Study On The Cyclic Performance,Dynamic Model And Damage Assessment Of PBL Shear Connectors In Hybrid Structures

The performance of perfobond rib shear connectors(PBL shear connectors)under monotonic loading has been studied comprehensively and deeply.The fatigue performance of PBL shear connectors has also been focused.However,the performance under push–pull low-cycle reciprocating loading is poorly understood.Through model tests and theoretical analyses,the push–pull cyclic performance,cyclic deterioration mechanism,“group effect”characteristics,restoring force model,performance level classification and damage assessment model were studied systematically in this dissertation.The major work and results are stated as follows:(1)Quasi-static tests on PBL shear connectors were designed.The global cyclic performance was ascertained through visual bearing characteristics,such as load-slip.Test methods such as distributed optical fiber sensing technology were used to obtain the local mechanical response.According to the results,the hysteretic curves of PBL shear connectors under presented large initial stiffness and good ductility.The gradual increase of the plumpness demonstrates its good energy dissipation performance as well.However,disadvantageous influence on hybrid structures may arise from the remarkable residual deformation of the PBL shear connectors.Morever,the peak bearing capacity decreased significantly when compared with that under monotonic loading,and the ultimate deformation capacity also degraded.(2)The influence of each design parameter on the cyclic performance of PBL shear connectors was investigated.The mechanism of deterioration during the cyclic loading process were revealed.The calculation method for the bearing capacity was proposed.The asperities of the concrete interface wear out due to the reciprocating action under hysteretic loading.Damage accumulated,and the shear-friction effect reduced quickly.The dowel action of the passing rebar bore more loads.The increase of the dowel deformation aggravated the progressive damage,and the increase of the reciprocating action caused the cumulative damage.The dowel action reduced by the coupling effect of the progressive damage and the cumulative damage.The maximum dowel force dropped when compared with that in the monotonic case,and the ultimate deformation capacity weakened obviously.Based on the deterioration mechanism,a degradation model accounting for the reduction of the shear-friction effect was established.Based on the model of a beam on an elastic foundation and consideration of the shear and kinking effect,the calculation model for the maximum dowel force was given.Together with the calculation model for the maximum dowel force incorporating the determination method for the corresponding slip at the peak bearing capacity by considering the deformation characteristics,a formula for estimating the bearing capacity of PBL shear connectors under cyclic loading was proposed and validated by the experimental results.Among the design parameters,the dimensions of PBL shear connectors and the steel-concrete interfacial adhesion influenced the overall cyclic performance most.(3)The unobvious group effect of the PBL shear connector group specimen under hysteretic loading was ascertained,and the reason was illustrated.According to the tests,the load-slip hysteretic behavior of PBL shear connectors in each row among the specimen was basically consistent.The stiffness and bearing compacity of the grouped PBL shear connectors had little difference with the corresponding superposition values of that from each PBL.The group effect was not obvious.The reson for this was that the shear-friction effect reduced quickly under low-cycle reciprocating loading.The influence scope of each PBL shear connector reduced significantly when compared with that under monotonic loading.Each PBL shear connector tend to be independent quickly under reciprocating loading,and the load shared by each was close.Thus,the peak bearing capacity of the grouped PBL shear connectors can be obtained by superposition of that of each PBL shear connector according to the proposed calculation method.The calculation values also agreed the test results well.(4)A hysteretic restoring force model with the characteristics of clear mechanical meaning,simple calculation,and obvious parameterization was established,which shall be beneficial to promotion and application.The skeleton curve model reflecting bearing mechanism of PBL shear connectors was proposed,and the determine method for the key parameters of the curve based on relevant theories,such as the calculation model of the interfacial resistance and the reduction model of the dowel action,was presented.According to the shear-slip characteristics,a double slipping axis model,which can effectively consider the slipping and pinching effect,was proposed.A hysteretic model incorporating strength and stiffness deterioration based on hysteretic energy dissipation was also proposed.Comparisons between the analytical solution and test results validated the proposed model,and the characteristics of slipping and pinching and the behavior of hysteretic deterioration were well reflected.(5)The performance level quantification system for PBL shear connectors was proposed,and the specific quantitative index as well as the damage index ranges were determined.Four performance levels,namely,elastically operational,operational,life safety and collapse,were proposed based on the representative performance level and corresponding damage state classification at home and abroad,as well as the stage performance and damage characteristics of PBL shear connectors.The quantitative performance index of the relative slip of PBL shear connectors under each performance level was determined.According to the corresponding four stages of damage state,the damage index ranges were given by considering the damage evolution characteristics of PBL shear connectors.(6)By considering the coupling effect of the large deformation effect and accumulation effect,a new damage assessment model without undetermined coefficient and meeting the requirements of boundary conditions was proposed.Results showed that the average values of each damage state limit calculated by the proposed model were very close to the damage state classification limit values for the PBL shear connectors,and the discreteness was significantly reduced when compared with that according to the existing models.Based on this new model,analyses on the damage evolution process and the influence of design parameters were made.The damage evolution process agreed with the stage classification of the damage state and the mechanism of cyclic deterioration well.The influence of the design parameters on the evolution process and the cyclic performance according to the tests as well as the theoretical analysis results confirmed each other.