阅读说明：本技术 一种桥梁体内纵向预应力筋有效应力的检测方法 (Method for detecting effective stress of longitudinal prestressed tendon in bridge body ) 是由 程雷 李承昌 于 2021-01-21 设计创作，主要内容包括：本发明属于桥梁预应力检测技术领域,提出一种桥梁体内纵向预应力筋有效应力的检测方法,本发明通过在试验机上张拉与现场实测预应力筋规格、型号、长度等参数相同的单根预应力筋,得到预应力筋张拉力与自振频率间的拟合曲线方程,在现场检测时,将测得的预应力筋的自振频率代入方程则可得到预应力筋当前的张拉力,再利用应力与力之间的关系计算出预应力筋的有效应力。本发明通过试验对拉力与频率的关系进行修正,能够有效提高纵向预应力筋有效应力的检测精度和桥梁正常使用状态评价的准确性。(The invention belongs to the technical field of bridge prestress detection, and provides a method for detecting the effective stress of a longitudinal prestressed tendon in a bridge body. The invention corrects the relation between the tension and the frequency through the test, and can effectively improve the detection precision of the effective stress of the longitudinal prestressed tendon and the accuracy of the evaluation of the normal use state of the bridge.)

1. A method for detecting the effective stress of a longitudinal prestressed tendon in a bridge body is characterized by comprising the steps of testing and analyzing in a test room, and testing and calculating on site; the method comprises the following specific steps:

(1) debugging parameters of the testing machine in a test room, anchoring two ends of a single prestressed tendon with the same specification and model as those of the prestressed tendon to be tested on the testing machine, wherein the distance between anchor points is the same as that between supporting points of the prestressed tendon to be tested, and arranging a high-sensitivity sensor at the middle point position of the prestressed tendon along the length direction and connecting the high-sensitivity sensor into a dynamic testing device to wait for testing;

(2) the prestressed tendons are gradually applied to 50kN to (sigma) according to the step difference of 10kN by adopting a step loading mode_conS) tension of kN, load holding for 1min per stage and frequency acquisition, and recording the spectrogram output by the dynamic testing equipment, wherein sigma_conS respectively represents the control tensile stress under the anchor of the longitudinal prestressed tendon and the cross section area of a single prestressed tendon;

(3) performing experimental analysis, obtaining the natural vibration frequency of the tested prestressed tendon to the stress value through the spectrogram recorded during loading at each stage, and obtaining a fitting equation between the tension force T and the natural vibration frequency F through regression analysis, namely T is A.F²+ B, wherein A and B are known coefficients obtained by regression analysis;

(4) determining the specific position of a prestressed tendon to be detected on a detection site, cutting concrete, and excavating a rectangular notch, wherein the length of the notch is more than 1 m; cleaning sundries around the notch and exposing the prestressed tendons, supporting two ends of 1 prestressed tendon to be tested by rigid supports, wherein the supporting distance is at least 1m, and except that supporting points at the two ends are contacted with the rigid supports, the rest parts of the prestressed tendon to be tested cannot be contacted with any object;

(5) connecting and debugging test equipment, arranging a high-sensitivity sensor at the midpoint position of the prestressed tendon to be tested along the length direction, connecting dynamic test equipment for testing to obtain a spectrogram of the actually measured prestressed tendon, analyzing to obtain the natural vibration frequency F of the actually measured prestressed tendon in the current state, and substituting the natural vibration frequency F into a fitting equation T which is A.F²In the step B, the tension force T of the actually measured prestressed tendon in the current state is obtained₁＝A·f²+B；

(6) And calculating the effective stress of the actually measured prestressed tendon in the current state by utilizing the relation between the stress and the force.

Technical Field

The invention belongs to the technical field of bridge prestress detection, and particularly relates to a method for detecting effective stress of a longitudinal prestressed tendon in a bridge body.

