JP5095258B2 - Stress measuring system and method for reinforced concrete members - Google Patents

Description

  The present invention relates to a stress measurement system and method for a reinforced concrete member, a program, a recording medium, and a reinforced concrete member that are suitable for accurately measuring the stress of a reinforced concrete member loaded with stress in one direction.

  In various bridges, a bending moment always acts between fulcrums on concrete girders that directly support the load of automobiles and the like. For this reason, it is a common practice to manufacture prestressed concrete in which prestress is introduced into the concrete constituting the T-girder, box girder, hollow floor slab, and plate girder to improve the strength of the girder.

  For such a reinforced concrete member loaded with stress in one direction, such as prestressed concrete, the magnitude of the effective stress level (or effective prestress) actually applied is determined to determine the magnitude of the reinforced concrete member. In some cases, it may be desirable to consider the situation in which the structures that make up the structure are placed and to examine the safety of use. Furthermore, there are cases where it is desired to optimize prestress introduction conditions based on the measured effective stress level.

  Here, for prestressed concrete used for the bridge shown in FIG. 5 and the like, when prestress is introduced in the x direction, a conventional method for measuring stress actually applied in the x direction (for example, (See Patent Document 1).

  First, the first strain gauge 71 is attached to the side surface of the concrete member 7 in the x direction, and the second strain gauge 72 is attached to the y direction corresponding to the direction perpendicular to the x direction so as to cross each other. An initial value of strain in the x and y directions is detected via the strain gauges 71 and 72. That is, a state in which the stress based on the introduced prestress is applied to the concrete is set as an initial value of strain.

Next, the concrete piece 74 is cut out from the concrete member 7 so as to include a side surface to which the first strain gauge 71 and the second strain gauge 72 are attached. The concrete piece 74 is in a state where the introduced prestress is released. At this stage, a measured strain value in the x direction (hereinafter referred to as a measured stress release strain value) due to the release of stress is measured via the first strain gauge 71, and the second strain gauge 72 is mounted. Then, an actual measurement value of stress release strain in the y direction is measured. Then, the strain ε _x is detected by subtracting the initial value of the strain in the x direction from the measured stress release strain value in the x direction, and the y direction is determined from the measured stress release strain value in the y direction. The distortion ε _y is detected by subtracting the initial value of the distortion. That is, by measuring the difference between the initial value of the strain measured with the prestress introduced and the elastic strain measured with the prestress released, it depends on the stress based on the actually introduced prestress. The strains ε _x and ε _y can be detected.

When the stress acting on the surface of the concrete member 7 due to prestress is defined as an effective stress, the strain ε _y is subtracted from the strain ε _x and based on the Poisson's ratio ν of the concrete, as shown in the equation (0). By performing the correction, the elastic strain Δε _{x, e} is calculated. Then, by adding the elastic modulus Ex _{, c} in the x direction of the concrete to the Δε _{x, e} , it is possible to almost estimate the effective stress σ _{x, c} in the x direction.

特開２００４−１０１３２２号公報

JP 2004-101322 A

  However, the concrete member 7 does not always have a stress state as designed due to creep, drying shrinkage, or the like. In particular, since the lack of recognition of the existence of internal restraint stress acting on the concrete member 7 and the mechanism thereof are not sufficiently grasped, there are not a few cases where the actually obtained stress deviates from the effective stress.

  Moreover, in the patent shown in the above-mentioned patent document 1, since the amount of restraint strain generated by restraining the creep strain by the steel material is not taken into consideration at all, an accurate effective stress cannot be calculated.

  Moreover, in the patent shown in the above-mentioned Patent Document 1, the depth of the groove to be drilled when the concrete piece 74 is cut out is set to a predetermined depth. The depth is such that the strain continuously measured while the hole is formed is constant. However, since the degree of progress of drying shrinkage is different in the depth direction, there is a problem that the influence of internal restraint stress due to this cannot be considered.

  Further, in the patent disclosed in Patent Document 1, it is necessary to find the depth of drilling holes in order to obtain a stable strain measurement value. However, it is necessary to perform continuous measurement of strain using a strain gauge. There was also a problem that an apparatus was required and measurement was expensive.

  Therefore, the present invention has been devised in view of the above-mentioned problems, and the object of the present invention is to classify and grasp the types and mechanisms of internal restraint stress acting on the concrete member, and then to the concrete member. It is an object to provide a concrete member stress measurement system and method, a program, a recording medium, and a reinforced concrete member capable of measuring the effective stress of the concrete member with high accuracy.

