CN113237588A - Support axial force monitoring method and system considering concrete shrinkage and creep influence - Google Patents
Support axial force monitoring method and system considering concrete shrinkage and creep influence Download PDFInfo
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- CN113237588A CN113237588A CN202110433776.2A CN202110433776A CN113237588A CN 113237588 A CN113237588 A CN 113237588A CN 202110433776 A CN202110433776 A CN 202110433776A CN 113237588 A CN113237588 A CN 113237588A
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- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
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Abstract
The invention belongs to the technical field of rock-soil mechanics monitoring, and particularly discloses a method and a system for monitoring a supporting axial force by considering the influence of concrete shrinkage and creep. The method comprises the following steps: installing a steel bar meter at the cut-off position of the main steel bar; arranging a shear force sensor along the length direction of the main rib, and attaching the pre-tensioned strain gauge to the main rib in a surrounding manner; welding and fixing the reinforcing steel bar meter at the main bar cutting position; and pouring concrete, after the concrete support construction is finished and before the foundation pit is not excavated, acquiring strain data measured by the shear force sensor, calculating the steel bar strain caused by concrete shrinkage creep and concrete elastic modulus change, deducting the steel bar strain from the strain data measured by the steel bar meter to obtain the real strain of the main bar, and finally calculating the real value of the support axial force based on an equal effect deformation method. The system comprises a reinforcing bar meter and a shear force sensor. The invention has the characteristics of high calculation precision of the reinforced concrete supporting axial force, low manufacturing cost, simple structure and the like.
Description
Technical Field
The invention belongs to the technical field of geotechnical monitoring, and particularly relates to a method and a system for monitoring a supporting axial force by considering the shrinkage and creep influence of concrete.
Background
The strain generated by the support under the action of external force needs to be obtained in the reinforced concrete support monitoring, in the actual monitoring process, the accuracy of the strain monitoring of the sensor is influenced by various factors including temperature, concrete shrinkage, creep, elastic modulus nonlinearity and the like, the strain obtained by monitoring is larger than the strain generated by the external force due to the factors, the phenomenon that the monitoring value of the support axial force is larger often occurs in engineering practice and sometimes even exceeds the bearing capacity of a member, but other monitoring data and field inspection are not abnormal. The open Wei supports through the cut concrete in the document 'analysis and research on the stress composition of the concrete supporting axial force of the supporting structure', and sets a concrete supporting axial force meter on the section to monitor the supporting axial force, and the test result shows that: the actual axial force value of the concrete is about 30-40% of the axial force value monitored on the concrete supporting site. The phenomenon that the difference between the axial force monitoring value and the actual supporting axial force value is large often troubles all parties.
At present, concrete supporting axial force monitoring is generally carried out by adopting a method of embedding a vibrating wire type reinforcing steel bar meter or a strain gauge, obtaining the strain capacity of a supporting beam by measuring the frequency change of a sensor, and calculating the supporting axial force by an axial force calculation formula. According to the technical specification for monitoring urban rail transit engineering GB50911-2013, the structural stress monitoring needs to eliminate the influence of factors such as temperature change and the like, and the reinforced concrete structure needs to eliminate the influence of concrete shrinkage, creep and cracks. At present, the influence of temperature is generally eliminated by performing temperature compensation on a monitoring value of a steel bar gauge, for example, in an optimization method of reinforced concrete support axial force monitoring data (CN201310536162.2) in the chinese patent of the invention, n steel bar stress gauges are arranged on a section of a reinforced concrete support in a uniformly distributed manner to form n monitoring points, the steel bar stress gauge is provided with a temperature measuring unit, and then the measured reinforced concrete support axial force is subtracted by a force generated by a temperature effect, so that a relatively true reinforced concrete support axial force can be obtained. For the influence of concrete shrinkage and creep and the elastic modulus of concrete, no effective monitoring method is available at present to consider the influence, and the axial force value of concrete support is generally calculated through theoretical derivation. Therefore, the difference between the support axial force monitoring value and the actual axial force value is large, and no effective monitoring method considering the influences of concrete shrinkage and creep and the concrete elastic modulus exists at present.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a method and a system for monitoring the supporting axial force by considering the concrete shrinkage and creep influence, wherein the characteristics of a reinforced concrete supporting structure and the process characteristics of the axial force measurement are combined, and the influence of the concrete shrinkage and creep and the change of the concrete elastic modulus on the reinforced concrete supporting axial force is not considered in the prior art, a plurality of reinforcing steel bar meters and shearing force sensors are arranged on the main reinforcement part of the reinforced concrete support, the plurality of shearing force sensors are correspondingly pre-tensioned and pasted, and meanwhile, the plurality of shearing force sensors are connected in series, in this way, the strain quantity detection of the supporting beam can be realized by the reinforcing steel bar meters, and simultaneously, the monitoring of the influence of the concrete shrinkage and creep on the reinforced concrete supporting axial force can be realized by the detection data of the plurality of shearing force sensors, the influence of the change of the elastic modulus of the concrete on the supporting axial force can be indirectly eliminated, and the calculation precision of the reinforced concrete supporting axial force is improved. The invention has the characteristics of high calculation precision of the reinforced concrete supporting axial force, low manufacturing cost, simple structure and the like, thereby being particularly suitable for monitoring the supporting axial force of the concrete of the foundation pit.
