Box beam reduced scale model design method based on ultimate strength similarity principle and test device

Abstract

The invention discloses a box beam reduced scale model design method based on an ultimate strength similarity principle and a test device, and the method comprises the steps: employing a dimensionless parameter as a core similarity parameter, and building a similarity criterion of bending ultimate strength of a box beam; according to the similarity criterion, obtaining a similarity ratio relationship between the original scale model and the reduced scale model; according to the similarity criterion, a reduced scale model is designed, and the obtained reduced scale model and the prototype ultimate strength meet the similarity relation; and calculating an equivalent loading amplitude and a distribution mode of the reduced scale model according to the actual surface load distribution of the original scale model in combination with the surface load similarity ratio relationship. According to the method, only a small number of similarity criteria need to be considered, the same reduced scale model can be designed, the model flexibility is greatly improved, and the design time and labor cost are reduced. By means of the testing device, the torsion boundary condition can be restrained, bending and torsion can be loaded at the same time, and the accuracy of the bending-torsion combined load ultimate strength test of the box beam is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of structural mechanics, ship and ocean engineering, and thin-walled structure design, and particularly relates to a design method and test device for a scaled model of a box girder based on the similarity principle of ultimate strength. Background Technique

[0002] The ultimate strength of a hull structure is one of the key indicators to measure its safety and has received extensive attention in recent years. The International Ship and Ocean Structure Congress has specifically established a special topic on ultimate strength to promote related research. In terms of research methods, model tests are an important means to obtain the ultimate strength of thin-walled box girders. Due to the limitations of laboratory conditions for direct tests on large box girders, scaled model tests are usually adopted, and the ultimate strength of large-scale box girders is deduced in combination with the similarity principle. At present, the commonly used similarity principles are divided into traditional similarity principles and similarity principles introducing ultimate strength-related criteria.

[0003] In recent years, bending-torsion synchronous loading test devices and methods have gradually emerged. These devices are usually based on a four-point bending test scheme, and torque is formed by the eccentricity of the loading points, thereby controlling the load ratio of bending moment and torque. However, the existing devices do not limit the warping degree of freedom of the test model during the test, resulting in free torsion of the test model instead of the required constrained torsion.

[0004] Although certain progress has been made in the research on the ultimate strength of hull structures in the existing technology, there are still some deficiencies. First, the traditional similarity principle is based on dimensional analysis and has a large error; while the similarity principle introducing strength criteria has poor flexibility, a complex design process, and relies on the experience of designers. Second, the bending-torsion synchronous loading test device cannot accurately achieve the expected boundary conditions under the combined action of bending-torsion-surface pressure, resulting in the ultimate strength obtained from the test not meeting the actual requirements. In addition, most of the existing devices adopt square ends, and after being combined with simply supported boundaries, the torsional center is not on the central axis, which will further affect the accuracy of the torsional ultimate strength. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a design method for a scaled model of a box girder based on the similarity principle of ultimate strength to solve the problems existing in the above-mentioned existing technology.

[0006] To achieve the above object, in the first aspect, the present invention provides a design method for a scaled model of a box girder based on the similarity principle of ultimate strength, including:

[0007] Based on the ultimate strength-dominated failure mode, using dimensionless parameters as the core similarity parameters, establish the similarity criterion for the bending ultimate strength of the box girder;

[0008] According to the similarity criterion, the similarity ratio relationship between the original scale model and the scaled model is obtained; the similarity relationship includes: the ultimate bending moment similarity ratio, the ultimate torque similarity ratio, and the surface load similarity ratio;

[0009] According to the similarity criterion, a scaled model is designed, and the ultimate strength of the scaled model and the prototype satisfies the similarity relationship;

[0010] According to the actual surface load distribution of the original scale model, combined with the surface load similarity ratio relationship, the equivalent loading amplitude and distribution pattern of the scaled model are deduced.

