CN110823699A - Improved temperature stress testing machine of strain acquisition system - Google Patents
Improved temperature stress testing machine of strain acquisition system Download PDFInfo
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- CN110823699A CN110823699A CN201911196555.7A CN201911196555A CN110823699A CN 110823699 A CN110823699 A CN 110823699A CN 201911196555 A CN201911196555 A CN 201911196555A CN 110823699 A CN110823699 A CN 110823699A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/36—Embedding or analogous mounting of samples
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/18—Performing tests at high or low temperatures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/36—Embedding or analogous mounting of samples
- G01N2001/366—Moulds; Demoulding
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Abstract
The invention relates to a concrete temperature stress testing machine, which comprises a free test piece strain acquisition part and a constraint test piece strain acquisition part; the free test piece strain acquisition part directly measures the concrete deformation by measuring the relative displacement of a prismatic rod which is pre-embedded in the concrete and passes through the hole of the movable assembly; the strain acquisition part of the constraint test piece can calculate the deflection of the vertical prism rod through a double displacement sensor, and the real horizontal strain of the central part of the concrete is obtained by subtracting the strain acquisition measured value of the free test piece from the measurement calculation value of the constraint test piece. The scheme improves the reliability and repeatability of the test; the whole operation is simple, and the measurement precision is high.
Description
Technical Field
The invention relates to the field of concrete buildings, in particular to a concrete temperature stress testing machine.
Background
Volume shrinkage phenomenon occurs due to changes in moisture contained in concrete, chemical reactions, temperature changes, and the like at the initial stage of setting or during hardening of concrete.
When the concrete is in a free state, the concrete shrinkage does not cause obvious adverse effects. However, in actual engineering, the concrete structure is restrained by the foundation, the steel bars or adjacent parts to be in different restraint states, so that concrete tensile stress is caused, and the concrete shrinkage cracks are easy to generate due to low tensile strength of the concrete. The generation of concrete cracks affects the bearing capacity and the service life of the structure slightly, and catastrophic accidents are caused seriously, so that huge loss is brought to national economy, and great threat is brought to the safety of people. Therefore, the evaluation of the cracking risk of the concrete in the early stage is significant.
The temperature stress tester (called TSTM) is an important tool for researching the early cracking resistance of concrete, and consists of a constraint test piece, a free shrinkage test piece, a temperature control system and a computer control system. The crack resistance and the crack risk of the concrete are comprehensively evaluated by recording the characteristics of free deformation, constrained deformation, temperature change, constrained stress and the like of the early concrete and using the parameters of the crack temperature, the crack stress and the like. Is one of the most advanced devices for evaluating the cracking risk of concrete at present.
However, the existing TSTM method for measuring concrete deformation has obvious defects.
In the aspect of deformation measurement of the constrained test piece, people directly measure the change of the relative distance between the transverse ends of the motor at first to represent the deformation of the constrained concrete test piece. However, a certain distance exists between the test mold and the concrete, and the shrinkage and expansion of the concrete cannot be timely transferred to the movement of the test mold. Similarly, in the deformation measurement of the free shrinkage test piece, there is a method of measuring the displacement of the movable end of the dog-bone shaped concrete test mold to express the shrinkage amount of the free test piece. The friction resistance between the test mold and the upper-layer cover and the lower-layer slide rail is neglected.
Most researchers embed two steel rods with fixed intervals at the side surface of concrete, and a long carbon fiber rod parallel to the concrete is connected to the top end of one steel rod, and a linear variable differential displacement transducer (LVDT) is connected to the other steel rod. The recording of the displacement of the carbon fiber rod by the LVDT represents the deformation of the concrete measurement zone. Considering the flowability and heat preservation requirements of fresh concrete, the opening of the side surface of the mould is not too large. Therefore, the method is more dependent on the experience of the operator. And the steel rod is difficult to ensure the level and is not contacted with the test die. If the overhanging steel rod contacts the open hole of the test mould, the steel rod will twist, and it should be measured that the shrinkage is the expansion. In addition, the complicated deformation of the concrete can also cause the steel rod to twist. This explains that much of the test data during the cooling phase is instead dilatant.
