| As the skeleton of concrete structural members,steel bars mainly play the role of bearing and construction.In order to ensure the continuous force and strong connection of members and joints in concrete structures,it is usually necessary to adopt effective ways to connect the reinforcement in the connecting area.At present,the common connection modes of steel bar are welding,mechanical connection and grouting sleeve connection.Although the connection mechanism adopted by these connection modes is different,they essentially rely on the connection joint to realize the indirect force transfer between steel bars.Compared with the direct force transfer mechanism of continuous steel bars,they are still weakened,and the reliability of steel bar connection is related to the overall mechanical performance and safety of the structure.Especially for assembling concrete structures with more connections,it is necessary to study the connection performance of steel bar connectors with different connection modes,especially when the steel bar connection area is in chloride corrosion environment.In addition,the bond performance between steel bar connectors and concrete in corroded environment is also an important factor affecting the structural performance,especially the steel bar connection area of assembled structure is vulnerable to external chloride environment invasion,which affects the bond performance between steel bar connectors and external concrete,so it is necessary to carry out targeted research on this.In view of this,the mechanical properties and failure modes of steel bar connectors with different connection modes under chloride corrosion environment and the bond-slip behavior between grouting sleeve connectors and concrete are studied in this paper.Specific research contents and conclusions are as follows:(1)The electrochemical corrosion tests were carried out on steel bar connectors with four different connection modes,i.e.double-sided arc welding,cold extrusion sleeve,upsetting straight thread and grouting sleeve,and the tensile properties of corroded steel bar connectors with different corrosion degrees were tested.The effects of corrosion rate,connection mode and diameter of steel bar on the tensile properties and failure modes of steel bar connectors under chloride corrosion environment were studied.Ring.The results show that the connectors can be divided into two types according to the location of failure: steel bar fracture and joint zone failure,and the failure modes of the connectors are different under different connection modes and corrosion degrees.The main failure modes are weld fracture,steel bar bond slip failure,sleeve fracture failure and steel bar fracture failure.The chloride corrosion resistance of steel bar connectors varies with the connection modes.Different from them,the corrosion resistance of double-sided arc welded joints is the strongest,followed by grouting sleeve and cold extrusion sleeve,upsetting straight thread is the weakest,and the corresponding ultimate failure strength decreases by 11.3%,16.1%,22.4% and 34.7% respectively when the actual corrosion rate reaches about 10%.The tensile load-deformation curve of steel bar joints shows different degrees of decline and deterioration with the increase of corrosion degree.The main manifestations are lower yield strength,shorter yield platform and worse ductility.Moreover,the deterioration degree of load-deformation curve of different connection modes is different.The deterioration degree of grouting sleeve and double-sided arc welding is relatively small,while that of cold extrusion and upsetting straight threads is more obvious.(2)Through the electrochemical corrosion test on the bonding performance of grouting sleeve reinforced bar connectors with concrete wrapped,and uniaxial pull-out test on grouting sleeve concrete bonding specimens with different corrosion degrees,the effects of corrosion rate of connectors and relative thickness of protective layer on bonding slip performance between grouting sleeve connectors and concrete under chloride corrosion environment were studied.The results show that the cracks along the reinforcement will appear at the bottom and side of the concrete bond specimens after corrosion,and the crack width increases with the increase of the corrosion rate.The main failure mode of the concrete bond specimens under corrosion environment is splitting-slip failure,and the higher the corrosion rate is,the smaller the average ultimate bond stress between the specimens and the concrete will be.The larger the diameter of grouting sleeve connector(i.e.the smaller the thickness of concrete cover)the smaller the average bond strength between connector and concrete.The bond stress-slip curve between corroded grouting sleeve connector and concrete can be roughly divided into three main stages: rising,strengthening and softening.With the increase of corrosion rate,the rising section of the curve tends to be flat,strengthened and softened.The slip failure is more evident than that of the other two stages,which are shortened or even disappeared in varying degrees.(3)Based on the test results of bond-slip behavior between steel bar connectors and concrete of corroded grouting sleeve,the effects of corrosion rate of sleeve connectors and diameter of connectors(i.e.thickness of concrete cover)on ultimate bond strength are analyzed,and the calculation model of average ultimate bond stress considering the effect of corrosion rate and thickness of concrete cover is established.Based on the analysis of the average bond stress-slip relationship curve,an average bond stress-slip relationship model considering the influence of maximum crack width,corrosion rate and relative thickness of protective layer is proposed.The calculated results of the model are in good agreement with the experimental curves and can be used to predict the bond stress-slip relationship between grouting sleeve connectors and concrete under chloride corrosion environment. |
PDF Full Text Request