Mechanical Behavior Of Corroded RC Columns Under Load And Environment

Reinforced concrete structure is under external loads while undergoing the environmental effects at the same time. The column is the vertical components of the structure, supporting beam, slab and other upper structure members. The damage caused by failure of column is more serious than other components. The chloride attack has always been regarded as one of the important degradation cause of service performance for reinforced concrete structure. Therefore, based on limitation of previous study on the properties of reinforced concrete column, this paper taking column as the research object, focus on study the behavior of corroded reinforced concrete column under load and environment. The main research works are as follows:(1) To study the applicability of accelerated corrosion methods of reinforcement and stirrup in concrete members, same specimens were accelerated using direct current (DC) with different connection and their bearing capacity were tested. The mass loss of reinforcement and stirrup, the color and distribution of corrosion rust, the distribution and development of rust expansion crack were compared between accelerated corrosion methods of the different connection. The surface morphology of corroded reinforcement and stirrup, and morphologies of corrosion products were analyzed. The effects of connection between reinforcement and stirrups on macroscopic behavior such as ultimate bearing capacity, load-displacement, failure features etc. were studied(2) To quantify the effect of corrosion of stirrups on load bearing capacity of short concrete column with axial compression, axially loaded compression bearing capacity of was tested on the stirrup corroded reinforced concrete short columns obtain by impressed current method. The distribution of stirrup rust expansion crack was analyzed. The effects of corrosion of stirrups on macroscopic behavior such as ultimate bearing capacity, failure features etc. were studied. Based on test results and theoretical analysis, load-bearing capacity model of axial short column considering the concrete cover spalling, reduction of concrete strength and supporting role of stirrup to main reinforcement caused by corrosion stirrup was established.(3) To study the behavior of reinforced concrete column under the coupling effects of load and environment, method for testing the behavior of reinforced concrete column under load and environment was put forward. The self-balanced system is applied to impose a constant sustained load. The impressed current method was used to accelerate both the reinforcement and stirrup. Therefore the effects of load and environment were simulated. The loading and positioning test device for compressed column including support system, vertical elevating system and horizontal movement system was developed. Totally30columns with different eccentricity, load level and corrosion rate of axis, small and larger eccentricity under the coupling effects of load and environment were tested. The effects of eccentricity, load level and corrosion rate on macroscopic behavior such as ultimate bearing capacity, failure features etc. were studied.(4) Based on the test of bearing capacity of corroded reinforced concrete, factors affecting the bearing capacity of corroded reinforced concrete columns were analyzed. And load bearing capacity model of corroded reinforced concrete column is established. Both the models of axially loaded column and eccentrically loaded column were based on equilibrium equations on which load-bearing capacity of R.C. column at given corrosion can be predicted considering the reduction of supporting role of stirrup to main reinforcement caused by stirrup corrosion, reduction of cross section of both rebar and stirrup, deteriorations of mechanical properties of rebar and stirrup, concrete section, and bond behavior between corroded reinforcement and concrete. For eccentrically loaded column, the equivalent cross section of corroded reinforced concrete column was adopted. The influence of long-term load effect was also considered.(5) To study the whole process of fracture and damage of reinforced concrete column, acoustic emission (AE) parameters for non-corroded and corroded eccentric compression columns under load were tested with the help of a hydraulic loading system and acoustic emission system. The acoustic emission characteristics and space-time evolution were analyzed. The damage of the concrete specimen was evaluated by clearance factor criterion based on the amplitude of the AE signals. Damage factor expressed by AE parameter of relative change of the accumulative energy was given.