Cable-stayed load adjustment system for rigid truss bridge reinforcement and its reinforcement method

Abstract

The present invention discloses a cable-stayed load adjustment system for the reinforcement of a rigid truss bridge, which comprises a cable-stayed tower and cable-stayed cables; the cable-stayed tower is mainly composed of a tower frame and a working platform, the working platform is fixed at the top of the tower frame, saddles and cable ducts are installed around the working platform, and the cable-stayed cables pass through the cable ducts. Accordingly, the inventor also establishes a corresponding reinforcement method, places the cable-stayed load adjustment system at the bridge pier, and performs cable-stayed load adjustment on the lower chord of the rigid truss bridge through the cable-stayed cables, so that the force system of the rigid truss bridge is transformed to effectively adjust the internal force of the bridge structure and improve the distribution of the internal force. Applying the present invention makes the internal force distribution of the reinforced bridge more reasonable, can greatly improve the problems of low bearing capacity and small stiffness of the rigid truss bridge, and gives full play to the strength of the reinforcement materials, achieving the purpose of improving the bearing capacity and structural durability of this type of bridge structure, and having good engineering popularization value.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge reinforcement in bridge and culvert engineering of the transportation industry, and particularly relates to a stay cable load adjustment system for rigid truss bridge reinforcement and a reinforcement method thereof. Background Technique

[0002] The reinforced concrete truss bridge is a new type of light bridge developed after the double-curved arch bridge structure. In 1966, the first agricultural reinforced concrete truss arch bridge in China was completed. Due to its outstanding advantages, this type of bridge has been rapidly popularized and applied across the country. Its structural advantages are mainly reflected in the following aspects:

[0003] 1) Simple construction: Prefabricated and assembled construction is often adopted, and the assembly methods include cantilever assembly, cableway hoisting, etc.

[0004] 2) Light weight: The sizes of the truss bridge components are relatively small, and the dead load is small.

[0005] 3) Low cost: The main construction materials are concrete and steel bars, with less usage and lower cost.

[0006] 4) Beautiful appearance: The structure is light and the appearance is beautiful.

[0007] However, with the vigorous development of China's transportation industry, the disadvantages of low bearing capacity and small stiffness of this type of structure bridge have gradually emerged, mainly reflected in: The construction years of the existing reinforced concrete truss bridges are generally early, the design load levels are low, the material strengths are low, the bearing capacities are small, and it is difficult to adapt to the current traffic conditions; due to the relatively small sizes of the components and the fact that they are assembled from multiple prefabricated members, the integrity is poor and the stiffness is small. As time goes by, the diseases of such bridges built in the early years gradually appear, and effective reinforcement methods must be adopted to deal with the diseases to ensure the safe operation of the bridges. In previous reinforcement designs, in most cases, the internal force redistribution of the bridge caused by the structural damage before reinforcement has not been fully considered, and there are significant differences in the internal forces of each member compared with those at the time of bridge completion. Due to the internal force redistribution of the bridge, some members have reached or are close to the bearing limit state under the action of the dead load. If they are directly reinforced, the raw materials may still be damaged in the secondary stress stage, endangering the overall safety of the bridge. Summary of the Invention

[0008] The technical problem to be solved by the invention is to provide a stay cable load adjustment system for rigid truss bridge reinforcement and a reinforcement method thereof, which are scientifically designed, reasonable in structure, simple in construction and excellent in reinforcement effect.

[0009] To solve the above technical problems, the invention adopts the following technical solutions:

[0010] The cable-stayed load adjustment system for the reinforcement of a rigid truss bridge includes a cable-stayed tower and cable-stayed cables. The cable-stayed tower mainly consists of a tower frame and a working platform. The working platform is fixed at the top of the tower frame. Saddle and cable ducts are installed around the working platform, and the cable-stayed cables pass through the cable ducts.

[0011] A base is provided at the bottom of the tower frame. The base is composed of a bottom cross beam and a bottom longitudinal beam of the tower. Diagonal braces are provided in the middle and lower parts of the tower frame.

[0012] The working platform is composed of longitudinal beams, cross beams and a panel. Saddle and cable ducts are symmetrically installed around the working platform, and both ends of the cable-stayed cables pass through two symmetric cable ducts.