ν：コンクリートのポアソン比
Δε_x、_cr：クリープ歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε _x 、 _sr ：乾燥収縮歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε _y 、 _sr ：乾燥収縮歪みの鋼材拘束によるy方向応力が開放されるときのy方向の弾性歪み
E_x、_c：x方向のコンクリートの弾性係数 The stress measurement system for a concrete member according to the present invention is the stress measurement system for a reinforced concrete member in which stress is applied in the x direction, the first strain gauge affixed to the side surface of the concrete member in the x direction, and Cut out to include the second strain gauge attached in the y direction corresponding to the direction perpendicular to the x direction, the first strain gauge, and the side surface to which the second strain gauge is attached. A strain detection means for detecting a strain ε _{x in the} x direction from the concrete piece via the first strain gauge, and detecting a strain ε _{y in the} y direction via the second strain gauge, and the strain detection the detected strain epsilon _x by means, on the basis of the epsilon _y below (22), the x-direction of the elastic strain [Delta] [epsilon] _x, computes _e, effective in the x direction on the basis of further following formula (3) Power sigma _x, characterized in that it comprises a calculating means for calculating _e.

ν: Poisson's ratio of concrete Δε _x , _cr : elastic strain in the x direction when the stress in the x direction due to creep restraint is released
Δε _x , _sr : Elastic strain in the x direction when the stress in the x direction due to steel restraint of drying shrinkage strain is released
Δε _y , _sr : Elastic strain in the y direction when the y direction stress due to the steel restraint of drying shrinkage strain is released
E _x , _c : Elastic modulus of concrete in x direction

ν：コンクリートのポアソン比
Δε_x、_cr：クリープ歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε _x 、 _sr ：乾燥収縮歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε _y 、 _sr ：乾燥収縮歪みの鋼材拘束によるy方向応力が開放されるときのy方向の弾性歪み
E_x、_c：x方向のコンクリートの弾性係数 The stress measurement method for a concrete member according to the present invention is the stress measurement method for a reinforced concrete member in which stress is applied in the x direction, wherein the first strain gauge is provided in the x direction on the side surface of the concrete member, and the x direction is provided. A second strain gauge is attached in the y direction corresponding to a direction perpendicular to the first direction, and the concrete piece is cut out so as to include the first strain gauge and the side surface to which the second strain gauge is attached. The strain ε _{x in the} x direction is detected through the strain gage of the first strain, and the strain ε _{y in the} y direction is detected through the second strain gauge. From the detected strains ε _x and ε _y , the following (22) The elastic strains Δε _x and _e in the x direction are calculated based on the formula, and the effective stresses σ _x and _e in the x direction are calculated based on the following formula (3).

ν: Poisson's ratio of concrete Δε _x , _cr : elastic strain in the x direction when the stress in the x direction due to creep restraint is released
Δε _x , _sr : Elastic strain in the x direction when the stress in the x direction due to steel restraint of drying shrinkage strain is released
Δε _y , _sr : Elastic strain in the y direction when the y direction stress due to the steel restraint of drying shrinkage strain is released
E _x , _c : Elastic modulus of concrete in x direction

In the present invention having the above-described configuration, it becomes possible to measure the effective stress on the concrete member with high accuracy after classifying and grasping the types and mechanisms of the internal restraint stress acting on the concrete member, and in particular, the effective stress σ When calculating _{x and e} , it is possible to improve the calculation accuracy especially by removing the influence of this creep distortion.

  Hereinafter, as a best mode for carrying out the present invention, a stress measurement system for a reinforced concrete member will be described in detail with reference to the drawings.

  As shown in FIG. 1, for example, the stress measurement system 1 measures the internal stress of a reinforced concrete member 3 in which an external force is applied in the x direction due to tension of a PC steel material or the like. The stress measurement system 1 includes, for example, a first strain gauge 11 attached to the side surface of the reinforced concrete member 3 in the x direction and a second strain attached in the y direction corresponding to a direction perpendicular to the x direction. A gauge 12, a first strain gauge 11, a switch box 13 connected to the second strain gauge 12, and a personal computer (PC) 14 connected to the switch box 13 are provided. Incidentally, this reinforced concrete member 3 has a steel material 24 embedded in the x direction.

  In the stress measurement system 1 configured as described above, strain based on the stress loaded on the reinforced concrete member 3 is converted into an electrical signal via the first strain gauge 11 and the second strain gauge 12, and this is converted into a switch box. 13, and the PC 14 calculates the effective stress in the x direction based on the detected electrical signal.

