# Effect of Load Transfer Section to Toughness for Steel Fiber-Reinforced Concrete
## 1 Introduction  
The quality of concrete is gradually deteriorated in the long-term degradation process involving minute cracks due to the dry shrinkage generated in the manufacturing process, the infiltration of damaging materials, and various loading conditions, and the concrete is eventually destroyed. The addition of fiber to concrete complements the brittleness of the concrete, thus enhancing the impact strength, delaying fracture, and greatly improving the ductility performance. Fiber-reinforced concrete can offer structural safety by transferring the load to the fiber after concrete matrix failure, and converts the concrete matrix failure to ductile fracture through the crack control process [1; 2]. Glass fiber, steel fiber, nylon fiber, Polypropylene (PP) fiber, or jute fiber can be mixed with the concrete, and steel fiber-reinforced concrete, with which thin and short steel fiber is mixed, exhibits a similar performance as the generic concrete in terms of the elastic modulus, but offers greatly improved flexural ductility after the concrete cracks thanks to the ductile behavior of steel fiber [3; 4; 5]. When continuous flexural load is applied to concrete, tensile load is generated from the lower part, in which the deflection of concrete starts, and after the progress of fine cracks, if an amount of stress exceeding what concrete can withstand is applied, fracture is instantaneously generated [6]. When the transferred cracks come in contact with the fiber, the fiber is detached or extended from the surface due to the binding force between the fiber and the matrix, at which some energy is dissipated thanks to the different material properties of concrete and steel fiber. The existing toughness evaluation methods of steel reinforced concrete often use the area up to a certain displacement of the load displacement graph. Among these methods, the flexural test using beam specimens is highly useful for toughness evaluation as it offers simpler specimen production and testing methods than any other test. The toughness evaluation method based on absolute valuesconsiders the area below the load displacement graph up to a displacement specified in the test method to be the energy absorbed by the steel reinforced concrete, and uses it as the toughness, whereas the other method based on relative values uses the ratio between the area below the load displacement graph up to the point at which the brittle failure of the material occurs, and the area of the nonlinear section. To date, Japan Society of Civil Engineers standard (JSC SF-4), Japan Concrete Institute standard (JCI SF-4), European Federation of National Associations Representing for Concrete standard (EFNARC), Korean Standards (KS F 2566) and American Society for Testing and Materials standard (ASTM C 1609) are the typical toughness evaluation methods based on absolute values, and French Standard P 18-409 and American Concrete Institute (ACI) 544 Guidelines are those based on relative values as shown in Table 1[3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Most of the latter methods, however, determine the dimensionless index by selecting the initial crack point and using the ratio between the area under the load deflection curve up to the deflection at the initial crack point and the area up to a certain deflection, and considerable differences may result based on the initial crack point selected by the tester in evaluating the toughness of fiber-reinforced concrete. Additionally, such difference in the selected initial crack point greatly influences the index value, resulting in inaccurate evaluation results.