CN115478569A - Pre-stress nondestructive testing method based on natural frequency of finish-rolled deformed steel bar anti-floating anchor rod - Google Patents
Pre-stress nondestructive testing method based on natural frequency of finish-rolled deformed steel bar anti-floating anchor rod Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 225
- 239000010959 steel Substances 0.000 title claims abstract description 225
- 238000007667 floating Methods 0.000 title claims abstract description 148
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000009659 non-destructive testing Methods 0.000 title claims description 14
- 238000001514 detection method Methods 0.000 claims abstract description 63
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- 238000010276 construction Methods 0.000 description 21
- 238000013461 design Methods 0.000 description 7
- 238000005096 rolling process Methods 0.000 description 7
- 238000004873 anchoring Methods 0.000 description 5
- 239000002002 slurry Substances 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 239000004567 concrete Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000009434 installation Methods 0.000 description 3
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- 230000004907 flux Effects 0.000 description 2
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- 238000013213 extrapolation Methods 0.000 description 1
- 239000011513 prestressed concrete Substances 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
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- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
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Abstract
The invention belongs to the technical field of prestress detection of an anti-floating anchor rod, discloses a prestress nondestructive detection method based on the natural frequency of a finish-rolled deformed steel bar anti-floating anchor rod, and aims to solve the problem that the anti-floating anchor rod lacks a prestress detection method which is simple in operation and reliable in performance. The invention comprises the following steps: (1) The method comprises the steps of obtaining a first-order natural frequency of an exposed section steel bar of a finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress in advance, and accordingly establishing a relation curve of a prestress value and the first-order natural frequency of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod; (2) Acquiring a first-order natural frequency of a steel bar of an exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, which is subjected to prestressing force on site, by a detection system; (3) And (3) obtaining the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod according to the relation curve between the prestress value and the first-order fixed frequency established in the step (1) and the first-order fixed frequency obtained in the step (2).
Description
Technical Field
The invention belongs to the technical field of prestress detection of an anti-floating anchor rod, and particularly relates to a prestress nondestructive detection method based on natural frequency of a finish-rolled deformed steel bar anti-floating anchor rod, which is used for detecting the prestress of the finish-rolled deformed steel bar anti-floating anchor rod.
Background
With the development and utilization of underground spaces, the problem of anti-floating of underground spaces comes with. The anti-floating anchor rod is widely applied to underground space anti-floating, but the anti-floating anchor rod is poor in durability and low in reliability due to cracking of grouting bodies at anchoring sections in the service process. In addition, as the technical standard for resisting floating of building engineering (JGJ 476-2019) is implemented in 3 and 1 months in 2020, more strict requirements are put on the durability of the anti-floating anchor rod: in the engineering with the anti-floating design grade of A, tensile stress is not generated in anchoring slurry; in the engineering with the anti-floating design grade of B grade, the tensile stress in the anchoring slurry is not greater than the axial tensile strength of the anchoring slurry; the anti-floating design grade is grade C, and the crack width of the anchoring slurry is not greater than the maximum crack limit value.
In order to control the crack of the anti-floating anchor rod and solve the problem of poor durability of the anti-floating anchor rod, engineering technicians apply prestress in the anti-floating anchor rod through tensioning anchor rod steel bars, namely, the anti-floating anchor rod is applied with prestress to achieve the purposes of controlling the crack of the anti-floating anchor rod and improving the durability.
Although the crack of the anti-floating anchor rod can be controlled and the durability can be improved by applying prestress to the anti-floating anchor rod, the prestress cannot reach a designed value and is lost due to the problems of the operation level of workers, the error of an oil meter, the installation of a prestressed anchor base plate and the like in the tensioning construction process of the steel bar; even after tensioning is completed for a short time, the prestressed reinforcement generates large prestress loss; therefore, the applied prestress can not meet the design requirement, and the durability of the anti-floating anchor rod is influenced.
Therefore, accurately applying prestress according to design requirements becomes a key link for controlling the crack of the anti-floating anchor rod. However, a method for detecting the prestress of the anti-floating anchor is not available, and the prestress application effect and the prestress loss of the anti-floating anchor cannot be evaluated.
