Method for directly measuring the bond performance on the bond surface of pec steel reinforced concrete

Abstract

The application discloses a method for directly measuring the bonding performance of a PEC type steel reinforced concrete bonding surface, the PEC type steel reinforced concrete is formed by pouring concrete between flanges and on both sides of a web of an H-shaped steel, and the method comprises the following steps: (1) pasting a strain gauge pair at each measuring point of the H-shaped steel, the strain gauge pair comprises a metal strain gauge for measuring the strain of the H-shaped steel and a non-metal strain gauge for measuring the strain of a concrete structure; (2) pouring concrete between the flanges and on both sides of the web of the H-shaped steel to obtain a steel reinforced concrete test piece; (3) loading the steel reinforced concrete test piece, collecting the strain values of each metal strain gauge and the corresponding non-metal strain gauge, and analyzing the bonding performance of the PEC type steel reinforced concrete bonding surface according to the collected strain values. The application can directly and accurately measure the strain of the concrete on the contact surface of the H-shaped steel and the concrete, so that the bonding performance of the PEC type steel reinforced concrete bonding surface is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of measuring the bonding performance of steel reinforced concrete, and particularly relates to a method for directly measuring the bonding performance on the bonding surface of PEC steel reinforced concrete. BACKGROUND

[0002] PEC column (partially encased concrete composite columns, abbreviated as PEC column) steel reinforced concrete composite structure is formed by pouring concrete between the flanges and on both sides of the web of H-shaped steel, and the web of the H-shaped steel is entirely wrapped in the concrete, and the flanges are exposed outside the concrete, so it is also called "partially encased concrete structure", see Figure 1 This new component can be used for the reinforcement and reconstruction of old buildings, and can also be used for multi-story structures of newly-built buildings.

[0003] In reinforced concrete structures, the bonding performance between steel bars and concrete is the basis for the cooperative work of the two materials, and is the key to ensuring the bearing capacity of the reinforced concrete structure. The bonding force in the reinforced concrete structure refers to the force existing on the surface of the steel bar and the concrete in the longitudinal direction of the steel bar. The force in the steel bar needs to be transmitted to the concrete by the bonding force or bonding structure measures at the anchoring end of straight bars and steel strands, at the lap joint of steel bars, and near cracks, and therefore the cracking of the component, the crack width, the deformation, the structural bearing capacity, and the amount of energy absorbed and dissipated by the structure under the action of earthquakes are directly or indirectly related to the bonding performance.

[0004] Similarly, in steel reinforced concrete composite structures, there is also a bonding effect and bonding problem between the steel and the concrete. The bonding performance between the steel and the concrete is an important factor affecting the stress performance, failure mode, bearing capacity, crack, and deformation of the steel reinforced concrete component. Therefore, the measurement of the bonding performance between the steel and the concrete is extremely important.

[0005] At present, the research on the bonding performance of steel reinforced concrete at home and abroad mainly includes:

[0006] (1) Most researchers measure the strain of the steel by opening slots on the surface of the steel, attaching strain gauges in the slots, and filling epoxy resin. Then the bonding stress at each position is calculated through the micro-section force balance relationship. This method considers that the strain of the concrete is very small and thus ignores the strain of the concrete. In addition, the part filled with epoxy resin in the test process replaces the bonding between the steel and the concrete, reduces the original bonding area between the steel and the concrete, and reduces the bonding performance, so that the calculated bonding stress is not the true value and there is a certain error.

[0007] (2) In the actual bonding slip process of the profile steel and the concrete, the strain of the concrete is not negligible. However, the contact surface of the profile steel and the concrete is inside the test piece, and the strain is difficult to be directly measured. Therefore, some researchers use an indirect measurement method to obtain the strain of the concrete on the contact surface, that is, strain gauges are attached to the outside of the concrete, and the strain of the concrete on the contact surface of the profile steel and the concrete is calculated according to certain empirical formula. This method is correct in theory, but the accuracy is affected by the empirical formula, and it is still difficult to accurately reflect the size of the strain of the concrete on the contact surface, and there is a certain error. SUMMARY

[0008] In view of the problems in the prior art, the present application provides a method for directly measuring the bonding performance of the bonding surface of PEC profile steel and concrete.