To achieve the above object, according to one aspect of the present invention, there is provided a method for monitoring a supporting axial force considering an influence of concrete shrinkage creep, comprising the steps of:
s1, before the reinforced concrete support is poured, cutting off a section of main reinforcement at the corresponding position of the middle points of the four corners or four edges of the reinforcement cage along the length direction of the reinforcement cage, wherein the cutting-off length is equal to that of the reinforcement meter, and installing the reinforcement meter at the cutting-off position of the main reinforcement;
s2, uniformly arranging a plurality of shear force sensors along the length direction of the main rib, namely pre-tensioning strain gauges of the shear force sensors to enable the strain gauges to be in a tensioned state, and attaching the pre-tensioned strain gauges to the main rib in a surrounding manner;
s3, welding and fixing the reinforcing steel bar meter at the corresponding main bar cutting position;
s4, pouring concrete, and after the concrete support construction is completed and before the foundation pit is not excavated, acquiring strain data measured by a reinforcing steel bar meter and a shearing force sensor;
s5, calculating the strain of the main reinforcement caused by the shrinkage creep of the concrete and the change of the elastic modulus of the concrete according to the shear strain measured by the shear force sensor, deducting the strain of the reinforcement from the strain data measured by the reinforcement meter to obtain the real strain of the main reinforcement, and finally calculating the real axial force of the reinforced concrete support based on the equal effect deformation method.
Preferably, in step S1, the cross-sectional area of the reinforcing bar meter is the same as the cross-sectional area of the main bar, and the reinforcing bar meters are distributed in a quadrilateral manner to form 4 monitoring points, specifically, four reinforcing bar meters are distributed at positions corresponding to the four corners or the middle points of the four corners of the reinforcing cage.
More preferably, step S2 specifically includes the following steps:
prestretching the strain gauge to enable the strain gauge to be in a tense state;
polishing and grinding the main ribs at the arrangement positions of the shearing force sensors along the length direction of the main ribs to enable the surfaces of the main ribs to be flat and smooth, and then cleaning the ground positions by dipping acetone or alcohol in absorbent cotton balls to prevent the influence of pollutants such as ground scraps, oil stains and the like;
and uniformly sticking the strain gauge in a tightened state to the cleaned main rib.
Further preferably, step S2 further includes the steps of:
after the strain gauge is pasted, the annular protection device is penetrated to the position where the strain gauge is pasted from one end of the cut main rib and stopped, and then screws for screwing the annular protection device are adopted, so that the annular protection device is tightly attached to the strain gauge.