To solve this problem, one has used two rods horizontally through the concrete and measured the relative displacement at the ends on both sides with LVDT, then the average of the readings on both sides represents the deformation in the centre of the measurement zone of the concrete. This deformation measurement method may cause great difficulty in removing the concrete specimen after the test, so that the accuracy of the instrument is impaired.
The lacing and Yu design a large "environmental box" that contains the concrete specimen and all equipment during the measurement process. Also, someone has even transformed the entire room into an "environmental box" and the deformation of the concrete is also measured by embedding steel rods on both sides. Since the displacement sensor is in an "environmental chamber," it is difficult to ignore the effects of temperature changes on the measurement device even if some compensation process is performed, which adds significant uncertainty to the measured data. More importantly, because the environmental chamber is too large, the concrete moisture is difficult to ensure and not to dissipate, the temperature change of the concrete is difficult to obtain the timely environmental chamber compensation, and the sensitivity of temperature control is greatly reduced. In addition, the high cost also makes the method difficult to popularize.
Some also embed an embedded displacement sensor directly into the concrete to test the "true deformation" of the concrete. This method is expensive because the sensor can only be used once, and the deformation it tests is a local deformation of the concrete and does not represent an overall deformation.
It is worth mentioning that the same deformation acquisition method is used for the free test piece and the constrained test piece of the current temperature stress testing machine. This is not necessary because the constraint specimen increases the difficulty of deformation acquisition due to the limitation of the loading end, and the free specimen can directly reflect the concrete deformation completely by the relative displacement of the two ends.
Theoretically, as long as the environmental influences such as temperature and humidity of the two test pieces and the self-pouring quality are ensured to be the same, the deformation of the concrete is accurately measured to be the same regardless of the measuring method.
Besides, the TSTM is a comprehensive test considering the influence of multiple factors, and the following points need to be ensured while accurately measuring the deformation:
1. the concrete needs to be sealed and insulated as much as possible to ensure no humidity loss. The temperature control needs to be as sensitive as possible without generating temperature gradients due to sudden changes in the external environment. In addition the temperature distribution of the concrete needs to be as uniform as possible.
2. Friction and contact of the concrete with external devices is minimized. In addition, the concrete has enough space to expand and contract. The stress uniformity of the concrete is not disturbed.
3. To ensure the convenience of concrete form removal, the precise attribute of the TSTM testing machine determines that the concrete must be as simple and quiet as possible when removed, and severe vibration and knocking are avoided.
In summary, it is urgently needed to improve the strain acquisition method of the current temperature stress testing machine on the premise of ensuring the heat preservation and insulation, small friction and convenient die removal of the test, and improve the reliability and repeatability of the test.
Disclosure of Invention
The invention improves the strain acquisition method of the current temperature stress tester on the premise of ensuring the heat preservation and insulation, small friction and convenient die removal of the test, and improves the reliability and repeatability of the test; the temperature stress testing machine is simple to operate, high in measurement precision and different in free and constrained test piece strain acquisition modes.
A concrete temperature stress testing machine comprises a free test piece strain acquisition part and a constraint test piece strain acquisition part; the free test piece strain acquisition part directly measures the concrete deformation by measuring the relative displacement of a prismatic rod which is pre-embedded in the concrete and passes through the hole of the movable assembly; the strain acquisition part of the constraint test piece can calculate the deflection of the vertical prism rod through a double displacement sensor, and the real horizontal strain of the central part of the concrete is obtained by subtracting the strain acquisition measured value of the free test piece from the measurement calculation value of the constraint test piece.
The fixed end assembly is used for fixing the displacement sensor and is kept immovable close to the end part of the mould.
The movable end assembly is made of light, hard and good heat insulation effect materials. The membrane is used to prevent concrete flow during concrete placement and additionally to prevent loss of concrete temperature.
The displacement sensor measures the position of the metal disc, the surface of the metal disc is polished smoothly, the metal disc is fixed to the top end of the prism rod, and the prism rod penetrates through the hole of the moving end and is not constrained by the moving end.
The steel block is clamped between the movable end and the fixed end and is used for propping the movable end to prevent the movable end from moving when concrete is poured, and the steel block is taken down after initial setting of the concrete.
The displacement sensor is a sensor with high LVDT precision (the measurement precision reaches more than 1 micron) for displacement measurement.