[0013] Both ends of the cable-stayed cables are respectively connected to the under-chord anchoring system. The under-chord anchoring system includes a cross beam fixing device, a tensioning cross beam and an anchor backing plate. The cross beam fixing device is a steel plate with stiffeners. The tensioning cross beam is composed of multiple I-beams.

[0014] For the reinforcement method using the above cable-stayed load adjustment system, place the cable-stayed load adjustment system at the pier. Conduct cable-stayed load adjustment on the lower chord of the rigid truss bridge through the cable-stayed cables, so that the force system of the rigid truss bridge changes to effectively adjust the internal force of the bridge structure and improve the distribution of internal forces.

[0015] To ensure the stability of the cable-stayed tower, the cable-stayed load adjustment system is fixed through the base. The base is provided at the bottom of the tower frame and is composed of a bottom cross beam and a bottom longitudinal beam of the tower. Fix the tower frame to the upper chord of the bridge by tensioning the precision-threaded steel bars. Diagonal braces are provided in the middle and lower parts of the tower frame.

[0016] For the above reinforcement method, install the under-chord anchoring system at the bottom of the lower chord of the rigid truss bridge. Apply an external force to the cable-stayed cables through the jacks arranged at the tensioning ends of the under-chord anchoring system. The vertical component of the external force plays a role in load adjustment. The vertical component force of the cable-stayed cables at the top of the tower is transmitted downward through the chords and web members of the rigid truss bridge to the pier foundation. The horizontal component of the external force is balanced by the shear force of the anchor bolts between the under-chord anchoring system and the lower chord. The horizontal component force of the cable-stayed cables at the top of the tower is borne by the longitudinal and cross beams arranged on the working platform. The cross beam fixing device of the under-chord anchoring system bears the tensile force of the cable-stayed cables and transmits the tensile force to the anchor bolts to achieve the balance of the horizontal component force and the application of the vertical component force.

[0017] The height of the cable-stayed tower is set to be 0.25 - 0.40 times the span; the designed allowable stress level of the steel strands of the cable-stayed cables is set to 0.4f pk .

[0018] The total area of the anchor bolts is controlled by the horizontal component force generated by the designed prestress N1 applied by the cable-stayed cables, and it conforms to the following formula:

[0019]

[0020] In the formula: As the sum of the areas of all the implanted anchor bolts at a crossbeam fixing device; α is the included angle between the stay cable and the bridge deck; f ud,t is the design value of the shear strength of the anchor bolt.

[0021] The stability calculation results of the stay cable tower and the working platform should meet the requirements that the structural stability safety factor of the first type of stability (i.e., the structural stability of elastic buckling) should not be less than 4, and the structural stability safety factor of the second type of stability (i.e., the elastoplastic strength stability considering the material nonlinear effect) should not be less than 1.75. The stress calculation results should be less than the allowable strength value of the material.

[0022] Aiming at the problems of low bearing capacity and small stiffness of the rigid truss bridge, the inventor proposes to use the stay cable structure system for the reinforcement of the rigid truss bridge, thereby designing a stay cable load adjustment system for the reinforcement of the rigid truss bridge, including a stay cable tower and stay cables; the stay cable tower is mainly composed of a tower frame and a working platform. The working platform is fixed at the top of the tower frame. Saddle and cable duct are installed around the working platform, and the stay cables pass through the cable ducts. Accordingly, the inventor also establishes a corresponding reinforcement method, places the stay cable load adjustment system at the bridge pier, and performs stay cable load adjustment on the lower chord of the rigid truss bridge through the stay cables, so that the force system of the rigid truss bridge changes to effectively adjust the internal force of the bridge structure and improve the internal force distribution. Applying the present invention makes the internal force distribution of the reinforced bridge more reasonable, can greatly improve the problems of low bearing capacity and small stiffness of the rigid truss bridge, and gives full play to the strength of the reinforcement materials, achieving the purpose of improving the bearing capacity and structural durability of this type of bridge structure, and having good engineering popularization value.

