Failure Mechanism And Degradation Model Of RC Structure Corroded By Chloride Attack

Research on the mechanical performance degradation of RC structures corroded by chlorideis one of the most important parts in the durability studies. The cloride ions erode rebars andconcrete, debase the statical and dynamical mechanical properties of RC members, and finallyreduce the mechanical performance of RC structures. Accelerated corrosion experiments inartificial climate environment of RC members and joints were finished to reveal the objectivemechanical capability degradation laws of RC structures corroded by chloride, and the relateddurability retrogression model were established.Based on the accelerated corrosion experiments in artificial climate environment anddetailed investigations on the corriosion states and corriosion pits on the surface of rebars incorroded RC members, probabilistical analysis and statistics of pit shapes and sizes wereproceeded, the occurrence probability models of each kind shape were established, as well as themechanism of growth and evolvement of corrosion pits. Tensile tests of corroded rebars wereconducted with statical loads. The judgement method of nominal corroded steel bar yeild pointwas built according to the above test results.Which was simplified as "YPPCR"menthod. Thenfinite element analysis were carried out to analyze and establish the pitting effect on nominalyeilding strength. With the help of the above effort, Probabilistical nominal yeilding strengthdegradation model was bulit.Retrogression of bond behaviour inside of beams were studied through experiments andtheorical analyze. The local bond-slip relation were bulit based on the comparison research ofpullout test and beam test. The corresponding local bond-slip retrogression were built.According to the experimental studies on statical loading of corroded RC beam, the effectsof steel corrosion, concrete cover cracking and bond retrogression on degradation of corrodedRC beam were investigated seperately. Then taking these effects into the strain coordinationrelation along the height of beam section at the critical transverse crack, where force andmoment equilibrium could be united to decide the concealed and real strain relation of concreteand rebars. With the help of accurater bond-slip retrogression model in the beam established inthe previous chapter of this dissertation, the accurater bending capacity degradation model wasbuilt. According to the phenomenon of bond failure at the bending-shear area with severercorrosion crack and corrosion degree than other area, the judgement method of failure modetransformation of bending beams were buit. It was found that, the balance between ultimateanchoring force of anchorage area and yeilding force of reinforcement in tension was not theonly critical state.Shear capacity degradation experiments of corroded RC beams were conducted to investigate the shear capacity retrogression laws with enhanced corrosion degree gradually.Influence of different stirrup space,shear span rate and corrosion degree were taken into account.It was found that, as the corrosion degree increased, the shear capacity degraded. Beam withsmaller shear span rate or smallerstirrup space had higher shear capacity, but with the samecorrosion rate, beam with larger stirrup span rate had severer shear capacity degradation. effectof stirrup corrosion had unvisible influence on shear capacity of beams with small shear span. Atthe same time, the effect of corrosion on critical inclined crack was investigated, the angle ofcritical inclined crack was tend to reduce as the corrosion degree increase, with significantdiscreteness. When the final failure mode was bond failue, the critical inclined crack was veryclosed to supports.Based on the experimental results and theorical analysis, the shear capacity dagradationmodel was built. The critical inclined crack angle degeneration model was built. Taking theinduced critical inclined crack angle into the equilibrium, the anchorage lenghth predictionmodel was built.Based on the anaylsis of critical failure state and the limit equilibriumtheory,The failue mode transformation model was built.Cyclic loading tests of corroded RC columns with constant axial force and RC joints wasperformed. They had similar degradation laws. The yeild capacity and ulitmate capacity debasedas the corrosion induced. The yeild diplacement had slight change, but the ultimate debasedclearly. Because of the corroded element had no significant yeild point in the load-displacementcurve, the yeild strengh was calculated by equal energe method, the test result of yeild strengthhad difference the actual one. The resilience curve showed that, as corrosion induced, the energydissipation capacity of columns and joints decreased gradually.Based on the strain equilibrium,force and moment equilibrium on the cross section, withconsideration of steel corrosion, concrete damage,bond degradation, the resilience capacitydegradation model was built separetely, with corresponding characteristic parametersdegradation model.Experimental study on seismic resistance performance degradation of RC Frame Corrodedby Cloride were carrided out. The numerical simulated cycle loaded analysis were proceededwith IDAC-2D and the mechanical degradation model of basic elements. The numerical analysismethod was proved by the test result.