Dynamic Increase Factor of Concrete Compressive Strength Considering the Pure Rate Effect

Dynamic increase factor;rate effect;inertia effect;strain rate;strain acceleration;split Hopkinson pressure bar;concrete compressive strength;624

공과대학 건설환경공학부 ;

University:서울대학교 대학원

关键词: Dynamic increase factor;    rate effect;    inertia effect;    strain rate;    strain acceleration;    split Hopkinson pressure bar;    concrete compressive strength;    624;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/137308/1/000000144919.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

Structures under extreme events like collision of car, ship, and aircraft, explosion, earthquake, tsunami, etc. are loaded at higher deformation rate than that under quasi-static state. Therefore, in order to design economically and analyze accurately concrete structures under extreme events, dynamic material properties of structures should be investigated.Meanwhile, concrete is the material having the rate dependent property, which is that material properties like compressive and tensile strength, critical strain, etc. are changed along strain rate. Especially, concrete compressive strength becomes higher as strain rate is increased. It is caused by two reasons. First, loading duration of extreme events is too short to propagate cracks. Second, water in voids induces the inertia effects to resist deformation. This phenomenon is called as the rate effect on concrete compressive strength, and dynamic increase factor (DIF) has been used widely to consider the rate effect in analysis and design of concrete structures.Various DIFs have been suggested until now, but the DIFs have common problems. First of all, DIF has been assumed as a function of only strain rate, so other variables like static strength, strain acceleration, specimen shape, density, etc., which can influence on results of dynamic material test, were not considered. Therefore, the test data of DIF was spread widely at a strain rate point. Furthermore, the test data of DIF includes the axial and radial inertia effects, but the inertia effects were misinterpreted as the rate effect. However, the inertia effects are already covered in the equation of motion, so unconservative results can be derived by considering repetitively the inertia effects in a constitutive equation with DIF.In this study, analytical model of split Hopkinson pressure bar (SHPB) test for a linear elastic specimen was investigated to find out important variables causing the inertia effects in dynamic material test. Then, apparent DIF was suggested with the key factors by conducting nonlinear regression analysis for concrete SHPB test results. Finally, DIF considering the pure rate effect was suggested by correcting the inertia effects in apparent DIF. In order to verify proposed DIF, finite element analyses for concrete SHPB tests with proposed and representative DIFs were performed, and it was confirmed that proposed DIF predicts apparent dynamic strength of specimens with high accuracy. Methodology correcting the inertia effects in results of dynamic material test in this study can be extended for evaluations of impact and explosion resistance performances of cementitious material like fiber reinforced concrete, etc. Furthermore, it is expected that the proposed DIF can be applied to design, evaluation of safety, and behavior analysis for concrete structures under extreme events.