• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.29-37
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• 2008

Stress-strain relation and stress block parameters of polymer concrete flexural compression members were experimentally investigated. For these purposes, a series of C-shaped polymer concrete specimens subjected to axial compressive load was tested. Based on the test results, we proposed an equation by which the stress-strain relation of polymer concrete can be predicted. In this model, we took account the slope of descending branch beyond the peak stress point of single curve. The proposed equation was numerically integrated to compute the rectangular stress block parameters. Computed ${\beta}_1$ was greater than the values prescribed in ACI 318 Code for cement concrete, and $\gamma$ was about 0.85 that is similar to the value regulated in the ACI.

• Computers and Concrete
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• v.19 no.1
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• pp.59-68
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• 2017

This study focused on modeling the behavior of the compressive stress using the average strain and ultrasonic test results in concrete. Feed-forward backpropagation artificial neural network (ANN) models were used to compare four types of concrete mixtures with varying water cement ratio (WC), ordinary concrete (ORC) and concrete with short steel fiber-reinforcement (FRC). Sixteen (16) $150mm{\times}150mm{\times}150mm$ concrete cubes were used; each contained eighteen (18) data sets. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record linear and nonlinear test response with multiple step loads. Statistical Spearman's rank correlation was used to reduce the input parameters. Different types of concrete produced similar top five input parameters that had high correlation to compressive stress: average strain (${\varepsilon}$), fundamental harmonic amplitude (A1), $2^{nd}$ harmonic amplitude (A2), $3^{rd}$ harmonic amplitude (A3), and peak to peak amplitude (PPA). Twenty-eight ANN models were trained, validated and tested. A model was chosen for each WC with the highest Pearson correlation coefficient (R) in testing, and the soundness of the behavior for the input parameters in relation to the compressive stress. The ANN model showed increasing WC produced delayed response to stress at initial stages, abruptly responding after 40%. This was due to the presence of more voids for high water cement ratio that activated Contact Acoustic Nonlinearity (CAN) at the latter stage of the loading path. FRC showed slow response to stress than ORC, indicating the resistance of short steel fiber that delayed stress increase against the loading path.

• Journal of Drive and Control
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• v.12 no.4
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• pp.77-81
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• 2015

In general, the gears of mixer reducer for concrete mixer truck make use of the differential type planetary gear system to rotate mixer drum smoothly on the initial conditions. The planetary gear system is very important part of mixer reducer for concrete mixer truck because of strength problem. In the present study, calculating the gear specifications and analyzing the gear bending & compressive stresses of the differential planetary gear system for mixer reducer are necessary to analyze gear bending and compressive stresses confidently, for optimal design of the planetary gear system in respect to cost and reliability. As a result, analyzing actual gear bending and compressive stresses of the planetary gear system using Lewes & Hertz equation and verifying the calculated specifications of the planetary gear system, evaluate the results with the data of allowable bending and compressive stress from the Stress-No. of cycles curves of gears.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.765-772
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• 2011

The present study summarizes a series of compressive tests on concrete cylinder in order to examine the stressstrain relationship of alkali-activated (AA) slag concrete. The compressive strength and unit weight of concrete tested ranged from 8.6 MPa to 42.2 MPa and from $2,186kg/m^3$ to $2,343kg/m^3$, respectively. A mathematical equation representing the complete stress-strain curve was developed based on test results recorded from 34 concrete specimens. The modulus of elasticity, strain at peak stress, slopes of ascending and descending branches of stress-strain curves were generalized as a function of compressive strength and unit weight of concrete. The mean and standard deviation of the coefficient of variance between measured and predicted curves were 6.9% and 2.6%, respectively. This indicates that the stress-strain relationship of AA slag concrete is represented properly with more accuracy in the proposed model than in some other available models for ordinary portland cement (OPC) concrete.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.481-488
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• 2016

Concrete member has been subjected to dead and live loads in use, and the induced stress can affect not only structural but also durability behavior. In mass concrete construction, construction joint are required, however cold joint usually occur due to poor surface treatment and delayed concrete placing. The concrete with joint is vulnerable to both shear stress and chloride ingress. This paper presents a quantitative evaluation of cold joint and loading conditions on chloride diffusion behavior. With increasing tensile stress from 30% to 60%, chloride diffusion coefficient gradually increases, which shows no significant difference from result in the sound concrete. However chloride diffusion coefficient under 30% level of compressive stress significantly increases by 1.70 times compared with normal condition. Special attention should be paid for the enlarged diffusion behavior cold joint concrete under compressive stress.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.141-149
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• 1996

