A method for detecting effective prestress of a structure in service based on steel strand alternating current impedance

Abstract

The application discloses a kind of in-service structure effective prestress detection methods based on steel strand alternating current impedance, it is related to civil engineering technical field.The method comprises the following steps: S1, obtaining the relevant parameters of in-service prestressed structure;S2, according to the sensitivity of alternating current impedance to effective prestress, the best excitation frequency of alternating current is calculated;S3, the steel strand that the anchor end extends is connected to the alternating current circuit to measure the capacitance and inductance value, and the steel strand access length is recorded;S4, the actual capacitance and inductance value measured by connecting the steel strand two ends to the alternating current circuit;S5, the actual effective prestress value of in-service structure is calculated;S6, the anchoring end is filled with concrete covering.This application only needs to be connected to the circuit and measured at both ends of anchoring, without pre-burying sensor, simple and convenient to operate, low in cost, it is a kind of method that can realize the rapid detection of in-service prestressed structure effective prestress.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering, in particular to a method for detecting effective prestress of a structure in service based on alternating current impedance of steel strand. BACKGROUND

[0002] Current effective prestress detection methods are divided into destructive detection and non-destructive detection. The destructive detection method includes stress release method and reverse tension method. The former causes great damage to the steel strand, and the latter increases the stress of the steel strand, which has certain adverse effects on the steel strand. At the same time, the reverse tension method is only applicable to before grouting, and cannot be used to measure the effective prestress of the structure in service. The non-destructive detection method is mostly based on the physical characteristics of sound, light, heat, electricity and magnetism to identify the effective prestress. The detection of effective prestress through light, electricity and magnetism often relies on pre-embedded sensors, and it is difficult to measure the effective prestress of the structure in service without pre-embedded sensors or damaged sensors. The effective prestress measurement based on acoustics does not require pre-embedded sensors, but this method is more suitable for thin-walled structures such as pipelines and plate structures, and it is difficult to measure the tension of the complex structure of the prestressed steel strand which is spirally wound by multiple steel wires. SUMMARY

[0003] The main purpose of the present application is to provide a method for detecting the effective prestress of a structure in service based on the alternating current impedance of a steel strand, so as to solve the above problems.

[0004] To achieve the above purpose, the present application provides a method for detecting the effective prestress of a structure in service based on the alternating current impedance of a steel strand, comprising the following steps:

[0005] S1, obtaining the relevant parameters of the structure in service;

[0006] S2, calculating the optimal excitation frequency of alternating current according to the sensitivity of alternating current impedance to effective prestress;

[0007] S3, connecting the steel strand extending from the anchor end to the alternating current circuit for capacitance and inductance value measurement, and recording the length of the steel strand connected;

[0008] S4, connecting the two ends of the steel strand to the alternating current circuit to measure the actual capacitance and inductance values;

[0009] S5, calculating the actual effective prestress value of the structure in service;

[0010] S6, covering and filling the anchoring end with concrete.

[0011] Further, in step S2, the following steps are included:

[0012] S201, determining the functional relationship between the steel strand tension and the structure parameters;

[0013] S202, calculating the optimal excitation frequency of alternating current according to the function relationship.

[0014] wherein:

[0015] υ: Poisson's ratio;

[0016] F: steel strand tension;

[0017] E: modulus of elasticity;

[0018] T: outer wire lay length;

[0019] r c : radius of the center wire of the steel strand under no stress;

[0020] l: length of the center wire of the steel strand under no stress;

[0021] r e : radius of the outer wire of the steel strand under no stress;

[0022] l e : length of the outer wire of the steel strand under no stress;

[0023] r c ′ : radius of the center wire of the steel strand under F tension;

[0024] l ′ : length of the center wire of the steel strand under F tension;

[0025] r e ′ : radius of the outer wire of the steel strand under F tension;

[0026] l e ′ : length of the outer wire of the steel strand under F tension;

