JP7146192B2 - Method for estimating residual prestress force of PC girder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for estimating residual prestress force (PC steel material tension force) of PC girders.

Many studies have been conducted on evaluation of PC steel materials for PC girders and estimation of residual prestress force.

For example, in Non-Patent Document 1, the relationship between the girder lower edge strain and the crack opening width is obtained for a PC girder with a crack extending in the direction perpendicular to the bridge axis, and the relationship between the girder lower edge strain and the crack opening width at the time of this load increase. The inflection point where is changed is the starting point where cracks start to open (starting point of crack re-opening), and from the strain distribution in the cross-sectional direction of the girder at the starting point of crack re-opening, the strain distribution of compression concrete, tension concrete, and PC steel materials The moment around the neutral axis of the resultant force is calculated, and the prestress force of the PC steel is estimated using the design formula.

In Patent Document 1, a plurality of circumferential strain gauges and a radial strain gauge are affixed in advance along the circumferential direction of concrete drilling in a post-process, and drilling is performed by a core drill in this state. I do. Then, the stress acting on the concrete structure is estimated from the combination pattern of the measured values of the strain gauges after drilling.

In Patent Document 2, a biaxial strain gauge is attached to a concrete surface, a cut is made by a concrete core cutter, and the strain released by the cut is obtained. In addition, using the difference between the released strain in the direction of action of the prestress force and the released strain in the direction perpendicular to the direction of action, the strain component due to internal restraint (the effects of drying shrinkage and creep strain) is removed, and the proposed equation is Find the effective stress intensity.

In Patent Document 3, by drilling a concrete hole in the center of the measurement target area of the structure to release the stress acting on the structure, and detecting the strain change that occurs around the drilled hole due to the release of the stress, Obtain the current stress in the area to be measured by analysis.

In Patent Document 4, the initial values including the permeability and stress of the rebar and the function of the permeability and temperature are measured, the existing stress of the object to be measured (rebar) is directly measured, and the structure (PC structure) is obtained from this. Obtain the stress state and stress change of In addition, the amount of reduction in prestress is obtained from the current stress of the reinforcing bars and the subsequent change, and the stress state of the PC structure is estimated.

In Patent Literature 5, soundness is evaluated by connecting a measuring instrument to the ends of one PC steel wire forming a multi-strand and measuring the electrical characteristic values between the ends with the measuring instrument.

Mitsuyoshi Tsunekuni, Yoshitaka Kato, Kento Uomoto: Examination on Structural Deterioration Diagnosis of Existing PC Girder, Japan Concrete Institute, Annual Proceedings of Concrete Engineering, Vol. 28, No. 1, pp. 1967-1972, 2006

Japanese Patent Application Laid-Open No. 2010-60490 Japanese Patent No. 5095258 JP 2007-303916 A JP-A-2004-264022 JP-A-2000-193620

Here, in Non-Patent Document 1, the tension of the PC steel material is back-calculated based on the feature that the bending crack closed by the tension of the PC steel material reopens when the load increases, and the bending crack reopens when the load increases. The starting point of the mouth is the inflection point (slope change point) where the relationship between the strain of the lower edge of the girder and the crack width changes when the load increases.

However, in Non-Patent Document 1, the tension of the PC steel is calculated backward based on the feature that the bending crack closed by the tension of the PC steel re-opens when the load increases. By evaluating the starting point of bending crack re-opening from the inflection point where the relationship between the strain of the girder lower edge and the crack width changes when the load increases, the strain of the girder lower edge and the crack width when the load increases is evaluated. In some cases, the relationship changes gradually due to the effects of tensile softening of concrete, and the inflection point does not appear clearly, causing variations in the reading (judgment/identification) of the starting point of crack re-opening.

Therefore, in Non-Patent Document 1, the accuracy of the back calculation value of the tension force of the PC steel material based on the bending moment cannot be sufficiently ensured, and there is a possibility that the residual prestress force of the PC steel material cannot be accurately estimated.

In Non-Patent Document 1, there is no clear basis for setting the measurement position of the strain at the lower edge of the girder, and the starting point of crack re-opening changes depending on the setting position. As a result, the evaluation of the bending moment at crack re-opening based on the strain distribution in the cross-sectional direction of the girder varies, and from this point as well, it is difficult to accurately estimate the residual prestress force of the PC steel material.

