River tributary steel trestle structure and stress calculation method thereof

Abstract

This invention belongs to the field of bridge construction technology. Addressing the technical problems of complex hydrological conditions in river tributaries, poor adaptability of traditional trestle bridge structures, high construction difficulty, low efficiency, and insufficient safety, it provides a steel trestle bridge structure for river tributaries and its stress calculation method. This application consists of a main trestle bridge perpendicular to the bridge direction and a steel platform extending along the bridge direction. Both include components such as steel pipe piles, double-section I-beam main crossbeams, Bailey bridge main beams, I-beam distribution beams, and steel plate bridge decks. Expansion joints are provided at specific locations on the main trestle bridge. Construction adopts the "fishing method," which uses crawler cranes to vibrate and sink steel pipe piles while simultaneously assembling the superstructure, advancing span by span. Simultaneously, the construction process employs a flow-line operation, dividing the work into sections based on spans. This application, through its unique vertical and horizontal combined structure, effectively adapts to changes in river topography and water flow; stress calculations and verification show that the steel trestle bridge structure has strong load-bearing capacity and good stability.

Description

Technical Field

[0001] This invention belongs to the field of bridge construction technology, specifically relating to a steel trestle bridge structure for a river tributary and its stress calculation method. Background Technology

[0002] The Ili River is an inland river in Central Asia, an international river that crosses China and Kazakhstan. Its main source, the Tekes River, originates on the northern side of the Khan Tengri Peak in the Tian Shan Mountains. It flows eastward through the Zhaosu Basin and Tekes Valley in Xinjiang, China, then northward across the Ishgorik Mountains, where it merges with the right-bank tributary, the Gongnaisi River, to form the Ili River. It then flows westward to the Khorgos River, entering Kazakhstan and flowing through canyons and deserts before emptying into Lake Balkhash in Central Asia. From its source to its mouth, the river is 1236 kilometers long, with a drainage area of ​​151,000 square kilometers, of which 442 kilometers are within China, covering a drainage area of ​​56,000 square kilometers. The Ili River's flow is highly seasonal. From May to July, the water level is high and very rapid. After the end of July, as snowmelt from the glaciers gradually decreases, the water level drops rapidly, exposing parts of the riverbed. During the flood season, the maximum water depth at the bridge site is about 5.0m, and during the dry season, the maximum water depth is about 3.0m. The bridge structure is difficult to construct and has low adaptability. Therefore, overcoming the above-mentioned technical problems and defects has become a key issue that needs to be addressed. Summary of the Invention

[0003] In order to solve at least one of the above-mentioned technical problems in the prior art, the present invention provides a steel trestle bridge structure for a river tributary and a method for calculating its stress.

[0004] According to the first aspect, a steel trestle bridge structure for a river tributary includes a main trestle bridge and a steel platform; The main trestle bridge is designed as a vertical bridge structure, with both ends fixed by piers; The steel platform is configured as a structure extending along the bridge direction, and is fixed at both ends by bridge piers; The main trestle bridge and steel platform both contain the following components: Steel pipe piles: vertically installed on river tributaries as foundation supports; Main crossbeam: installed at the top of the steel pipe pile; Main beam: erected on the main crossbeam; Distribution beam: laid transversely on the main beam; Bridge deck: laid on the distribution beam; Meanwhile, the main trestle is equipped with two expansion joints, located at the first and second preset positions, respectively, starting from the farthest point on the left. At the predetermined location on the riverbank, the first and second rows of steel pipe piles are vibrated and driven down using a crawler crane, while the main beam is pre-assembled at the work site on the bank. The main crossbeam is placed in the groove at the top of the steel pipe pile, thus completing the erection of the first span of the main beam. Then the bridge deck is laid. The crane travels to the erected first span of the bridge deck and continues to vibrate and drive down the steel pipe piles of the next span. The above steps are repeated, advancing span by span until the steel trestle bridge is erected on the opposite bank.

[0005] Preferably, the main trestle bridge uses 3 steel pipe piles per row with a nominal diameter of 630×10mm, and the lateral spacing is set to at least 3.1m; The steel platform uses 18 steel pipe piles per row with a nominal diameter of 630×10mm, and the lateral spacing is set to be no less than 3.3m and no more than 3.5m. The main trestle bridge and the steel platform are connected by 20d channel steel to form a scissor bracing structure with horizontal and diagonal bracing.