[0011] Preferably, the similarity criterion for establishing the ultimate bending strength of the box girder includes:

[0012] Based on the non-dimensionalization of the buckling strength corresponding to the structural failure mode, dimensionless parameters including material yield strength, section modulus, and load strength are extracted as core similarity parameters, and at the same time, the similarity constraint on the cross-sectional geometry is relaxed to establish the similarity criterion for the ultimate bending strength of the box girder.

[0013] Preferably, the similarity criterion includes the rib slenderness ratio, the lateral buckling slenderness ratio, and the plate slenderness ratio;

[0014] The formula for the rib slenderness ratio is:

[0015] where a is the spacing of the transverse members of the stiffened plate, that is, the length of the stiffener, A C is the cross-sectional area of the stiffener and its attached plate, I C is the moment of inertia of the stiffener and its attached plate, σ y is the yield strength, and E is the elastic modulus;

[0016] The formula for the lateral buckling slenderness ratio is:

[0017] where σ CT is the critical stress of lateral buckling of the stiffener and its attached plate;

[0018] The formula for the plate slenderness ratio is:

[0019] where b is the spacing of the stiffeners of the stiffened plate and t is the plate thickness;

[0020] The similarity criterion is:

[0021] Preferably, the formula for the ultimate bending moment similarity ratio is:

[0022] where C I is the ratio of the moments of inertia of the cross-sections of the box girder, C e is the ratio of the neutral axis heights of the box girder, Cσy is the ratio of yield strength;

[0023] The formula of the limit torque similarity ratio is:

[0024] Among them, C Iω is the ratio of the fan-shaped moment of inertia of the box beam cross section, C t is the plate thickness reduction ratio, C Sω is the ratio of the fan-shaped static moment of the box beam failure position, C σy is the ratio of yield strength;

[0025] The formula for the surface load similarity ratio is:

[0026] Among them, C L is the main scale ratio, R is the ideal maximum deflection under unit surface load, C R is the ratio of R between the scaled model and the prototype, is the bending stiffness of the plate under surface pressure, μ is Poisson's ratio, t p is the thickness of the plate.

[0027] Preferably, designing a scale model includes:

[0028] Scaling the box girder prototype according to the main scale ratio and plate thickness scale ratio to obtain the design basis of the scaled model;

[0029] According to the design basis, the number of reinforcements is adjusted to meet the similarity criteria;

[0030] For similar parameters that affect each other, an optimization problem is constructed and solved to obtain a scaled model that meets the similarity criterion.

[0031] Preferably, the formula for adjusting the number of reinforcement ribs is:

[0032]

[0033] Among them, C L The main scale ratio, C t is the plate thickness reduction ratio, is the ratio of yield strength, n p is the number of stiffeners in the stiffened plate prototype, n m is the number of reinforcement ribs in the scaled model, C E is the ratio of Young's modulus, and [·] is the rounding operator.

[0034] In a second aspect, the present invention also provides a test device applicable to the design method of the box girder reduced-scale model based on the principle of similarity of ultimate strength, including: a fixed-end support, a support end, a loading section, a loading arm, a bending and torsion hydraulic actuator, a surface pressure hydraulic actuator, sandbags, a test box girder, a reaction frame, and a transmission shaft; the structural design of the test device is used to simulate the constrained torsion boundary conditions and the bending boundary conditions to achieve simultaneous loading of bending and torsion;

[0035] Among them, the reaction frame is fixed to the ground to provide support for the bending and torsion hydraulic actuator;

[0036] The sandbags are used to cooperate with the surface pressure hydraulic actuator for loading and provide uniform surface pressure;

[0037] The loading section includes a loading arm, a transmission shaft, and a main structure, and is used to transmit the bending moment and torque generated by the bending and torsion hydraulic actuator.

[0038] Preferably, the loading section is connected to the support end by a cylindrical transmission shaft, and the torsion center of the transmission shaft is the same as that of the test model.

