A composite beam member testing device and method

Abstract

The application discloses a kind of composite action lower beam component test device and method.The device includes: the beam component supported by the rotation support in the middle of bottom;With vertical loading system mechanical separation transverse loading system, it is connected with the both ends of beam component by first, second end rotation piece rotation, slot cross bar and transverse bottom actuator are connected with end rotation piece by reaction force transmission unit respectively, and there is eccentricity with beam component axis, contact connection is formed between reaction force transmission unit and beam component, only horizontal force is transmitted, and no bending moment is transmitted;And vertical loading system for applying vertical pressure to the middle of beam component.Transverse loading system applies axial tension and end negative bending moment to beam component, and superimposes positive bending moment generated with vertical loading system.This device realizes independent control and accurate application of composite action to beam shear span area, i.e.axial force, shear force and bending moment, effectively solves the technical problems that it is difficult to accurately apply composite action force and easy to occur bending damage in long beam shear damage test.

Description

Technical Field

[0001] This invention relates to the field of civil engineering testing equipment technology, and particularly to a testing device and method for beam components under combined loads. Background Technology

[0002] Beams are widely used in civil engineering structures such as buildings, bridges, and underground tunnels. They are key load-bearing components in bridge engineering, buildings, and underground structures. Research on their mechanical properties is of great guiding significance for enhancing the safety of engineering design and improving the service life of structures.

[0003] Analysis of the stress on common reinforced concrete continuous beam members reveals that when a continuous beam is rigidly connected to a column-pier joint, the shrinkage and temperature changes of the concrete after cast-in-place construction create strong constraints on the axial deformation of the beam, resulting in significant axial tensile forces. Simultaneously, beam members often bear the combined effects of shear force and bending moment; therefore, the shear strength of the beam is significantly affected by axial forces, and the adverse effects of axial tensile forces on the beam's shear strength need to be considered.

[0004] The mechanism by which axial tension affects shear capacity lies in its reduction of the shear-compression zone height of the concrete. In flexural members, shear force is primarily borne by the concrete in the compression zone. When a member is simultaneously subjected to axial tension, the tension causes tensile deformation. To balance the tension, the entire or part of the cross-section is subjected to tension, which significantly reduces or even eliminates the height of the concrete compression zone at the beam ends. This results in a reduction in the area of ​​the shear-compression zone, significantly decreasing the concrete's ability to directly resist shear force.

[0005] Although some patent documents have proposed experimental devices for shear failure of beams, it is not easy to actually achieve shear failure of long beams, mainly due to the following challenges:

[0006] (1) In order to study the shear failure of beams, the conventional three-point bending test device supports the bottom of the beam end of a beam member on two hinged supports, and applies vertical concentrated pressure to the top surface of the beam through jacks or actuators. When the concentrated pressure is far away from the supports, long beams are more likely to undergo bending failure rather than shear failure; when the concentrated pressure is too close to the hinged supports of the beam, most of the concentrated pressure is borne by the supports, and the shear force on the beam is very small. Large jacks are required to break the beam. When studying the shear failure of large beam members, the loading conditions of the laboratory are very demanding.

[0007] (2) In order to achieve shear failure, one of the current approaches is to design special beam cross-sections, that is, to increase the beam's cross-sectional height and width while reducing the beam's length, turning a long beam into a short beam, or to change the reinforcement structure, that is, to increase the cross-sectional area of ​​the longitudinal reinforcement. Although this approach can achieve shear failure of the beam, it changes the actual reinforcement structure and cross-sectional dimensions of the beam in actual engineering. The test results are difficult to reflect the actual stress situation and have low reference value for engineering design.

[0008] (3) More importantly, there is currently little research on the influence of combined action on the shear performance of beams. The traditional three-point bending test method cannot take into account the influence of axial force on the shear bearing capacity of beams. Not taking into account the influence of axial force will lead to an overestimation of the shear bearing capacity of beams, which is unsafe.

[0009] The aforementioned challenges prevent current testing devices for shear failure of beams from simultaneously achieving the combined effects of axial tension, shear force, negative end bending moment, and positive mid-span bending moment, and also make it difficult to maintain the actual engineering reinforcement structure and cross-sectional characteristics of the beam. Therefore, there is an urgent need for a new type of testing device that can realistically simulate the combined stress state and accurately test the shear bearing capacity of large-size beam members. Summary of the Invention

[0010] Technical Objective: To address the aforementioned technical problems, this application proposes a test device and method for beam members under combined action. This test device can test the shear bearing capacity of the shear span zone of beam members under different tensile and bending moment combined actions, effectively realizing the shear failure mode of beams. Moreover, the test method is simple, can quickly replace damaged beam members, and systematically conduct tests on multiple beam members, showing good application prospects.

[0011] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0012] A test apparatus for beam members under combined loads, comprising:

[0013] The beam member is horizontally supported on a rigid ground by a mid-span rotation support with an internal gap on its left and right sides at the bottom.

