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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korea Concrete Institute
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Korea Concrete Institute
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Volume & Issues
Volume 17, Issue 6 - Dec 2005
Volume 17, Issue 5 - Oct 2005
Volume 17, Issue 4 - Aug 2005
Volume 17, Issue 3 - Jun 2005
Volume 17, Issue 2 - Apr 2005
Volume 17, Issue 1 - Feb 2005
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Numerical Modeling of Heat Transfer in Reinforced Concrete Columns Exposed to Fire
Lee Chadon ; Shin Yeong-Soo ; Lee Seung-Whan ; Lee Chang-Eun ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 871~878
DOI : 10.4334/JKCI.2005.17.6.871
Reinforced concrete columns exposed to fire experience severe deterioration in material properties and subsequent structural capacities. Degree of losses in structural capacity of a column due to fire-damage mainly depends on the amount of heat transferred into the column during the fire. A reasonable heat transfer model of fire-damaged reinforced concrete column needs to take into account the heat-dependent nonlinear properties of heat conductivity and heat capacity of concrete as well as the evaporation of moistures in a section during the fire. Compared to the previously suggested models, the developed model in this study has included all these parameters in its numerical expressions based on explicit finite difference method. The developed model could predict the temperature changes with a reasonable accuracy for the columns exposed to fire.
Experimental Study on Setting Time of Cement Paste Mixed Accelerating Admixtures
Heo Gweon ; Choi Hong-Shik ; Yi Seong-Tae ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 879~884
DOI : 10.4334/JKCI.2005.17.6.879
The setting time is a very important factor affecting the quality of tunnel lining and reinforcement of inclined slope etc. Currently, however, the quality criteria of accelerating admixture to improve it is not established well. In this study, evaluation on setting time measuring methods of cement mixed a accelerating admixture (AA) was performed using Gillmore and Vicat needle test methods. For both test methods, the setting time for addition at a time was better than post addition regardless of initial setting and final setting. For Gillmore needle test method, two types of measuring methods were selected and it is noted that setting time with cement type under the same accelerating admixture can be different. Accordingly, manufacturing company shall develop a less sensitive accelerating admixture to cement type. For Vicat needle test method, six types of measuring methods were used and a proper measuring method of the admixture were proposed as follows: (1) the temperature of materials used shall be controlled exactly and (2) to evaluate its properties, an admixture usage of
(ratio of cement weight) is recommended.
Investigation on Behaviors of Concrete Interfaces Repaired Using Anchors
Song Hyung-Soo ; Lee Chin-Yong ; Yoon Dong-Yong ; Min Chang-Shik ; Choi Dong-Uk ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 885~892
DOI : 10.4334/JKCI.2005.17.6.885
Recently, the damaged concrete structures are often strengthened or repaired using the polymer concrete or the polymer cement mortar. In the repaired concrete structures at early ages, internal stresses could be developed due to the differential drying shrinkage of the repair material. Due to the difference of the thermal coefficients of the repair material and existing concrete, additional stresses also could be developed as the structures are subjected to the ambient temperature changes. Theses environmentally-induced stresses can sometimes be large enough to cause damage to the structures, such as debonding of the interface between the two materials. In this study, a rational procedure was developed where anchors can be designed and installed to prevent damages in such structures by thermally-induced stresses. Finally, through the experimental study and numerical study, the effects of the repair method using anchors with debonding was investigated and discussed the results.
Numerical Modeling of Residual Behavior of Fire-Damaged Reinforced Concrete Interior Columns
Lee Chadon ; Shin Yeong-Soo ; Lee Seung-Whan ; Lee Chang-Eun ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 893~902
DOI : 10.4334/JKCI.2005.17.6.893
Reasonable prediction of residual capacity of fire-damaged reinforced columns is important for both the safety measurement and the rehabilitation of the reinforced concrete structures suffered from exposure to extensive fire. In order to predict the residual behavior of fire-damaged reinforced concrete columns, its predictive model must be able to take into account the amount of heat transferred into the column, the level of deterioration of constituent materials and various column geometries. The numerical model presented in this research includes all these factors. The model has been shown to reasonably predict the residual behavior of fire-damaged columns. Parametric studies were performed using this model for the effects of cover thickness, exposure time to fire and column geometries on the residual behavior of reinforced concrete columns. It was found that serious damage on the residual capacity of column resulted from a longer exposure time to fire but only marginal differences from other factors.
