Theoretical And Experimental Research On Damage Identification Of Reinforced Concrete Structures With Modal Flexibility

Structural identification (St-Id) is an interdisciplinary comprehensive study,which has been an active research since the1970s. ASCE-SEI is devoted to normalizethe St-Id research in latest decade, which has been adopted by many researchers.According to the ‘theory-test-decision’ research idea, St-Id process composes of sixsteps:(1)observation and conceptualization,(2)a priori modeling,(3)controlledexperimentation,(4)processing and interpretation of data,(5)model calibration andparameter identification and (6)utilization of model for simulation. This papersummarized the domestic and foreign excellent results of St-Id research, andconducted static and modal tests on a reinforced concrete (RC) simply-supportedbeam, a RC continuous beam and a RC space frame. The detailed contents are listed inthe following:(1)Theoretically expanding the concept of modal flexibility, and proposing aalgorithm of modal flexibility based on the intercept at0Hz of frequency responsefunction. For a currently limited application to displacement response, in this papermoment impulse and angle response were introduced to obtain its extensive definition.The numerical static and dynamic analysis were carried out on a thin-walled squaresteel tube cantilever beam to verify the rationality of suggested algorithm. Resultsshow displacement-based mode shape generally has lower mass participation factorthan angle-based mode shape. Therefore, accurate synthesis of modal flexibility needsmore angle-based mode shapes.(2)Natural frequencies were decreased with successive damage of RCsimply-supported tested beam, while damping ratios were increased with the damage.Strain mode shape is more sensitive to identify the damage location than displacementmode shape, and modal flexibility can comprehensively indicate the location anddegree of the damage. Nonlinar phenomenon of concrete made modal flexibilitygenerated displacement and static displacement being different force bearingcondition, consequently, the error between them were increased with the increment ofthe damage. Boundary conditions have great influences on modal parameters of a RCsimply-supported beam, and a trapezoidal distribution of stiffness degradation isidentified via Strand7API–Matlab model updating for different damage scenarios.(3)Due to compensation of measurement error and model error in St-Id process, traditional single model St-Id shows its shortcoming. Ten thousand finite elementmodels, which are made up of four model fragments: elastic modulus Ec, density ofconcrete ρc, axial stiffness of middle support K1and two boundary supports K2, aremodelled for multiple St-Id research. Sensitivity analysis of model fragments,maximum entropy of transducer optimal configure and model selection based on errorthreshold are studied using static displacement and modal frequency results of thetested RC continuous beam.(4)In-filled wall significantly affects modal parameters of a RC space frame.Three modal expriment cases, which are empty frame test, brick frame test andin-filled wall frame test, were designed for comparison study of the influence ofinfilled awall additional mass and stiffness to modal parameters. Results show thein-filled wall lead to the coupling of certain modes, modal frequencies were decreasedby additional mass of in-filled walls while frequencies were increased by additionalstiffness, and change magnitude of the RC space frame modal parameters depend onposition of in-filled wall.