| The prefabricated molded shell is a permanent formwork made of reinforced concrete.The concrete is poured into the shell to form a composite column.The use of prefabricated molded shell composite column can not only save the template loss and reduce the time of setting up the template,but also the self-weight of the prefabricated shell is lighter than that of the full prefabricated column,which is more convenient for engineering hoisting.In addition,the core post-casting area of the prefabricated molded shell composite column is connected with other components by casting in situ,which can improve the structural integrity of the prefabricated structure.However,as a new structural form,the mechanical properties of the prefabricated molded shell composite column are not well understood,which hinders the promotion of the product.In this paper,according to the area ratio of the prefabricated molded shell section to the column section,the prefabricated shell is divided into low prefabricated rate molded shell(area ratio below 33%)and high prefabricated rate molded shell(area ratio 33%~67%),and the mechanical properties of the composite column and beam-column joint with different prefabricated rate shell are studied.The main research contents and conclusions are as follows:(1)In order to study the axial compression performance of the composite column with different prefabricated molded shells,a cast-in-place column ZY-1,a composite column ZY-2 with low prefabricated rate molds and a composite column ZY-3 with high prefabricated rate molds were tested under axial compression.The results show that: a)the failure of the composite column with low rate of prefabricated molded shell is manifested as the split at the corner of the prefabricated shell,while the failure of the composite column with high rate of prefabricated molded shell is manifested as the split between the prefabricated molded shell and the core post-cast area.b)The ultimate bearing capacity of the prefabricated molded shell composite column is similar to that of the cast-in-place column.The axial compression capacity of low and high prefabricated molded shell composite column is 2.8% and 6.8% lower than that of cast-in-place column,respectively.(2)In order to study the bending and shearing properties of composite columns with different prefabricated rate molded shells,a cast-in situ column KZ-1,a composite column KZ-2 with low prefabricated rate molds and a composite column KZ-3 with high prefabricated rate molds were carried out under low cycle reciprocating loading tests in the horizontal direction.The test results show that: a)the failure mode of the three specimens is the bending failure of the column.b)The "hysteretic loops" of the hysteretic loops of the three specimens are all relatively full "bows".c)The prefabricated shell has little influence on the peak load of the composite column.The ratio of peak load of the three specimens was KZ-1: KZ-2:KZ-3= 1:0.996:0.979.d)The prefabricated shell has little effect on the ductility coefficient of the composite column,and the ratio of the ductility coefficient of the three specimens is KZ-1: KZ-2: KZ-3= 1:1.047:1.044.e)The prefabricated shell has little effect on the accumulated energy dissipation capacity of the composite column.When loaded up to 86 mm,the ratio of cumulative energy consumption of the three specimens was KZ-1: KZ-2: KZ-3= 1:0.972:0.922.f)The initial stiffness of the composite column is greatly affected by the high prefabricated rate molds.When loaded up to 10 mm,the ratio of stiffness of the three specimens is KZ-1: KZ-2:KZ-3= 1:0.946:0.862.After the specimen yield,the stiffness of the three is basically the same.(3)In order to study the seismic performance of prefabricated molded shell composite column beam-column joints with different prefabricated rates,low-cycle reciprocating load tests on the beam end of a cast-in-place joint LZ-1,a low-rate composite column joint LZ-2 and a high-rate composite column joint LZ-3 were conducted.The test results show that: a)the bending failure of the beam ends occurred in all three specimens,which conforms to the design concept of "strong shear and weak bending,strong column and weak beam,strong joint and weak component".b)The "hysteretic loop" of the hysteretic curve of the cast-in-place joint and the composite column with low prefabricated rate molded shell is full "bow".However,the hysteretic loop of the beam-column joints with high precast rate shows a pinched "S" shape,which indicates that the seismic performance of the composite column is worse than the previous two.c)The ratio of peak load of the three specimens is LZ-1: LZ-2: LZ-3= 1:1.019:0.961.d)The initial stiffness of the beam-column joint is greatly affected by the high prefabricated shell.When loaded up to 10 mm,the stiffness ratio of the three specimens was LZ-1: LZ-2: LZ-3=1:1.022:0.759.e)The cumulative energy dissipation capacity of beam-column joints is greatly affected by high prefabricated rate molds.When loaded up to 82 mm,the ratio of cumulative energy consumption of the three specimens was LZ-1: LZ-2:LZ-3=1:0.995:0.840.f)The ratio of ductility coefficients of the three specimens is LZ-1: LZ-2: LZ-3= 1:1.13:0.98.(4)In order to further study the mechanical properties of the prefabricated molded shell composite column,a numerical calculation finite element model was established in this paper,and the calculated results were compared with the experimental values to verify: a)In this paper,the equivalent friction force was chosen to simulate the tangential action between the prefabricated molded shell and the concrete in the core post-pouring area,and the equivalent friction coefficient was set as 0.4.The "hard" contact is used to define the normal action between them.b)During modeling,the influence of grouting sleeve is ignored and the column reinforcement is connected up and down;c)The simulation results show that the failure modes and peak loads of the model specimens under the action of bending and shearing loads are consistent with the test results,which proves that the finite element modeling method adopted in this paper can reflect the stress conditions of the prefabricated composite shell column under the action of bending and shearing loads.The finite element model was used to numerically study the effects of the bond strength between the prefabricated molded shell and the concrete in the core post-cast area,the axial compression ratio and the concrete strength grade on the flexural and shear performance of the prefabricated molded shell composite column.The results show that: a)the strength of the bond between the prefabricated molded shell and the concrete in the core post-cast area has little effect on the peak bearing capacity of the prefabricated molded shell composite column.When the equivalent friction coefficient between the prefabricated molded shell and the core concrete is increased from 0.2 to 0.8,the peak bearing capacity of the specimen is only 5% different;b)Increasing the axial compression ratio of the column can increase the peak value of the flexural shear capacity of the prefabricated molded shell composite column,but when the axial compression ratio is too high,the increase range of the peak value of the load decreases;c)The enhancement of the concrete strength grade of the prefabricated molded shell has a greater effect on the peak flexural shear bearing capacity of the prefabricated molded shell composite column than that of the enhancement of the concrete strength grade of the core post-pouring zone.(5)Summing up the experimental and numerical results,the formulas for calculating the axial compression bearing capacity and bending bearing capacity of the prefabricated molded shell composite column are given.Suggestions for engineering application,such as adding stirrups to low prefabricated rate molded shells and increasing concrete strength of high prefabricated rate molded shell,are given.There are 118 figures,28 tables and 84 references in this paper. |
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