scholarly journals Time-Dependent Behavior of Rock Materials

2021 ◽  
Author(s):  
Chrysothemis Paraskevopoulou
Keyword(s):  
Rock Mass ◽  
Stress Relaxation ◽  
Time Dependent ◽  
Cost Overruns ◽  
Rock Materials ◽  
Dependent Behavior ◽  
Rock Mass Deformation ◽  
Waste Repositories ◽  
Long Term Behavior

Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in underground projects such as nuclear waste repositories. The lifespan can exceed one million years or other openings where the project’s lifetime and sustainability are the critical design parameter. In such cases, progressive rock mass deformation that can lead to instabilities, time-dependent overloading of support and delayed failure are considered the product of time-dependent phenomena. Understanding and predicting the overall impact of such phenomena aims to achieve design optimization, avoiding dlivery delays and thus cost overruns. This chapter provides more insight into the time-dependent behavior of rocks. Simultaneously, the emphasis is given to investigating and analyzing creep deformation and time-dependent stress relaxation phenomenon at the laboratory scale, and in-depth analyses are presented. This work further develops the understanding of these phenomena, and practical yet scientific tools for estimating and predicting the long-term strength and the maximum stress relaxation of rock materials is presented. The work presented in this chapter advances the scientific understanding of time-dependent rock, and rock mass behavior increases the awareness of how such phenomena are captured numerically and lays out a framework for dealing with such deformations when predicting tunnel deformations.

scholarly journals Long-term behavior of connections for glubam-concrete composite beams

2019 ◽  
Vol 275 ◽  
pp. 01001
Author(s):  
Xin Ye ◽  
Bo Shan ◽  
Qian Yue ◽  
Zhenyu Wang
Keyword(s):  
Concrete Slab ◽  
Constitutive Models ◽  
Time Dependent ◽  
Construction Technique ◽  
Relative Slip ◽  
Laminated Bamboo ◽  
Dependent Behavior ◽  
Bcc Structure ◽  
Long Term Behavior

Glubam-concrete composite (BCC) structure is a construction technique where glue-laminated bamboo beam is connected to an upper concrete slab using different types of connectors. The long-term behavior and creep mechanism of BCC system are very complex due to different time-dependent behavior of three components. This paper performed a series long-term push-out tests on four types of connections under static load. The tests lasted for a period of seven months in uncontrolled sheltered indoor condition. Important results such as the relative slip-time curves are presented in order to characterize time-dependent behavior of connectors. Furthermore creep coefficient constitutive models are provided for predicting the long-term behavior of connections.

scholarly journals Theoretical Investigation of Nonlinear Time-Dependent Behavior of Two-Way High-Strength Concrete Walls

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Yue Huang ◽  
Rui Rao ◽  
Yonghui Huang ◽  
Zilin Zhong
Keyword(s):  
Geometric Nonlinearity ◽  
High Strength Concrete ◽  
High Strength ◽  
Time Dependent ◽  
Fourier Series Expansion ◽  
Time Step ◽  
Strength Concrete ◽  
Dependent Behavior ◽  
Long Term Behavior

High-strength concrete (HSC) walls have been increasingly used in the past decades. However, the time-dependent behavior of HSC wall panels in two-way action was not investigated, and the time effect of creep is not included in the design codes in most countries. For this purpose, the nonlinear long-term behavior of two-way HSC wall is investigated in this paper. A theoretical model is developed using time-stepping analysis considering geometric nonlinearity and creep of concrete. A rheological material model that is based on the generalized Maxwell chain is adopted to model the concrete creep. Von Karman plate theory is used to derive the incremental governing equations. The equations are solved numerically at each time step based on a Fourier series expansion of the deformations and loads and numerical multiple shooting method. It shows that the model can effectively predict the time-dependent behavior of two-way HSC panels, where the out-of-plane deflection and internal bending moments increase with time due to the combined effects of creep and geometric nonlinearity, which may ultimately lead to creep buckling failures. A parametric study shows that the long-term behavior of the panel is very sensitive to the in-plane load level and eccentricity, slenderness ratio, aspect ratio, and edge support conditions.

