Study On On-way Distribution Of Bonded Prestress Based On Magnetic Flux Sensing Technology

With the continuous development of science and technology, the prestressed concrete structure can improve the structural performance, make full use of high-strength materials, and achieve good economic benefits and other advantages. The prestressed concrete structure is increasingly and widely applied in the field of civil engineering, especially in the bridge structures. In the prestressed concrete structure, the prestressed losses will directly affect the effective prestress, thereby affecting the performance of the whole components. Therefore, the value of the effective prestress in the prestressed concrete structure has been one of the important research topics. However, there are many factors affecting the prestress losses, therefore, the accurate calculation of the prestress losses is a complex task, and is currently in the exploratory stage. Now there are many effective prestress testing methods, but there is no a quick and effective testing method for engineering applications. In this paper, a novel non-destructive testing method (for measuring the changes in steel beam magnetoconductivity) is introduced for the rapid measurement of the prestress of structure in the tensioning stage, so as to achieve the quality control of the construction period, and to study prestress losses along the distribution in the tension stage and find out the law of prestress losses. In this paper, combined with the magnetic flux sensor developed by Liugong OVM Company, the following researches are carried out:(1) Introduction of the concept of prestressing, the characteristics of prestressed concrete structures as well as a basic overview of the prestress losses, and the domestic and foreign detection methods for effective prestress in the prestressed concrete structure.(2) Detailed discussion of the prestress loss theory and the corresponding calculation formula, especially the formula for prestressed friction loss in the tension stage recommended in the relevant references.(3) Combined with actual projects, the magnetic flux sensor is used to test the effective prestress of relevant cross sections of New Whitewater Bridge in the prestressed tension stage in Guangyuan, Sichuan.(4) On the basis of on-site testing, the field data are compared with the design values in the specification, and the sources of error are analyzed; the friction loss in the prestress loss is studied, and the changes in two important factors for friction loss in the tension stage-the friction coefficient k and μ are analyzed and the numeric range is proposed, and the correction proposal is put forward for friction loss formula for the tension stage.(5) Through the monitoring of effective prestress of key parts in the dropthrough section in the tension stage of expansion project for Chengdu Shuangliu International Airport at Dajian Road, and the comparison between the actual measured value and the theoretical value of the correction formula in this paper, it is proved that the correction formula meets the general engineering accuracy.(6) The main conclusions of this paper are summarized, and the relevant problems are put forward in the next study.