[0039] Preferably, the transmission shaft and the support end are connected by bearing cooperation, and the transmission shaft is placed inside the support end, which releases the torsional degree of freedom and restricts the longitudinal displacement to form the constrained torsion boundary conditions;

[0040] The support end cooperates with the fixed-end support, and the support end can rotate around the round steel at the top of the fixed-end support to form the bending boundary conditions;

[0041] Through the constrained torsion boundary conditions and the bending boundary conditions, a complex load condition ultimate strength test with simultaneous action of bending and torsion is carried out.

[0042] In a third aspect, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the method described in the first aspect are implemented.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] The present invention provides a design method for a reduced-scale model of a box girder based on the principle of similarity of ultimate strength. First, based on the dominant failure mode of ultimate strength, dimensionless parameters are used as the core similarity parameters to establish the similarity criterion for the bending ultimate strength of the box girder. Second, according to the similarity criterion, the similarity ratio relationship between the full-scale model and the reduced-scale model is obtained. The similarity relationship includes: the similarity ratio of ultimate bending moment, the similarity ratio of ultimate torque, and the similarity ratio of surface load. Further, according to the similarity criterion, the reduced-scale model is designed, and the ultimate strength of the obtained reduced-scale model and the prototype satisfies the similarity relationship. Finally, according to the actual surface load distribution of the full-scale model and in combination with the surface load similarity ratio relationship, the equivalent loading amplitude and distribution pattern of the reduced-scale model are deduced.

[0045] The present invention only uses dimensionless parameters related to ultimate strength as similarity parameters, ignores the similarity of sectional geometric properties, and uses a new similarity relationship to handle the deviation caused by geometric dissimilarity. Therefore, the design process of the reduced-scale model only needs to consider a small number of similarity criteria, and the design process of the reduced-scale model is standardized and simplified. In addition, any designer can design the same reduced-scale model according to the design process. There is no experience guidance in the design process of the reduced-scale model, and the results have high consistency.

[0046] The reduced-scale model obtained according to the similarity principle and the design method of the reduced-scale model of the present invention can be used for both hogging and sagging load conditions at the same time. When the loading direction changes, there is no need to adjust the reduced-scale model, which greatly improves the flexibility of the model and reduces the design time and labor costs.

[0047] The similarity relationship of torsional ultimate strength proposed by the present invention can accurately predict the torsional ultimate strength of the prototype according to the torsional ultimate strength of the reduced-scale model.

[0048] The test device provided by the present invention can simulate the boundary conditions of restrained torsion, restore the expected torsional boundary conditions of the test model, and is more in line with the expectations and the test results are more accurate compared with the free torsional boundary provided by the existing test devices. In addition, the test device of the present invention uses a cylindrical transmission shaft connected to the bearing to support the end and the test section, ensuring that the torsional center of the test model coincides with the central axis of the effective test section, and can accurately simulate the expected torsional behavior of the effective test section. Description of the Drawings

[0049] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0050] Figure 1 It is a flowchart of a rapid design method for an ultimate strength reduced-scale model that satisfies the similarity criterion in an embodiment of the present invention;

[0051] Figure 2Schematic diagram of the ultimate strength test device for a box girder under the combined loads of bending-torsion-surface pressure according to an embodiment of the present invention;

[0052] Figure 3 Partial enlarged view of the loading section, support end and fixed end support of the test device according to an embodiment of the present invention;

[0053] Figure 4 Schematic diagram of the support end and its internal structure in the test device according to an embodiment of the present invention;

[0054] Wherein, 1. Fixed end support; 1(a). Round steel at the top of the fixed end support; 2. Support end; 2(a). Circular groove at the bottom of the support end; 3. Loading section; 4. Loading arm; 5. Bending-torsion hydraulic actuator; 6. Surface pressure hydraulic actuator; 7. Sandbag; 8. Test box girder; 9. Reaction frame; 10. Transmission shaft; 11. Bearing. Detailed implementation manners

[0055] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0056] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0057] Embodiment 1

