CN111551326B - Displacement monitoring method for settlement foundation layered casting concrete beam - Google Patents

Displacement monitoring method for settlement foundation layered casting concrete beam Download PDF

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CN111551326B
CN111551326B CN202010470561.3A CN202010470561A CN111551326B CN 111551326 B CN111551326 B CN 111551326B CN 202010470561 A CN202010470561 A CN 202010470561A CN 111551326 B CN111551326 B CN 111551326B
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concrete beam
support
layer
displacement
layer concrete
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CN111551326A (en
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郝天之
马跃腾
甘剑剑
谢军
陈建恒
江京翼
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Nanning urban construction investment development Co.,Ltd.
Guangxi Jiaoke Group Co Ltd
Guangxi Beitou Transportation Maintenance Technology Group Co Ltd
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Nanning Urban Construction Investment Development Co ltd
Guangxi Jiaoke Group Co Ltd
Guangxi Beitou Transportation Maintenance Technology Group Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0041—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining deflection or stress
    • G01M5/005—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining deflection or stress by means of external apparatus, e.g. test benches or portable test systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0008—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings of bridges

Abstract

The invention relates to the field of bridge and culvert engineering in the transportation industry, and particularly discloses a displacement monitoring method for a settlement foundation layered pouring concrete beam. And obtaining a discrimination formula of the displacement safety state of the first-layer beam of the concrete beam support in the layered pouring process by establishing a concrete beam support layered pouring structure model under the foundation settlement. In order to conveniently and quickly judge the state of the first layer beam of the layered cast concrete beam, the total station is adopted to monitor the elevation and the displacement of each control point before and after the action of each main construction working condition by arranging the prism on the concrete beam. The geometrical form of the first-layer concrete beam is obtained or identified by regularly observing the space coordinate change of the control points, the bridge construction state is timely and visually evaluated by combining a displacement judgment formula, and data support is provided for construction control of layered pouring concrete beams. Greatly reduces the safety risk of cracking of the first-layer concrete beam caused by foundation settlement in the construction process of the first-layer concrete beam in layered pouring, and has good economic benefit and engineering value.

Description

Displacement monitoring method for settlement foundation layered casting concrete beam
Technical Field
The invention relates to the field of bridge and culvert engineering in the transportation industry, and particularly discloses a displacement monitoring method for a settlement foundation layered pouring concrete beam.
Background
Concrete bridges are widely used in bridge construction with the advantages of good stress performance, service performance, construction maturity and the like. Most concrete beams are not formed by one-time pouring, and particularly, the concrete beams with higher beam height or complicated detailed structures generally need to be poured in layers for many times. Aiming at the cast-in-place of the support, particularly for a concrete beam which is supported by a full-framing support and cast in a layered manner, the shrinkage of the concrete cast in a layered manner is poor, the support is settled, the hydration temperature of the concrete is reduced, the construction process and the like can cause cracks to appear on the concrete, the carbonization of the concrete is accelerated, the corrosion resistance of the structure is reduced, and finally the strength and the stability of the building are reduced, so that the service life of the structure is reduced, and the safety and the durability of the concrete are seriously influenced. However, for the soft foundation layered cast concrete beam, the problems of concrete cracking and safety and durability are often caused by overlarge stress of a cast beam body in the early stage, uneven settlement of the foundation can generate large influence on the stress and deflection of the control section of the upper structure of the bridge, the influence amplitude is continuously increased along with the increase of the settlement value, and the instability of the whole structure of the concrete beam and the induction of serious safety accidents are possibly caused in the construction process. Therefore, when the concrete beam has a condition of uneven foundation settlement, a deformation observation and judgment method is urgently needed to quickly judge the construction safety state, so that the safety state of the layered pouring concrete beam is effectively monitored, and the occurrence of the diseases is prevented from bringing great harm to the life and property safety of people.
Disclosure of Invention
The invention aims to provide a displacement monitoring method for a settlement foundation layered pouring concrete beam, which can quickly judge the construction safety state when the concrete beam has the condition of uneven settlement of the foundation.