More preferably, step S5 specifically includes the following steps:
s51, the shrinkage and creep of the concrete enable a shearing acting force to exist between the concrete and the main reinforcement wrapped by the concrete, the shearing strain measured by the shearing force sensor is substituted for the formula (1) to calculate, and the shearing stress at each shearing force sensor is obtained:
τij＝Gs·γij (1)
in the formula: tau isijI is an integer from 1 to n, n is the number of main bars on which the shear force sensors are mounted, j is an integer from 1 to m, m is the number of shear force sensors mounted on the ith main bar, GsThe shear modulus of the steel bar; gamma rayijThe shear strain measured by the shear force sensor;
s52, calculating the strain of the main reinforcement caused by the shrinkage and creep of the concrete and the change of the elastic modulus of the concrete according to the arrangement condition of the shear force sensors and the shear stress at each shear force sensor:
in the formula: epsiloniStrain of the main reinforcement caused by shrinkage and creep of the concrete and change of the elastic modulus of the concrete, EsThe elastic modulus of the steel bar is shown, R is the diameter of the main bar, and l is the distance between adjacent shear force sensors on the same main bar;
s53, strain data measured by the reinforcing steel bar meter is substituted into the formula (3) to obtain the average strain of the section of the main reinforcement:
in the formula:
to monitor cross-sectional average strain;
the strain measured by the ith reinforcing steel bar meter is measured, and n is the number of the reinforcing steel bar meters;
s54, calculating the real axial force of the reinforced concrete support according to the average strain of the main bar section and by combining the equivalent strain method of the support section, wherein the concrete formula is as follows:
in the formula: f-axial force of the reinforced concrete support, EcModulus of elasticity of concrete, EsModulus of elasticity of the reinforcing bar, AcConcrete area of section, As-cross-sectional rebar area.
Further preferably, in step S51, the shear force acting on the main reinforcement due to the shear force existing between the concrete and the main reinforcement wrapped by the concrete is calculated by the following model:
in the formula: fiThe shear force of the ith main reinforcement caused by the creep of the concrete, R is the diameter of the main reinforcement, l is the distance between adjacent shear force sensors on the same main reinforcement, m is the number of the shear force sensors arranged on the ith main reinforcement, and tauijIs the shear stress at the shear force sensor.
Preferably, the installation of the steel bar meter and the shearing force sensor is carried out when a main reinforced concrete supporting bar is bound, the steel bar meter is uniformly distributed on the supporting section, the shearing force sensor is uniformly distributed along the length direction of the main bar, and meanwhile, a protective sleeve is adopted to sleeve the lead wires of the steel bar meter and the shearing force sensor and then lead out.
According to another aspect of the present invention, there is also provided a support axial force monitoring system taking into account the effects of concrete shrinkage creep, the system being adapted to implement the method of any one of claims 1 to 7, comprising a plurality of reinforcing bars, a plurality of shear force sensors and a master control module, wherein,
cutting off a section of main reinforcement at the corresponding position of the middle points of four corners or four edges of the reinforcement cage along the length direction of the reinforcement cage, wherein the cutting-off length is equal to that of a reinforcement meter, and the reinforcement meter is welded and fixed with the main reinforcement at the corresponding main reinforcement cutting-off position;
the shear force sensor comprises strain gauges, the strain gauges are pre-tensioned and then uniformly attached to the main ribs in a surrounding mode, and the strain gauges on each main rib are uniformly arranged at intervals;
the main control module is in communication connection with the plurality of steel bar meters and the plurality of shear force sensors and is used for collecting data obtained by measurement of the steel bar meters and the shear force sensors, calculating main bar strain caused by concrete shrinkage creep and concrete elastic modulus change according to the shear strain measured by the shear force sensors, deducting the steel bar strain from the strain data measured by the steel bar meters to obtain real strain of a main bar, and finally calculating the real axial force of the reinforced concrete support based on an equal effect transformation method.
Preferably, the shear force sensor further comprises an annular protection device, the annular protection device is sleeved on the steel bar meter, and two ends of each strain gauge are provided with one annular protection device;
the strain gauge is a friction type strain gauge, and the cross section of the steel bar meter is the same as that of the main bar.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. aiming at the problems that the prior art does not consider the influence of concrete shrinkage and creep and the concrete elastic modulus on the reinforced concrete supporting axial force, a plurality of steel bar meters and shearing force sensors are arranged on a main bar part of a reinforced concrete support, the plurality of shearing force sensors are subjected to corresponding pre-tensioning and pasting treatment, and meanwhile, the plurality of shearing force sensors are connected in series, so that the strain quantity detection of a supporting beam can be realized through the steel bar meters, meanwhile, the monitoring of the influence of the concrete shrinkage and creep on the reinforced concrete supporting axial force can be realized through the detection data of the plurality of shearing force sensors, the influence of the concrete elastic modulus change on the supporting axial force can also be indirectly eliminated, and the calculation precision of the reinforced concrete supporting axial force is improved. The invention has the characteristics of low manufacturing cost, simple structure and the like.