  Next, a method for measuring the effective stress in the x direction for the reinforced concrete member 3 actually stressed in the x direction using the stress measurement system 1 will be described.

  First, the first strain gauge 11 is attached to the side surface of the concrete member 3 so as to cross the first strain gauge 11 in the x direction and the second strain gauge 12 in the y direction corresponding to the direction perpendicular to the x direction. It is desirable that the strain gauges 11 and 12 have a gauge length of about 60 mm.

  An initial value of strain in the x and y directions is detected via the strain gauges 11 and 12. The state in which the stress based on the introduced prestress is applied to the concrete is defined as an initial value of strain.

  Next, the concrete piece 22 is cut out from the concrete member 3 so as to include the side surface to which the first strain gauge 11 and the second strain gauge 12 are attached. The concrete piece 22 is usually formed in a columnar shape, and the core diameter is desirably about 100 mm. The reason is that the strain measured by the strain gauge is known to be affected by the coarse aggregate of the concrete, and the strain gauge length should be at least three times the maximum aggregate size of the concrete. Has been. This is because the core diameter obtained by cutting out the concrete piece 22 needs to be about 100 mm in order to satisfy the strain gauge length requirement.

  The depth of the concrete piece 22 is preferably configured by the thickness of the concrete member 3. However, when the drilling of the concrete piece 22 is stopped halfway, it is necessary to perform post-processing. Incidentally, when the concrete piece 22 is drilled, it is desirable to drill in a dry manner without using water. The reason for this is that the wet method of cooling with water can cause additional strain due to swelling of the concrete, and can also cause the peeling of strain gauges and the cause of poor insulation. This is because those risks can be reduced. In the case of dry drilling, the core concrete temperature rises due to frictional heat, so it is desirable to use a core drill having a cooling function. By using such a coring technique that hardly causes a temperature rise, the detection accuracy by the first strain gauge 11 and the second strain gauge 12 is improved without being sensitively influenced by a temperature change. Is possible.

Incidentally, the cut concrete piece 22 is in a state in which the introduced prestress is released. At this stage, a measured strain value in the x direction (hereinafter referred to as a measured stress release strain value) due to the release of stress is measured via the first strain gauge 11, and the second strain gauge 12 is mounted. Then, an actual measurement value of stress release strain in the y direction is measured. Then, the strain ε _x is detected by subtracting the initial value of the strain in the x direction from the measured stress release strain value in the x direction, and the y direction is determined from the measured stress release strain value in the y direction. The distortion ε _y is detected by subtracting the initial value of the distortion. Incidentally, the calculation of the strains ε _x and ε _y is executed by the PC 14 described above. Moreover, it is desirable that the strains ε _x and ε _y are detected continuously for about half a day after drilling the concrete piece 22 from the viewpoint of preventing variation in data.

  In addition, when the core after the concrete piece 22 is cut out is formed in a cylindrical shape, excessive stress concentration or the like hardly occurs in the concrete around the core, and the core is made of expansive concrete or mortar. By backfilling, it is possible to return to a stress state close to that before drilling.

  Moreover, concrete is inferior in homogeneity compared with steel materials etc., and there are many dispersion | variation in a physical property. For this reason, a certain amount of error occurs in the distortion measurement. Therefore, a plurality of concrete pieces 22 may be cut out by drilling holes at a plurality of locations, and the obtained strain measurement values may be averaged. Furthermore, by measuring strain over a plurality of locations within the same cross section, the stress distribution in the cross section due to bending can be estimated, and the accuracy of stress estimation can be improved.

Next, the effective stress σ _{x, e} in the x direction is calculated based on the detected strains ε _x , ε _y . The calculation of the effective stress σ _{x, e} is executed based on the concept described below.

  2A to 2C show the types and mechanisms of internal restraint stress acting on the reinforced concrete member 3. As the types of internal restraint stress, restraint strain α1 caused by non-uniformity in the depth direction of drying shrinkage as shown in FIG. 2 (a) and drying shrinkage as shown in FIG. 2 (b). There is a restraining strain α2 generated when the steel material 24 restrains the strain, and a restraining strain α3 generated when the steel material restrains the creep strain as shown in FIG. 2 (c).

In particular, α2 and 3 are distortions that may occur due to the presence of the steel material 24, and are parameters that must be taken into account when measuring internal stress in the reinforced concrete member 3 as a concept including prestressed concrete. These constrained strains α1 to α3 can be expressed as a difference value between each potential amount and actual strain. When actually measuring the effective stress σ _{x, e} , it is necessary to measure a stress based on pure pre-stress from which the influence of the constraint strains α1 to α3 is removed.

