Experimental Research On Reinforced Concrete Columns Reinforced With Prefabricated Shell With Bulit-in Steel Plates Under Axial Compression

A large number of structures have suffered different degrees of damage due to material aging,steel corrosion,fire and earthquake.It is urgent to strength / repair those structures to meet the use requirements again.The main reinforcement methods of RC columns include enlarging cross-section,bonding steel plate,FRP strengthen and so on.Numerous applications in engineering have utilized these methods,however there are some disadvantages in these methods.The technology of enlarging cross-section is simple,while the field wet operation is heavy and the weight of the structure is increased,which has notable influence on architectural appearance and headroom.The method of bonding steel plate has little impact on the use of space,however the bonding material of steel plate is restricted by the application environment,and the steel plate is prone to environmental corrosion and fire resistance.FRP reinforcement method is convenient in construction and has good corrosion resistance,but the fire resistance and high temperature resistance of the resin matrix are relatively weak.Considering these problems mentioned above,this paper proposes a new idea of using the prefabricated method to strengthen the structure,aiming to find a quick and effective method to strengthen the reinforced concrete structure.The research is of great significance to extend the technology of structural reinforcement.Steel plate prefabricated shell（SPPS）is a new method to strength RC columns.Steel plate and grouting material are used as reinforcement layer to provide effective restraint to the original column and improve the bearing capacity of columns.During the construction,the prefabricated shell（composed of steel framework and high-strength non shrinkage grouting material）is installed first,and then the formwork is erected for pouring the high-strength non shrinkage grouting material after welding.The advantages of this method are convenient construction,thin reinforcement layer and less impact on the original space.Prefabricated shell can be made in the factory,and then assembled and reinforced on site,which can improve the reinforcement efficiency and shorten the construction period.High strength grouting material can be used as the protective layer of the steel plates in the prefabricated shell,including improvement of corrosion resistance and fire resistance.In this paper,the axial compression test and theoretical research of the SPPS-strengthened intact and damaged concrete square columns were carried out.The main research contents were as follows:（1）The steel mould and steel framework were designed and manufactured,and ten groups of prefabricated shells with different steel plate hoop reinforcement ratio were poured with high strength non shrinkage grouting material.Ten concrete columns with different stirrup ratio and initial damage grade were designed.After pre-damage loading,prefabricated shells were used to reinforce the concrete square columns and the strengthened columns were tested under axial compression.The failure modes and mechanical performances of SPPS-strengthened RC columns were investigated.（2）Based on the test data,the load-displacement curve,the bearing capacity,ductility and energy dissipation index,and the strain characteristics of steel bar and steel hoop were analyzed.The effects of steel plate hoop spacing,stirrup spacing and initial damage level on the axial compression performance of SPPS-strengthened columns were also studied.It was indicated that SPPS can effectively improve the peak bearing capacity of RC columns,the reinforcement effect was more significant with the decrease of the stirrup ratio and the increase of steel plate hoop reinforcement ratio.The peak bearing capacity of reinforced damaged RC columns can recover to the peak bearing capacity of the original RC columns,but as the damage degree increased,the recovery capacity of bearing capacity is limited.The pre-damaged RC columns exhibited lower initial axial stiffness,which can not be repaired by reinforcement.（3）The restraint mechanism of stirrups and steel plate hoop was discussed.Based on the existing restraint model,a calculation method for the axial compression bearing capacity of SPPS-strengthened intact columns was proposed,considering the effect of stirrups and steel plates.Based on the damage evaluation index of corresponding area,the calculation formula of bearing capacity considering initial damage was proposed.It was believed that the proposed model was effective for its calculated results fitting the experiment well.In practical application,considering the details of a specific project,the prefabricated shell can be optimized to make the reinforcement scheme more reasonable.