2. The invention can monitor the shearing force between the concrete and the steel bar, calculate the real axial force of the reinforced concrete support according to the relevant standard regulation and the reinforced concrete mechanics calculation formula and combining the equivalent strain method of the support section, and has the characteristics of simple calculation model and high calculation precision of the reinforced concrete support axial force.
3. The invention only adds a plurality of shear force sensors with lower manufacturing cost, and is beneficial to saving the monitoring cost compared with the traditional monitoring method.
4. The installation process of the shear force sensor is simple and convenient, and the shear force sensor can be installed together with a steel bar meter, so that the labor cost is saved.
5. The cross sectional area of the reinforcing steel bar meter is the same as that of the main reinforcing steel bars, the reinforcing steel bar meter is distributed in a quadrilateral shape to form 4 monitoring points, and meanwhile, a plurality of strain gauges on each main reinforcing steel bar are uniformly arranged at intervals, so that the effective and comprehensive monitoring of the reinforced concrete supporting axial force can be realized.
6. According to the invention, a plurality of shear force sensors are arranged in series, and the annular protection device is adopted to fix and protect the shear force sensors, so that data acquisition is facilitated, interference of other frequency signals is eliminated, and the measurement precision is high.
Drawings
FIG. 1 is a flow chart of a method for monitoring support axial force with consideration of the effect of concrete shrinkage creep according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of a support axial force monitoring system that takes into account the effects of concrete shrinkage creep according to a preferred embodiment of the present invention;
fig. 3 is a schematic view of the structure of the shear force sensor shown in fig. 2.
In all the figures, the same reference numerals denote the same features, in particular: the device comprises a steel bar meter 1, a shear force sensor 2, a main reinforcement 3, a stirrup 4, a friction type strain gage 2-1, a screw 2-2 and an annular protection device 2-3.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1 and fig. 2, a supporting axial force monitoring method considering the effect of concrete shrinkage and creep provided by an embodiment of the present invention is mainly implemented by arranging a steel bar meter 1 and a shear force sensor 2 on a main bar 3 of a concrete support. The supporting shaft force measuring points are generally arranged at 1/3 positions in the middle of the support or between two supporting points, the reinforcing steel bar meters 1 are arranged on the main reinforcements 3 at four corners or four edges of the positions, and the shearing force sensors 2 are uniformly arranged along the length direction of the main reinforcements 3; the shear force sensor 2 consists of a friction type strain gauge 2-1, an annular protection device 2-3 and an elastic screw 2-2; the steel bar meter 1 is matched with a friction type strain gauge 2-1 on the shearing force sensor 2 for use, and monitoring of the foundation pit concrete supporting axial force is completed together.
Specifically, the method for monitoring the supporting axial force by considering the shrinkage and creep influence of the concrete comprises the following steps of:
(1) before the reinforced concrete supports and pours, at the position that need lay the vibration wire formula rebar gauge, cut one section with the main muscle of steel reinforcement cage four corners or four sides mid point corresponding position, the intercepting length equals with the rebar gauge, specifically speaking, cuts one section with the main muscle of steel reinforcement cage four corners or four sides mid point corresponding position along steel reinforcement cage length direction, and the intercepting length equals with the rebar gauge to at main muscle department of cutting installation rebar gauge. In the invention, the cross-sectional area of the reinforcing steel bar meters is the same as that of the main reinforcing steel bars, the reinforcing steel bar meters are distributed in a quadrilateral way to form 4 monitoring points, and specifically, the four reinforcing steel bar meters are distributed at the corresponding positions of four corners or the middle points of four sides of the reinforcing steel bar cage.
(2) And uniformly arranging a plurality of shear force sensors at the position where the main rib is cut off along the main rib degree direction, determining the number of the shear force sensors according to the length and the arrangement distance of the main rib, and identifying the arrangement position of the shear force sensors. In the invention, the shearing force sensors on each main rib are the same in number and the arrangement intervals are also the same, and meanwhile, the plurality of shearing force sensors are arranged in series.
(3) Polishing and grinding the reinforcing steel bars at the arrangement positions of the shearing force sensors to enable the surfaces of the reinforcing steel bars to be flat and smooth. And then the polished part is cleaned by dipping the absorbent cotton ball in acetone or alcohol, so that the influence of pollutants such as polished scraps, oil stains and the like is prevented.