And a group of fixed end assembly and movable end assembly are respectively arranged at the left side and the right side in the test mould. The fixed end assembly is made of stainless steel materials with high density, high durability and low cost, is used for fixing the displacement sensor and keeps stable and immovable by abutting against the end part of the mold.
The steel block plays an auxiliary role, and when concrete is poured, the steel block is clamped between the fixed end assembly and the movable end assembly, so that the movable end assembly is fixed. When the measurement is started, the small steel blocks are removed, the movable end assembly can move along with the expansion of the concrete, the concrete cannot be prevented from moving when the concrete shrinks, and the measured data are free deformation of the concrete.
The prismatic rods are hard, low density materials with low expansion rates, such as small engineering plastics that are affected by temperature changes. And screwing the metal disc which is polished to be smooth into the screw hole at the end part of the prismatic rod. The prism is then inserted into the mold through the hole of the moving end assembly. To keep the prism rod horizontally fixed, a rigid foam ring is padded in the hole of the moving end assembly to keep the prism horizontal and no settlement occurs. And when the concrete is initially set, the foam ring is taken down to be replaced by the low-density sponge ring with larger holes, so that the temperature loss is prevented on the premise of ensuring the free displacement of the prism. And finally representing the free deformation of the concrete through the relative horizontal displacement of the left prism and the right prism which are pre-embedded in the concrete. Eliminating the influence of torsional deformation of concrete. And finally, installing a displacement sensor on the fixed end and compressing the displacement sensor on the metal disc at the end part of the prismatic rod to a middle proper position to ensure that the tension and compression have enough measurement range, and representing the free deformation of the concrete through the relative horizontal displacement of the left prismatic rod and the right prismatic rod which are pre-embedded in the concrete.
The test mold cover only covers the concrete test piece and the two side moving ends, but does not cover components such as a displacement sensor. Thus, the core assembly for testing concrete deformation is the same as the surrounding environment and is not influenced by the temperature change of the concrete.
The free test piece strain acquisition part of the concrete temperature stress testing machine comprises:
the fixed end, the steel block and the movable end assembly are placed on two sides of the test mold close to the end part of the mold, and the steel block is clamped between the movable end and the fixed end and used for supporting the movable end to prevent the movable end from moving when concrete is poured. The metal disc is screwed into the screw hole in the end of the prismatic rod and inserted into the mold through the hole in the movable end assembly, held horizontally in place by the hard foam. And pouring concrete into the test mold, and compacting by using a vibrating rod to wrap the prismatic pole. After the concrete is initially set, the cushion block is taken down, the foam ring on the hole prism rod is replaced with a large-hole soft sponge ring, the displacement sensor is installed on the fixed end, and the position is adjusted to enable the displacement sensor to be pressed on the metal disc at the end part of the prism rod. And finally representing the free deformation of the concrete through the relative horizontal displacement of the left and right prismatic rods pre-embedded in the concrete.
The invention relates to a strain acquisition part of a restraint test piece of a concrete temperature stress testing machine, which comprises: the device comprises a die, an installation frame, a displacement sensor, a prism rod and a metal disc part thereof, a foam fixing plate, a foam heat insulation plate and a light sponge block.
The displacement sensor measures the displacements of the prism rod at different heights by adopting an upper LVDT and a lower LVDT, takes the distortion deformation of the concrete into consideration, and can obtain the real displacement of the central part of the concrete through calculation.
The installation frame is fixed on the girder steel of testing machine both sides. A double-displacement sensor is arranged on the mounting frame. The frame is made of a material with low temperature deformation coefficient, high strength and high stability.
The prism rod and the prism rod for the free test piece are made of the same material and are prisms with rectangular sections. The prism rod is inserted into the middle of the concrete to enable the prism rod to deform synchronously with the concrete, screw holes are arranged at fixed intervals for installing metal discs, the upper displacement sensor and the lower displacement sensor are respectively pressed on the corresponding metal discs to record the displacement of the discs, and the real deformation of the center layer of the concrete is reflected through calculation. Finally, strain is obtained through the relative displacement of the concrete center.