[0009] The method for directly measuring the bonding performance of the bonding surface of PEC profile steel and concrete provided by the present application comprises the following steps:

[0010] (1) A pair of strain gauges are attached to each measurement point of the H-shaped steel, the pair of strain gauges comprising a metal strain gauge for measuring the strain of the H-shaped steel and a non-metal strain gauge for measuring the strain of the concrete structure;

[0011] The pair of strain gauges attached to the flange, wherein the metal strain gauge and the non-metal strain gauge are attached to the outside and the inside of the measurement point of the flange, respectively;

[0012] The pair of strain gauges attached to the web, wherein the metal strain gauge and the non-metal strain gauge are attached to the inside and the outer surface of the measurement point of the web, respectively;

[0013] (2) The concrete is poured between the flanges of the H-shaped steel and on both sides of the web to obtain a profile steel and concrete test piece;

[0014] (3) The profile steel and concrete test piece is loaded, and the strain values of each metal strain gauge and its corresponding non-metal strain gauge are collected, and the bonding performance of the bonding surface of the PEC profile steel and concrete is analyzed according to the collected strain values.

[0015] Further, the metal strain gauge is attached to the inside of the measurement point of the web, specifically:

[0016] A reverse "Xu" shaped groove is opened on the web, the reverse "Xu" shaped groove comprising a first layer of groove at the bottom and a second layer of groove at the upper part;

[0017] The metal strain gauge is attached to the bottom of the first layer of groove, and the first layer of groove is filled with epoxy resin;

[0018] After the epoxy resin is cured, a web cover plate matching the size of the second layer of groove is covered on the second layer of groove, the web cover plate is made of the same material as the web, and the web cover plate and the web are welded into a whole.

[0019] The bottom of the inverted "convex" groove is pasted with one metal strain gauge, or a plurality of metal strain gauges are pasted at equal intervals.

[0020] As preferred, before step (2) is performed, the method further comprises the step of:

[0021] A layer of AB glue is dripped on the surface of the non-metallic strain gauge and is pressed by a scraper, then, washed quartz sand is sprinkled on the surface of the non-metallic strain gauge; after the AB glue is completely hardened, the excess quartz sand is scraped off.

[0022] Further, the analyzing the bonding performance on the PEC steel-concrete bonding surface according to the collected strain values comprises:

[0023] The difference between the strain values of each metal strain gauge and the corresponding non-metallic strain gauge is obtained, that is, the bonding slip value between the H-shaped steel and the concrete at the corresponding measurement point.

[0024] Further, the analyzing the bonding performance on the PEC steel-concrete bonding surface according to the collected strain values comprises:

[0025] The H-shaped steel stress and the concrete stress are obtained according to the strain values of each metal strain gauge and the corresponding non-metallic strain gauge, and the difference between the H-shaped steel stress and the concrete stress, that is, the bonding stress between the H-shaped steel and the concrete at the corresponding measurement point.

[0026] Further, the analyzing the bonding performance on the PEC steel-concrete bonding surface according to the collected strain values comprises:

[0027] According to the strain values of each metal strain gauge and the corresponding non-metallic strain gauge, the average bonding stress of the test piece is calculated, so as to draw the corresponding average bonding stress-strain curve.

[0028] The method can directly and accurately measure the strain of the concrete on the contact surface of the steel and the concrete, measure the strain of the steel under the condition of ensuring the original bonding interface between the H-shaped steel web and the concrete, and calculate the corresponding concrete stress and steel stress, and the difference between the two is the bonding stress between the H-shaped steel and the concrete.

[0029] The method has the following advantages and beneficial effects:

[0030] (1) The inverted "convex" groove design can effectively solve the influence of the previous epoxy resin filling after the strain gauge is pasted in the groove of the steel web on the bonding performance between the steel web and the concrete, ensure the bonding area, and reduce the test error.

[0031] (2) The argon arc welding can effectively solve the damage to the internal strain gauge caused by high temperature during welding.

[0032] (3) After welding, select M20 dry sandpaper for grinding, which can solve the influence of the uneven surface of the web caused by welding or insufficient thickness precision of the cover plate on its bonding performance. At the same time, the size of the M20 dry sandpaper particles is just right to make the surface of the web cover plate and the welding after grinding the same roughness as the original steel surface, reducing the test error.

[0033] (4) It can directly measure the contact surface concrete strain, solving the technical problem that the contact surface concrete strain cannot be directly measured in the past.

[0034] (6) The test results are more direct and accurate than the calculation results of the previous empirical formula, reducing the error.

[0035] (5) Simple operation, easy to obtain materials, and low measurement cost. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a schematic diagram of the cross section of the PEC column steel reinforced concrete composite structure;

[0037] Figure 2 is a schematic diagram of the cross section of the PEC column steel reinforced concrete composite structure in the embodiment;

[0038] Figure 3 is a partial schematic diagram of the web slotting method in the embodiment;

[0039] Figure 4 is a schematic diagram of the welding of the web cover plate and the web in the embodiment;

[0040] Figure 5 is the bonding stress-strain curve of the steel reinforced concrete composite structure in the embodiment.

