In-service structure effective prestress detection method based on steel strand alternating current impedance

Abstract

The invention discloses an in-service structure effective prestress detection method based on steel strand alternating current impedance, and relates to the technical field of civil engineering. Comprising the following steps: S1, acquiring related parameters of an in-service prestressed structure; s2, calculating the optimal excitation frequency of the alternating current according to the sensitivity of the alternating current impedance to the effective pre-stress; s3, the steel strand extending out of the anchor end is connected into an alternating current circuit for capacitance and inductance measurement, and the connection length of the steel strand is recorded; s4, connecting the two ends of the steel strand into an alternating current circuit to measure actual capacitance and inductance values; s5, the actual effective prestress value of the in-service structure is obtained through calculation; and S6, the anchoring end is covered and filled with concrete. According to the method, only circuit access and measurement need to be carried out at the two anchoring ends, sensor pre-burying does not need to be carried out, operation is easy and convenient, cost is low, and the method can achieve rapid effective prestress detection of the in-service prestress structure.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering, and in particular to a method for detecting effective prestress of an in-service structure based on alternating current impedance of a steel strand. Background Art

[0002] At present, effective prestress detection methods are divided into destructive detection and non-destructive detection. Destructive detection methods include stress release method and reverse pull method. The former will cause greater damage to the steel strand, and the latter will increase the stress of the steel strand, which will have a certain adverse effect on the steel strand. At the same time, the reverse pull method is only applicable before grouting, and it is impossible to measure the prestressed structure in service. Most non-destructive detection methods are based on physical characteristics such as sound, light, heat, electricity, and magnetism to identify effective prestress. Detecting effective prestress through physical characteristics such as light, electricity, and magnetism often relies on pre-embedded sensors, which makes it difficult to measure effective prestress in service structures without pre-embedded sensors or damaged sensors. Effective prestress measurement based on acoustics does not require pre-embedded sensors, but this method is more suitable for thin-walled structures, such as pipes and plate structures. It is difficult to measure tension in complex structures such as prestressed steel strands that are spirally wound with multiple steel wires. Summary of the invention

[0003] The main purpose of the present invention is to provide a method for detecting effective prestress of an in-service structure based on the AC impedance of a steel strand to solve the above-mentioned problem.

[0004] To achieve the above object, the present invention provides a method for detecting effective prestress of an in-service structure based on AC impedance of a steel strand, comprising the following steps:

[0005] S1. Obtain relevant parameters of the in-service prestressed structure;

[0006] S2. Calculate the optimal excitation frequency of AC power according to the sensitivity of AC impedance to effective prestress;

[0007] S3, connect the steel strand extending from the anchor end to the AC circuit to measure the capacitance and inductance, and record the connected length of the steel strand;

[0008] S4, connect the two ends of the steel strand to an AC circuit to measure the actual capacitance and inductance values;

[0009] S5. Calculate the actual effective prestress value of the in-service structure;

[0010] S6. Cover and fill the anchor end with concrete.

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

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

[0013]

[0014] Where:

[0015] υ: Poisson's ratio;

[0016] F: Steel strand tension;

[0017] E: elastic modulus;

[0018] T: external wire lay length;

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

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

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

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

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

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

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

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

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

[0028]

[0029] Where:

[0030] C: Capacitance;

[0031] L: inductance;

[0032] R: resistance;

[0033] N: number of turns;

[0034] μ: magnetic permeability of steel strand;

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

[0036] ρ: resistivity of steel strand;

[0037] ε: electrical conductivity of steel strand;

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

[0039]

[0040] Where:

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

[0046] S301, determine the position of the prestressed steel strand at one end of the anchor, and chisel away part of the concrete at the anchor end;

[0047] S302. Use an angle grinder to grind the steel strand extending from one end of the anchorage until it is smooth and rust-free;

[0048] S303, using two shielded twisted pair cables to connect the LCR digital bridge and the extended steel stranded wire;

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

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

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

[0052] S402, connecting the ends of the steel strands at both ends of the anchorage to the AC circuit in the same manner as S303;

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

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

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

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

[0057] Furthermore, in step S303, the connection between the shielded twisted pair and the steel stranded wire is fixed with conductive silver glue.

[0058] The present invention uses the prestressed steel strand as the measurement object to avoid the problem of pre-embedding and damage of the sensor. 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 is calculated by measuring the alternating current impedance. This method only requires circuit access and measurement at both ends of the anchor, and does not require pre-embedding of sensors. The operation is simple and convenient, and the cost is low. It is a method that can realize the rapid detection of effective prestress of in-service prestressed structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The present invention is a flow chart of a method for detecting effective prestress of an in-service structure based on the AC impedance of steel strands.

[0060] Figure 2 The present invention is a schematic diagram of an LCR digital bridge connection of an effective prestress detection method for an in-service structure based on the AC impedance of a steel strand.

[0061] Figure 3 This is an enlarged view of point A of a method for detecting effective prestress of an in-service structure based on the alternating current impedance of steel strands according to the present invention.

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

[0063] In order to achieve the above-mentioned purpose and effect, the technical means and structures adopted by the present invention are described in detail with reference to the accompanying drawings for the features and functions of the preferred embodiments of the present invention.