[0006] Preferably, the main crossbeam is a double-slab 45b I-beam, and the main crossbeam is placed in the groove at the top of the steel pipe pile; The bottom of the main crossbeam and both sides of the steel pipe pile are equipped with reinforcing ribs.

[0007] Preferably, the main beam of the main trestle bridge is composed of 5 sets of Bailey beams arranged at equal intervals along the transverse direction of the bridge. Each set contains 10 Bailey beams, and the internal structure of each Bailey beam is connected by a 90cm support frame. The spacing between each set of Bailey beams is 0.75m. The main beam of the steel platform consists of 22 sets of Bailey beams arranged at equal intervals along the transverse direction of the bridge. Each set contains 4 Bailey beams, and each set of Bailey beams is connected by a 45cm support frame. The spacing between each set of Bailey beams is 0.9m.

[0008] Preferably, the distribution beams of the main trestle bridge are made of 20b I-beams, spaced 0.2m apart in the longitudinal direction of the bridge; the distribution beams of the steel platform are made of 40b I-beams, spaced 0.2m apart in the longitudinal direction of the bridge.

[0009] Preferably, the bridge deck of the main trestle is a 10mm thick steel plate laid along its entire length, on which a main trestle guardrail is installed. The main trestle guardrail is made of No. 12 I-beams welded to the bridge deck, with a height of at least 1.24m and a spacing of 1.4m along the bridge direction. A wheel guard is installed below the main trestle guardrail. The bridge deck of the steel platform is made of 10mm thick steel plates, on which a steel platform guardrail is installed. The guardrail posts are made of No. 12 I-beams welded to the bridge deck. The guardrail posts are 1.24m high and spaced 2.0m apart along the bridge direction. The guardrail posts of the steel platform are connected by three 48.3×3.5mm steel pipes in a horizontal bracing as the guardrail, and a wheel guard is installed below.

[0010] Preferably, the lower part of the main trestle is provided with gabion revetment, and the connection position between the main trestle and the steel platform is provided with a back plate for fixation.

[0011] According to the second aspect, a method for calculating the stress on a steel trestle bridge over a river tributary, applicable to the steel trestle bridge structure of a river tributary as described in the first aspect and any preferred embodiment, includes: The average water flow velocity and water density under the straight-line steel trestle bridge are obtained, and the water pressure on the pier is calculated based on the preset pier shape coefficient and pier water-blocking area. The design reference wind speed at the bridge reference height is designed, and the static gust wind speed is calculated based on the design reference wind speed. Then, the first lateral static gust wind load on a single Bailey beam and the second lateral static gust wind load on a single steel pipe pile are calculated based on the static gust wind speed.

[0012] Preferably, the formula for calculating water pressure is: In the formula, Preset pier shape coefficient; The water-blocking area of ​​the bridge pier; The specific gravity of water; The average water flow velocity; This is the acceleration due to gravity.

[0013] Preferably, the formula for calculating the first lateral static gust load is: In the formula, air density; For calm gusts of wind; The truss shading coefficient; The drag coefficient of a single Bailey beam; This represents the actual area ratio of a single Bailey panel; The water-blocking area of ​​the bridge pier. The formula for calculating the second lateral static gust load is: In the formula, The wind resistance coefficient of a single steel pipe pile; The diameter is the steel pipe pile diameter.

[0014] Compared with the prior art, the beneficial effects of the present invention are: In the steel trestle bridge structure of the river tributary of this invention, the combination of a main trestle bridge set perpendicular to the bridge direction and a steel platform set along the bridge direction perfectly adapts to the differences in river topography and water flow direction during the flood season, solving the problem of low adaptability of traditional single structures in complex direct current scenarios. Moreover, the main trestle bridge uses 3 steel pipe piles per row with a nominal diameter of 630×10mm to meet the foundation bearing requirements, while the steel platform uses 18 steel pipe piles per row with a nominal diameter of 630×10mm to better cope with concentrated loads from construction machinery. The arrangement of the main crossbeams can significantly improve the shear resistance of the pile-beam joint, and the modular arrangement of Bailey beams can also achieve efficient load transfer. Furthermore, the contraction joints set at the first and second preset positions of the main trestle bridge can effectively eliminate temperature stress deformation. In addition, the entire bridge uses steel guardrails, wheel guards, and three steel pipe horizontal railings to form multiple fall protection barriers, fully ensuring construction safety. The addition of gabion revetment at the bottom of the main trestle bridge can also effectively resist water erosion.

