|主題||Effect of Flexural Stiffness of Lateral Reinforcement on Confinement of Reinforced Concrete Columns|
|筆頭著者||Paulus Irawan（The University of Tokyo）|
|連名者1||Tirath Manojya Pallewatta（The University of Tokyo）|
|連名者2||Koichi Maekawa（The University of Tokyo）|
A way to achieve the required ductility in the critical regions of seismic resistant reinforced concrete columns is to use lateral reinforcement. Lateral bars that surround the core concrete will give some resistance in the form of three-dimensional confinement to the core concrete. As widely known, this confinement will increase the strength and ductility of the core concrete. Degree of influence of lateral bars to three-dimensional stresses and in turn to the strength gain and ductility of core concrete depends on geometrical factors, such as volumetric ratio of steel, shape and distribution of reinforcement, spacing, and properties of steel and concrete.
Since lateral bars will affect the stress distribution inside core concrete, accurate modeling of the lateral bars in the analysis is crucial. In general, truss modeling of lateral bars, which is rooted in axial stiffness of bars and causes "corner action", is regarded as appropriate for lightly reinforced lateral steel. However, it was also reported that large reinforcement induces additional confinement owing to the shear and flexural stiffness of bars. The aim of this study is to experimentally and analytically verify how large the influence of beam actions of ties to the confinement of core concrete and how effectively it gives rise to the strength and ductility gain.
It is concluded that from experiments and analytical study that shear and flexural stiffness of lateral bars will affect the stress and fracture distribution in core concrete. Shear and flexural stiffness of lateral bars will improve the confinement to the core concrete, which will create more uniform distribution of stress and fracture. This additional confinement will increase the strength gain and ductility.
Triaxial elasto-plasticity and continuum fracturing concrete model based finite element program "COM3"is verified to be able to predict the stress-strain of confined column and confinement stress arising in the reinforcing bars quite well for both truss- and beam-idealized analyses of reinforcing bars.
It is also shown that for square section, shear and flexural stiffness (beam action) is negligibly small if the lateral reinforcement ratio is smaller than 1.5% and the square of bar diameter to its span [(φ/L)2] is less than 2%. Above this range, beam action of lateral ties should be taken into account in the analysis of three-dimensional reinforced concrete column members. Here, full three-dimensional finite element analysis was used as a simulator in order to reproduce the perfect truss and beam actions and to separate their effects.