[0023] Compared with the conventional reinforcement method, the present invention has the following main advantages:

[0024] 1) This method belongs to the active reinforcement method, can improve the structural force, and can give full play to the strength of the reinforcement materials. It has good reinforcement performance and can improve the structural bearing capacity and durability.

[0025] 2) The structure is simple, the calculation is simple, the construction is fast, the economic performance is good, and there is no need to add a foundation.

[0026] 3) The adopted stay cable load adjustment system can be a permanent retaining structure or a temporary structure, and can be reused, with good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 are the structural schematic diagram and the usage state schematic diagram of the stay cable load adjustment system and its reinforcement method for the reinforcement of the rigid truss bridge of the present invention.

[0028] Figure 2 is Figure 1 the structural schematic diagram of the chord lower anchoring system in the stay cable load adjustment system.

[0029] Figure 3 is Figure 1 Schematic diagram of the structure of the working platform and the saddle in the stay - cable load - adjusting system.

[0030] Figure 4 It is a reinforcement schematic diagram of the double - deck bridge deck prestressed concrete continuous rigid truss bridge applying the present invention.

[0031] Figure 5 It is a discrete diagram of the stay - cable tower structure.

[0032] Figure 6 It is a discrete diagram of the structure of the under - chord anchorage system.

[0033] Figure 7 It is the von Mises stress nephogram of the working platform.

[0034] Figure 8 It is the von Mises stress nephogram of the tower.

[0035] In the figure: 1 working platform; 2 stay - cable; 3 stay - cable tower; 4 longitudinal beam at the tower bottom; 5 high - strength precision rolled thread steel; 6 cross beam at the tower bottom; 7 under - chord anchorage system; 8 under - chord anchorage system; 9 cable duct; 10 bracing; A1 cross - beam fixing device; A2 anchor bolt; A3 tensioning cross - beam; A4 tensioning end; A5 stiffening rib. Specific implementation manners

[0036] I. Establishment of the stay - cable load - adjusting system for rigid truss bridge reinforcement and its reinforcement method

[0037] 1. Basic principle

[0038] By introducing the stay - cable load - adjusting system, the internal force distribution of the rigid truss bridge structure is fundamentally improved, and the strength of the reinforcement materials is fully exerted, so as to achieve the purpose of improving the bearing capacity and structural durability of this type of bridge structure.

[0039] 2. Specific steps

[0040] Such as Figures 1 to 3As shown in the figure, the position of the cable-stayed tower 3 is marked during the pier positioning and lofting. The cable-stayed tower is mainly composed of a tower frame and a working platform. First, install the bottom cross beam 6, bottom longitudinal beam 4 and high-strength precision-threaded steel bars 5 at the corresponding positions to form the foundation of the cable-stayed tower 3. After the longitudinal and cross beams of the foundation are fixed, construct the tower frame and diagonal braces 10 upwards. The diagonal braces are arranged in the middle and lower parts of the tower frame. Then, install the longitudinal and cross beams and the panel of the working platform 1, and weld the connection between the working platform 1 and the top of the tower frame. Install the cable saddles and cable ducts 9 around the working platform 1 to facilitate the cable-stayed cables 2 to pass through the ducts without causing the cable-stayed cables 2 to entangle with each other. Thus, the construction of the bridge structure is completed. During the construction of the bridge structure, the construction of the structure under the bridge can be carried out synchronously. The structure under the bridge is mainly the under-chord anchorage system, including the cross beam fixing device, the tensioning cross beam and the anchor backing plate. First, drill holes at the designated positions on the lower chord of the bridge. When drilling, it is necessary to strictly determine the hole positions, hole diameters and hole depths according to the design requirements, and avoid damaging the original structural steel bars and prestressed steel bars during drilling. After drilling, implant the anchor bolts A2 as required, install the cross beam fixing device A1, and pour self-compacting concrete into the cavity of the cross beam fixing device A1 after the anchor bolts A2 are completely fixed. Install the tensioning cross beam A3 and the anchor backing plate under the bridge, pass the cable-stayed cables 2 through, and use the vertical component force generated by the tensioning of the cable-stayed cables to eliminate as much as possible some of the internal forces that are unfavorable to the bridge reinforcement, so that the internal forces and linearity of the structure are more reasonable. The load adjustment needs to tension the cable-stayed cables in stages and symmetrically until the design cable force. Thus, the cable-stayed load adjustment of the rigid truss bridge is completed. During the load adjustment process, the structural deformation and the stresses at key parts should be monitored in real time to avoid exceeding the allowable stress of the components or structural instability. If the cable-stayed load adjustment system is a temporary structure, the removal order of the components after construction should be distributed in the reverse order of the installation order described above. It should be noted that the relaxation of the cable-stayed cables 2 should also follow the principles of staging and symmetry. Among them,