The foam fixing plate is a thick plate which is protruded with a certain height and used for fixing the prism and is made of foam materials for preventing the prism from inclining and settling, the thick plate is respectively covered at two ends of the dog bone test mould, and when the foam fixing plate is inserted into the upper section of the prism rod with a specific size, the other end of the prism can be ensured to be in the middle layer position of the test mould.
The foam insulation board is a thick foam board with a large rectangular hole, and the rectangular hole is arranged to prevent the foam insulation board from contacting the prism rod in the test process and prevent the prism rod from moving along with the concrete. And after the concrete is initially set, the foam fixing plate is changed into a foam insulation plate, a layer of sponge block with extremely low quality is sleeved on the prism, and the large hole in the foam plate is covered by the sponge block, so that the temperature loss through the hole in the measuring process is reduced on the premise of ensuring that the displacement of the prism rod is not influenced.
The concrete temperature stress testing machine is applied to the constraint test piece strain acquisition condition:
two fixed foam boards are respectively covered at two ends of the dog bone test mould, and the prismatic rod is vertically inserted to ensure that the bottom of the prismatic rod is in the middle layer position of the test mould. And after the concrete is initially set, the fixed foam board is changed into a foam insulation board with large holes, and a layer of sponge block with extremely low quality is sleeved on the prism rod to ensure that the large holes on the foam board are covered by the sponge block. Two LVDTs were mounted on the mounting frame and compressed against metal discs on the prism bars, with two contact points L from the bottom of the prism bars, respectively1And L2. The translation distances of the upper LVDT and the lower LVDT recording discs after a certain time are respectively X1And X2And the real displacement of the concrete center is X, then X can be calculated by the formula 1.
The mold and the cover of the temperature stress testing machine are both provided with temperature control devices, and the temperature control devices achieve the purpose of temperature control by arranging water pipes and introducing hot water into the water pipes; in the arrangement of the temperature control water inlet pipe, the water inlet pipe and the water outlet pipe are distributed at intervals, so that the surface of the concrete is heated more uniformly in the process of heating and cooling the concrete.
Lubricating oil, a vinyl film, lubricating oil and a vinyl film are laid at the bottom of the position where the test piece is placed in the temperature stress testing machine from bottom to top. The use of two films has the advantage of better friction reduction and prevention of moisture loss.
The two sides of the position for placing the test piece in the temperature stress testing machine are provided with the thin foaming plates for brushing oil, and when the concrete is expanded in the initial stage of hydration and heat release, the foaming plates can absorb transverse expansion, so that transverse restraint is reduced, and friction is further reduced.
The method for measuring the real displacement of the concrete center by using the concrete temperature stress testing machine comprises the following steps:
step 1: laying oil and a vinyl film in a free test mold;
step 2: placing two groups of fixed end assemblies, a steel block and a movable end assembly on two sides of a test mold; screwing a metal disc into a screw hole at the end of the prismatic rod; inserting the prism into the mold through the hole of the movable end assembly, and padding a hard foam ring in the hole of the movable end assembly to keep the prism rod horizontally fixed and not to settle;
and step 3: and pouring concrete into the test mold, compacting by using the vibrating rod, and enabling the concrete not to be higher than the test mold. After leveling, the cover is covered with vinyl film and the heat preservation cover is immediately sealed. Adjusting the prism rod through a level gauge to keep the prism rod horizontally fixed;
and 4, step 4: after the concrete is initially set, the cushion block is taken down, the foam ring on the hole prism rod is replaced with a large-hole soft sponge ring, the displacement sensor is installed on the fixed end, the position is adjusted to enable the displacement sensor to be compressed on the metal disc at the end part of the prism rod, and finally the free deformation X of the concrete is represented through the relative horizontal displacement of the left prism rod and the right prism rod which are embedded in the concretef；
And 5: laying oil and a vinyl film in a constraint test mould according to the friction reducing method;
step 6: and pouring concrete into the test mold, compacting by using the vibrating rod, and enabling the concrete not to be higher than the test mold. Covering a film and then covering a heat preservation cover;
and 7: the method comprises the following steps of respectively covering two fixed foam plates at two ends of a dog bone test mould, ensuring that the other end of a prism rod is in the middle layer position of the test mould when an upper screw hole of the prism rod is just completely inserted into the fixed foam plates, mounting a displacement sensor, firstly fixing mounting frames at two ends of the test mould, then respectively mounting two displacement sensors on the mounting frames, adjusting the positions of the mounting frames to enable the displacement sensors to compress small metal discs on the prism rod, and ensuring that the tension and compression have enough measurement ranges to the middle proper position to fix the mounting frames;
and 8: the two displacement sensors respectively measuring X1And X2Two different displacements;
and step 9: two areThe distance between each contact point and the bottom of the prism rod is L1And L2After a certain time, the upper and lower displacement sensors record the translation distances of the disc as X respectively1And X2The specimen displacement is restricted to XrThen XrCalculated from equation 1.
