scholarly journals Rate-Type Age-Dependent Constitutive Formulation of Concrete Loaded at an Early Age

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 514 ◽  
Author(s):  
Seung-Gyu Kim ◽  
Yeong-Seong Park ◽  
Yong-Hak Lee
Keyword(s):  
Elastic Modulus ◽  
Constitutive Equations ◽  
Experimental Result ◽  
Early Age ◽  
Time Varying ◽  
Numerical Application ◽  
Age Dependent ◽  
Sustained Loads ◽  
Constitutive Formulation ◽  
Ageing Phenomenon

A general formulation framework for an age-dependent constitutive equation of concrete is presented to account for the development of the elastic modulus at an early age. This is achieved by expanding the total stress vs. strain relation with respect to the time-varying elastic modulus. Two types of constitutive formulation frameworks are derived depending on whether (or not) the time-varying effect of the elastic modulus was taken into account in the linearized series expansion. The causes for the age-dependent deformations under sustained loads are defined in the formulation based on the two internal mechanisms of delayed elasticity and the ageing phenomenon. The ageing phenomenon is incorporated in a conventional delayed strain concept in terms of the variable elastic modulus with time. Four cases of age-dependent constitutive equations are formulated within the presented formulation framework by employing different types of creep models. The mechanical characteristics of the terms that comprise the various constitutive equations are examined and compared. Numerical application of the time-dependent test results of cylindrical specimens indicate that the creep formulation that considered the elastic modulus development showed a good agreement with the experimental result while the formulation that did not consider the elastic modulus development underestimated the result by 15%.

Development of strength and elastic modulus of concrete sealed in steel tube under sustained load at early age

2020 ◽  
pp. 136943322097814
Author(s):  
Yuying Jiao ◽  
Bing Han ◽  
Huibing Xie ◽  
Li Zhu ◽  
Dilum Fernando ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Structural Engineering ◽  
Early Stage ◽  
Concrete Strength ◽  
High Stress ◽  
Sustained Load ◽  
Early Age ◽  
Hydration Kinetics ◽  
Load Carrying ◽  
Sustained Loads

Concrete-Filled Steel Tubular Structures (CFSTSs) have become popular among the structural engineering community due to significantly higher load carrying capacity compared to conventional reinforced-concrete structures. Much research has been conducted on understanding the behavior of CFSTSs under various loading conditions and design theories have been established to predict the load carrying capacities of such structures. However, existing models do not consider the effects of sustained early loads on concrete strength and elastic modulus development of CFSTSs. With the need for rapid construction, CFSTSs may be subjected to loading at an early stage before concrete is fully cured. Such early loading may incur negative effects on strength and elastic modulus development of concrete within the confined environment. This paper propose theoretical models based on the compressive packing model (CPM) to simulate strength and elastic modulus development of early-age concrete under sustained stress. Development of concrete properties at early age is described using Hydration kinetics, and maximum paste thickness in the CPM model is modified using energy conservation to simulate sustained loads. Early concrete strength and the elastic modulus development rules were investigated experimentally for sustained loads. Predictions from the proposed models are compared with conventional models from CEB-FIP Model Code. Results showed that when loaded at a very early stage, a relatively high stress to strength ratio will result in causing damage in concrete. Such damage significantly affects the strength and elastic modulus development. Compared with concrete loaded at 28 days, concrete loaded at early stages showed significant reduction in concrete strength and elastic modulus.

Research on dynamic characteristics of gear system considering the influence of temperature on material performance

2021 ◽  
pp. 107754632110026
Author(s):  
Zhou Sun ◽  
Siyu Chen ◽  
Xuan Tao ◽  
Zehua Hu
Keyword(s):  
Elastic Modulus ◽  
Dynamic Characteristics ◽  
Poisson’S Ratio ◽  
Gear System ◽  
Poisson's Ratio ◽  
Effect Of Temperature ◽  
Time Varying ◽  
Influence Of Temperature ◽  
Meshing Stiffness ◽  
Influence Of Temperature On

Under high-speed and heavy-load conditions, the influence of temperature on the gear system is extremely important. Basically, the current work on the effect of temperature mostly considers the flash temperature or the overall temperature field to cause expansion at the meshing point and then affects nonlinear factors such as time-varying meshing stiffness, which lead to the deterioration of the dynamic transmission. This work considers the effect of temperature on the material’s elastic modulus and Poisson’s ratio and relates the temperature to the time-varying meshing stiffness. The effects of temperature on the elastic modulus and Poisson’s ratio are expressed as functions and brought into the improved energy method stiffness calculation formula. Then, the dynamic characteristics of the gear system are analyzed. With the bifurcation diagram, phase, Poincaré, and fast Fourier transform plots of the gear system, the influence of temperature on the nonlinear dynamics of the gear system is discussed. The numerical analysis results show that as the temperature increases, the dynamic response of the system in the middle-speed region gradually changes from periodic motion to chaos.