[0058] In this embodiment, the key influencing factors of the ultimate strength of the box girder are used as the similarity parameters, and the similarity criterion that the similarity parameters of the prototype and the scaled model are equal is used. The similarity of section geometric properties in the existing similarity criterion is ignored (such as the similarity of section area C A =C L C t , and the similarity of section moment of inertia C I =C L 3 C t , where C L is the main scale reduction ratio, and C t is the plate thickness reduction ratio). The ultimate strength similarity relationship is re-derived for the scaled model, instead of using the classical similarity relationship C M =C L 2 C t obtained by dimensional analysis. Thus, the consideration of a large number of section geometric property similarity criteria in the scaled model design is avoided, and further, the scaled model design process is simplified to form a standardized and process-based design process.

[0059] In this embodiment, a design method for a reduced-scale model of a box girder based on the similarity principle of ultimate strength is provided, including:

[0060] S1. Establish the similarity criterion for the bending ultimate strength of the box girder;

[0061] The stiffened panel is the basic component unit of the hull structure and the box girder structure. Based on the buckling critical stress of the stiffened panel, the control parameters for each failure mode of the stiffened panel are defined. The obtained control parameters are selected as similarity parameters, and the similarity criterion is that the similarity parameters of the reduced-scale model and the prototype are equal. The similarity criterion for the box girder structure is the sum of the similarity criteria of all the stiffened panels that make it up.

[0062] In this embodiment, the progressive collapse behavior of the box girder under the action of a bending load can be regarded as the compression buckling failure of the corresponding compressed stiffened panel; the compression failure of the stiffened panel is divided into three categories, and a similarity criterion is formed with the buckling critical stress as the key parameter. The selected similarity criteria are the rib slenderness ratio λ, the plate slenderness ratio β, and the lateral slenderness ratio λ of the stiffener and its attached plate T . The compression failure of the stiffened panel specifically includes:

[0063] (1) Overall failure and beam-column failure:

[0064] [[ID=

[17] The control parameter is the rib slenderness ratio

[0065] where a is the spacing of the transverse members of the stiffened panel, that is, the length of the stiffener, A C is the cross-sectional area of the stiffener and its attached plate, I C is the moment of inertia of the stiffener and its attached plate, σ y is the yield strength, and E is the elastic modulus.

[0066] (2) Web failure and lateral buckling failure:

[0067] The control parameter is the lateral slenderness ratio

[0068] where σ CT is the lateral buckling critical stress of the stiffener and its attached plate, and the specific expression of σ CT is:

[0069]

[0070] where I p is the polar moment of inertia of the stiffener, I T is the Saint-Venant moment of inertia of the stiffener, I W is the warping constant, ε is the correction coefficient, h w is the web height, t w is the web thickness, A w is the cross-sectional area of the web, b f is the width of the flange plate, tf is the thickness of the wing plate, A f is the cross-sectional area of the wing plate, e f is the distance from the wing plate to the strip plate.

[0071] (3) Local plate grid buckling failure:

[0072] The control parameter is the plate slenderness ratio

[0073] where b is the stiffening pitch of the stiffened plate and t is the plate thickness.

[0074] Therefore, the similarity criterion is taken as

[0075]

[0076] where C SL = SL m / SL p represents the ratio of the physical quantity SL of the model to the prototype. SL can represent any physical quantity, such as the main dimension L, the plate thickness t, the plate slenderness ratio β, etc. The subscript m represents the model and p represents the prototype. When the scale model and the prototype satisfy the similarity criterion formula, it is considered that the scale model of the stiffened plate is similar to the prototype. When each stiffened plate in the box girder satisfies the similarity criterion formula, the box girder prototype and the scale model satisfy the similarity criterion.

