Long-term pull-out test device and test method for steel-concrete composite beam after cracking damage

Abstract

The invention provides a long-term pull-out test device and a long-term pull-out test method for a cracked and damaged steel-concrete composite beam, and belongs to the field of steel-concrete composite beam tests. The problem how to enable the concrete wing plate in the composite beam to be in a specific cracking damage degree is solved; the invention aims to solve the problem of how to apply a durable and stable pull-out load to a steel-concrete composite beam test piece by adopting a common pressure jack and a pressure sensor and continuously monitor the pull-out load. According to the invention, the jack is changed from pressing to pulling, and the pressure jack is adopted to apply a lasting and stable pulling load to the steel-concrete composite beam test piece; the pull-out load is changed into pressure from pull, and the pull-out load in the test process is continuously monitored by adopting a pressure sensor. The test process is complete, functions are complete, cracking damage of the steel-concrete composite beam is achieved through one test device, and a complete steel-concrete interface bonding-sliding constitutive model after cracking damage can be obtained through all steps of loading, load holding and load supplementing of a long-term pull-out test.

Description

Technical Field

[0001] The invention belongs to the field of steel - concrete composite beam tests, and particularly relates to a long - term pull - out test device and test method for a steel - concrete composite beam after cracking damage. Background Technique

[0002] In the study of the longitudinal shear performance of the steel - concrete composite beam interface, the traditional test method is to obtain the bond - slip performance constitutive model of the steel - concrete interface through a push - out test and apply it to all interface areas of the composite beam calculation model, ignoring the situation that the concrete slab in the negative moment area of the composite beam is in a tensile stress state, which is inconsistent with the compressive state of the concrete in the push - out test. When further considering the development of concrete cracks in the negative moment area, the bond - slip performance of the steel - concrete composite beam interface in the negative moment area will degenerate significantly. Therefore, it is urgent to carry out long - term pull - out tests on composite beams after cracking damage to obtain the bond - slip performance of the steel - concrete composite beam interface in the negative moment area considering crack development and further achieve refined simulation of the long - term performance of the composite beam.

[0003] For this reason, three problems need to be solved: 1) how to make the concrete slab in the composite beam reach a specific cracking damage degree; 2) how to apply a persistent and stable pull - out load to the steel - concrete composite beam specimen using a common pressure jack; 3) how to continuously monitor this pull - out load using a common pressure sensor. Summary of the Invention

[0004] In view of this, to solve the technical problems proposed in the above - mentioned background technique, the invention provides a long - term pull - out test device and test method for a composite beam after cracking damage.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A long-term pull-out test device for a composite beam after cracking damage, comprising four fixed cross beams, two fixed screws, a number of fixed screw nuts, three movable end plates, two movable screws, two lower movable screw nuts, two middle and lower movable screw nuts, two middle movable screw nuts, two upper and middle movable screw nuts, two upper movable screw nuts, a jack, two springs, a pressure sensor, a steel-concrete composite beam pull-out specimen, a number of steel bar anchors, a number of bolts and a number of displacement sensors. The four fixed cross beams and the two fixed screws vertically form the test device frame. The two movable screws pass through the upper and upper-middle fixed cross beams, and are respectively fixed to the lower movable end plate through the lower movable screw nuts, fixed to the upper-middle fixed cross beam through the middle and lower movable screw nuts, fixed to the middle movable end plate through the middle movable screw nuts, fixed to the upper movable end plate through the upper and middle movable screw nuts, and fixed to the upper fixed cross beam through the upper movable screw nuts. The jack is placed between the upper fixed cross beam and the upper movable end plate. The two springs are located between the upper and middle movable end plates and are penetrated by the movable screws. The pressure sensor is placed between the middle movable end plate and the upper-middle fixed cross beam. A steel-concrete composite beam pull-out specimen is installed below the lower movable end plate. The bottom of the steel-concrete composite beam pull-out specimen and the middle and lower fixed cross beam are fixed by anchoring the longitudinal steel bars through a number of steel bar anchors.

[0006] Furthermore, the steel-concrete composite beam pull-out specimen is formed by connecting a profiled steel bar and symmetrically arranged profiled steel sheet-concrete composite slabs with a number of shear connectors. The profiled steel sheet-concrete composite slab includes profiled steel sheets, concrete, longitudinal steel bars and transverse steel bars. The concrete is integrally formed by casting with the shear connectors, profiled steel sheets, longitudinal steel bars and transverse steel bars. And both ends of the longitudinal steel bars extend out of the concrete by a sufficient length for steel bar anchoring.