[0015] The steel trestle bridge structure for a river tributary of this invention employs a "fishing method" for construction. To ensure the construction period, a crawler crane is used to vibrate and sink steel pipe piles at predetermined locations on the riverbank. Simultaneously, Bailey bridge beams are assembled. Steel pile extensions are performed on-site, while the pre-assembly of the Bailey bridge beams is carried out at the work site on the bank. The first and second rows of steel pipe piles are vibrated and sunk; the main crossbeams are placed; the first span of the Bailey bridge beams is erected, and the bridge deck is laid; the crane travels to the steel bridge deck of the first span, drives in the next span of steel pipe piles, and places the main crossbeams; the second span of the Bailey bridge beams is then erected. For the installation of the second span of the bridge deck, the above steps are repeated to erect the steel trestle bridge span by span to the opposite bank. The structure is stable. At the same time, according to the construction characteristics of the steel trestle bridge, the flow rhythm is divided into one flow interval, with one span as one flow section and three spans as one flow segment. Each flow interval is divided into: material processing → surveying and setting out → steel pipe pile sinking → scissor bracing reinforcement → crossbeam erection → Bailey beam installation → distribution beam installation → bridge deck paving → guardrail installation. The installation process is simple and the installation method can be adjusted in time according to the construction requirements, which greatly improves the construction efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the main structure of the steel trestle bridge structure for a river tributary of the present invention; Figure 2This is a left-side structural schematic diagram of the steel trestle bridge structure for a river tributary of the present invention; Figure 3 This is a top view schematic diagram of the steel trestle bridge structure for a river tributary of the present invention; Figure 4 This invention is based on the self-weight action diagram in the "General Specifications for Design of Highway Bridges and Culverts" (JTGD60-2015).

[0018] In the diagram: 1-Bridge deck, 2-Back panel, 3-Gabion revetment, 4-Bailey beam, 5-Guardrail, 6-Support frame, 7-Main crossbeam, 8-Scissor bracing, 9-Steel pipe pile, 10-Pier, 11-Distribution beam, 12-Reinforcing rib. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should fall within the scope of the technical content disclosed in the present invention. It should be noted that in this specification, relational terms such as "first" and "second" are only used to distinguish one entity from several other entities, and do not necessarily require or imply any actual relationship or order between these entities.

[0021] See Figures 1-3 A steel trestle bridge structure for a river tributary includes a main trestle bridge and a steel platform; the main trestle bridge is configured as a structure perpendicular to the bridge direction and is fixed at both ends by piers 10. The steel platform is configured as a structure extending along the bridge direction, and is fixed at both ends by piers 10; The main trestle bridge and steel platform both contain the following components: Steel pipe pile 9: Vertically installed on the straight section of the river as a foundation support; Main crossbeam 7: Located at the top of the steel pipe pile 9; Main beam: erected on the main crossbeam 7; Distribution beam 11: laid transversely on the main beam; Bridge deck 1: laid on the distribution beam 11; Meanwhile, the main trestle is equipped with two expansion joints, located at the first and second preset positions, respectively, starting from the farthest point on the left. At the predetermined location on the riverbank, the first and second rows of steel pipe piles are vibrated and driven down using a crawler crane, while the main beam is pre-assembled at the work site on the bank. The main crossbeam is placed in the groove at the top of the steel pipe pile, thus completing the erection of the first span of the main beam. Then the bridge deck is laid. The crane travels to the erected first span of the bridge deck and continues to vibrate and drive down the steel pipe piles of the next span. The above steps are repeated, advancing span by span until the steel trestle bridge is erected on the opposite bank.

[0022] In this embodiment, the construction process is divided into a flow rhythm, with one span as a flow interval and three spans as a flow section. Each flow interval executes the following procedures in sequence: material processing → surveying and setting out → steel pipe pile sinking → scissor bracing reinforcement → crossbeam erection → Bailey beam installation → distribution beam installation → bridge deck paving → guardrail installation.

[0023] In this embodiment, the main trestle bridge is configured as a structure perpendicular to the bridge direction, with gabion revetment 3 at its lower part. The steel platform is configured as a structure extending along the bridge direction, with both ends fixed by piers 10. The structures of the main trestle bridge and the steel platform both include steel pipe piles 9, main crossbeams 7, main beams, distribution beams 11, and bridge deck 1. The back plate 2 is set at the connection position between the main trestle bridge and the steel platform to fix the main trestle bridge and the steel platform. The main trestle bridge is also equipped with expansion joints.