[0077] S2. According to the similarity criterion, the ultimate bending moment relationship, the ultimate torque relationship, and the surface load similarity relationship of the box girder are derived;

[0078] Specifically, according to the thin-walled structure theory, the physical quantities such as the bending normal stress and deflection of the box girder under the action of the bending moment can be derived. Substituting the similarity criterion and the geometric relationship between the scale model and the prototype, the ultimate bending moment relationship between the scale model and the prototype is:

[0079]

[0080] where C I is the ratio of the moment of inertia of the cross-section of the box girder, C e is the ratio of the neutral axis height of the box girder, C σy is the ratio of the yield strength.

[0081] As an innovative implementation method, according to the thin-walled structure theory, the physical quantities such as the shear stress of the box girder under the constrained torsion can be derived. Substituting the similarity criterion and the geometric relationship between the scale model and the prototype, the ultimate torque relationship between the scale model and the prototype is:

[0082]

[0083] where C Iω is the ratio of the sectorial moment of inertia of the cross-section of the box girder, C tis the plate thickness scale ratio, C Sω is the ratio of the sectorial static moment of the failure part of the box girder, C σy is the ratio of the yield strength.

[0084] On the other hand, the influence of the surface pressure on the ultimate strength of the box girder can be evaluated by the local deflection it causes to the bottom plate. Therefore, the maximum deflection generated when the surface load acts alone on the stiffened plate is taken as an index to evaluate the influence of the surface load on the ultimate strength. The derivation of the similarity relationship of the surface load can be transformed into the derivation of the flexural stiffness relationship of the stiffened plate between the scaled model and the prototype. To further simplify this problem, the maximum deflection of the surface load acting on the stiffened plate is simplified to the sum of the maximum deflections generated when the surface load acts alone on the stiffeners and the plate grids, approximately expressing the stiffness trend rather than the true value at one time. Therefore, it can be derived that the maximum deflection is

[0085]

[0086] where p is the magnitude of the uniform surface load, is the bending stiffness of the plate grid, t p is the plate thickness of the plate grid.

[0087] When the ratio of the maximum deflections between the scaled model and the prototype is the same as the main dimension scale ratio C L , it can be considered that the influence of the surface load on the ultimate strengths of the two is similar. Therefore, the similarity relationship of the surface load magnitude is

[0088]

[0089] where C L is the main dimension scale ratio, R is the idealized maximum deflection under the action of the unit surface load, C R is the ratio of R between the scaled model and the prototype, is the bending stiffness of the plate where the surface pressure acts, μ is the Poisson's ratio, t p is the plate thickness of the plate.

[0090] In the derivation of this embodiment, dimensional analysis is not used, and the similarity conditions of the sectional geometric properties are not considered. The derivation is carried out based on the relationship between the deformation and the ultimate strength of the prototype and the scaled model under the corresponding loads. The obtained similarity relationship does not depend on the similarity of the sectional geometric properties. Together with the similarity criterion, the magnitude of the surface load of the scaled model that can cause a similar influence can be accurately predicted according to the magnitude of the surface load of the prototype, and the ultimate moment of the prototype can be accurately predicted using the ultimate moment of the scaled model.

[0091] S3. According to the similarity ratio relationship, design a scaled model so that the scaled model satisfies the similarity criterion;

[0092] Specifically, when designing a scale model, only the similarity criterion needs to be considered, without considering the similarity of the cross-sectional geometric properties, which makes the scale model design standardized and streamlined.

[0093] Based on the obtained similarity criteria, a simple and standardized scale model design method can be proposed. Figure 1 The design steps are as follows:

[0094] S301, according to the main scale scale ratio C L and plate thickness reduction ratio C t Scaling the box girder prototype to obtain the design basis of the scaled model;

[0095] S302, adjust the number of reinforcement ribs according to the formula to meet the similarity criterion C β =1.

[0096]

[0097] Among them, C L The main scale ratio, C t is the plate thickness reduction ratio, is the ratio of yield strength, n p is the number of stiffeners in the prototype of the stiffened plate, n m is the number of reinforcement ribs in the scaled model, C E is the ratio of Young's modulus, and [·] is the rounding operator.