[0007] Furthermore, a number of displacement sensors are arranged at the interface position of the steel-concrete composite beam pull-out specimen to measure the relative slip displacement between the profiled steel bar and the profiled steel sheet during the test.

[0008] A long-term pull-out test for a steel-concrete composite beam after cracking damage using the long-term pull-out test device for a composite beam after cracking damage specifically includes the following steps: Step 1: Anchor the upper and lower ends of the longitudinal steel bars of the steel-concrete composite beam pull-out specimen to the lower movable end plate and the middle and lower fixed cross beam respectively through a number of steel bar anchors; Step 2: Loosen two middle-lower movable screw nuts and two middle movable screw nuts. Monitor the load value through the pressure sensor and apply the jack to the designed cracking load. Lock two middle-upper movable screw nuts, remove the jack. After a sufficient time, the profiled steel sheet-concrete composite slab completes the cracking damage. Then install the jack again, load it to the specified load, loosen two middle-upper movable screw nuts, then unload the jack, and lock two middle-lower movable screw nuts and two middle movable screw nuts; Step 3: Cut off the part of the longitudinal reinforcement of the steel-concrete composite beam pull-out specimen that extends out of the specimen at the upper end, and fix the profiled steel in the steel-concrete composite beam pull-out specimen to the lower movable end plate through several bolts; Install several displacement sensors at the interface position of the steel-concrete composite beam pull-out specimen to measure the relative slip displacement between the profiled steel and the profiled steel sheet during the test; Loosen two middle-lower movable screw nuts and two middle movable screw nuts. Monitor the load value through the pressure sensor and apply the jack to the designed pull-out load. Lock two middle-upper movable screw nuts, remove the jack, and continuously monitor the values of the pressure sensor and several displacement sensors.

[0009] Furthermore, during the loading process, if the value of the pressure sensor is lower than 2% of the initial value, the jack should be installed again, loaded to the initial pull-out load, and two middle-upper movable screw nuts should be locked again, then the jack should be removed until the test ends.

[0010] Furthermore, in Step 1, the upper and lower ends of the longitudinal reinforcement of the steel-concrete composite beam pull-out specimen should extend out of the concrete edge by a sufficient length for anchoring with the lower movable end plate and the middle-lower fixed cross beam.

[0011] Compared with the prior art, the beneficial effects of the long-term pull-out test device and test method for a composite beam after cracking damage of the present invention are as follows: 1. The test process of the present invention is complete and the functions are perfect. Using a set of test devices, all steps of cracking damage, long-term pull-out test loading, load holding, and supplementary loading of the steel-concrete composite beam can be realized, and a complete constitutive model of the bond-slip performance of the steel-concrete interface after cracking damage can be obtained, which cannot be achieved by traditional test methods.

[0012] 2. The present invention reasonably controls the concrete of the steel-concrete composite beam pull-out specimen to be in a specific cracking damage degree. The cracking damage degree of the concrete is directly related to the longitudinal reinforcement stress and the load holding time. In this test, the jack is applied to the designed cracking load by monitoring the load value through the pressure sensor in Step 1, so that the longitudinal reinforcement reaches a specific stress and maintains for a sufficient time. Combining measures such as monitoring the crack spacing and crack width, the concrete of the steel-concrete composite beam pull-out specimen is in a specific cracking damage degree.

[0013] 3. The present invention is rationally designed to convert the jack from "pushing" to "pulling", and a common pressure jack is used to apply a lasting and stable pulling load to the steel-concrete composite beam specimen. The pressure jack compresses the spring under the upper movable end plate by relying on the upper fixed cross beam. After locking the movable screw nut, the compressed spring can directly release the elastic force to achieve the conversion from "pushing" to "pulling".

[0014] 4. The present invention is rationally designed to convert the pulling load from "pulling" to "pushing", and a common pressure sensor is used to continuously monitor the pulling load during the test. Since the lower part of the spring directly acts on the middle movable end plate, the pressure sensor and the upper-middle fixed cross beam, during the test, the pressure sensor always monitors the elastic force of the spring. From the force balance, it can be known that this load is also the pulling load during the test process.

[0015] 5. The present invention completes the load holding through the spring system, and the load holding process does not depend on the force holding of the jack. The traditional long-term performance test method depends on the long-term force holding of the pressure jack, requiring a large number of pressure jacks and consuming a large amount of energy. This device relies on the spring system to complete the load holding, which is more in line with the concept of "green and low-carbon".