[0041] The number of cable-stayed cables arranged, the angles and the magnitudes of the tensile forces must be determined after detailed modeling calculations of the structure. The calculations should consider the damage conditions of the original structure, the internal force distribution and safety of each component during the process of applying the tensile force, and the bearing capacity of the structure after completion of the bridge. From the perspective of structural safety, the design allowable stress level of the steel strands of the cable-stayed cables 2 is set to 0.4f pk .

[0042] Determine the specific structures of the under-chord anchorage system, the cable-stayed tower and the working platform according to the number of cable-stayed cables 2 arranged, the angles and the magnitudes of the tensile forces.

[0043] The cross beam fixing device is a steel plate with stiffeners. The thickness of the steel plate and the arrangement of the stiffeners need to be determined after strength and stability calculations according to the magnitude of the tensile force. The tensioning cross beam A3 is composed of multiple I-beams. Through the tensioning cross beam A3, the cable-stayed cables 2 can be threaded and tensioned without damaging the original structure of the bridge.

[0044] 3. Force analysis

[0045] An external force is applied to the stay cable through a jack installed at the tension end of the chord-down anchoring system. The vertical component of the external force plays a load-adjusting role. The vertical component of the stay cable at the top of the tower is transmitted downward through the chord members and web members of the rigid truss bridge to the pier foundation. The horizontal component of the external force is balanced by the shear force of the anchor bolts between the chord-down anchoring system and the lower chord. The horizontal component of the stay cable at the top of the tower is borne by the longitudinal and cross beams installed on the working platform. The cross beam fixing device of the chord-down anchoring system bears the tensile force of the stay cable and transmits the tensile force to the anchor bolts to achieve the balance of the horizontal component and the application of the vertical component.

[0046] 4. Design calculation

[0047] For the repair and reinforcement of rigid truss structure bridges, the adverse effects brought by the internal force redistribution of the bridge before reinforcement should be fully considered during calculation, and the change of boundary conditions caused by the damage of component connection points should be considered.

[0048] The design calculation should consider the additional load during the construction process and the influence of the construction process on the internal force of the structure. It is necessary to ensure that the structure of the bridge is always in a safe state during all construction stages, and the bearing capacity at the completed bridge stage meets the requirements of the specifications.

[0049] The height of the stay tower has a greater impact on the load-adjusting efficiency and project cost. If the height of the stay tower is too small, it may lead to low load-adjusting efficiency or failure to achieve the expected load-adjusting effect. If the stay tower is set too high, it will cause high costs and poor economy. After comprehensive trial calculation, it is recommended that the tower height be set to 0.25 - 0.40 times the span.

[0050] From the perspective of structural safety, the design allowable stress level of the stay cable steel strand is set to 0.4f pk .

[0051] The total area of the anchor bolts is controlled by the horizontal component generated by the design prestress N1 applied by the stay cable. The specific relationship is as follows:

[0052]

[0053] In the formula: As is the sum of the areas of all implanted anchor bolts at the position of a cross beam fixing device A1; α is the included angle between the stay cable 2 and the bridge deck; f ud,t is the design shear strength value of the anchor bolt.

[0054] Strength and stability checks should be carried out on the stay tower and the working platform. A spatial finite element model is used to analyze the stability of the working platform and the tower. The stability calculation results should meet the requirements that the structural stability safety factor of the first type of stability (i.e., the structural stability of elastic buckling) should not be less than 4, and the structural stability safety factor of the second type of stability (i.e., the elastic-plastic strength stability considering the influence of material nonlinearity) should not be less than 1.75. And the structural stress calculation results should be less than the allowable strength value of the material.

