Bridge engineering teaching and experiment model capable of automatically and cyclically simulating loading

Abstract

The invention provides a bridge engineering teaching and experimental model capable of automatically and cyclically simulating loading, and relates to the technical field of bridge engineering teaching. The model comprises a three-dimensional truss, two supporting pedestals and a cyclic simulation loading system. The cyclic simulation loading system comprises a plurality of loading wheels connected in series, two upper guide rails, two lower guide rails, a lifting mechanism and a turning guide rail. After the model is started, the loading wheels connected in series automatically move forwards along an upper guide rail mounted on a truss lower parallel connection, automatically slide to the lower guide rail along an arc deformation guide rail after reaching a far-end supporting pedestal, return to a near-end supporting pedestal under the action of gravity, and are automatically captured and lifted to the upper guide rail by a lifting mechanism, so that automatic simulation loading is realized. The model can be used for demonstration experiments of courses of bridge engineering, structural mechanics, engineering mechanics and the like, and can also provide a basic experiment platform for related scientific research tasks in the fields of bridge engineering, structural mechanics and the like.

Description

Technical Field

[0001] The invention relates to the technical field of bridge engineering teaching, in particular to a bridge engineering teaching and experimental model with automatic cycle simulation loading. Background Art

[0002] Bridge engineering is one of the core professional courses in the direction of highway and urban road engineering (road and bridge) in the civil engineering major, and is often included in the training plan of civil engineering majors in various training units in the form of elective courses. This course mainly introduces the structural characteristics of various bridges and the force calculation principles, and often uses knowledge points such as "internal forces", "influence lines", and "most unfavorable live load positions" in professional basic courses such as structural mechanics and material mechanics.

[0003] In teaching practice, intuitive teaching is a teaching principle in which teachers guide students to directly perceive things and models in the real world or describe learning objects through figurative language, so that students can gain perceptual knowledge. It can enable students to establish a connection between abstract concepts and concrete images in their minds, easily learn knowledge points in the course, and stimulate learning interest. Intuitive teaching includes three types: real object intuition, model image intuition, and verbal intuition. Although real object intuition has a strong sense of reality, it is often difficult to highlight the essential laws of things, and it is difficult to use due to the limitations of time and space; model image intuition uses teaching models and teaching aids as sensory transmitters. Through special design, it can highlight key concepts and improve learning effects. It is not limited by time and space and is easy to use. However, the common teaching models of bridge engineering, structural mechanics, and material mechanics on the market can generally only statically display the structural characteristics of load-bearing structures such as bridges or trusses. The materials are mostly engineering plastics, which are not durable enough, and the model is also low in sophistication. The biggest problem is that it cannot achieve dynamic loading in a figurative way, and the effect of its application in teaching needs to be improved.

[0004] Therefore, the research and development of a bridge engineering teaching model with dynamic loading function can improve the teaching effect of courses such as bridge engineering, structural mechanics and material mechanics, increase students' learning interest, and has broad application prospects. Summary of the invention

[0005] In order to solve the technical problem that the existing bridge engineering teaching model does not have automatic simulation loading, the embodiment of the present invention provides a bridge engineering teaching and experimental model with automatic cycle simulation loading, which can effectively improve the teaching effect of bridge engineering courses. The technical solution is as follows:

[0006] A bridge engineering teaching and experimental model with automatic cyclic simulation loading, the model comprising a three-dimensional truss, a proximal support pedestal, a distal support pedestal and a cyclic simulation loading system.

[0007] The cyclic simulation loading system includes a metal loading wheel, an upper guide rail, a lower guide rail, an automatic lifting mechanism, a changeable guide rail, a hinge support, a roller support and a proximal transition guide rail.

