Double-layer steel truss girder shearing hysteresis analysis test method

Abstract

The invention discloses a double-layer steel truss girder shearing hysteresis analysis test method. A test device comprises a four-column type loading hydraulic machine, a top plate distribution beam, a jack, a bottom plate distribution beam and a rigid spring. The top plate distribution beam is horizontally arranged, the middle of the top plate distribution beam is fixedly connected with the lower end of a piston rod of the loading hydraulic machine, and the top plate distribution beam is pressed on a double-layer steel truss girder top plate in use and used for applying pressure load to the double-layer steel truss girder top plate. The bottom plate distribution beam is horizontally arranged under the top plate distribution beam. The rigid springs are connected between the left end and the right end of the top plate distribution beam and the left end and the right end of the bottom plate distribution beam. During use, the bottom plate distribution beam is arranged between the top and the bottom plate of the double-layer steel trussed beam in a penetrating mode and presses the bottom plate of the double-layer steel trussed beam downwards, and the bottom plate distribution beam is used for applying pressure loads to the bottom plate of the double-layer steel trussed beam. The multiple jacks are arranged between the top plate distribution beam and the bottom plate distribution beam.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering mechanics tests, and in particular relates to a shear lag analysis test method for a double-layer steel truss beam. Background Art

[0002] Double-deck steel truss bridges have been widely used in urban transportation, highways, railways and other fields due to their significant advantages. Double-deck steel trusses make full use of the vertical space of the bridge, improve traffic capacity and traffic efficiency, have excellent mechanical properties and stability, and can withstand large loads and deformations. The overall structure is affected by the randomness and asymmetry of the upper and lower loads. The steel trusses will be accompanied by bending, shear lag, torsion and distortion effects, and their spatial stress state is particularly prominent. Model testing is the most convenient means to study the overall spatial effects of such structures. The loading device currently used for double-deck steel trusses only acts on the upper bridge deck (top plate), and it is impossible to achieve simultaneous loading of the upper and lower decks of the double-deck steel trusses ( Figure 3 The upper and lower decks of the double-layer steel truss are loaded simultaneously (as shown in the figure). Summary of the invention

[0003] In order to solve the current problem that it is impossible to load the top and bottom plates of a double-layer steel truss bridge at the same time, the present invention provides a shear lag analysis test method for a double-layer steel truss, which provides technical support for actual load test research on such structures.