In Situ Tests on Creep Behavior of Rock Mass with Joint or Shearing Zone in Foundation of Large-Scale Hydroelectric Projects

2004 ◽  
Vol 261-263 ◽  
pp. 1097-1102 ◽  
Author(s):  
Jian Liu ◽  
Xia Ting Feng ◽  
Xiu Li Ding ◽  
Huo Ming Zhou
Keyword(s):  
Rock Mass ◽  
Creep Behavior ◽  
Large Scale ◽  
Time Dependent ◽  
Three Gorges Project ◽  
Three Gorges ◽  
The Three Gorges ◽  
The Three Gorges Project

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

Delayed arteriolar relaxation after prolonged agonist exposure: functional remodeling involving tyrosine phosphorylation

2003 ◽  
Vol 285 (2) ◽  
pp. H849-H856 ◽  
Author(s):  
Michael A. Hill ◽  
Simon J. Potocnik ◽  
Luis A. Martinez-Lemus ◽  
Gerald A. Meininger
Keyword(s):  
Tyrosine Phosphorylation ◽  
Prolonged Exposure ◽  
Time Dependent ◽  
Physiological Salt Solution ◽  
Microtubule Network ◽  
Biochemical Alterations ◽  
Dependent Behavior ◽  
Functional Remodeling ◽  
Short And Long Term

Although arteriolar contraction is dependent on Ca2+-induced myosin phosphorylation, other mechanisms including Ca2+ sensitization and time-dependent phenomena such as cytoskeletal and cellular reorganization may contribute to contractile events. We hypothesized that if arteriolar smooth muscle exhibits time-dependent behavior this may be manifested in differences in relaxation after short- and long-term exposure to contractile agonists. Studies were conducted in isolated arterioles pressurized to 70 mmHg. In initial experiments ( n = 10), rate of relaxation was measured after acute (5 min) or prolonged (4 h) exposure to 5 μM norepinephrine (NE). Prolonged exposure to NE resulted in significantly ( P < 0.05) increased time for relaxation in physiological salt solution. Rapid relaxation of vessels exposed to NE for 4 h was observed after superfusion with 0 mM Ca2+ buffer, indicating that the alteration in relaxation was reversible and Ca2+ dependent. A similarly impaired dilation was not observed with 4-h exposure to KCl (75 mM). To determine mechanisms contributing to the effects of prolonged NE exposure, studies were performed in the presence of the microtubule depolymerizing agent demecolcine (10 μM) or a series of tyrosine phosphorylation inhibitors. Although demecolcine caused significant vasoconstriction ( P < 0.05) and potentiated NE vasoconstriction, it did not prevent the effect of long-term NE exposure on relaxation. Genistein, although having no effect on acute NE-induced contraction, concentration-dependently inhibited prolonged NE constriction. Similarly, Src (PP1) and p42/44 MAP kinase (PD-98059) inhibitors prevented maintenance of long-term NE contraction. The data indicate that prolonged exposure to NE induces biochemical alterations that impair relaxation after removal of the agonist. The contractile effects are Ca2+ dependent and involve tyrosine phosphorylation but do not appear to involve the polymerization state of the microtubule network.

scholarly journals Constitutive Modeling of Time-Dependent Response of Human Plantar Aponeurosis

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
P. G. Pavan ◽  
P. Pachera ◽  
C. Stecco ◽  
A. N. Natali
Keyword(s):  
Experimental Data ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Transverse Isotropy ◽  
Model Fitting ◽  
Viscoelastic Behavior ◽  
Time Dependent ◽  
Plantar Aponeurosis ◽  
Structural Conformation ◽  
Dependent Behavior

The attention is focused on the viscoelastic behavior of human plantar aponeurosis tissue. At this purpose, stress relaxation tests were developed on samples taken from the plantar aponeurosis of frozen adult donors with age ranging from 67 to 78 years, imposing three levels of strain in the physiological range (4%, 6%, and 8%) and observing stress decay for 240 s. A viscohyperelastic fiber-reinforced constitutive model with transverse isotropy was assumed to describe the time-dependent behavior of the aponeurotic tissue. This model is consistent with the structural conformation of the tissue where collagen fibers are mainly aligned with the proximal-distal direction. Constitutive model fitting to experimental data was made by implementing a stochastic-deterministic procedure. The stress relaxation was found close to 40%, independently of the level of strain applied. The agreement between experimental data and numerical results confirms the suitability of the constitutive model to describe the viscoelastic behaviour of the plantar aponeurosis.

scholarly journals Finite Element Modeling of FRP-Strengthened RC Beam under Sustained Load

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Shiyong Jiang ◽  
Weilai Yao ◽  
Jin Chen ◽  
Tao Cai
Keyword(s):  
Finite Element ◽  
Field Performance ◽  
Adhesive Layer ◽  
Aging Effect ◽  
Time Dependent ◽  
Sustained Load ◽  
Fe Model ◽  
Rc Beam ◽  
Long Term Behavior