[0008] One end of the bottom of the three-dimensional truss is installed on the proximal support pedestal through a hinge support, and the other end of the bottom of the three-dimensional truss is installed on the distal support pedestal through a roller support;

[0009] The upper guide rail is mounted on the inner bottom of the three-dimensional truss, the end of the upper guide rail is connected to the upper end of the changeable guide rail through a remote support pedestal, and the changeable guide rail is mounted on the changeable guide rail bracket;

[0010] The lower end of the deflection guide rail is connected to the lower guide rail, and the lower guide rail is supported by a lower guide rail bracket;

[0011] The end of the lower guide rail is connected to the lower part of the automatic lifting mechanism at the proximal support seat, and the upper part of the automatic lifting mechanism is connected to the proximal transition guide rail, and the proximal transition guide rail cooperates with the upper guide rail;

[0012] The metal loading wheel moves along the upper guide rail, the change-direction guide rail, and the lower guide rail, and can be lifted from the lower guide rail to the proximal transition guide rail by an automatic lifting mechanism, thereby returning to the upper guide rail.

[0013] There are no less than two metal loading wheels, and multiple metal loading wheels are connected in series, and the diameter of the metal loading wheel is smaller than the height of the three-dimensional truss.

[0014] The metal loading wheel comprises a wheel disc, a wheel axle, a bearing and a hook.

[0015] The two wheel discs are coaxial through a wheel axle, and a semicircular wheel rim groove is provided on the edge of the wheel disc. During operation, the steel pipes of the upper guide rail and the lower guide rail are embedded in the wheel rim groove;

[0016] The bearing is arranged at the midpoint of the wheel axle, the inner ring of the bearing cooperates with the wheel axle, the outer ring of the bearing is connected to two hooks, the two hooks are symmetrically arranged, and the multiple metal loading wheels are connected to the hooks by thin steel wire ropes to form a closed wheel string.

[0017] The axle of the metal loading wheel is longer than the outer profile of the wheel disc. When the metal loading wheel runs to the far end support pedestal, the excess length of the axle is used to get stuck in the groove of the arc-shaped turning guide rail to achieve reversal of the running direction.

[0018] The three-dimensional truss is made of metal and has a trapezoidal structure as a whole. The upper side of the three-dimensional truss is formed by connecting the upper chord rods end to end to form two parallel structures, and the parallel structures are connected at each intersecting ball node through the upper parallel straight web rods, and the adjacent upper parallel straight web rods are connected end to end through the upper parallel diagonal web rods, and multiple upper parallel diagonal web rods form a W-shaped structure.

[0019] The lower side of the three-dimensional truss is the same as the upper structure of the three-dimensional truss, and two parallel structures are formed by connecting the lower chord rods end to end. The parallel structures are connected at each intersecting ball node through the lower parallel straight web rods, and the adjacent lower parallel straight web rods are connected end to end through the lower parallel diagonal web rods. Multiple lower parallel diagonal web rods form a W-shaped structure.

[0020] The lower side of the three-dimensional truss is longer than the upper side, forming a trapezoidal structure as a whole.

[0021] The upper side and the lower side of the three-dimensional truss are aligned and connected by straight web bars, and oblique web bars are arranged on the front and back of the three-dimensional truss to form a parallel and symmetrical W-shaped structure.

[0022] A hinge support is arranged at one end of the lower side of the three-dimensional truss, and a roller support is arranged at the other end.

[0023] The upper chord, lower chord, straight web, diagonal web, upper parallel-connected straight web, upper parallel-connected diagonal web, lower parallel-connected straight web and lower parallel-connected diagonal web are distinguished by sealing with plastics of different colors.

[0024] The automatic lifting mechanism comprises a motor, a frequency converter, a single chip microcomputer, a proximity switch, a wire displacement meter, a transmission chain, a sprocket, a transmission shaft, a linear guide rail, an L-shaped metal support beam, a fish mouth hook and a support frame.

[0025] The support frame is a rectangular outer frame of the automatic lifting mechanism, an L-shaped metal support beam is arranged near the proximal support pedestal in the support frame, a vertical linear guide rail is arranged opposite the L-shaped metal support beam, the fish mouth hook is fixed on the L-shaped metal support beam, and is used to capture the metal loading wheel, a transmission shaft is installed at the bottom of the support frame, the transmission shaft is driven by a motor, a sprocket is installed on the transmission shaft, a transmission chain passes around the sprocket, and the transmission chain pulls the L-shaped metal support beam and runs up and down along the linear guide rail; the proximity switch is installed on the lower side of the support frame, and the pull-wire displacement meter is installed in the upper center of the support frame, and is used to provide the position information of the loading wheel to the single-chip microcomputer, and input the control signal to the frequency converter through the control logic program to realize the automatic lifting of the loading wheel; the proximity switch uses the method of emitting infrared rays and detecting reflected infrared rays to sense the arrival of the metal loading wheel, and the pull-wire displacement meter is used to sense the vertical position of the L-shaped metal support beam.