[0014] A lateral loading system, used to apply axial tensile force and negative bending moment to the end segments of a beam member, includes:

[0015] The first end rotating member has its middle part rotatably connected to one end of the beam member, and is able to rotate in the XZ plane;

[0016] The second end rotating member has its middle part rotatably connected to the other end of the beam member, and can rotate in the XZ plane;

[0017] A slotted crossbar is arranged parallel to the longitudinal axis of the beam member on the upper part of the beam member, with a first eccentricity e between it and the beam member. One end of the slotted crossbar abuts against the upper end of the first end rotating member through a first reaction force transmission unit; the other end of the slotted crossbar abuts against the upper end of the second end rotating member through a transverse top actuator and a second reaction force transmission unit.

[0018] A transverse bottom actuator is arranged parallel to the longitudinal axis of the beam member at the lower part of the beam member, and there is a second eccentricity e between the transverse bottom actuator and the beam member; one end of the transverse bottom actuator abuts against the lower end of the first end rotating member through a third reaction force transmission unit; the other end of the transverse bottom actuator abuts against the lower end of the second end rotating member through a fourth reaction force transmission unit.

[0019] Among them, the first reaction force transmission unit and the top of one end of the beam member, the second reaction force transmission unit and the top of the other end of the beam member, the third reaction force transmission unit and the bottom of one end of the beam member, and the fourth reaction force transmission unit and the bottom of the other end of the beam member are all rolling contact connections that can only transmit force in the horizontal direction and do not transmit bending moment.

[0020] The transverse top actuator and transverse bottom actuator apply horizontal forces N1 and N2 to the ends of the beam member through the first end rotating member and the second end rotating member. The lines of action of the horizontal forces N1 and N2 are respectively eccentrically e from the central axis of the beam member, thereby applying a negative bending moment to the ends of the beam member.

[0021] The vertical loading system is used to apply a vertical pressure F in the Z direction to the upper side of the middle segment of the beam member to form a positive bending moment at mid-span. It is mechanically separated from the transverse loading system and the deformations do not interfere with each other, thus achieving a combined loading effect.

[0022] Furthermore, the first reaction force transmission unit, the second reaction force transmission unit, the third reaction force transmission unit, and the fourth reaction force transmission unit have the same structure, all including: a horizontal adapter and a force transmission beam connected to each other, and vertical grooves are respectively provided on the first end rotating member and the second end rotating member. The force transmission beam is slidably disposed in the vertical groove and is horizontally limited between the reaction seat and the end rotating member. The force transmission beam makes rolling contact with the beam component through rollers.

[0023] Furthermore, the horizontal adapter includes:

[0024] The connecting plate has one side for contacting the slotted crossbar or actuator, and two symmetrically arranged ear plates on the other side.

[0025] The web plate has one end inserted between two ear plates and connected to the two ear plates by a first pin, and the other end is fixedly connected to the force transmission beam.

[0026] The reaction seat is provided at one end of the force transmission beam that connects to the web.

[0027] Furthermore, the vertical loading system includes:

[0028] The reaction frame is supported on a rigid ground.

[0029] Vertical actuator, mounted on the reaction frame;

[0030] A vertical adapter, with its upper end connected to the vertical actuator and its lower end able to pass through the slot on the slotted crossbar to apply vertical pressure F to the middle of the beam member;

[0031] The slotted crossbars constrain the vertical adapter in the XZ plane by setting multiple rows of circular pins in the longitudinal direction, which prevents the beam component from overturning and losing stability in the YZ plane under large deformation loading conditions; the position of the pins can be adjusted in time according to the changes in the loading position of the vertical adapter.

[0032] Furthermore, the two end rotating parts are respectively hinged to the beam member by passing through the circular holes at the ends of the beam member with second pins. The end rotating parts also include retaining rings and reinforcing plates, with the reinforcing plates sleeved on the second pins by the retaining rings.

[0033] Furthermore, the main body of the beam member is made of reinforced concrete, and longitudinal bars, horizontal stirrups and vertical stirrups are densely arranged in the opening sections of the circular holes at both ends of the beam member. The stirrup ratio of the horizontal stirrups and vertical stirrups is 3 times that of the middle reinforced concrete section, and the reinforcement ratio of the longitudinal bars is 1.5 times that of the middle concrete section.

[0034] Furthermore, the mid-span rotating support includes a top plate, a cylindrical shaft, side plates, and a bottom plate. The bottom plate is vertically symmetrically provided with two side plates, and the top of the two side plates is provided with an arc-shaped mounting groove. The bottom of the top plate is rotatably connected to the arc-shaped mounting groove through the cylindrical shaft.

[0035] A gap is formed between the side plate and the bottom plate, through which the lateral bottom actuator can pass.

[0036] Another aspect of the present invention discloses an installation method for the test device of the beam member under the combined action, comprising the following steps:

[0037] S1: Two mid-span rotation supports are arranged symmetrically with respect to the center of the beam member on a rigid ground, and the beam member is placed on the mid-span rotation supports;

[0038] S2: Install the first end rotating component and the second end rotating component;

[0039] S3: Install the transverse top horizontal actuator and slotted crossbar on the upper part of the beam member. One end of the slotted crossbar is connected to the first reaction force transmission unit, and the other end abuts against the upper end of the second end rotating part through the transverse top actuator and the second reaction force transmission unit. The second reaction force transmission unit and the top of the other end of the beam member are in a contact connection that only transmits horizontal force and not bending moment. The distance between the axis of the slotted crossbar and the axis of the beam member is e.