[0004] To this end, the present invention adopts the following technical solutions: A double-layer steel truss shear lag analysis test method includes a test device for loading the top and bottom plates of the double-layer steel truss, the test device includes a four-column loading hydraulic press, a top plate distribution beam, a jack, a bottom plate distribution beam and a rigid spring; The top plate distribution beam is arranged horizontally and the middle part thereof is fixedly connected to the lower end of the piston rod of the loading hydraulic press. When in use, the top plate distribution beam is pressed on the top plate of the double-layer steel truss beam, and the top plate distribution beam is used to apply pressure load to the top plate of the double-layer steel truss beam; The bottom plate distribution beam is horizontally arranged directly below the top plate distribution beam, and the rigid spring includes a plurality of springs connected between the top plate distribution beam and the left and right ends of the bottom plate distribution beam; when in use, the bottom plate distribution beam passes between the top and bottom plates of the double-layer steel truss beam and presses down the bottom plate of the double-layer steel truss beam, and the bottom plate distribution beam is used to apply pressure load to the bottom plate of the double-layer steel truss beam; The jacks include a plurality of jacks arranged between the top plate distribution beam and the bottom plate distribution beam; Two upper loading blocks are arranged at intervals on the bottom surface of the top plate distribution beam, and two lower loading blocks are arranged at intervals on the bottom surface of the bottom plate distribution beam. The spacing between the two upper loading blocks is adjustable, and the spacing between the two lower loading blocks is adjustable; The test method comprises the following steps: Step 1: Design loading conditions ① Load condition 1 Adjust the positions of the upper loading block and the lower loading block symmetrically, move the upper loading block to the intersection of the double-layer steel truss top plate and the truss web, and move the lower loading block to the intersection of the double-layer steel truss bottom plate and the truss web, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; ② Load case 2 Adjust the positions of the upper loading block and the lower loading block symmetrically, with the upper loading block at 1 / 4 and 3 / 4 of the top plate of the double-layer steel truss beam, and the lower loading block at 1 / 4 and 3 / 4 of the bottom plate of the double-layer steel truss beam, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; ③ Load case 3 Adjust the positions of the upper loading block and the lower loading block symmetrically, move the upper loading block to the center of the double-layer steel truss top plate, and the lower loading block to the center of the double-layer steel truss bottom plate, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; ④ Load condition 4 Adjust the positions of the upper and lower loading blocks symmetrically, with the upper loading block at 1 / 4 and 3 / 4 of the top plate of the double-layer steel truss, and the lower loading block at the center of the bottom plate of the double-layer steel truss, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; ⑤Load condition 5 Adjust the upper and lower loading blocks symmetrically, with the upper loading block at the center of the double-layer steel truss top plate and the lower loading block at 1 / 4 and 3 / 4 of the double-layer steel truss bottom plate, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; ⑥ Load condition 6 Adjust the position of the upper loading block symmetrically, move the upper loading block to the intersection of the double-layer steel truss top plate and the truss web, and fix it with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press, and control the jacks on the left and right sides to test synchronously. After mechanical transmission, the loading of the top plate and the lower layer of the double-layer steel truss beam is shown in working condition 10; Step 2: Attach the strain gauge The longitudinal strain gauges are pasted on the mid-span section of the double-layer steel truss top plate and the double-layer steel truss bottom plate. The strain gauge pasting positions are symmetrical in the center, such as Fig.11 ; Step 3: Shear Lag Longitudinal Stress Calculation When calculating the shear lag longitudinal stress of the double-layer steel truss top plate and the double-layer steel truss bottom plate, the longitudinal stress is obtained based on the longitudinal strain of the measuring point obtained from the test: in is the shear lag longitudinal stress at the measuring point; E is the elastic modulus of steel; is the longitudinal strain at the measuring point.

[0005] Furthermore, the top plate distribution beam and the bottom plate distribution beam are I-beam structures.

[0006] Furthermore, the top surface and the bottom surface of the jack are respectively padded with pressure plates.

[0007] The beneficial effects of the present invention are: 1. By setting the jack between the top plate distribution beam and the bottom plate distribution beam, the vertical load of the hydraulic press can be applied to the bottom plate of the double-layer steel truss. Two distribution beams with infinite rigidity (the loading position can be adjusted) are placed on the top and bottom plates of the double-layer steel truss. The hydraulic press applies the load to the top plate distribution beam, starts the jack and controls its reading, and the vertical load of the hydraulic press can be transferred to the bottom plate of the double-layer steel truss.

[0008] 2. The top plate distribution beam and the bottom plate distribution beam are connected by a rigid spring. Using a rigid spring to connect the bottom plate distribution beam reduces the influence of the deadweight of the bottom plate distribution beam during loading. The easy disassembly of the structure provides convenience for the assembly of the device.