[0027] S202, determining a functional relationship of the steel strand tension, the excitation frequency, and the capacitance, the inductance, and the resistance;

[0028]

[0029] wherein:

[0030] C: capacitance;

[0031] L: inductance;

[0032] R: resistance;

[0033] N: number of turns;

[0034] μ: magnetic permeability of the steel strand;

[0035] ω: frequency of the sinusoidal alternating current in the steel strand;

[0036] ρ: resistivity of the steel strand;

[0037] ε: steel strand conductivity;

[0038] S203, using the formula in S202, calculate the sensitivity of the capacitance, inductance and resistance to the steel strand tension F under different sinusoidal alternating current frequencies, and obtain the optimal excitation frequency;

[0039]

[0040] In the formula:

[0041] F1, F2: F under different tensions;

[0042] Z1: theoretical capacitance, inductance or resistance value under the action of F1;

[0043] Z2: theoretical capacitance, inductance or resistance value under the action of F2;

[0044] α: sensitivity coefficient.

[0045] Further, in step S3, the following steps are included:

[0046] S301, determine the position of the anchoring end of the prestressed steel strand, and chisel off the concrete at the anchoring end;

[0047] S302, polish the steel strand protruding from the anchoring end to be smooth and rust-free using an angle grinder;

[0048] S303, connect the LCR digital bridge and the protruding steel strand using two shielded twisted pairs;

[0049] S304, measure C0, L0, and R0, and record the effective length of the steel strand connected to the circuit.

[0050] Further, in step S4, the following steps are included:

[0051] S401, repeat steps S301-S302 to process the other end of the anchoring;

[0052] S402, connect the steel strand ends at both ends of the anchoring to the alternating current circuit, and the connection method is the same as S303;

[0053] S403, measure C, L, and R, and record the effective length of the steel strand connected to the circuit.

[0054] Further, in step S5, the following steps are included:

[0055] S501, bring C0, L0, and R0 into the formula in S202 to calculate the fixed parameters μ, ρ, and ε;

[0056] S502, bring C, L, R into S202 formula of known fixed parameters, calculate to obtain steel strand tension F C L R , obtain the average value to obtain the tension F, complete the detection of the effective prestress of the in-service structure.

[0057] Further, in step S303, the connection between the shielded twisted pair and the steel strand is fixed by using conductive silver glue.

[0058] The prestressed steel strand is taken as the measurement object in the application, so that the problems of pre-burial and damage of the sensor can be avoided.According to the structural characteristics of the prestressed steel strand and the distribution characteristics of the alternating current, the prestressed steel strand is connected to the alternating current circuit, and the effective prestress size is calculated by measuring the alternating impedance.This method only needs to be connected to the circuit and measured at both ends of the anchor, without the need of pre-burial of the sensor, and is simple and convenient to operate, low in cost, and is a method for realizing the rapid detection of the effective prestress of the in-service prestressed structure. BRIEF DESCRIPTION OF DRAWINGS

[0059] Fig. 1 The flowchart of the in-service structure effective prestress detection method based on the alternating current impedance of the steel strand is provided in the application.

[0060] Fig. 2 The LCR digital bridge connection schematic diagram of the in-service structure effective prestress detection method based on the alternating current impedance of the steel strand is provided in the application.

[0061] Fig. 3 The enlarged view of A of the in-service structure effective prestress detection method based on the alternating current impedance of the steel strand is provided in the application.

[0062] 1-steel strand; 2-concrete; 3-LCR digital bridge; 4-shielded twisted pair; 5-conductive silver glue. DETAILED DESCRIPTION

[0063] In order to achieve the above-mentioned purposes and effects, the technical means and structure adopted by the application are described in detail in combination with the preferred embodiments of the application, and the characteristics and functions are described.