In order to achieve the purpose, the invention provides a displacement monitoring method for a layered pouring concrete beam under foundation settlement, which specifically comprises the following steps:
s1, erecting a full-framing support on the hardened foundation, laying a template on the full-framing support, binding first-layer steel bars on the template after pre-pressing the full-framing support, pouring a first-layer concrete beam, binding steel bars of a second-layer concrete beam when the first-layer concrete beam is hardened to a certain strength, and pouring the second-layer concrete beam;
s2, acquiring the length of the equal-section concrete beam of the first-layer concrete beam and the uniform load of the second-layer concrete beam on the first-layer concrete beam;
s3, simulating the action of the full framing on the first concrete beam by adopting an analysis model with an elastic support, and constructing a basic differential equation of the unevenly settled elastic support first concrete beam of the support by combining the uniform load of the second concrete beam on the first concrete beam;
s4, solving a basic differential equation to obtain the internal force of the elastic support first-layer concrete beam under uneven settlement;
s5, obtaining the displacement of the uneven settlement support, and solving the internal force of the elastic support under movement based on the force equation of the elastic support;
s5, acquiring the deflection and tensile stress of the full framing layered casting first-layer concrete beam under uneven settlement according to the internal force of the elastic supporting first-layer concrete beam and the internal force of the elastic support under movement;
s6, obtaining the compressive strength of the first-layer concrete beam, and obtaining the maximum tensile strength of the first-layer concrete beam according to the compressive strength;
s7, acquiring the maximum tensile stress of the first-layer concrete beam according to the maximum tensile strength, and acquiring the maximum allowable deflection of the first-layer concrete beam according to the maximum tensile stress;
and S8, arranging a reflecting prism at the monitoring point on the first-layer concrete beam, periodically measuring the space coordinate change range of the monitoring point through the reflecting prism, and monitoring whether the deflection is greater than the maximum allowable deflection in real time.
Preferably, in the above technical solution, the stiffness coefficient of the analysis model with elastic support is:
Figure GDA0003279214430000021
formula (1) wherein: e (m) is the modulus of elasticity of the scaffold material; h (m) is the full shelf height; a (m) is the area of the supporting section of the full framing per square meter; i ismyAnd ImzThe inertia moments of the Y axis and the Z axis of the full support are respectively; mu is Poisson's ratio. Because the full-length scaffold is mainly resistant to compression, neglecting shearing and bending torsion, the spring stiffness K of the full-length scaffold per linear meter is E (m)/H (m).
Preferably, in the above technical solution, based on a beam deflection differential equation and a coordination condition of support top settlement and deflection deformation of the first-layer beam, S ═ ω, that is:
P＝K0S＝K0ω (2)
K0the elastic coefficient of the bracket system represents the pressure intensity required by unit deformation; p is the pressure strength of any point on the top of the bracket; s is vertical deformation on the P action position, and omega is the deflection of the first-layer concrete beam.
Preferably, in the above technical solution, in step S3, according to an elastic mechanics analysis, an equation of the first-layer concrete beam is as follows:
Figure GDA0003279214430000031
Figure GDA0003279214430000032
Figure GDA0003279214430000033
in formulae (3) to (5): m is the bending moment to which the concrete beam is subjected, FsThe shearing force borne by the first-layer concrete beam, E is the elastic modulus of the first-layer concrete beam, omega is the deflection of the first-layer concrete beam, and P (x) is the uniform load on the micro-section of the first-layer concrete beam. Applying equation (3), the basic differential equation of the elastic support first-layer beam of the differential settlement of the support is:
Figure GDA0003279214430000034
wherein, P0Uniformly distributing load to the first layer of concrete beam;
in step S4:
Figure GDA0003279214430000035
the solution of equation (6) is:
Figure GDA0003279214430000036
the boundary condition is
Figure GDA0003279214430000037
Then: c3＝C4＝0
Order to
Figure GDA0003279214430000038
Δ' ═ cosh2 γ + cos2 γ then:
similarly, the internal force of the elastic support first-layer concrete beam under the condition of uneven settlement is solved as
Figure GDA0003279214430000039
Preferably, in the above technical solution, in step S5, the full support is divided into n spans in the direction of the beam length L, and the span length of each span is divided by the elastic supportIs 1iLet c be1、c2The vertical displacement of the support 1 and the support 2 at the left end and the right end of the ith span beam is respectively taken as the area 1 from the 1 st span to the i-1 st span, and the area 1 provides the rotational rigidity Kz1Taking the (i +1) th span to the (n) th span as a region 2, the region 2 provides a rotational stiffness Kz2，