[0009] 3. Six different loading conditions are designed, and the loading size and loading position are controlled. The loading position and load size can be appropriately adjusted according to experimental requirements or material structure, and the shear lag longitudinal stress of the double-layer steel truss under any symmetrical load can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural front view of the test device of the present invention; Figure 2 It is a structural side view of the test device of the present invention; Figure 3 It is a schematic diagram of the loading of the top and bottom plates of double-layer steel trusses; Figure 4 It is a schematic diagram of the overall loading force of the double-layer steel truss; Figure 5 It is the force diagram of the top plate distribution beam; Figure 6 It is the force diagram of the bottom plate distribution beam; Figure 7 It is a schematic diagram of the force on a double-layer steel truss; Figure 8 It is a schematic diagram of the working force of the jack; Fig. 9 It is a flowchart of the test method of the present invention; Fig.10 is a load condition diagram of the present invention; Fig.11 It is a schematic diagram of the arrangement of strain gauges of the present invention; Fig.12 is a schematic cross-sectional view of a double-layer steel truss girder according to an embodiment of the present invention; Fig.13 It is the finite element model and deformation diagram of six working conditions of the embodiment of the present invention; Fig.14 is a shear lag longitudinal normal stress curve diagram of the upper wing plate section at mid-span of an embodiment of the present invention; Fig.15 is a shear lag longitudinal normal stress curve diagram of the lower wing plate section at the mid-span of an embodiment of the present invention; In the figure: 1-filter, 2-oil filling tank, 3-master oil cylinder, 4-first round nut, 5-cross beam, 6-flange, 7-piston rod, 8-pressure sensor, 9-first pressure plate, 10-second round nut, 11-column, 12-top plate distribution beam, 13-upper loading block, 14-second pressure plate, 15-piston top plate, 16-piston push rod, 17-oil cylinder, 18-rigid spring, 19-lower loading block, 20-bottom plate distribution beam, 21-oil pipe, 22-diverter and collector valve, 23-pressure gauge, 24-motor, 25-pressure control valve, 26-oil pump. DETAILED DESCRIPTION

[0011] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Figure 1 and 2 As shown, the present invention includes the following components: Filter 1: It can effectively remove impurities and pollutants in the oil, reduce the wear of particles on key components such as valve bodies, pumps, hydraulic cylinders, and reduce the occurrence of failures caused by impurities blocking valves.

[0012] Filling tank 2: Stores hydraulic oil, cools oil, precipitates impurities and provides bubble separation to reduce cavitation in the hydraulic system and ensure stable operation of the system.

[0013] Main cylinder 3: Provides a power source to drive the hydraulic press through the action of hydraulic oil. The piston rod 7 of the main cylinder 3 generates linear motion under the action of pressure oil to provide a corresponding pressure source.

[0014] The first round nut 4: The first round nut bears part of the gravity and other forces of the slider during movement, and transmits these forces to the column of the hydraulic press.

[0015] Crossbeam 5: The pressure generated by the hydraulic cylinder is transmitted to the crossbeam 5 through the slider, and the crossbeam 5 evenly distributes the pressure to the four columns to ensure the stability of the entire hydraulic press structure and uniform force.

[0016] Flange 6: During the operation of the hydraulic press, flange 6 can transmit the torque generated by the hydraulic cylinder to the slider or other working parts, ensuring the effective transmission and distribution of force. Flange 6 is made of high-strength material and can withstand the high pressure generated when the hydraulic press is working, ensuring the stability and safety of the connecting parts.

[0017] Piston rod 7: It is used to convert the pressure provided by the hydraulic oil into mechanical energy and provide guidance to transmit it to the lower pressure plate. During the operation of the hydraulic press, it not only transmits force but also supports the weight of components such as the slider to maintain the stability of the hydraulic press.

[0018] Pressure sensor 8: used to monitor the pressure value in the hydraulic system, ensure that the hydraulic press works within the set pressure range, prevent system overload, protect the key components of the hydraulic press from damage and record the pressure data during the operation of the hydraulic press.

[0019] The first pressing plate 9 is used to connect the top plate distribution beam 12 and evenly distribute the pressure of the hydraulic press to the top plate distribution beam 12 .

[0020] The first round nut 4: The first round nut 4 bears part of the gravity and other forces of the slider during movement, and transmits these forces to the column of the hydraulic press.

[0021] Column 11: It provides a solid support frame for the crossbeam and workbench of the hydraulic press, ensuring the stability of the entire machine. When the hydraulic press is working, column 11 bears the huge pressure generated by the hydraulic cylinder.

[0022] Top plate distribution beam 12: The pressure generated by the hydraulic press is evenly distributed to the top plate of the double-layer steel truss beam, and the distribution is performed by I-beams, so that the upper loading block can change the loading position when the steel truss beam is transversely loaded.

