Experimental Device for Bond Performance of Reinforced Cluster Concrete under Repeated Load

Abstract

The present invention relates to an experimental device for the bond performance of steel bar clusters under cyclic loading, which includes a loading device, a steel bar cluster lap joint specimen, a specimen anchoring device, and a data acquisition component. The loading device includes a reaction wall, on which a load actuator is installed, and the end of the load actuator is connected to the specimen anchoring device through a loading head. The specimen anchoring device includes a steel beam, which includes a first steel beam and a second steel beam, and there is a gap between the first steel beam and the second steel beam. One side of the steel bar cluster lap joint specimen is installed in the gap through a clamping component, and the other side is screwed to the steel beam through a steel bar. A steel bottom beam is fixedly installed at the bottom of the second steel beam. The data acquisition component includes a plurality of dial gauges and steel bar strain gauges. The dial gauges are installed on one side of the steel bar cluster lap joint specimen, and the strain gauges are pasted on the surface of the steel bar, and the dial gauges and the steel bar strain gauges are respectively electrically connected to a data acquisition instrument. This device can accurately measure various parameters of the bond performance between steel bar clusters and concrete under cyclic loading.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and particularly to an experimental device for the bond performance of reinforced cluster concrete under cyclic loading. Background Art

[0002] The spacing of steel bars is an important factor affecting the bond performance between steel bars and concrete. Untrauer configured steel bars with different numbers and clear spacings in beams and conducted bending tests. The results showed that, as Figure 1 shown, when the number of steel bars is large and the clear spacing is small, the beam undergoes horizontal splitting failure and the bond strength is significantly reduced.

[0003] In order to ensure the dense pouring of concrete, the "Code for Design of Concrete Structures" in China stipulates the minimum spacing requirements for longitudinal bars in beams and columns: the clear horizontal spacing of the upper steel bars in the beam shall not be less than 30 mm and 1.5d, and the clear spacing of the longitudinal bars in the column shall not be less than 50 mm. According to Untrauer's research, for steel bars with a diameter of 28.6 mm, within the range where the clear spacing is less than 300 mm, the bond strength will decrease as the clear spacing decreases. The clear spacing of steel bars stipulated in the "Code for Design of Concrete Structures" is not sufficient to ensure the full play of the bond strength, and the code does not give a reasonable explanation for this phenomenon, and there is little research in relevant literature. As Figure 2 shown, the interaction between multiple steel bars is similar to the "shielding effect" in the "pile group effect", resulting in a reduction in the bond strength and bond stiffness of a single steel bar, which is called the "group bar effect" in this patent. A similar phenomenon also appears in the "group stud effect" in concrete stud anchorage. Currently, the research on the "group bar effect" of reinforced concrete is still blank, and an important reason is the lack of a loading device for the bond performance test of reinforced cluster concrete.

[0004] Generally, the test devices for the bond performance of ordinary reinforced concrete are all for the bond performance test of a single steel bar and concrete. Therefore, how to provide a method and its loading device for accurately testing the bond-slip performance of reinforced cluster concrete, so as to accurately study the influence of factors such as steel bar spacing, steel bar quantity, embedment length, and arrangement method on the bond performance, and then propose a bond-slip constitutive model considering the influence of the "group bar effect" for application in practical engineering is a technical problem urgently to be solved by those skilled in the art. Summary of the Invention

[0005] Based on this, in view of the above technical problems, it is necessary to provide an experimental device for the bond performance of reinforced cluster concrete under cyclic loading that can accurately study the steel bar spacing, steel bar quantity, embedment length, and arrangement method.

[0006] An experimental device for the bond performance of steel bar clusters under cyclic loading, comprising a loading device, a steel bar cluster lap joint specimen, a specimen anchoring device and a data acquisition component. The loading device includes a reaction wall, on which a load actuator is installed. The end of the load actuator is connected to the specimen anchoring device through a loading head.