Figure GDA0003279214430000041
In formula (8): delta1C、Δ2CShowing the displacement c of the support 1 and the support 2 respectively on the basic structure1、c2When in use, the support bases 1 and 2 are superposed under certain rotational rigidity to obtain displacement; gamma rayici/liRepresenting the deformation influence, gamma, of the adjacent span of the support iiIs a correlation influence coefficient;
the force equation of the movement of the region 1 model in the elastic support is as follows:
δX+ΔC＝0 (9)
solving a coefficient matrix of a mechanical equation of the movement of the region 1 model in the elastic support:
Figure GDA0003279214430000042
the matrix of the excess unknown force is X ═ X1，X2，…Xm]T
The basic structure is displaced c in the elastic support 11Generated edge XiThe displacement matrix formed by the directions is:
Figure GDA0003279214430000043
then, the internal force of the i-1 st span is:
Figure GDA0003279214430000044
Figure GDA0003279214430000045
to obtain
Figure GDA0003279214430000046
In the same way
Figure GDA0003279214430000047
When the ith span beam is selected, a mechanical equation can be obtained by using the deformation condition of the structure:
Figure GDA0003279214430000048
in the formula: x1、X2The internal force of the rotary support of which the elastic support 1 and the support 2 are replaced by the redundant unknown force on the basic structure is shown;
solving (11) to obtain:
Figure GDA0003279214430000049
only considering the selected ith span under the movement of the elastic support, linear interpolation can obtain the internal force as follows:
Figure GDA0003279214430000051
selecting and controlling the ith span beam, and pouring the first-layer concrete beam in a layered mode by considering the combination of the step (7) and the step (14), namely considering the deflection function of the support under the condition of uneven settlement:
Figure GDA0003279214430000052
preferably, in the above technical solution, step S7 specifically includes the tensile strength f of the first-layer concrete beamt,nTo resist compressionStrength fcu,n0.05 times, i.e. ft,n＝0.05fcu,n；
The concrete does not crack and must satisfy sigma<ft,nI.e. by
Figure GDA0003279214430000053
Simplified backstage type (17)
Figure GDA0003279214430000054
Figure GDA0003279214430000055
ωcu,nIs the maximum allowable deflection.
Preferably, in the above technical scheme, the deflection function for mid-span displacement judgment of the first-layer concrete beam is as follows:
Figure GDA0003279214430000061
preferably, in the above technical scheme, the deflection function for the safe judgment of the displacement of 8 points of the first-layer concrete beam is as follows:
Figure GDA0003279214430000062
compared with the prior art, the invention has the following beneficial effects:
based on the elastic mechanics plane problem analysis, the invention establishes and simulates a concrete beam support layered pouring structure model under foundation settlement by taking a related calculation method of foundation uneven settlement as a theoretical basis of research, and obtains a primary beam displacement safety discrimination formula of concrete beam support layered pouring concrete. In order to conveniently and quickly judge the state of the first layer beam of the layered cast concrete beam, the total station is adopted to monitor the elevation and the displacement of each control point before and after the action of each main construction working condition by arranging the prism on the concrete beam. The method comprises the steps of regularly monitoring the space coordinate change of a control point by using a total station, obtaining or identifying the geometric form of the formed first-layer concrete beam, and timely and intuitively evaluating the bridge construction state by using the displacement judgment formula provided by the invention so as to provide data support for construction control of the layered pouring concrete beam. The construction of the layered concrete beam due to foundation settlement under the full-framing construction method can be effectively guided, the safety state of the concrete beam can be conveniently and quickly judged by monitoring the displacement of the first-layer concrete beam in the construction process, the safety risk of cracking of the first-layer concrete due to foundation settlement in the construction process under layered pouring is greatly reduced, and the method has good economic benefit and engineering value.
Drawings
FIG. 1 is a simplified model of the invention considering that the equivalent elastic beam is uniformly loaded under the foundation settlement.
Fig. 2 shows a model of the area 1 when the movement takes place at the support according to the invention.
FIG. 3 shows the simplified model of the present invention under a single-unit load
Figure GDA0003279214430000063
A simple diagram.
FIG. 4 is a schematic view of a stent of the present invention.
Fig. 5 is a schematic model diagram of embodiment 1 of the present invention.