[0040] S4: A transverse bottom actuator is arranged below the beam member. One end of the transverse bottom actuator abuts against the lower end of the first end rotating member through a third reaction force transmission unit. The third reaction force transmission unit and the bottom of one end of the beam member are in a contact connection that transmits only horizontal force and not bending moment. The other end of the transverse bottom actuator abuts against the lower end of the second end rotating member through a fourth reaction force transmission unit. The fourth reaction force transmission unit and the bottom of the other end of the beam member are in a contact connection that transmits only horizontal force and not bending moment. The transverse bottom actuator passes through the internal gap of the mid-span rotating support. There is an eccentricity e between the axis of the transverse bottom actuator and the axis of the beam member.

[0041] S5: Install a vertical loading system;

[0042] S6: Install displacement and strain measurement devices and data acquisition systems.

[0043] A third aspect of this invention provides a testing method for the test device of the beam member under the aforementioned combined action, comprising the following steps:

[0044] Loading steps: Step 1, activate the transverse top actuator to apply a horizontal force N1 in the X direction, which is transmitted to the top of the beam member through the slotted crossbar and the first and second reaction force transmission units. Activate the transverse bottom actuator to directly apply a horizontal force N2, which is transmitted to the bottom of the beam member through the third and fourth reaction force transmission units. The horizontal forces N1 and N2 have an eccentricity e with the longitudinal axis of the beam member, which together form a combined effect of axial force and negative bending moment at the end. Step 2, activate the vertical loading unit to apply a vertical pressure F in the Z direction to form a positive bending moment at the mid-span, causing shear failure of the beam member's shear span under the combined action of axial force, shear force, and bending moment.

[0045] Furthermore, the loading step selects one of the following modes according to the experimental requirements:

[0046] When studying the mechanical properties of beam members under the combined action of axial tensile force, shear force and negative bending moment, loading is performed according to Mode A.

[0047] A: First, adjust the horizontal force N1 output by the top horizontal actuator to be greater than the horizontal force N2 output by the bottom horizontal actuator, and N1 and N2 should be in the same direction. Then, adjust the vertical force F output by the vertical actuator.

[0048] When the beam member is not subjected to tensile force, but only to the combined action of shear force and negative bending moment, it is loaded according to mode B.

[0049] B: First, adjust the horizontal force N1 output by the top horizontal actuator to be equal to the horizontal force N2 output by the bottom horizontal actuator. However, N1 is a tension force and N2 is a compression force. That is, the output forces of the top and bottom actuators are equal in magnitude but opposite in direction. Then, adjust the vertical force F output by the vertical actuator.

[0050] When a beam member is subjected to axial tensile force and shear force but not negative bending moment, it is loaded according to mode C;

[0051] C: First, adjust the horizontal force N1 output by the top horizontal actuator to be equal to the horizontal force N2 output by the bottom horizontal actuator, and both N1 and N2 are tension forces, that is, the output forces of the top and bottom actuators are equal in magnitude and in the same direction. Then, adjust the vertical force F output by the vertical actuator to generate a positive bending moment.

[0052] Beneficial effects:

[0053] (1) The present application proposes a bidirectional composite loading system, which has independent lateral and vertical loading capabilities. That is, the axial deformation of the beam caused by the lateral loading system will not affect the vertical loading of the beam. The lateral and vertical loading systems of this device are independent because the actuators used in the lateral and vertical loading systems are independent, and the lateral and vertical support systems are independent, so that they do not interfere with each other. This mechanically separated connection method ensures that the vertical deformation in the middle of the beam span and the rotational deformation of the lateral loading system at the ends do not interfere with each other, resulting in higher accuracy of the test results.

[0054] (2) The bidirectional loading system of this application enables effective shear failure in the shear span zone of the beam member. By designing two end rotating loading supports and two upper and lower lateral loading actuators to apply horizontal forces, the two horizontal forces are deviated from the beam axis by a certain distance, thereby generating axial tensile force and constant negative bending moment at the beam ends. The so-called constant negative bending moment means that the negative bending moment along the longitudinal axis of the beam remains constant and does not change linearly with the beam axis.

[0055] To accurately test the shear capacity of beam members and ensure that the beam segment between the point of concentrated force application and the support (referred to as the shear span zone) exhibits the desired shear failure mode, it is necessary to prevent premature bending failure of long beams, which could lead to beam member failure. Current experimental setups address this by adding short cantilever sections to the beam member and applying concentrated forces at the cantilever ends to increase the negative bending moment at the supports, thereby reducing the influence of the positive bending moment in the shear failure zone. However, this method has the drawback that the negative bending moment decreases linearly along the beam's longitudinal axis, reaching its maximum at the supports and half its value at mid-span. This makes it difficult to effectively reduce the positive bending moment in the shear failure zone, and the likelihood of the beam ultimately undergoing bending failure remains relatively high. It fails to effectively induce the desired shear failure in the beam segment, which is precisely the shear capacity issue of long beams that this experiment needs to address.

