CN1025240C - Detecting method of concrete absolute stress and elastic modulus - Google Patents

Abstract

The present invention relates to a novel detecting method of concrete absolute stress and elastic modulus, particularly to a ' blind hole relaxation-pressurization method', which is suitable for a built concrete member in which a sensor can not be buried in advance. The newly developed HJY-1 concrete absolute stress detecting device can reliably detect the absolute stress and the elastic modulus of various built concrete members.

Description

Detecting method of concrete absolute stress and elastic modulus

This method belongs to force measurement.

Application number is a kind of piezomagnetic concrete absolute stress pick-up unit that can directly demonstrate stress value of 88108972.9, is a kind of its sensor to be embedded in pick-up unit in the concrete member in advance, and is for built structure that can't pre-buried sensor, then inapplicable.

On built structure, detect the concrete absolute stress, two kinds of methods were once arranged.One says the core method of getting, promptly on the concrete member, drill through the concrete core, elder generation is the good strain-gauge rosette of surface arrangement of core before drilling through, detect because concrete core when being separated from member with strainmeter, the lax strain that causes, extrapolate original stress of measuring point more according to this, required elastic mould value is done experiment with the concrete core and is obtained.The required concrete core that drills through of this method is very big, and drilling machine is heavy and damage member or the like shortcoming, fails to promote.Another says the slit stress restoration, promptly cut out a slit on the concrete surface, put into lifting jack in the groove, exert pressure with sidewall to groove, set strainometer and displacement meter on the concrete surface of the both sides of groove in advance, detect since the lax strain that causes of grooving, lax displacement and since pressurization cause add compressive strain and pressurization displacement, when lax strain, lax displacement and when adding compressive strain, pressurization displacement equal and opposite in direction, opposite in sign, this moment, lifting jack institute applied pressure value was the absolute stress value of the former existence of concrete.This method a groove can only draw the stress value of a direction, and the grooving size is big, and is bigger to component damage, and can't draw the elastic mould value of concrete, and this value is a very important parameter, so also fail to promote the use of.So at present at home and abroad, Shang Wuke is put to the apparatus and method that practical concrete absolute stress and elastic modulus to built structure detect.

Purpose of the present invention just is to propose the concrete absolute stress of built structure and principle that elastic modulus detects, designs and manufactures pick-up unit and propose detection method.Manage to find out concrete member measuring point lax strain, add the relation between compressive strain and moulding pressure value and absolute stress and the elastic modulus, solve this problem.

The main points of this method are, at first bore the system blind hole, around blind hole point, arrange foil gauge or strain-gauge rosette earlier at concrete measuring point place, the size of blind hole, want to satisfy the requirement of detected value precision, do not influence the normal use of member again, especially will be applicable to small-sized concrete member, with a cover pressue device, to the sidewall pressurization of blind hole, the use instrument detecting goes out the lax strain around the blind hole and adds compressive strain, and to blind pore wall applied pressure value.After instrument is handled signal, the major principal stress value of promptly exportable measuring point concrete, least principal stress value, principle stress angle and elastic mould value.We claim this method to be " blind hole relaxes-pressurization ".

Accompanying drawings it

Fig. 1 is stress analysis of member measuring point and strain-gauge rosette arrangenent diagram.

1,2,3 answer the sheet sheet for resistance, L is the gauge length of resistance strain gage, and r. θ is a polar coordinates, and O is an initial point, and a is the radius of manhole,, r ₁For the resistance strain gage near-end to hole centre distance, r ₂Be the distance of resistance strain gage far-end to the center, hole, 6 ₁Be major principal stress, 6 ₂Be least principal stress, θ is resistance strain gage 1 and 6 ₁Angle, θ+- ₄Be resistance strain gage 2 and 6 ₁Angle, θ+- ₂Be resistance strain gage 3 and 6 ₁Angle.