Background

The prestressed tendons are important components of prestressed concrete structural members, and the effective stress level of the longitudinal prestressed tendons in the bridge structure determines the normal use state of the bridge structure, including cracks, deflection and the like. Over time, the effective prestress of the longitudinal prestressed reinforcement will be gradually lost under the influence of the friction between the prestressed reinforcement and the pipeline wall, the deformation of the anchorage device, the retraction of the reinforcement, the joint compression of the assembled component, the elastic compression of the concrete, the stress relaxation of the prestressed reinforcement, the shrinkage and creep of the concrete and the like. The reduction of the effective stress can cause the unfavorable phenomena of cracking or crack development of the structure, midspan downwarping of the main beam and the like. Therefore, the effective stress of the longitudinal prestressed tendons in the bridge structure is accurately detected, the working performance and the operation level of the bridge structure can be comprehensively and accurately mastered, and important support is provided for bridge reinforcement decision and design.

The method for detecting the effect of the longitudinal prestressed tendon in the in-service bridge body mainly comprises a transverse tension displacement increment method, a stress release method and a dynamic measurement method. The principle of the transverse tension displacement increment method is that transverse load is applied to the prestressed tendon, and the transverse displacement increment and the corresponding transverse load increment are substituted into a practical empirical formula to obtain the current tension of the prestressed tendon; according to the method, a steel cable tension tester is matched with a digital display instrument to realize field tension test, but the instrument is heavy and inconvenient to operate, and meanwhile, the error of a test result is large due to the fact that transverse tension and displacement display data are asynchronous. The stress release method is to release the constrained stress in the prestressed tendon by adopting a mechanical cutting method and substitute the measured strain increment into a section balance formula to solve the prestress, but the method is limited to single-point stress release and has lower test precision. The dynamic measurement method is based on a vibration principle and a tension string theory, utilizes dynamic measurement equipment to obtain the natural vibration frequency of the prestressed tendon, obtains the tension according to a related formula, and has larger error on the test result of the prestressed tendon with short length and small force value.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for detecting the effective stress of the longitudinal prestressed tendon in the bridge body, which can realize high-precision test on the effective stress of the longitudinal prestressed tendon in the bridge body with different types, specifications and lengths.

The invention provides a method for detecting effective stress of a longitudinal prestressed tendon in a bridge body, which comprises the following specific steps:

(1) debugging the parameters of the testing machine in a test room, anchoring two ends of a single prestressed tendon with the same specification and model as those of the prestressed tendon to be tested on the testing machine, wherein the distance between anchor points is the same as that between supporting points of the prestressed tendon to be tested, and arranging a high-sensitivity sensor at the middle point position of the prestressed tendon along the length direction and connecting the high-sensitivity sensor into a dynamic testing device to wait for testing.

(2) The prestressed tendons are gradually applied to 50kN to (sigma) according to the step difference of 10kN by adopting a step loading mode_conS) tension of kN, load holding for 1min per stage and frequency acquisition, and recording dynamic measurement settingReady output spectrogram of σ_conAnd S respectively represents the control tensile stress under the anchor of the longitudinal prestressed tendon and the cross section area of a single prestressed tendon.

(3) Performing experimental analysis, obtaining the natural vibration frequency of the tested prestressed tendon to the stress value through the spectrogram recorded during loading at each stage, and obtaining a fitting equation between the tension force T and the natural vibration frequency F through regression analysis, namely T is A.F²+ B, where A and B are both known coefficients obtained by regression analysis.

(4) Determining the specific position of a prestressed tendon to be detected on a detection site, cutting concrete, and excavating a rectangular notch, wherein the length of the notch is more than 1.00 m; cleaning sundries around the notch and exposing the prestressed tendons, supporting two ends of 1 prestressed tendon to be tested by rigid supports, wherein the supporting distance is at least 1.00m, and except that supporting points at the two ends are contacted with the rigid supports, the rest parts of the prestressed tendon to be tested cannot be contacted with any object.

(5) Connecting and debugging test equipment, arranging a high-sensitivity sensor at the midpoint position of the prestressed tendon to be tested along the length direction, connecting dynamic test equipment for testing to obtain a spectrogram of the actually measured prestressed tendon, analyzing to obtain the natural vibration frequency F of the actually measured prestressed tendon in the current state, and substituting the natural vibration frequency F into a fitting equation T which is A.F²+ B, the tension T1 of the actual measurement prestressed tendon in the current state is obtained as A.f²+B。

(6) And calculating the effective stress of the actually measured prestressed tendon in the current state by utilizing the relation between the stress and the force.

