Experimental And Theoretical Study On Reinforced Concrete Median Long Column Strengthened By Jacketing

The jacketing technique is an effective method which is widely used for strengthening the reinforced concrete compression members in the engineering practice.Currently,much more research works mainly focus on the short column reinforcement,but a little on median-long column.Actually,many medium-long columns are used for bridges and other engineering structures,so it will have great theoretical value and application prospect to strengthen the reinforced concrete columns by jacketing technique.In this dissertation,based on the related research at home and abroad,the experimental and theoretical studies on RC median-long column strengthed by jacketing technique are conducted.The main results are as follows:?1?On the basis of static tests of eight specimens,the influences of hoop layer on the reinforced concrete axial compression and eccentric compression median-long column are studied,including the ultimate bearing capacity increase effect,damage process,failure characteristics and the failure mechanism.The results show that the ultimate bearing capacity increased doubly by the reinforcement of hoop layer.For the axial compression column,the greater slenderness ratio,the more obvious strengthening effect;for the eccentric column,the greater slenderness ratio and eccentricity,the more obvious strengthening effect.Besides,the full-section strain distribution of the strengthened column also obeys the plane-section assumption and the transverse flexure deformation of the member also conforms to the sinusoidal curve distribution law.?2?The numerical simulation calculation analysis to model tests is carried out by finite element analysis software,and the analysis results are verified by comparing with the experiment results,as well as,the mechanical behaviors of the strengthened member are further studied.The research results show that the most likely failure area of the new and old concrete joint surface may occur near the end of strengthened column.For the axial compression strengthened column,when the initial load level?<0.7,?has no effect on the ultimate bearing capacity,when the?>0.7,the bearing capacity begins to decrease with the increased?.Because of the changed?,two damage ultimate states may appear to the eccentric strengthened column.When the?>0.7,the ultimate bearing capacity of bias strengthened column obviously decreases with the increased?.?3?According to the tangent modulus theory,material constitutive relation and the force equilibrium conditions,the calculation method of elastic-plastic stability bearing capacity of the strengthened RC axial pressure median long column by the jacketing technique was derived.And then the effects of several parameters on the elastic-plastic stability bearing capacity of the strengthened column are studied.Research results show that when the initial load level?<0.7,?has no effect on the bearing capacity,when the?>0.7,the bearing capacity begins to decrease with the increased?.The effect of slenderness ratio l₀/b on the bearing capacity of the strengthened column is obvious;the bearing capacity of strengthened column decreases with the increased l₀/b.The bearing capacity of strengthened column increases with the increased the hoop layer concrete strength.The bearing capacity of the strengthened column increases with increased reinforcement in the hoop layer.On the basis of essential meaning of stability coefficient,the influence of concrete strength and reinforcement amount of the hoop layer on the stability coefficient?of the strengthened column is studied,the results show that when the l₀/b?8,there is no obvious change in the?in various states and the?equal to or close to 1.When the l₀/b>8,when the slenderness ratio is certain,the?decreases with the increased jacket layer concrete strength,the?increases with the increased reinforcement amount of the jacket layer.On the basis of the above research,a method which can determine the stability coefficient?of the strengthened column is given.?4?Based on the experiment,finite element analysis and the corresponding assumptions,the concrete ultimate compression strain position of the reinforced cross section under the secondary load state is analyzed.The two main damage limit states of the strengthened RC bias media-long column by jacketing technique are defined;the neutral depth of compression zone of the large and small eccentricity under the limit state is analyzed;the longitudinal deformation coordination equation of the strengthened column is derived;the two order nonlinear effect of strengthened component is carried out by the deformation control method and taking the middle span section as the failure control section.The analysis shows that the nonlinear analysis is in good agreement with the experiment results.The nonlinear parameter analysis shows that the maximum additional deformation f_max of the strengthened column parabolic increased with the increased slenderness ratio under the certain eccentricity,f_maxax increases linearly with the increased eccentricity under the certain slenderness ratio,f_maxax increases with the increased first phase load level?,f_max decreases with the increased jacket layer concrete strength grade.A simplified formula of two order effect that can obtain the eccentricity enlargement coefficient is derived,and then a practical method for calculating the bearing capacity was obtained by analyzing the actual stress distribution of concrete and steel bar of the strengthened section.?5?Some reinforcement design recommendations and construction measures are given by researching the key technology for engineering application of RC medium-long columns strengthened by jacketing,such as the concrete material of hoop layer,the bond interface processing,the column ends reinforcement and the thickness of concrete cover of the hoop layer.