(4) The strain gauge is pre-tensioned before being pasted, the pre-tensioning force during pre-tensioning is 1 Newton force, the strain gauge is in a tensioned state, the polished and polished part of the steel bar is fixed by 502 glue at fixed points, the friction type strain gauge is attached to the surface of the steel bar in a surrounding mode, then the strain gauge is pasted completely by epoxy resin, and the epoxy resin is required to be coated uniformly.
(5) And threading the annular protection device from one end of the cut steel bar to the position where the strain gauge is adhered, and screwing the tightening screw to enable the annular protection device to be tightly attached to the strain gauge.
(6) And welding and fixing the reinforcing steel bar meter at the corresponding reinforcing steel bar cutting position.
(7) The installation of the steel bar meter and the shear force sensor is required to be carried out when steel bars are bound, the steel bar meter is uniformly distributed on the supporting cross section, the shear force sensor is uniformly distributed along the length direction of the steel bars, and meanwhile, the protective sleeve for protecting the lead is required to be led out.
(8) After the concrete support construction is completed and before a foundation pit is not excavated, reading is carried out by adopting a vibrating wire type frequency reading instrument, the temperature is recorded, and corresponding strain data is calculated through a measured frequency value. And calculating the main bar strain caused by concrete shrinkage creep and concrete elastic modulus change according to the shear strain measured by the shear force sensor, deducting the steel bar strain from the strain data measured by the steel bar meter to obtain the real strain of the main bar, and finally calculating the real axial force of the reinforced concrete support based on an equal effect deformation method.
The concrete shrinkage creep and the supporting axial force caused by the change of the concrete elastic modulus are calculated and considered, and the concrete shrinkage creep and the supporting axial force specifically comprise the following steps:
firstly, the shrinkage and creep of the concrete enable a shearing acting force to exist between the concrete and a main reinforcement wrapped by the concrete, the shearing strain measured by a shearing force sensor is substituted for formula (1) to calculate, and the shearing stress at each shearing force sensor is obtained:
τij＝Gs·γij (1)
in the formula: tau isijI is an integer from 1 to n, n is the number of main bars on which the shear force sensors are mounted, j is an integer from 1 to m, m is the number of shear force sensors mounted on the ith main bar, GsThe shear modulus of the steel bar; gamma rayijIs the shear strain measured by the shear force sensor.
The shear force calculation model acting on the main reinforcement is as follows:
in the formula: fiThe i-th main reinforcement is subjected to shearing force due to the shrinkage and creep of the concrete.
Secondly, calculating the strain of the main reinforcement caused by the shrinkage and creep of the concrete and the change of the elastic modulus of the concrete according to the arrangement condition of the shear force sensors and the shear stress at each shear force sensor:
in the formula: epsiloniStrain of the main reinforcement caused by shrinkage and creep of the concrete and change of the elastic modulus of the concrete, EsThe elastic modulus of the steel bar is shown, R is the diameter of the main bar, and l is the distance between adjacent shear force sensors on the same main bar;
and then, substituting strain data measured by a reinforcing bar meter into the formula (3) to obtain the average strain of the section of the main bar:
in the formula:
to monitor cross-sectional average strain;
the strain measured by the ith reinforcing steel bar meter is measured, and n is the number of the reinforcing steel bar meters;
and finally, calculating the real axial force of the reinforced concrete support according to the average strain of the section of the main reinforcement and by combining an equivalent strain method of the support section, wherein the concrete formula is as follows:
in the formula: f-axial force of the reinforced concrete support, EcModulus of elasticity of concrete, EsModulus of elasticity of the reinforcing bar, AcConcrete area of section, As-cross-sectional rebar area.