Research on influencing factors and time-varying model of thermal conductivity of concrete at early age

2021 ◽  
pp. 125638
Author(s):  
Jinpeng Dai ◽  
Qicai Wang ◽  
Ruixiao Bi ◽  
Chong Wang ◽  
Zhuowei Han ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Influencing Factors ◽  
Early Age ◽  
Time Varying

scholarly journals Study on estimation of creep behaviour of concrete at early age considering temperature effect

2019 ◽  
Vol 289 ◽  
pp. 10010
Author(s):  
Kayo Ohashi ◽  
Jun-ichi Arai ◽  
Toshiaki Mizobuchi
Keyword(s):  
Thermal Stress ◽  
Temperature Effect ◽  
Creep Strain ◽  
Prediction Accuracy ◽  
Creep Behaviour ◽  
Test Method ◽  
Control Measures ◽  
Experimental Result ◽  
Early Age ◽  
And Control

Clarifying the creep behaviour of concrete at early age not only improves the accuracy of temperature stress analysis but also contributes to prediction accuracy and control measures in cracks caused by thermal stress. However, most past researches on creep behaviour were investigated after 28 days. Currently, it is difficult to accurately perceive the creep behaviour of concrete at an early age in the test method of creep which is generally carried out. Therefore, it is necessary to evaluate the creep behaviour of concrete at early age and to establish a convenient test method to estimate the creep behaviour. Therefore, in this study, experiments were carried out for concrete at early age within one week. As the result of the experiments, it was shown that the creep strain is proportional to the load stress of concrete at an early age and the strain of specific creep decreases as the loaded age increases. In addition, based on the experimental results, an estimation equation for creep strain at early age was proposed. Within the scope of this experimental result, it was confirmed that the estimation equation proposed in this study accurately represented the creep behaviour of concrete at early age.

Lack of Age-Dependent Development of the Contingent Negative Variation (Cnv) in Migraine Children?

Cephalalgia ◽  
2002 ◽  
Vol 22 (2) ◽  
pp. 132-136 ◽  
Author(s):  
S Bender ◽  
M Weisbrod ◽  
U Just ◽  
U Pfüller ◽  
P Parzer ◽  
...  
Keyword(s):  
Contingent Negative Variation ◽  
Group Differences ◽  
Early Age ◽  
Healthy Controls ◽  
Age Dependency ◽  
Stimulus Interval ◽  
Dependent Development ◽  
Inter Stimulus Interval ◽  
Cortical Hyperexcitability ◽  
Age Dependent

Increased negativity of contingent negative variation (CNV) in adult migraineurs is thought to reflect cortical hyperexcitability. CNV amplitude changes with age in healthy adults. Recently, evidence emerged that this might not be the case for migraineurs. Our study investigates age-dependency of CNV during childhood age. Seventy-six healthy controls and 61 children with migraine without aura (IHS code 1.1) between 6 and 18 years were examined using an acoustic S1-S2-CNV-paradigm with a 3-s inter-stimulus interval. The amplitude of the late component of CNV, as well as total CNV at the vertex (Cz according to the international 10-20 system), were significantly higher in migraineurs without aura than in controls. Healthy controls showed increasing amplitudes of CNV with age, whereas in migraine children without aura amplitudes did not change. Thus group differences were reduced during adolescence. Increased CNV negativity might reflect a biological vulnerability to migraine, rather than being a result of chronification. Migraineurs seem to lack age-dependent development of CNV also during early age, which supports the hypothesis of migraine as a maturation disorder.

Resistance Analysis of Reinforced Concrete Structures in Construction

2011 ◽  
Vol 368-373 ◽  
pp. 1535-1538
Author(s):  
Nan Zhao ◽  
Wen Yan
Keyword(s):  
Concrete Strength ◽  
Early Time ◽  
Reduction Factor ◽  
Resistance Force ◽  
Early Age ◽  
Time Varying ◽  
Structural Components ◽  
Utilization Coefficient ◽  
Flexural Member ◽  
Early Age Concrete

This paper analyses the characteristics of resistance of structural components, puts forward the concept of early resistance force of structural components, and discuss the main factors which affect it based on the field measurement investigation and theoretical analysis. Besides, in the paper the reduction factor is applied to reflect time-varying features of early-age concrete strength, and utilization coefficient of concrete strength is utilized to present the influence of early time-varying features of cohesive action on resistance. The paper finally deduces the formula of early-age resistance force of typical flexural member, and gives the time-changing law of early resistance by using a case.

Incremental Formulation of Concrete Creep under Stress History

2017 ◽  
Vol 865 ◽  
pp. 313-319
Author(s):  
Si Hyung Park ◽  
Yeong Seong Park ◽  
Ta Lee ◽  
Yong Hak Lee
Keyword(s):  
Elastic Modulus ◽  
Constitutive Equation ◽  
Drying Shrinkage ◽  
Concrete Specimen ◽  
Creep Model ◽  
Beam Specimen ◽  
First Order ◽  
Age Dependent ◽  
Incremental Formulation ◽  
Basic Equations

An incremental format of the age-dependent constitutive equation was derived by expanding the total form of the constitutive equation by using the first-order Taylor series to describe the persistent change in the creep-causing stress state as well as drying shrinkage and the development of the elastic modulus. The resulting incremental constitutive equation was defined by three basic equations for basic creep, drying shrinkage, and the development of the elastic modulus. Three types of laboratory experiments were carried out to validate the performance of the presented age-dependent constitutive equation; these included cylindrical concrete specimen tests with and without axial reinforcements and reinforced beam specimen tests. The performance of the creep model was compared with those calculated by the other age-dependent constitutive equations.

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