Patent document 1, patent document 2, and patent document 3 are techniques that utilize the stress release of concrete at a specific location, and estimate the compressive stress at that location from the measurement of the strain of the concrete accompanying the release of the stress. As such, drilling of the core is required to release the stress, resulting in a destructive or micro-destructive test.

In addition, since it is a measurement of local strain, it is easily affected by the internal restraint of steel materials against drying shrinkage and creep. It is necessary to take countermeasures such as using a separate analysis.

Patent Documents 4 and 5 are techniques for directly measuring the stress of reinforcing bars or PC steel materials inside concrete. Since the reinforcing bars and PC steel materials are inside the concrete, when applying it to the existing PCT girder, a chip with a large depth is required, which is practically difficult to apply.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method for estimating a residual prestress force of a PC girder, which can easily and accurately estimate the residual prestress force of a PC girder.

In order to achieve the above objects, the present invention provides the following means.

A residual prestress force estimation method for a PC girder of the present invention is a method for estimating the residual prestress force of a PC girder in which bending cracks have occurred. A strain measuring means for measuring strain is installed, and a crack opening width measuring means for measuring the crack opening width of the PC girder is installed, and the measurement results of the strain measuring means and the crack opening width measuring means are used. Then, the relationship between the average strain of the tensile reinforcing bars of the PC girder and the bending moment or load acting on the cross section of the PC girder is obtained, and the inflection point at which the relationship changes is set as the starting point of crack re-opening, and the crack re-opens. The bending moment or load at the starting point of the mouth is assumed to be the bending moment or load when crack opening occurs, and the bending moment or load when crack opening occurs is used to estimate the residual prestress force of the PC girder. characterized by

Further, in the method for estimating the residual prestress force of the PC girder of the present invention, a π-type displacement gauge is used as the crack opening width measuring means, and the average strain ε _sm of the tensile reinforcing bars before the crack opening is calculated by the following formula (1) , the average strain ε _sm of the tensile reinforcing bar after crack opening is calculated using the following equation (2).

_εg is the value of the lower edge strain gauge between cracks, _wmax is the value of the π-type displacement gauge at the crack, _lmax is the maximum crack spacing, and _dp is the gauge length of the π-type displacement gauge.

Furthermore, in the residual prestress force estimation method of the PC girder of the present invention, an optical fiber is used as the crack opening width measuring means, and the crack opening width of the entire measurement section including a plurality of cracks is collectively measured by the optical fiber. In the case, the average strain ε _sm of the tensile reinforcing bars before crack opening is calculated using the following formula (3), and the average strain ε _sm of the tensile reinforcing bars after crack opening is calculated using the following formulas (4) and (5). calculate.

ε _g is the value of the lower edge strain gauge between cracks, ε _o is the value of the lower edge optical fiber, n is the number of cracks included in the measurement range, _{w mean} is the average crack width, l _mean is the average crack interval, do is the light is the length of the fiber.

In the method for estimating residual prestress force of PC girders of the present invention, the relationship between the bending moment and the average strain of tensile reinforcing bars before and after the crack opening of the PC girder is grasped using the vehicle load, etc., and the bending crack reopens from that relationship. By determining the starting point of , it becomes possible to estimate the residual prestress force of the PC girder (the tension force of the PC steel material) non-destructively and with higher accuracy than before.

In addition, by using tensile reinforcing bar strain under load, it is not affected by drying shrinkage, creep, etc., which are problems in estimating local concrete stress by stress release method, etc., and high accuracy is also obtained from this point. , it is possible to estimate the residual prestress force of the PC girder.

Furthermore, by measuring the strain in the cross-sectional height direction at the sound portion between cracks, it is possible to estimate the bending moment acting on the girder at the same time, eliminating the need to directly measure the vehicle load, etc. It is possible to simply and accurately estimate the residual prestress force of the PC girder (the tension force of the PC steel material). In addition, it is possible to improve the reliability of the estimation result by repeated measurement at the same location, and continuous monitoring becomes possible.

