Study On Fatigue State Assessment Model Of Concrete Bridge Based On Residual Strain Monitoring

Small structural defects inevitably tend to exist as microcosmic cracks in concretebridges. In long service period, because of erosion of the environment, materials aging,natural disasters and fatigue effect of repeated traffic loads, the fatigue damage causedby these tiny defects accumulates, resulting in the overall capacity of bridge structuresto resist natural disasters, even the normal service ability decreases. Limited by researchmethods and testing techniques, previous structural fatigue analysis can only limit tovisible fatigue cracks on bridge member or surface. In recent years, the long-term bridgemonitoring technology has made great progress. It is a topic worth exploring for bridgeresearchers that how to take full advantage of the bridge online operations monitoringmeasures and technical advantages, and how to detect the fatigue damage and track theevolution of damage accumulation. At present, there aren't many systematic researchachievements in that field. Based on theories of Fracture and Damage Mechanics andfatigue crack propagation law of reinforced concrete bridges, this paper aims at gettingthe characteristic factors who can characterize the fatigue damage. Meanwhile based ona large number of real-time monitoring data, the paper strives to discover the fatiguecharacteristic parameters, accordingly realizing the security status assessment of fatiguedamage for concrete bridge in service. The main contents and conclusions are asfollows:?After analysis in crack propagation mechanism of reinforced concrete, andbased on restoring force model, this paper proposes the amendatory Paris Equation withintegration of residual stress factor. The numerical results of a reinforced concrete beamshow that the effect on crack propagation with residual stress considered differssignificantly to that of no consideration of residual stress, which has stronger influenceon crack propagation and more practical.?Based on microscopic mechanism of concrete fatigue damage, and combinedwith two fracture criterion of fatigue crack propagation, this paper establishes acomputational model of residual strain and studies the model with real-time residualstrain, which allows a wider scope for the model, particularly for the reinforced concretebridges in service. The model is proven to meet the actual situation. The paper alsodivides condition grades of fatigue damage by the amount of cumulative residual strain,which realizes real-time assessment of the security situation of bridge fatigue. ?Through nonlinear numerical simulation analysis for RC beam, the paper getsdifferent development and changes situation under recycle loads of the beam, especiallythe plastic deformation. According to the fatigue test of RC beam under single-stage andmulti-stage loads, stress intensity factor with residual stress considered expresses thecrack propagation rate better. The numerical model proposed residual stress shows thatthe residual stress is in good agreement with the initial, while the latter is slightly higher,which proves that the assessment based on residual stress is safer to assess structuralfatigue security situation under cycle loads.?In order to effectively eliminate abnormal information of monitoring data andreduce the amount of data, according to the characteristics of the cyclically changingmonitoring data, standard circle block method is provided by means of wavelet analysis.In addition, considering the fatigue safety situation assessment's demand for circulationcharacteristic parameters (the peak value imaxand the corresponding cyclesni). Theimproved average peak counting method is put forward on the basis of following theprinciple of count. Moreover, the actual monitoring data is calculated and analyzed forApplication.?Choosing the typical concrete continuous rigid frame bridge with awell-performed health monitoring system-Bridge Longhe as modeling project, withreal-time monitoring data, the paper gets current fatigue characteristic parameters (thepeak value imaxand the corresponding cyclesni). And the computational model ofresidual strain gets the current magnitude of residual strain for the relative position of atypical cross section, which is very small, and proves that Bridge Longhe is in greatfatigue security situation, and also in line with the actual security situation of the bridge.Therefore, the assessment model based on residual strain meets the demand of fatigueanalysis of the security situation for in-service bridges.