[0024] In this embodiment, two expansion joints are provided on the main trestle bridge, located at a first preset position and a second preset position, respectively, starting from the farthest point on the left. In actual construction, the first preset position can be at 135 meters and the second preset position can be at 243 meters, and both expansion joints are 10 cm wide to cope with stress deformation caused by temperature.

[0025] In this embodiment, the main trestle bridge uses 3 steel pipe piles 9 with a nominal diameter of 630×10mm per row, with a lateral spacing of 3.1m between the steel pipe piles 9. The scissor bracing 8 for horizontal and diagonal bracing between the steel pipe piles 9 is connected by 20d channel steel. The steel platform uses 18 steel pipe piles 9 with a nominal diameter of 630×10mm per row in the transverse direction. The scissor bracing 8 for horizontal and diagonal bracing between the steel pipe piles 9 is connected by 20d channel steel.

[0026] In this embodiment, the main steel platform adopts The piles are 9 steel pipe piles with a nominal diameter of 630×10mm. The horizontal spacing of the piles is 3.3 to 3.5m. The horizontal bracing and diagonal bracing between the piles are connected by 20b type channel steel. Steel plate stiffening ribs are set below the main crossbeam at the top of the piles.

[0027] In this embodiment, a double-splitting 45b I-beam main crossbeam 7 is installed on the top of the steel pipe piles 9 of the main trestle bridge and the steel platform. The main crossbeam 7 is placed in the pile top groove of the steel pipe pile 9, and reinforcing ribs 12 are installed on both sides of the steel pipe pile 9 at the bottom of the main crossbeam 7.

[0028] In this embodiment, the top of the steel pipe piles 9 of the steel platform is equipped with double 45b I-beams, and the two 45b I-beams are connected by welding with a partition plate. The main crossbeam 7 is placed in the groove at the top of the steel pipe piles 9, and reinforcing ribs 12 are provided on both sides of the bottom of the main crossbeam 7 and the steel pipe piles 9. Ribs are welded to the main crossbeam 7 at the placement location of the Bailey beam 4 and the support location of the steel pipe piles to strengthen the stress.

[0029] In this embodiment, the main beam of the main trestle bridge consists of 5 groups of 10 Bailey beams 4, arranged at equal intervals in the transverse direction. Each group of Bailey beams 4 is connected by a 90cm support frame 6, and adjacent support frames 6 of each group of Bailey beams 4 are connected by channel steel diagonal bracing. The spacing between each group of Bailey beams 4 is 0.75m. The main beam of the steel platform consists of 22 groups of 88 Bailey beams 4, arranged in the transverse direction as needed. Each group of Bailey beams 4 is connected by a 45cm support frame 6, and the spacing between each group of Bailey beams 4 is 0.9m.

[0030] In this embodiment, 20b I-beams are placed laterally on the main beam of the main trestle bridge as distribution beams 11, with a longitudinal spacing of 0.2m; 40b I-beams are placed laterally on the main beam of the steel platform as distribution beams 11, with a longitudinal spacing of 0.2m.

[0031] In this embodiment, a 10mm thick steel plate is laid along the entire length of the main trestle bridge's distribution beam 11 as the bridge deck 1. The main trestle bridge guardrail 5 is installed on the steel plate of the bridge deck 1. The main trestle bridge guardrail 5 is made of No. 12 I-beams welded to the bridge deck 1, with a height of 1.24 meters and a spacing of 1.4 meters along the bridge direction. A wheel guard is installed at the bottom. The steel platform's bridge deck 1 is fully covered with 10mm thick steel plates. A steel platform guardrail 5.1 is installed on the steel plate of the bridge deck 1. The posts of the steel platform guardrail 5.1 are made of No. 12 I-beams welded to the bridge deck 1, with a height of 1.24 meters and a spacing of 2.0 meters along the bridge direction. Three 48.3mm thick railings are used between the posts. 3.5 steel pipes are used as railings, with wheel guards at the bottom.

[0032] In this embodiment, all steel used in the steel trestle structure, except for the Bailey bridge beams, is Q235 steel. The design values ​​for the tensile, compressive, and bending strengths of Q235 steel are 190 MPa; the design value for the shear strength is 110 MPa. The Bailey bridge beams are unreinforced and made of Q345 steel. The design values ​​for the tensile, compressive, and bending strengths of Q345 steel are 275 MPa; the design value for the shear strength is 160 MPa.

