Mechanical Characteristic of Steel Reinforced Concrete Columns With Low-Strength Concrete

Abstract eng:
Steel reinforced concrete structure possesses the properties of both concrete and steel, and by appropriate design it is possible to provide good earthquake resistance in such structures. High-rise buildings of steel reinforced concrete construction showed good earthquake-resistant capacity under the Kanto earthquake (1923) as compared with ordinary reinforced concrete structures. Since then the encased structural system, a form of composite construction, has been employed in Japan for most building frames higher than seven stories. Though no steel reinforced concrete buildings had been collapsed by the previous earthquakes in Japan, it was reported that steel reinforced concrete buildings were damaged seriously owing to Hyogoken-Nanbu earthquake (1995) in Japan. Those buildings were existing buildings which had been built before the law revision in 1981. After the Hyogoken-Nanbu earthquake, seismic evaluation and retrofit in concrete buildings were executed aggressively. According to some reports of seismic evaluations of existing reinforced concrete buildings, the presence of reinforced concrete buildings with low-strength concrete has been confirmed. In the standard for seismic evaluation of existing concrete buildings by the Japan Building Disaster Prevention Association (JBDPA), coverage of concrete compression strength is assumed to be 13.5N/mm2 or more. It is necessary for evaluation and retrofitting to clarify the mechanical characteristics of low strength concrete and seismic performance of low strength concrete members and frames. Over the past few years, several studies have been made on mechanical characteristic of reinforced concrete members and frames with low-strength concrete. However, seismic evaluation and retrofit of steel reinforced concrete buildings with lowstrength concrete has never been studied so far. Therefore, little is known about mechanical characteristic of steel reinforced concrete buildings with low-strength concrete. In this research, shear strength of steel reinforced concrete columns with low-strength concrete are investigated through the seismic loading tests under the constant vertical load. The considered parameters in the tests are as follows, steel type, axial load level and concrete strength. Concrete specified design was assumed to be 9N/mm2 and 18N/mm2. Main discussion is concentrated on the maximum strength, the behavior before and after the attainment of the maximum strength and hysteretic characteristics. From the test results, it is found that the ultimate shear strength cannot be evaluated using the present equation recommended in JBDPA, design standard for the steel reinforced concrete columns with low-strength concrete. On the other hand, we confirmed that the ultimate shear strength can be estimated the equation based on the theory of truss and arch mechanism in Architectural Institute of Japan (AIJ) design for the steel reinforced concrete standard with low-strength concrete.

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