Detailed Description
The following detailed description of the present invention is provided in conjunction with the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.
A large number of engineering practices show that the local uneven settlement of the foundation can generate additional internal force on the first-layer beam in the layered pouring of the support, further influence the mechanical property of the first-layer beam, accelerate the carbonization of concrete and reduce the corrosion resistance of the structure. Although a designer considers the influence of local uneven settlement on a bridge according to geological conditions in the design of a continuous bridge and gives a certain degree of safe reserve to the bridge in the design, the influence cannot be achieved due to uneven settlement of a foundation due to a plurality of reasons and complex conditions. The embodiment provides a displacement monitoring method for a layered pouring concrete beam under foundation settlement, which specifically comprises the following steps:
firstly, analyzing and providing a stress mechanism and a state of a first-layer concrete beam, and assuming as follows:
(1) simplified analysis is carried out on the first layer of formed concrete beam which is cast by the full-framing in a layered mode, wherein the length of the concrete beam with the equal section is L, the beam end is simply supported, concrete is cast by the full-framing in a layered mode, and uniformly distributed loads P are used0The effect of the steel reinforcement and concrete of the second layer beam on the first layer was simulated, and due to the symmetry of the problem, the origin of coordinates was taken at the midpoint of the beam, as shown in fig. 1 and 4.
(2) The existence of the support of the full support of the actual beam structure can simulate the effect of support on the concrete beam by adopting an analysis model with an elastic support. The conversion matrix method is adopted, and the middle part is provided with an elastic support. The full-scale support is processed according to an elastic foundation, the rigidity coefficient of the full-scale support is K, the counter force of the elastic foundation is in direct proportion to the deflection omega of the first-layer beam, the direction of the counter force is opposite to omega, for the full-scale support, the elastic support is used for simulating the action on the first-layer beam, the elastic constraint coupling effect is calculated and considered, at the moment, the general elastic support type is shown as the following formula (1), non-zero values except the diagonal line in the formula are the effect of considering the mutual influence and the mutual correlation of certain degrees of freedom, and the horizontal elastic support is not considered.
Formula (1) wherein: e (m) is the modulus of elasticity of the scaffold material; h (m) is the full shelf height; a (m) is the area of the supporting section of the full framing per square meter; i ismyAnd ImzThe inertia moments of the Y axis and the Z axis of the full support are respectively; mu is Poisson's ratio. Because the full-length scaffold is mainly resistant to compression, neglecting shearing and bending torsion, the spring stiffness K of the full-length scaffold per linear meter is E (m)/H (m).
Figure GDA0003279214430000071
(3) Upper supportThe pressure intensity of one point is in direct proportion to the vertical deformation S of the point, and P is equal to K0S，K0Foundation bed coefficient, which represents the pressure strength required to produce unit deformation; p is the pressure intensity of any point on the foundation; s is the vertical deformation at the p-action position. According to the flexural differential equation of the beam and the coordination condition of the support top settlement and the flexural deformation of the first-layer beam, S is omega, namely:
P＝K0S＝K0ω (2)
(4) as shown in FIG. 1, a model diagram with total length L of n spans is formed by dividing each span by elastic supports, and c is assumed1、c2The vertical displacement of the left and right end supports of the beam end i respectively, and the span length of the structure is liThe structural section of the first-layer beam section is the same in size and material, the bending rigidity is EI, the (1) th span to the (i-1) th span are taken as an area 1, and the area provides the rotational rigidity Kz1With the (i +1) th to (n) th spans as region 2, which provides the rotational stiffness Kz2。
Figure GDA0003279214430000081
In formula (3): delta1C、Δ2CShowing the displacement c of the supports 1, 2, respectively, on the basic structure1、c2When in use, the support bases 1 and 2 are superposed under certain rotational rigidity to obtain displacement; gamma rayici/liRepresenting the deformation influence, gamma, of the adjacent span of the support iiIs the correlation coefficient of influence.