The principle of this method is that as shown in Figure 1, the stress of member measuring point always can be regarded principle stress 6 as ₁, 6 ₂Two dimensional stress state, the stress of locating for (r, θ) at distance initial point polar coordinates is:

Tangential stress

$6_{\theta }=\frac{6_1{\mathrm{+6}}_2}{2}-\frac{6_1{\mathrm{-\; 6}}_2}{2}\mathrm{cos2\; \theta }$

Radial stress (1)

$6_1=\frac{6_1{\mathrm{+6}}_2}{2}+\frac{6_1{\mathrm{-\; 6}}_2}{2}\mathrm{cos2\; \theta }$

Drill through the manhole that radius is a at 0.After the perforate, (r, the θ) stress of locating according to Elasticity Kirsch formula are:

$6_0\mathrm{＇\; =}\frac{6_1{\mathrm{+\; 6}}_2}{2}\mathrm{(1+}\frac{a^2}{r^2}\mathrm{)\; -}\frac{6_1{\mathrm{-\; 6}}_2}{2}\mathrm{(1\; +}\frac{{\mathrm{3a}}^4}{r^4}\mathrm{)cos2\; \theta }$

$6_r{}^1=\frac{6_1{\mathrm{+\; 6}}_2}{2}\mathrm{(1-}\frac{q^2}{r}\mathrm{)\; +}\frac{6_1{\mathrm{-\; 6}}_2}{2}\mathrm{(1\; +}\frac{{\mathrm{3a}}^4}{r^4}-\frac{{\mathrm{4a}}^2}{r^4}\mathrm{)\; cos\; 2\theta \; (2)}$

Stress value was changed to (2)-(1) before and after boring caused (r, θ) boring

Be △ 6 _θ=6 ' _θ-6 _θ

△6 _r＝6′ _r-6 _r

To get in (1) (2) formula substitutions (3)

${\mathrm{△\; 6}}_{\theta }=\frac{6_1{\mathrm{+\; 6}}_2}{2}\times \frac{a^2}{r^2}-\frac{6_1{\mathrm{-\; 6}}_2}{2}\times \frac{{\mathrm{3a}}^4}{r^4}\mathrm{cos2\; \theta }$

${\mathrm{△\; 6}}_r=\frac{6_1{\mathrm{+\; 6}}_2}{2}\times \frac{a^2}{r^2}+\frac{6_1{\mathrm{-\; 6}}_2}{2}\mathrm{\times (}\frac{{\mathrm{3a}}^4}{r^4}-\frac{{\mathrm{4a}}^2}{r^2}\mathrm{)\; cos2\; \theta \; (4)}$

According to Hooke's law, locate at (r, θ), because the radial strain value △ ε that boring causes is:

△ε＝（△6 _r-μ△6 _θ）/E （5）

In fact, radial strain sheet as shown in Figure 1 is not a bit, but L=r ₂-r ₁, the mean strain value that foil gauge reflected is:

In (4) substitution (6), integration gets:

△ε _m＝A（6 ₁+6 ₂）+B（6 ₁-6 ₆）cos2θ （7）

In the formula

$\mathrm{A\; =\; -}\frac{a^2}{{\mathrm{2r}}_1{r}_2}\times \frac{\mathrm{1\; +\; \mu }}{E}$

$\mathrm{B\; =\; -}\frac{{\mathrm{2a}}^2}{r_1{r}_2}\times \frac{1}{E}\mathrm{［\; 1\; -}\frac{a^2{\mathrm{(1\; +\; \mu \; )\; (r}}^2{}_1{\mathrm{+\; r}}_1{r}_2{\mathrm{+\; r}}^2{}_2)}{{\mathrm{4r}}^2{}_1{r}^2{}_2}\mathrm{(8)}$

If form strain-gauge rosette by layout three sheet resistance foil gauges shown in Figure 1, counterclockwise compiling is 1,2, No. 3, with 6 ₁The angle of direction is respectively θ. and θ+π/4.0+ pi/2, it is because the strain value that boring causes is respectively △ ε _1m, △ ε _2mWith △ ε _3mIn its substitution (7): △ ε _1m=A(6 ₁+ 6 ₂)+B(6 ₁-6 ₂) cos2 θ

△ε _2m＝A（6 ₁+6 ₂）-B（6 ₁-6 ₂）sin2θ （9）

△ε _3m＝A（6 ₁+6 ₂）-B（6 ₁-6 ₂）cos2θ

Separating (9) gets:

Learn by (10), wish to get accurately 6 ₁, 6 ₂With the value of θ, △ ε accurately must be arranged _1m, △ ε _2m, △ ε _3m, the value of A and B, △ ε _1m, △ ε _2m, △ ε _3mCan record by detecting instrument.From (8), learn, remove a, r ₁, r ₂, outside can obtaining after bore diameter and foil gauge arrangement are determined, μ and E the unknown are arranged still.Known μ numerical fluctuations is little, but E has very big discreteness, and is also big to the influence of measurement result, so must reach out for elastic modulus E accurately.