[0098] S303: For similar parameters that affect each other, an optimization problem is constructed and solved to obtain a scaled model that satisfies the similarity criterion as much as possible.

[0099] Adjust the remaining rib size to meet the similarity criterion C λ =1 and C λT = 1. The adjustment method is: take two scaling factors k w and k f , used to adjust the web and flange sizes respectively.

[0100] By solving the following optimization problem, we can get the optimal solution to make the scale distortion model satisfy C as much as possible: λ =1 and C λT =1 w and k f .

[0101]

[0102] The scaled model obtained through the above steps can reflect the main failure modes of the prototype. According to the ultimate strength similarity relationship described in S2, the ultimate strength of the scaled model can be used to accurately predict the ultimate strength of the prototype.

[0103]

[0104] Wherein is the predicted prototype bending ultimate strength, is the measured bending ultimate strength of the scaled model, is the predicted prototype torsional ultimate strength, is the measured torsional ultimate strength of the scaled model.

[0105] S4. According to the actual surface load distribution of the full-scale model, combined with the surface load similarity relationship described in S2, the equivalent loading amplitude and distribution pattern of the scaled model are deduced.

[0106] p m = p p *C p

[0107] Where p m is the surface load amplitude of the scaled model, p p is the surface load amplitude of the prototype, and C p is the surface load similarity relationship described in S2.

[0108] Advantages of this embodiment:

[0109] In the present invention, the similarity criterion only uses the dimensionless parameters related to the ultimate strength as the similarity parameters, ignores the similarity of the section geometric properties, and uses the similarity relationship to handle the deviation caused by geometric dissimilarity. Therefore, the scaled model design process only needs to consider a small number of similarity criteria, and the scaled model design process is standardized and simplified. Any designer can design the same scaled model according to the design process. There is no experience guidance in the scaled model design process, and the obtained scaled models have high consistency. The scaled models obtained by using the present invention can be used for both hogging and sagging conditions at the same time, and the scaled model does not need to be adjusted when the loading direction changes, which greatly improves the flexibility of the model and reduces the design time and labor costs. According to the similarity principle and scaled model design method of the present invention, the scaled model can accurately predict the prototype ultimate strength and the main failure modes.

[0110] This embodiment innovatively proposes the idea of "letting go of the section geometric similarity, reducing the number of similarity criteria, and re-deriving the similarity relationship to make up for geometric dissimilarity", breaking the inherent paradigm of similarity theory research: relying on increasing the number of similarity criteria to force the ultimate strength of the scaled model to approach the traditional similarity relationship (obtained by dimensional analysis).

[0111] The scaled model design method and similarity principle proposed in this embodiment can quickly and efficiently design the scaled model of the box girder, and accurately predict the prototype ultimate strength by using the ultimate strength of the scaled model;

[0112] Embodiment Two

[0113] This embodiment provides a test device for applying the box girder scaled model design method based on the principle of similarity of ultimate strength described in Embodiment 1, that is, a test device for the ultimate strength of a box girder under combined bending-torsion-surface pressure loads, including: a fixed-end support 1, a support end 2, a loading section 3, a loading arm 4, a bending-torsion hydraulic actuator 5, a surface pressure hydraulic actuator 6, sandbags 7, a test box girder 8, a reaction frame 9, a transmission shaft 10, and bearings 11;

[0114] The reaction frame 9 is fixed to the ground to provide support for the hydraulic actuator;

[0115] The sandbags 7 are used to cooperate with the hydraulic actuator to provide a uniform surface pressure during loading;

[0116] The loading section 3 includes a loading arm 4, a transmission shaft 10, and a main structure, which are used to transmit the bending moment and torque generated by the bending-torsion hydraulic actuator 6. The main structure is connected to the test model (either by welding or bolt connection), and the specific structural form depends on the structural form of the test model;

