الفهرس | Only 14 pages are availabe for public view |
Abstract Composite column is a structural member that uses a combination of structural steel shapes and reinforced concrete to provide adequate load carrying capacity to sustain either axial compressive loads alone or a combination of axial loads and bending moments. The most usual types of composite columns are the concrete-filled steel tubes and the partially or fully encased steel profiles. Fully encased composite column provides compressive strength, stability, stiffness, improved fire proofing, and better corrosion protection. There is limited information on the performance of encased steel-concrete (ESC) columns constructed of high-strength concrete. For instance, the analytical approach of Eurocode 4 applies only to columns made of normal weight concrete in the strength classes C20/25 to C50/60. As such, this thesis presents an experimental and numerical investigation of the mechanical behavior of ESC columns made from normal strength (NS) concrete class C24/30 and high strength (HS) concrete class C56/70. The experiments comprise twelve ESC columns: four of which are axially loaded, while the other eight are subjected to axial load combined with lateral cyclic loads. The main design parameters investigated in the conducted experiments are concrete compressive strength, encased steel ratio, and axial compression load ratio (percentage of applied load to the nominal compressive strength of the composite column). Relative effects of these parameters on strength enhancement, stiffness degradation, displacement ductility, and mode of failure are examined. Measured experimental results showed that ESC columns built of HS concrete failed abruptly with cracks passing through aggregates, whereas ESC columns made of NS concrete failed more gradually. For columns with encased steel ratios of 4% and 6%, the ESC columns made of HS concrete had ductility indices that are less than those made of NS concrete by up to 25% and 22%, respectively. Nevertheless, ESC columns built of HS concrete were able to withstand up to 24% more lateral loads than corresponding ESC columns made of NS concrete. Furthermore, increasing the axial load ratio resulted in a loss in ductility and stiffness degeneration beyond the peak point. The finite element models are developed using the finite element program, Diana v.10.5. First, the results of the created FE model are compared to those of experimental research. It is found that the FE predictions reasonably agree with the corresponding experimental behavior. Subsequently, the validated FE model is utilized in an extensive parametric study to investigate the performance of encased steel-high strength concrete columns under different design and loading situations. The analyzed cases comprised columns with encased steel ratios of over 10% carrying various levels of axial compression. These cases are investigated with respect to column crack patterns, modes of failure, lateral strength, and ductility. The numerical results showed that increasing the encased steel ratio results in increased lateral strength and ductility. Moreover, in all cases, increasing the axial compression load level adversely affected the cyclic behavior of encased steel-high strength concrete columns by accelerating the degradation of column strength and stiffness. |