Restoring Force Characteristics Evaluation for Steel Concrete Composite Columns Without Cover Concrete

Abstract eng:
A steel reinforced concrete structure possesses the properties of both concrete and steel, and by having an appropriate design it is possible for such a structure to provide good earthquake resistance. High-rise concrete buildings with steel reinforcements displayed a good earthquake-resistance capacity when subjected to the Kanto earthquake (1923) as compared to ordinary reinforcements. Since then, the encased structural system, which is a form of composite construction, has been employed in Japan for most building frames taller than seven stories. However, the construction of ordinarily steel reinforced concrete buildings has decreased because of the demand for the reduction of the construction cost. That is because steel reinforced concrete structures used the steel, it is higher than reinforced concrete structures on both sides of material cost and construction cost. This situation is that the excellent mechanical property of steel concrete composite structure cannot be used. Thus, this research investigates how steel concrete composite columns can be earthquake-resistant, workable, and economical. Proposed new type steel concrete composite structure which can be used by changing into reinforced concrete structure is the best use of the characteristic of steel reinforced concrete columns and concrete filled steel tubular columns. This paper discusses steel concrete composite columns without cover concrete. The mechanical behavior of the columns with symmetric and asymmetric cross sections was confirmed through seismic loading tests under a constant vertical load. The test specimens were cantilever that assumes the behavior below the inflection point of the column. The experimental parameters were axial force ratio and shape of the steel. All the test specimens were designed so that failure under flexure occurred earlier than failure under shear. The test results showed that under the hysteresis characteristics of the columns with a symmetrical cross section under low axial compression, the hysteresis loop indicated a spindle-shape. Moreover, large ductility and a small amount of degradation in the strength due to repeated loading was observed. At the hysteresis characteristics of columns with an asymmetrical cross section, it is observed that the hysteresis loop indicated a spindleshape with some pinching, and columns under low axial compression displayed ductility. On the other hand, under the hysteresis characteristics of the columns with a symmetrical cross section under high axial compression, drastic strength deterioration after reaching the maximum carrying capacity was seen. Furthermore, a reduction in the deformation capacity became remarkable for the columns with an asymmetrical cross section. The structural tests made it clear that ultimate flexural strength could be evaluated by the superposed strength method, in which the ultimate strength of the steel flange, steel web and concrete. Moreover, we showed that the proposed evaluation method of restoring force characteristics matches the test result well.

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