[0056] (3) The innovative transverse loading system of this application applies axial tension and negative bending moment through the end rotating component, which conforms to the actual shear force distribution in the beam shear span zone and the testing method is reasonable. Existing test devices apply concentrated force to the cantilever end of the beam member, which changes the actual shear force distribution in the shear span zone, and the test results differ significantly from the actual stress distribution. Using this test device will not generate additional shear force on the beam, keeping the shear stress state of the beam consistent with the stress distribution of the beam in actual engineering, and the research results are more referential for engineering design. This test device generates negative bending moment at the support of the beam segment by applying horizontal concentrated force, unlike applying concentrated load to the cantilever segment, and will not generate additional shear force on the beam. Therefore, the shear force distribution studied has not changed. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of a test device for beam components under combined action according to the present invention;

[0058] Figure 2 This is a schematic diagram of the end loading component structure of the present invention;

[0059] Figure 3 This is a schematic diagram of the loading beam of the present invention;

[0060] Figure 4 This is a schematic diagram of the end rotating component of the present invention.

[0061] Figure 5 This is a schematic diagram of a beam component with end openings according to the present invention;

[0062] Figure 6 This is a schematic diagram of the reinforcing steel bars around the opening in this invention;

[0063] Figure 7 This is a schematic diagram of the bidirectional loading system of the present invention;

[0064] Figure 8 This is a schematic diagram of the lateral loading system of the present invention;

[0065] Figure 9 This is a schematic diagram of the slotted crossbar of the present invention;

[0066] Figure 10 This is a schematic diagram of the vertical loading system of the present invention;

[0067] Figure 11 This is a schematic diagram of the mid-span rotation support of the present invention;

[0068] Figure 12 This is a force diagram showing the combined effects of axial force, shear force, and bending moment on the beam member of the present invention.

[0069] Wherein: 1-Force transmission beam; 101-Force transmission beam web; 102-Roller; 103-Reaction seat;

[0070] 2-First end rotating component; 201-Channel steel; 202-Reinforcing plate; 203-Snap ring; 204-Rotating component pin;

[0071] 3-Horizontal adapter; 301-Connecting plate; 302-Ear plate; 303-Body plate; 304-First pin;

[0072] 4-Beam member; 401-Reinforced concrete intermediate section; 402-End opening section; 403-Circular hole; 404-Longitudinal reinforcement; 405-Horizontal stirrups; 406-Vertical stirrups;

[0073] 5-Slotted crossbar; 501-Outer crossbar; 502-Internal slot; 503-Crossbar pin;

[0074] 6-Horizontal top actuator;

[0075] 7-Mid-span rotation support; 701-Top plate; 702-Cylindrical shaft; 703-Side plate; 704-Bottom plate;

[0076] 8-Reaction column; 9-Horizontal bottom actuator; 10-Vertical adapter; 11-Vertical actuator; 12-Reaction frame; 13-Second end rotating component; 14-Rigid ground. Detailed Implementation

[0077] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0078] The following description, with reference to the accompanying drawings, describes a test apparatus and testing method for beam components under combined loads proposed in an embodiment of the present invention.

[0079] A test apparatus for beam members under combined loads, comprising:

[0080] Beam member 4, with its bottom left and right sides respectively supported horizontally on a rigid ground 14 by a mid-span rotation support 7 with an internal gap, is as follows. Figure 1 and Figure 10 As shown;

[0081] A transverse loading system is used to apply axial tensile force and negative bending moment to the two end segments 402 of beam member 4, such as... Figure 7 and Figure 8 As shown, it includes:

[0082] The first end rotating member 2 has its middle part rotatably connected to one end of the beam member 4, and there is a gap between it and the rigid ground 14, so that it can rotate in the XZ plane;

[0083] The second end rotating member 13 has its middle part rotatably connected to the other end of the beam member 4, and has a gap with the rigid ground 14, allowing it to rotate in the XZ plane. Figure 4 As shown;

[0084] The slotted crossbar 5 is arranged parallel to the longitudinal axis of the beam member 4 on the upper part of the beam member 4, and there is a first eccentricity e between it and the beam member 4. One end of the slotted crossbar 5 abuts against the upper end of the first end rotating member 2 through the first reaction force transmission unit. The first reaction force transmission unit and the top of one end of the beam member 4 are in a contact connection that only transmits horizontal force and not bending moment. The other end of the slotted crossbar 5 abuts against the upper end of the second end rotating member 2 through the transverse top actuator 6 and the second reaction force transmission unit. The second reaction force transmission unit and the top of the other end of the beam member 4 are in a contact connection that only transmits horizontal force and not bending moment.

[0085] A transverse bottom actuator 9 is arranged parallel to the longitudinal axis of the beam member 4 at the lower part of the beam member 4, and there is a second eccentricity e between it and the beam member 4; one end of the transverse bottom actuator 9 abuts against the lower end of the first end rotating member 2 through a third reaction force transmission unit, and the third reaction force transmission unit and the bottom of one end of the beam member 4 are in a contact connection that transmits only horizontal force and not bending moment; the other end of the transverse bottom actuator 9 abuts against the lower end of the second end rotating member 2 through a fourth reaction force transmission unit, and the fourth reaction force transmission unit and the bottom of the other end of the beam member 4 are in a contact connection that transmits only horizontal force and not bending moment.

[0086] like Figure 7 As shown, the transverse top actuator 6 and transverse bottom actuator 9 apply horizontal forces N1 and N2 to the beam member 4 through the first end rotating member 2 and the second end rotating member 13. The horizontal forces N1 and N2 have an eccentricity e with the central axis of the beam member 4, thereby applying a negative bending moment at the end of the beam member 4.