At present, the prestress detection methods for other prestress structures such as a prestressed concrete continuous (steel structure) box girder bridge web plate include an oil meter changing algorithm, a pressure sensor method, a strain gauge testing method, a magnetic flux detection method, a retraction amount detection method and an ultrasonic stress detection method. However, these methods have disadvantages, such as the oil pressure gauge changing algorithm is only suitable for the construction unit to control the stress during tensioning, and is not suitable for post detection and spot check; the pressure sensor test method has high instrument purchase cost and is not suitable for engineering practice; the test period of the strain gauge test method is long, and the strain gauge is easy to peel off and lose efficacy; the current technology of magnetic flux detection methods is still immature, so the reliability of the test result of the method is still examined; the retraction amount detection method has poor precision and has certain safety risk when measuring the retraction amount; the ultrasonic stress detection method has the advantages of fast energy loss and large error. Therefore, the method for detecting the prestress of the existing other prestress structures is difficult to modify and apply to the prestress anti-floating anchor rod structure.
Disclosure of Invention
The invention provides a prestress nondestructive testing method based on the natural frequency of a finish-rolled deformed steel bar anti-floating anchor rod, aiming at solving the problem that the anti-floating anchor rod lacks a prestress testing method which is simple to operate and reliable in performance, so that the prestress testing of the anti-floating anchor rod can be completed quickly and reliably, and the gap of prestress testing of the anti-floating anchor rod is filled.
In order to solve the technical problem, the technical scheme adopted by the invention is as follows:
a prestress nondestructive testing method based on the natural frequency of a finish-rolled deformed steel bar anti-floating anchor rod is characterized by comprising the following steps:
(1) The method comprises the steps of obtaining a first-order natural frequency (called a fundamental frequency for short) of an exposed section steel bar of a finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress in advance, and accordingly establishing a relation curve of the prestress value and the first-order natural frequency of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod;
(2) Acquiring a first-order natural frequency of a steel bar of an exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, which is subjected to prestressing force on site, by a detection system;
(3) And (3) obtaining the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod according to the relation curve between the prestress value and the first-order fixed frequency established in the step (1) and the first-order fixed frequency obtained in the step (2).
In some embodiments, in the step (1), a first-order fixed frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress is obtained through a detection system.
In some embodiments, the detection system comprises a first acceleration sensor and a second acceleration sensor, the first acceleration sensor is installed at the upper end of the steel bar at the exposed section of the finish-rolled deformed steel bar, the second acceleration sensor is installed at the lower section of the steel bar at the exposed section of the finish-rolled deformed steel bar, the upper end of the first acceleration sensor is flush with the upper end face of the steel bar at the exposed section of the finish-rolled deformed steel bar, the lower end face of the second acceleration sensor is attached to the upper end face of the prestressed anchor head at the lower end of the steel bar at the exposed section of the finish-rolled deformed steel bar, and the first acceleration sensor and the second acceleration sensor are both electrically connected with the signal collector.
In some embodiments, the first acceleration sensor is used for monitoring an acceleration time course curve input by the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the second acceleration sensor is used for monitoring an acceleration time course curve responded by the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod; the signal collector is used for carrying out time-frequency analysis on the received signals so as to obtain acceleration excellent frequency f1 corresponding to the first acceleration sensor and acceleration excellent frequency f2 corresponding to the second acceleration sensor, and the acceleration excellent frequency f2 is divided by the acceleration excellent frequency f1 to obtain the first-order natural frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod.
In some embodiments, the prestress value P of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor is obtained by the following formula:
wherein f is the first-order natural frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, R is the average value of the diameter of the anchor head and the diameter of the finish-rolled deformed steel bar, M is the mass of the anchor head, L is the length of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, rho is the linear density of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and a and b are experimental parameters.