[0041] In the figure: 1-H steel, 110-flange, 120-web, 121-groove, 122-web cover plate; 2-concrete, 3-concrete strain gauge, 4-steel strain gauge, 5-epoxy resin. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0043] EMBODIMENT

[0044] The present embodiment mainly includes the following steps:

[0045] I. Arrangement of steel strain gauges

[0046] Referring to Figures 2-3A steel strain gauge 4 is pasted at the corresponding steel strain measurement point outside the flange 110 of the H-shaped steel 1. Since the two sides of the web 120 are in contact with the concrete, the steel strain gauge cannot be directly pasted on the surface of the web 120. Therefore, a groove 121 is opened on the surface of the web 120, and the steel strain gauge 4 is pasted in the groove 121 and filled with epoxy resin 5. Considering that the contact between the epoxy resin and the concrete surface will affect the bonding performance of the whole web with the concrete, a new type of groove 121, i.e. a reverse "convex" groove 121, is designed.

[0047] Referring to Figure 3 The groove 121 is divided into two layers. The groove opening method is as follows: first, a groove with a width of 4 mm and a depth of 1.0 mm is opened along the longitudinal axis of the web 120, which is the first layer groove, used for arranging the steel strain gauge 4. Then, a groove with a width of 5 mm and a depth of 0.5 mm is opened along the longitudinal axis of the web 120 above the first layer groove, which is the second layer groove, used for placing the web cover plate 122. Then, the steel strain gauge 4 is arranged at the bottom of the first layer groove, and the epoxy resin 5 is filled in the first layer groove. One steel strain gauge 4 can be arranged in the first layer groove, or multiple steel strain gauges 4 can be arranged at equal intervals. Finally, after the epoxy resin 5 is cured, the web cover plate 122 matching the size of the second layer groove is covered on the second layer groove. The web cover plate 122 is made of the same material as the web 120, and the web cover plate 122 and the web 120 are welded into one whole. Considering that the heat-affected zone of the welding may damage the internal steel strain gauge 4, argon arc welding with a small heat-affected zone is selected, and welding is performed from the middle to both sides, as shown in Figure 4 After welding, the connection between the web cover plate 122 and the web 120 is polished flat with M20 dry sandpaper to become one whole.

[0048] In this embodiment, the steel strain gauge 4 is a metal resistance strain gauge with the model BSF120-6AA-T.

[0049] II. Arrangement of concrete strain gauges

[0050] Before arranging the concrete strain gauges, the following materials should be prepared: transparent tape, double-sided tape, AB glue, 502 glue, clean quartz sand, concrete strain gauges, and wires. The concrete strain gauges are non-metallic strain gauges with the model BSQ120-40AA.

[0051] The arrangement steps of the concrete strain gauges are as follows:

[0052] (1) The concrete strain gauge 3 is welded with the wire, and AB glue is applied to the welding site to make the concrete strain gauge 3, the AB glue, and the wire firmly bonded together as one whole.

[0053] (2) On the reverse side of the concrete strain gauge 3, stick a double-sided tape with the same size as the concrete strain gauge 3 to completely cover the reverse side of the concrete strain gauge 3.

[0054] (3) Mark the concrete strain measurement points on the H-shaped steel. The concrete strain measurement points correspond to the steel strain measurement points one by one. The opposite concrete strain measurement points and steel strain measurement points on the flange 110 are located on the inner side and the outer side of the same position of the flange 110 respectively. The opposite concrete strain measurement points and steel strain measurement points on the web 120 are located on the outer surface and the inner part of the same position of the web 120 respectively, so as to ensure that the concrete strain and the steel strain on the contact surface of the steel and the concrete are collected.

[0055] (4) Clean the inner side of the H-shaped steel and stick a transparent tape with the same size as the concrete strain gauge 3 at each marked point.

[0056] (5) Stick the reverse side of the concrete strain gauge 3 in step (2) to the transparent tape at each marked point by using 502 glue to fix the position of the concrete strain gauge 3. After pouring the concrete, the reverse side of the concrete strain gauge 3 contacts the H-shaped steel and the front side contacts the concrete.

[0057] (6) Clean the surface of the fixed concrete strain gauge 3, then drop a layer of AB glue on the surface of the concrete strain gauge 3 and repeatedly press it with a scraper to make the AB glue fully penetrate into the concrete strain gauge 3 and make the AB glue layer on the surface of the concrete strain gauge 3 as thin as possible to improve the measurement accuracy. Then, sprinkle clean quartz sand on the surface of the concrete strain gauge 3. After the AB glue is completely hardened, gently scrape off the excess quartz sand, which means that the bonding of a concrete strain gauge 3 is completed.

