Study On Basic Mechanical Behavior And Seismic Performance Of SRC-RC Transfer Columns

Steel reinforced concrete elements equipped with steel and form the steel reinforced concrete composite structures with excellent seismic performance. Not only strength and stiffness significantly increased, but also ductility greatly improved. On the other hand, higher project cost of steel reinforced concrete structure relative to the reinforced concrete structure caused by construction shape steel limits its applications in multi-storey buildings. Even in high-rise buildings, steel concrete structure is mainly used in a area of economically developed. In the economically underdeveloped areas, project cost is an important factor for structure application promoting. SRC-RC hybrid structure sets SRC columns in bottom floors with large axial force and RC columns in upper floors with relatively small axial force, so SRC structure and RC structure play their benefits in a more economic way. Short columns are avoided in bottom floors by shape steel strengthening which is mainly due to the large axial force, seismic performance of the structure promote without significant raise in project cost.SRC-RC hybrid framework exists the tansfer from steel reinforced concrete columns to reinforced concrete columns, mutations of bearing capacity and stiffness along the vertical floors are easy to form weak layers. For a comprehensive analysis on seismic performance of SRC-RC hybrid framework and looking for reasonable vertical conversion mode,7 working conditions of push-over analysis have been completed, the vertical transfer mode satisfy the requirement of relative order and code in China. In order to play the seismic performance of SRC-RC hybrid framework better, necessary measures should be taken for avoiding the appearance of weak layers and strengthening the positions where weak layers appropriately appear:to ensure beam hinge mechanism can be realized, the ratio of SRC floors to the total floors should not less than 1/3; increasing the number of longitudinal reinforcement appropriately in the bottom layers of RC part and reducing shape steel ratio of SRC columns in the floor adjacent to RC part can make the transition from SRC columns to RC columns rational.Experimental study on 21 SRC-RC transfer columns and 1 reinforced concrete column under low cyclic reversed loading is completed. The study mainly focuses on seismic behavior of transfer columns affected by extent ratio of shape steel, ratio of shape steel, axial compressive ratio and various conformations. Some factors of seismic behavior are studied and analyzed, such as hysteretic loops, skeleton curves, bearing ability, rotation angle, displacement ductility, degeneration ratio and energy dissipation ability. The study can provide research basis for the extensive applications of SRC-RC hybrid structures.Axial compression ratio of SRC-RC transfer columns must satisfy the basic seismic requirements ofμ≥3 and Ru≥0.02. The axial compressive ratios for different failure mode has been given respectively, according to failure features and failure locationThe extension length and configuration of shape steel in SRC-RC transfer columns are both the key factors for seismic performance determination, and generally concerned by a number of scholars. The minimum limits of shape steel extension is given based on the test data of SRC-RC transfer columns from Japanese scholars, which can guarantee the shape steel achieving the bend yield condition during loading period. The minimum extension length of shape steel is to ensure that steel can fully play its role, but the minimum requirements can not guarantee that SRC-RC transfer columns in the best working state, so the identified extension length of shape steel is ensured based on the consideration of the following four states:(1) SRC-RC transfer columns obtain the ductility for engineering applications; (2) shear force beard by shape steel is minimum; (3) the positon where shape shape steel truncated deviated from the potential plastic hinge region; (4) bending moment of the positon where shape shape steel truncated is minimum. Partially existence of shape steel in SRC-RC transfer columns generated the special shear failure pattern, thereby ductility and deformation capacity of the specimens can be promoted by reducing shape steel ratio. The shape steel ratio should not exceed 4% by setting hoops normally like reinforced concrete columns. The limit can go up to 6% by setting double hoops all over the height of columns, but not more than 8%. Three calculation methods for shear resistance capacity are proposed based on the shear mechanism of bond failure, shear failure and bending failure, which are applicable for the three failure patterns respectively. Equivalent shear span ratio of transfer columns is proposed based on the special configuration arrangement of shape steel, which displays the effect of partially existence shape steel on shear resistance capacity, and therefore the formula for shear resistance capacity calculation is derived in order to facilitate engineering application. The calculated results are consistent with those of the test.