According to the related knowledge of elastic mechanics, the equation of the first-layer beam is as follows:
Figure GDA0003279214430000082
Figure GDA0003279214430000083
Figure GDA0003279214430000084
in formulae (4) to (6): m is the bending moment to which the concrete beam is subjected, FsThe shearing force borne by the first-layer concrete beam, E is the elastic modulus of the first-layer concrete beam, omega is the deflection of the first-layer concrete beam, and P (x) is the uniform load on the micro-section of the first-layer concrete beam. Applying equation (4), the basic differential equation of the elastic support first-layer beam of the differential settlement of the support is:
Figure GDA0003279214430000085
suppose that:
Figure GDA0003279214430000086
the solution of equation (7) is:
Figure GDA0003279214430000087
the boundary condition is
Figure GDA0003279214430000088
Then: c3＝C4＝0
Order to
Figure GDA0003279214430000091
Δ' ═ cosh2 γ + cos2 γ then:
similarly, the internal force of the elastic support first-layer beam under the condition of uneven settlement is solved
Figure GDA0003279214430000092
The following fig. 2 shows the basic mechanical system of the region 1 when the elastic support moves, fig. 3 shows
Figure GDA0003279214430000093
A simple diagram, thenThe force equation of the movement of the region 1 model in the elastic support is as follows:
δX+ΔC＝0 (9)
wherein, the solution is obtained by using a unit load method
Figure GDA0003279214430000094
The coefficient matrix of the mechanical equation can be obtained in a simple diagram:
Figure GDA0003279214430000095
the matrix of the excess unknown force is X ═ X1，X2，…Xm]T
The basic structure is displaced c in the elastic support 11Generated edge XiThe displacement matrix formed by the directions is:
Figure GDA0003279214430000096
then, the internal force of the (i-1) th span corresponding to FIG. 3 is:
Figure GDA0003279214430000097
Figure GDA0003279214430000098
to obtain
Figure GDA0003279214430000099
In the same way
Figure GDA00032792144300000910
When the section i shown in fig. 1 is selected, the mechanical equation can be obtained by using the deformation condition of the structure:
Figure GDA00032792144300000911
in the formula: x1、X2Representing an additional internal force on the basic structure on its support 1, 2 replaced by an excess unknown force on the elastic support.
Solving (11) to obtain:
Figure GDA00032792144300000912
considering only the selected i segments under the movement of the elastic support, linear interpolation can obtain the internal force as:
Figure GDA0003279214430000101
selecting a control span i section beam, and pouring the first layer of the support in a layered mode under the consideration of the combination of (8) and (14), namely the consideration of uneven settlement
Figure GDA0003279214430000102
Figure GDA0003279214430000103
When the second layer of beam steel bars are bound and concrete is poured, the age of the first layer of concrete is n days, and when the first layer of concrete is cured for n days under the same condition with the same batch of concrete cubic test blocks of the first layer of concrete, the average value of the test compressive strength of the first layer of concrete is fcu,nBased on the relationship between the compressive strength and the tensile strength of the concrete, namely, the tensile strength of the concrete is generally 0.05-0.1 time of the compressive strength, and considering the non-uniformity and the size effect of the concrete, the invention safely takes the tensile strength of the concrete as 0.05 time of the compressive strength, namely, the tensile strength of the concrete is 0.05 time
ft,n＝0.05fcu,n。
The concrete does not crack, so that the safety and the durability of the first-layer concrete beam can be ensured, and the requirement of sigma must be met<ft,nI.e. by
Figure GDA0003279214430000104
Simplified backstage type (17)
Figure GDA0003279214430000105
Figure GDA0003279214430000106
(18) The method is characterized in that a reflecting prism is arranged at a proper position (meeting the principle of stable measuring points and convenient observation) of a first-layer concrete beam, the reflecting prism is fixed at a monitoring point, the change range of the space coordinate of the observation point is periodically measured by a total station, whether the deflection reaches a settlement threshold value according to the formula (18) observation is determined, the requirement is met, and the position of a specific measuring point is determined according to the site. According to the measured field measured data, if the settlement exceeds a threshold value, the construction is immediately stopped, and the problem is solved through construction modes such as local reinforcement or multi-setting layering.
And (3) midspan displacement judgment:
Figure GDA0003279214430000111
and 8, judging the safety of point displacement:
Figure GDA0003279214430000112
this patent is through observing the amount of deflection of concrete measurement station relevant position, brings formula (18) into and judges whether to satisfy the requirement, can effectively guide to adopt the construction of layered concrete roof beam under the full hall support construction method because of the basis subsides, through the displacement of monitoring the first floor concrete roof beam in the work progress, conveniently and swiftly judge the safe state of concrete roof beam, greatly reduced the safe risk of the first floor concrete of layered pouring because of the fracture under the basis subsides in the work progress, had fine economic benefits and engineering value.