If in circular hole shown in Figure 1, along hole wall apply uniform pressure q, then (r, θ) locate and will cause stress:

${\sigma }_1\mathrm{=\; -}\frac{a^2}{r^2}\mathrm{\times \; q}$

${\sigma }_{\theta }=\frac{a^2}{r^2}\mathrm{\times \; q\; (11)}$

(11) are made ess-strain by Hooke's law convert and carry out integration, can draw resistance strain gage radially owing to apply the mean strain value that uniform pressure q causes along hole wall and be:

${\mathrm{△\; \epsilon }}_1\mathrm{=\; -}\frac{a^2}{r_1{r}_2}\times \frac{\mathrm{1\; +\; \mu }}{E}\mathrm{\times \; q\; =\; 2Aq\; (12)}$

Then the elastic modulus of concrete is:

$\mathrm{E\; =\; -}\frac{a^2}{r_1{r}_2}\times \frac{\mathrm{1+\mu }}{{\mathrm{△\; \epsilon }}_1}\mathrm{\times q\; (13)}$

As seen, as long as detect q and △ ε _j, can obtain E.So far, in theory, 6 of measuring point concrete ₁, 6 ₂, θ and E all can record exactly.

According to analyzing and test, we get aperture a=3.5cm, foil gauge gauge length L=8cm, and its near-end is apart from center, hole r ₁=4.5cm, its far-end is apart from center, hole r ₂=12.5cm, μ=1/6, the relevant formula in difference substitution front can draw:

And

E＝-0.25q/△ε _j

When measuring point is a two-dimensional state of stress, but principal direction of stress is known, then only needs along two principal directions of stress 6 ₁, 6 ₂, arrange that two foil gauges get final product.Principle stress formula and (14) are together.

When measuring point is a uniaxial stressed state, and principal direction of stress is known, then only needs to arrange that along 6 directions a slice foil gauge get final product.Its principle stress formula is:

6＝0.57×q×△ε _m/△ε _j

Above-mentioned being " blind hole relaxes-pressurization " detected the ultimate principle of concrete absolute stress and elastic modulus, design in view of the above, succeeded in developing by sensor, drilling machine, added and present a theatrical performance as the last item on a programme and pick-up unit that concrete absolute stress detector is formed, named and be HJY-1 structure concrete absolute stress pick-up unit.

Formula (14) (15) (16) is to derive out according to the theory of elasticity that drills through the hole on the infinite field elastic sheet.For blind hole, for satisfying (14) (15) (16) three formulas, still need and solve hole depth, aperture problem, solution and satisfy measuring point and have enough lax and add compressive strain output and do not influence again under the normal situation about using of member, this this great problem of gauge length much and foil gauge of blind hole solves measuring point place this great problem of member boundary dimensions.For this reason, we have carried out mechanical analysis, result of calculation, blind hole aperture 70mm, hole depth 70-80mm, foil gauge gauge length are 80mm, near-end is apart from center, hole 4.5cm, far-end is apart from center, hole 12.5mm, and moulding pressure is 5MPa, in the case, drill through the strain output that blind hole causes, resolving accuracy for detecting instrument is enough big, and the poroid stress that causes with circular port is concentrated minimum, and very limited in the concentrated scope of blind hole ambient stress, it is also fast to decay, the 3.5cm place has only 22% influence from the limit, hole, from 7cm place, limit, hole, has not influenced substantially.That is to say, drill through such blind hole, do not influence the normal use of member.Result of calculation also shows, if the minimum border of member from the measuring point center greater than 17.5cm(2.5 times of aperture), the test error that causes by the border

Can ignore.This is enough to explanation, and " blind hole relaxes-pressurization " is applicable to the bridge member of all kinds and other engineering component, and this is that " slit stress restoration " is incomparable.

What no matter arrange is a slice foil gauge or strain-gauge rosette, after arranging, gathers the lax strain around the blind hole and adds compressive strain with this same foil gauge or strain-gauge rosette.

If measuring point is arranged in defective member position just, locate as crack, hole etc., or the sticking Quality of foil gauge is not good, the capital has influence on the reliability of testing result, and to this, determination methods is, under the pressure effect of 5MPa, pressurization strain value effective range gets-80 * 10 ^-6～-25 * 10 ^-6, every foil gauge pressurization strain value and on the same group between difference and the mean strain value of strain rosette pressurization strain mean the absolute value of ratio just prove that less than 20% testing result is reliable, effective.