[0007] The specimen anchoring device includes a steel beam, which includes a first steel beam and a second steel beam. There is a gap between the first steel beam and the second steel beam. One side of the steel bar cluster lap joint specimen is installed in the gap through a clamping component, and the other side is screwed to the steel beam through a steel bar. A steel bottom beam is fixedly installed at the bottom of the second steel beam.

[0008] The data acquisition component includes a plurality of dial gauges and steel bar strain gauges. The dial gauges are installed on one side of the steel bar cluster lap joint specimen, and the strain gauges are pasted on the surface of the steel bar. The dial gauges and the steel bar strain gauges are respectively electrically connected to a data acquisition instrument.

[0009] Further, the steel bottom beam includes a cross plate, a plurality of vertical plates and an anti-slip device. The plurality of vertical plates are welded to the bottom of the cross plate, and the anti-slip devices are symmetrically screwed to both ends of the steel bottom beam. Pressing beams are symmetrically screwed to both ends of the top of the cross plate to press the steel bottom beam.

[0010] Further, the clamping component includes an adjustable rod and clamping plates arranged oppositely. One end of the clamping plate is fixedly connected through the adjustable rod, and the other ends of the clamping plates respectively extend into the gap and clamp the steel bar cluster lap joint specimen.

[0011] Further, the clamping plates are in the form of angle steels, and one side of the clamping plates close to the steel beam is fixedly connected to the first steel beam and the second steel beam respectively through steel hinges.

[0012] Further, short steel bars are fixedly welded to the steel bar loading end of the steel bar cluster lap joint specimen.

[0013] Further, the load actuator adopts an MTS actuator.

[0014] Further, rotating shafts are oppositely installed on the same side of the first steel beam and the second steel beam. Through holes corresponding to the steel bars are opened on the rotating shafts, and the steel bars are screwed in the through holes through nuts.

[0015] Further, dial gauge baffles matching the dial gauges are arranged in the gaps between the steel bars. One end of the dial gauge baffle extending into the gap is fixedly connected to the steel bar, and the pointer of the dial gauge points to the dial gauge baffle.

[0016] The above experimental device for the bond performance of steel bar clusters and concrete under repeated loads, when in use, the load actuator set on the reaction wall is connected to the specimen anchoring device through the loading head, and can provide repeated loads. The combination of the steel beam and the steel bottom beam makes the device more stable during use and makes the measurement results more accurate. The setting of multiple dial gauges, steel bar strain gauges and data acquisition instruments. The dial gauges are used to measure the relative displacements of the free end and the loading end of the steel bars and the concrete, the steel bar strain gauges are used to measure the strain at the loading end of the steel bars, and the data acquisition instrument is used to collect the data measured by the dial gauges and the steel bar strain gauges. Therefore, the device can objectively and accurately measure various parameters of the bond performance between the steel bar clusters and the concrete under repeated loads, and the method is simple and the test is convenient. Description of the Drawings

[0017] Figure 1 Schematic diagram of the influence of steel bar net spacing on bond strength;

[0018] Figure 2 Schematic diagram of the "shielding effect" of bond stress of steel bar clusters in UHPC;

[0019] Figure 3 Schematic diagram of the overall structure of the experimental device for the bond performance of steel bar clusters and concrete under repeated loads in an embodiment of the present invention;

[0020] Figure 4 is Figure 3 Enlarged schematic diagram of partial A in;

[0021] Figure 5 Schematic diagram of the overall structure of the specimen anchoring device in this embodiment;

[0022] Figure 6 is Figure 5 Enlarged schematic diagram of partial B in.

