Research On Bearing Capacity Of Strengthened Axial Compression Column Under The Different Initial Stress Levels

With the rapid development of urban construction,the reinforcement and reconstruction of building structure has become an important branch in the field of civil engineering.In practical project,the reinforced concrete column often needs to be reinforced because of its insufficient bearing capacity.And the traditional method of increasing section,it is widely used in strengthening engineering because of its simple construction process and reliable force.The mechanical performance of reinforced structure is different from the structure of monolithic casting,the secondary loading problem is prominent.Previous studies have mainly focused on theoretical research.it is very difficult to simulate the secondary loading of the reinforced structure in the experiment,and the previous experiments are mainly based on the primary force.With the development of finite element software,it can be used to simulate all kinds of complicated nonlinear processes.In this paper,through finite element analysis we could discusses the different initial stress levels on the bearing capacity of reinforced concrete columns under axial compression load,and compare the effects of different design parameters on the reinforcement bearing capacity after reinforcement.In actual engineering,when the structure can not be unloaded effectively,the reinforcement and design suggestions for strengthening the axial compression concrete column are put forward.The main work of this paper as follows:(1)The stress characteristics of strengthening structure different from primary casting structure are introduced.Because the original structure is subjected to a certain load level,there is a certain stress and strain,which leads to the hysteresis of the stress and strain of the new concrete and steel bars;the joint work of the old and new parts is the key to ensure the effect of the reinforcement.(2)Based on the calculation formula in current code,considering the enhanced coefficient k of core concrete strength due to the effect of the strengthened new section,and the strength reduction factor ?_c ??_s of new concrete and steel by the initial stress level ? of the original column.Therefore,a more reasonable formula for calculating the bearing capacity of axially loaded columns is proposed.(3)The finite element analysis is carried out on six members of the pre-reinforcement members.one stress bearing member and the initial stress level of the secondary loading from 0.3 to 0.6.By comparing and analyzing the bearing capacity,it is found that the higher the stress level of the econdary loading,the lower the ultimate bearing capacity.The main reason of low bearing capacity is that the strength coefficient of new section concrete and reinforcing steel decreases with the increase of initial stress level.The higher the initial stress level is,the more obvious the hysteresis effect of stress and strain of new concrete and steel.The hysteresis of stress and strain runs through the whole process from the initial stage of loading to the failure of members.The results of finite element analysis are compared with the theoretical results in this paper.It is found that the results of finite element numerical analysis agree well with the theoretical results.The rationality of the formula in this paper is explained.(4)On the basis of verifying the rationality of the theoretical formula in this paper,it is found that it is unreasonable to suggest the reduction coefficient of unified value is 0.8.When the ? is higher than 0.7,the strength coefficient of new concrete is lower than the standard value.When the coefficient of strength utilization of new reinforcement material is higher than the initial stress level.The utilization coefficient of material strength decreases linearly,and the standard value is unsafe.(5)By using stirrups to restrain concrete theory,the stirrup ratio of new section is only changed,it is found that the bearing capacity of the strengthened member and the strength coefficient of the new section are all improved to some extent.The greater the initial stress level,the more obvious the increase value.Change the thickness and strength of concrete reinforcement,found new strength utilization coefficient of section material after reinforcement is basically unchanged,describes the new material strength utilization coefficient only by the initial pre reinforcement component of the stress level of the decision,and verify the theoretical formula is more reasonable.(6)The analysis of examples in practical project,the results of this study will be applied in practical engineering,and gives the corresponding method of reinforcement design suggestions about increasing section.