[0064] As shown in the drawings, the application provides an in-service structure effective prestress detection method based on the alternating current impedance of the steel strand, which comprises the following steps: Figs. 1-3 S1, obtaining the related parameters of the in-service prestressed structure, including the structural parameters of the steel strand 1;

[0065] S2, calculating the optimal excitation frequency of the alternating current according to the sensitivity of the alternating current impedance to the effective prestress, comprising the following steps:

[0066]

[0067] ​​​S201, determine the function relationship of the steel strand 1 tension and the structure parameters;

[0068]

[0069] In the formula:

[0070] υ: Poisson's ratio;

[0071] F: steel strand 1 tension;

[0072] E: elastic modulus;

[0073] T: external steel wire lay;

[0074] r c : the radius of the center steel wire of the steel strand under no stress;

[0075] l: the length of the center steel wire of the steel strand under no stress;

[0076] r e : the radius of the external steel wire of the steel strand under no stress;

[0077] l e : the length of the external steel wire of the steel strand under no stress;

[0078] r c ′ : the radius of the center steel wire of the steel strand under F tension;

[0079] l ′ : the length of the center steel wire of the steel strand under F tension;

[0080] r e ′ : the radius of the external steel wire of the steel strand under F tension;

[0081] l e ′ : the length of the external steel wire of the steel strand under F tension;

[0082] S202, determine the function relationship of the steel strand 1 tension, the excitation frequency and the capacitance, the inductance and the resistance;

[0083]

[0084] In the formula:

[0085] C: capacitance;

[0086] L: inductance;

[0087] R: resistance;

[0088] N: number of turns;

[0089] μ: steel strand permeability;

[0090] ω: frequency of the sinusoidal alternating current in the strand;

[0091] p: electrical resistivity of the strand;

[0092] e: electrical conductivity of the strand;

[0093] S203: using the formula in S202, calculate the sensitivity of the capacitance, inductance, and resistance to the strand 1 tension F at different sinusoidal alternating current frequencies, and obtain the optimal excitation frequency;

[0094]

[0095] wherein:

[0096] F1, F2: F under different tensions;

[0097] Z1: theoretical capacitance, inductance, or resistance value under the action of F1;

[0098] Z2: theoretical capacitance, inductance, or resistance value under the action of F2;

[0099] a: sensitivity coefficient.

[0100] S3, connect the strand 1 extending from the anchor end to the alternating current circuit for capacitance and inductance value measurement, and record the strand 1 connection length, including the following steps:

[0101] S301, determine the position of the prestressed strand 1 at one end of the anchor, and chisel off part of the concrete 2 at the anchor end;

[0102] S302, polish the strand 1 extending from the anchor end to be smooth and rust-free using an angle grinder;

[0103] S303, connect the LCR digital bridge 3 and the extending strand 1 using two shielded twisted pairs 4, and use conductive silver paste 5 to fix the connection between the shielded twisted pair 4 and the strand 1;

[0104] S304, measure C0, L0, and R0, and record the effective length of the strand 1 connected to the circuit.

[0105] S4, connect both ends of the strand 1 to the alternating current circuit to measure the actual capacitance and inductance values, including the following steps:

[0106] S401: repeat steps S301-S302 to process the other end of the anchor;

[0107] S402: connect the strand 1 ends at both ends of the anchor to the alternating current circuit, with the same connection method as S303;

[0108] S403: measure C, L, and R, and record the effective length of the strand 1 connected to the circuit.

[0109] S5, calculate the actual effective prestress value of the in-service structure, comprising the following steps:

[0110] S501: bring C0, L0 and R0 into the formula S202 to calculate the fixed parameters μ, ρ and ε;

[0111] S502: bring C, L and R into the formula S202 with known fixed parameters to calculate the steel strand 1 tension F C , F L , F R , and obtain the average value to obtain the tension F, and complete the detection of the effective prestress of the in-service structure.

[0112] S6, the concrete 2 covering filling is carried out on the anchoring end.