[0023] In the figure: 100, reaction wall; 110, load actuator; 120, loading head; 200, steel beam; 210, first steel beam; 220, second steel beam; 230, rotating shaft; 300, steel bar cluster lap specimen; 310, steel bar; 311, short steel bar; 400, clamping plate; 410, adjustable connecting rod; 420, steel hinge; 500, steel bottom beam; 510, anti-slip device; 520, cross plate; 530, vertical plate; 600, pressing beam; 700, dial gauge; 710, dial gauge baffle; 800, steel bar strain gauge. Detailed Embodiment

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] As Figures 3 to 6 shown, in one embodiment, an experimental device for the bond performance of a steel bar cluster under cyclic loading includes a loading device, a steel bar cluster lap joint specimen, a specimen anchoring device, and a data acquisition component. The loading device includes a reaction wall 100, on which a load actuator 110 is installed. The load actuator 110 uses an MTS actuator. The specimen anchoring device includes a steel beam 200, which includes a first steel beam 210 and a second steel beam 220. The end of the load actuator 110 is fixedly connected to the first steel beam 210 through a loading head 120. The steel beam 200 uses a vertical steel beam. There is a gap between the first steel beam 210 and the second steel beam 220. The steel bar cluster lap joint specimen 300 is clamped and arranged in the gap through a clamping component. The clamping component includes two relatively arranged clamping plates 400 and adjustable connecting rods 410. The clamping plates 400 are in the form of angle steel. The adjustable connecting rods 410 are used to connect the upper and lower clamping plates 400. The ends of the two clamping plates 400 extending into the gap are respectively fixed to the opposite sides of the first steel beam 210 and the second steel beam 220 through steel hinges 420. The specimen anchoring device also includes a steel bottom beam 500 and a pressing beam 600. The steel bottom beam 500 includes a cross plate 520. The bottom of the second steel beam 220 is welded to the middle position of the top of the cross plate 520. The pressing beams 600 are symmetrically arranged at both ends of the cross plate 520 and are fixed by nuts and screws for pressing the entire steel bottom beam 500. The steel bottom beam 500 also includes a plurality of vertical plates 530 and anti-slip devices 510. The plurality of vertical plates 530 are longitudinally welded to the bottom of the cross plate 520. The anti-slip devices 510 are fixedly installed at both ends of the steel bottom beam 500 through screws and nuts. The steel bottom beam 500 and the pressing beam 600 cooperate with each other to jointly maintain the stability of the device.

[0026] In this embodiment, a plurality of steel bars 310 are fixedly connected to both ends of the side of the steel bar lap joint specimen 300 away from the adjustable connecting rod 410. Rotating shafts 230 are arranged at positions of the first steel beam 210 and the second steel beam 220 corresponding to the steel bars 310. A plurality of through holes matching the steel bars 310 are opened on the rotating shafts 230. The steel bars 310 penetrate through the through holes and are screwed in the through holes through nuts. A short bar 311 is fixedly welded to each steel bar 310 to prevent the steel bar 310 from buckling under compression.

[0027] In this embodiment, the data acquisition component includes a plurality of dial indicators 700 and reinforcing bar strain gauges 800. The body of the dial indicator 700 is fixedly installed on the side surface of the reinforcing bar cluster lap specimen 300. A dial indicator baffle 710 corresponding to the dial indicator 700 is arranged in the gap between the reinforcing bars 310. One end of the dial indicator baffle 710 located in the gap is fixedly connected to the reinforcing bar 310, and the pointer of the dial indicator 700 points to the dial indicator baffle 710. During use, the pointer of the dial indicator 700 points to the dial indicator baffle 710 to measure the relative displacement between the concrete and the reinforcing bar cluster. The reinforcing bar strain gauges 800 are pasted on the surface of each reinforcing bar 310. Both the dial indicator 700 and the reinforcing bar strain gauges 800 are electrically connected to a data acquisition instrument. The dial indicator 700 is used to measure the relative displacement between the free end and the loading end of the reinforcing bar 310 and the concrete, and the reinforcing bar strain gauges 800 are used to measure the strain of the loading end of the reinforcing bar. The data acquisition instrument is used to collect the data measured by the dial indicator 700 and the reinforcing bar strain gauges 800 and send them to the terminal for display to the user.