[0033] This invention also provides a method for calculating the stress on a steel trestle bridge over a river tributary, which can be applied to the steel trestle bridge structure over a river tributary described in the above embodiments, including: The average water flow velocity and water density under the straight-line steel trestle bridge are obtained, and the water pressure on the pier is calculated based on the preset pier shape coefficient and pier water-blocking area. The design reference wind speed at the bridge reference height is designed, and the static gust wind speed is calculated based on the design reference wind speed. Then, the first lateral static gust wind load on a single Bailey beam and the second lateral static gust wind load on a single steel pipe pile are calculated based on the static gust wind speed.

[0034] In this embodiment, the formula for calculating the water pressure acting on the bridge pier is: In the formula, Preset pier shape coefficient; The water-blocking area of ​​the bridge pier; The specific gravity of water; The average water flow velocity; This is the acceleration due to gravity.

[0035] In this embodiment, the pier shape coefficient is preset. The value is 0.8; the water-blocking area of ​​the bridge pier. Considering the area above the general scour line, which is typically 3 meters below the riverbed, a value of 2.4 is taken; the specific gravity of water... Values Average water flow velocity Based on the hydrological calculations of the Ili River during its flood season, the flow rate is set at 4.4 m / s.

[0036] Based on the above parameter settings, the calculated result of the water pressure acting on the bridge pier is as follows: In this embodiment, based on conventional design data, the basic wind speed at the bridge site of the steel trestle bridge is set as: once in a hundred years. Once in a decade According to the "Specifications for Wind Resistance Design of Highway Bridges" (JTG / T3360-01-2018), the design reference wind speed at the reference height Z of the steel trestle bridge is... Calculate using the following formula: In the formula, The design reference wind speed at the bridge's reference height Z can be designed based on both the 100-year return period basic wind speed and the 10-year return period basic wind speed. This refers to the wind resistance risk factor. This is the terrain condition coefficient, which is set to 1.0 in this embodiment; The value is 1.08, which is used as the surface type conversion and wind speed height correction factor in this embodiment.

[0037] The design reference wind speed at the bridge site of the steel trestle bridge can be calculated using the above formula as follows: In the formula, Design benchmark wind speed for a once-in-a-century extreme wind; The design reference wind speed is based on a normal working period that occurs once every ten years.

[0038] In this embodiment, the windward area of ​​a single Bailey beam is: In the formula, The ratio of the actual area of ​​a single Bailey beam. Let be the outline area of ​​a single Bailey beam.

[0039] In this embodiment, the wind speed of the still gust is: In the formula, For calm gusts of wind; This is the coefficient for calm gusts.

[0040] In this embodiment, the static gust coefficient Then substitute the maximum wind design reference wind speed into each value. and the design reference wind speed during normal working period ,get: The first lateral static gust of wind acting on a single Bailey beam is: In the formula, air density; For calm gusts of wind; The truss shading coefficient; The drag coefficient of a single Bailey beam; This represents the actual area ratio of a single Bailey panel; This refers to the area of ​​the bridge pier that blocks water.

[0041] In this embodiment, air density Values The drag coefficient of a single Bailey beam Value is 1.7; Truss obstruction coefficient The value is 0.8.

[0042] Substituting, we get: .

[0043] In this embodiment, the calculation formula for the second lateral static gust load acting on the steel pipe pile is: In the formula, The wind resistance coefficient of a single steel pipe pile; The diameter is the steel pipe pile diameter.

[0044] In this embodiment, the wind resistance coefficient of the single steel pipe pile The value is 0.5; the diameter of the steel pipe pile The value is 0.63. Substituting, we get: .

[0045] Optionally, the strength of the steel trestle = load factor 1 × structural self-weight + load factor 2 × vehicle load; the stiffness of the steel trestle = 1.0 × vehicle load.

[0046] In this embodiment, as Figure 4 The diagram shown is based on the self-weight action diagram in the "General Specifications for Design of Highway Bridges and Culverts" (JTGD60-2015). The partial factor is 1.2, and the partial factors for other load actions are all 1.4. The trestle and platform are temporary structures with a service life of less than 5 years, the design safety level is level three, and the structural importance factor is 0.9. Therefore, the corrected partial factors for load action 1 and 2 are 1.08 and 1.26, respectively.