Step 10: the temperature stress testing machine is used for creep test, and the creep of the concrete is Xc＝Xr—Xf。
The invention has the positive and beneficial effects that:
(1) for strain acquisition of a free test piece, a mode of arranging a displacement sensor in a test mold is adopted, the sensor is directly placed in the test mold to measure concrete self-shrinkage, the self-shrinkage of the concrete can be obtained more directly, errors generated in the deformation transfer process are reduced, and the measurement precision is increased.
(2) For strain acquisition of a constrained test piece, a double-displacement sensor is adopted, the twisting and rotation of the prism rod are considered, the real displacement of the center of the concrete can be calculated by utilizing the readings of the two sensors, and the reliability of concrete deformation measurement is improved.
(3) The form removal of the free test piece is more convenient, and when the test is finished, the exposed prism rod can be directly used for removing the concrete from the mold.
(4) Considering the transverse friction between the concrete and the test mold, the thin foaming plate with brushing oil is adopted to absorb the transverse expansion, so that the transverse restraint is reduced, and the friction is further reduced.
Drawings
FIG. 1 is a three-view illustration of a free trial core assembly comprising: (a) side view (b) top view (c) fixed end elevation view (d) moving end elevation view.
Fig. 2 is a schematic diagram of the placement of the free specimen core assembly during testing.
FIG. 3 is an axonometric view of a constraining specimen core assembly during an experiment
FIG. 4 is a schematic view of a restraining specimen fixing prism rod
In the figure, 1 is a fixed end component, 2 is a movable end component, 3 is a supporting plate for placing a displacement sensor, 4 is a hole for inserting a prism rod, 5 is a hole for inserting a displacement sensor, 6 is a steel block, 7 is a displacement sensor (LVDT), 8 is a prism rod, 9 is a metal disc, 10 is a test die, 11 is a test die cover, 12 is an installation frame and a supporting foot stand thereof, 13 is a double LVDT, 14 is a metal disc part, 15 is a prism rod, 16 is a heat preservation foam board, and 17 is a fixed foam board.
Detailed Description
The invention is further illustrated below with reference to specific examples.
First, strain acquisition of a free test piece, see fig. 1 and 2, includes a fixed end assembly 1, a movable end assembly 2 and a supporting plate 3 which are coaxially and horizontally arranged. The prism is placed parallel to the longitudinal axis of the test mould through the holes 4 in the moving end assemblies on both sides. The displacement sensor is inserted into a hole 5 in the pallet 3 and pressed against a metal disc 9 on the prism.
The measuring device and the method are used for measuring the free shrinkage of the early age concrete, and the method comprises the following steps:
① spreading oil and vinyl film in the test mould according to the friction reducing method.
② two sets of fixed end modules 1, steel blocks 6 and moving end modules 2 are placed on either side of the test mold.A metal disc 9 is screwed into the threaded hole in the end of the prismatic rod 8. the prism is inserted into the mold through the hole 4 in the moving end module.A rigid foam ring is padded in the hole 4 in the moving end module to keep the prismatic rod 8 horizontally stationary and without settling.
③ pouring concrete in the test mould, compacting with a vibrating rod, leveling, covering with vinyl film, sealing, and adjusting the prism rod by a level meter to keep it horizontally fixed.