In summary, when the concrete beams are cast in layers, the first layer of concrete beam bears the weight of the subsequent cast concrete beam and transmits the weight to the support and the foundation, so that the first layer of concrete beam generates bending moment deformation, tensile stress occurs at the bottom of the span middle beam, and when the stress causes the first layer of concrete beam to crack, the safety and durability of the concrete beam are affected. Based on the analysis of the elastic mechanics plane problem, the subsequent poured concrete is used as a load, the foundation, the primary concrete beam and the subsequent poured concrete are actually a force transmission system, the deformation mechanism of the primary beam of the layered poured concrete beam adopting a soft foundation is provided and analyzed, based on the mechanism, the prism edge angles are arranged on the concrete beam, and the elevation and the displacement of each control point are tested and monitored by adopting a total station before and after the action of each main construction working condition. The method comprises the steps of periodically measuring the space coordinate change of an observation point monitoring control point by using a total station, obtaining or identifying the geometric form of the formed first-layer concrete beam, and timely and intuitively evaluating the bridge construction state by using the displacement judgment formula provided by the invention so as to provide test data support for construction control of the layered pouring concrete beam. The construction of the layered concrete beam due to foundation settlement under the full-framing construction method can be effectively guided, the safety state of the concrete beam can be conveniently and quickly judged by monitoring the displacement of the first-layer concrete beam in the construction process, the safety risk of cracking of the first-layer concrete due to foundation settlement in the construction process under layered pouring is greatly reduced, and the method has good economic benefit and engineering value.
Examples
For a concrete beam bridge, the cross section is in the form of a single box and a single chamber, the transverse bridge direction is composed of four box beams, and the total width of the bridge deck is 15 m. The box girder is made of C50 concrete, the bridge deck cast-in-place layer is made of C40 concrete, 100 elastic supports are arranged in 150m span, the rigidity of each elastic support is 10^6KN/m, the influence on the structure when uneven settlement is considered is corrected when different displacements of the structure exist under the condition that limited uneven settlement values exist, and the method is shown in the following figure 5. The main beam adopts a longitudinal prestressed tendon system, and the prestressed tendon is fpk1860MPa high-strength low-relaxation steel strandThe wires are all stretched by two sections, and the stress delta is controlled by stretchingcon＝0.75fpk1395MPa, nominal diameter
Figure GDA0003279214430000121
Nominal area 139mm2Modulus of elasticity EP1.95 × 105MPa, adopting R235 and HRB335 steel bars as steel materials, and adopting HRB335 steel bars with the diameter being more than or equal to 12 mm; the main beam adopts prestressed concrete precast box beam, single box single chamber section; the width of the top plate of the side box girder is 3.48m, the width of the top plate of the middle box girder is 3.4m, and the thickness is 18 cm; the bottom plates of the side box girders and the middle box girders are 1m wide and 18cm thick; the height of the beam is 1.2 m; and establishing a finite element model according to the actual working condition, wherein the epsilon is a correction coefficient, and the value is 0.70 through repeated tests.
TABLE 1 comparative analysis of results of transwell stress (unit: MPa)
Table 1 Comparative analysis of mid-span stress results(Unit:MPa)
Working conditions Sigma (analytic solution) E.g. sigma (analytic solution) Sigma (finite element solution) Error (%)
The sedimentation value of the support 1, 2 is 5mm 1.01 0.71 0.82 13.78
Setting of supports 1, 2A value of 10mm 1.10 0.77 0.69 11.59
The sedimentation value of the support 1, 2 is 15mm 1.11 0.78 0.70 11.00
The sedimentation value of the support 1, 2 is 20mm 1.45 1.02 1.10 7.73
When the first layer is poured and the second layer of concrete needs to be poured, whether the second layer of concrete to be poured under the soft foundation can damage the stress safety of the first layer of concrete beam or not is judged through the formula (17), and if the requirement is not met, the reinforcement technology under the judgment method can be adopted. When reinforcement is not the conclusion of reconstruction, reinforcement methods such as foundation expansion, pile foundation supplement and the like can be generally adopted to reinforce the bridge foundation. Therefore, the remediation can be performed by a forced landing rectification method or the like according to the equation (17). Mainly, the forced landing rectification is carried out, meanwhile, the relation between the normal working state and the basic working state is judged, and the forced landing rectification scheme is adjusted in real time according to the monitoring result.