[0117] The loading arm 4 is used to provide an eccentric loading action point, so as to generate a bending moment and torque on the test model at the same time. The length of the loading arm depends on the required ratio of bending moment and torque;

[0118] The transmission shaft 10 is used to connect the main structure of the loading section to the support end 2. Bearings are arranged inside the support end 2 to cooperate with the transmission shaft 10, so as to release the torsional degree of freedom of the model and limit the longitudinal movement of the transmission shaft, thereby limiting the warping degree of freedom;

[0119] An arc-shaped groove slightly larger than the diameter of the round steel 1(a) at the top of the fixed-end support is arranged at the bottom of the support end 2. The circular groove 2(a) at the bottom of the support end cooperates with the round steel 1(a) at the top of the fixed-end support to provide vertical support for the model while allowing bending rotation, and limits the occurrence of warping displacement, realizing the simulation of the constrained torsion boundary condition and the bending boundary condition, and realizing the simultaneous loading of bending and torsion.

[0120] Furthermore, the loading section 3 and the support end 2 are connected by a cylindrical transmission shaft, and the torsion center of the transmission shaft 10 is the same as that of the test model.

[0121] Furthermore, the transmission shaft 10 and the support end 2 are connected by means of bearings 11, and the transmission shaft 10 does not penetrate the support end but is placed therein. Therefore, while releasing the torsional degree of freedom, the longitudinal displacement can be limited. When the support end 2 does not undergo longitudinal displacement, a constrained torsion boundary condition can be formed.

[0122] Furthermore, the circular groove 2(a) at the bottom of the support end is fitted with the round steel 1(a) at the top of the fixed-end support. Lubricating oil is added before the test. While the fixed support restricts the longitudinal and vertical displacements of the support end, the support end 2 can rotate around the round steel 1(a) at the top of the fixed-end support. Therefore, the test model can freely undergo bending deformation and constrained torsional deformation, making the simulation effect of the test section boundary closer to the expectation and the test results more accurate.

[0123] Advantages of this embodiment:

[0124] The box girder ultimate strength test device for combined bending-torsion-surface pressure proposed in this embodiment can simultaneously apply bending moment, torque, and surface pressure to the box girder test model, and always maintain the ratio of bending moment to torque during the loading process, and can correctly simulate the constrained torsional boundary conditions of the test model.

[0125] Different from the existing test devices, the test device proposed in this embodiment can restrict the warping degree of freedom of the test model and ensure that the torsional center of the model is located on the central axis of the box girder, so as to better simulate the constrained torsional boundary conditions of the test model and obtain more accurate test results.

[0126] Embodiment III

[0127] This embodiment also discloses a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described in Embodiment I are implemented.

[0128] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A design method for a reduced-scale model of a box girder based on the principle of similarity of ultimate strength, characterized in that, It includes the following steps: Based on the failure mode dominated by the ultimate strength, using dimensionless parameters as the core similarity parameters, establish the similarity criterion for the flexural ultimate strength of the box girder; According to the similarity criterion, obtain the similarity ratio relationship between the full-scale model and the scaled model; Wherein the similarity relationship includes: the similarity ratio of the ultimate bending moment, the similarity ratio of the ultimate torque, and the similarity ratio of the surface load; According to the similarity criterion, design the scaled model, and the ultimate strength of the obtained scaled model and the prototype satisfies the similarity relationship; According to the actual surface load distribution of the full-scale model, combined with the surface load similarity ratio relationship, deduce the equivalent loading amplitude and distribution mode of the scaled model.

2. The method according to claim 1, characterized in that Establishing the similarity criterion for the flexural ultimate strength of the box girder includes: Based on the dimensionlessization of the buckling strength corresponding to the structural failure mode, extract the dimensionless parameters including the material yield strength, section modulus and load strength as the core similarity parameters, and at the same time relax the similarity constraints on the cross-sectional geometry to establish the similarity criterion for the flexural ultimate strength of the box girder.