The Prediction of Debonding Strength on the Reinforced Concrete Beams Strengthened with fiber Reinforced Polymer
Hong Geon-Ho ; Shin Yeong-Soo ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 903~910
DOI : 10.4334/JKCI.2005.17.6.903
In recent years, fiber reinforced polymer(FRP) plates have shown a great promise as an alternative to steel plates for reinforced concrete beam rehabilitation. Reinforced concrete beams strengthened with externally bonded FRP sheets to the tension face can exhibit ultimate flexural strengths several times greater than their original strength if their bond strength is enough. Debonding failure, however, may occur before the strengthened beam can achieve its enhanced flexural strength. The purpose of this paper is to investigate the debonding failure strength of FRP-strengthened reinforced concrete beams. An analytical procedure for calculating debonding load between concrete and strengthening FRP is presented. Based on the local bond stress-slip relationship in the previous studies, uniform bond stress is assumed on the effective bond length. The analytical expressions are developed from linear elastic theory and statistical analyses of experimantal results reported in the literature. The proposed method is verified by comparisons with experimental results reported in the previous researches.
Strain-Based Shear Strength Model for fiber Reinforced Concrete Beams
Choi Kyoung-Kyu ; Park Hong-Gun ; Wight James K. ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 911~922
DOI : 10.4334/JKCI.2005.17.6.911
A theoretical study was performed to investigate the behavioral chracteristics and shear strength of fiber reinforced concrete slender beams. In the fiber reinforced concrete beam, the shear force applied to a cross section of the beam was resisted by both compressive zone and tensile zone. The shear capacity of the compressive zone was defined addressing the interaction with the normal stresses developed by the flexural moment in the cross section. The shear capacity of the tensile zone was defined addressing the post-cracking tensile strength of fiber reinforced concrete. Since the magnitude and distribution of the normal stresses vary according to the flexural deformation of the beam, the shear capacity of the beam was defined as a function of the flexural deformation of the beam. The shear strength of the beam and the location of the critical section were determined at the intersection between the shear capacity and shear demand curves. The proposed method was developed as a unified shear design method which is applicable to conventional reinforced concrete as well as fiber reinforced concrete.
An Experimental Study on the High Strength Lightweight Self-Compacting Concrete
Choi Yun-Wang ; Kim Yong-Jic ; Moon Han-Young ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 923~930
DOI : 10.4334/JKCI.2005.17.6.923
This paper was to evaluate the high strength lightweight self-compacting concrete(HLSCC) manufactured by Nan-Su, which main factor, Packing Factor(PF) for mixing design, has been modified and improved. We have examined HLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition. The evaluation of HLSCC fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability(slump-flow), segregation resistance ability(time required to reach 500mm of slump-flow and time required to flow through V-funnel) and filling ability(U-box test) of fresh concrete. The compressive strength of HLSSC at 28 days has come out to more than 30MPa in all mixes. The relationship between the compressive strength-splitting tensile strength and compressive strength-modulus of elasticity of HLSSC were similar those of typical lightweight concrete. Compressive strength and dry density of HLSCC at 28 days from the multiple regression analysis resulted as $f_c
Applicability of Colormetric Method for Estimation of Chloride Penetration in Concrete Structures
Yang Eun-Ik ; Kim Myung-Yu ; Leem Young-Moon ; Park Hae-Geun ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 931~938
DOI : 10.4334/JKCI.2005.17.6.931
When concrete structures are exposed under marine condition for a long time, the steel in concrete is corroded due to the ingression of chlorides in the seawater. Because the damages of corrosion resulting from the chloride ion are very serious, many researches have been performed. Silver nitrate colormetric method that can measure easily penetration depth of chloride ion has been executed, recent)y. However, characteristics of silver nitrate colormetric method were not fully examined. Therefore, the objective of this paper Is to study the applicability of colormetric method. For the purpose of this, effect factors and reaction mechanism of colormetric method were investigated, and the colormetric method is applied for marine concrete structures. According to the results of silver nitrate colored method, two reactions such as white reaction of AgCl and brown reaction of AgOH were shown when
was sprayed in splited section. And velocity constant ratio(K) of two reactions appeared that white reaction, AgCl reacts with the fast speed by 3240. When the colormetric method was applied in concrete, it is reasonable that
solution more than 0.05N concentration was sprayed. It is confirmed that the colormetric method is useful tool for estimating the chloride of concrete structures in situ. The average chloride amount of colored parts indicates
per concrete unit weight.
