ASEISMATIC PERFORMANCE OF HYBRID STEEL COLUMN CONSISTS OF HIGH STRENGTH STEEL FLANGE AND CONVENTIONAL STEEL WEB

Abstract

Recently in Japan, the pulse type earthquakes that cause large displacement responses have been more noticeable. Some of them are predicted to become much larger than the magnitude level used in the current design, so it is promoted to set new seismic wave levels for design and to study about new design methods. To reduce damage of buildings against huge earthquakes, it has been considered to increase the elastic limit deformation using high strength steels in columns and girders. In this study, on the contrary, we propose the frames using conventional girders and hybrid H-section columns that consist of flange manufactured from high strength steel and web made with conventional strength steel. In order to apply the hybrid H-section columns to a building, the following items should be clarified; (1) method of evaluating full-plastic strength, (2) understanding the behavior of the hybrid H-section alone, (3) understanding the behavior of the hybrid H-section column in a frame. To investigate these items, we fabricated several specimens and conducted stub column tests, bending and shear tests, and cruciform tests. The experimental findings are complemented by a finite element simulation study. In Chapter 2, at first, we derive a full-plastic moment of hybrid H-section column under combined stress, including axial force, shear force and bending moment. Secondly we assumed the application limit of the formula. The following chapter describes that the stub-column tests and bending and shear tests were conducted to comprehend the elasto-plastic behavior caused by local buckling. Chapter 5 and 6 describes that we conducted the beam-to-column subassemblages test to verify the effects on high strength steel flange caused by axial force and plastic deformation of beam-column connection. By the series of experiments and analyses, we obtained the following results; (1) Full-plastic moment of hybrid H-section column and the application limit are shown in chapter 2. (2) Within the limit of application, platicizing of conventional strength steel web has little effects on high strength steel flange, therefore the hybrid H-section column can be regarded as elastic member until it reaches full-plastic strength. Further, if the width-thickness ratio satisfies the FA rank, the axial-yield of the web in an early stage has little effects on flange local buckling strength and plastic deformation capacity. (3) The extension of axial tensile strain, which is one of the factors of the stress degradation, can be reduced by column axial force. “Break by tensile strain” of the hybrid H-section column can be avoided unless the column axial force is neutralized by the fluctuating axial force in the case of earthquakes. (4) The relationship between column-to-beam strength ratio and the deformability of a cruciform frame is revealed by finite-element analyses in chapter 6. We proposed the design method of the hybrid H-section column that consists of flange made with high strength steels and web made with conventional strength steels. We expect the hybrid H-section column to be utilized as reasonable aseismatic column member for reducing the damage against huge earthquakes.