[0087] like Figure 10As shown, the vertical loading system is used to apply vertical pressure F to the upper side of the middle segment of beam member 4 to form a positive bending moment at mid-span. It is mechanically separated from the transverse loading system and the deformations do not interfere with each other, thus achieving composite loading.

[0088] like Figure 2 As shown, the first reaction force transmission unit, the second reaction force transmission unit, the third reaction force transmission unit, and the fourth reaction force transmission unit have the same structure, all including: a horizontal adapter 3 and a force transmission beam 1 connected to each other. The first end rotating member 2 and the second end rotating member 2 are respectively provided with vertical grooves. The force transmission beam 1 is slidably disposed in the vertical groove and is horizontally limited by the reaction seat 103 and the end rotating member. The force transmission beam 1 rolls in contact with the beam member 4 through the roller 102 and applies pressure to the beam member 4. The horizontal adapter 3 only transmits horizontal force and does not transmit bending moment.

[0089] The horizontal adapter 3 includes:

[0090] The connecting plate 301 has one side for abutting against the slotted crossbar 5 or the actuator, and two ear plates 302 arranged symmetrically on the other side.

[0091] The web plate 303 has one end inserted between two ear plates and connected to the two ear plates 302 via a first pin 304, and the other end is fixedly connected to the force transmission beam 1.

[0092] The reaction seat 103 is provided at one end of the force transmission beam 1 that is connected to the web plate 303.

[0093] like Figure 5 As shown, the beam member 4 consists of a reinforced concrete main section 401, an end-hole section 402, and a circular hole 403; as Figure 6 As shown, in order to avoid cracking of the end opening section 402 and affect the loading test, the horizontal stirrups 405 and vertical stirrups 406 in the end opening section 402 are densified. The stirrup ratio of the horizontal stirrups 405 and vertical stirrups 406 is 3 times that of the concrete intermediate main section 401 in the beam member 4, and the reinforcement ratio of the longitudinal bars 404 in the end opening section 402 is 1.5 times that of the concrete intermediate main section 401.

[0094] like Figure 9 As shown, the slotted crossbar 5 consists of an outer crossbar 501, an inner slot 502, and a crossbar pin 503. The slotted crossbar 5 is parallel to the longitudinal axis of the beam member 4, and the distance between it and the longitudinal axis of the beam member 4 is e.

[0095] like Figure 10 As shown, the vertical loading system consists of a mid-span rotating support 7, a reaction column 8, a vertical adapter 10, a vertical actuator 11, a reaction beam 12, and a rigid ground 14.

[0096] like Figure 7 As shown, the vertical actuator 11 is located at the top of the beam member 4, perpendicular to the longitudinal axis of the beam member 4; the top of the vertical actuator 11 is connected to the reaction frame 12, and the bottom applies vertical pressure F to the beam member 4 through the vertical adapter 10; the vertical adapter 10 passes vertically through the internal slot 502 of the slotted crossbar 5, and can move along the longitudinal axis of the beam member 5, changing the distance a between the vertical pressure F and the center of the mid-span rotating support 7; the reaction force 8 achieves stable connection with the rigid laboratory ground 14 to balance the force of the vertical actuator 11; the horizontal force generated by the upper transverse actuator 6 and the tensile force borne by the beam member 4 are mutually balanced; the slotted crossbar 5 constrains the vertical adapter 10 in the XZ plane through multiple rows of circular pins 503 arranged longitudinally, preventing the beam member from overturning and losing stability under large deformation loading conditions; the position of the pins 503 can be adjusted in time according to the change of the loading position of the vertical adapter 10.

[0097] like Figure 11 As shown, the mid-span rotation support 7 is composed of a top plate 701, a cylindrical shaft 702, a side plate 703, and a bottom plate 704; the transverse bottom actuator 6 passes through the internal gap formed by the side plate 703 and the bottom plate 704; the mid-span rotation support 7 is symmetrically arranged at the bottom of the beam member 7, and plays the role of supporting the beam member 4.

[0098] The horizontal force N1 applied by the transverse top actuator 6 and the horizontal force N2 applied by the transverse bottom actuator are transmitted to the horizontal adapter 3 and the force transmission beam 1 through the slotted crossbar 5. The force transmission beam 1 transmits the horizontal forces (N1 and N2) to the end rotating member 2 and the second pin 204, and the second pin 204 transmits the horizontal forces to the beam member 4.