[0055] II. Application Examples

[0056] 1. Construction

[0057] Carry out according to the specific steps of the aforementioned reinforcement method.

[0058] 2. Calculation

[0059] As Figure 4 shown, this bridge is a 60m + 3×100m + 60m double-deck prestressed concrete continuous rigid truss bridge. The height of the bridge tower is set at 26.5m. The angles between the stay cables and the bridge deck are 38.5° and 52° respectively. The cable tension forces are 368.4kN and 429.4kN. The maximum stay cable stress does not exceed 0.4f pk = 744MPa, and the distribution of the number of anchor bolts is 22 sets and 18 sets. Finite element analysis is carried out on the structure, and the results are as follows:

[0060] 1) During the construction stage, the maximum tensile stress of the bridge concrete components is 0.78MPa, and the maximum compressive stress is -13.84MPa, both of which are less than the specification limits and meet the specification requirements.

[0061] 2) After the completion stage of the bridge, the checking calculation results of the ultimate limit state of the bridge bearing capacity are shown in Table 1, and the checking calculation results of the serviceability limit state are shown in Tables 2 - 4.

[0062] Table 1 Summary Table of the Checking Calculation Results of the Bearing Capacity of the Most Adversely Stressed Components of the Main Bridge

[0063]

[0064] The above table only lists the checking calculation results of the most adversely stressed components among all components of the same type. A negative axial force indicates compression, and a positive value indicates tension.

[0065] Table 2 Table of the Deformation Checking Calculation Results of the Main Bridge

[0066]

[0067] Table 3 Table of the Crack Checking Calculation Results of the Main Bridge under Load Combination I

[0068]

[0069] The allowable nominal tensile stress of the concrete has been corrected according to the non-prestressed steel bar reinforcement ratio in the table; "--" indicates that no tensile stress appears. The same below.

[0070] Table 4 Table of the Crack Checking Calculation Results of the Main Bridge under Load Combination II

[0071]

[0072] The above calculation results show that the internal force distribution of the reinforced bridge is reasonable, and the bearing capacity of the bridge meets the specification requirements.

[0073] 3) Calculation of the stay cable tower and the working platform

[0074] An finite element model of the stay cable tower is established by ANSYS. The working platform is divided by shell181 elements. Except for the connection section between the top of the tower and the working platform which is divided by shell181 elements, the rest of the tower is divided by beam189 elements. The stay cable tower consists of a total of 19,528 shell181 elements and 350 beam189 elements, with a total of 19,726 nodes.

[0075] The maximum von mises stress of the working platform at the top of the stay cable tower is 108 MPa, and the maximum von mises stress of the tower is 130 MPa, both of which are less than the strength design value of Q345, which is 310 MPa.

[0076] (2) Overall stability check of the working platform and the tower

[0077] For the stay cable tower composed of the working platform and the tower, the first 5 instability modes are all out-of-plane instability of the web plate of the working platform. The critical load coefficient of the first-order instability is 8.162 > 4, meeting the requirement that the structural stability safety factor of the first type of stability of the structural system (i.e., the structural stability safety factor of elastic buckling) should not be less than 4.

[0078] The critical load coefficient of the instability of the working platform and the tower is 4.338 > 1.75, meeting the requirement that the structural stability safety factor of the second type of stability of the structural system (i.e., the elastic-plastic strength stability considering the influence of material nonlinearity) is not less than 1.75.

[0079] 4) Calculation of the under-chord anchoring system

[0080] An finite element model is established by ANSYS. The under-chord anchoring system is divided by shell181 elements, the anchor bolts are divided by beam189 elements, and the lower chord rod and the concrete cushion are divided by solid45 elements. The calculation model consists of a total of 2,472 shell181 elements, 198 beam189 elements, and 10,360 solid45 elements, with a total of 15,649 nodes.

[0081] (1) Strength of the lower anchor point

[0082] The maximum von mises stress of the under-chord anchoring system is 89.0 MPa, which is less than the strength design value of Q345, which is 310 MPa.

[0083] (2) Force analysis of the anchor bolts at the bottom of the concrete cushion

[0084] Assume that the friction force between the top plate of the under-string anchoring system and the cushion layer is 0, and all the horizontal components of the cable forces of the stay cables are borne by the anchor bolts. The angle between the stay cable and the horizontal is 38.5°, the horizontal component of the stay cable force is 686.7 kN, and the horizontal force of each under-string anchoring system is 1373.4 kN.