[0028] For the above experimental device for the bond performance of reinforcing bar clusters under repeated loads, during use, the MTS actuator arranged on the reaction wall is connected to the steel beam through a loading head and can provide repeated loads. The short reinforcing bars arranged at the loading end of the reinforcing bars of the reinforcing bar cluster lap specimen can effectively prevent the reinforcing bars from buckling under compression. In addition, the cooperation between the pressure beam and the steel bottom beam can support the device more stably, reduce the measurement error, and make the measurement results more accurate. The clamping component clamps the reinforcing bar cluster lap specimen between the gaps of the steel beam so that it can bear tension. With the arrangement of a plurality of dial indicators and reinforcing bar strain gauges, the dial indicators are used to measure the relative displacement between the free end and the loading end of the reinforcing bars and the concrete, and the reinforcing bar strain gauges are used to measure the strain of the loading end of the reinforcing bars. At the same time, both the dial indicators and the reinforcing bar strain gauges are electrically connected to the data acquisition instrument. Therefore, this device can objectively and accurately measure various parameters of the bond performance between the reinforcing bar cluster and the concrete under repeated loads, and the method is simple and the test is convenient.

[0029] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. An experimental device for the bond performance of steel bar clusters and concrete under cyclic loading, characterized in that, it includes a loading device, a steel bar cluster lap joint specimen, a specimen anchoring device and a data acquisition component. The loading device includes a reaction wall, on which a load actuator is installed. The end of the load actuator is connected to the specimen anchoring device through a loading head; The specimen anchoring device includes a steel beam, which includes a first steel beam and a second steel beam. There is a gap between the first steel beam and the second steel beam. One side of the steel bar cluster lap joint specimen is installed in the gap through a clamping component, and the other side is screwed to the steel beam through a steel bar. The clamping component includes an adjustable rod and oppositely arranged clamping plates. One end of the clamping plate is fixedly connected through the adjustable rod. The other ends of the clamping plates respectively extend into the gap and clamp the steel bar cluster lap joint specimen. The clamping plate is in the form of an angle steel, and one side of the clamping plate close to the steel beam is fixedly connected to the first steel beam and the second steel beam through steel hinges respectively. Rotating shafts are oppositely installed on the same side of the first steel beam and the second steel beam. Through holes corresponding to the steel bars are opened on the rotating shafts, and the steel bars are screwed in the through holes through nuts. A steel bottom beam is fixedly installed at the bottom of the second steel beam; The data acquisition component includes a plurality of dial gauges and steel bar strain gauges. The dial gauges are installed on one side of the steel bar cluster lap joint specimen, and the strain gauges are pasted on the surface of the steel bars. The dial gauges and the steel bar strain gauges are respectively electrically connected to a data acquisition instrument.

2. The experimental device for the bond performance of steel bar clusters and concrete under cyclic loading according to claim 1, characterized in that, the steel bottom beam includes a transverse plate, a plurality of vertical plates and an anti-slip device. The plurality of vertical plates are welded to the bottom of the transverse plate, and the anti-slip device is symmetrically screwed to both ends of the steel bottom beam. Pressing beams are symmetrically screwed to both ends of the top of the transverse plate to press the steel bottom beam.

3. The experimental device for the bond performance of steel bar clusters and concrete under cyclic loading according to claim 1, characterized in that, short steel bars are fixedly welded to the steel bar loading end of the steel bar cluster lap joint specimen.

4. The experimental device for the bond performance of steel bar clusters and concrete under cyclic loading according to claim 1, characterized in that, the load actuator adopts an MTS actuator.

5. The experimental device for the bond performance of steel bar clusters and concrete under cyclic loading according to claim 1, characterized in that, a dial gauge baffle matching the dial gauge is arranged in the gap between the steel bars. One end of the dial gauge baffle extending into the gap is fixedly connected to the steel bar, and the pointer of the dial gauge points to the dial gauge baffle.

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