CN100443879C - Double arm type tester for shear strength - Google Patents

Abstract

The present invention discloses a double arm type tester for shear strength. The double arm type tester mainly comprises a load sensor, shear strength heavy frames, a press plate, a positioning screw rod and a shear strength supporting seat, wherein the shear strength heavy frames are connected with the load sensor; the press plate is arranged above a test piece; the positioning screw rod is movably connected with the press plate; the shear strength supporting seat is used for supporting the test piece; two shear strength heavy frames are convenient for stress and reduce self-weight supporting arms with variable cross sections; a special clamping tool for fixing fiber cloth at both sides of a piece to be tested is arranged at the lower end of each of the supporting arms for positioning and skid prevention; the present invalid has the advantages of simple structure, favorable centering effect and stable performance; the load sensor not only can accurately and sensitively reflect load at all levels but also can be connected with a computer to directly sample and process the relation curve of the load and the output of other testing instruments on the test piece; the shear strength heavy frames are core components of the present invention; in the test, each of the supporting arms mainly bear bending load; for the test piece, the stress direction of the fiber cloth keeps unchanged; the test data is accurate with little error.

Description

Double arm type tester for shear strength

Technical field:

The present invention relates to a kind of testing tool, relate in particular to the double arm type tester for shear strength of cohesive strength between a kind of fiber cloth that in engineering construction and scientific research, is used for testing concrete and reinforcing engineering

Background technology:

Be about to fiber cloth and be affixed on concrete surface since fiber cloth material is used for engineering construction with enhancing, reinforcing, mending concrete structure, thereby improved greatly since the technology popularization of structure tension performance, more and more deep around the experimental study of mechanical property, adhesive method, fiber cloth and the concrete cohesive strength etc. of fiber cloth material.The fiber cloth material comprises carbon cloth CFRP, glass fabric GFRP, aryl fiber cloth AFRP, hybrid fiber cloth etc.The fiber cloth that is applied in the reinforcing engineering mainly is carbon cloth and glass fabric, and its tensile strength is substantially between 2000～4000Mpa.

Following several method is mainly adopted in the test of research fiber cloth and concrete binding intensity both at home and abroad at present:

1. curved scissors method: by two concrete blocks of casting with condition by fiber cloth in bottom adhesive, load by testing machine then.By can directly measuring stressed load on the testing machine.Can calculate concrete shearing strength by the actual loading area between fiber cloth and the concrete.Zhengzhou University etc. adopt this method test.This method is fairly simple, can directly utilize testing machine to load.Stressed each position of the fulcrum is clear and definite.But practical operation is difficulty relatively, is easy to make produce between fiber cloth and the concrete peel off, and the success of the test rate is low.And the stressed back of test specimen born pure shear and carried out the transition to gradually to bear to press and cut by initial between fiber cloth and the concrete because the extension of fiber cloth causes after the amount of deflection of test specimen increases, and makes that the shear value between fiber cloth and the concrete is bigger than normal.Be applied to cause the dangerous of engineering in the actual engineering with this calculated value of doing the basis.

2. single armed draws the method for cutting: this method is in fiber cloth tension process, and direction is constant always, promptly is in pure shearing between fiber cloth and the concrete always.Do so stressed clear and definite, convenience of calculation.The document of having seen has relevant scholars such as Dalian University of Technology, The Hong Kong Polytechnic University all to use this test method.But under this principle, test method is different.Its common feature is that auxiliary equipments such as the balance that needs, location, power transmission are many, test unit expense height, and install complicatedly, and the test difficulty is big, also changes in test stress condition easily, and test findings also can be different because of test method.

3. the double-arm method of cutting of drawing: this method in process of the test, concrete both sides fiber cloth stress balance, and do not change from start to finish and be subjected to force direction, it is clear and definite to shear mechanism, is desirable testing program.But the actual tests difficulty is big.No matter how strict because construction technology and test operation, fail in shear all can not take place in two faces simultaneously that paste fiber cloth on the concrete, always has successively.Like this at failure stage, if do not have good safeguard procedures and device, then be easy to cause the accident, and in fact the both sides patch can only obtain and destroy shear value on one side at first, another side can't be tested difficulty and gets its value because of lacking equilibrium condition.So, can only in relevant document, find the test that Zhao Hai Dong of Tongji University loads with lifting jack so far.But his this test method need be with an attached lifting lifting jack.Not only annex is many, and installation centering difficulty is big, and the placement of test specimen horizontal direction, and pin joint is many.Also can make payload values bigger than normal during loading because of the friction force of supporting.

