Device and method for replacing bridge support with curved bridge bottom surface

Abstract

The invention provides a device and a method for replacing a bridge support with a curved bridge bottom surface, and belongs to the technical field of bridge maintenance. The problems that the bottom face of a curved-surface bridge body is in the curve trend, the bent surface is not matched with the horizontal working face of jacking equipment, and synchronous jacking is difficult to achieve in the support replacing process to unload the support are solved. The device comprises a structural adhesive layer, a jacking support device, a temporary support and a filling steel plate layer, the structural adhesive layer is arranged on the top face of the jacking supporting device and used for fixedly connecting the bottom face of the bridge with the jacking supporting device. The jacking supporting device comprises an arc-shaped top plate, a plurality of supporting plates and a bottom plate, the radian of the arc-shaped top plate is matched with the radian of the bottom face of the bridge, the supporting plates are vertically arranged, the top ends of the supporting plates are fixedly connected with the arc-shaped top plate, the bottom ends of the supporting plates are fixedly connected with the bottom plate, and the bottom face of the bottom plate is a horizontal flat surface used for being assembled with jacking equipment to lift the bridge. The device is mainly used for replacing a bridge support with a curved bridge bottom surface.

Description

Technical Field

[0001] The present invention belongs to the technical field of bridge maintenance, and in particular relates to a bridge support replacement device and a replacement method for a bridge with a curved bottom surface. Background Art

[0002] With the surge in social traffic volume and the increase in heavy-loaded vehicles, the service environment of bridge bearings has become increasingly severe, resulting in a significant increase in the frequency of damage and replacement. There are many reasons for bearing damage, such as the load burden brought by overloaded and oversized vehicles, rainwater accumulation, and accelerated corrosion caused by the infiltration of deicing salt. A large number of bridges built in the early days have entered a concentrated period of bearing aging. The technical difficulty and risk of replacing bearings on curved bridges are particularly prominent. Since the bottom surface of the bridge body is curved, the curved surface does not match the horizontal working surface of the jacking equipment. It is difficult to achieve synchronous jacking to unload the bearings during the replacement process. The curved beam body makes the space for the bearings below narrow, making operation difficult. Summary of the Invention

[0003] In view of this, in order to solve the problem that the bottom surface of the curved bridge body is curved and the curved surface does not match the horizontal working surface of the jacking equipment, and it is difficult to achieve synchronous jacking to unload the bearings during the bearing replacement process, the present invention proposes a bridge bearing replacement device and replacement method with a curved bottom surface of the bridge, a jacking support device with an arc-shaped top surface is used to adapt to the curved surface of the bridge, and the bottom surface of the jacking support device is a horizontal surface to adapt to the jacking equipment, ensuring that the jacking equipment has no slope in the horizontal direction, uniform force, and can achieve rapid jacking, ensuring the safety of the jacking process, and the bridge is now synchronously jacked by the jacking equipment, and then the jacking support device is supported by temporary supports to support the raised bridge, and finally the bearing replacement operation is carried out.

[0004] To achieve the above-mentioned object, the present invention adopts the following technical solution: a bridge bearing replacement device with a curved bottom surface, comprising a structural adhesive layer, multiple pairs of jacking support devices, multiple temporary bearings and a filling steel plate layer; The structural adhesive layer is provided on the top surface of the jacking support device and is used to securely connect the bottom surface of the bridge to the jacking support device; The jacking support device is symmetrically arranged on both sides below the bridge, and includes a curved top plate, a plurality of support plates and a bottom plate. The curvature of the curved top plate matches the curvature of the bottom surface of the bridge. The support plates are arranged vertically, with the top ends fixedly connected to the curved top plate and the bottom ends fixedly connected to the bottom plate. The bottom surface of the bottom plate is a horizontal flat surface for assembling with the jacking equipment to lift the bridge. The temporary support is placed on the bridge pier, directly below the jacking support device, and is used to provide a support site for the jacking support device; The filling steel plate layer is arranged between the jacking support device and the temporary support and has an adjustable thickness, and is used to transmit the supporting force.

[0005] Furthermore, the structural adhesive layer is a steel-bonding structural adhesive layer.

[0006] Furthermore, the arc-shaped top plate, multiple support plates and bottom plate are all steel plates.

[0007] Furthermore, the plurality of support plates are arranged vertically and cross-sectionally with each other, and the cross sections of the plurality of support plates are in the shape of grid lines.

[0008] Furthermore, the temporary support includes a supporting cylinder and a plurality of I-beams, the plurality of I-beams are evenly arranged along the circumference of the cylindrical surface of the supporting cylinder, the supporting cylinder is vertically arranged, the waist plate of the I-beam is vertically arranged and facing the axial direction of the supporting cylinder, the bottom surface of the I-beam and the bottom surface of the supporting cylinder are located in the same horizontal plane, and an arc-shaped notch is vertically opened at one end of the I-beam and fixedly connected to the cylindrical surface of the supporting cylinder.