[0047] In actual construction, the steel trestle bridge structure for the river tributary constructed by this invention has a total length of 432.2m and a bridge deck width of 8m. Furthermore, based on the characteristics of the Ili River channel and the utilization rate of the steel platform, the steel platform is divided into 9 longitudinal spans (6+1.5+5). (6+3+4.5)

[0048] In this embodiment, to further verify the stability of the steel trestle bridge structure for a river tributary constructed according to the present invention, based on... Figure 4 The content includes working condition analysis and strength verification.

[0049] The construction loads consider two load combinations: structural self-weight and variable loads. The variable load is the vehicle load. Considering all factors, the loads are divided into two working conditions as shown in Table 1. The strength and stiffness analysis uses two sets of coefficient combinations.

[0050] Table 1 Stiffness verification: Tests showed that the maximum mid-span deformation was 4.3 mm under the action of a 50-ton tanker truck, 5.1 mm under the action of a 90-ton trailer, and 9.8 mm under the action of a 141-ton rotary drilling rig. The steel trestle bridge experienced the greatest overall deformation when the trailer and rotary drilling rig passed through the mid-span of the temporary bridge. According to relevant specifications, the maximum allowable deformation of a 9m span steel trestle bridge is 9000 / 500 = 18 mm.

[0051] Strength verification: When vehicles are in motion, the maximum stress on the bridge deck is 73.3 MPa, which is less than the allowable value of 190 MPa and meets the safety requirements. Tests showed that the maximum stress was 49.6 MPa under the action of a 50-ton tanker truck, 40.5 MPa under the action of a 90-ton trailer, and 73.3 MPa under the action of a 141-ton rotary drilling rig.

[0052] When vehicles are in motion, the maximum stress on the steel temporary bridge's distribution beam is 67.8 MPa, which is less than the allowable stress value of 190 MPa, meeting the safety requirements. Tests showed that under the action of a 50-ton tanker truck, the maximum stress was 58.8 MPa; under the action of a 90-ton trailer, the maximum stress was 67.8 MPa; and under the action of a 141-ton rotary drilling rig, the maximum stress was 67.3 MPa.

[0053] A single Bailey beam is a simple truss structure, consisting of upper and lower chords connected by web members. Longitudinally, the Bailey beams are connected as a whole by Bailey pins, and every two Bailey beams are connected as a group by support frames. Stress calculations were performed on the chords and web members of the Bailey beams. The maximum stress in the chords was 254 MPa, and the maximum stress in the web members was 215 MPa, both less than the allowable stress value of 275 MPa. Under load cases one and two, the maximum stress in the chords was 238 MPa, and the maximum stress in the web members was 203 MPa. Under load cases three and four, the maximum stress in the chords was 260 MPa, and the maximum stress in the web members was 215 MPa. Under load case five, the maximum stress in the chords was 254 MPa, and the maximum stress in the web members was 145 MPa. Under load case six, the maximum stress in the chords was 203 MPa, and the maximum stress in the web members was 142 MPa.

[0054] The maximum stress on the steel column cap beam under the six working conditions is 90.8 MPa, which is less than the allowable stress value of 190 MPa. Under working conditions one and two, the maximum stress of the cap beam is 62.6 MPa. Under working conditions three and four, the maximum stress of the cap beam is 99.3 MPa. Under working condition five, the maximum stress of the cap beam is 90.8 MPa. Under working condition six, the maximum stress of the cap beam is 71.5 MPa.

[0055] The maximum stress of the pipe pile is 99.3 MPa, which is less than the allowable stress value of 190 MPa, thus meeting the strength requirements. Under working conditions one and two, the maximum stress of the pipe pile is 31.1 MPa; under working conditions three and four, the maximum stress is 41.3 MPa; under working condition five, the maximum stress is 42.1 MPa; under working condition five, the maximum stress is 56 MPa; under horizontal braking force calculation, the maximum stress is 17.8 MPa; under flood resistance calculation, the maximum stress is 4.9 MPa; under wind resistance calculation, the maximum stress is 15.3 MPa.

[0056] Stability verification: The maximum exposed length of the pipe pile is 6.7m. For safety, considering a river scour depth of 2m, the calculation length is taken as... .

[0057] The nominal diameter of the column section of the steel pipe pile is 630×10mm; Cross-sectional area of ​​steel pipe pile column Moment of inertia of cross section Section modulus Radius of gyration of the cross section =219.3mm; Calculated based on hinged ends: ,in, Indicates the slenderness ratio. Indicates the calculated length.

