Kompozit Kolon Elemanların Modal Davranışlarının Belirlenmesi

Many structures built in the past was made of wood and stone. But timely, new materials are developed such as reinforced concrete and steel. This provides strength and safety structures. However, composite elements are started to use to build more economic, safer, more ductility and taller structures. A composite element is generally defined as usage of steel and concrete together. In a composite element, concrete core is covered with steel tubes, or a steel profile is replaced to a concrete volume. Nowadays in the world and especially in Turkey, many high-rise building started to build. However, Turkey is placed on an active fault which was produced huge earthquakes in the past. So these high-rise buildings have to be designed against to huge earthquakes. The earthquake behavior of the structures is related to modal responses of the structures. Modal responses of the structures contains of dynamic characteristics of structures such as natural frequencies and mode shapes. According to literature review and practices, in a composite element, steel covers the concrete and this makes to response of concrete as a compression in three directions; and concrete prevent to steel to inward buckling. So the axial loading capacity of the element is increased, also rigidity and ductility of the element are increased. This makes the composite elements more preferable in construction of the buildings. In the literature it is seen that there are several composite element section typ. In this study, modal responses of composite columns are investigated. For the purpose, a composite column with eight different section but the same height are selected which are commonly used in literature and practice and 3D modeled in ANSYS software. Before starting analyses, a ideal finite element mesh model is examined for a composite column performing free vibration analyses, and other models are constituted similar numbers of finite elements and nodes with the ideal finite element mesh model. Free vibration analyses of all models are performed and natural frequencies and mode shapes are obtained. The dynamic characteristics are compared to each model and presents as tables and graphs. Also, the comments for different composite columns are presented in the study. The eight different composite sections subjected to numerical example are defined as; C Model: Concrete-filled one-skin steel circular tube (Figure 2a), C_C Model. Concrete-filled double-skin steel circular tube (Figure 2b), C_C_L Model: Reinforced concrete-filled doubleskin steel circular tube (Figure 2c), R Model: Concrete-filled one-skin steel rectangular tube (Figure 2d), R_R Model: Concrete-filled double- skin steel rectangular tube (Figure 2e), R_R_L Model: Reinforced concrete-filled doubleskin steel rectangular tube (Figure 2f), R_C Model: Concrete filled double-skin steel circular tube (Figure 2g), R_C_L Model: Reinforced concrete filled doubleskin steel circular tube (Figure 2h), The all section types are 3D modeled as a composite column in ANSYS finite element software (See Figure 4) and free vibration analyses are performed. The natural frequencies and mode shapes are presented in Table 6 and Figures 7 and 8. According to analyses results, first eleven natural frequencies are changed between 36-945 Hz. The mode shapes are obtained as lateral bending modes in X, Y directions and torsion modes in vertical direction. Compared to models, it is seen that the natural frequencies of C_C model is lower than these of C model. However the natural frequencies of C_C_L model similar to these of C_C model. This shows that the C model has %10 more rigidity than C_C and C_C_L models. Similar results obtained for R, R_R and R_R_L models compared to each other. On the other hand, circular composite columns have % 8-10 more flexibility than rectangular composite columns (R, R_R, R_R_L models). But the reinforced composite columns (R_C, R_C_L models) behave similarly as other composite columns ((R_R, R_R_L models)