[0016] 6. The device of the present invention has a simple structure, is convenient for disassembly, assembly and maintenance, and has a wider application range. The entire test device uses mechanical connections such as screws, nuts, and anchorages, and can be disassembled, assembled and replaced with parts at any time, and is applicable to pull-out specimens, jacks, springs and force sensors of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic structural diagram of the steel-concrete composite beam pull-out specimen for the cracking damage step in the test of the present invention; Figure 2 is a schematic structural diagram of the steel-concrete composite beam pull-out specimen for the pull-out test step in the test of the present invention; Figure 3 is a schematic structural diagram of the test device for the cracking damage step in the test of the present invention; Figure 4 is a schematic structural diagram of the test device for the cracking damage step in the test of the present invention; In the figure: fixed crossbeam 1, fixed screw 2, fixed screw nut 3, movable screw 4, movable end plate 5, lower movable screw nut 6, middle and lower movable screw nut 7, middle movable screw nut 8, middle and upper movable screw nut 9, upper movable screw nut 10, jack 11, spring 12, pressure sensor 13, steel-concrete composite beam pull-out specimen 14, steel bar anchor 15, bolt 16, displacement sensor 17; Section steel 14-1, shear connector 14-2, profiled steel sheet 14-3, concrete 14-4, longitudinal steel bar 14-5, transverse steel bar 14-6. Specific implementation mode

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0019] See Figures 1-4 Referring to this embodiment, a long-term pull-out test device for a composite beam after cracking damage, a long-term pull-out test device for a composite beam after cracking damage, includes four fixed crossbeams 1 (respectively the upper fixed crossbeam, the upper-middle fixed crossbeam, the lower-middle fixed crossbeam and the lower fixed crossbeam), two fixed screws 2, several fixed screw nuts 3, three movable end plates 5 (respectively the upper movable end plate, the middle movable end plate and the lower movable end plate), two movable screws 4, two lower movable screw nuts 6, two middle and lower movable screw nuts 7, two middle movable screw nuts 8, two middle and upper movable screw nuts 9, two upper movable screw nuts 10, a jack 11, two springs 12, a pressure sensor 13, a steel-concrete composite beam pull-out specimen 14, several steel bar anchors 15, several bolts 16, and several displacement sensors 17. The four fixed crossbeams 1 and the two fixed screws 2 form the test device framework. The two movable screws 4 pass through the upper and upper-middle fixed crossbeams 1 and are fixed to the lower movable end plate 5 through the lower movable screw nut 6, fixed to the upper-middle fixed crossbeam 1 through the middle and lower movable screw nut 7, fixed to the middle movable end plate 5 through the middle movable screw nut 8, fixed to the upper movable end plate 5 through the middle and upper movable screw nut 9, and fixed to the upper fixed crossbeam 1 through the upper movable screw nut 10. The jack 11 is placed between the upper fixed crossbeam 1 and the upper movable end plate 5. The two springs 12 are located between the upper and middle movable end plates 5 and are penetrated by the movable screw 4. The pressure sensor 13 is placed between the middle movable end plate 5 and the upper-middle fixed crossbeam 1. A steel-concrete composite beam pull-out specimen 14 is installed below the lower movable end plate 5. The bottom of the steel-concrete composite beam pull-out specimen 14 is fixed to the lower-middle fixed crossbeam 1 through several steel bar anchors 15 to anchor the longitudinal steel bars 14-5.

[0020] The steel-concrete composite beam pull-out specimen 14 is composed of a steel section 14-1 and profiled steel sheet-concrete composite slabs symmetrically arranged, which are connected by a number of shear connectors 14-2. The profiled steel sheet-concrete composite slab includes a profiled steel sheet 14-3, concrete 14-4, longitudinal steel bars 14-5 and transverse steel bars 14-6. The concrete 14-4 is integrally formed by casting with the shear connectors 14-2, the profiled steel sheet 14-3, the longitudinal steel bars 14-5 and the transverse steel bars 14-6, and both ends of the longitudinal steel bars 14-5 extend out of the concrete by a sufficient length for steel bar anchoring.

[0021] A number of displacement sensors 17 are arranged at the interface position of the steel-concrete composite beam pull-out specimen 14 to measure the relative slip displacement between the steel section 14-1 and the profiled steel sheet 14-3 during the test.