[0064] like Figure 1-Figure 3 As shown, the present invention provides a method for detecting effective prestress of an in-service structure based on AC impedance of a steel strand, comprising the following steps:

[0065] S1. Obtain relevant parameters of the in-service prestressed structure, including structural parameters of the steel strand 1;

[0066] S2. Calculate the optimal excitation frequency of AC power according to the sensitivity of AC impedance to effective prestress, including the following steps:

[0067] S201, determining the functional relationship between the tension of the steel strand 1 and the structural parameters;

[0068]

[0069] Where:

[0070] υ: Poisson's ratio;

[0071] F: Tension of steel strand 1;

[0072] E: elastic modulus;

[0073] T: external wire lay length;

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

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

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

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

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

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

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

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

[0082] S202, determining the functional relationship between the tension of the steel strand 1, the excitation frequency, and the capacitance, inductance, and resistance;

[0083]

[0084] Where:

[0085] C: Capacitance;

[0086] L: inductance;

[0087] R: resistance;

[0088] N: number of turns;

[0089] μ: magnetic permeability of steel strand;

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

[0091] ρ: resistivity of steel strand;

[0092] ε: electrical conductivity of steel strand;

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

[0094]

[0095] Where:

[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] α: sensitivity coefficient.

[0100] S3, connecting the steel strand 1 extending from the anchor end to an AC circuit to measure capacitance and inductance values, and recording the connected length of the steel strand 1, including the following steps:

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

[0102] S302, grinding the steel strand 1 extending from one end of the anchorage to be smooth and rust-free by using an angle grinder;

[0103] S303, using two shielded twisted pair cables 4 to connect the LCR digital bridge 3 and the extended steel stranded cable 1, and using conductive silver glue 5 to fix the connection between the shielded twisted pair cables 4 and the steel stranded cable 1;

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

[0105] S4, connecting the two ends of the steel strand 1 to an AC 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 ends of the steel strand 1 anchored at both ends to the AC circuit in the same manner as S303;

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

[0109] S5. Calculating the actual effective prestress value of the in-service structure includes the following steps:

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

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

[0112] S6. Cover and fill the anchor end with concrete 2.

[0113] The above descriptions are only preferred embodiments of the present invention, not all embodiments. Anyone should be aware that any structural changes made under the inspiration of the present invention, and any technical solutions that are the same or similar to the present invention, belong to the protection scope of the present invention.

Claims

1. A method for detecting effective prestress of in-service structures based on AC impedance of steel strands, characterized in that: The following steps are involved: S1. Obtain relevant parameters of the in-service prestressed structure; S2. Calculate the optimal excitation frequency of AC power according to the sensitivity of AC impedance to effective prestress; S3, connect the steel strand extending from the anchor end to the AC circuit to measure the capacitance and inductance, and record the connected length of the steel strand; S4, connect the two ends of the steel strand to an AC circuit to measure the actual capacitance and inductance values; S5. Calculate the actual effective prestress value of the in-service structure; S6. Cover and fill the anchor end with concrete.

2. The method for detecting effective prestress of in-service structures based on AC impedance of steel strands according to claim 1, characterized in that: In step S2, the following steps are included: S201, determining the functional relationship between the steel strand tension and the structural parameters; Where: υ: Poisson's ratio; F: Steel strand tension; E: elastic modulus; T: external wire lay length; r c : The radius of the central wire of the steel strand under no stress; l: The length of the center wire of the steel strand under no stress; r e : The outer wire radius of the steel strand under no stress; l e : The length of the outer steel wire of the steel strand under no stress; r c ′ : F is the radius of the central wire of the steel strand under tension; l ′ : F is the length of the center wire of the steel strand under tension; r e ′ : F is the outer wire radius of the steel strand under tension; l e ′ : F is the length of the outer steel wire of the steel strand under tension; S202, determining the functional relationship between the steel strand tension, the excitation frequency, and the capacitance, inductance, and resistance; Where: C: Capacitance; L: inductance; R: resistance; N: number of turns; μ: magnetic permeability of steel strand; ω: frequency of sinusoidal alternating current in steel strand; ρ: resistivity of steel strand; ε: electrical conductivity of steel strand; S203, using the formula in S202, calculate the sensitivity of capacitance, inductance, and resistance to the tension F of the steel strand at different sinusoidal alternating current frequencies, and obtain the optimal excitation frequency; Where: F1, F2: F under different tensions; Z1: Theoretical capacitance, inductance or resistance value under the action of F1; Z2: Theoretical capacitance, inductance or resistance value under the action of F2; α: sensitivity coefficient.

3. The method for detecting effective prestress of in-service structures based on AC impedance of steel strands as claimed in claim 2, characterized in that: In step S3, the following steps are included: S301, determine the position of the prestressed steel strand at one end of the anchor, and chisel away part of the concrete at the anchor end; S302. Use an angle grinder to grind the steel strand extending from one end of the anchorage until it is smooth and rust-free; S303, using two shielded twisted pair cables to connect the LCR digital bridge and the extended steel stranded wire; S304. Measure C0, L0, and R0, and record the effective length of the steel strand connected to the circuit.

4. A method for detecting effective prestress of in-service structures based on AC impedance of steel strands as claimed in claim 3, characterized in that: In step S4, the following steps are included: S401, repeat steps S301-S302 to process the other end of the anchor; S402, connecting the ends of the steel strands at both ends of the anchorage to the AC circuit in the same manner as S303; S403. Measure C, L, and R, and record the effective length of the steel strand connected to the circuit.

5. The method for detecting effective prestress of in-service structures based on AC impedance of steel strands as claimed in claim 4, characterized in that: In step S5, the following steps are included: S501, substituting C0, L0, R0 into the formula S202 to calculate the fixed parameters μ, ρ, ε; S502, put C, L, R into S202 formula with known fixed parameters, and calculate the steel strand tension F C 、F L 、F R , calculate the average value to get the tension F, and complete the detection of effective prestress of the in-service structure.

6. The method for detecting effective prestress of in-service structures based on AC impedance of steel strands as claimed in claim 3, characterized in that: In step S303, the connection between the shielded twisted pair and the steel strand is fixed with conductive silver glue.

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