FIG. 2 is a diagram showing the concept/procedure of a PC girder residual prestress force estimation method according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of installation of a strain measuring means and a crack opening width measuring means on a PC girder in a method for estimating a residual prestress force of a PC girder according to an embodiment of the present invention; FIG. 2 is a diagram showing an example of installation of a strain measuring means and a crack opening width measuring means on a PC girder in a method for estimating a residual prestress force of a PC girder according to an embodiment of the present invention; FIG. 4 is a diagram showing the relationship between the average strain of tensile reinforcing bars and the bending moment acting on the cross section of the PC girder at the position where the strain of the PC girder and the like are measured. FIG. 3 is a diagram comparing an estimated bending moment estimated by a PC girder residual prestress force estimation method according to an embodiment of the present invention and an actually measured measured bending moment. FIG. 4 is a diagram showing the relationship between the average strain of tensile reinforcing bars and the bending moment acting on the cross section of the PC girder at the position where the strain of the PC girder and the like are measured.

Hereinafter, a residual prestress force estimation method for a PC girder according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG.

First, as shown in FIG. 1, the method for estimating the residual prestress force of a PC girder according to this embodiment is applied to cracks that are closed when a dead load is applied due to the residual prestress force, or cracks whose opening width does not change. measures the behavior of opening again due to the action of Then, assuming that the stress at the lower edge (pulling edge) of the girder at this time is zero, the residual prestress force of the PC girder (tension of the PC steel material) is estimated.

That is, in the method for estimating the residual prestress force of the PC girder of this embodiment, as shown in FIGS. 2 to estimate the residual prestress force. Incidentally, the “axis-perpendicular crack 2 occurring in the PC girder 1” includes a substantially axis-perpendicular crack, in other words, it means a crack extending in a direction intersecting with the axial direction O1.

Specifically, in the PC girder residual prestress force estimation method of this embodiment, as shown in FIGS. A plurality of strain measuring means 3 are attached to measure the strain, and a crack opening width measuring means 4 is attached to the lower edge (lower end face) to measure the opening width of the bending crack.

The strain measuring means 3 and the crack opening width measuring means 4 are not particularly limited. 4a, an optical fiber 4b, and the like.

Also, even if the opening width of one crack 2 (opening width of each crack 2) is measured by a π-type displacement meter 4a, an optical fiber 3b, etc., the opening width of a plurality of cracks 2, that is, the opening width of a plurality of cracks The opening width of the crack 2 in the entire measurement section including the crack 2 may be collectively measured by the optical fiber 4b or the like. When three or more cracks 2 are observed (see FIG. 3), the portion where the interval between adjacent cracks 2 is the largest is specified, and the portion between the adjacent cracks 2 of this largest portion is regarded as a sound portion and is placed on the tension side. It is preferable to attach the strain measuring means 3 (3a) and attach the optical fiber 4b as the crack opening width measuring means 4 so as to continuously straddle these adjacent cracks 2. FIG.

In this embodiment, strain measuring means 3 and crack opening width measuring means 4 measure the strain and crack opening width of the PC girder 1 of a bridge in service where the live load changes due to the running of automobiles. In addition, a dead load and a live load are intentionally applied to the PC girder 1 by stopping or running a dump truck at a predetermined position, and the strain of the PC girder 1 and the crack opening width at that time are measured. Of course, the means 3 and the crack opening width measuring means 4 may be used for measurement.

Then, in the method for estimating the residual prestress force of the PC girder of the present embodiment, the crack re-opening starting point is specified/estimated from the measurement results by the strain measuring means 3 and the crack opening width measuring means 4, and the crack re-opening starting point Estimate the residual prestress force of the PC girder 1 based on

Specifically, in estimating crack re-opening, the average strain (ε _s ) of the tensile reinforcing bars shown in FIG. Find the relationship with the bending moment (M) acting on the cross section of the PC girder 1 at the position where

The bending moment acting on the cross-section of the PC girder at the position where the strain of the PC girder was measured was measured by strain measuring means 3 such as strain gauges 3a and optical fibers 3b installed on the tension side and compression side when a live load was applied. It is obtained from the strain and the installation height of each strain measuring means 3 using the following equation (6).

E is the concrete elastic modulus (kN/m ² ), I is the geometrical moment of inertia (m ⁴ ), ε _l is the strain (measured value) of the strain measuring means on the tension edge, and ε _f is the strain of the strain measuring means on the compression side. (measured value), h _l is the installation height (m) of the strain measuring means on the tension edge side, and h _f is the installation height (m) of the strain measuring means on the compression side.