The invention has the beneficial effects that: the method comprises the steps of carrying out a graded loading test on the prestressed tendon with the same specification, model and length as those of the prestressed tendon actually measured on site, obtaining an actual fitting curve equation between the tension applied to the prestressed tendon and the natural vibration frequency of the prestressed tendon, substituting the measured natural vibration frequency of the prestressed tendon into the equation during the on-site detection to calculate the current tension of the prestressed tendon, and calculating the effective stress of the prestressed tendon by utilizing the relation between the stress and the force. The method for detecting the effective stress of the longitudinal prestressed tendon in the bridge body provides test data support for field detection, greatly improves the detection precision of the effective stress of the prestressed tendon, and improves the accuracy of the evaluation of the normal use state of the bridge.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention.

Detailed Description

The method is practically applied to the detection work of the effective stress of the longitudinal prestressed tendons in the body of a yellow river highway bridge for the first time, the bridge main bridge is a 660m five-span one-linkage variable cross-section prestressed concrete continuous rigid frame-continuous beam bridge, the span is arranged to be (65+160+210+160+65) m, and after operation for nearly 20 years, the bridge web has more inclined cracks and the main span has serious downward deflection, and researches consider that the excessive longitudinal prestress loss is an important reason for generating the diseases, so that the detection method of the effective stress of the longitudinal prestressed tendons in the main beam of the bridge is deeply researched, and the bridge is successfully applied. At present, the method is applied to the detection of the effective stress of the in-vivo longitudinal prestressed tendons of a plurality of bridges, and the effect is good.

The long beam and the short beam of each span are selected to be detected, the specification and the model of the prestressed tendon to be detected are determined according to data such as design drawings, a single prestressed tendon with the same specification and model and the length of 1.50m is selected to be tested in a laboratory, the distance between anchor points is 1.00m, and a high-sensitivity sensor is arranged at the midpoint of the prestressed tendon along the length direction and is connected into a dynamic testing device to wait for testing.

And step loading is adopted, 50 kN-187 kN of pulling force is applied to the prestressed tendons step by step according to the step difference of 10kN, the load is maintained for 1min at each step, frequency acquisition is carried out, and meanwhile, a spectrogram output by the dynamic testing equipment is recorded.

Performing experimental analysis, obtaining the natural vibration frequency of the tested prestressed tendon to the stress value through the spectrogram recorded during loading at each stage, and obtaining a fitting equation between the tension force T and the natural vibration frequency F through regression analysis, namely T is A.F²+ B, where A and B are both known coefficients obtained by regression analysis.

The concrete position of the prestressed tendon to be tested is determined according to data such as design drawings, the longitudinal prestressed tendon of the bottom plate in the box is scanned and positioned by combining a ground penetrating radar on site, after the position of the corresponding prestressed tendon is determined, concrete is cut, notches of a longitudinal bridge in the direction of about 1.20m and a transverse bridge in the direction of about 0.20m are excavated, sundries are cleared, the prestressed tendon is exposed, two ends of 1 prestressed tendon to be tested are supported by a phi 12 steel bar, and the supporting distance is 1.00 m. Except that the two end support points are contacted with the steel bar, the rest parts of the prestressed tendon to be tested are not contacted with any object.

Connecting and debugging dynamic test equipment, arranging a high-sensitivity sensor at the midpoint of the prestressed tendon along the length direction to pick up the excitation signal, determining the natural vibration frequency F of the prestressed tendon according to the spectrogram output by the dynamic test equipment, and substituting the natural vibration frequency F into a fitting equation T which is A.F²In the step B, the tension force T of the actually measured prestressed tendon in the current state is obtained₁＝A·f²+B。

And calculating the effective stress of the actually measured prestressed tendon in the current state by utilizing the relation between the stress and the force.

The above description is only for the preferred embodiment of the present invention and does not limit the scope of the present invention, so that equivalent variations made by applying the contents of the present specification and the drawings are included in the scope of the present invention.