④ after the concrete is initially solidified, the cushion block is taken down and the foam ring on the prism rod with 4 holes is replaced by a large-hole soft sponge ring, so as to reduce the temperature loss through the holes in the measurement process on the premise of ensuring that the displacement of the prism rod is not influenced, the LVDT7 is installed on the fixed end, the position is adjusted to ensure that the LVDT7 is compressed on the metal disc 9 at the end part of the prism rod, and the adequate measurement range is ensured to be available for tension and compression to the middle proper position, and finally the free deformation of the concrete is represented by the relative horizontal displacement of the left prism rod 8 and the right prism rod 8 pre-embedded in the concrete.
And secondly, restraining strain acquisition of the test piece, referring to fig. 3 and 4, the strain acquisition device comprises a mounting frame and a supporting frame 12 thereof, wherein two displacement sensors 13 are respectively arranged on the mounting frame 12 at positions 175mm and 225mm away from the bottom end of the prism and are compressed with a metal disc 14 on a prism rod 15.
The measuring device and the method are used for measuring the concrete under the constraint condition, and the method comprises the following steps:
① spreading oil and vinyl film in the test mould according to the friction reducing method.
② pouring concrete in the test mould, compacting with a vibrating rod, covering with a film and a heat-insulating cover.
③ two fixed foam boards 17 with 50mm thick and 100mm high upper protruding cylinder are covered on two ends of the dog bone test mould respectively, when the upper screw hole of the 250mm prism 15 is just inserted into the fixed foam board 17 completely (the upper screw hole is 150mm away from the concrete surface), the other end of the prism rod 15 is ensured to be in the middle layer position of the test mould, the fixed foam board is changed into the foam board 16 with a large hole after the concrete is initially solidified, in addition, a layer of sponge block with extremely low quality is sleeved on the prism rod 15 and the large hole on the foam board is ensured to be covered by the sponge block, and under the premise of ensuring that the displacement of the prism rod 15 is not influenced, the temperature loss through the hole in the measuring process is reduced.
④ installing sensors by fixing the mounting frame 12 at both ends of the test mould, then installing the double LVDT13 on the mounting frame 12 (100 mm, 150mm from the concrete surface respectively), adjusting the position of the mounting frame 12 to make the LVDT compress the small metal disc 14 on the prism rod 15, and fixing the mounting frame 12 to the middle proper position to ensure that the tension and compression have enough measuring range, the test is to obtain the strain of the concrete by detecting the displacement of the prism rod 15.
⑤ calculating the central displacement of concrete, if the displacements measured by the double LVDT13 are the same, the prism does not deflect, if the displacements measured by the double LVDT13 are X respectively1And X2Two are differentThe actual displacement X can be represented by the formula
The calculation is as follows. The true displacement is determined and then the concrete is represented by the relative displacement of the left and right prisms.
Claims (11)
1. The utility model provides a concrete temperature stress test machine which characterized in that: the concrete temperature stress testing machine comprises a free test piece strain acquisition part and a constraint test piece strain acquisition part; the free test piece strain acquisition part directly measures the concrete deformation by measuring the relative displacement of a prismatic rod which is pre-embedded in the concrete and passes through the hole of the movable assembly; the strain acquisition part of the constraint test piece can calculate the deflection of the vertical prism rod through a double displacement sensor, and the real horizontal strain of the central part of the concrete is obtained by subtracting the strain acquisition measured value of the free test piece from the measurement calculation value of the constraint test piece.
2. The concrete temperature stress tester according to claim 1, characterized in that: the free specimen strain acquisition part includes: testing a mold and a mold cover; fixed terminal assembly and movable terminal assembly
The two sides of the test die are provided with a fixed end component, a steel block and a movable end component, and the steel block is clamped between the movable end and the fixed end; a supporting plate for placing a displacement sensor is fixedly arranged on the fixed end component, and the displacement sensor is arranged above the supporting plate;
the movable end assembly is provided with a hole, one end of the prismatic rod penetrates through the hole of the movable end and is not restrained by the movable end, and the metal disc part which is polished smoothly is screwed into the end part of the other end of the prismatic rod.
3. The concrete temperature stress tester according to claim 2, characterized in that: a fixing device is arranged in the hole of the movable end component.
4. The concrete temperature stress tester according to claim 2, characterized in that: the test mould cover only covers the concrete test piece and the two side moving ends.
5. The concrete temperature stress tester according to claim 2, characterized in that: the sensor adopts an LVDT high-precision sensor.