External bonding of FRP laminates to the tension soffit of concrete members has become a popular method for flexural strengthening. However, the long-term field performance of FRP-strengthened RC members under service conditions is still a concern, and more work needs to be done. Based on concrete smeared-crack approach, this paper presents a finite-element (FE) model for predicting long-term behavior of FRP-strengthened RC beam, which considers the time-dependent properties of all components including the aging effect of concrete. According to the comparison between theoretical predictions and test results, the validity of the FE model is verified. The interfacial edge stresses in adhesive layer were determined through appropriate mesh refinement near the plate end, and their time-dependent characteristics were investigated. The results show that creep of concrete and epoxy resin cause significant variations of the edge stresses with time. According to the research in this paper, the FE approach is found to be able to properly simulate the long-term behavior of the FRP-strengthened beam and help us better understand the complex changes in the stress state occurring over time.

Numerical Investigation on Factors Influencing the Time-Dependent Stability of the Rock Slopes with Weak Structure Planes

2013 ◽  
Vol 353-356 ◽  
pp. 177-182
Author(s):  
Lian Chong Li ◽  
Shao Hua Li
Keyword(s):  
Rock Mass ◽  
Rock Slope ◽  
Failure Time ◽  
Time Dependent ◽  
Catastrophic Failure ◽  
Long Term Stability ◽  
Stability Of Slopes ◽  
Factors Influencing ◽  
Weak Structure

Under the combined effects of various external factors, such as temperature, seepage, alternate wetting and drying and so on, the mechanical properties of rock mass are susceptible to be deteriorated, and its strength characteristics are significantly degraded with time. The mesoscopic damage accumulated inside the rock, contributing the rock slope instability with weak structure planes, generate the time-dependent deformation, and eventually lead to the slope failure. Given the time-dependent deformation of the rock, numerical simulations are conducted to investigate the key factors influencing the long-term stability of slopes. Numerical results show that the catastrophic failure time of slopes is linear to its cohesion, and the bigger cohesion and friction angle increase catastrophic failure time, i.e., the stability of rock slope increase. In addition, the configuration of the intact rock bridge can also influence the time-dependent slope stability. Slope height can significantly affect the slope stability and the maximum horizontal displacement. Differences in rock mass storage environment play an important role in the long-term stability of slopes.

Rock Mass Deformation Long-Term Forecast via DRNN Neural Network Model

2012 ◽  
Vol 433-440 ◽  
pp. 770-774
Author(s):  
Sha Ma ◽  
Zhi Quan Huang
Keyword(s):  
Neural Network ◽  
Rock Mass ◽  
Network Stability ◽  
Term Forecast ◽  
Link Weight ◽  
Network Output ◽  
Rock Mass Deformation ◽  
Long Term Prediction ◽  
Mass Deformation

The question of rock mass deformation Long-term forecast is researched base on DRNN. The construction of neural network is optimized via reconstructed chaotic phase space, and the all nodes of DRNN are interconnected, and the feedback between nodes and that of node itself is included, and mult-linkage branch is build between two nerves, and the linkage branch stands for the link weight and the time delay of regular step. So the current moment network output of node depends on not only current moment network iutput, but also the node output of Some moment before current, so the chaotic prediction sensibility to initial condition is reduced effectively. The calculating velocity and network stability is improved effectively. Examples show that results are reasonable and the long-term prediction is reasonable and feasible.

New Actinide Waste Forms with Pyrochlore and Garnet Structures

2010 ◽  
Vol 73 ◽  
pp. 142-147
Author(s):  
Tatiana Livshits ◽  
Sergey Yudintsev ◽  
Sergey V. Stefanovsky ◽  
Rodney Charles Ewing
Keyword(s):  
Corrosion Behavior ◽  
Pyrochlore Structure ◽  
Radiation Stability ◽  
Alkaline Solutions ◽  
Waste Forms ◽  
Underground Disposal ◽  
Waste Repositories ◽  
Long Term Behavior

Cubic oxides with pyrochlore and garnet structures are promising matrices for long-lived actinides immobilization. Their isomorphic capacity with respect to An and REE was determined. To predict the long-term behavior of these matrices under their underground disposal radiation stability of synthetic pyrochlores and garnets was studied. Most of titanate phases have the critical (amorphization) doses close to 0.2 displacements per atom at 298 K. This value is significantly higher for Sn- and Zr-rich pyrochlores. Corrosion behavior of the pyrochlore- and garnet-composed matrices was investigated. The lowest actinides leach rates were observed in water and alkaline solutions most typical for underground waste repositories. Amorphization of the phases has a low influence on their corrosion behavior in solutions. Possibility for joint incorporation of actinides and Tc into zirconate- and titanate-based matrices with the pyrochlore structure is discussed.

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