Research On Stress Measurement Of Prestressed Steel Strand Based On LC Electromagnetic Oscillation

In existing structure steel strand,prestress detection evaluation has an important value.Analysis of the structure has a certain guiding role,regardless of the evaluation of the load capacity or the design of existing structures.The size and loss of prestress load is the concrete embodiment of the prestress state.At present,the prestress detection methods can be divided into: destructive detecting,non-destructive detecting and online monitoring.Non-destructive detecting methods are diverse,and are in a vigorously developing stage.However,the use of electromagnetic methods,in the international,is still in its infancy.Electromagnetic method,using magneto-elastic effect to realize non-destructive detecting of steel strand stress,has achieved important progress in the no bond detection and new structure bonded online monitoring.But magnetic loading problems exist in the existing structure with bonded prestressed steel strand non-destructive stress detecting.Based on the domain analysis,the detection of effective prestress of prestressed steel strand,by LC electromagnetic oscillation method,has been studied mainly on the following aspects:1.We propose a method of steel strand stress detecting only in the end: LC electromagnetic oscillation detecting method.This new non-destructive detecting method can accurately detect the effective prestress of prestressed steel strand in tension and in the working process,and determine the prestressed loss of prestressed mixed concrete structures.2.Based on the domain,the domain structure and magneto elastic effect of magnetic materials,we deeply study the causes of the form of the prestressed reinforcement's permeability,master the rule of magnetization,and derive the relationship of stress-permeability.To clarify the relationship between stress and permeability,it provides a concrete formula for the effective stress conversion from the permeability.We deeply study the equivalent inductance of the prestressed steel strand,and deduce the relationship between the equivalent inductance and the permeability.The influence of elongation after tension of steel strand on the oscillation frequency is discussed.Eventually,we complete in theory: the formulas for the calculation of inductance and the magnetic permeability;the formulas for the calculation of oscillation frequency and stress,and provide a theoretical basis for the effective prestress detection.3.Based on above-mentioned deeply theoretical researches,a set of prestressed steel strand of detecting system has been set up.So many experiments are carried out.At last,we combine theories and experiments,the experiments' results are compared and deeply analyzed.The existing problems have been improved continuously.In the determination of frequency drift and the continuous detection,frequency changes are regular with stress loading and unloading.Through the theoretical research and experimental exploration,we have a clear understanding of the magneto elastic effect,and have a profound understanding of the electromagnetic non-destructive stress detecting.