Mechanical Property Of Concrete Columns With Welded Reinforcement Grids And Longitudinal Inner Ribs

The principal objective of this thesis is to investigate the mechanical behavior of a new cross-section type of RC columns. The concrete columns are confined with Welded Reinforcement Grids(WRG) as transverse reinforcement, and multiply longitudinal inner rids are embedded in core concrete. This type of columns has two features compared to conventional RC columns. One is that stirrups are replaced by WRG, the other one is that high-strength longtitudinal rids are embedded in the core concrete, which is similar to steel reinforced concrete(SRC) columns. The section size of frame columns are effectively reduced with multiple longitudinal inner rids. WRGs are prefabricated in factory with low dimensional tolerances, and the columns with WRG become easier and faster in assembling compared to ones with conventional tie reinforcements. Sixteen concrete columns wiht different corss sections were tested under axial compression loads or cyclic loads. The purpose of this thesis is to evaluate the mechanical behavior of WRG columns based on test results, finite element analysis(FEA) and theoretical analysis. The main research works and results are as follows:(1) Six WRG columns and two RC columns were tested under monotonic compression load. The tests are trying to analyse the effectiveness of WRG in providing lateral confinement of core concrete. The ultimate axial bearing capacity of WRG columns is highly improved with high strength longitudinal rids embedded in it. The results indicate that WRG and the longitudinal inner rids work together in good performance. The lateral restraint provided by WRG ensures the material strength of longitudinal inner rids and concrete are fully utilized.(2) The mechanism of WRG columns is investigated using FEM software due to the stress of core concrete and stirrups. The increasing coefficient of core concrete strength confined with WRG is anslysed according to the test results and current available researches. The results show that C60 specimens have a higher increasing cofficient than FEA results and theoretical results in current articles. Howerer, the core concrete strength of C80 specimens increases less than that of C60.(3) Low reversed cyclic loading tests were also conducted with the same specimens. Hysteresis behavior, ductility, energy dissipation capacity and failure modes were analyzed. The results indicate that both WRG and longitudinal inner rids improve the seismic performance of RC columns.With the increase of longitudinal steel ratio, the ductility of RC columns decrease under the same axial compression ration. However, the specimen WRC-9 with the highest the longitudinal steel ratio behave well in ductility, whose displacement ductility factor reach 4.6, greater than 3.0. It indicates the specimens meet the seismic design requirements well.(4) According to the test results and current codes, this thesis proposes a series of ansys method, consist of normal section strength calculation, general design requirements, ultimate bearing capacity and the limit value of axial compression ratio. The analytical results suggest that the limit value of axial compression ratio of WRG columns should be adjusted with the longitudinal steel ratio.