Summary of the invention:

For the accuracy that improves cohesive strength between test fiber cloth and the concrete and the security of test, reduce test error, reduce and detect labour intensity and troublesome poeration, the invention provides a kind of simple in structure, installation, easy to operate, safety, the double arm type tester for shear strength that test data is accurate, error is little.

Technical scheme of the present invention realizes in the following manner:

A kind of double arm type tester for shear strength, it mainly comprise load transducer, be connected with load transducer cut strong heavy frame, it is characterized in that: cutting strong heavy frame has two both to be convenient to stressed, can reduce the variable cross section sway brace of deadweight again, test specimen both sides fiber cloth is all arranged fixedly with location and anti-skidding special anchor clamps at the lower end of each arm, place pressing plate above the test specimen, be connected with pressing plate work usefulness the location screw mandrel, be used to support the strong bearing of cutting of test specimen.

Cut and cut the supporting of strong basis seat under the strong bearing, the location screw mandrel is four, surrounds rectangle, and each screw mandrel upper end is connected on the pressing plate by screw thread, nut, and the lower end spiral is connected on the pedestal.

In order accurately to test the pulling force that fiber cloth is born on the test specimen, on each sway brace, be provided with strainometer by Wheatstone bridge principle group bridge, stable performance.

Good effect of the present invention is:

1, utilize the testing machine load operation convenient, centering is effective, stable performance, and also common laboratory has, and can directly develop its function.Cutting on the disposable crossbeam that is installed on testing machine of strong instrument, just can save later installation, to medium operation, reduce labor intensity greatly.Load control is also than being easier to.

2, load transducer both can reflect loads at different levels accurately, in high sensitivity, can be connected the relation curve of other test instrumentations outputs on Direct Sampling and processing load and the test specimen again with computing machine.Load transducer can be selected product or oneself making of instrument manufacturing plant production according to testing requirements for use.

3, cutting strong heavy frame is core component of the present invention, and in the test, each support arm all mainly bears curved pressure load, but for test specimen, fiber cloth is subjected to force direction constant always.In order accurately to measure the pulling force that fiber cloth is born on the test specimen, the present invention lays the strainometer of high sensitivity, high stability specially on each support arm, thereby the warranty test data are accurately reliable.

Description of drawings:

Fig. 1 is a structural representation of the present invention.

Fig. 2 is the Wheatstone bridge principle schematic of strainometer of the present invention.

Embodiment:

The invention will be further described below in conjunction with accompanying drawing:

As seen from Figure 1: the present invention mainly comprise load transducer 1, be connected with load transducer 1 cut strong heavy frame 3, place pressing plate 4 above the test specimen 5, be connected the screw mandrel 6 that is used to locate with pressing plate work, be used to support the strong bearing 8 of cutting of test specimen 5, it cuts strong heavy frame 3 has two both to be convenient to stressed, can reduce the variable cross section sway brace of deadweight again, the lower end of each arm is provided with the location and the anti-skidding special anchor clamps of anchoring fiber cloth.

Be it can also be seen that by Fig. 1: cut strong bearing and cut 9 supportings of strong basis seat for 8 times, location screw mandrel 6 surrounds rectangular parallelepiped and is installed on around the test specimen.Each screw mandrel upper end is connected on the pressing plate 4 by screw thread, nut, and the lower end is connected on the pedestal 9.

By Fig. 1, Fig. 2 as can be seen: in the test, each arm all mainly bears curved pressure load, but for test specimen, fiber cloth is subjected to force direction constant always.In order accurately to measure the pulling force that fiber cloth is born on the test specimen, the present invention lays on each arm specially and presses Wheatstone bridge principle group bridge, the high sensitivity of stable performance, the strainometer of high stability, when the testing machine loading, fiber cloth on the test specimen just passes to power cuts strong support force arm, this power also acts on counter-force on the support by the support entablature, and reach dynamic balance, thereby make support arm bear curved pressure effect, be installed in support arm two foil gauges up and down and produce stretching and compression deformation respectively.If the resistance before strainometer is not stressed is respectively R ₁And R ₂, its resistance of stressed back becomes R respectively ₁+ Δ R ₁, R ₂-Δ R ₂Because the variation of environment temperature also can make the strainometer resistance produce Δ R _T1With Δ R _T2Variation.Use for convenience, the strainometer that the present invention pastes on arm is same resistance, same specification, with technology, so Δ R ₁=Δ R ₂=Δ R and Δ R _T1=Δ R _T2=Δ R _t, under the acting in conjunction of external force and temperature, the resistance of two foil gauges is respectively like this:

R ₁→R+ΔR+ΔR _t，R ₂→R-ΔR+ΔR _t

The fundamental formular of Wheatstone bridge output is:

$\mathrm{\ΔU}=\frac{U}{4}(\frac{\mathrm{\Δ}{R}_1}{R_1}-\frac{{\mathrm{\ΔR}}_2}{R_2}+\frac{{\mathrm{\ΔR}}_3}{R_3}-\frac{\mathrm{\Δ}{R}_4}{R_4})---\left(2\right)$

Because $\frac{\mathrm{\ΔR}}{R}=\mathrm{k\ϵ}---\left(3\right)$

So, when single armed is worked:

$\mathrm{\&Delta;U}=\frac{\mathrm{<figure-callout\; id="4"\; label="U"\; filenames="C20051001759800081.png"\; state="\{\{state\}\}">U</figure-callout>}}{4}\&CenterDot;\frac{\mathrm{\&Delta;R}}{R}=\frac{\mathrm{<figure-callout\; id="4"\; label="Uk"\; filenames="C20051001759800081.png"\; state="\{\{state\}\}">Uk</figure-callout>}}{4}\mathrm{\&epsiv;}---\left(4\right)$

The present invention adopts the half-bridge connected mode with two strainometers, and then it is output as:

$\mathrm{\&Delta;U}=\frac{U}{4}[\frac{\mathrm{\&Delta;R}+{\mathrm{\&Delta;R}}_t}{R}-\left(\frac{-\mathrm{\&Delta;R}+\mathrm{\&Delta;}{R}_t}{R}\right)]=\frac{U}{2}\&CenterDot;\frac{\mathrm{\&Delta;R}}{R}=\frac{\mathrm{Uk}}{2}\mathrm{\&epsiv;}---\left(5\right)$

Compare (4) and (5) as can be seen, its sensitivity output doubled when the senser element that adopts half-bridge to form was worked than single armed, but also can carry out temperature self-compensation.The present invention simultaneously not only makes sensor output sensitivity height, and stable performance.In test in continuous 4 hours, its temperature change value is no more than 4 μ ε, almost completely can omit.

During test, test specimen 5 is placed on cuts on the strong bearing 8, with pressing plate 4 and location screw mandrel 6 with test specimen 5 location.Sensor 1 by connecting screw 2 with cut strong heavy frame 3 and be connected, with the special anchor clamps of cutting two sway brace lower ends on the strong heavy frame 3 fiber cloth of test specimen 5 both sides is clamped and can carry out load test.

Generally speaking, the bearing capacity of Reinforced concrete Structure Experiment equipment all will unconditionally surpass more than 70% of test specimen limit load.The sensing element of heavy frame of the present invention and each supporting arm is carrying out under the identical stress condition with test in the demarcation under the loads at different levels, and calibration range exceeds test specimen estimation ultimate load.From the test calibration curve as can be seen, it is very approaching to cut two outputs of arm under loads at different levels of strong instrument, and " zero wafts " value of instrument less than 4 μ ε, reached complete negligible degree in 4 hours simultaneously.This shows makes the precision height, and the barbola work of strainometer is good.And under every grade of load, the output valve of two sway brace strain output total values and upper load sensor is very identical.Illustrate that the moving reactivity worth of cutting strong instrument is very good, also got rid of various disturbing factors in the explanation work.Therefore, the test value in the test is accurately believable.This explanation is cut Qiang Yicong and is designed into making and all reaches a high level.

Claims (2)

1, a kind of double arm type tester for shear strength, it mainly comprises load transducer (1), what be connected with load transducer (1) cuts strong heavy frame (3), it is characterized in that: cutting strong heavy frame (3) has two both to be convenient to stressed, can reduce the variable cross section sway brace of deadweight again, the special anchor clamps of fixing test specimen both sides fiber cloth are all arranged with location and anti-skidding at the lower end of each arm, place the pressing plate (4) above the test specimen (5), with the pressing plate location screw mandrel (6) that is connected usefulness alive, what be used to support test specimen (5) cuts strong bearing (8), is provided with on each sway brace by Wheatstone bridge principle group bridge, the strainometer of stable performance.

2, double arm type tester for shear strength according to claim 1, it is characterized in that: cut and cut strong basis seat (9) supporting under the strong bearing (8), location screw mandrel (6) is four, surround rectangle, each screw mandrel upper end is connected on the pressing plate (4) by screw thread, nut, and the lower end spiral is connected on the pedestal (9).

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