Numerical Homogenization in Concrete Materials Using Multi-Resolution Analysis
Rhee In-Kyu ; Roh Young-Sook ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 939~946
DOI : 10.4334/JKCI.2005.17.6.939
The stiffness properties of heterogeneous concrete materials and their degradation were investigated at different-levels of observations with aids of the opportunities and limitations of multi-resolution wavelet analysis. The successive Haw transformations lead to a recursive separation of the stiffness properties and the response into coarse-and fine-scale features. In the limit, this recursive process results in a homogenization parameter which is an average measure of stiffness and strain energy capacity at the coarse scale. The basic concept of multi-resolution analysis is illustrated with one and two-dimensional model problems of a two-phase particulate composite representative of the morphology of concrete materials. The computational studies include the meso-structural features of concrete in the form of a hi-material system of aggregate particles which are immersed in a hardened cement paste taking due to account of the mismatch of the two elastic constituents.
Development of Optimum Grip System in Developing Design Tensile Strength of GFRP Rebars
You Young-Chan ; Park Ji-Sun ; You Young-Jun ; Park Young-Hwan ; Kim Keung-Hwan ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 947~953
DOI : 10.4334/JKCI.2005.17.6.947
Previous test results showed that the current ASTM(American Standard for Testing and Materials) grip adapter for GFRP(Glass Fiber Reinforced Polymer) rebar was not fully successful in developing the design tensile strength of GFRP rebars with reasonable accuracy. It is because the current ASTM grip adapter which is composed of a pair of rectangular metal blocks of which inner faces are grooved along the longitudinal direction does not take into account the various geometric characteristics of GFRP rebar such as surface treatment, shape of bar cross section as well as physical characteristics such as poisson effect, elastic modulus in the transverse direction and so on. The objective of this paper is to provide how to proportion the optimum diameter of inner groove in ASTM grip adapter to develop design tensile strength of GFRP rebar. The proportioning of inner groove in ASTM grip adapter is based on the force equilibrium of GFRP rebar between tensile capacity and minimum frictional resistance required along the grip adapter. The frictional resistance of grip adapter is calculated based on the compressive strain compatibility in radial direction induced by the difference between diameter of GFRP rebar and inner groove In ASTM grip. All testing procedures were made according to the CSA S806-02 recommendations. From the preliminary test results on round-type GFRP rebars, it was found that maximum tensile loads acquired under the same testing conditions is highly affected by the diameter of inner groove in ASTM grip adapter. The grip adapter with specific dimension proportioned by proposed method recorded the highest tensile strength among them.
Reliability of Load-Carrying Capacity of RC Deep Beams
Cheon Ju-Hyun ; Kim Tae-Hoon ; Lee Sang-Cheol ; Shin Hyun-Mock ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 955~962
DOI : 10.4334/JKCI.2005.17.6.955
Still no accurate theory exists for predicting ultimate shear strength of deep reinforced concrete beams because of the structural and material non-linearity after cracking. Currently, the load capacity assesment is performed for the upper structure of the bridges and containing non-reliability in the applications and results. The purpose in this study is to evaluate analytically the complex shear behaviors and normal strength for the reinforced concrete deep beams and to offer the accuracy load capacity assesment method based on the reliability theories. This paper presents a method for the load capacity assesment of reinforcement concrete deep beams using nonlinear finite element analysis. A computer program named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material non-linearity is taken Into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. From the results, determine the reliability index for the failure base on the Euro Code. Then, calculate additional reduction coefficient to satisfy the goals from the reliability analysis. The proposed numerical method for the load capacity assesment of reinforced concrete deep beams is verified by comparison with the others methods.
Shear Behavior of Large Prestressed Concrete Beams Cast with High Strength Concrete and the Effect of Draped Tendon on their Shear Behavior
Kim Kang-Su ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 963~974
DOI : 10.4334/JKCI.2005.17.6.963
This paper presented four shear test results from experimental tests of two large prestressed concrete beams cast with high strength concrete. In particular, this experiment investigated the effects of draped strands on shear behavior of these full-scaled beams. This study indicated that the use of draped strands increased the ultimate shear capacity as well as the web-shear cracking load. The test results also showed that draped strands reduced strand slip at ends of beams, which represented that these strands were effective to relieve the anchorage stresses. The test results were compared to predictions by two major codes; ACI 318-02 Building Code and AASHTO LRFD(2002). The shear design provisions in these codes provided conservative results on the shear strengths of all test specimens with reasonable margins of safety, and these provisions were particularly more conservative for test specimens having draped strands.