[0009] Furthermore, the temporary support also includes a plurality of bolts, a plurality of nuts and a plurality of strip plates corresponding to the I-beams one by one. The plurality of strip plates are vertically arranged and evenly arranged along the circumference of the cylindrical surface of the supporting cylinder. The side edges of the strip plates are fixedly connected to the cylindrical surface of the supporting cylinder. The plate surface of the strip plates is tightly fitted with the waist plate of the I-beam, and a plurality of through holes are opened through the strip plates and the waist plate of the I-beam. The bolts are assembled with the nuts after passing through the through holes.

[0010] Furthermore, there are 4 I-beams, 4 through holes, and 16 bolts and nuts.

[0011] A method for replacing a bridge bearing with a curved bottom surface comprises the following steps: S1. Construction preparation and on-site review and inspection: Before jacking, arrange several displacement and centerline observation points on the bridge deck, accurately measure the elevation value and bridge deflection of each point, and keep records to determine the exact jacking height of each point; S2. Clean the bottom surface of the bridge for bonding and fixing the jacking support device; S3. Apply a structural adhesive layer on the top surface of the jacking support device; S4. Use the lifting equipment to raise the lifting support device until the structural adhesive layer contacts the bottom surface of the bridge, and apply appropriate pressure to squeeze the adhesive out of the edge seam of the curved top plate; S5. Use a spirit level to level the bottom surface of the base plate, then use a filling steel plate layer to fill the space between the bottom surface of the jacking support device and the top surface of the temporary support to fix the support, wait for the structural adhesive layer to solidify, and then debug the jacking equipment after the structural adhesive layer solidifies; S6. Debugging of jacking equipment: First, conduct a trial jacking. According to the load tonnage of each point displayed on the jacking equipment computer, calculate the actual reaction force value and compare it with the reaction force value in the design drawing. When the comparison value error is less than or equal to 10%, jacking can continue. When the comparison value is greater than 10%, stop the machine to confirm the cause of the error and confirm it with the design before continuing jacking. After the trial jacking is completed, check and confirm the synchronization of the jacking equipment. After confirming synchronization, restore the jacking equipment to the original position and prepare for the bridge jacking operation. S7, bridge jacking operation: start the jacking equipment and run it to S1 to determine the precise jacking height of each point. During the jacking process, manually adjust the thickness of the filling steel plate layer to ensure that the space between the bottom surface of the jacking support device and the top surface of the temporary support is fully filled; S8. Replace the bridge bearings, remove the old bearings and install new ones; S9. Equipment dismantling and site cleaning: After the new bearings meet the design requirements, start the jacking equipment to lift the bridge, remove the filling steel plate layer, and then control the jacking equipment to return to the original position. During the descent of the bridge, the new bearings are assembled, the jacking equipment and temporary bearings are removed, and the structural adhesive layer is destroyed with an electric hammer to remove the jacking support device. The structural adhesive layer remaining on the bottom surface of the bridge is grinded with a grinder.

[0012] Compared with the prior art, the bridge bearing replacement device and replacement method of the present invention with a curved bottom surface have the following beneficial effects: 1. The present invention is provided with a jacking support device with an arc-shaped top surface and a horizontal bottom surface, which indirectly assembles the curved surface of the bridge with the horizontal working surface of the jacking equipment, ensuring that the working surface of the jacking equipment has no slope and is evenly stressed, thereby ensuring the safety of the jacking process.

[0013] 2. The jacking support devices of the present invention are symmetrically arranged in pairs on both sides of the bottom surface of the bridge, avoiding the central area at the bottom of the bridge. There are structural parts such as drainage pipes in the central area of the bottom of some bridges. The present invention can be used to replace bridge supports with fixed structures in the center of the bottom end of the bridge, and is widely applicable.

[0014] 3. The temporary support of the present invention is fixed with multiple I-beams, which increase the bottom area of the temporary support, thereby increasing the friction force and the anti-slip coefficient of the temporary support, avoiding the temporary support from slipping during construction and ensuring the stability of the box girder jacking.

[0015] 4. The temporary support of the present invention and the I-beam are fixed by welding the I-beam's arc-shaped notch and fixing it with strip-shaped bolts. The components are firmly fixed, thereby improving the overall strength of the temporary support.

[0016] 5. The bridge bearing replacement device of the present invention can be used with hydraulic jacks to achieve overall lifting. The hydraulic jacks can be arranged in three or four groups. The overall lifting tonnage is large and it is suitable for replacing ball steel bearings and rubber bearings of urban elevated bridges. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 This is a front view of the bridge support according to the present invention; Figure 2 It is a left side view of the bridge support according to the present invention; Figure 3 This is a front view of a bridge support replacement device with a curved bottom surface when assembled with the bridge according to the present invention; Figure 4 For the present invention Figure 3 A partial enlarged view of point B in the middle; Figure 5 This is a left side view of a bridge support replacement device with a curved bottom surface when assembled with the bridge according to the present invention; Figure 6 For the present invention Figure 5 A partial enlarged view of point D in the middle; Figure 7 It is a structural schematic diagram of the jacking support device of the present invention; Figure 8 This is a front view of the jacking support device of the present invention; Figure 9 It is a left side view of the jacking support device of the present invention; Figure 10 This is a schematic structural diagram of the temporary support according to the present invention; Figure 11 This is a front view of the temporary support according to the present invention; Figure 12 For the present invention Figure 11 Cross-sectional view in the middle E direction; In the figure: A-bridge; C-lifting equipment; 1-structural adhesive layer; 2-lifting support device; 3-temporary support; 4-filling steel plate layer; 21-arc top plate; 22-support plate; 23-bottom plate; 31-support column; 32-I-beam; 33-strip plate. DETAILED DESCRIPTION