[0023] Upper loading block 13: applies the pressure on the top plate distribution beam 12 evenly to the top plate of the double-layer steel truss beam, and the loading position can be changed by adjustment.

[0024] The second pressing plate 14 is used to adjust the distance between the separation hydraulic press and the top plate, and to evenly apply the pressure on the top plate, so as to adjust the pressure on the top plate.

[0025] Piston top plate 15: Increase the contact area between the jack and the distribution beam so that the pressure generated by the jack can be evenly applied to the top plate distribution beam.

[0026] Piston push rod 16: converts the pressure provided in the oil cylinder into mechanical energy and moves upward, playing a role in transmitting force and moving during the operation of the jack.

[0027] Cylinder 17: The cylinder is the part of the jack that contains hydraulic oil and generates thrust. The piston moves in the cylinder to extend or retract the jack.

[0028] Rigid spring 18 : fixes the bottom plate distribution beam 20 , adjusts the bottom plate distribution beam 20 , and reduces the influence of the deadweight of the bottom plate distribution beam 20 .

[0029] Lower loading block 19: applies the pressure on the bottom plate distribution beam 20 evenly to the bottom plate of the double-layer steel truss beam, and the loading position can be changed by adjustment.

[0030] Bottom plate distribution beam 20: The pressure generated by the hydraulic press is evenly distributed to the bottom plate of the double-layer steel truss. I-beams are used for distribution so that the loading block can change the loading position when the steel truss is transversely loaded.

[0031] Oil pipe 21: used to connect the oil pump and oil cylinder of the jack to ensure that the hydraulic oil can flow under the pressure generated by the oil pump, thereby transmitting the pressure to the piston in the oil cylinder.

[0032] Diverter and collector valve 22: Divides a single oil flow into multiple branches, controls the flow of each branch, and ensures that each cylinder or actuator obtains appropriate working pressure and speed.

[0033] Pressure gauge 23: used to detect the pressure generated by the jack to prevent damage to components caused by excessive pressure.

[0034] Electric motor 24: provides energy source for the oil pump of the jack.

[0035] Pressure control valve 25: adjusts the maximum pressure generated by the jack.

[0036] Oil pump 26: The oil pump is the power source of the hydraulic system. It converts mechanical energy into hydraulic energy, provides pressure and flow for the entire hydraulic system, and enables the hydraulic oil to circulate in the system and transfer energy.

[0037] The design principle of the present invention is as follows: (1) Based on the existing extension-compression type four-column hydraulic press, a bottom plate distribution beam is added.

[0038] The existing four-column loading hydraulic press is used to first fix the top plate distribution beam 12 on the pressure plate of the loading machine, and then the bottom plate distribution beam 20 passes through the web of the truss and is pressed on the corresponding position of the bottom plate of the double-layer steel truss beam. In order to reduce the influence of the deadweight of the bottom plate distribution beam 20 on the loading, a rigid spring 18 is added between the top plate distribution beam 12 and the bottom plate distribution beam 20 to fix them.

[0039] (2) Use separate jacks to apply vertical loads to the top and bottom plate distribution beams.

[0040] Two jacks are used and placed on the top and bottom plate distribution beams respectively. The load on the bottom plate of the double-layer steel truss is applied by changing the readings of the two symmetrical jacks.

[0041] (3) Consider the pressure control of the separate jack Use the same pump source for the two jacks and a hydraulic pump with synchronous control function. Before the test, debug the pressure control valve so that the jacks can provide the required pressure.

[0042] The force-bearing principle of the present invention is as follows: like Figures 3 to 8 The figure shows the force analysis diagram of double-layer steel truss loading. The top plate distribution beam 12 is fixed on the loading device, and the bottom plate distribution beam 20 is connected to the top plate through the rigid spring 18. The specific force process is as follows: (1) The hydraulic press and the jack start working at the same time. First, when the top plate distribution beam 12 acts downward, the presence of the jack will reduce the downward force of the top plate distribution beam 12 to a certain extent, and the reduced force will be distributed to the bottom plate of the double-layer steel truss beam.

