• International Journal of Railway
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• v.3 no.2
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• pp.73-82
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• 2010

Global and local behaviors of a lightly RC shear walls are investigated in this paper. For the sake of cyclic behaviors, nominal ground accelerations of 0.15 g, 0.40 g and 0.55 g which associated with natural periods of the walls are applied as listed in French CAMUS-2000 shake table test. Modified Kent & Park model, Drucker-Prager model for concrete material and $Giufr\acute{e}$-Menegotto-Pinto model for rebar are used for time history analyses using fiber/solids elements respectively. Alternatively, Eulerian beam analysis are discussed by imposing inelastic hinges at the most possible plastic hinge location using modified Takeda's trilinear model with stiffness reduction. Relative displacements, base shears, bending moments of 5-story shear building with 36-tons of mass under bi-lateral seismic excitation are extracted and compared with EC-8, PS-92 and KBC-09 provisions. Multi-scaled degradation process; material damage, elemental fracture and structural failure in turn is discussed in the view of numerical accuracy, efficiency and limitation depending on three different model-based analyses.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.157-160
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• 2006

Carbon fiber reinforced polymer (CFRP) laminates can be used more efficiently in strengthening applications by applying prestress to the CFRP laminates. A key problem for prestressing with CFRP laminates is anchoring the laminates. These may include fracture to the CFRP laminates due to excessive gripping force or slippage of the CFRP laminates out of the anchorage zone caused by low friction between the anchor device and the lamiantes. The main objective of this study is the development of an applicative wedge-type anchorage system for prestressed CFRP laminates through experimental study. The experimental parameters were the type of anchorage and the effect of elastic modulus of tab. The test results showed that the developed anchor assures 100% CFRP laminate strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.229-232
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• 2006

The HPFRCCs show that the multiple crack propagation, high tensile strength and ductility due to the interfacial bonding of the fibers to the cement matrix. Moreover, performance of cement composites varies according to type and weight contents of reinforcing fiber. and HPFRCCs with hybrid fiber have better performance than HPFRCCs with single fiber in damage tolerance. Total four cylindrical specimens were tested, and the main variables were the type and weight contents of fiber, which was polyvinylalchol (PVA), polyethylene (PE). In order to clarify effect of hybrid types on the characteristics of fracture and damage process in cement composites, AE method was performed to detect micro-cracking in HPFRCCs under cyclic compression. Loading conditions of the uniaxial compression test were monotonic and cyclic loading. And from AE parameter value, it is found that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cvcle.

• Advances in concrete construction
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• v.13 no.2
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• pp.199-213
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• 2022

Experimental and discrete element approaches were used to examine the effects of F shape non-persistent joints on the failure behaviour of concrete under uniaxial compressive test. concrete specimens with dimensions of 200 cm×200 cm×50 cm were provided. Within the specimen, F shape non-persistent joint consisting three joints were provided. The large joint length was 6 cm, and the length of two small joints were 2 cm. Vertical distance between two small joints change from 1.5 cm to 4.5 cm with increment of 1.5 cm. In constant joint lengths, the angle of large joint change from 0° to 90° with increments of 30°. Totally 12 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, numerical simulation (Particle flow code in two dimension) were performed on the models containing F shape non-persistent joint. Distance between small joints and joint angles were similar to experimental one. the results indicated that the failure process was mostly governed by both of the Distance between small joints and joint angles. The axial loading rate on the model was 0.05 mm/min. The compressive strengths of the samples were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. In the first, there were only a few acoustic emission (AE) hits in the initial stage of loading, and then AE hits rapidly grow before the applied stress reached its peak. Furthermore, a large number of AE hits accompanied every stress drop. Finally, the failure pattern and failure strength are similar in both approaches i.e., the experimental testing and the numerical simulation approaches.

• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.569-582
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• 2018

Effects of crack separation, bridge area, on the tensile behaviour of concrete are studied experimentally and numerically through the Brazilian tensile test. The physical data obtained from the Brazilian tests are used to calibrate the two-dimensional particle flow code based on discrete element method (DEM). Then some specially designed Brazilian disc specimens containing two parallel cracks are used to perform the physical tests in the laboratory and numerically simulated to make the suitable numerical models to be tested. The experimental and numerical results of the Brazilian disc specimens are compared to conclude the validity and applicability of these models used in this research. Validation of the simulated models can be easily checked with the results of Brazilian tests performed on non-persistent cracked physical models. The Brazilian discs used in this work have a diameter of 54 mm and contain two parallel centred cracks ($90^{\circ}$ to the horizontal) loaded indirectly under the compressive line loading. The lengths of cracks are considered as; 10 mm, 20 mm, 30 mm and 40 mm, respectively. The visually observed failure process gained through numerical Brazilian tests are found to be very similar to those obtained through the experimental tests. The fracture patterns demonstrated by DEM simulations are mostly affected by the crack separation but the tensile strength of bridge area is related to the fracture pattern and failure mechanism of the testing samples. It has also been shown that when the crack lengths are less than 30 mm, the tensile cracks may initiate from the cracks tips and propagate parallel to loading direction till coalesce with the other cracks tips while when the cracks lengths are more than 30 mm, these tensile cracks may propagate through the intact concrete itself rather than that of the bridge area.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.158-170
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• 1994