The reinforcement technology in the layered pouring construction process under the soft foundation of the concrete beam adopts a forced landing rectification method, which mainly comprises the following steps:
determining the cause and the condition of the uneven settlement of the foundation, the working state of an upper structure, the foundation state of an uneven settlement area of the foundation and the condition of a surrounding field;
determining the position, forced falling amount and rectification method of rectification according to the formula (17);
comprehensively considering the working condition of the upper structure and the surrounding field conditions, determining the sequence and the scheme and preparing construction equipment;
fourthly, forced landing rectification and reinforcement are carried out on the uneven settlement foundation;
and fifthly, judging the renovation effect by using the formula (17) again to ensure the stress safety of the concrete beam.

Claims (8)

1. The displacement monitoring method of the settlement foundation layered pouring concrete beam is characterized by comprising the following steps of:
s1, erecting a full-framing support on the hardened foundation, laying a template on the full-framing support, binding first-layer steel bars on the template after pre-pressing the full-framing support, pouring a first-layer concrete beam, binding steel bars of a second-layer concrete beam when the first-layer concrete beam is hardened to a certain strength, and pouring the second-layer concrete beam;
s2, acquiring the length of the equal-section concrete beam of the first-layer concrete beam and the uniform load of the second-layer concrete beam on the first-layer concrete beam;
s3, simulating the action of the full framing on the first concrete beam by adopting an analysis model with an elastic support, and constructing a basic differential equation of the unevenly settled elastic support first concrete beam of the support by combining the uniform load of the second concrete beam on the first concrete beam;
s4, solving a basic differential equation to obtain the internal force of the elastic support first-layer concrete beam under uneven settlement;
s5, obtaining the displacement of the uneven settlement support, and solving the internal force of the elastic support under movement based on the force equation of the elastic support;
s5, acquiring the deflection and tensile stress of the full framing layered casting first-layer concrete beam under uneven settlement according to the internal force of the elastic supporting first-layer concrete beam and the internal force of the elastic support under movement;
s6, obtaining the compressive strength of the first-layer concrete beam, and obtaining the maximum tensile strength of the first-layer concrete beam according to the compressive strength;
s7, acquiring the maximum tensile stress of the first-layer concrete beam according to the maximum tensile strength, and acquiring the maximum allowable deflection of the first-layer concrete beam according to the maximum tensile stress;
and S8, arranging a reflecting prism at the monitoring point on the first-layer concrete beam, periodically measuring the space coordinate change range of the monitoring point through the reflecting prism, and monitoring whether the deflection is greater than the maximum allowable deflection in real time.
2. The method for monitoring the displacement of the settlement foundation layered casting concrete beam according to claim 1, wherein the rigidity coefficient of the analysis model with the elastic support is as follows:
Figure FDA0003339198610000021
formula (1) wherein: e (m) is the modulus of elasticity of the scaffold material; h (m) is the full shelf height; a (m) is the area of the supporting section of the full framing per square meter; i ismyAnd ImzThe inertia moments of the Y axis and the Z axis of the full support are respectively; mu is Poisson's ratio, because the Manger stent is mainly resistant to compression, and neglecting shearing and bending torsion, the spring stiffness K of the Manger stent is E (m)/H (m) per linear meter.
3. The method for monitoring the displacement of the settlement foundation layered casting concrete beam as claimed in claim 2, wherein according to the flexural differential equation of the beam and the coordination condition of the settlement of the bracket top and the flexural deformation of the first layer beam, S ═ ω, namely:
P＝K0S＝K0ω (2)
K0the elastic coefficient of the bracket system represents the pressure intensity required by unit deformation; p is the pressure strength of any point on the top of the bracket; s is vertical deformation on the P action position, and omega is the deflection of the first-layer concrete beam.