[0099] The first end rotating component 2 passes through the circular hole 403 in the end opening section 402 of the beam component 4 via the second pin 204; the reinforcing plate 202 is fitted onto the second pin 204 via a retaining ring 203, which enhances the overall firm connection between the second pin 204 and the beam component 4 and prevents the beam component 4 from detaching from the second pin 204 during combined lateral and vertical loading; when the beam component 4 is damaged by test loading and data acquisition is completed, the retaining ring 203 and the reinforcing plate 202 are removed first, then the second pin 204 is pulled out, and finally the beam component 4 is moved laterally along the central axis out of the vertical groove of the first end rotating component 2, and a new beam component 4 is quickly installed for test studies in different modes;

[0100] like Figure 7 and Figure 12as shown, the eccentricity distance between the horizontal force N1 applied by the transverse top actuator 6 and the axis of the beam member 4 is e, and the eccentricity distance between the horizontal force N2 applied by the transverse bottom actuator 9 and the axis of the beam member 4 is e; as can be known from the basic concept of structural mechanics, the end negative moment M of the beam member 4 — =(N1-N2)e, the axial force N0=N1+N2. When the transverse top actuator outputs a compressive force, N1>0 is defined, and when the transverse top actuator outputs a tensile force, N1<0 is defined, the sign of N2 follows the same rule;

[0101] the distance between the vertical compressive force F of the vertical actuator 10 and the first mid-span rotating support 7 is defined as a (a<L / 2), and the distance between F and the second mid-span rotating support 7 is (L-a), where L is the distance between the first mid-span rotating support 7 and the second mid-span rotating support 7 at the bottom of the beam member 7; the concentrated compressive force applied to the beam member 4 by the vertical loading system is F, as can be known from the basic concept of structural mechanics, the mid-span positive moment M + =F(L-a)a / L, by superimposing the positive moment and the negative moment, it can be known that the end moment of the beam member 4 is M — =(N1+N2)e, and the mid-span moment of the beam member 4 is M0= M — + M + .

[0102] The installation method of the beam member test apparatus under composite action includes the following steps:

[0103] S1: Two said mid-span rotating supports 7 are arranged symmetrically about the center of the beam member 4 on the rigid ground 14, the beam member 4 is placed on said mid-span rotating supports 7, the distance L between the two mid-span rotating supports 7 is recorded, as Figure 10 shown;

[0104] S2: The first end rotating member 2 and the second end rotating member 13 are installed, as Figure 2 shown;

[0105] S3: The transverse top horizontal actuator 6 and the slotted cross bar 5 on the upper part of the beam member 4 are installed. One end of the slotted cross bar 5 is connected to the first reaction force transmission unit, the other end abuts against the upper end of the second end rotating member 2 through the transverse top actuator 6 and the second reaction force transmission unit, the contact connection between the second reaction force transmission unit and the top of the other end of the beam member 4 only transmits horizontal force without transmitting moment, and the distance between the axis of the slotted cross bar 5 and the axis of the beam member 4 is e, as Figure 8 shown;

[0106] S4: A transverse bottom actuator 9 is arranged below the beam member 4. One end of the transverse bottom actuator 9 abuts against the lower end of the first end rotating member through a third reaction force transmission unit. The third reaction force transmission unit and the bottom of one end of the beam member 4 are in a contact connection that transmits only horizontal force and not bending moment. The other end of the transverse bottom actuator 9 abuts against the lower end of the second end rotating member through a fourth reaction force transmission unit. The fourth reaction force transmission unit and the bottom of the other end of the beam member 4 are in a contact connection that transmits only horizontal force and not bending moment. The transverse bottom actuator 9 passes through the internal gap of the mid-span rotating support 7. The axis of the transverse bottom actuator 9 has an eccentricity e with the axis of the beam member 4.

[0107] S5: Install a vertical loading system, such as Figure 10 As shown;

[0108] S6: Install displacement and strain measurement devices and data acquisition systems.

[0109] The experimental method is as follows:

[0110] Loading steps: The horizontal top actuator 6 is activated to apply a horizontal force N1, which is transmitted to the top of the beam member 4 through the slotted crossbar 5 and the first and second reaction force transmission units. The horizontal bottom actuator 9 is activated to directly apply a horizontal force N2, which is transmitted to the bottom of the beam member 4 through the third and fourth reaction force transmission units. The horizontal forces N1 and N2 have an eccentricity e with the longitudinal axis of the beam member 4, which together form a combined effect of axial force and negative bending moment at the end. The vertical loading unit 11 is activated to apply vertical pressure to form a positive bending moment at the mid-span, causing the shear span of the beam member 4 to undergo shear failure under the combined action of axial force, shear force and bending moment.

[0111] Preferably, the loading step selects one of the following modes according to the experimental requirements:

[0112] When beam member 4 is subjected to the combined effects of axial tensile force, shear force and negative bending moment, loading is performed according to step A;

[0113] A: Adjust the horizontal force N1 output by the top horizontal actuator 6 to be greater than the horizontal force N2 output by the bottom horizontal actuator 9, and make sure that N1 and N2 are in the same direction. Adjust the vertical actuator to output the vertical pressure F.

[0114] When beam member 4 is not subjected to tensile force, but only to the combined action of shear force and negative bending moment, load is applied according to step B;

[0115] B: Adjust the horizontal force N1 output by the top horizontal actuator 6 to be equal to the horizontal force N2 output by the bottom horizontal actuator 9. However, N1 is a tension force and N2 is a compression force. That is, the output forces of the top and bottom actuators are equal in magnitude but opposite in direction. Adjust the vertical actuator to output the vertical compression force F.

[0116] When beam member 4 is subjected to axial tensile force and shear force but not negative bending moment, load is applied according to step C;

[0117] C: Adjust the horizontal force N1 output by the top horizontal actuator 6 to be equal to the horizontal force N2 output by the bottom horizontal actuator 9, and both N1 and N2 are tension forces, that is, the output forces of the top and bottom actuators are equal in magnitude and in the same direction. Adjust the vertical actuator to output the vertical pressure F.

