The Compressive Bearing Capacity Of Normal Section Of RC Short Column Reinforced By Section-increased Method Considering Secondary Loading

The section-increased method is one of common used methods of RC structure reinforcement.A simplified formula is used in the current design code for strengthening concrete structure in China,when calculating the normal section compressive bearing capacity of RC axial compression members reinforced by the section-increased method,which has not considered the second load and the constraint effect from the newly added concrete and steel bars.Aiming at the formula problems existing in the current design code,the research methods such as model test,numerical simulation and theoretical analysis are put forward in this paper,an improved practical design formula of RC axial compression short column reinforced by the section-increased method is intensively studied,in order to correct the formula in current design code.The main research work and conclusions are as follows:(1)Considering the thickness ratio of new and old concrete,the strength ratio of new and old concrete,the stress level index and the longitudinal reinforcement ratio of newly added rebar,and using the orthogonal test method,16 RC axial compression short column specimens were designed and manufactured.(2)The range analysis and variance analysis of orthogonal test results show that:new concrete thickness has the greatest influence on the compressive bearing capacity of the normal section,followed by the new concrete strength and stress levels,and the influence of new longitudinal reinforcement ratio on the compressive bearing capacity of normal section is the least,when reinforced RC axial compression short column by section-increased method.(3)Through theoretical analysis,a calculation formula for compressive bearing capacity of normal section of reinforced RC short columns by section-increased method is established,which can be considered the second load and the new reinforced concrete constraint.(4)The compressive bearing capacity of normal section of reinforced RC short columns by section-increased method is regarded as a random variable,and then the mathematical statistics analysis is conducted based on the existing test data in China.The results show that:the compressive bearing capacity of normal section is subject to the log normal distribution.(5)A practical formula for calculating the compressive bearing capacity of normal section with 95%guaranteed rate is established based on the probability theory.