Fig. 5 shows the result of calculating the bending moment (estimated bending moment) of the measured cross-section at the time of initial cracking using formula (6) for PC girders with different prestress forces, and the actual bending moment (measured bending moment). It compares with the result obtained by measurement. FIG. 5 shows the current introduction rate (%) with respect to the original design value. In the figure, 100% means the state where the same prestress as the design value is acting. As shown in this figure, it has been confirmed that the bending moment can be obtained with high accuracy for any introduced prestress force by using the method of this embodiment.

Next, in FIG. 4, state I indicates the state before cracking (before crack re-opening), and state II indicates the state after cracking (after crack re-opening).
The strain of tensile reinforcement in state I is ε _s1 , and ε _sm is the strain when the tensile load of concrete after cracking is considered. On the other hand, ε _s2 indicates the strain when it is assumed that the reinforcing bars bear all the tension and the concrete does not bear the tensile load.

In the method for estimating the residual prestress force of a PC girder according to the present embodiment, in the range where the bending moment is small, the bending crack is closed by the compressive stress due to the residual prestress force (or the crack width does not change), and before the crack occurs is assumed to be equal to the elastic behavior of That is, the tensile bar strain is assumed to be equal to ε _s1 in state I.

Let ε _sm be the strain of the tension rebar after the crack reopens due to the increase in bending moment.

Then, the intersection/bending point between ε _s1 in state I and the strain ε _sm of the tensile reinforcing bar after the crack reopens is obtained, and this intersection/bending point is calculated by dividing the average strain of the tensile reinforcing bar, the strain of the PC girder, etc. The inflection point where the relationship with the bending moment acting on the cross section of the PC girder at the measured position changes is defined as the starting point P of crack re-opening. Also, the acting bending moment M _dec at the crack re-opening starting point P, that is, the bending moment M _dec when crack re-opening occurs is determined.

In the method for estimating the residual prestress force of the PC girder of this embodiment, the relationship between the strain of the lower edge of the girder and the crack width when the load is increased as in Non-Patent Document 1 is not used, but the average strain of the tensile reinforcing bars as described above and the bending moment acting on the cross-section of the PC girder at the position where the strain, etc. of the PC girder was measured. It becomes possible to identify the starting point of the mouth.

Here, as shown in Fig. 6, after the cracks in the PC girder are opened, if the bending moment increases further, the bending moment and the tensile reinforcing bar will increase like RC (reinforced concrete; "virtual RC" in the figure) without prestress. The average strain relationship of is almost linear. Using this feature, the strain ε _sm of the tension _rebar after the crack _reopens is linearly approximated, and the intersection/flexion A point may be determined and this intersection/inflection point may be taken as the starting point P' for crack re-opening. In this way, by linearly approximating the strain ε _sm of the tension reinforcing bar after the crack reopens and then determining the crack reopening starting point, it is possible to more clearly identify the crack reopening starting point. . In the following description, when the strain ε _sm of the tensile reinforcing bar after crack reopening is linearly approximated to identify the starting point of crack reopening, the bending moment M _dec when crack reopening occurs is _Mcr can be substituted.

In the residual prestress force estimation method of the PC girder of this embodiment, the bending moment at the crack re-opening starting point determined in this way is defined as the "moment M when the compressive stress of the tensile edge becomes zero and the crack reopens. _dec ” to estimate the residual prestress force.

On the other hand, in this embodiment, ε _s1 in state I and the strain ε _sm of the tension reinforcing bar after the crack reopens are obtained as follows.

First, the strain of the tension reinforcing bar in state II is based on the idea shown in the following formula (7). That is, Equation (7) uses the average strain to show the idea that the difference between the reinforcing bar strain and the concrete strain between adjacent cracks is integrated over the distance between the cracks and corresponds to the crack width. .

ｗはひび割れ幅、ｌはひび割れ間隔、ε_ｓｍはひび割れ間の鉄筋の平均引張ひずみ、ε_ｃｍはひび割れ間のコンクリートの平均引張ひずみである。

w is the crack width, l is the crack spacing, ε _sm is the average tensile strain of the rebar between the cracks, and ε _cm is the average tensile strain of the concrete between the cracks.

As shown in Fig. 2, when the opening width of one crack (the opening width of each crack) is measured with a π-type displacement gauge, the π-type displacement gauge shows that until a closed crack opens due to compressive stress, If this is not done, the accuracy of setting the crack re-opening starting point and the accuracy of estimating the residual prestress force of the PC girder will be lowered, so it is necessary to remove this effect.