[0026] When the model is used, the motor of the automatic lifting mechanism is powered by 220V AC, and the metal loading wheels are connected to the hooks on the outer ring of the middle bearing of the wheel shaft by steel wire ropes to form a closed wheel string;

[0027] After starting, the metal loading wheel located on the lower guide rail runs along the lower guide rail to the proximal support pedestal due to the action of gravity, and the metal loading wheel located on the upper guide rail runs from the proximal support pedestal along the upper guide rail to the distal support pedestal under the traction of the wire rope; after the metal loading wheel reaches the distal support pedestal, it automatically slides along the arc-shaped turning guide rail to the sloped lower guide rail, runs to the proximal support pedestal under the action of its own gravity, and is automatically captured by the automatic lifting mechanism and lifted to the upper guide rail to realize automatic cyclic simulated loading.

[0028] The lower guide rail brackets are provided with three, and the height of the lower guide rail brackets gradually decreases from the far end support seat to the near end support seat, so that the lower guide rail forms a slope, and the slope generally ranges from 3 to 10%. Preferably, the slope is 3.5%.

[0029] In the model, two support pedestals are used to simulate the piers of the bridge, a hinge support and a roller support are used to simulate the bridge support, and multiple metal wheels are connected in series with thin steel wire ropes to simulate the vehicle load on the bridge. The model uses a lifting mechanism controlled by a single-chip microcomputer to lift the metal wheels, uses proximity sensors and pull-rope displacement meters to provide loading wheel position information and control signals, and uses a lower guide rail with a set slope to achieve automatic unidirectional rolling of the metal wheels.

[0030] The three-dimensional truss uses metal round tubes as the rods of the truss, and a ball node is designed to assemble and connect the rods into a whole. The rods are connected to the ball node through bolts inserted into them. The bolts can be rotated synchronously through pins and sleeves to facilitate the tight connection between the rods and the ball node. With this connection method, the tightness of the connection between the rods and the ball node can be adjusted. For example, a certain rod can be appropriately loosened to simulate the effect of looseness between the rods and the node plates of the truss bridge on the deformation and bearing capacity of the bridge structure, which is used for the development of early warning algorithms for bridge health monitoring systems. Different types of rods of the metal truss are sealed with different colors to facilitate the explanation of the concept of truss rod categories in teaching; the metal balls of the metal truss nodes are polished to reflect the exquisiteness of the manufacturing process and convey the inherent beauty of the metal material.

[0031] The proximal and distal support pedestals are used to simulate the piers or abutments of a bridge and support the three-dimensional metal trusses. The pedestals are made of bent metal plates, have large bearing capacity and are light in weight. They can be connected to the lifting mechanism frame or the guide rail bracket through the base or other connectors, and have good stability.

[0032] A metal hinge support is set above the proximal support pedestal and connected to the support node of the three-dimensional truss, which can simulate the hinge support in the real bridge structure. A metal roller support with a bearing is set above the distal support pedestal and connected to the support node of the three-dimensional truss. The hinge support and roller support can achieve full constraint and flexural deformation of the superstructure of the model bridge.

[0033] The steel pipe guide rail includes an upper guide rail placed on the lower parallel joint of the three-dimensional truss and a lower guide rail under the truss, both of which are bent from round steel pipes and connected to the lower parallel joint of the truss or the lower guide rail bracket by bolts. The lower guide rail is supported on three brackets with gradually decreasing heights to form a downward slope, and the gravity of the loading wheel is used to achieve automatic rolling. At one end of the lower guide rail at the proximal support pedestal, an arc with an inner diameter equal to the outer diameter of the loading wheel disc is provided to play a buffering role.