Base Isolation of the 1/3 Scaled RC Building with the Laminated Rubber Bearings
Chang Kug-Kwan ; Chun Young-Soo ; Kim Dong-Young ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 975~982
DOI : 10.4334/JKCI.2005.17.6.975
Scientific community agrees about the fact that base Isolation provides interesting solutions to minimize the seismic risk. Reliability of such a technique is nowadays proofed by a large number of applications like public buildings, nuclear plants, bridges, etc. This paper reports the results of performance verification tests of the base isolated RC building with the laminated rubber bearings which is manufactured by enterprise in Korea. The shaking table tests were performed using a three story model scaled to 1/3 of the prototype RC apartment building. Several major earthquake records were scaled to different peak ground accelerations and used as input base excitations. Especially in this study, effect of earthquake characteristics on response reduction and effect of the intensity of excitations are studied. Through the verification tests, the validity of the applied base isolaion device and the response reduction effect against earthquakes are confirmed
Evaluation of the Shear Strength of Reinforced Concrete Beams Strengthened with Continuous fiber Reinforced Polymer
Lee Jung-Yoon ; Hyang Hyun-Bok ; Kim Ji-Hyun ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 983~992
DOI : 10.4334/JKCI.2005.17.6.983
The shear failure modes of fiber reinforced polymer(FRP) strengthened concrete beams are quite different to those of the beams strengthened with steel stirrups. When the beams are strengthened with larger amount of FRP composites, the beams normally fail in shear due to concrete crushing before the FRP reaches its rupture strain. In order to predict the shear strength of such beams, the actual rupture strain must be known. The equations previously reported in the technical literature adopt an effective reduction factor for the rupture strain. These equations may not be applicable to FRP strengthened RC beams that are beyond the experimental application limits, because most of these equations are empirical in nature. This paper presents the results of an analytical study on the performance of reinforced concrete beams externally wrapped with FRP composites and internally reinforced with conventional steel stirrups.
Rip-off Failure Mechanism of Reinforced Concrete Beams Strengthened with CFRP Plate
Sim Jong-Sung ; Moon Do-Young ; Park Cheol-Woo ; Park Sung-Jae ; Choi Kwang-Min ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 993~1000
DOI : 10.4334/JKCI.2005.17.6.993
Various types of FRP materials have been applied for structural strengthening of RC beams in various forms. When CFRP plates are used, a premature failure used to occur before enough strengthening effect appears. This is primarily due to the rip-off of CFRP Plate attached on RC beams. Despite of numerous studies on the rip-off failure of externally strengthened RC beams, its failure mechanism is not definitely clarified yet. Investigations from literatures have shown that the rip-off failure is dependant on the vertical and shear stresses at the level of main reinforcements in RC beams. This study suggests an analytical model to Investigate the rip-off failure load based on the stress states at the level of main reinforcements. The proposed model is relatively simple and produces very comparable results to the test data. It is believed that the proposed model can be successfully used to provide more information on the rip-off failure mechanisms and its prevention.
Behavior and Failure Mode of Steel Coupling Beams Joint with FBP
Song Han-Beom ; Yi Waon-Ho ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1001~1009
DOI : 10.4334/JKCI.2005.17.6.1001
The usefulness of walls in the structural planning of multistory buildings has long been recognized. When walls are situated in advantageous positions in a buildings, they can be very efficient in resisting lateral load. Specially coupled shear wall system is the primary lateral load resisting system of buildings. It is customary to refer to such walls as being `coupled` by coupling beams. The coupling beams must exhibit excellent strength, stiffness ductility and energy dissipation capacity. To achieve these demands for steel coupling beam, steel coupling beam with Face Bearing Plate(FBP) embedded in the reinforced concrete walls is proposed. A comprehensive experimental test involving 2 steel coupling beam with and without FBP has been performed. Through experimental study, the evaluation of the advantage of that was establish and proposed the failure mode.