" blind hole is lax "-pressurization " and supporting HJY-1 type concrete absolute stress pick-up unit, be the breakthrough of concrete absolute stress detection technique, the real initiative that belongs to.

China's existing highway bridge 4,220,000 linear meter(lin.m.)s.Press the minimum flow measuring and calculating, also there is 4% substandard bridge to rebuild, investment at least also needs 2,000,000,000 yuan, if the method and the supporting pick-up unit thereof that propose with us detect and estimate, then needn't all rebuild, only need to drop into the 20-30% of reconstruction expenses, suitably reinforce, can recover and improve the bearing capacity of old bridge, thereby be that country saves a large amount of valuable funds, also may be used in the concrete member of engineerings such as road, harbour, tunnel, dam, house.Promote generally and use, can obtain remarkable economic efficiency and social benefit.

Claims (6)

1, a kind of new concrete absolute stress detection method, at concrete measuring point surface arrangement resistance strain gage, and resistance strain gage is connected with concrete absolute stress pick-up unit, hole at the measuring point place, concrete absolute stress pick-up unit records lax strain and stores, evenly exert pressure to hole wall with adding to present a theatrical performance as the last item on a programme, being pressurizeed and recorded the pressurization strain value by the control of concrete absolute stress pick-up unit also stores with the force value that applies, and concrete absolute stress pick-up unit calculates absolute stress value and the elastic modulus and the printout of measuring point; The method that resistance strain gage is arranged is, when measuring point is a two-dimensional state of stress, and principal direction of stress is known, then along two principle stresses 6 ₁, 6 ₂Direction is arranged two sheet resistance foil gauges, if measuring point is a uniaxial stressed state, and principal direction of stress is known, then arranges a slice resistance strain gage along 6 directions, except that above two kinds of situations, then arranges three sheet resistance foil gauges, and L102=L203=- ^π ₄, it is characterized in that the hole of being bored is a blind hole, the hole is rounded, and aperture 70mm, hole depth 70-80mm, resistance strain gage gauge length 80mm, near-end are apart from center, hole 45mm, and far-end is apart from center, hole 125mm, and the uniform pressure value that applies to hole wall is 5MPa.

2, a kind of according to claim 1 new concrete absolute stress detection method is characterized in that the minimum border of measuring point centre distance concrete member is greater than 175mm.

3, a kind of according to claim 1 new concrete absolute stress detection method is characterized in that the method for judging testing result validity is, under the effect of 5MPa pressure, pressurization strain value effective range gets-80 * 10 ^-6-25 * 10 ^-6, the absolute value of the ratio between the equal strain value of difference peace of every sheet resistance foil gauge pressurization strain value and resistance-strain film clips pressurization strain mean on the same group is less than 20%.

4, a kind of new concrete elastic modulus detection method, hole at measuring point, be connected at the measuring point surface arrangement resistance strain gage of concrete and with concrete absolute stress pick-up unit, evenly exert pressure to hole wall with adding to present a theatrical performance as the last item on a programme, controlled pressurization and recorded the pressurization strain value and force value that applies and storage by concrete absolute stress pick-up unit, concrete absolute stress pick-up unit calculates the elastic modulus and the printout of this measuring point; The method that resistance strain gage is arranged is, when measuring point is a two-dimensional state of stress, and principal direction of stress is known, then along two principle stresses 6 ₁, 6 ₂Direction is arranged two sheet resistance foil gauges, if measuring point is a uniaxial stressed state, and principal direction of stress is known, then arranges a slice resistance strain gage along 6 directions, except that above two kinds of situations, then arranges three sheet resistance foil gauges, and＜102=＜203=- ^π ₄, it is characterized in that the hole of being bored is a blind hole, the hole is rounded, and aperture 70mm, hole depth 70-80mm, resistance strain gage gauge length 80mm, near-end are apart from center, hole 45mm, and far-end is apart from center, hole 125mm, and the uniform pressure value that applies to hole wall is 5MPa.

5,, it is characterized in that the minimum border of measuring point centre distance concrete member is greater than 175mm as a kind of new concrete elastic modulus detection method as described in the claim 4.

6, as a kind of new concrete elastic modulus detection method as described in the claim 4, it is characterized in that the method for judging testing result validity is, under the effect of 5MPa pressure, pressurization strain value effective range gets-80 * 10 ^-6～-25 * 10 ^-6, the absolute value of the ratio between the equal strain value of difference peace of every sheet resistance foil gauge pressurization strain value and resistance-strain film clips pressurization strain mean on the same group is less than 20%.