6. The concrete temperature stress tester according to claim 1, wherein the restrained specimen strain acquisition section includes: a mold, a mounting frame, a measurement component;
the mounting frame is fixed on steel beams on two sides of the concrete temperature stress testing machine;
the measuring component is arranged on the frame and comprises a double-displacement sensor arranged on the frame, and the sensor is connected to the prism rod through a metal disc;
the foam insulation board is a thick foam board with a large rectangular hole, and is used for replacing a foam fixing board after concrete is initially set.
7. The concrete temperature stress tester according to claim 6, wherein: the sponge blocks are sleeved on the prisms and ensure that the large holes on the foam plate are covered by the sponge blocks.
8. The concrete temperature stress tester according to claim 1, characterized in that: and thin foaming plates for brushing oil are arranged on two sides of the position for placing the test piece in the temperature stress testing machine.
9. The concrete temperature stress tester according to claim 1, characterized in that: the test die and the test die cover of the temperature stress testing machine are both provided with temperature control devices, and the temperature control devices achieve the purpose of temperature control by arranging water pipes and introducing hot water into the water pipes; the temperature control water inlet pipe is arranged by adopting the water inlet pipe and the water outlet pipe which are distributed at intervals.
10. The concrete temperature stress tester according to claim 1, characterized in that: lubricating oil, a vinyl film, lubricating oil and a vinyl film are laid at the bottom of the position where the test piece is placed in the temperature stress testing machine from bottom to top.
11. A method for measuring the real displacement of the center of concrete by using the concrete temperature stress tester of claims 1-10, which is characterized by comprising the following steps:
step 1: laying oil and a vinyl film in a free test mold;
step 2: placing two groups of fixed end assemblies, a steel block and a movable end assembly on two sides of a test mold; screwing a metal disc into a screw hole at the end of the prismatic rod; inserting the prism into the mold through the hole of the movable end assembly, and padding a hard foam ring in the hole of the movable end assembly to keep the prism rod horizontally fixed and not to settle;
and step 3: and pouring concrete into the test mold, compacting by using the vibrating rod, and enabling the concrete not to be higher than the test mold. After leveling, the cover is covered with vinyl film and the heat preservation cover is immediately sealed. Adjusting the prism rod through a level gauge to keep the prism rod horizontally fixed;
and 4, step 4: after the concrete is initially set, the cushion block is taken down, the foam ring on the hole prism rod is replaced with a large-hole soft sponge ring, the displacement sensor is installed on the fixed end, the position is adjusted to enable the displacement sensor to be compressed on the metal disc at the end part of the prism rod, and finally the free deformation X of the concrete is represented through the relative horizontal displacement of the left prism rod and the right prism rod which are embedded in the concretef；
And 5: laying oil and a vinyl film in a constraint test mould according to the friction reducing method;
step 6: and pouring concrete into the test mold, compacting by using the vibrating rod, and enabling the concrete not to be higher than the test mold. Covering a film and then covering a heat preservation cover;
and 7: the method comprises the following steps of respectively covering two fixed foam plates at two ends of a dog bone test mould, ensuring that the other end of a prism rod is in the middle layer position of the test mould when an upper screw hole of the prism rod is just completely inserted into the fixed foam plates, mounting a displacement sensor, firstly fixing mounting frames at two ends of the test mould, then respectively mounting two displacement sensors on the mounting frames, adjusting the positions of the mounting frames to enable the displacement sensors to compress small metal discs on the prism rod, and ensuring that the tension and compression have enough measurement ranges to the middle proper position to fix the mounting frames;
and 8: the two displacement sensors respectively measuring X1And X2Two different displacements;
and step 9: the distance between the two contact points and the bottom of the prism rod is L respectively1And L2After a certain time, the upper and lower displacement sensors record the translation distances of the disc as X respectively1And X2The specimen displacement is restricted to XrThen XrCalculated from equation 1.
Step 10: the temperature stress testing machine is used for creep test, and the creep of the concrete is Xc＝Xr—Xf。
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2019106216252 | 2019-07-10 | ||
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| CN110376049A (en) * | 2019-07-19 | 2019-10-25 | 东南大学 | A kind of temperature stress testing machine improving strain acquisition system |
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