FIG. 3 shows an example in which strains ε _x and ε _y are measured over time. The strain ε _y includes components of constraint strains α1 and α2. The strain ε _x includes an elastic strain A based on an external force loaded in the x direction in addition to the components of the constraint strains α1, α2, and α3.

For this reason, the components of the constraint strains α1 and α2 can be eliminated by simply obtaining the difference between the strains ε _x and ε _y based on the equation (0) as in the conventional patent document 1, but the constraint strain The α3 component cannot be erased, and eventually the α3 + A component remains. In other words, the conventional technique disclosed in Patent Document 1 can accurately measure the internal stress of unreinforced concrete, but the reinforced concrete member 3 in which the reinforcing bars are embedded can be measured with high accuracy. Can not.

Therefore, in order to obtain the final component of A, as in A = ε _x -ε _y -α3, strain epsilon _x, unless Yara pull the α3 ingredient based on further creep strain from the difference of epsilon _y I must.

The stress measurement method to which the present invention is applied specializes in improving the calculation accuracy by calculating the effective stress σ _{x, e} , particularly by removing the influence of α 3 based on the creep strain. It is. Hereinafter, the actual calculation process will be described in detail.

ここで、
σ_x,e：x方向の有効応力度（持続荷重によりコンクリート部材断面に作用する応力度）
σ_y,e：y方向の有効応力度（持続荷重によりコンクリート部材断面に作用する応力度）
E_x,c：x方向のコンクリートの弾性係数
E_y,c：y方向のコンクリートの弾性係数
ε_x：コア削孔より開放されるx方向の歪み
ε_y：コア削孔より開放されるy方向の歪み
Δε_x,e：x方向有効応力が開放されるときのx方向の弾性歪み
Δε_y,xe：x方向有効応力が開放されるときのy方向のポアソン歪み=−νΔε_x,e
Δε_y,e：y方向有効応力が開放されるときのy方向の弾性歪み
Δε_x,ye：y方向有効応力が開放されるときのx方向のポアソン歪み=−νΔε_y,e
Δε_x,si：乾燥収縮歪みの深さ方向の不均一性に起因する内部拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε_y,xsi：乾燥収縮歪みの深さ方向の不均一性に起因する内部拘束によるx方向応力が開放されるときのy方向のポアソン歪み=−νΔε_x,si
Δε_y,si：乾燥収縮歪みの深さ方向の不均一性に起因する内部拘束によるy方向応力が開放されるときのy方向の弾性歪み
Δε_x,ysi：乾燥収縮歪みの深さ方向の不均一性に起因する内部拘束によるy方向応力が開放されるときのx方向のポアソン歪み=−νΔε_y,si
Δε_x,sr：乾燥収縮歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε_y,xsr：乾燥収縮歪みの鋼材拘束によるx方向応力が開放されるときのy方向のポアソン歪み=−νΔε_x,sr
Δε_y,sr：乾燥収縮歪みの鋼材拘束によるy方向応力が開放されるときのy方向の弾性歪み
Δε_x,ysr：乾燥収縮歪みの鋼材拘束によるy方向応力が開放されるときのx方向のポアソン歪み=−νΔε_y,sr
Δε_x,cr：クリープ歪みの鋼材拘束によるx方向応力が開放されるときのx方向の弾性歪み
Δε_y,xcr：クリープ歪みの鋼材拘束によるx方向応力が開放されるときのy方向のポアソン歪み=−νΔε_x,cr
Δε_y,cr：クリープ歪みの鋼材拘束によるy方向応力が開放されるときのy方向の弾性歪み
Δε_x,ycr：クリープ歪みの鋼材拘束によるy方向応力が開放されるときのx方向のポアソン歪み=−νΔε_y,cr First, equations (1) to (4) show the relationship between the strain released by the drilling of the concrete piece 22 and the degree of stress.