[0043] (2) The jack parameters are set so that the pressure applied by them is exactly the pressure required to be loaded on the top plate of the double-layer steel truss. Assuming that the overall force to be loaded is P, the jack parameters are adjusted so that the maximum pressure is P / 6. ​​During the operation of the overall device, the jacks on both sides will generate a pressure of P / 6. ​​At this time, the jacks are supported by the bottom plate distribution beam 20, and an interaction force of P / 6 will be generated between the jacks and the top plate of the double-layer steel truss. Similarly, the force generated by the jack on the top plate distribution beam 12 is 2P / 3. At this time, after analyzing the force on the top plate distribution beam 12, it is found that the force acting on the top plate of the double-layer steel truss is 2P / 3.

[0044] (3) If Figure 8As shown, the force analysis of the jack shows that the bottom plate distribution beam 20 will generate a support force of P / 6 on it. According to Newton's third law, the force analysis of the bottom plate distribution beam 20 shows that the force exerted by the bottom plate distribution beam on the bottom plate of the double-layer steel truss beam is P / 3. In this way, the force loaded on the top plate of the double-layer steel truss beam and the bottom plate of the double-layer steel truss beam can be distributed.

[0045] (4) If Figure 5 As shown, the upward force of the top plate distribution beam is analyzed: the upward pressure of the left jack P / 6, the upward pressure of the right jack P / 6, and the reaction force of the double-layer steel truss top plate on the top plate distribution beam 12, and the sum of the upward forces is P. The external forces in the vertical direction are zero, in a balanced state, which conforms to the law of force.

[0046] (5) If Figure 6 As shown, the downward force of the force analysis on the bottom plate distribution beam 20 is: the downward pressure of the left jack is P / 6, and the downward pressure of the right jack is P / 6. ​​The reaction force of the double-layer steel truss bottom plate on the bottom plate distribution beam 20 is upward, and the sum of the external forces in the vertical direction is zero, which conforms to the force law.

[0047] (6) If Figure 7 As shown, the force analysis of the steel truss is carried out, and the sum of all downward pressures is P, which is equal to the magnitude of the expected loading force and meets the loading purpose. Specific embodiment: In order to reveal the distribution law of shear lag effect of double-layer steel truss beams, a 72m simply supported double-layer steel truss beam is taken as an example. The cross-sectional dimensions and web dimensions are as follows: Fig.12 As shown, the steel type is Q345qD, and the concentrated load at the mid-span is 2 P =1200kN, elastic modulus E =2.06×10 5 MPa, Poisson's ratio µ =0.3; Abaqus software is used to analyze Fig.13 The deformation diagram of the steel truss for the six load conditions shown is as follows: Fig.13 As shown in the figure, it can be seen that under different load conditions, the deflection of the mid-span section of the double-layer steel truss beam is somewhat different. Compared with the concrete beam, the steel truss beam is more significantly affected by the local effect, and the deformation and stress concentration effects are particularly obvious. Fig.14 and 15As shown in the figure, there is a big difference in the peak longitudinal stress of the top plate and the cantilever plate, which changes with the change of the concentrated load position, and the stress peaks corresponding to each load condition are not equal, which is completely different from the rule that the peak longitudinal stress of the cross section is equal under the lateral displacement of the load of the concrete box girder bridge; except for condition 6, the longitudinal stress of the bottom plate under other load conditions is greatly affected by the local bending deformation, all of which show compressive stress, and its stress distribution pattern is approximately horizontal. The main reason is that the local flexibility of the orthotropic steel bridge deck is large and the deformation is prominent.