In some embodiments, experimental parameters a and b are obtained by:
when the finish-rolled deformed steel bar is tensioned in stages, a first-order natural frequency f of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the load is obtained through a first acceleration sensor, a second acceleration sensor and a signal collector during tensioning of each stage of load, and then a prestress value P applied to the finish-rolled deformed steel bar anti-floating anchor rod is obtained through a feed-through pressure sensor; after the finish-rolled deformed steel bar anti-floating anchor rod is subjected to multi-stage load loading, a plurality of pairs of f and P values are obtained; and finally, performing curve fitting on a plurality of pairs of f and P values to obtain the values of a and b.
In some embodiments, the finish-rolled deformed steel bar should be stationary for a certain period of time under each load.
Compared with the prior art, the invention has the following beneficial effects:
the prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod obtains a relation curve between the first-order natural frequency and the magnitude of the prestress value of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod in advance (obtained in an indoor laboratory). When the field construction is based on the finish-rolled deformed steel bar anti-floating anchor rod, the detection system (the first acceleration sensor, the second acceleration sensor and the signal collector) is used for acquiring the first-order natural frequency of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod on the field, namely the pre-stress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod can be acquired through a relationship curve of the first-order natural frequency and the pre-stress value acquired in advance.
According to the invention, the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod can be obtained by obtaining the first-order natural frequency of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the gap of prestress detection of the prestress anti-floating anchor rod is filled. Compared with the prior art which adopts a strain gauge test method, the method has the characteristics of short acquisition time of the prestress value and avoids the problems of trouble, easy falling and failure in the installation of the strain gauge. Compared with the prior art which adopts a retraction amount detection method, the method has the advantages of high precision and high operation safety. Compared with the ultrasonic stress detection method adopted in the prior art, the method has the characteristic of high precision.
When the method is used for on-site detection, only one-step natural frequency of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor rod needs to be obtained through a detection system (namely the first acceleration sensor, the second acceleration sensor and the signal collector), and the method has the characteristics of high detection speed, convenience in on-site operation, stability and reliability, greatly saves the time for detecting the prestress of the anti-floating anchor rod, so that the construction progress is not influenced by the prestress detection, and finally the aim of saving the construction cost is fulfilled.
The detection system can be repeatedly used, and the prestress detection cost is greatly reduced.
The invention obtains the relation curve of the first-order natural frequency and the prestress value of the exposed section steel bar of the finish rolling deformed steel bar anti-floating anchor rod in advance in an indoor laboratory, and can obtain the relation curve of the first-order natural frequency and the prestress value of the whole batch only by calibrating one anti-floating anchor rod, thereby further improving the detection speed of the prestress of the anti-floating anchor rod. The invention can synchronously carry out indoor (like an experimental room, a relation curve of the first-order natural frequency of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor rod and the magnitude of the prestress value) and field detection, does not influence the detection progress of the field prestress anti-floating anchor rod, and further achieves the purpose of improving the detection speed.
Drawings
FIG. 1 is a schematic structural view of an embodiment of a finish-rolled deformed steel bar anti-floating anchor rod;
FIG. 2 is a schematic view of a partial structure of a finish-rolled deformed steel bar before prestress is applied to an anti-floating anchor rod;
FIG. 3 is a schematic structural diagram of the detection system of the present invention when detecting a pre-stressed finish-rolled deformed steel bar anti-floating anchor rod;
FIG. 4 is a schematic structural diagram of the detection system of the present invention when acquiring a relationship curve between a prestress value and a first-order natural frequency of an exposed steel bar of a finish-rolled deformed steel bar anti-floating anchor rod indoors (or in a laboratory);
FIG. 5 is a graph schematically illustrating a relationship curve between a prestress value and a first-order natural frequency of an exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod according to the embodiment of the invention, which is obtained in advance;
the labels in the figure are: 1. anchor eye, 2, finish rolling screw-thread steel, 3, supporting body, 4, sleeve pipe, 5, bed course, 6, prestressing force backing plate, 7, prestressing anchor head, 8, supporting anchor plate, 9, supporting anchor head, 10, basic or water-resistant plate, 11, first acceleration sensor, 12, second acceleration sensor, 13, signal collector, 14, rubber hammer, 15, jack and counterforce device, 16, power transmission component, 17, punching type pressure sensor.
