| Effective prestress is a key factor affecting the service performance of existing prestressed concrete structures,and accurate evaluation of the real-time distribution characteristics of effective prestress is the fundamental premise for scientific evaluation of the service performance of existing structures.However,due to the fact that the prestressed ribs are buried deep in concrete and the measurement is difficult,the effective effective prestress in-situ detection method has only been gradually promoted and applied in recent years,and the research on the "measured probability and statistical characteristics-true distribution evaluation of structure" of effective prestress is not perfect,and even the scattered effective prestress data cannot accurately characterize the effective prestress distribution characteristics in the structure.In addition,the existing evaluation methods mainly start from the structural design state,and infer the effective prestress value of the structure according to the theoretical formula,and do not consider the actual distribution characteristics of the unevenness and uncertainty of the effective prestress,and the evaluation method of the service performance of the structure based on the measured data is seriously missing,resulting in a large deviation in the evaluation results,which brings potential safety hazards to the service of the structure.Therefore,this paper intends to carry out a series of studies on the targeted evaluation of structural service performance based on the effective prestress distribution law of the prestressed structural system,and the main research work is as follows:(1)Considering the discrete characteristics of each influencing parameter of prestress loss,the overall effective prestress distribution model based on the measured data is established.Based on the statistical characteristics of the main influencing parameters such as tensile control stress and friction coefficient,Monte Carlo numerical simulation of effective prestress of typical concrete components was carried out to explore the probability distribution law of prestress loss in the structure.Combined with the law of overall prestress loss,the Gaussian mixture model is introduced to accurately characterize the measured overall effective prestress probability distribution,and the model is deconstructed with the help of the maximum expectation algorithm(EM),which provides a theoretical basis for the subsequent research of the prestressed structural system.(2)Combined with the statistical characteristics of the sampled sample,an engineering sequential sampling method for the overall effective prestress of the existing structure was established.In the structures to different distributions,random sampling was carried out to simulate the measured results of effective prestress of different structures,and the evaluation characteristic values under the 95%guarantee rate were introduced to quantitatively characterize the service performance of the structure,and the estimation accuracy of the eigenvalues of different sample sizes under the limited conditions was analyzed under the constraint of "estimated confidence interval/estimated mean",and the minimum sample size calculation method was established to find out the reasonable sample number corresponding to different prestress distributions.(3)Combined with the limit state design method in the specification,a presumption method for the bearing capacity of components based on the characteristic values of bearing capacity evaluation is established.Considering the cumulative effect of each prestressed rib on the bearing capacity of the component,the characteristic values of bearing capacity evaluation are defined,and a calculation method for extracting the characteristic values of bearing capacity evaluation by applying the principle of normal distribution superposition and feature weighting method is proposed.Monte Carlo numerical simulation is used to verify the accuracy of the feature weighting method applied to multiple sets of models to calculate the eigenvalues of bearing capacity evaluation.(4)Taking a practical project as an example,the validity of the minimum sample size theory and the accuracy of service performance evaluation are verified.Taking the unbonded prestressed concrete slab after long-term service as the engineering background,combined with the minimum sample theory,the measured samples of the effective prestress of the structure were obtained by the critical stress method,and the design review method and the eigenvalue method were used to evaluate the service performance of the structure respectively.The results show that compared with the current evaluation methods,the eigenvalue method can fit the actual situation well under the condition of ensuring the safety and reliability of the structure,and can provide a reference for the performance evaluation and reinforcement design of the existing prestressed concrete structure. |