4. The method for monitoring the displacement of the settlement foundation layered casting concrete beam as claimed in claim 2, wherein in the step S3, according to the elastography analysis, the equation of the first layer concrete beam is as follows:
Figure FDA0003339198610000022
Figure FDA0003339198610000023
Figure FDA0003339198610000024
in formulae (3) to (5): m is the bending moment to which the concrete beam is subjected, FsThe shear force borne by the first-layer concrete beam, E is the elastic modulus of the first-layer concrete beam, omega is the deflection of the first-layer concrete beam, P (x) is the uniform load on the micro-section of the first-layer concrete beam, and by applying the formula (3), the basic differential equation of the elastic support first-layer concrete beam of the uneven settlement of the support is as follows:
Figure FDA0003339198610000025
wherein, P0Uniformly distributing load to the first layer of concrete beam;
in step S4:
Figure FDA0003339198610000026
the solution of equation (6) is:
Figure FDA0003339198610000031
the boundary condition is
Figure FDA0003339198610000032
Then: c3＝C4＝0
Order to
Figure FDA0003339198610000033
Then:
similarly, the internal force of the elastic support first-layer concrete beam under the condition of uneven settlement is solved as
Figure FDA0003339198610000034
5. The method for monitoring the displacement of the settlement foundation layered casting concrete beam as claimed in claim 1, wherein in step S5, the full framing is divided into n spans in the direction of the beam length L, and the span length of each span divided by the elastic support is LiLet c be1、c2The vertical displacement of the support 1 and the support 2 at the left end and the right end of the ith span beam is respectively taken as the area 1 from the 1 st span to the i-1 st span, and the area 1 provides the rotational rigidity Kz1Taking the (i +1) th span to the (n) th span as a region 2, the region 2 provides a rotational stiffness Kz2，
Figure FDA0003339198610000035
In formula (8): delta1C、Δ2CShowing the displacement c of the support 1 and the support 2 respectively on the basic structure1、c2When in use, the support bases 1 and 2 are superposed under certain rotational rigidity to obtain displacement; gamma rayici/liRepresenting the deformation influence, gamma, of the adjacent span of the support iiIs a correlation influence coefficient;
the force equation of the movement of the region 1 model in the elastic support is as follows:
δX+ΔC＝0 (9)
solving a coefficient matrix of a mechanical equation of the movement of the region 1 model in the elastic support:
Figure FDA0003339198610000036
the matrix of the excess unknown force is X ═ X1，X2，…Xm]T
The basic structure is displaced c in the elastic support 11Generated edge XiThe displacement matrix formed by the directions is:
Figure FDA0003339198610000037
then, the internal force of the i-1 st span is:
Figure FDA0003339198610000038
Figure FDA0003339198610000041
to obtain
Figure FDA0003339198610000042
In the same way
Figure FDA0003339198610000043
When the ith span beam is selected, a mechanical equation can be obtained by using the deformation condition of the structure:
Figure FDA0003339198610000044
in the formula: x1、X2The internal force of the rotary support of which the elastic support 1 and the support 2 are replaced by the redundant unknown force on the basic structure is shown;
solving (11) to obtain:
Figure FDA0003339198610000045
only considering the selected ith span under the movement of the elastic support, linear interpolation can obtain the internal force as follows:
Figure FDA0003339198610000046
selecting and controlling the ith span beam, and combining the step (7) and the step (14), namely the deflection function of the bracket layered casting first-layer concrete beam under the uneven settlement is as follows:
Figure FDA0003339198610000047
6. the method for monitoring the displacement of the settlement foundation layered casting concrete beam as claimed in claim 5, wherein the step S7 specifically comprises the tensile strength f of the first layer concrete beamt,nTo compressive strength fcu,n0.05 times, i.e. ft,n＝0.05fcu,n；
The concrete does not crack and must satisfy sigma<ft,nI.e. by
Figure FDA0003339198610000048
Simplified backstage type (17)
Figure FDA0003339198610000051
Figure FDA0003339198610000052
Figure FDA0003339198610000053
ωcu,nIs the maximum allowable deflection.
7. The method for monitoring the displacement of the settlement foundation layered pouring concrete beam as claimed in claim 6, wherein the deflection function of the midspan displacement judgment of the first layer concrete beam is as follows:
Figure FDA0003339198610000054
8. the method for monitoring the displacement of the settlement foundation layered pouring concrete beam as claimed in claim 6, wherein the deflection function of the safe judgment of the 8-point displacement of the first layer concrete beam is as follows:
Figure FDA0003339198610000055
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