Detailed Description
The present invention will be further described with reference to the following examples, which are intended to illustrate only some, but not all, of the embodiments of the present invention. Other embodiments used by those skilled in the art can be obtained without any creative effort based on the embodiments in the present invention, and all of them belong to the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention; the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, as they may be fixedly connected, detachably connected, or integrally connected, for example; may be a mechanical connection; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood by those of ordinary skill in the art in conjunction with specific situations.
With reference to fig. 1 and fig. 2, the structural schematic diagram of an embodiment of the finish-rolled deformed steel bar anti-floating anchor rod taught by the present invention is shown, the finish-rolled deformed steel bar anti-floating anchor rod includes an anchor hole 1 and a finish-rolled deformed steel bar 2 disposed in the anchor hole 1, a space between the anchor hole 1 and the finish-rolled deformed steel bar 2 is used for filling concrete, after the concrete is solidified, an anchor body is formed, a cushion layer 5 is laid on a soil body at an upper end of the anchor hole 1, and an upper end of the finish-rolled deformed steel bar 2 penetrates through the cushion layer 5 and is provided with a prestressed anchor plate 6 and a prestressed anchor head 7, wherein a plurality of supporting bodies 3 are disposed at intervals on a lower section of the finish-rolled deformed steel bar 2, and a sleeve 4 is sleeved on a periphery of the finish-rolled deformed steel bar 2 at a free section of the anchor hole. When the concrete of the finish-rolled deformed steel bar anti-floating anchor rod reaches a certain strength, prestress needs to be applied to the finish-rolled deformed steel bar 2, and after the prestress is applied, the finish-rolled deformed steel bar 2 is locked through the prestressed anchor head 7 and the prestressed base plate 6. After the prestress of the finish-rolled deformed steel bar 2 is applied, the prestress value needs to be detected, if the prestress value meets the design requirement, a matched anchor plate 8 and a matched anchor head 9 are sleeved on the upper section of the finish-rolled deformed steel bar 2, and finally a foundation or a water-resistant plate 10 is poured to pre-embed the matched anchor plate 8 and the matched anchor head 9.
The construction, prestress application and locking of the finish rolled deformed steel bar anti-floating anchor rod belong to the prior art, and can be understood and understood by those skilled in the art, and are not described in detail herein.
With reference to the attached drawings 1 to 4, the prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod comprises the following steps:
(1) The method comprises the steps of obtaining a first-order natural frequency (called a fundamental frequency for short) of an exposed section steel bar of a finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress in advance, and accordingly establishing a relation curve of the prestress value and the first-order natural frequency of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod; wherein, the exposed section steel bar stated in the invention refers to: and the finish rolling screw steel 2 is positioned above the prestressed anchor head 7.
(2) Acquiring a first-order natural frequency of a steel bar of an exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, which is subjected to prestressing force on site, by a detection system;
(3) And (3) obtaining the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod according to the relation curve between the prestress value and the first-order fixed frequency established in the step (1) and the first-order fixed frequency obtained in the step (2). Thereby rapidly obtaining the prestress value of the finish rolling screw steel anti-floating anchor rod.
The invention discloses a prestress nondestructive testing method based on the natural frequency of a finish-rolled deformed steel bar anti-floating anchor rod. When the field construction is based on the finish-rolled deformed steel bar anti-floating anchor rod, the detection system (the first acceleration sensor, the second acceleration sensor and the signal collector) is used for acquiring the first-order natural frequency of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod on the field, namely the pre-stress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod can be acquired through a relationship curve of the first-order natural frequency and the pre-stress value acquired in advance.
