a solidifying Kelvin chain is adopted for the rate-type formulation, which greatly reduces computational burdens of the conventional integral-type formulation. The LGED-XMPS model regularizes mesh-sensitivity of creep deformation intertwined with damage and cracking, which is rarely reported elsewhere. Furthermore, the model are validated with several tests reported in literatures. Specifically, the time-to-failure of concrete specimens subject to high level stresses is well predicted, along with the long-term deflections of simply-supported beams affected by crack growths. It is highlighted that the model is competitive for predicting nonlinear long-term deformation of creep- and crack-sensitive structures.

A general theory of rock glacier creep based on in‐situ and remote sensing observations

AbstractThe ongoing acceleration in rock glacier velocities concurrent with increasing air temperatures, and the widespread onset of rock glacier destabilization have reinforced the interest in rock glacier dynamics and in its coupling to the climate system. Despite the increasing number of studies investigating this phenomenon, our knowledge of both the fundamental mechanisms controlling rock glacier dynamics, and their long‐term behaviour at the regional scale remain limited. We present a general theory to investigate rock glacier dynamics, its spatial patterns and temporal trends at both regional and local scale. To this end, we combine a model to calculate rock glacier thickness with an empirical creep model for ice‐rich debris, in order to derive the Bulk Creep Factor (BCF), which allows to disentangle the two contributions to the surface velocities from (i) material properties and (ii) geometry. Thereafter, we provide two examples of possible applications of this approach at a regional and local scale.

Skyrmion lattice creep at ultra-low current densities

Magnetic skyrmions are well-suited for encoding information because they are nano-sized, topologically stable, and only require ultra-low critical current densities jc to depin from the underlying atomic lattice. Above jc skyrmions exhibit well-controlled motion, making them prime candidates for race-track memories. In thin films thermally-activated creep motion of isolated skyrmions was observed below jc as predicted by theory. Uncontrolled skyrmion motion is detrimental for race-track memories and is not fully understood. Notably, the creep of skyrmion lattices in bulk materials remains to be explored. Here we show using resonant ultrasound spectroscopy—a probe highly sensitive to the coupling between skyrmion and atomic lattices—that in the prototypical skyrmion lattice material MnSi depinning occurs at {j}_{c}^{* } that is only 4 percent of jc. Our experiments are in excellent agreement with Anderson-Kim theory for creep and allow us to reveal a new dynamic regime at ultra-low current densities characterized by thermally-activated skyrmion-lattice-creep with important consequences for applications.

Creep Behaviours of Argillaceous Sandstone: An Experimental and Modelling Study

Understanding the creep behaviours of rocks is essential for the long-term stability of underground excavations in mining engineering. Creep behaviours are more important when the mining depth is greater, which leads to the emergence of weak rock masses and high in situ stresses. In this study, the creep behaviours of argillaceous sandstone (AS) were systematically investigated. For the experimental investigation, creep tests were conducted on AS with different confining pressures (3, 6, 9, 12, 15, and 18 MPa) using an MTS815.02 rock mechanics test system. The mechanical characteristics of AS were analysed. For the numerical study, a nonlinear creep model of AS under equal and different confining pressures was established based on rock creep theory and plastic theory. The results showed that confining pressure could effectively improve the creep failure strength of AS, accelerating its creep deformation rate and process and reducing the final expansion volume. The nonlinear creep model was embedded in the FLAC3D software, and the experimental and numerical results agreed well. The experimental investigation and proposed creep model can provide important guidance in underground mines for safe long-term stability of underground excavations.

Time-domain coupled dynamic simulation for SFT-mooring-train interaction in waves and earthquakes

In this study, Submerged Floating Tunnel (SFT)-mooring-train coupled dynamics is solved in the time domain to investigate their dynamic and hydro-elastic interactions under wave and earthquake excitations. The SFT is modeled by the rod-FE (finite element) theory, and it is connected to mooring lines through dummy-connection-mass and linear and rotational springs. A 3D rigid-multi-body dynamic model is developed for train dynamics that consists of seven rigid bodies. The tunnel-train interaction is taken into consideration based on the wheel-rail correspondence assumption and the simplified Kalker linear creep theory. The developed computer simulation program is validated through comparisons with commercial programs and published results when possible. In the case of earthquake-induced dynamics of the coupled system, the effects of soil conditions, tunnel length, mooring interval, seismic-wave propagation, and seaquake are investigated. The magnitudes of the SFT downward motions induced by the moving train are small compared with the motions induced by earthquakes. The earthquake causes transient SFT responses especially at their lowest wet natural frequencies while high-frequency motions are induced by seaquake effect. Structural damping and seismic propagation play an important role in dynamic responses. The interaction of the tunnel and moving train is also evaluated for various train speeds in terms of the derailment and offload factors and riding-comfort criterion. For the given SFT and train designs, the offload factor and riding-comfort criterion can slightly exceed their limits at certain earthquake conditions with the speed as high as 70 m/s, which can be adjusted by reducing train speed.

Dmytro Vasylovych Breslavsky – an outstanding scientist - mechanic (on the 60th anniversary of birth)

The article contains an essay about the outstanding scientist - mechanic, doctor of technical sciences, professor Dmytro Vasylovych Breslavsky. A brief summary of the main scientific results obtained by D.V. Breslavsky in various branches of informatics and flight control, mechanics: the theory of creep, continuum mechanics of damage, the theory of plates and shells. The description of the scientific path of Dmytro Vasylovych Breslavsky from the student's bench to the scientific leadership of graduate students and doctoral students is given, as well as the path of the administrator, head of the Department and Faculty. Scientific achievements are presented in international cooperation with the Otto von Guericke Magdeburg University and the Martin Luther University in Halle, Germany, as well as cooperation with enterprises and institutions of Ukraine. A description of the applied research of devices, equipment, machines and structures is given. The article contains main scientific publications of Professor, Doctor of Technical Sciences Dmytro Vasylovych Breslavsky. He is the author of 200 scientific publications, co-author of four monographs, two textbooks. Research interests: physically nonlinear problems of mechanics of a deformable solid (creep, fracture under cyclic and impact loads), finite element method, computer modeling of technical processes, IT-technologies in problems of mechanics.The result of many years of work in the direction of creating a theory of dynamic and cyclic creep of materials and structural elements was provided in scientific reports D.V. Breslavsky and O.K. Morachkovsky, made at world scientific conferences in Belgrade and Montreal and published in scientific publications.

Dependencies of nonlinear hereditary creep theory for concrete and creep type equations of hardening under plane stress

Concrete creep is of great practical importance and is taken into account in calculation and design of structures. The article discusses various options for describing the theory of creep of concrete, which are divided into three main groups: the theory of an elastic-creeping body (hereditary theory of aging), the theory of elastic heredity (the theory of an visco-elastic body), and the theory of aging. The main advantages and disadvantages of their use are demonstrated depending on various conditions and processes. Collisions in the study of concrete creep are clearly visible when considering expressions for the creep measure, as well as creep and relaxation nuclei. Different scientists propose their own modification of expressions that reflect various features of the material, and which are often very different from each other. The authors of the article obtained the full creep equations of structural materials.