The Hydraulic Characteristics of Liquid Shotcrete Accelerators within Cement System
Shin Jin-Yong ; Kim Jae-Young ; Hong Ji-Sook ; Suh Jeong-Kwon ; Rho Jae-Seong ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1011~1018
DOI : 10.4334/JKCI.2005.17.6.1011
The influence of liquid shotcrete accelerators(alkali aluminate, two types of alkali-free) was investigated. Comparing to the existing alkali aluminate accelerator, new alkali-free accelerator, AF2, shortened initial and final setting of cement system, and after curing for 1 day compressive strength was analogous with others. On the other hand, compressive strength of specimen cured for 12 hour was the highest by the addition of alkali aluminate accelerator, but final strength was the lowest by that. But compressive strengths of AF1, AF2 were similar to Plain up to 28day. Further from XRD(X-Ray Diffractometer) and DSC(Differential Scanning Calorimeter) analyses, we confirmed that setting promoted by alkali aluminate was mainly because of Ca(OH)2(calcium hydroxide), but the accelerating behavior of alkali-free was influenced by the needle-like ettringite
Effect of Various Superplasticizers on the Hydration of Cement Paste
Shin Jin-Yong ; Kim Jae-Young ; Hong Ji-Sook ; Suh Jeong-Kwon ; Lee Young-Seok ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1019~1024
DOI : 10.4334/JKCI.2005.17.6.1019
To research effects of various chemical superplasticizers(Lignosulfonic acid, Naphthalene sulfonated formaldehyde condensate, melamine sulfonated formaldehyde condensate, and Polycarboxylate) on the hydration of cement, experiments involving XRD, SEM, and DSC have been analysed with cement paste specimens. Regardless of types and dosages of superplasticizers, hydration reaction of specimen applied superplasticizer was delayed to 3 day, but then it showed similarity to plain which don`t add superplasticizer. Moreover, the hydrating rate of cement paste was retarded as dosage of superplasticizer was increased. Also, kinetics related with hydrate of cement paste was slow in order of lignosulfonic acid, polycarboxylate, melamine and naphthalene sulfonated formaldehyde condensate. Nevertheless, when all kinds of chemical admixtures were used, morphologies of these hydrates were denser and more uniform than those of plain.
Long-Term Behavior of Square CFT Columns with Diaphragm
Kwon Seung-Hee ; Kim Tae-Hwan ; Kim Yun-Yong ; Kim Jin-keun ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1025~1032
DOI : 10.4334/JKCI.2005.17.6.1025
This paper presents experimental and analytical studies on long-term behavior of square CFT columns with diaphragm. In order to investigate the effect of the diaphragm on the long~term behavior, experiments for six specimens with two diaphragms and three different column length, and three-dimensional finite element analysis for each specimen have been performed. The finite element models considering the interface behavior between the steel tube and the inner concrete were verified from comparison of the test results with the analysis results. From the test and the analysis results, the following conclusions were obtained. The confinement effect created by the diaphragm does not depends on column length and influences only a part of the whole column that is from the end to the depth which is the same to the width of the column. The shortening of the column with diaphragm which covers more than a half of the cross sectional area of the inner concrete is the same as that of the column under a load applied on the steel tube and the entire section of the inner concrete.
Experimental Evaluation of Effective Flexural Rigidity in Reinforced Concrete Beams Considering Tension Stiffening Effect
Lee Seung-Bea ; Jang Su-Youn ; Kim Sang-Sik ; Lee Jin-Seop ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1033~1042
DOI : 10.4334/JKCI.2005.17.6.1033
Until recently tensile stresses in concrete have not been considered, since it does not affect the ultimate strength of reinforced concrete flexural members significantly However, to verify the load-deflection relationship, the effect of tensile stresses between reinforcing bars and concrete, so-called tension stiffening effect must be taken into account. Main parameters of the tension stiffening behavior are known as concrete strength, and bond between concrete and reinforcing bars. In this study total twenty specimens subjected to bending were tested with different concrete strength, coverage, and de-bonding length of longitudinal bars. The effects of these parameters on the flexural rigidity, crack initiation and propagation were carefully checked and analyzed.