According to another aspect of the present invention, as shown in fig. 2 and 3, there is also provided a system for implementing the above method, the system comprising a plurality of reinforcing bar meters 2, a plurality of shear force sensors 3, and a main control module. The main reinforcement at the corresponding positions of four corners or four sides of the reinforcement cage is cut by one section along the length direction of the reinforcement cage, the cut length is equal to the reinforcement meter, the reinforcement meter is installed at the corresponding position of the cut main reinforcement, and the two ends of the reinforcement meter are fixedly connected with the main reinforcement in a welding mode. Generally, in order to reduce the stress of the concrete support structure, the cross-sectional area of the reinforcing bar gauge is the same as the cross-sectional area of the main bar. Concrete bearing structure is square, then distributes and is called main muscle in the reinforcing bar of its transversal gluten cage four corners collectively, cuts one section along the main muscle that steel reinforcement cage length direction corresponds the position in steel reinforcement cage four corners or four sides mid point, and is preferred, along main muscle length direction, and the position and the length that every main muscle was cut are the same, and with this mode, the monitoring of every main muscle support axial force variation value is realized. In the invention, after the main reinforcement and the reinforcement meter are welded, the welding part needs to be polished and cleaned, so that the surface of the welding part is uniform, smooth and clean, and meanwhile, the cross section area of the welding part is ensured to be the same as that of the main reinforcement.
In addition, the shear force sensor 3 includes strain gauges, the strain gauges are uniformly attached to the main bars in a surrounding manner after being pre-tensioned, and the strain gauges on each main bar are uniformly arranged at intervals. As shown in fig. 2, in one embodiment of the present invention, the shear force sensors 3 are uniformly spaced along two main bars arranged oppositely, and the distance between adjacent shear force sensors 3 can be determined according to the size of the concrete support structure, the supporting force, and the measuring range and accuracy of the shear force sensors 3. In order to further improve the measurement accuracy, the plurality of shear force sensors 3 are connected in series, so that data acquisition can be facilitated, and interference of other frequency signals is eliminated.
In the present invention, the strain gauge is a friction type strain gauge 2-1 for converting strain on the test piece into a change in resistance, and the strain of the test piece is calculated by measuring the change in resistance. In a preferred embodiment of the present invention, the friction type strain gauge 2-1 provided by the present invention comprises a metal foil and an insulating substrate, i.e. on the insulating substrate, a metal foil with a specified thickness is etched on the insulating substrate by photolithography or deposition, etc., and the metal foil can be made into various required shapes. Generally speaking, the thickness of the strain gauge is not more than 0.1mm, the strain gauge has small transverse effect, large strain sensitivity coefficient, large allowable current density and strong adaptability, and can be suitable for static measurement and dynamic measurement. The sensitivity coefficient calculation model of the strain gauge is as follows:
κ＝ΔR/(Rε)
the main control module is in communication connection with the plurality of reinforcing steel bar meters 2 and the plurality of shearing force sensors 3 and is used for acquiring data obtained by measuring the reinforcing steel bar meters 2 and the shearing force sensors 3, processing the data, calculating main bar strain caused by concrete shrinkage creep and concrete elastic modulus change, and further calculating real strain of the main bar and a real value of supporting axial force by combining strain data measured by the reinforcing steel bar meters, so that monitoring of the supporting axial force is realized.
The shear force sensor 3 further comprises annular protection devices 2-3, the annular protection devices 2-3 are sleeved on the steel bar meter 2, and the two ends of each strain gauge are provided with the annular protection devices 2-3. Specifically, before a steel bar meter is not installed, the annular protection device 2-3 is sleeved on the main bar, then the annular protection device 2-3 is moved to the strain gauge 2-1, and the screw 2-2 is screwed down, so that the annular protection device 2-3 is tightly attached to the strain gauge. In the invention, two ends of the strain gage are respectively provided with an annular protection device 2-3.
In the invention, the main control module acquires the shear stress at each shear force sensor according to a shear force calculation formula at the shear force sensor and the shear stress measured by the shear force sensor; then according to the arrangement condition of the shearing force sensors and the shearing stress at each shearing force sensor, calculating the main bar strain caused by concrete shrinkage creep and concrete elastic modulus change, then according to strain data measured by a reinforcing bar meter and a calculation formula of the main bar section average strain, calculating the main bar section average strain, and finally, according to the main bar section average strain, calculating the actual value of the reinforced concrete supporting shaft force by combining an equivalent strain method of a supporting section:
in the formula, F-reinforced concrete supports the axial force, EcModulus of elasticity of concrete, EsModulus of elasticity of the reinforcing bar, AcConcrete area of section, As-the area of the steel reinforcement in the cross-section,
to monitor the average strain of the main rib section.
