ICF10 0900OR EFFECT OF IMPACT LOADING ON TENSILE STRENGTH OF CONCRETES M. DAIMARUYA, H. KOBAYASHI H. SHIZAWA, R.A. SIREGAR and Y. ISHIHATA Department of Mechanical Engineering Systems Muroran Institute of Technology 27-1 Mizumoto, Muroran, Hokkaido 050-8585, Japan ABSTRACT The tensile strength and strain rate sensitivity of concretes under impact loadings were examined by means of the method of reflected tensile stress waves. The experimental method is conducted by the Hopkinson bar technique and it is based on the superposition and concentration of tensile stress waves reflected both from the free ends of a striking bar and a specimen bar. The impact tensile experiment for concretes was carried out and the tensile strength of concretes under impact loadings was discussed as well as the effect of strain rates. This study focused on the estimation and measurement of strain rates using crack gages. As a result, the impact tensile strength of concrete at the strain rate of 100 sec-1 was found to be approximately twice of the static tensile strength, and it was remarkably influenced by strain rates ranging from 100 to 101sec-1. KEYWORDS Impact tensile strength, Concentration of tensile stress waves, Cumulative fracture probability, Strain rate, Crack gage, Concrete. INTRODUCTION The investigation of the mechanical characteristics and the fracture strength of concrete under high loading rate is increasingly important for the safe assessment of most engineering structures against impact loadings such as impingement of projectiles, explosions and enormous earthquakes [1-3]. Since concrete is inherently weak in tension, it is commonly used as a compressive member material in civil engineering structures. On the other hand, concrete is also used in protective structures designed to resist impulsive loads. Although impulsive loads are originally compressive, they may produce tensile stress waves in structural members developed at the free boundary and so on. It is difficult to isolate concrete structures from impact tensile stresses, even though static tensile loads on concrete members are avoided. Even in static tests, precise measurement of the tensile strength of concrete is known to be difficult as well as rocks and ceramics. For determining the static tensile strength of concrete materials, the splitting-tensile test is commonly used to avoid some difficulties associated with the direct tension. Many investigations on impact tensile strength of concrete materials
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