[0058] (7) Repeat steps (5) to (6) to complete the bonding of all concrete strain gauges 3.

[0059] (8) After all the concrete strain gauges 3 are pasted, the wires connected to the concrete strain gauges 3 are led out and the concrete is poured. The surface of the concrete strain gauge 3 is bonded with quartz sand, thereby enhancing the bonding force between the concrete strain gauge 3 and the concrete. After the concrete reaches the design strength, the concrete strain gauge 3 establishes a firm bond with the concrete.

[0060] Three, measure the bonding stress and bonding slip

[0061] Load the steel reinforced concrete specimen, collect the strain values of each concrete strain gauge and the corresponding steel strain gauge, and the difference between the two is the bonding slip value of the corresponding measurement points between the H-shaped steel and the concrete. According to the strain value, the corresponding steel stress and concrete stress are calculated, and the difference between the two is the bonding stress of the corresponding measurement points between the H-shaped steel and the concrete.

[0062] Four, test results

[0063] According to the strain values measured by the concrete strain gauges and the steel strain gauges, the average bond stress-bond stress-strain curves are drawn, specifically as follows:

[0064] The anchorage length of the test piece is denoted as L, and the average bond stress tau of the test piece can be obtained by dividing the external load P by the contact surface area S of the steel and the concrete, that is, The average bond stress tau can reflect the size of the sliding resistance capacity of the interface between the steel and the concrete from a macroscopic point of view, but does not contain the position influence. The data collected by the concrete strain gauges attached to the surface of the concrete are processed to obtain the strain values epsilon and the corresponding external loads P at each marked point. The corresponding average bond stress is calculated by the formula and is drawn into the average bond stress-strain curve, as shown in Figure 5 .

[0065] Referring to Figure 5 , the average bond stress-strain curve obtained by using the method of the embodiment is shown. As can be seen from the figure, the curve includes a no-slip segment, an ascending segment and a descending segment. When the load is small, the chemical adhesion force plays a major role, and with the loss of the chemical adhesion force, the loading end begins to slip, at this time the corresponding load is the initial slip load Ps, the friction and the mechanical interlocking force begin to play a role until the ultimate load is reached. When the ultimate load is reached, the friction and the mechanical interlocking force are not enough to resist the interface shear stress, and the test piece is damaged, and there is residual stress after the test piece is damaged. After the loading test is completed, the test piece is disassembled, and it is found that all the strain gauges are intact and bonded with the concrete, and there is no phenomenon of falling off.

[0066] From the above test results, it can be seen that the method of the present application is simple to operate, has low cost, and has small test error. When used for measuring the bond performance of steel reinforced concrete, the strain of the concrete on the contact surface of the steel and the concrete, the strain of the steel and the bond stress can be directly measured.

[0067] The above embodiment is only one of a plurality of embodiments, and for those skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and the other changes or variations derived from the essential spirit of the present application still belong to the protection scope of the present application.

