Study On Fatigue Behavior Of Offshore Concrete Structure

ABSTRACT Offshore concrete structures shall be subjected to such alternating forces as wind, waves and sometimes earthquakes. These alternating forces may cause fatigue failure at the load below the ultimate static strength of reinforced concrete members. In order to know the fatigue characteristics, model tests have been carried out in static loading, alternating loading and cyclic compressive loading on various kind of large concrete beams by means of a electro-hydraulic fatigue testing machine. The results indicate that fatigue strength of shear failure is considerably smaller than that of flexural failure. It might be advisable that the allowable stress of reinforcement is 1, 800kg/cm2 in the case of reinforcement ? sy = 3,500kgjcm 2. And the maximum crack width under cyclic loading is roughly two times as wide as that under static loading. INTRODUCTION Many studies on fatigue characteristics of reinforced concrete members have been systematically carried out in Japan since 1963, because, at the time of introducing of high-tension deformed bars, it was presumed that fatigue strength of deformed bars would be lower than those of round bars. In those studies loads subjected to models were cyclic compressive loads : hereafter one-way loading, as to highway and railway bridges. However, considering the importance of alternative loads such as caused by waves, the present study paid much attention to the fatigue characteristics and fatigue strength of reinforced concrete under alternative loading: hereafter two-way loading. In this study it is scheduled to carry out a number of static loading, one-way loading and two-way loading tests of reinforced concrete beams. The experimental variables included were reinforcement ratios, concrete strengths and stirrup quantities. Measurement are made on the deflection of beams, strain of reinforcing bars and concrete, crack width and states of crack growth, the ultimate static strength and the fatigue strength. The present paper reports on ten of the static test results and the results of fatigue tests of twenty-one testing beams. The final report will be made up later, including the results of fatigue tests on the remaining test beams. ABRICATION OF TEST BEAMS The reinforcement ratio, concrete strength and stirrup quantity may be considered as the factors influencing fatigue strength. Reinforcement ratio adopted were 0.7% 1 .11 % and 1 .59% in consideration of the reinforcement ratio and concrete strength adopted for the outer wall of actual caissons for breakwaters. These reinforcement. ratio s are slightly on the high side compared with those of actual caissons. Two levels of concrete strength were taken, that is, 240kg/cm2 and 330kg/cm2. Stirrup quantities were determined with the ultimate strength design method regarding the ultimate strength to be the design load and all of the shear force due to design load to be beared by stirrups.