Claims

1. A double-layer steel truss shear lag analysis test method, characterized in that: It includes a test device for loading the top and bottom plates of a double-layer steel truss beam, and the test device includes a four-column loading hydraulic press, a top plate distribution beam, a jack, a bottom plate distribution beam and a rigid spring; The top plate distribution beam is arranged horizontally and the middle part thereof is fixedly connected to the lower end of the piston rod of the loading hydraulic press. When in use, the top plate distribution beam is pressed on the top plate of the double-layer steel truss beam, and the top plate distribution beam is used to apply pressure load to the top plate of the double-layer steel truss beam; The bottom plate distribution beam is horizontally arranged directly below the top plate distribution beam, and the rigid spring includes a plurality of springs connected between the top plate distribution beam and the left and right ends of the bottom plate distribution beam; when in use, the bottom plate distribution beam passes between the top and bottom plates of the double-layer steel truss beam and presses down the bottom plate of the double-layer steel truss beam, and the bottom plate distribution beam is used to apply pressure load to the bottom plate of the double-layer steel truss beam; The jacks include a plurality of jacks arranged between the top plate distribution beam and the bottom plate distribution beam; Two upper loading blocks are arranged at intervals on the bottom surface of the top plate distribution beam, and two lower loading blocks are arranged at intervals on the bottom surface of the bottom plate distribution beam. The spacing between the two upper loading blocks is adjustable, and the spacing between the two lower loading blocks is adjustable; The test method comprises the following steps: Step 1: Design loading conditions ① Load condition 1 Adjust the positions of the upper loading block and the lower loading block symmetrically, move the upper loading block to the intersection of the double-layer steel truss top plate and the truss web, and move the lower loading block to the intersection of the double-layer steel truss bottom plate and the truss web, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; ② Load case 2 Adjust the positions of the upper loading block and the lower loading block symmetrically, with the upper loading block at 1 / 4 and 3 / 4 of the top plate of the double-layer steel truss beam, and the lower loading block at 1 / 4 and 3 / 4 of the bottom plate of the double-layer steel truss beam, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; ③ Load case 3 Adjust the positions of the upper loading block and the lower loading block symmetrically, move the upper loading block to the center of the double-layer steel truss top plate, and the lower loading block to the center of the double-layer steel truss bottom plate, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; ④ Load condition 4 Adjust the positions of the upper and lower loading blocks symmetrically, with the upper loading block at 1 / 4 and 3 / 4 of the top plate of the double-layer steel truss, and the lower loading block at the center of the bottom plate of the double-layer steel truss, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; ⑤Load condition 5 Adjust the upper and lower loading blocks symmetrically, with the upper loading block at the center of the double-layer steel truss top plate and the lower loading block at 1 / 4 and 3 / 4 of the double-layer steel truss bottom plate, and fix them with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; ⑥ Load condition 6 Adjust the position of the upper loading block symmetrically, move the upper loading block to the intersection of the double-layer steel truss top plate and the truss web, and fix it with bolts; set the hydraulic press loading load to 2 P , the maximum pressure of the jack is P / 2, start the hydraulic press and control the jacks on the left and right sides to test synchronously; Step 2: Attach the strain gauge Longitudinal strain gauges are pasted on the mid-span sections of the double-layer steel truss top plate and the double-layer steel truss bottom plate, and the strain gauge pasting positions are symmetrical in the center; Step 3: Shear Lag Longitudinal Stress Calculation When calculating the shear lag longitudinal stress of the double-layer steel truss top plate and the double-layer steel truss bottom plate, the longitudinal stress is obtained based on the longitudinal strain of the measuring point obtained from the test: in is the shear lag longitudinal stress at the measuring point; E is the elastic modulus of steel; is the longitudinal strain at the measuring point.

2. The shear lag analysis test method for double-layer steel truss beams according to claim 1 is characterized in that: The top plate distribution beam and the bottom plate distribution beam are I-beam structures.

3. The shear lag analysis test method for double-layer steel truss beam according to claim 1, characterized in that: The top surface and the bottom surface of the jack are respectively padded with pressure plates.

4. The shear lag analysis test method for double-layer steel truss beam according to claim 1, characterized in that: In step 2, the pasting position is the center of the top plate and the bottom plate of the double-layer steel truss girder and the intersection with the web plate, and the strain gauges at other positions are evenly arranged according to the spacing; the longitudinal strain of the corresponding measuring point position is obtained by the strain acquisition instrument, and the data is collected.

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