On the other hand, in the method for estimating the residual prestress force of a PC girder according to this embodiment, when the opening width of one crack is measured by a π-type displacement gauge, the average strain _ε It is calculated using the following equations (8) and (9) from the measurement of the strain change of the concrete between cracks and the length change of the cracked portion when the load is increased by using a mold displacement meter.
Equation (8) applies to the average strain ε _sm of the tension rebar before crack opening, and Equation (9) applies to the average strain ε _sm of the tension rebar after crack opening.

ε _g is the value of the lower edge strain gauge between cracks, w _max is the value of the π-type displacement gauge at the crack (mm), l _max is the maximum crack interval (mm), d _p is the gauge length of the π-type displacement gauge ( mm).

When one crack is targeted, the crack interval that can be obtained from the bar arrangement (reinforcing bar cover, steel center interval, steel diameter) is the maximum crack interval. When a plurality of cracks are generated, it is preferable to perform measurement targeting the section with the maximum crack interval. The fact that the crack interval can be obtained from the bar arrangement is described in the Public Interest Incorporated Association of Japan Society of Civil Engineers: Concrete Standard Specifications, Design Edition, established in 2012, pp. 223 "2.3.4 Calculation of Design Response Value of Bending Crack Width", and Koji Otsuka, Masami Shoya, Masanao Sotomon, Tadakatsu Hara: Reinforced Concrete Engineering, pp. 73 "Formula (5.24)".

Then, in equation (9), the elastic deformation amount obtained by multiplying the strain gauge value between the cracks by the rating distance of the π-type displacement gauge is subtracted from the π-type displacement gauge value, and the crack is measured after the crack reopens. Since the length change between the scored distances before re-opening is not added, the average strain ε _sm of the tension reinforcing bar is obtained using equations (8) and (9), so that after crack re-opening It is possible to improve the accuracy of estimating the average strain of tensile reinforcing bars.

Next, as shown in FIG. 3, when the crack opening width of the entire measurement section including multiple cracks is collectively measured with an optical fiber, the length change of the crack part included in the length is measured at the same time. Resulting in. Therefore, subtract the strain measured by the strain gauge from the strain measured by the optical fiber, and multiply the result by the optical fiber rating distance (for example, 1000 mm) to determine the change in the length of the crack. Then, the average crack width per crack is obtained by dividing the change in the length of the crack by the number of cracks included in the evaluation distance of the optical fiber.

In other words, when the crack opening width of the entire measurement section including multiple cracks is collectively measured with an optical fiber, the strain change of the concrete between cracks and the crack From the measurement of the length change of the part, the average strain ε _sm of the tension reinforcing bar is calculated using the following equations (10), (11) and (12).
Equation (10) applies to the average strain ε _sm of the tension rebar before crack opening, and Equations (11) and (12) apply to the average strain ε _sm of the tension rebar after crack opening.

ε _g is the value of the lower edge strain gauge between cracks, ε _o is the value of the lower edge optical fiber, n is the number of cracks included in the measurement range, w _mean is the average crack width (mm), l _mean is the average crack interval (mm ), do is the length of the optical _fiber (mm).

As shown in Equation (12), the change in the length of the crack is obtained by subtracting the strain gauge value at the lower edge between cracks from the strain at the lower edge measured by the optical fiber, and dividing it by the number of cracks. It can be evaluated as a single width, which can improve the accuracy of estimating the average strain of tension rebar after crack re-opening.

When estimating the residual prestress force of the PC girder, the following formulas (13) (formula (14)) for calculating the prestress force of the tension edge in the design of the PC girder are used.

_Wc is the section modulus of concrete, We is the effective section modulus of concrete, _Ac is the cross-sectional area of concrete, _ep is the distance between the _{centroid of the concrete section and the centroid of the PC steel group, Md is} the bending due to the dead load. Moment.

At the moment when the flexural crack reopens due to the live load, the prestress force on the tensile edge, the left-hand side, becomes zero, as shown in Eq. (13). If the cross-sectional area A _c on the right side, the section modulus W _c , W _e , the distance _ep from the center of the cross-section to the PC steel group, and the bending moment M _d due to dead load are obtained from the as-built drawing, etc., the unknowns in equation (13) are There is only an effective prestress force P _e . Using equation (14) developed for the effective prestress force, it is possible to estimate the prestress force when the crack reopens, ie the residual prestress force.