[0085] There is no lever wall for the anchor bolts at this location, and there are a total of 22 anchor bolts. The shear bearing capacity of the anchor bolts is:

[0086] The shear resistance meets the requirements.

Claims

1. A cable-stayed load adjustment system for the reinforcement of a rigid truss bridge, characterized in that It includes a stay tower and stay cables; the stay tower is mainly composed of a tower frame and a working platform. The working platform is fixed at the top of the tower frame. Saddle and cable ducts are installed around the working platform, and the stay cables pass through the cable ducts. The two ends of the stay cables are respectively connected to the under-chord anchoring system. The under-chord anchoring system includes a crossbeam fixing device, a tensioning crossbeam and an anchor plate. The crossbeam fixing device is a steel plate with stiffeners, and the tensioning crossbeam is composed of multiple I-beams.

2. The cable-stayed load adjustment system for rigid truss bridge reinforcement according to claim 1, wherein: A pedestal is arranged at the bottom of the tower frame. The pedestal is composed of a bottom tower crossbeam and a bottom tower longitudinal beam, and diagonal braces are arranged in the middle and lower parts of the tower frame.

3. The cable-stayed load adjustment system for the rigid truss bridge reinforcement according to claim 1, characterized in that: The working platform is composed of longitudinal beams, crossbeams and a panel. Saddle and cable ducts are symmetrically installed around the working platform, and the two ends of the stay cables pass through two symmetric cable ducts.

4. The reinforcement method using the stay cable load adjustment system according to claim 1, characterized in that: Place the stay cable load adjustment system at the pier, and perform stay cable load adjustment on the lower chord of the rigid truss bridge through the stay cables, so that the force system of the rigid truss bridge changes to effectively adjust the internal force of the bridge structure and improve the distribution of internal force.

5. The reinforcement method according to claim 4, characterized in that: The stay cable load adjustment system is fixed through the pedestal; the pedestal is arranged at the bottom of the tower frame. The pedestal is composed of a bottom tower crossbeam and a bottom tower longitudinal beam. The tower frame is fixed to the upper chord of the bridge by tensioning high-strength threaded steel bars, and diagonal braces are arranged in the middle and lower parts of the tower frame.

6. The reinforcement method according to claim 4, wherein: Install the under-chord anchoring system at the bottom of the lower chord of the rigid truss bridge, and apply an external force to the stay cables through the jacks arranged at the tensioning ends of the under-chord anchoring system; the vertical component of the external force plays a role in load adjustment, and the vertical component of the stay cables at the top of the tower is transmitted downward through the chords and web members of the rigid truss bridge until it reaches the pier foundation; the horizontal component of the external force is balanced by the shear force of the anchor bolts between the under-chord anchoring system and the lower chord, and the horizontal component of the stay cables at the top of the tower is borne by the longitudinal and crossbeams arranged on the working platform; the crossbeam fixing device of the under-chord anchoring system bears the tensile force of the stay cables and transmits the tensile force to the anchor bolts to achieve the balance of the horizontal component and the application of the vertical component.

7. The reinforcement method according to claim 4, characterized in that: The height of the cable-stayed tower is set to be 0.25 to 0.40 times the span; the design allowable stress level of the steel strands of the stay cables is set to 0.4f pk .

8. The reinforcement method according to claim 4, characterized in that: The total area of the anchor bolts is controlled by the horizontal component generated by the designed prestress N1 applied by the stay cables, which conforms to the following formula: Where: A s is the sum of the areas of all the implanted anchor bolts at a crossbeam fixing device; α is the angle between the stay cable and the bridge deck; f ud,t is the design value of the shear strength of the anchor bolt.

9. The reinforcement method according to claim 4, characterized in that: The calculation results of the stability of the stay tower and the working platform should meet the requirement that the structural stability safety factor of the first type of stability should not be less than 4, and should also meet the requirement that the structural stability safety factor of the second type of stability is not less than 1.

75. Its stress calculation results should be less than the allowable strength value of the material.

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