The invention provides a circular shear force sensor used in cooperation with a reinforcing steel bar meter, which is used for monitoring additional stress caused by concrete shrinkage and creep on reinforcing steel bars; in order to accurately measure the shearing force between the concrete and the steel bar, a deformable vibrating wire type friction strain gauge is adopted; furthermore, in order to encapsulate and protect the strain gauge, a ring-shaped protection device with adjustable tightness is adopted; furthermore, in order to measure the distribution condition of the shearing force between the concrete and the steel bar along the length direction of the steel bar, n shearing force sensors are arranged in an evenly distributed mode according to needs, the shearing force sensors are connected in series, data acquisition is facilitated, and interference of other frequency signals is eliminated. In general, the invention can monitor the shearing force between concrete and steel bars, and calculate the real axial force of the reinforced concrete support according to relevant specification and a reinforced concrete mechanical calculation formula and by combining an equivalent strain method of a support section. Meanwhile, due to the influence of factors such as concrete support construction and the like, the concrete modulus is not equal everywhere, and the invention arranges a plurality of shear force sensors in a uniform distribution mode along the length direction of the reinforcing steel bar, thereby indirectly eliminating the influence of the change of the concrete elastic modulus on the support axial force. Compared with the traditional monitoring method, the invention only adds a plurality of shear force sensors with lower manufacturing cost, thereby being beneficial to saving the monitoring cost and the labor cost.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "provided" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A method for monitoring supporting axial force considering concrete shrinkage and creep influence is characterized by comprising the following steps:
s1, before the reinforced concrete support is poured, cutting off a section of main reinforcement at the corresponding position of the middle points of the four corners or four edges of the reinforcement cage along the length direction of the reinforcement cage, wherein the cutting-off length is equal to that of the reinforcement meter, and installing the reinforcement meter at the cutting-off position of the main reinforcement;
s2, uniformly arranging a plurality of shear force sensors along the length direction of the main rib, namely pre-tensioning strain gauges of the shear force sensors to enable the strain gauges to be in a tensioned state, and attaching the pre-tensioned strain gauges to the main rib in a surrounding manner;
s3, welding and fixing the reinforcing steel bar meter at the corresponding main bar cutting position;
s4, pouring concrete, and after the concrete support construction is completed and before the foundation pit is not excavated, acquiring strain data measured by a reinforcing steel bar meter and a shearing force sensor;
s5, calculating the strain of the main reinforcement caused by the shrinkage creep of the concrete and the change of the elastic modulus of the concrete according to the shear strain measured by the shear force sensor, deducting the strain of the reinforcement from the strain data measured by the reinforcement meter to obtain the real strain of the main reinforcement, and finally calculating the real axial force of the reinforced concrete support based on the equal effect deformation method.
2. The method as claimed in claim 1, wherein in step S1, the cross-sectional area of the reinforcement bars is the same as the cross-sectional area of the main reinforcement bars, and the reinforcement bars are distributed in a quadrilateral shape to form 4 monitoring points, specifically, four reinforcement bars are distributed at positions corresponding to the four corners or the middle points of the four sides of the reinforcement cage.
3. The method for monitoring the supporting axial force by considering the shrinkage and creep influence of the concrete as claimed in claim 1, wherein the step S2 comprises the following steps:
prestretching the strain gauge to enable the strain gauge to be in a tense state;
polishing and grinding the main ribs at the arrangement positions of the shearing force sensors along the length direction of the main ribs to enable the surfaces of the main ribs to be flat and smooth, and then cleaning the ground positions by dipping acetone or alcohol in absorbent cotton balls to prevent the influence of pollutants such as ground scraps, oil stains and the like;
and uniformly sticking the strain gauge in a tightened state to the cleaned main rib.
4. The method for monitoring the supporting axial force by considering the shrinkage and creep influence of the concrete according to claim 3, wherein the step S2 further comprises the following steps:
after the strain gauge is pasted, the annular protection device is penetrated to the position where the strain gauge is pasted from one end of the cut main rib and stopped, and then screws for screwing the annular protection device are adopted, so that the annular protection device is tightly attached to the strain gauge.