On the Implementation of Fuzzy Arithmetic for Prediction Model Equation of Corrosion Initiation
Do Jeong-Yun ; Song Hun ; Soh Yang-Seob ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1045~1051
DOI : 10.4334/JKCI.2005.17.6.1045
For critical structures and application, where a given reliability must be met, it is necessary to account for uncertainties and variability in material properties, structural parameters affecting the corrosion process, in addition to the statistical and decision uncertainties. This paper presents an approach to the fuzzy arithmetic based modeling of the chloride-induced corrosion of reinforcement in concrete structures that takes into account the uncertainties in the physical models of chloride penetration into concrete and corrosion of steel reinforcement, as well as the uncertainties in the governing parameters, including concrete diffusivity, concrete cover depth, surface chloride concentration and critical chloride level for corrosion initiation. The parameters of the models are regarded as fuzzy numbers with proper membership function adapted to statistical data of the governing parameters and the fuzziness of the corrosion time is determined by the fuzzy arithmetic of interval arithmetic and extension principle
Cohesive Interface Model on Concrete Materials
Rhee In-Kyu ; Roh Young-Sook ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1053~1064
DOI : 10.4334/JKCI.2005.17.6.1053
The mechanical damage of concrete is normally attributed to the formation of microcracks and their propagation and coalescence into macroscopic cracks. This physical degradation is caused from progressive and hierarchical damage of the microstructure due to debonding and slip along bimaterial interfaces at the mesoscale. Their growth and coalescence leads to initiation of hairline discrete cracks at the mesoscale. Eventually, single or multiple major discrete cracks develop at the macroscale. In this paper, from this conceptual model of mechanical damage in concrete, the computational efforts were made in order to characterize physical cracks and how to quantify the damage of concrete materials within the laws of thermodynamics with the aid of interface element in traditional finite element methodology. One dimensional effective traction/jump constitutive interface law is introduced in order to accommodate the normal opening and tangential slips on the interfaces between different materials(adhesion) or similar materials(cohesion) in two and three dimensional problems. Mode I failure and mixed mode failure of various geometries and boundary conditions are discussed in the sense of crack propagation and their spent of fracture energy under monotonic displacement control.
Bearing Strength of Hybrid Coupled Shear Wall Connections
Park Wan-Shin ; Yun Hyun-Do ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1065~1074
DOI : 10.4334/JKCI.2005.17.6.1065
Due to lack of information, current design methods to calculate bearing strength of connections are tacit about cases in which hybrid coupled walls have connection details of stud bolts and horizontal ties. In this study, analytical study was carried out to develop model for calculating the connections strength of embedded steel section. The bearing stress at failure in the concrete below the embedded steel coupling beam section is related to the concrete compressive strength and the ratio of the width of the embedded steel coupling beam section to the thickness of the shear walls. Experiments were carried out to determine the factors influencing the bearing strength of the connection between steel coupling beam and reinforced concrete shear wall. The test variables included the reinforcement details that confer a ductile behavior in connection between steel coupling beam and shear wall, i. e., the auxiliary stud bolts attached to the steel beam flanges and the transverse ties at the top and the bottom steel beam flanges. In addition, additional test were conducted to verify the strength equations of the connection between steel coupling beam and reinforced concrete shear wall. The results of the proposed equations in this study are in good agreement with both our test results and other test data from the literature.
Estimation of Concrete Strength Using Improved Probabilistic Neural Network Method
Kim Doo-Kie ; Lee Jong-Jae ; Chang Seong-Kyu ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1075~1084
DOI : 10.4334/JKCI.2005.17.6.1075
The compressive strength of concrete is commonly used criterion in producing concrete. However, the tests on the compressive strength are complicated and time-consuming. More importantly, it is too late to make improvement even if the test result does not satisfy the required strength, since the test is usually performed at the 28th day after the placement of concrete at the construction site. Therefore, accurate and realistic strength estimation before the placement of concrete is being highly required. In this study, the estimation of the compressive strength of concrete was performed by probabilistic neural network(PNN) on the basis of concrete mix proportions. The estimation performance of PNN was improved by considering the correlation between input data and targeted output value. Improved probabilistic neural network was proposed to automatically calculate the smoothing parameter in the conventional PNN by using the scheme of dynamic decay adjustment (DDA) algorithm. The conventional PNN and the PNN with DDA algorithm(IPNN) were applied to predict the compressive strength of concrete using actual test data of two concrete companies. IPNN showed better results than the conventional PNN in predicting the compressive strength of concrete.
Structural Response of Reinforced Concrete Beams Strengthened with CERP Rod
Moon Do-Young ; Sim Jong-Sung ; Oh Hong-Seob ;
Journal of the Korea Concrete Institute, volume 17, issue 6, 2005, Pages 1085~1090
DOI : 10.4334/JKCI.2005.17.6.1085
Rod-type fiber reinforced polymer plastics(FRPs) similar to reinforcing steel bars have rarely been considered. In this study, an experiment was performed using beams strengthened with rod-type CFRPs and high-strength mortar overlay. The test results show that the strengthened beams not only had improved endurance limits but also improved load carrying capacities, stiffness values, and cracking loads as compared to a non-strengthened beam. Strengthened beams anchored with bolts throughout their entire span had more efficient structural behaviors, including composite behavior on the interface between the concrete and mortar, and load carrying capacity, than a strengthened beam anchored only on the end block.