Research On Axial Compressive Load Bearing Capacity Strengthening By Section Enlargement Based On The Concept Of Confined Beam-column Joint

Reinforcement of RC frame column by traditional section enlargement methodneeds a overlapping layer．When the overlapping layer cannot be achieved due to thelimited conditions，the upper load cannot be effectively transfer to the lower newconcrete section，and can’t reach the expected effect of reinforcement．Our groupproposed a innovation method to reinforce the compression bearing capacity of RCframe column by section enlargement based on the concept of confined beam-columnjoint，under the condition of non overlapping layer，setting the joint enclosure to ensurethe upper load can completely transfer to the lower new concrete section in the jointheight range，and to ensure the reinforcement effective．In this paper，keeping in closeconnection with the three nearly full-scale component test by our group， thecompression bearing capacity of the RC frame column reinforced by the new methodwas analyzed，with the numerical simulation using the finite element analysis softwareABAQUS．The main research contents of this paper as follows：①Based on summing the typical failure modes of the concrete and reinforcedconcrete under axial compression and local compression，combining with the previousexperimental results，analyze the several possible failure modes and present thecorresponding countermeasures．Introduce the concrete constitutive model and failurecriterion in ABAQUS，determine the concrete damaged plasticity model parameters，and deduce the concrete constitutive model based on the experimental data．②Reasonably simplify the research object and establish the finite element modelbased on the experimental data．Through the core column model，the column reinforcedby traditional section enlargement have overlapping layer and non overlapping layermodel， respectively verify the result reliability using ABAQUS to analyze thecompression bearing capacity of the core column and the column reinforced bytraditional section enlargement under the full section compression load，and verify thenecessity to strengthen the beam-column joint without overlapping layer．Through thethree models based on the experimental data，verify the feasibility to strengthen thebeam-column joint without overlapping layer．Then，compare the calculated results withthe experiment results．③From the concrete principal stress trajectory，the concrete pressure diffusion along the height，the inner and outer longitudinal steel stress distribution along thecolumn height direction，and the stirrup stress process analysis，combined with theconstant stress distribution and new to old concrete interface shear stress，explain theworking mechanism to transfer load of the constrained beam-column joint．④Changing the three main parameters that affect the constraint effect，establish aseries of finite element models，obtain the compression bearing capacity under thedifferent parameter levels．Define the compression bearing capacity conversion factor，determine the limits of the three parameters．Use the statistical software SPSS tomultiple linear regression，obtain the regression formula which fit goodness up to0.969，and acquire the regression formula having the envelope meaning after theinspection by modify．⑤According to the analysis of ABAQUA calculation and statistical data，combining with engineering practice， put forward the calculation formula ofcompression bearing capacity and the beam-column joint construct connection detailabout the RC frame column reinforced by section enlargement based on the concept ofconfined beam-column joint，and put forward the construction technical requirements．...