here,
σ _{x, e} : Effective stress level in the x direction (stress level acting on the cross section of concrete member due to sustained load)
σ _{y, e} : Effective stress level in the y direction (stress level acting on the cross section of the concrete member due to sustained load)
E _{x, c} : Elastic modulus of concrete in the x direction
E _{y, c} : Elastic modulus of concrete in y direction ε _x : Strain in x direction released from core drilling ε _y : Strain in y direction released from core drilling Δε _{x, e} : Effective stress in x direction Elastic strain Δε _{y, xe in the} x direction when released: Poisson strain in the y direction when the effective stress in the x direction is released = −νΔε _{x, e}
Δε _{y, e} : elastic strain in y direction when y-direction effective stress is released Δε _{x, ye} : Poisson strain in x direction when y-direction effective stress is released = −νΔε _{y, e}
Δε _{x, si} : Elastic strain in the x direction when the stress in the x direction due to internal constraints due to nonuniformity in the depth direction of the drying shrinkage strain is released Δε _{y, xsi} : Non-uniformity in the depth direction of the drying shrinkage strain Poisson strain in the y direction when the stress in the x direction due to internal constraints due to uniformity is released = −νΔε _{x, si}
Δε _{y, si} : Y-direction elastic strain when the stress in the y-direction due to internal constraints due to non-uniformity in the depth direction of drying shrinkage strain is _released Δε _{x, ysi} : Non-uniformity in the depth direction of drying shrinkage strain Poisson strain in the x direction when the y direction stress due to internal constraints due to uniformity is released = -νΔε _{y, si}
Δε _{x, sr} : Elastic strain in the x direction when the stress in the x direction due to steel restraint of dry shrinkage strain is _released Δε _{y, xsr} : _Y direction in which the stress in the x direction due to steel restraint of dry shrinkage strain is _released Poisson distortion = −νΔε _{x, sr}
Δε _{y, sr} : Elastic strain in the y direction when the stress in the y direction due to steel restraint of drying shrinkage is _released Δε _{x, ysr} : Stress in the y direction when the stress in the y direction due to steel restraint of drying shrinkage strain is _released Poisson distortion = -νΔε _{y, sr}
Δε _{x, cr} : Elastic strain in the x direction when the stress in the x direction due to creep restraint is _released Δε _{y, xcr} : Poisson strain in the y direction when the stress in the x direction due to creep restraint is released = −νΔε _{x, cr}
Δε _{y, cr} : Elastic strain in the y direction when the y-direction stress due to creep restraint is _released Δε _{x, ycr} : Poisson strain in the x direction when the y-direction stress due to creep restraint is released = −νΔε _{y, cr}

  Next, consider a case where an external force is applied only in the x direction and no external force is applied in the y direction.

First, when an external force is applied only in the x direction, it can be expressed as follows.

Here, since concrete is considered isotropic from a macro perspective, the following relationship holds.

When the x-direction steel ratio and the y-direction steel ratio are equal

ここで、φ_x,r：x方向の鋼材比、φ_y,r：y方向の鋼材比とする。 Further, consider the case where the steel material 24 has the same x-direction steel material ratio and the y-direction steel material ratio. When it is assumed that the x-direction steel material ratio and the y-direction steel material ratio are equal, the following relationship holds.

Here, φ _{x, r} : steel material ratio in the x direction, and φ _{y, r} : steel material ratio in the y direction.

Therefore, the difference between the strain in the x direction and the strain in the y direction that is opened by drilling the concrete piece 22 can be expressed as follows.

ここで、
E_x,s：x方向の鋼材の弾性係数
A_x,c：x方向のコンクリートの断面積
A_x,s：x方向の鋼材の断面積
ε_{cp t,x}：材齢tにおける鋼材による拘束がない場合のx方向のコンクリートの全クリープ歪み
t：測定時におけるコンクリートの材齢
とする。このときの、Δε_ｘ、ｃｒ、ε_{ｃｐ ｔ、ｘ}の関係を図４(a)に示す。鋼材２４がないコンクリートに外力（σ_x,e）が負荷された場合は、大きさε_{ｃｐ ｔ、ｘ}のクリープひずみが発生するが、鋼材２４が存在する場合には、クリープひずみは、その一部が鋼材２４によって拘束されて、Δε_ｘ、ｃｒだけ小さくなることが示されている。このとき、プレストレスや死荷重などの持続荷重に加えて、鋼材２４の存在によって拘束応力が新たに発生する。従って、クリープ歪みΔε_{ｃｐ ｔ、ｘ}を下記（９）式のように表すことができる。 Considering the balance between the restraining force of steel due to creep strain and the reaction force acting on the concrete, it can be expressed as follows.

here,
E _{x, s} : Elastic modulus of steel in x direction
A _{x, c} : Cross section of concrete in x direction
A _{x, s} : Cross section of steel in x direction ε _{cp t, x} : Total creep strain of concrete in x direction when there is no restraint by steel at age t
t: Age of concrete at the time of measurement. In this case, [Delta] [epsilon] _{x, cr,} shown epsilon _{cp t,} the relationship between _x in Figure 4 (a). When an external force (σ _{x, e} ) is applied to the concrete without the steel material 24 _, a creep strain of magnitude ε _{cpt, x} is generated, but when the steel material 24 is present, the creep strain is one of them. It is shown that the portion is constrained by the steel material 24 and becomes smaller by Δε _{x, cr} . At this time, in addition to continuous loads such as pre-stress and dead load, restraint stress is newly generated due to the presence of the steel material 24. Accordingly, the creep strain Δε _{cp t, x} can be expressed by the following equation (9).