[0058] The column section of the steel pipe pile belongs to category B. To cope with different situations, stability coefficients are set for axially compressed members in different characteristic directions. .

[0059] Based on the model calculation results, the maximum axial force and corresponding bending moment of the steel pipe pile are as follows: , .

[0060] The calculation results from the model show that the stability of the steel pipe piles meets the requirements.

[0061] By comparison, under load condition six, the steel pipe pile exhibits the largest column base reaction force, with a maximum value of 791 kN. According to the "Code for Design of Highway Bridge and Culvert Foundations" (JTG3363-2019), the characteristic value of the axial compressive bearing capacity of a single pile supported in soil can be calculated using the following formula: In the formula, The allowable bearing capacity of a single steel pipe pile under axial compression is given by the difference between the self-weight of the single steel pipe pile and the weight of the replacement soil (when the self-weight is included in the buoyancy, the weight of the replacement soil is also included in the buoyancy). The perimeter of a single steel pipe pile; The number of soil layers; , These are the influence coefficients of vibratory pile driving on the pile side friction and pile end bearing capacity of each soil layer, respectively. For hammer driving and static pressure driving, the value is taken as 1.0. The thickness of each soil layer below the bottom surface of the foundation or the local scour line; To and The standard values ​​of the corresponding soil-pile side friction resistance of each layer should be determined by single steel pipe pile friction resistance test or static penetration test. The standard value of the bearing capacity of the soil at the end of a single steel pipe pile should be determined by a single steel pipe pile test or a static cone penetration test. This is the soil plugging effect coefficient at the end of a single steel pipe pile. For closed piles, take 1.0; for open piles, take 0.3~0.4 when 1.2m<d≤1.5m, and take 0.2~0.3 when d>1.5m.

[0062] In actual project construction, the steel trestle bridge on the river tributary constructed by this invention can be a temporary structure, and the effective pile length of the steel pipe piles is measured from the general scour line. According to the "Engineering Geological Survey Report of the Preliminary Design Stage of the Yili River Third Bridge Project", there are two boreholes in the area of ​​the bridge site, namely CQZK-03 and CQZK-04. The soil layer information of the borehole locations is shown in Table 2 below.

[0063] Table 2 Based on the soil layer information at the above borehole points, the pile side resistance of fine sand and plain fill is very small, and these two types of soil are easily eroded and lost under the bridge span. Therefore, the influence of these two types of soil on the pile is not considered when calculating the penetration length of a single steel pipe pile.

[0064] (1) The effective pile length of a single row of steel pipe piles is taken as 5.5m for verification: When using CQZK-03 soil layer, the characteristic value of the compressive bearing capacity of a single pile is: ; When the soil layer is CQZK-04, the characteristic value of the compressive bearing capacity of a single steel pipe pile is: ; Based on the model calculations, the maximum pier top reaction force for a single row of piles is 791 kN, which is less than the calculated value mentioned above. Considering pile scour, it is recommended that the penetration depth of a single pile in a single row be 7.5 m.

[0065] (2) The effective pile length of the double-row steel pipe piles is taken as 4.5m for verification: When using CQZK-03 soil layer, the characteristic value of the compressive bearing capacity of a single pile is: ; When the soil layer is CQZK-04, the characteristic value of the compressive bearing capacity of a single steel pipe pile is: ; Based on the model calculations, the maximum pier top reaction force for a single-row pile is 435kN, which is less than the calculated value mentioned above. Considering pile scour, it is recommended that the penetration depth of a single pile in a double-row pile be 6.5m.

[0066] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A steel trestle bridge structure for a river tributary, characterized in that, Including the main trestle bridge and steel platform; The main trestle bridge is designed as a vertical bridge structure, with both ends fixed by piers; The steel platform is configured as a structure extending along the bridge direction, and is fixed at both ends by bridge piers; The main trestle bridge and steel platform both contain the following components: Steel pipe piles: vertically installed on river tributaries as foundation supports; Main crossbeam: installed at the top of the steel pipe pile; Main beam: erected on the main crossbeam; Distribution beam: laid transversely on the main beam; Bridge deck: laid on the distribution beam; Meanwhile, the main trestle is equipped with two expansion joints, located at the first and second preset positions, respectively, starting from the farthest point on the left. At the predetermined location on the riverbank, the first and second rows of steel pipe piles are vibrated and driven down using a crawler crane, while the main beam is pre-assembled at the work site on the bank. The main crossbeam is placed in the groove at the top of the steel pipe pile, thus completing the erection of the first span of the main beam. Then the bridge deck is laid. The crane travels to the erected first span of the bridge deck and continues to vibrate and drive down the steel pipe piles of the next span. The above steps are repeated, advancing span by span until the steel trestle bridge is erected on the opposite bank.