[0022] A long-term pull-out test on a cracked and damaged steel-concrete composite beam is carried out by using a long-term pull-out test device for a composite beam after cracking damage, which specifically includes the following steps: Step 1: The upper and lower ends of the longitudinal steel bars 14-5 of the steel-concrete composite beam pull-out specimen 14 are respectively anchored to the lower movable end plate 5 and the middle-lower fixed cross beam 1 through a number of steel bar anchors 15.

[0023] Step 2: Loosen the two middle-lower movable screw nuts 7 and the two middle movable screw nuts 8. Monitor the load value through the pressure sensor 13 and apply the jack 11 to the designed cracking load. Lock the two upper-middle movable screw nuts 9, remove the jack 11. After a sufficient time, the profiled steel sheet-concrete composite slab completes the cracking damage. Then install the jack 11 again, load it to the specified load, and loosen the two upper-middle movable screw nuts 9. Then unload the jack 11, and lock the two middle-lower movable screw nuts 7 and the two middle movable screw nuts 8.

[0024] The sufficient time here means that the cracking damage degree of the concrete is directly related to the longitudinal steel bar stress and the holding time. In this test, the jack is applied to the designed cracking load by monitoring the load value through the pressure sensor in Step 1, so that the longitudinal steel bars reach a specific stress and maintain for a sufficient time. Then, by combining measures such as monitoring the crack spacing and crack width, the concrete of the steel-concrete composite beam pull-out specimen is in a specific cracking damage degree.

[0025] The completion of the cracking damage of the profiled steel sheet-concrete composite slab here means that after monitoring for a period of time and the crack width no longer increases significantly, it is considered that the profiled steel sheet-concrete composite slab has completed the cracking damage.

[0026] Step 3: Cut off the part of the upper end of the longitudinal steel bar 14-5 of the steel-concrete composite beam pull-out specimen 14 that extends out of the specimen, and fix the profiled steel bar 14-1 in the steel-concrete composite beam pull-out specimen on the lower movable end plate 5 through a number of bolts 16; install a number of displacement sensors 17 at the interface position of the steel-concrete composite beam pull-out specimen 14 to measure the relative slip displacement between the profiled steel bar 14-1 and the profiled steel sheet 14-3 during the test; loosen the two middle and lower movable screw nuts 7 and the two middle movable screw nuts 8, apply the jack 11 to the designed pull-out load by monitoring the load value through the pressure sensor 13, lock the two upper and middle movable screw nuts 9, remove the jack 11, and continuously monitor the values of the pressure sensor 13 and a number of displacement sensors 17.

[0027] During the loading process, if the value of the pressure sensor 13 is lower than 2% of the initial value, the jack 11 should be installed again, loaded to the initial pull-out load, the two upper and middle movable screw nuts 9 should be locked again, and the jack 11 should be removed until the end of the test.

[0028] In Step 1, the upper and lower ends of the longitudinal steel bar 14-5 of the steel-concrete composite beam pull-out specimen 14 should extend out of the edges of the concrete 14-4 by a sufficient length for anchoring with the lower movable end plate 5 and the middle and lower fixed cross beam 1.

[0029] The embodiments of the present invention disclosed above are only used to help explain the present invention. The embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. According to the content of this specification, many modifications and changes can be made. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well.

Claims

1. A long-term pull-out test device for steel-concrete composite beams after cracking damage, characterized in that: It includes four fixed crossbeams (1), two fixed screws (2), two movable screws (4), three movable end plates (5), several movable nuts, a jack (11), two springs (12), a pressure sensor (13), a steel-concrete composite beam pull-out specimen (14) and several steel bar anchors (15); The four fixed crossbeams (1) and the two fixed screws (2) perpendicularly form the test device framework. The two movable screws (4) penetrate the upper fixed crossbeam and the middle-upper fixed crossbeam, and are respectively fixed to the three movable end plates (5) through several movable nuts. The jack (11) is placed between the upper fixed crossbeam and the upper movable end plate. The two springs (12) are located between the upper movable end plate and the middle movable end plate and are penetrated by the movable screw (4). The pressure sensor (13) is placed between the middle movable end plate and the middle-upper fixed crossbeam. A steel-concrete composite beam pull-out specimen (14) is installed below the lower movable end plate. The bottom of the steel-concrete composite beam pull-out specimen (14) and the middle-lower fixed crossbeam are fixed by anchoring the longitudinal steel bars (14-5) through several steel bar anchors (15).

