• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.95-104
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• 2016

Flexural strength of concrete ground slab reinforced with steel fiber is evaluated using the equivalent flexural strength ratio of steel fiber reinforced concrete based on the yield line theory. Recently, the European standard specifies that the tensile performance of the steel fiber reinforced concrete be evaluated directly from the residual flexural strength after the cracking of concrete. Thus, in the study, an experiment was carried out to evaluate the conventional equivalent flexural strength ratio and the residual flexural strength of the steel fiber reinforced concrete. Then the design flexural strength was investigated according to the location of a point load, based on the ratio of the radius of contact area of the load to the radius of relative stiffness. Design flexural capacity obtained from ACI 360R-10 was smaller than that from TR 34 (2003 & 2013). In addition, TR 34 (2013), which evaluates the design flexural capacity based on the residual flexural strength, showed slightly smaller value than TR 34 (2003).

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.47-54
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• 2016

In this study, the flexural capacity of fiber reinforced concrete floor slabs were evaluated using main design loads, racking and moving loads. Based on design standards and guidelines, the magnitude and loaded area of each load were determined, and its relationship was assessed. For the application of a single load, flexural capacity should be evaluated in the edge of a floor slab. In addition, the slab with thickness and concrete strength, greater than 180mm and 35MPa, respectively, sufficiently satisfied flexural capacity with a minimum of equivalent flexural strength ratio. The combination of racking loads required the largest equivalent flexural strength ratio to satisfy the flexural capacity of the floor slab. The combination of racking and moving loads showed equivalent flexural strength ratio smaller than the case of combination of racking loads, but larger than the application of single racking or moving loads. The results of this study indicated that the flexure of fiber reinforced concrete floor slabs should be designed using the combination of design loads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.49-58
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• 2013

Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with constant axial load. Test specimens were designed with 4.5 aspect ratio. The selected test variables are longitudinal steel ratio, transverse steel ratio, yielding strength of longitudinal steel and axial load ratio. The test results of columns with different longitudinal steel ratio, transverse steel ratio and axial load ratio showed different seismic performance such as equivalent damping ratio, residual displacement and effective stiffness. It was found that the column with low strength of longitudinal steel showed significantly reduced seismic performance, especially for equivalent damping ratio and residual displacement. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications (Limited state design).

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.2
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• pp.145-154
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• 2020

Steel set is a structure that stabilize the NATM tunnel until the installation of shotcrete, and it is combined after the shotcrete is installed to improve stability. In this study, determination approach for the equivalent elastic modulus of shotcrete-lattice girder composite is newly suggested for tunneling simulation. Also, a method was presented to calibrate the equivalent elastic modulus through the comparison of the full 3D model and equivalent model. When the conventional equivalent elastic modulus is used for shotcrete-lattice girder composite, the flexural strength of equivalent model is 130% smaller than that of full 3D model. Equivalent elastic modulus is adjusted considering the error of flexural strength. It is found that the error of flexural strength obtained from adjusted equivalent model using adjusted equivalent elastic modulus is reduced less than 1%.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.51-60
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• 2010

Recently, a new type of polyolefin fiber having a good mechanical properties is being developed, and it is necessary to examine a possibility for the new fiber together to be used as a reinforcing fiber with other types of fiber or by itself. The objective of this study is to find flexural toughness and tensile strength of concrete reinforced with steel and polyolefin fibers. Four point beam tests were performed with 324 specimens following two standard tests methods: KS F 2566 and ASTM C 1399-02. From the test results, the effects of volume fraction of fibers, and aspect ratio of steel fiber on the toughness and tensile strength were investigated, and the optimal ratio of steel fiber to polyolefin fiber was suggested.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.365-372
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• 2002

This experimental investigation was conducted to examine the behavior of eight a third scale columns made of high-strength concrete(HSC). The columns were subjected to constant axial load corresponding to target value of 30 percent of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement(Ps=1.58, 2.25 ％), tie configuration(hoop-type, cross-type, diagonal-type) and tie yield strength(fy=5,600, 7,950 kgf/$\textrm{cm}^2$). Test results indicated that the flexural strength of all the columns did not exceed calculated flexural capacities based on the equivalent concrete stress block used in current design code. Columns with 42 percent higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-99 were shown ductile behavior. With axial load of 30 percent of the axial load capacity, the use of high-strength steel as transverse reinforcement may lead to equal or higher ductility than would be achieved with low-strength steel.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.638-644
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• 2002