According to the invention, the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod can be obtained by obtaining the first-order natural frequency of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the gap of prestress detection of the prestress anti-floating anchor rod is filled. Compared with the prior art which adopts a strain gauge testing method, the method has the characteristics of short acquisition time of the prestress value, and avoids the problems of trouble, easy falling off and failure in the installation of the strain gauge. Compared with the prior art which adopts a retraction amount detection method, the method has the advantages of high precision and high operation safety. Compared with the prior art which adopts an ultrasonic stress detection method, the method has the characteristic of high precision.
In some embodiments, in the step (1), a first-order fixed frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress is obtained through a detection system.
In some embodiments, the detection system includes a first acceleration sensor 11 and a second acceleration sensor 12, the first acceleration sensor 11 is installed at the upper end of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor, the second acceleration sensor 12 is installed at the lower section of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor, the upper end of the first acceleration sensor 11 is flush with the upper end surface of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor, the lower end surface of the second acceleration sensor 12 is attached to the upper end surface of the prestressed anchor head 7 at the lower end of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor, and both the first acceleration sensor 11 and the second acceleration sensor 12 are electrically connected to the signal collector 13.
In some embodiments, the first acceleration sensor 11 is used for monitoring an acceleration time course curve of the input of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the second acceleration sensor 12 is used for monitoring an acceleration time course curve of the response of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod; the signal collector 13 is configured to perform time-frequency analysis on the received signal to obtain an acceleration excellent frequency f1 corresponding to the first acceleration sensor 11 and an acceleration excellent frequency f2 corresponding to the second acceleration sensor, and divide the acceleration excellent frequency f2 by the acceleration excellent frequency f1 to obtain a first-order natural frequency of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod. With reference to fig. 3 and the accompanying drawings, the detection system needs to knock the top of the finish-rolled deformed steel bar 2 by using the rubber hammer 14 during testing, so that the top of the finish-rolled deformed steel bar is monitored by using the first acceleration sensor and the second acceleration sensor.
In some embodiments, the prestress value P of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor is obtained by the following formula:
wherein f is the first-order natural frequency of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod, R is the average value of the diameter of the anchor head and the diameter of the finish-rolled deformed steel bar, M is the mass of the anchor head, L is the length of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod, rho is the linear density of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod, and a and b are experimental parameters.
In some embodiments, experimental parameters a and b are obtained by:
with reference to the attached drawing 4, when the finish-rolled deformed steel bar 2 is tensioned in stages, a first-order natural frequency f of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the load is obtained through a first acceleration sensor 11, a second acceleration sensor 12 and a signal collector 13 during tensioning of each stage of load, and then a prestress value P applied to the finish-rolled deformed steel bar anti-floating anchor rod is obtained through a center-through pressure sensor 17; after the finish-rolled deformed steel bar anti-floating anchor rod is subjected to multi-stage load loading, a plurality of pairs of f and P values (namely a first-order natural frequency corresponds to a P value) are obtained; and finally, performing curve fitting on the multiple pairs of f and P values to obtain the values of a and b.
In some embodiments, the finish-rolled deformed steel bar should be allowed to stand for a certain period of time (e.g., 5min, 10 min) under each load, i.e., the magnitude of the prestress applied to the finish-rolled deformed steel bar 2 is not changed during the period of time.
When the prestress is applied to the finish-rolled screw steel anti-floating anchor rod (namely, the finish-rolled deformed steel bar is tensioned), the prestress is not increased to a set value at one time, but is gradually applied through tensioning equipment (such as a jack and a counterforce device), and after a prestress value with one size is applied, the prestress needs to be kept for a period of time on the premise of the size of the prestress; and then, increasing the applied prestress value, and repeating the steps until the applied prestress value reaches the design requirement. Will be apparent and understood by those skilled in the art and will not be described in detail herein.