2. The steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main trestle bridge uses 3 steel pipe piles per row with a nominal diameter of 630×10mm, and the lateral spacing is set to at least 3.1m. The steel platform uses 18 steel pipe piles per row with a nominal diameter of 630×10mm, and the lateral spacing is set to be no less than 3.3m and no more than 3.5m. The main trestle bridge and the steel platform are connected by 20d channel steel to form a scissor bracing structure with horizontal and diagonal bracing.

3. The steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main crossbeam is a double-span 45b I-beam, and the main crossbeam is placed in the groove at the top of the steel pipe pile; The bottom of the main crossbeam and both sides of the steel pipe pile are equipped with reinforcing ribs.

4. The steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main beam of the main trestle bridge is composed of 5 sets of Bailey beams arranged at equal intervals along the transverse direction of the bridge. Each set contains 10 Bailey beams, and each set of Bailey beams is connected by a 90cm support frame. The spacing between each set of Bailey beams is 0.75m. The main beam of the steel platform consists of 22 sets of Bailey beams arranged at equal intervals along the transverse direction of the bridge. Each set contains 4 Bailey beams, and each set of Bailey beams is connected by a 45cm support frame. The spacing between each set of Bailey beams is 0.9m.

5. A steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main trestle bridge's distribution beams are made of 20b I-beams, spaced 0.2m apart in the longitudinal direction; the steel platform's distribution beams are made of 40b I-beams, spaced 0.2m apart in the longitudinal direction.

6. A steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main trestle bridge deck is made of a 10mm thick steel plate laid along its entire length, on which a main trestle bridge guardrail is installed. The main trestle bridge guardrail is made of No. 12 I-beam steel railings welded to the bridge deck, with a height of at least 1.24m and a spacing of 1.4m along the bridge direction. A wheel guard is installed below the main trestle bridge guardrail. The bridge deck of the steel platform is made of 10mm thick steel plates, on which a steel platform guardrail is installed. The guardrail posts are made of No. 12 I-beams welded to the bridge deck. The guardrail posts are 1.24m high and spaced 2.0m apart along the bridge direction. The guardrail posts of the steel platform are connected by three 48.3×3.5mm steel pipes in a horizontal bracing as the guardrail, and a wheel guard is installed below.

7. A steel trestle bridge structure for a river tributary according to claim 1, characterized in that, The main trestle is reinforced with gabion revetment at the bottom, and a back plate is provided at the connection between the main trestle and the steel platform for fixation.

8. A method for calculating the stress on a steel trestle bridge over a river tributary, characterized in that, Capable of being applied to the steel trestle bridge structure for river tributaries as described in any one of claims 1-7, comprising: The average water flow velocity and water density under the straight-line steel trestle bridge are obtained, and the water pressure on the pier is calculated based on the preset pier shape coefficient and pier water-blocking area. The design reference wind speed at the bridge reference height is designed, and the static gust wind speed is calculated based on the design reference wind speed. Then, the first lateral static gust wind load on a single Bailey beam and the second lateral static gust wind load on a single steel pipe pile are calculated based on the static gust wind speed.

9. The method for calculating the stress on a steel trestle bridge over a river tributary according to claim 8, characterized in that, The formula for calculating the water pressure is: In the formula, Preset pier shape coefficient; The water-blocking area of ​​the bridge pier; The specific gravity of water; The average water flow velocity; This is the acceleration due to gravity.

10. The method for calculating the stress on a steel trestle bridge over a river tributary according to claim 8, characterized in that, The formula for calculating the first lateral static gust load is: In the formula, air density; For calm gusts of wind; The truss shading coefficient; The drag coefficient of a single Bailey beam; This represents the actual area ratio of a single Bailey panel; The water-blocking area of ​​the bridge pier. The formula for calculating the second lateral static gust load is: In the formula, The wind resistance coefficient of a single steel pipe pile; The diameter is the steel pipe pile diameter.

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