Study On Compressive Behavior Of Precast Concrete Columns With Large-diameter Rebars

In this paper,relying on the national "13th Five-Year" key R&D project-the theory of high efficiency reinforcement and performance-based design of precast concrete members,it is put forward that in prefabricated concrete columns,large diameter steel bars are used instead of small diameter rebars.In the case of the same reinforcement ratio,the spacing of the longitudinal reinforcement is increased and the joints in the prefabricated columns can be optimized.The connection mode eliminates the excessive distribution of the longitudinal rebar in the specimen making,the concrete is difficult to be poured and the pouring is not compacted,so that the component is simple to be made,and the installation is convenient,and the production efficiency of the component is improved.In this paper,the static tests of 5 prefabricated concrete axial columns with large diameter steel bars and 5 prefabricated concrete columns with large diameter rebars are carried out.The failure modes of axial compression columns and eccentric columns are studied.The influence of the diameter of steel bar,the strength grade of rebar and the distance between the longitudinal reinforcement on the mechanical behavior of the axial compression columns and the diameter of the rebar and the eccentricity are analyzed.The influence law of the force performance of the eccentric pressure column.The applicability of the current specification formula to the ultimate bearing capacity of longitudinal compression columns with large diameter rebars and large spacing reinforcement is studied.The main conclusions are as follows:(1)The axial compression test specimen with large diameter rebar,when the specimen reaches the ultimate bearing capacity,the failure form is the longitudinal reinforcement to yield strength,the concrete is crushed in the middle of the column,and the damage characteristic is the same as the axial compression reinforced concrete column;(2)In the small eccentric compression test of large diameter rebar,when the test piece reaches the ultimate bearing capacity,the failure form is that the compression bar at the near side of the distance loading point basically reaches the yield strength,the concrete reaches the ultimate compressive strain and is crushed;the rebar from the far side of the loading point is not yielded,and the damage characteristic is the same as the small eccentric reinforced concrete compression column;through the measured strain distribution,it can be concluded that the large diameter precast concrete small eccentrically loaded columns conform to the plane section assumption;(3)The comparative analysis of the bearing capacity calculated by the measured ultimate bearing capacity of axial compression and small eccentric pressure specimens and the relevant formulas of GB50010-2010(2015 Edition)of the concrete structure design code of China shows that the prefabricated concrete axial compression columns and small eccentric compression columns are adopted in the axial compression test parts and the small partial pressure specimens.The column can still use our current specification formula and has enough safety reserves.The unidirectional static test was carried out.It is necessary to do further research on the performance of large diameter precast reinforced concrete columns under seismic action,so that they can be applied in engineering.