When the detection system of the present invention is used to obtain the relationship curve between the prestress value and the first-order natural frequency of the exposed steel bar of the finish-rolled deformed steel bar anti-floating anchor rod with reference to fig. 3 and 4, the detection system further includes (or is equipped with) a jack and counterforce device 15, a force transmission component 16 (e.g., a steel cylinder), and a feed-through pressure sensor 17. Namely, when the calibration is carried out indoors (such as a laboratory) or at other places, the finish-rolled deformed steel bar anti-floating anchor rod is modeled by using the cushion layer 5, the finish-rolled deformed steel bar 2, the pre-stressed anchor head 7, the pre-stressed base plate 6, the force transmission part 16 and the through-center pressure sensor 17 together. Referring to the attached drawing 4, the upper end of the finish rolling deformed steel bar 2 penetrates through the cushion layer 5 and is provided with a prestressed backing plate 6 and a prestressed anchor head 7 in a matched mode, the prestressed backing plate 6 is in contact with the cushion layer 5, a force transfer part 16 is arranged below the cushion layer 5, the lower section of the finish rolling deformed steel bar 2 penetrates through the force transfer part 16 and is provided with the prestressed backing plate 6 and the prestressed anchor head 7 in a matched mode, the prestressed backing plate 6 below the cushion layer 5 is in contact with the force transfer part 16, and the lower end face of the prestressed anchor head 7 below the cushion layer 5 is provided with a through type pressure sensor 17 which is sleeved on the finish rolling deformed steel bar 2 in a matched mode. When the detection system is used, a jack and a counterforce device 15 are used for applying prestress on the finish-rolled deformed steel bar 2, a prestress value P applied to the finish-rolled deformed steel bar 2 is obtained through a center-through pressure sensor 17, a first-order natural frequency of an exposed-section steel bar of the finish-rolled deformed steel bar 2 is obtained through a first acceleration sensor 11, a second acceleration sensor 12 and a signal collector 13, and a plurality of pairs of f and P values (namely, one first-order natural frequency corresponds to one P value) are obtained after the finish-rolled deformed steel bar is loaded with multi-stage load; and finally, performing curve fitting on a plurality of pairs of f and P values to obtain the values of a and b. The values of f and P are substituted into the following formula to carry out reverse extrapolation to obtain the values of a and b:
the formula is as follows:
when the finish-rolled deformed steel bar anti-floating anchor rod is constructed on site, the straight-through pressure sensor 17 is not suitable for detection on the construction site due to high cost.
The detection system has a simple structure in a construction site of the anti-floating anchor rod, namely the first acceleration sensor 11, the second acceleration sensor and the signal collector 13 form the detection system (matched with the rubber hammer 14 or directly utilizing the rubber hammer in the construction site) in the construction site, and the detection system has the characteristics of low cost, recycling, and simplicity and reliability in operation.
Due to the same construction site, the size of the finish-rolled deformed steel bar 2, the size of the prestressed anchorage head 7 and the size of the prestressed anchorage plate 6 used are substantially the same. Therefore, the invention can carry out prestress detection on each anti-floating anchor rod of the whole construction project by acquiring the relation curve of the prestress value of an exposed section of steel bar and the first-order natural frequency in advance aiming at the construction project, thereby greatly improving the efficiency of prestress detection and reducing the cost of prestress detection.
Certainly, for different construction sites, the sizes of the finish-rolled deformed steel bar 2 and the prestressed anchor head 7 of the designed anti-floating anchor rod are different, and then the relation curve of the prestress value and the first-order natural frequency of the exposed section of the steel bar is obtained according to the conditions of the construction sites.
When the method is used for on-site detection, only one-step natural frequency of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor rod needs to be obtained through a detection system (namely the first acceleration sensor, the second acceleration sensor and the signal collector), and the method has the characteristics of high detection speed, convenience in on-site operation, stability and reliability, greatly saves the time for detecting the prestress of the anti-floating anchor rod, so that the construction progress is not influenced by the prestress detection, and finally the aim of saving the construction cost is fulfilled.
According to the invention, a relation curve of the first-order natural frequency and the prestress value of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor rod is obtained in advance in an indoor laboratory, and the relation curve of the first-order natural frequency and the prestress value of the whole batch can be obtained only by calibrating one anti-floating anchor rod, so that the detection speed of the prestress of the anti-floating anchor rod is further improved. The invention can synchronously carry out indoor (like an experimental room, a relation curve of the first-order natural frequency of the exposed section of the steel bar of the finish-rolled deformed steel bar anti-floating anchor rod and the magnitude of the prestress value) and field detection, does not influence the detection progress of the field prestress anti-floating anchor rod, and further achieves the purpose of improving the detection speed.