Claims

1. A method for directly measuring the bond performance on the bond interface of PEC type steel reinforced concrete formed by pouring concrete between the flanges and on both sides of the web of H-shaped steel, characterized in that, The method comprises the following steps: (1) a strain gauge pair is pasted at each measuring point of the H-shaped steel, the strain gauge pair comprising a metal strain gauge for measuring the strain of the H-shaped steel and a non-metal strain gauge for measuring the strain of the concrete structure; the strain gauge pair pasted on the flange, wherein the metal strain gauge and the non-metal strain gauge are pasted on the outer side and the inner side of the measuring point on the flange respectively; the strain gauge pair pasted on the web, wherein the metal strain gauge and the non-metal strain gauge are pasted on the inner side and the outer surface of the measuring point on the web respectively; the metal strain gauge is pasted on the inner side of the measuring point on the web, specifically: a "inverted U" shaped groove is opened on the web, the "inverted U" shaped groove comprising a first layer of groove at the bottom and a second layer of groove at the upper part; the metal strain gauge is pasted on the bottom of the first layer of groove, and the first layer of groove is filled with epoxy resin; after the epoxy resin is cured, a web cover plate matching the size of the second layer of groove is covered on the second layer of groove, the web cover plate is made of the same material as the web, and the web cover plate and the web are welded into an integral whole; (2) the concrete is poured between the flanges of the H-shaped steel and on both sides of the web to obtain a steel reinforced concrete test piece; (3) the steel reinforced concrete test piece is loaded, and the strain values of each metal strain gauge and the corresponding non-metal strain gauge are collected, and the bonding performance of the PEC steel reinforced concrete bonding surface is analyzed according to the collected strain values; the analysis of the bonding performance of the PEC steel reinforced concrete bonding surface according to the collected strain values comprises: the difference between the strain values of each metal strain gauge and the corresponding non-metal strain gauge is obtained, that is, the bonding slip value between the H-shaped steel and the concrete at the corresponding measuring point; or, the H-shaped steel stress and the concrete stress are obtained according to the strain values of each metal strain gauge and the corresponding non-metal strain gauge, and the difference between the H-shaped steel stress and the concrete stress, that is, the bonding stress between the H-shaped steel and the concrete at the corresponding measuring point; or, the average bonding stress of the test piece is calculated according to the strain values of each metal strain gauge and the corresponding non-metal strain gauge, and the corresponding average bonding stress-strain curve is drawn; the arrangement steps of the concrete strain gauge are as follows: (1) the concrete strain gauge and the wire are welded, and AB glue is applied to the welding position to bond the concrete strain gauge, the AB glue and the wire firmly into an integral whole; (2) a double-sided adhesive tape with the same size as the concrete strain gauge is pasted on the back of the concrete strain gauge to completely cover the back of the concrete strain gauge; (3) the concrete strain measuring points are marked on the H-shaped steel; the concrete strain measuring points and the steel strain measuring points correspond to each other, and the opposite concrete strain measuring points and the steel strain measuring points on the flange are located on the inner side and the outer side of the same position of the flange respectively; the opposite concrete strain measuring points and the steel strain measuring points on the web are located on the outer surface and the inner side of the same position of the web respectively, so that the concrete strain and the steel strain on the contact surface of the steel and the concrete can be collected; (4) the inner side of the H-shaped steel is cleaned, and a transparent adhesive tape with the same size as the concrete strain gauge is pasted at each marked point. (5) Use 502 glue to stick the reverse side of the concrete strain gauge in step (2) to the transparent tape at each marked point to fix the position of the concrete strain gauge; after pouring the concrete, the reverse side of the concrete strain gauge contacts the H-shaped steel, and the front side contacts the concrete; (6) Clean the surface of the fixed concrete strain gauge, then drop a layer of AB glue on the surface of the concrete strain gauge, and repeatedly press it with a scraper to make the AB glue fully penetrate into the concrete strain gauge and make the AB glue layer on the surface of the concrete strain gauge as thin as possible to improve the measurement accuracy; then, sprinkle clean quartz sand on the surface of the concrete strain gauge, and gently scrape off the excess quartz sand after the AB glue is completely hardened, which completes the bonding of a concrete strain gauge; (7) Repeat steps (5) to (6) to complete the bonding of all concrete strain gauges; (8) After all the concrete strain gauges are pasted, the wires connected to the concrete strain gauges are led out, and the concrete is poured, and the quartz sand is bonded on the surface of the concrete strain gauge, thereby enhancing the bonding force between the concrete strain gauge and the concrete; after the concrete reaches the design strength, the concrete strain gauge establishes a firm bond with the concrete; According to the strain values measured by the concrete strain gauges and the steel strain gauges, the average bonding stress-strain curve of the bonding stress is drawn, which is specifically: The anchorage length of the test piece is denoted as L, and the average bond stress τ of the test piece can be obtained by dividing the external load P by the contact surface area S of the steel and the concrete, i.e. The average bond stress τ can reflect the size of the slip resistance of the interface between the steel and the concrete from a macro perspective, but does not contain the position influence; the data collected by the concrete strain gauges attached to the surface of the concrete are processed to obtain the strain value ε at each marked point and the corresponding external load P; the corresponding average bond stress is calculated through the formula The average bond stress-strain curve is drawn. The curve includes a no-slip segment, an ascending segment and a descending segment; when the load is small, the chemical adhesion force plays a major role, and with the loss of chemical adhesion force, the loading end begins to slip, at this time the corresponding load is the initial slip load Ps, the friction and mechanical interlocking force begin to play a role until the ultimate load is reached; when the ultimate load is reached, the friction and mechanical interlocking force are not enough to resist the interfacial shear stress, and the specimen is destroyed, and after the destruction, the specimen has residual stress, and after the loading test is completed, the specimen is disassembled, and it is found that all the strain gauges are intact and bonded with the concrete without falling off.

2. The method of claim 1, characterized in that: The bottom of the inverted "U" shaped groove is pasted with one metal strain gauge, or multiple metal strain gauges are pasted at equal intervals.

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