2. The long-term pull-out test device for steel-concrete composite beams after cracking damage according to claim 1, characterized in that: The steel-concrete composite beam pull-out specimen (14) is formed by connecting a section steel (14-1) and symmetrically placed profiled steel sheet-concrete composite slabs through several shear connectors (14-2). The profiled steel sheet-concrete composite slab includes a profiled steel sheet (14-3), concrete (14-4), longitudinal steel bars (14-5) and transverse steel bars (14-6). The concrete (14-4) is integrally cast with the shear connectors (14-2), the profiled steel sheet (14-3), the longitudinal steel bars (14-5) and the transverse steel bars (14-6).

3. The long-term pull-out test device for a steel-concrete composite beam after cracking damage according to claim 2, characterized in that: Both ends of the longitudinal steel bars (14-5) extend out of the concrete by a sufficient length for steel bar anchoring.

4. The long-term pull-out test device for a steel-concrete composite beam after cracking damage according to claim 3, characterized in that: Several displacement sensors (17) are arranged at the interface position of the steel-concrete composite beam pull-out specimen (14) to measure the relative slip displacement between the section steel (14-1) and the profiled steel sheet (14-3) during the test.

5. The long-term pull-out test device for steel-concrete composite beams after cracking damage according to claim 4, characterized in that: The several movable nuts include two lower movable screw nuts (6), two middle-lower movable screw nuts (7), two middle movable screw nuts (8), two middle-upper movable screw nuts (9) and two upper movable screw nuts (10). The two movable screws (4) are respectively fixed to the lower movable end plate (5) through the lower movable screw nuts (6), fixed to the middle-upper fixed crossbeam (1) through the middle-lower movable screw nuts (7), fixed to the middle movable end plate (5) through the middle movable screw nuts (8), fixed to the upper movable end plate (5) through the middle-upper movable screw nuts (9), and fixed to the upper fixed crossbeam (1) through the upper movable screw nuts (10).

6. A test method for the long-term pull-out test of a steel-concrete composite beam after cracking damage using the long-term pull-out test device for a steel-concrete composite beam after cracking damage as described in claim 5, characterized in that: Specifically, it includes the following steps: Step 1: Anchor the upper and lower ends of the longitudinal steel bars (14-5) of the steel-concrete composite beam pull-out specimen (14) to the lower movable end plate (5) and the middle-lower fixed crossbeam respectively through several steel bar anchors (15); Step 2: Loosen two middle-lower movable screw nuts (7) and two middle movable screw nuts (8). Monitor the load value through the pressure sensor (13) and apply the jack (11) to the designed cracking load. Lock two upper-middle movable screw nuts (9), remove the jack (11). After a sufficient time, the profiled steel sheet-concrete composite slab completes cracking damage. Then install the jack (11) again, load it to the specified load, loosen two upper-middle movable screw nuts (9), then unload the jack (11), and lock two middle-lower movable screw nuts (7) and two middle movable screw nuts (8). Step 3: Cut off the part of the longitudinal reinforcement (14-5) of the steel-concrete composite beam pull-out specimen (14) that extends out of the specimen, and fix the profiled steel (14-1) in the steel-concrete composite beam pull-out specimen to the lower movable end plate (5) through several bolts (16). Install several displacement sensors (17) at the interface position of the steel-concrete composite beam pull-out specimen (14) to measure the relative slip displacement between the profiled steel (14-1) and the profiled steel sheet (14-3) during the test. Loosen two middle-lower movable screw nuts (7) and two middle movable screw nuts (8). Monitor the load value through the pressure sensor (13) and apply the jack (11) to the designed pull-out load. Lock two upper-middle movable screw nuts (9), remove the jack (11), and continuously monitor the values of the pressure sensor (13) and several displacement sensors (17).

7. The test method for the long-term pull-out test of a steel-concrete composite beam after cracking damage using the long-term pull-out test device for a steel-concrete composite beam after cracking damage according to claim 6, characterized in that: During the loading process, if the value of the pressure sensor (13) is lower than 2% of the initial value, the jack (11) needs to be installed again, loaded to the initial pull-out load, and two upper-middle movable screw nuts (9) are locked again, then the jack (11) is removed until the end of the test.

8. The test method for the long-term pull-out test of a steel-concrete composite beam after cracking damage using the long-term pull-out test device for a steel-concrete composite beam after cracking damage according to claim 6, characterized in that: In Step 1, the longitudinal reinforcement (14-5) of the concrete composite slab needs to extend out of the edge of the concrete (14-4) by a sufficient length for fixing with the movable end plate (5) and the lower fixed cross beam.

Images