[0034] In the automatic lifting mechanism, the fish mouth hook can automatically capture the axle of the loading wheel when the loading wheel runs to the arc part of the lower rail to achieve lifting. When the loading wheel is lifted to the height of the upper rail, a metal stopper pushes the wheel disc to achieve unhooking, and the loading wheel can run along the proximal transition rail to the upper rail. The proximity switch and the pull-rope displacement meter are used as sensors to send the loading wheel position information to the single-chip microcomputer and control the motor according to the set control logic.

[0035] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0036] This model can be used for demonstration experiments and experimental courses in bridge engineering, structural mechanics, engineering mechanics and other courses in colleges and universities, which can improve students' interest in the courses and enhance their understanding of the knowledge points involved in the courses; it can also be used to provide a basic experimental platform for scientific research tasks related to bridge engineering, structural mechanics and other fields. Compared with the existing bridge engineering teaching model, the advantage is that it can not only provide a visualized bridge shape for intuitive teaching, but also this model is made of metal materials with high processing accuracy. After installing displacement meters, force sensors and strain sensors, it can not only be used for teaching bridge engineering concepts such as "influence lines", "most unfavorable load positions", and "change laws of internal forces of constant live loads of bridge components", but also can be used as a research platform for damage criteria in bridge engineering and structural engineering health monitoring research, and has a wider range of uses. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 It is a schematic diagram of the structure of a bridge engineering teaching and experimental model with automatic cyclic simulation loading provided by an embodiment of the present invention;

[0039] Figure 2 It is a schematic diagram of a three-dimensional truss structure in a bridge engineering teaching and experimental model with automatic cyclic simulation loading provided by an embodiment of the present invention;

[0040] Figure 3 It is a schematic diagram of the structure of a metal loading wheel in a bridge engineering teaching and experimental model for automatic cyclic simulated loading provided by an embodiment of the present invention.

[0041] Among them: 1-three-dimensional truss; 2-proximal support pedestal; 3-distal support pedestal; 4-metal loading wheel; 5-upper guide rail; 6-lower guide rail; 7-automatic lifting mechanism; 8-changeable guide rail; 9-changeable guide rail bracket; 10-hinge support; 11-roller support; 12-lower guide rail bracket; 13-proximal transition guide rail; 14-transmission shaft; 15-transmission chain; 16-support frame;

[0042] 101-upper chord; 102-lower chord; 103-ball node; 104-straight web; 105-diagonal web; 106-upper parallel-connected diagonal web; 107-upper parallel-connected straight web; 108-lower parallel-connected diagonal web; 109-lower parallel-connected straight web;

[0043] 201-wheel disc; 202-axle; 203-bearing; 204-hook; 205-wheel rim groove. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0045] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0046] In the embodiments of the present invention, sometimes the subscripts such as W 1 It may be written in non-subscript form such as W1. When the difference is not emphasized, the meaning is the same.

[0047] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0048] The embodiment of the present invention provides a bridge engineering teaching and experimental model with automatic cyclic simulation loading. Figure 1 The bridge engineering teaching and experimental model structure with automatic cyclic simulation loading shown includes a three-dimensional truss 1, a proximal support pedestal 2, a distal support pedestal 3 and a cyclic simulation loading system.

[0049] The cyclic simulation loading system comprises a metal loading wheel 4 , an upper guide rail 5 , a lower guide rail 6 , an automatic lifting mechanism 7 , a direction-changing guide rail 8 , a hinge support 10 , a roller support 11 and a proximal transition guide rail 13 .

[0050] One end of the bottom of the three-dimensional truss 1 is installed on the proximal support pedestal 2 through a hinge support 10 , and the other end of the bottom of the three-dimensional truss 1 is installed on the distal support pedestal 3 through a roller support 11 .

[0051] The upper guide rail 5 is erected on the inner bottom of the three-dimensional truss 1 , and the end of the upper guide rail 5 is connected to the upper end of the changeable guide rail 8 through the remote support pedestal 3 , and the changeable guide rail 8 is installed on the changeable guide rail bracket 9 .

[0052] The lower end of the deflection guide rail 8 is connected to the lower guide rail 6 , and the lower guide rail 6 is supported by a lower guide rail bracket 12 .