[0113] The above only describes the preferred embodiments of the present application, not all embodiments, and anyone should know that the structural changes made under the inspiration of the present application, any technical solution with the same or similar to the present application, belongs to the protection scope of the present application.

Claims

1. A method for detecting the effective prestress of a structure in service based on the AC impedance of a steel strand, characterized in that, The method comprises the following steps: S1, obtaining relevant parameters of the in-service prestressed structure; S2, calculating the optimal excitation frequency of alternating current according to the sensitivity of alternating current impedance to effective prestress; S3, connecting the steel strand extending from the anchor end to the alternating current circuit for measuring the capacitance and inductance value, and recording the steel strand connection length; S4, connecting the two ends of the steel strand to the alternating current circuit to measure the actual capacitance and inductance value; S5, calculating the actual effective prestress value of the in-service structure; S6, filling the concrete covering at the anchoring end; In step S2, the following steps are included: S201, determining the functional relationship between the steel strand tension and the structure parameters; In the formula: υ : Poisson's ratio; F :Strand tension; E : Elastic modulus; T : outer steel wire lay length r c : radius of center wire of steel strand under no stress; l : length of center strand of steel strand under no stress; r e : radius of outer wire of steel strand under no stress; l e : length of outer steel wire of steel strand under no stress; r c ′ : F radius of the center wire of the steel strand under tension l ′ : F Length of center strand of steel strand under tension r e ′ : F radius of the outer steel wires of the steel strand under tension l e ′ : F Length of outer steel wires of steel strand under tension S202, determining the functional relationship between the steel strand tension, excitation frequency, and capacitance, inductance, and resistance; In the formula: C : capacitor L : inductance R : resistance N : number of turns; μ : Steel strand magnetic permeability; ω : frequency of the sinusoidal alternating current in the steel strand; ρ : Steel strand resistivity; ε : Steel strand electrical conductivity; S203, using the formula in S202, calculate the effect of capacitance, inductance, and resistance on the tension of the steel strand at different sinusoidal AC frequencies. F sensitivity to obtain the optimal excitation frequency; In the formula: F 1 , F 2 : different tension F ; Z 1 : F 1 Theoretical capacitance, inductance or resistance values under the action of Z 2 : F 2 under the influence of the applied voltage. α : sensitivity coefficient.

2. A method for detecting the effective prestress of a structure in service based on the AC impedance of steel strand according to claim 1, characterized in that, In step S3, the following steps are included: S301, determining the position of the prestressed steel strand at one end of the anchor, and chiseling away part of the concrete at the anchor end; S302, polishing the steel strand extending from the anchoring end to be smooth and rust-free by using an angle grinder; S303, connecting the LCR digital bridge and the extending steel strand by using two shielded twisted pairs; S304、measure C 0 、 L 0 、 R 0 , and record the effective length of the steel strand into the circuit.

3. A method for detecting the effective prestress of a structure in service based on the AC impedance of steel strand according to claim 2, characterized in that, In step S4, the following steps are included: S401, repeating steps S301-S302 to process the other end of the anchor; S402, connecting the end of the steel strand at both ends of the anchor to the alternating current circuit, and the connection mode is the same as S303; S403、Measure to obtain C 、 L 、 R And record the effective length of the steel strand into the circuit.

4. A method for detecting the effective prestress of a structure in service based on the AC impedance of steel strand as claimed in claim 3, characterized in that, In step S5, the following steps are included: S501, the C 0 , L 0 , R 0 Bringing into the formula S202 to calculate the fixed parameters μ , ρ , ε ; S502, the C , L , R The formula S202 is brought into the known fixed parameters, and the steel strand tension is calculated F C , F L , F R The average value is obtained to obtain the tension F The detection of the effective prestress of the structure in service is completed.

5. A method for detecting the effective prestress of a structure in service based on the AC impedance of steel strand as claimed in claim 2, characterized in that, In step S303, conductive silver adhesive is used to fix the connection between the shielded twisted pair and the steel strand.

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