[0118] After the loading test of beam member 4 is completed and the beam member fails, remove the retaining ring 203 and the reinforcing plate 202, take out the second pin 204, remove the loaded beam member 4 along the transverse direction, and reinstall the next beam member 4 to conduct test loading under different combined actions.

[0119] In summary, this embodiment achieves a realistic simulation of the combined stress state of axial force, shear force, and bending moment in the shear span of a beam member by independently applying axial tensile force and constant negative bending moment at the ends through a transverse loading system, and by applying positive bending moment at mid-span through a vertical loading system. At the same time, each reaction force transmission unit only transmits horizontal force and not bending moment to the beam member, ensuring that vertical deformation and deformation of the transverse loading system do not interfere with each other, effectively solving the technical problem of accurately applying combined forces and the tendency to bend failure in long beam shear failure tests.

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make some modifications or alterations to the disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A test device for beam members under combined action, characterized in that, include: The beam member (4) is horizontally supported on a rigid ground (14) by a mid-span rotation support (7) with an internal gap on its left and right sides. A transverse loading system for applying axial tensile force and negative bending moment to the two end segments (402) of the beam member (4), comprising: The first end rotating member (2) is rotatably connected to one end of the beam member (4) and can rotate in the XZ plane; The second end rotating member (13) is rotatably connected to the other end of the beam member (4) and can rotate in the XZ plane; The slotted crossbar (5) is arranged parallel to the longitudinal axis of the beam member (4) on the upper part of the beam member (4), and there is a first eccentricity e between it and the beam member (4). One end of the slotted crossbar (5) abuts against the upper end of the first end rotating member (2) through the first reaction force transmission unit; the other end of the slotted crossbar (5) abuts against the upper end of the second end rotating member (2) through the transverse top actuator (6) and the second reaction force transmission unit. A transverse bottom actuator (9) is arranged parallel to the longitudinal axis of the beam member (4) at the lower part of the beam member (4), and there is a second eccentricity e between it and the beam member; one end of the transverse bottom actuator (9) abuts against the lower end of the first end rotating member (2) through the third reaction force transmission unit; the other end of the transverse bottom actuator (9) abuts against the lower end of the second end rotating member (13) through the fourth reaction force transmission unit. Among them, the first reaction force transmission unit and the top of one end of the beam member (4), the second reaction force transmission unit and the top of the other end of the beam member (4), the third reaction force transmission unit and the bottom of one end of the beam member (4), and the fourth reaction force transmission unit and the bottom of the other end of the beam member (2) are all rolling contact connections that can only transmit force in the horizontal direction and do not transmit bending moment. The transverse top actuator (6) and transverse bottom actuator (9) apply horizontal forces N1 and N2 to the ends of the beam member (4) through the first end rotating member (2) and the second end rotating member (13). The lines of action of the horizontal forces N1 and N2 are respectively eccentrically e from the central axis of the beam member (4), thereby applying a negative bending moment at the ends of the beam member (4). The vertical loading system is used to apply vertical pressure F to the upper side of the middle segment (401) of the beam member (4) to form a positive bending moment at mid-span. It is mechanically separated from the transverse loading system, and the deformations do not interfere with each other, thus achieving composite loading.

2. The test device for beam components under combined action according to claim 1, characterized in that, The first reaction force transmission unit, the second reaction force transmission unit, the third reaction force transmission unit and the fourth reaction force transmission unit have the same structure, all including: a horizontal adapter (3) and a force transmission beam (1) connected to each other. The first end rotating part (2) and the second end rotating part (13) are respectively provided with vertical grooves. The force transmission beam (1) is slidably arranged in the vertical groove and is horizontally limited between the reaction seat (103) and the end rotating part. The force transmission beam (1) is in rolling contact with the beam member (4) through the roller (102).

3. The test device for beam components under combined action according to claim 2, characterized in that, The horizontal adapter (3) includes: The connecting plate (301) has one side for contacting the slotted crossbar or actuator, and the other side is provided with two symmetrically arranged ear plates (302). The web plate (303) is inserted between two ear plates at one end and connected to the two ear plates (302) by a first pin (304), and the other end is fixedly connected to the force transmission beam (1); The reaction seat (103) is provided at one end of the force transmission beam (1) that is connected to the web plate (303).

4. The test device for beam components under combined action according to claim 1, characterized in that, The vertical loading system includes: The reaction frame (12) is supported on a rigid ground (14); A vertical actuator (11) is mounted on a reaction frame (12); The vertical adapter (10) is connected at the upper end to the vertical actuator (11), and at the lower end it can pass through the slot (502) on the slotted crossbar (5) to apply vertical pressure F, i.e. Z-direction pressure, to the middle part of the beam member (4). The slotted crossbar (5) constrains the vertical adapter (10) in the XZ plane by setting multiple rows of circular pins (503) in the longitudinal direction, so as to prevent the beam component from overturning in the YZ plane under large deformation loading conditions and losing stability; the position of the pins (503) can be adjusted in time according to the change of the loading position of the vertical adapter (10).