[0053] The end of the lower guide rail 6 is connected to the lower part of the automatic lifting mechanism 7 at the proximal support base 2 , and the upper part of the automatic lifting mechanism 7 is connected with a proximal transition guide rail 13 , and the proximal transition guide rail 13 cooperates with the upper guide rail 5 .

[0054] The metal loading wheel 4 moves along the upper guide rail 5 , the change-direction guide rail 8 , and the lower guide rail 6 , and can be lifted from the lower guide rail 6 to the proximal transition guide rail 13 by the automatic lifting mechanism 7 , thereby returning to the upper guide rail 5 .

[0055] The automatic lifting mechanism 7 includes a motor, a frequency converter, a single chip microcomputer, a proximity switch, a wire displacement meter, a transmission chain, a sprocket, a transmission shaft, a linear guide rail, an L-shaped metal support beam, a fish mouth hook and a support frame.

[0056] The support frame 16 is a rectangular outer frame of the automatic lifting mechanism. An L-shaped metal support beam is arranged inside the support frame 16 near the proximal support pedestal 2. The vertical linear guide rail is arranged opposite the L-shaped metal support beam. The fish mouth hook is fixed on the L-shaped metal support beam to capture the metal loading wheel. A transmission shaft 14 is installed at the bottom of the support frame 16. The transmission shaft 14 is driven by a motor. A sprocket is installed on the transmission shaft 14. A transmission chain 15 bypasses the sprocket. The transmission chain 15 pulls the L-shaped metal support beam and runs up and down along the linear guide rail. The proximity switch is installed on the lower side of the support frame, and the wire displacement meter is installed in the upper center of the support frame, which is used to provide the position information of the loading wheel to the single-chip microcomputer, and input a control signal to the frequency converter through the control logic program to realize automatic lifting of the loading wheel.

[0057] like Figure 3 The metal loading wheel includes a wheel disc 201 , an axle 202 , a bearing 203 and a hook 204 .

[0058] The two wheel discs 201 are coaxial through a wheel axle 202 , and a semicircular wheel rim groove is provided on the edge of the wheel disc. During operation, the steel pipes of the upper guide rail and the lower guide rail are embedded in the wheel rim groove 205 .

[0059] The bearing 203 is arranged at the midpoint of the axle 202, the inner ring of the bearing cooperates with the axle, the outer ring of the bearing is connected to two hooks 204, the two hooks are symmetrically arranged, and multiple metal loading wheels are connected to the hooks by thin steel wire ropes to form a closed wheel string.

[0060] like Figure 2 The three-dimensional truss 1 is made of metal and has a trapezoidal structure as a whole. The upper side of the three-dimensional truss is formed by connecting the upper chord 101 end to end to form two parallel structures, and the parallel structures are connected at each intersecting ball node 103 through the upper parallel straight web member 107, and the adjacent upper parallel straight web members 107 are connected end to end through the upper parallel diagonal web member 106, and multiple upper parallel diagonal web members 106 form a W-shaped structure.

[0061] The lower side of the three-dimensional truss is the same as the upper structure of the three-dimensional truss, and two parallel structures are formed by connecting the lower chord 102 end to end, and the parallel structures are connected at each intersecting ball node 103 through the lower parallel straight web member 109, and the adjacent lower parallel straight web members 109 are connected end to end through the lower parallel diagonal web member 108, and multiple lower parallel diagonal web members 108 form a W-shaped structure.

[0062] The lower side of the three-dimensional truss is longer than the upper side, forming a trapezoidal structure as a whole.

[0063] The upper and lower sides of the three-dimensional truss are aligned and connected via a straight web member 104, and oblique web members 105 are arranged on the front and back of the three-dimensional truss to form a parallel and symmetrical W-shaped structure.

[0064] A hinge support 10 is arranged at one end of the lower side of the three-dimensional truss, and a roller support 11 is arranged at the other end.

[0065] In the actual design, the upper chord, lower chord, straight web, diagonal web, upper parallel straight web, upper parallel diagonal web, lower parallel straight web and lower parallel diagonal web are distinguished by using different colors of sealing plastic.