The detection method has the characteristics of simple and convenient operation, high reliability and high detection speed, and because the number of the prestressed anti-floating anchor rods on one construction site is large and each anti-floating anchor rod needs to be detected, a large amount of detection time can be saved on the whole, so that the construction period of the anti-floating anchor rods is shortened, and the construction cost is reduced.
Claims (7)
1. The prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod is characterized by comprising the following steps of:
(1) The method comprises the steps of obtaining a first-order natural frequency of an exposed section steel bar of a finish-rolled deformed steel bar anti-floating anchor rod under the action of prestress in advance, and accordingly establishing a relation curve of a prestress value and the first-order natural frequency of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod;
(2) Acquiring a first-order natural frequency of a steel bar of an exposed section of a finish-rolled deformed steel bar anti-floating anchor rod to which prestress is applied on site through a detection system;
(3) And (3) obtaining the prestress value of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod according to the relation curve of the prestress value and the first-order fixed frequency established in the step (1) and the first-order fixed frequency obtained in the step (2).
2. The prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod in the claim 1 is characterized in that in the step (1), the first-order fixed frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the action of the prestress is obtained through a testing system.
3. The prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod is characterized in that the testing system comprises a first acceleration sensor and a second acceleration sensor, the first acceleration sensor is installed at the upper end of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, the second acceleration sensor is installed at the lower section of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, the upper end of the first acceleration sensor is flush with the upper end face of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, the lower end face of the second acceleration sensor is attached to the upper end face of the prestress anchor head at the lower end of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the first acceleration sensor and the second acceleration sensor are both electrically connected with the signal collector.
4. The prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod as claimed in claim 3, wherein the first acceleration sensor is used for monitoring an acceleration time course curve input by a steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and the second acceleration sensor is used for monitoring an acceleration time course curve responded by the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod; the signal collector is used for carrying out time-frequency analysis on the received signals so as to obtain acceleration excellent frequency f1 corresponding to the first acceleration sensor and acceleration excellent frequency f2 corresponding to the second acceleration sensor, and the acceleration excellent frequency f2 is divided by the acceleration excellent frequency f1 to obtain the first-order natural frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod.
5. The prestress nondestructive testing method based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod as claimed in claim 4, wherein the prestress value P of the exposed section steel bar of the finish-rolled deformed steel bar anti-floating anchor rod is obtained by the following formula:
wherein f is the first-order natural frequency of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, R is the average value of the diameter of the anchor head and the diameter of the finish-rolled deformed steel bar, M is the mass of the anchor head, L is the length of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, rho is the linear density of the steel bar of the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod, and a and b are experimental parameters.
6. The finish-rolled deformed steel bar anti-floating anchor rod natural frequency-based prestress nondestructive testing method according to claim 5, wherein the experimental parameters a and b are obtained by the following steps:
when the finish-rolled deformed steel bar is tensioned in stages, a first-order natural frequency f of the steel bar at the exposed section of the finish-rolled deformed steel bar anti-floating anchor rod under the load is obtained through a first acceleration sensor, a second acceleration sensor and a signal collector during tensioning of each stage of load, and then a prestress value P applied to the finish-rolled deformed steel bar anti-floating anchor rod is obtained through a through type pressure sensor; after the finish-rolled deformed steel bar anti-floating anchor rod is subjected to multi-stage load loading, a plurality of pairs of f and P values are obtained; and finally, performing curve fitting on a plurality of pairs of f and P values to obtain the values of a and b.
7. The non-destructive testing method for the prestress based on the natural frequency of the finish-rolled deformed steel bar anti-floating anchor rod according to claim 6, wherein when the finish-rolled deformed steel bar is subjected to the step-by-step tensioning, the finish-rolled deformed steel bar is allowed to stand for a certain time under each step of load.
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