Therefore, in the method for estimating the residual prestress force of PC girders according to this embodiment, the relationship between the bending moment and the average strain of the tensile reinforcing bars before and after the crack opening of the PC girders is captured by using the load of a vehicle that is generally running. , By determining the starting point of bending crack re-opening from that relationship, it is possible to estimate the residual prestress force of the PC girder (the tension force of the PC steel material) non-destructively and with higher accuracy than before. .

In other words, by estimating the bending moment acting on the cross-section to be measured using the strain on the concrete surface, there is no need to measure the weight of a moving vehicle, etc., and the PC girder can be measured non-destructively, simply, and accurately. It becomes possible to estimate the residual prestress force (tension force of PC steel material).

In addition, by using tensile reinforcing bar strain under load, it is not affected by drying shrinkage, creep, etc., which are problems in estimating local concrete stress by stress release method, etc., and high accuracy is also obtained from this point. , it is possible to estimate the residual prestress force of the PC girder.

Furthermore, it is possible to improve the reliability of the estimation result by repeated measurement at the same location, and continuous monitoring is also possible.

In addition, since the residual prestress force of PC girders can be accurately estimated with inexpensive strain gauges and π-type displacement gauges, it can be applied to many bridges. That is, it is possible to realize/provide a highly versatile method for estimating the remaining prestress force of a PC girder.

An embodiment of the PC girder residual prestress force estimation method according to the present invention has been described above. be.

For example, in the present embodiment, the bending moment acting on the measured cross section of the PC girder is obtained from the measurement results of the strain measuring means and the crack opening width measuring means. The load acting on the measured cross section of the PC girder may be obtained, and the inflection point at which the relationship between the average strain of the tensile reinforcing bars of the PC girder and the load acting on the cross section of the PC girder changes may be set as the starting point of crack re-opening. That is, even if the bending moment in this embodiment is replaced with a load, it is possible to achieve the configuration (logical configuration) and effects of the present invention.

1 PC girder 2 Crack 3 Strain measuring means 3a Strain gauge 3b Optical fiber 4 Crack opening width measuring means 4a π-type displacement gauge 4b Optical fiber O1 Axial direction (bridge axis direction)
P Crack opening starting point (inflection point)
P' starting point of crack opening (inflection point)

Claims (3)

A method for estimating the residual prestress force of PC girders in which bending cracks have occurred,
A strain measuring means for measuring the strain on the compression side and the tension side of the PC girder is attached to the surface of the PC girder, and a crack opening width measuring means for measuring the crack opening width of the PC girder is attached,
Using the measurement results of the strain measuring means and the crack opening width measuring means, determine the relationship between the average strain of the tensile reinforcing bars of the PC girder and the bending moment or load acting on the cross section of the PC girder,
The inflection point where the relationship changes is the starting point of crack re-opening,
The bending moment or load at the crack opening initiation point is defined as the bending moment or load at which the crack opening occurs,
A method for estimating a residual prestress force of a PC girder, characterized by estimating the residual prestress force of the PC girder using a bending moment or load when the crack opening occurs. In the residual prestress force estimation method for PC girders according to claim 1,
Using a π-type displacement meter as the crack opening width measuring means,
A PC characterized in that the average strain ε _sm of the tensile reinforcing bars before crack opening is calculated using the following formula (1), and the average strain ε _sm of the tensile reinforcing bars after crack opening is calculated using the following formula (2). Girder residual prestress force estimation method.

where _εg is the value of the lower edge strain gauge between cracks, _wmax is the value of the π-type displacement gauge at the crack, _lmax is the maximum crack spacing, and _dp is the gauge length of the π-type displacement gauge. In the residual prestress force estimation method for PC girders according to claim 1,
When using an optical fiber as the crack opening width measuring means and measuring the crack opening width of the entire measurement section including a plurality of cracks collectively with the optical fiber,
Calculate the average strain ε _sm of the tensile reinforcing bars before crack opening using the following formula (3), and the average strain ε _sm of the tensile reinforcing bars after crack opening using the following formulas (4) and (5). A PC girder residual prestress force estimation method characterized by:

where, ε _g is the value of the lower edge strain gauge between cracks, ε _o is the value of the lower edge optical fiber, n is the number of cracks included in the measurement range, w _mean is the average crack width, l _mean is the average crack interval, d _o is the length of the optical fiber.

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