[0066] When the model is used, it is powered by 220V AC. After startup, multiple metal loading wheels connected in series automatically run from the proximal support pedestal along the upper guide rail installed on the three-dimensional truss. After the metal loading wheels reach the distal support pedestal, they automatically slide along the arc-shaped turning guide rail to the sloped lower guide rail, run to the proximal support pedestal under the action of their own gravity, and are automatically captured by the automatic lifting mechanism and lifted to the upper guide rail to realize automatic cyclic simulation loading.

[0067] The application scenarios of the model of the present invention are as follows:

[0068] (1) Demonstration experiment of the course Introduction to Bridge Engineering

[0069] In the courses of "Introduction to Civil Engineering" and "Bridge Engineering" in colleges and universities, the overview chapter teaching involving knowledge points such as bridge types and stress characteristics can be demonstrated to students in the laboratory with this model as a teaching aid. This model represents a bottom-supported truss bridge, and the loading wheel represents the train or car load. Through strain gauges, pressure sensors and static strain acquisition and analysis systems, the stress and support reaction changes of the upper structure members of the truss bridge (upper and lower chords, web members, etc.) during the movement of the wheel load are recorded and displayed, and the stress characteristics of the simply supported truss bridge are summarized.

[0070] (2) Explanation of the concept of influence lines in the structural mechanics course

[0071] The concept of influence line is involved in the teaching of "Structural Mechanics". In the laboratory, this model is used to explain the definition of influence line, and the shape of influence line is intuitively demonstrated through loading test using the lower chord or upper chord as an example, and compared with the theoretical calculation results.

[0072] (3) As a structural damage identification experimental platform

[0073] In the research work of the secondary disciplines of civil engineering, such as structural engineering, bridge and tunnel engineering, damage identification is an important research direction of structural health monitoring technology. Using this model, defects can be artificially set on truss members and nodes to simulate structural damage, such as reducing the cross-sectional area of ​​the member or loosening its node bolts, which can simulate the weakening of the cross-sectional area of ​​the truss bridge member after corrosion and the loosening of the connection between the member and the node plate. By comparing the static and dynamic responses of the structure before and after damage, the indicators and judgment criteria for structural damage identification can be studied.

[0074] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A bridge engineering teaching and experimental model with automatic cyclic simulation loading, characterized in that: The model includes a three-dimensional truss, a proximal support pedestal, a distal support pedestal and a cyclic simulation loading system. The cyclic simulation loading system includes a metal loading wheel, an upper guide rail, a lower guide rail, an automatic lifting mechanism, a changeable guide rail, a hinge support, a roller support and a proximal transition guide rail. One end of the bottom of the three-dimensional truss is installed on the proximal support pedestal through a hinge support, and the other end of the bottom of the three-dimensional truss is installed on the distal support pedestal through a roller support; The upper guide rail is mounted on the inner bottom of the three-dimensional truss, the end of the upper guide rail is connected to the upper end of the changeable guide rail through a remote support pedestal, and the changeable guide rail is mounted on the changeable guide rail bracket; The lower end of the deflection guide rail is connected to the lower guide rail, and the lower guide rail is supported by a lower guide rail bracket; The end of the lower guide rail is connected to the lower part of the automatic lifting mechanism at the proximal support seat, and the upper part of the automatic lifting mechanism is connected to the proximal transition guide rail, and the proximal transition guide rail cooperates with the upper guide rail; The metal loading wheel moves along the upper guide rail, the change-direction guide rail, and the lower guide rail, and can be lifted from the lower guide rail to the proximal transition guide rail by an automatic lifting mechanism, thereby returning to the upper guide rail.

2. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: There are no less than two metal loading wheels, and multiple metal loading wheels are connected in series, and the diameter of the metal loading wheel is smaller than the height of the three-dimensional truss.

3. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: The metal loading wheel comprises a wheel disc, a wheel axle, a bearing and a hook. The two wheel discs are coaxial through a wheel axle, and a semicircular wheel rim groove is provided on the edge of the wheel disc. During operation, the steel pipes of the upper guide rail and the lower guide rail are embedded in the wheel rim groove; The bearing is arranged at the midpoint of the wheel axle, the inner ring of the bearing cooperates with the wheel axle, the outer ring of the bearing is connected to two hooks, the two hooks are symmetrically arranged, and the multiple metal loading wheels are connected to the hooks by thin steel wire ropes to form a closed wheel string.

4. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 3 is characterized in that: The axle of the metal loading wheel is longer than the outer profile of the wheel disc. When the metal loading wheel runs to the far end support pedestal, the excess length of the axle is used to get stuck in the groove of the arc-shaped turning guide rail to achieve reversal of the running direction.

5. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: The three-dimensional truss is made of metal and has a trapezoidal structure as a whole. The upper side of the three-dimensional truss is formed by connecting the upper chord rods end to end to form two parallel structures, and the parallel structures are connected at each intersecting ball node through the upper parallel straight web rods, and the ends of adjacent upper parallel straight web rods are connected by upper parallel diagonal web rods, and multiple upper parallel diagonal web rods form a W-shaped structure; The lower side of the three-dimensional truss is the same as the upper structure of the three-dimensional truss, and is formed by connecting the lower chord rods end to end to form two parallel structures, and the parallel structures are connected at each intersecting ball node through the lower horizontal straight web rods, and the ends of adjacent lower horizontal straight web rods are connected by the lower horizontal diagonal web rods, and multiple lower horizontal diagonal web rods form a W-shaped structure; The lower side of the three-dimensional truss is longer than the upper side, forming a trapezoidal structure as a whole; The upper and lower sides of the three-dimensional truss are aligned and connected by straight webs, and oblique webs are arranged on the front and back of the three-dimensional truss to form a parallel and symmetrical W-shaped structure; A hinge support is arranged at one end of the lower side of the three-dimensional truss, and a roller support is arranged at the other end.

6. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 5 is characterized in that: The upper chord, lower chord, straight web, diagonal web, upper parallel-connected straight web, upper parallel-connected diagonal web, lower parallel-connected straight web and lower parallel-connected diagonal web are distinguished by sealing with plastics of different colors.

7. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: The automatic lifting mechanism includes a motor, a frequency converter, a single-chip microcomputer, a proximity switch, a wire displacement meter, a transmission chain, a sprocket, a transmission shaft, a linear guide rail, an L-shaped metal joist, a fish mouth hook and a support frame; The support frame is a rectangular outer frame of the automatic lifting mechanism, an L-shaped metal support beam is arranged near the proximal support pedestal in the support frame, a vertical linear guide rail is arranged opposite to the L-shaped metal support beam, the fish mouth hook is fixed on the L-shaped metal support beam, and is used to capture the metal loading wheel, a transmission shaft is installed at the bottom of the support frame, the transmission shaft is driven by a motor, a sprocket is installed on the transmission shaft, a transmission chain passes around the sprocket, and the transmission chain pulls the L-shaped metal support beam to run up and down along the linear guide rail; The proximity switch is installed on the lower side of the support frame, and the wire displacement meter is installed in the upper center of the support frame, which is used to provide the position information of the loading wheel to the single-chip microcomputer, and input the control signal to the frequency converter through the control logic program to realize the automatic lifting of the loading wheel.

8. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: When the model is used, the motor of the automatic lifting mechanism is powered by 220V AC, and the metal loading wheels are connected to the hooks on the outer ring of the middle bearing of the wheel shaft by steel wire ropes to form a closed wheel string; After starting, the metal loading wheel located on the lower guide rail runs along the lower guide rail to the proximal support pedestal due to the action of gravity, and the metal loading wheel located on the upper guide rail runs from the proximal support pedestal along the upper guide rail to the distal support pedestal under the traction of the wire rope; after the metal loading wheel reaches the distal support pedestal, it automatically slides along the arc-shaped turning guide rail to the sloped lower guide rail, runs to the proximal support pedestal under the action of its own gravity, and is automatically captured by the automatic lifting mechanism and lifted to the upper guide rail to realize automatic cyclic simulated loading.

9. The bridge engineering teaching and experimental model with automatic cyclic simulated loading according to claim 1 is characterized in that: The lower guide rail brackets are provided with three, and the height of the lower guide rail brackets gradually decreases from the distal support pedestal to the proximal support pedestal, so that the lower guide rail forms a slope of 3% to 10%.

Images