5. The method for monitoring the supporting axial force by considering the shrinkage and creep influence of the concrete as claimed in claim 1, wherein the step S5 comprises the following steps:
s51, the shrinkage and creep of the concrete enable a shearing acting force to exist between the concrete and the main reinforcement wrapped by the concrete, the shearing strain measured by the shearing force sensor is substituted for the formula (1) to calculate, and the shearing stress at each shearing force sensor is obtained:
τij＝Gs·γij (1)
in the formula: tau isijI is an integer from 1 to n, n is the number of main bars on which the shear force sensors are mounted, j is an integer from 1 to m, m is the number of shear force sensors mounted on the ith main bar, GsThe shear modulus of the steel bar; gamma rayijThe shear strain measured by the shear force sensor;
s52, calculating the strain of the main reinforcement caused by the shrinkage and creep of the concrete and the change of the elastic modulus of the concrete according to the arrangement condition of the shear force sensors and the shear stress at each shear force sensor:
in the formula: epsiloniStrain of the main reinforcement caused by shrinkage and creep of the concrete and change of the elastic modulus of the concrete, EsThe elastic modulus of the steel bar is shown, R is the diameter of the main bar, and l is the distance between adjacent shear force sensors on the same main bar;
s53, strain data measured by the reinforcing steel bar meter is substituted into the formula (3) to obtain the average strain of the section of the main reinforcement:
in the formula:
to monitor cross-sectional average strain;
the strain measured by the ith reinforcing steel bar meter is measured, and n is the number of the reinforcing steel bar meters;
s54, calculating the real axial force of the reinforced concrete support according to the average strain of the main bar section and by combining the equivalent strain method of the support section, wherein the concrete formula is as follows:
in the formula: f-axial force of the reinforced concrete support, EcModulus of elasticity of concrete, EsModulus of elasticity of the reinforcing bar, AcConcrete area of section, As-cross-sectional rebar area.
6. The method for monitoring the supporting axial force considering the effect of the concrete shrinkage and creep according to claim 5, wherein in step S51, the shear force acting on the main reinforcement caused by the shear force acting between the concrete and the main reinforcement wrapped by the concrete is calculated by the following model:
in the formula: fiThe shear force of the ith main reinforcement caused by the creep of the concrete, R is the diameter of the main reinforcement, l is the distance between adjacent shear force sensors on the same main reinforcement, m is the number of the shear force sensors arranged on the ith main reinforcement, and tauijIs the shear stress at the shear force sensor.
7. The method for monitoring the supporting axial force by considering the concrete shrinkage and creep influence according to claim 1, wherein the installation of the reinforcing bar meter and the shearing force sensor is carried out when a main reinforced concrete supporting bar is bound, the reinforcing bar meter is uniformly distributed on the supporting section, the shearing force sensor is uniformly distributed along the length direction of the main bar, and meanwhile, a protective sleeve is adopted to sleeve and lead out a lead of the reinforcing bar meter and the shearing force sensor.
8. A support axial force monitoring system considering the effect of concrete shrinkage creep, characterized in that the system is used for implementing the method according to any one of claims 1-7, and comprises a plurality of reinforcing bar meters (2), a plurality of shear force sensors (3) and a main control module, wherein,
cutting off a section of main reinforcement at the corresponding position of the middle points of four corners or four edges of the reinforcement cage along the length direction of the reinforcement cage, wherein the cutting-off length is equal to that of the reinforcement meter, and the reinforcement meter (2) is welded and fixed with the main reinforcement at the corresponding cutting-off position of the main reinforcement;
the shear force sensor (3) comprises strain gauges, the strain gauges are uniformly attached to the main ribs in a surrounding mode after being pre-tensioned, and the strain gauges on each main rib are uniformly arranged at intervals;
the main control module is in communication connection with the plurality of steel bar meters (2) and the plurality of shear force sensors (3) and is used for collecting data obtained by measurement of the steel bar meters (2) and the shear force sensors (3), calculating main bar strain caused by concrete shrinkage creep and concrete elastic modulus change according to the shear strain measured by the shear force sensors (3), deducting the steel bar strain from the strain data measured by the steel bar meters (2) to obtain real strain of a main bar, and finally calculating the real axial force of the reinforced concrete support based on an equal effect deformation method.
9. The supporting shaft force monitoring system considering the concrete shrinkage and creep influence is characterized in that the shear force sensor (3) further comprises an annular protection device (2-3), the annular protection device (2-3) is sleeved on the reinforcing bar meter (2), and two ends of each strain gauge are provided with the annular protection devices (2-3);
the strain gauge is a friction type strain gauge (2-1), and the cross section of the steel bar meter is the same as that of the main reinforcement.
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