ここで、
φ_ｔ、ｘ：材齢tにおけるx方向のコンクリート部材３のクリープ係数（JSCEコンクリート標準示方書などによる）

here,
φ _{t, x} : Creep coefficient of concrete member 3 in x direction at age t (according to JSCE concrete standard specifications, etc.)

By the way, this φ _{t, x} is published by the Japan Society of Civil Engineers "Standard Specification for Concrete [Structural Performance Review]", March 2002, 3.2.9 Creep, pp.34- 37 may be applied. In such a case, ε ′ _cc (t, t ′, t _o ) / σ ′ _cp is calculated according to the equations (solution 3.2.15) and (solution 3.2.20) in this document, and the obtained ε ′ _cc (t , t ', t _o ) / σ' _{cp multiplied} by Ex, c gives the creep coefficient φt, x. Note that the creep coefficient φt, x may be simply determined according to Tables 3.2.3 and 3.2.4 in the document. Table 3.2.3 is shown in Table 1 and Table 3.2.4 is shown in Table 2.

In addition, this φ _{t, x} is, for example, literature (ACI-209R-92, “Prediction of Creep, Shrinkage, and Temperature Effects in Concrete Structures” April, 1994, pp.209R-1 to 209R-47) and literature (“CEB-FIP MODEL CODE 1990”, June, 1991, 2.1.6.4 Creep and Shrinkage pp. 53-58) may be used to obtain the value.

here,
Δσ _x : Additional stress generated by restraining the creep and drying shrinkage strain that occurs in concrete, in other words steel restraining stress

ここでγ_1xを(12)のように定義したとき、式(11)は(13)に書き換えられる。

Substituting the relationship shown in equation (10) into equation (9) and then into equation (8) gives the following.

Here, when γ _1x is defined as (12), equation (11) is rewritten as (13).

Substituting equation (14) into equation (6) yields:

ここで、
ε_{ｓｈｔ、ｘ}：材齢tにおける鋼材による拘束がない場合のx方向のコンクリートの全乾燥収縮歪み（JSCEコンクリート標準示方書などによる） Furthermore, considering the balance between the restraining force of the steel due to drying shrinkage and the reaction force acting on the concrete, it can be expressed as follows.

here,
ε _{sht, x} : Total drying shrinkage strain of concrete in the x direction when there is no restraint by steel at age t (according to JSCE concrete standard specifications, etc.)

By the way, this ε _{sht, x} is as described in the Japan Society of Civil Engineers "Concrete Standard Specification [Structural Performance Review Edition]", March 2002 edition, 3.2.8 Shrinkage, pp.30-34 It may be obtained using the equations (Solution 3.2.3) to (Solution 3.2.5) and (Solution 3.2.6) to (Solution 3.2.14).
FIG. 4B shows the relationship between Δε _{x, sr} , ε _{sh t, x} at this time. When drying shrinkage occurs in concrete without the steel material 24 _, a drying shrinkage strain having a size ε _{sht, x} occurs. However, when the steel material 24 is present, a part of the drying shrinkage strain is the steel material 24. It is shown that it becomes smaller by Δε _{x, sr} .
Substituting equation (19) into equation (17) yields:

From the elastic strain Δε _{x, e in} the x direction calculated from the equation (20), the effective stress σ _{x, e} in the x direction is further calculated based on the following equation (3).

When the x-direction steel ratio and the y-direction steel ratio are not equal

Further, regarding the steel material 24, consider the case where the x-direction steel material ratio and the y-direction steel material ratio are not equal. When the x-direction steel material ratio and the y-direction steel material ratio are not equal, the following relationship holds.

The difference between the x-direction strain ε _x and the y-direction strain ε _y released by the core drilling based on the cutting of the concrete piece 22 can be expressed as follows.

When considering the balance between the restraining force of the steel due to drying shrinkage strain and the reaction force acting on the concrete, the elastic strain Δε _{x, sr} in the x direction when the stress in the x direction due to the steel restraining of the drying shrinkage strain is released is It can be expressed as follows.