The reinforced high-strength-concrete beam subjected to flexure moment behaves more brittly than the moderate-strength-concrete beam reinforced with equal reinforcement ratio($\rho$/$\rho_b$). Test results show that when the concrete strength exceeds 830kg/$cm^2$, the maximum reinforcement ratio should be less than $0.6{\rho}_b$ for ductile behavior (${\rho}_b$=balanced steel ratio). The ratio of flexural strength between experimental results and analytical results with rectangular stress block decrease as the compressive strength of concrete increase. The shape of the compressive stress block distributed triangularly. because the ascending part of the stress-strain curve shows fairly linear response up to maximum stress in contrast to the nonlinear behavior of the medium and low strength specimens.

• Structural Engineering and Mechanics
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• v.64 no.6
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• pp.793-802
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• 2017

The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce.

• Computers and Concrete
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• v.22 no.6
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• pp.563-572
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• 2018

Uniaxial compressive strength test and uniaxial compression creep one were produced on four groups of twelve concrete specimens with different hole number by RLW-2000 rock triaxial rheology test system. The relationships between horizontal holes and instantaneous failure stress, the strain, and creep failure stress, the strain, and the relationships between stress level and instantaneous strain, creep strain were studied, and the relationship between horizontal holes and failure mode was determined. The results showed that: with horizontal hole number increasing, compressive strength of the specimens decreased whereas its peak strain increased, while both creep failure strength and its peak strain decreased. The relationships between horizontal holes and compressive strength of the specimens, the peak strain, were represented in quadratic polynomial, the relationships between horizontal holes and creep failure strength, the peak strain were represented in both linear and quadratic polynomial, respectively. Instantaneous strain decreased with stress level increasing, and the more holes in the blocks the less the damping of instantaneous strain were recorded. In the failure stress level, instantaneous strain reversally increased, creep strain showed three stages: decreasing, increasing, and sharp increasing; in same stress level, the less holes the less creep strain rate was recorded. The compressive-shear failure was produced along specimen diagonal line where the master surface of creep failure occurred, the more holes in a block, the higher chances of specimen failure and the more obvious master surface were.

• Computers and Concrete
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• v.33 no.3
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• pp.309-324
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• 2024

Internal curing, a widely used method for mitigating early-age shrinkage in concrete, also offers notable advantages for concrete durability. This paper explores the potential of internal curing by partial replacement of sand with fine lightweight aggregate for enhancing the behavior of high-performance concrete at elevated temperatures. Such a technique may prove economical and safe for the construction of skyscrapers, where explosive spalling of high-performance concrete in fire is a potential hazard. To reach this aim, the physico-mechanical features of internally cured high-strength concrete specimens, including mass loss, compressive strength, strain at peak stress, modulus of elasticity, stress-strain curve, toughness, and flexural strength, were investigated under different temperature exposures; and to predict some of these mechanical properties, a number of equations were proposed. Based on the experimental results, an advanced stress-strain model was proposed for internally cured high-performance concrete at different temperature levels, the results of which agreed well with the test data. It was observed that the replacement of 10% of sand with pre-wetted fine lightweight expanded clay aggregate (LECA) not only did not reduce the compressive strength at ambient temperature, but also prevented explosive spalling and could retain 20% of its ambient compressive strength after heating up to 800℃. It was then concluded that internal curing is an excellent method to enhance the performance of high-strength concrete at elevated temperatures.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.501-506
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• 1998

This paper is an experimental study on the flexural strength and ductility capacity of reinforced high performance concrete beams with the concrete which has compressive strength of 600~700kg/$\textrm{cm}^2$, slump value of 20~25cm and slump-flow value of 60~70cm. Total 8 beams with different tensile reinforcement ratio and pattern of loading were tested. Form the results of reinforced high performance concrete beams, the equivalent stress block parameters proposed by MacGregor et al. or New Zealand code are recommended to use. Also, an extreme fiber concrete compressive strain of reinforced high performance concrete beams are distributed 0.0033~0.0048. In reinforced high performance concrete beams, reinforcement ratio in order to insure curvature ductility index 2 and 4 propose by ACI code should be less than those of reinforced normal strength concrete beams.