The stress-strain relationship of polymer concrete flexural member was evaluated using C-shaped polyester concrete specimen, the compressive strength of which is 1400 kgf/$\textrm{cm}^2$. Eccentric compression test was performed to estimate the parameters, ${\alpha}$, ${\beta}$1, ${\gamma}$ for equivalent rectangular stress block. The ultimate moment strength ware obtained from the bending test on reinforced polymer concrete beams which were prepared with S different tensile steel ratios with a shear span ratio of 4.0. These values were compared with theoretical ultimate moment strengths, which were obtained using the parameters ${\alpha}$=0.61 and ${\beta}$1=0.73 from stress-stain curves of C-shaped specimens. The results showed that, when tensile steel ratio was over 0.50 $\rho$b, the experimentally obtained moment strengths were well matched with theoretically calculated values. In order to develop accurate criteria for polymer concrete flexural members, however, many other expermental studies for parameter determination are necessary using C-shaped specimens which have various compressive strengths and different sizes.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.117-124
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• 1998

본 연구는 고성능 철근콘크리트 보의 연성능력에 관한 실험이다. 실험변수로는인장철근비( )와 하중재하형태(1점가력과 2점가력)가 있다. 콘크리트의 실린더 압축강도가 800-900㎏/㎠, 슬럼프 20∼25㎝ 및 슬럼프 플로우가 60∼70㎝인 고성능 철근콘크리트 보의 휨 실험 결과,고성능 콘크리트는 일반강도 콘크리트보다 취성적인 성질을 나타냈으며, 이러한 성질은 고성능 콘크리트의 연성능력을 감소시켰다. 고성능철근콘크리트의 경우 등가응력블록 변수는 MacGregor블록이나 New Zealand 규준을 사용하는 것이 바람직하다. 또한, 극한 곡률을 구할때는 cu= 0.0042값을 사용하는 것이 타당하다고 사료된다. 고성능 철근콘크리트 보의 경우, 현재 ACI 규준의 철근비에서 허용하는 2 및 4 이상의 연성지수 확보는 각각 '/ 0.30 범위에서 정적하중 상태의 경우 철근비가 - '=0.60 b이하에서 가능하고 휨 부재의 모멘트 재분배를 위한 경우는 철근비를 - '=0.33 b이하로 낮추어야 할 것으로 판단된다.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.365-376
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• 2011

The current Concrete Structural Design Code (2007) prescribe the equivalent rectangular stress block of the ACI 318 Building Code as concrete compressive stress distribution for design of concrete structures. The rectangular stress block may be enough for flexural strength calculation, but realistic stress-strain relationship is required for performance verification at selected limit state in performance-based design. Moreover, the ACI rectangular stress block provides non-conservative flexural strength for high strength concrete columns. Therefore a new stress distribution model is required for development of performance-based design code. This paper proposes a concrete compressive stress-strain distribution model for design and performance verification. The proposed model has a parabolic-rectangular shape, which is adopted by Eurocode 2 and Japanese Code (JSCE). It was developed by investigation of experimental test results conducted by the authors and other researchers. The test results cover high strength concrete as well as normal strength concrete. The stress distribution parameters of the proposed models are compared to those of the ACI 318 Building Code, Eurocode 2, Japanese Code (JSCE) and Canadian Code (CSA) as well as the test results.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.335-343
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• 2003

In the previous experimental study, it is verified that the ultimate strain of concrete (${\varepsilon}$$_{cu}$=0.003) and coefficient of equivalent stress block (${\beta}$$_1$) can be used for the analysis of RC beams under biaxial and uniaxial bending moment. However, the characteristics of stress distribution of non rectangular compressed area in the RC columns are different to those of rectangular compressed area. The properties of compressive stress distribution of concrete have minor effect on the pure bending moment such as beams, but for the columns subjected to combined axial load and biaxial bending moment, the properties of compressive stress distribution are influencing factors. Nevertheless, in ACI 318-99 code, the design tables for columns subjected to axial loads with bidirectional eccentricities are based on the parameters recommended for rectangular stress block(RSB) of rectangular compressed areas. In this study the characteristics of stress distribution through both angle and depth of neutral axis are observed and formulated rationally. And the modified parameters of rectangular stress block(MRSB) for non rectangular compressed area is proposed. And the computer program using MRSB for the biaxial bending analysis of RC columns is developed and the results of MRSB are compared to RSB and experimental results respectively.