The results of an experimental study on the manufacture and the mechanical properties of carbon fiber rekforced silica fume . cement composites and light weight fly ash . cement composites are presented in this paper. 11s the test results show, the flexural strength, fracture toughness and ductility of CF reinforced silica fume . cement composites were remarkably increased by the increase of carbon fiber contents. And the workability of the fly ash . cement composites were improved, but the compressive and flexural strength and bulk specific gravity of them are decreased by increasing the ratio of fly ash to cement. And the compressive and flexural strength of the fly ash cement composites by cured under the hot water were improved than those by mositure cured. Also, the manufacturing process technology of lightweight fly ash . cement composites in replacement of general autoclaved lightweight concrete was developed and its optimum mix proportions were proposed.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.323-331
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• 2012

This paper presents a new strengthening method on concrete column against seismic loads for structural performance tests. An X-bracing using high performance carbon fiber threads called the "Carbon fiber anchor X-bracing system" is used to connect RC frames internally. The carbon fiber sheet is wrapped around the column to fix the top and bottom of the column after Super anchor was installed by drilling hole on the column. The structural performance was evaluated experimentally and analytically. Two types of columns specimens were made; flexure fracture scaled model and shear fracture scaled model. For the performance evaluation, cyclic loading tests were conducted on moment and shear resisting columns with and without X bracing. Test results confirmed that the bracing system installed on RC columns enhanced the strength capacity and provided adequate ductility.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.447-455
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• 2006

A general purpose of 4-node co-rotational resultant shell element is developed for the solution of nonlinear problems of reinforced concrete, steel and fiber-reinforced composite structures. The formulation of the geometrical stiffness presented here is defined on the mid-surface by using the second order kinematic relations and is efficient for analyzing thick plates and shells by incorporating bending moment and transverse shear resultant forces. The present element is free of shear locking behavior by using the ANS (Assumed Natural Strain) method such that the element performs very well as thin shells. Inelastic behaviour of concrete material is based on the plasticity with strain hardening and elasto-plastic fracture model. The plasticity of steel is based on Von-Mises Yield and Ivanov Yield criteria with strain hardening. The transverse shear stiffness of laminate composite is defined by an equilibrium approach instead of using the shear correction factor. The proposed formulation is computationally efficient and versitile for most civil engineering application and the test results showed good agreement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.414-423
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• 2020

Fiber-reinforced polymer (FRP) laminate sheets, which are lightweight with high strength, are commonly used to reinforce concrete structures. The bonding strength is vital in structural design. Therefore, experiments and analytical studies with differing variables (concrete compressive strength and tensile strength, the elastic modulus of concrete and FRP, thickness of concrete and FRP, width of concrete and FRP, bond length, effective bond length, fracture energy, maximum bond stress, maximum slip) have been conducted to obtain an accurate numerical model of the bond strength between an FRP sheet and concrete. Although many models have been proposed, no validated model has emerged that could be used easily in practice. Therefore, this study analyzed the parameters that influence the bond strength that were used in 23 of the proposed models (Khalifa model, Iso model, Maeda model, Chen model, etc.) and compared them to the test results of 188 specimens via the numerical results of each model. As a result, an easy-to-use practical model with a simple and high degree of expression was proposed based on the Iso model combined with the effective bond length model that was proposed by Holzenkӓmpfer.

• Computers and Concrete
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• v.29 no.2
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• pp.81-92
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• 2022

The influence of normal stress perpendicular to the potential shear plane was always neglected in existing researches, which may lead to a serious deviation of the shear strength of concrete members in practice designs and numerical analyses. In this study, a series of experimental studies are carried out in this paper, which serves to investigate the shear behavior of concrete under compression shear loading. Based on the test results, a three-phase shear failure model for cohesive elements are developed, which is able to take into consideration the influence of normal stress on the shear strength of concrete. To identify the accuracy and applicability of the proposed model, numerical models of a double-noted concrete plate are developed and compared with experimental results. Results show that the proposed constitutive model is able to take into consideration the influence of normal stress on the shear strength of concrete materials, and is effective and accurate for describing the complex fracture of concrete, especially the failure modes under compression shear loadings.