• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.2
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• pp.101-111
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• 2021

Two different types of shear-friction tests were classified by external loadings and referred to as a push-off and a pull-off test. In a pull-off test, a tension force is applied in the transverse direction of the test specimen to produce a shear stress at the shear plane. This paper presents a method to evaluate shear transfer strengths of uncracked pull-off specimens. The method is based on the compression field theory and different constitutive laws are applied in some ways to gain accurate shear strengths considering softening effects of concrete struts based on Modified Compression Field Theory (MCFT) and Softened Truss Model (STM). The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with the predicted values. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked pull-off test specimens. A shear strength evaluation formula considering the effective compressive strength of a concrete strut was proposed, and the applicability of the proposed formula was verified by comparing with the experimental results in the literature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.101-110
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• 2015

Recently, nine $1397{\times}1397{\times}178mm$ RC panels were tested under in-plane pure-shear monotonic loading condition using the Panel Element Tester by Hsu (1997, ACI). By combining the equilibrium, compatibility, and the softened stress-strain relationship of concrete in biaxial state, Modern Truss Model (MCFT, RA-STM) are capable of producing the nonlinear analysis of RC membrane panel through the complicated trial-and-error method with double loop. In this paper, an efficient algorithm with one loop is proposed for the refined Mohr compatibility Method based on the strut-tie failure criteria. This algorithm can be speedy calculated to analyze the shear history of RC membrane element using the results of Hsu test. The results indicate that the response of shear deformation energy at Big Bang of shear strain significantly influenced by the principal compressive stress-strain (crushing failure).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.217-224
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• 2020

In this study, a framework for optimizing the opening in an outrigger wall is proposed. To solve a constrained bounded optimization problem, an in-house finite element program and SQP algorithm in Python SciPy library are utilized. The openings of the outrigger wall are located according to the strut-tie behavior of the outrigger wall deep beam. A linear interpolation method is used to obtain differentiable continuous functions required for optimization, whereas a database is used for the efficiency of the optimization program. By comparing the result of the two-variable optimization through the moving path of the search algorithm, it is confirmed that the algorithm efficiently determines the optimized result. When the size of each opening is set to individual variables rather than the same width of all openings, the value of the objective function is minimized to obtain better optimization results. It was confirmed that the optimization time can be effectively reduced when using the database in the optimization process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.187-196
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• 2008

The punching shear strength of RC slabs is estimated analytically by the simple truss model. To avoid intrinsic difficulties in punching shear analysis of reinforced concrete slabs, the slabs were divided into three sub-structures as the punching cone and the remaining parts. The strength of the punching cone was evaluated by the stiffness of inclined strut. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement which passed through the punching cone. Initial angle of struts was determined by curve fitting method of the experimental data with variable reinforcement ratio in order to compensate for uncertainties in the slab's punching shear, the simplification errors and the stiffness of the remaining sub-structures. The validity of computed punching shear strength by simple truss model was shown by comparing with experimental results. The punching shear strength, which was determined by snap-through critical load of shallow truss, can be used effectively to examine punching shear strength of RC slabs.

• Earthquakes and Structures
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• v.26 no.1
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• pp.31-48
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• 2024

In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

• Journal of the Korea Institute of Building Construction
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• v.10 no.4
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• pp.11-20
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• 2010

This study carried out a Mock-up test to apply Low-heat Cement (CF) that is adjusted to a fineness of $3,000\;{\pm}\;200\;cm^2/g$ by substituting Coarse particle Cement (CC) and fly ash with ordinary Portland Cement (OPC), then applied it on-site. The result of the test is as follows. The Mock-up test showed that the amount of admixture in CF increased SP agent and AE agent slightly more compared to OPC, while temperature history showed that the highest temperature of CF was around $6{\sim}10^{\circ}C$ lower than that of OPC. Compressive strength in CF was low compared to that of OPC, but the strength width became narrow at the age of 28 days, which is not considered to be significant. In on-site application, slump, air content and chloride content all satisfied the target values, while the temperature history showed that the highest temperature in the center by each cast was about $34^{\circ}C$ in the first cast, $42^{\circ}C$ in the second cast, and $39^{\circ}C$ in the third cast. Compressive strength of specimen for strut management showed low value compared to standard curing, but its strength was reduced at the age of 28 days.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.347-358
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• 2009

Recently, it is getting into a good situation for the flat-plate slab system to be applied. The flat-plate slab without beam, however, is often too weak to control deflection properly compared to other typical slab-beam structures, for which the post-tension method is generally regarded as one of best solutions. The post-tension (PT) method can effectively control deflection without increase of slab thickness. Despite this good advantage, however, the application of PT method has been very limited due to cost increase, technical problems, and lack of experiences. Therefore, in order to reduce difficulties on applying full PT method under the current domestic circumstances and to enhance constructability of PT system, this research proposed the partial PT method with top jacking anchorage applied in a part of span as need. For the top jacking anchorage system, the efficiency of deflection control shall be considered in detail because it can vary widely depending on the location of anchorage that can be placed anywhere as need, and tensile stresses induced at back of the anchorage zone also shall be examined. Therefore, in this study, analysis were performed on the efficiency of deflection control depending on the location of anchorage and on tensile stresses or forces using finite element method and strut and tie model in the proposed top jacking anchorage system. The proposed jacking system were also applied to the floor slabs at a construction site to investigate its applicability and the analysis results of slab behavior were compared to the measured values obtained from the PT slab constructed by the partial PT method. The result of this study indicates that the partial PT method can be very efficiently applied with little cost increase to control deflection and tensile stresses in the region as a need basis where problem exists.