5. The test device for beam components under combined action according to claim 1, characterized in that, Two end rotating parts (2) are respectively hinged to the beam member (4) by passing through the circular hole (403) at the end of the beam member (4) via the second pin (204). The end rotating parts (2) also include a retaining ring (203) and a reinforcing plate (202). The reinforcing plate (202) is sleeved on the second pin (204) by the retaining ring (203).

6. The test device for beam components under combined action according to claim 5, characterized in that, The main body of the beam member (4) is made of reinforced concrete. The opening section (402) of the circular hole (403) at both ends of the beam member (4) is densely provided with longitudinal bars (404), horizontal stirrups (405) and vertical stirrups (406). The stirrup ratio of the horizontal stirrups (405) and the vertical stirrups (406) is 3 times that of the middle reinforced concrete section (401), and the reinforcement ratio of the longitudinal bars (404) is 1.5 times that of the middle concrete section (401).

7. The test device for beam components under combined action according to claim 1, characterized in that, The mid-span rotation support (7) includes a top plate (701), a cylindrical shaft (702), a side plate (703), and a bottom plate (704). The base plate (704) is vertically symmetrically provided with two side plates (703), and the top of the two side plates is provided with an arc-shaped mounting groove. The bottom of the top plate (701) is rotatably connected to the arc-shaped mounting groove through a cylindrical shaft (702). A gap is formed between the side plate (703) and the bottom plate (704), through which the transverse bottom actuator (9) can pass.

8. A method for installing the test apparatus for beam members under combined action as described in claim 3 or 4, characterized in that, Includes the following steps: S1: Two mid-span rotation supports (7) are arranged symmetrically with respect to the center of the beam member (4) on a rigid ground (14), and the beam member (4) is placed on the mid-span rotation supports (7); S2: Install the first end rotating part (2) and the second end rotating part (13); S3: Install the horizontal top actuator (6) and slotted crossbar (5) on the upper part of the beam member (4). One end of the slotted crossbar (5) is connected to the first reaction force transmission unit, and the other end is connected to the upper end of the second end rotating part (2) through the horizontal top actuator (6) and the second reaction force transmission unit. The second reaction force transmission unit is in contact with the top of the other end of the beam member (4) to transmit only horizontal force and not bending moment. The distance between the axis of the slotted crossbar (5) and the axis of the beam member (4) is e. S4: Arrange a transverse bottom actuator (9) below the beam member (4). One end of the transverse bottom actuator (9) abuts against the lower end of the first end rotating member through a third reaction force transmission unit. The third reaction force transmission unit and the bottom of one end of the beam member (4) are in a contact connection that transmits only horizontal force and not bending moment. The other end of the transverse bottom actuator (9) abuts against the lower end of the second end rotating member through a fourth reaction force transmission unit. The fourth reaction force transmission unit and the bottom of the other end of the beam member (4) are in a contact connection that transmits only horizontal force and not bending moment. The transverse bottom actuator (9) passes through the internal gap of the mid-span rotating support (7). The axis of the transverse bottom actuator (9) and the axis of the beam member (4) have an eccentricity e. S5: Install a vertical loading system; S6: Install displacement and strain measurement devices and data acquisition systems.

9. A test method using the test apparatus for beam members under combined action as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Loading steps: Step 1, start the transverse top actuator (6) to apply a horizontal force N1 in the X direction and transmit it to the top of the beam member (4) through the slotted crossbar (5) and the first and second reaction force transmission units. Start the transverse bottom actuator (9) to directly apply a horizontal force N2 and transmit it to the bottom of the beam member (4) through the third and fourth reaction force transmission units. The horizontal forces N1 and N2 have an eccentricity e with the longitudinal axis of the beam member, which together form a combined action of axial force and end negative bending moment. Step 2, start the vertical loading unit (11) to apply a vertical pressure F in the Z direction to form a positive bending moment at the mid-span, so that the shear span of the beam member will undergo shear failure under the combined action of axial force, shear force and bending moment.

10. The test method according to claim 9, characterized in that, The loading step selects one of the following modes based on the experimental requirements: When studying the mechanical properties of beam member (4) under the combined action of axial tension, shear force and negative bending moment, loading is performed according to mode A; A: First, adjust the horizontal top actuator (6) to output a horizontal force N1 greater than the horizontal bottom actuator (9) to output a horizontal force N2, and N1 and N2 are in the same direction. Then adjust the vertical actuator to output a vertical pressure F. When beam member (4) does not bear tension, but only bears the combined action of shear force and negative bending moment, it is loaded according to mode B; B: First, adjust the horizontal top actuator (6) to output the horizontal force N1, which is equal to the horizontal bottom actuator (9) to output the horizontal force N2, but in different directions. N1 is tension and N2 is pressure. That is, the output forces of the top and bottom actuators are equal in magnitude but opposite in direction. Then adjust the vertical actuator to output the vertical pressure F. When beam member (4) is subjected to axial tensile force and shear force, but not negative bending moment, it is loaded according to mode C; C: First, adjust the horizontal force N1 output by the top horizontal actuator (6) to be equal to the horizontal force N2 output by the bottom horizontal actuator (9), and both N1 and N2 are tension forces, that is, the magnitude of the output force of the top and bottom actuators is equal and the direction is the same. Then adjust the vertical actuator to output the vertical pressure F to generate a positive bending moment.

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