3. The method according to claim 1, characterized in that The similarity criterion includes the rib slenderness ratio, the roll slenderness ratio and the plate slenderness ratio; The formula for the slenderness ratio of the rib is as follows: Among them, a is the spacing of the transverse members of the stiffened plate, that is, the length of the stiffener, A C is the cross-sectional area of the stiffener and its attached plate, I C is the moment of inertia of the stiffener and its attached plate, σ y is the yield strength, and E is the elastic modulus; The formula for the slenderness ratio of roll is as follows: Among them, σ CT is the critical stress of lateral-torsional buckling of the stiffener and its attached plate; The formula for the slenderness ratio of the plate is as follows: Wherein, b is the spacing of the stiffeners of the stiffened plate, and t is the plate thickness; The similarity criteria are as follows:

4. The method according to claim 1, characterized in that The formula for the similarity ratio of the ultimate bending moment is as follows: Among them, C I is the ratio of the moment of inertia of the box girder cross-section, C e is the ratio of the height of the neutral axis of the box girder, C σy is the ratio of the yield strength; The formula for the limit torque similarity ratio is as follows: Among them, C Iω is the ratio of the sectorial moment of inertia of the box girder cross-section, C t is the thickness scale ratio of the plate, C Sω is the ratio of the sectorial static moment of the failure part of the box girder, C σy is the ratio of the yield strength; The formula for the surface load similarity ratio is as follows: Among them, C L is the main scale ratio, R is the idealized maximum deflection under the action of unit surface load, C R is the ratio of R between the scaled model and the prototype, is the bending stiffness of the plate under the action of surface pressure, μ is the Poisson's ratio, t p is the plate thickness of the plate.

5. The method according to claim 1, characterized in that Designing the scaled model includes: Scale the box girder prototype according to the main scale scaling ratio and the plate thickness scaling ratio to obtain the design basis of the scaled model; According to the design basis, adjust the number of stiffeners to make it meet the similarity criterion; For the mutually influencing similarity parameters, construct and solve the optimization problem to obtain the scaled model that meets the similarity criterion.

6. The method according to claim 1, characterized in that The formula for adjusting the number of stiffeners is: Among them, C L is the main dimension scale ratio, C t is the plate thickness scale ratio, is the yield strength ratio, n p is the number of stiffeners of the prototype stiffened plate, n m is the number of stiffeners of the scaled model, C E is the Young's modulus ratio, and [·] is the rounding operator.

7. An experimental device for the design method of a reduced-scale model of a box girder applying the similarity principle of ultimate strength according to any one of claims 1-6, characterized in that, It includes: Fixed end support, support end, loading section, loading arm, bending and torsion hydraulic actuator, surface pressure hydraulic actuator, sandbag, test box girder, reaction frame and transmission shaft; through the structural design of the test device to simulate the constrained torsion boundary condition and the bending boundary condition, realize the simultaneous loading of bending and torsion; Wherein, the reaction frame is fixed on the ground to provide support for the bending and torsion hydraulic actuator; The sandbag is used to cooperate with the surface pressure hydraulic actuator for loading and provide a uniform surface pressure; The loading section includes a loading arm, a transmission shaft and a main structure, and is used to transmit the bending moment and torque generated by the bending and torsion hydraulic actuator.

8. The test device according to claim 7, characterized in that The loading section is connected to the support end by a cylindrical transmission shaft, and the torsion center of the transmission shaft is the same as that of the test model.

9. The test device according to claim 7, characterized in that The transmission shaft is connected to the support end by a bearing, and the transmission shaft is placed inside the support end, and its torsional degree of freedom is released and the longitudinal displacement is restricted to form a constrained torsion boundary condition; The support end cooperates with the fixed end support, and the support end can rotate around the round steel at the top of the fixed end support to form a bending boundary condition; Perform a complex load condition ultimate strength test with simultaneous bending and torsion by means of the described constrained torsion boundary conditions and the described bending boundary conditions.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1-6.

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