If γ _1y is defined as (26), the elastic strain Δε _{y, sr in} the y direction when the y direction stress due to the steel material constraint of the drying shrinkage strain is released can be expressed as follows.

here,
E _{y, s} : Elastic modulus of steel in y direction
A _{y, c} : Cross section of concrete in y direction
A _{y, s} : sectional area ε _sht of steel material in y direction _{, x} : total drying shrinkage strain of concrete in y direction when not restrained by steel material at age t

Therefore, equation (22) can be rewritten as:

Considering the balance between the restraining force of steel due to creep strain and the reaction force acting on the concrete, it can be expressed as follows.

Since the steel material restrains the creep and drying shrinkage strain generated in the concrete, and the steel material restraint stress is generated as an additional stress, the creep strain of the concrete can be expressed as follows.

By substituting this relationship into equation (31), Δε _{x, cr} can be expressed as follows.

Further substitution into equation (29) yields:

From the elastic strain Δε _{x, e in} the x direction calculated from (39), the effective stress σ _{x, e} in the x direction is further calculated based on the following equation (3).

In the formula (19), the following formula (in Japanese) published by the Japan Society of Civil Engineers "Standard Specification for Concrete [Structural Performance Review]", March 2002 edition, 3.2.8 Shrinkage, pp. 30-34 It may be obtained using Solution 3.2.3) to (Solution 3.2.5).

here,
RH: Relative humidity (%)
W: Unit water volume (kg / m ³ )
V: Volume (mm ³ )
S: Surface area in contact with outside air (mm ² )
V / S: Volume surface area ratio (mm)
t0 and t: The effective age of concrete at the start of drying and during drying, and the value corrected by the equation (solution 3.2.5) is used.
Δti: Days during which the temperature is T (° C.) T 0: Temperature until the start of drying (° C.)
And

Here, when RH is 60, W is 165, V is 4.8 × 10 ⁸ , S is 4800000, t0 is 5, t1 is 365, T0 is 20, and T is 20, the above equation 3.2.3) Substituting in (solution 3.2.5), ε ′ _sh was 534 (× 10 ⁻⁶ ).

It is a figure which shows the stress measurement system of the reinforced concrete member to which this invention is applied. It is a figure which shows the kind and mechanism of internal restraint stress which act on a reinforced concrete member. It is a figure which shows the example of a measurement with time of distortion | strain (epsilon) _x , (epsilon) _y . It is a figure for demonstrating the relationship of the magnitude | size of each distortion. It is a figure for demonstrating a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stress measuring system 3 Reinforced concrete member 11 1st strain gauge 12 2nd strain gauge 13 Switch box 14 Personal computer 22 Concrete piece 24 Steel

Claims (9)

In the stress measurement system for reinforced concrete members loaded with stress in the x direction,
A first strain gauge affixed to the side surface of the concrete member in the x direction, and a second strain gauge affixed in the y direction corresponding to a direction perpendicular to the x direction;
While detecting the strain ε _{x in the} x direction through the first strain gauge from the concrete piece cut out to include the side surface to which the first strain gauge and the second strain gauge are attached, Strain detecting means for detecting a strain ε _{y in the} y direction via a second strain gauge;
Based on the following equations (22) from the strains ε _x and ε _y detected by the strain detecting means, the elastic strains Δε _x and _e in the x direction are calculated, and further in the x direction based on the following equation (3). A stress measuring system for a concrete member, comprising: a calculating means for calculating an effective stress σ _x , _e .

ν: Poisson's ratio of concrete Δε _x , _cr : elastic strain in the x direction when the stress in the x direction due to creep restraint is released
Δε _x , _sr : Elastic strain in the x direction when the stress in the x direction due to steel restraint of drying shrinkage strain is released
Δε _y , _sr : Elastic strain in the y direction when the y direction stress due to the steel restraint of drying shrinkage strain is released
E _x , _c : Elastic modulus of concrete in x direction Said calculation means, when the x-direction steel ratio in the y direction steel ratio are equal, according to claim 1, wherein the calculating the x direction of the elastic strain [Delta] [epsilon] _x, the _e on the basis of the following equation (20) Stress measurement system for concrete members.

Where γ _1x = E _x , _s · A _x , _s / (E _x , _c · A _x , _c + E _x , _s · A _x , _s )
φ _t , _x : creep coefficient E _x of concrete in the x direction at age t, _s : elastic modulus A _x of steel in the x direction, _s : cross sectional area A _x of steel in the x direction, _c : concrete in the x direction _Cross- sectional area ε _sht , _x : total drying shrinkage strain of concrete in x direction when there is no restraint by steel material at age t 2. The calculation means calculates the elastic strain Δε _x , _e in the x direction based on the following formula (39) when the x-direction steel material ratio and the y-direction steel material ratio are different. Stress measurement system for concrete members.

Where γ _1x = E _x , _s · A _x , _s / (E _x , _c · A _x , _c + E _x , _s · A _x , _s )
γ _1y = E _y , _s · A _y , _s / (E _y , _c · A _y , _c + E _y , _s · A _y , _s )
φ _t , _x : creep coefficient E _x of concrete in the x direction at age t, _s : elastic modulus A _x of steel in the x direction, _s : cross sectional area A _x of steel in the x direction, _c : concrete in the x direction sectional area E _{y, s:} elastic modulus of the y direction of the steel a _{y, s:} cross-sectional area E _y in the y direction of the steel material, _c: elastic modulus of the y direction of the concrete a _{y, c:} sectional area of the y direction of the concrete ε _sht , _x : total drying shrinkage strain of concrete in x direction when there is no restraint by steel material at age t In the stress measurement method for reinforced concrete members in which stress is applied in the x direction,
The first strain gauge is attached to the side surface of the concrete member in the x direction, and the second strain gauge is attached in the y direction corresponding to the direction perpendicular to the x direction,
The concrete piece is cut out so as to include the first strain gauge and the side surface to which the second strain gauge is attached, and the strain ε _{x in the} x direction is detected via the first strain gauge, and the second The strain ε _{y in the} y direction is detected through the strain gauge of
Based on the detected strains ε _x and ε _y , the elastic strain Δε _x , _e in the x direction is calculated based on the following equation (22) , and the effective stress σ _x in the x direction is calculated based on the following equation (3): _A method for measuring stress of a concrete member, characterized in that _e is calculated.

ν: Poisson's ratio of concrete Δε _x , _cr : elastic strain in the x direction when the stress in the x direction due to creep restraint is released
Δε _x , _sr : Elastic strain in the x direction when the stress in the x direction due to steel restraint of drying shrinkage strain is released
Δε _y , _sr : Elastic strain in the y direction when the y direction stress due to the steel restraint of drying shrinkage strain is released
E _x , _c : Elastic modulus of concrete in x direction 5. The stress of a concrete member according to claim 4, wherein when the x-direction steel material ratio and the y-direction steel material ratio are equal, the elastic strain Δε _x , _e in the x direction is calculated based on the following formula (20). Measuring method.

Where γ _1x = E _x , _s · A _x , _s / (E _x , _c · A _x , _c + E _x , _s · A _x , _s )
φ _t , _x : creep coefficient E _x of concrete in the x direction at age t, _s : elastic modulus A _x of steel in the x direction, _s : cross sectional area A _x of steel in the x direction, _c : concrete in the x direction _Cross- sectional area ε _sht , _x : total drying shrinkage strain of concrete in x direction when there is no restraint by steel material at age t 5. The stress of a concrete member according to claim 4, wherein when the x-direction steel material ratio and the y-direction steel material ratio are different, the elastic strain Δε _x , _e in the x direction is calculated based on the following formula (39). Measuring method.

Where γ _1x = E _x , _s · A _x , _s / (E _x , _c · A _x , _c + E _x , _s · A _x , _s )
γ _1y = E _y , _s · A _y , _s / (E _y , _c · A _y , _c + E _y , _s · A _y , _s )
φ _t , _x : creep coefficient E _x of concrete in the x direction at age t, _s : elastic modulus A _x of steel in the x direction, _s : cross sectional area A _x of steel in the x direction, _c : concrete in the x direction sectional area E _{y, s:} elastic modulus of the y direction of the steel a _{y, s:} cross-sectional area E _y in the y direction of the steel material, _c: elastic modulus of the y direction of the concrete a _{y, c:} sectional area of the y direction of the concrete ε _sht , _x : total drying shrinkage strain of concrete in x direction when there is no restraint by steel material at age t A program for causing a computer to calculate the elastic strain Δε _x , _e in the x direction in the stress measurement method for a concrete member according to any one of claims 4 to 6.   A recording medium on which the program according to claim 7 is recorded. A reinforced concrete member in which the stress to be applied in the x direction is adjusted based on the effective stresses σ _x and _e calculated based on the stress measurement method for a concrete member according to any one of claims 4 to 6. .

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