[0017] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely explain the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features therein can be combined with each other in the absence of conflict, and the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0018] 1. Specific implementation method 1, see Figure 1-12 To illustrate this embodiment, a bridge bearing replacement device with a curved bottom surface described in this application includes a structural adhesive layer 1, multiple pairs of jacking support devices 2, multiple temporary bearings 3 and a filling steel plate layer 4; The structural adhesive layer 1 is arranged on the top surface of the jacking support device 2 and is used to fix the bottom surface of the bridge to the jacking support device 2; The jacking support device 2 is symmetrically arranged on both sides below the bridge, and it includes a curved top plate 21, multiple support plates 22 and a bottom plate 23. The curvature of the curved top plate 21 matches the curvature of the bottom surface of the bridge. The support plates 22 are vertically arranged, the top end is fixedly connected to the curved top plate 21, and the bottom end is fixedly connected to the bottom plate 23. The bottom surface of the bottom plate 23 is a horizontal flat surface for assembling with the jacking equipment to lift the bridge; the jacking equipment can be a hydraulic jack, and the hydraulic jack can be arranged in a three-span and a four-span arrangement to achieve overall jacking. The jacking tonnage is large and is suitable for replacing ball steel bearings and rubber bearings of urban elevated bridges.

[0019] The temporary support 3 is placed on the bridge pier, directly below the jacking support device 2, and is used to provide a support site for the jacking support device 2; The infill steel plate layer 4, with adjustable thickness, is disposed between the jacking support device 2 and the temporary support 3 and is used to transmit the supporting force. The infill steel plate layer 4 is pre-filled before jacking and continuously increases in thickness during the jacking process and at the highest position to ensure that the temporary support 3 can fully support the jacking support device 2.

[0020] The structural adhesive layer 1 is a steel structural adhesive layer. The steel structural adhesive is formed by combining two components, A and B. Before use, it should be subjected to on-site quality inspection. If qualified, it should be prepared according to the ratio of A:B = 2:1. Be careful to avoid rainwater from entering the container during stirring. Stir in the same direction and there should be no oil stains in the container. After the structural adhesive is prepared, apply it on the steel plate surface with a spatula. The arc-shaped top plate 21, multiple support plates 22 and bottom plate 23 are all steel plates with a thickness of 20 mm. The curvature of the arc-shaped top plate 21 is bent and formed in the processing plant according to the actual size. The jacking support device 2 is welded by the arc-shaped top plate 21, multiple support plates 22 and bottom plate 23 using E50 welding rods and then transported to the construction site.

[0021] The multiple support plates 22 are arranged vertically and cross-sectionally with each other. The cross-sections of the multiple support plates 22 are in the shape of grid lines. The cross-vertical layout enables the structure to effectively transfer loads in both the longitudinal and transverse directions, forming a bidirectional compressive and tensile system, which significantly improves the overall stiffness and stability of the jacking support device.

[0022] The temporary support 3 includes a supporting cylinder 31 and a plurality of I-beams 32. The plurality of I-beams 32 are evenly arranged along the circumference of the cylindrical surface of the supporting cylinder 31. The supporting cylinder 31 is vertically arranged. The waist plate of the I-beam 32 is vertically arranged and faces the axial direction of the supporting cylinder 31. The bottom surface of the I-beam 32 and the bottom surface of the supporting cylinder 31 are located in the same horizontal plane. An arc-shaped notch is vertically opened at one end of the I-beam 32 and is fixedly connected to the cylindrical surface of the supporting cylinder 31.

[0023] The temporary support 3 also includes a plurality of bolts, a plurality of nuts and a plurality of strip plates 33 corresponding to the I-beams 32. The plurality of strip plates 33 are vertically arranged and evenly arranged along the circumference of the cylindrical surface of the supporting cylinder 31. The side edges of the strip plates 33 are fixedly connected to the cylindrical surface of the supporting cylinder 31. The plate surface of the strip plates 33 fits tightly with the waist plate of the I-beam 32. A plurality of through holes are opened through the strip plates 3 and the waist plate of the I-beam 3. The bolts pass through the through holes and are assembled with the nuts.

[0024] I-beam 32 is pre-cut with an arc-shaped notch and then fully welded to support cylinder 31. The waist plate of I-beam 32 is then bolted to strip plate 33 on the cylindrical surface of support cylinder 31. High-strength bolts made of grade 8.8 or higher are used to achieve dual fixation, improve the overall structural strength of temporary support 3, increase the anti-slip coefficient of temporary support 3, and ensure the stability of box girder jacking.

[0025] There are four I-beams 32 , four through holes, and sixteen bolts and nuts.

[0026] A method for replacing a bridge bearing with a curved bottom surface comprises the following steps: S1. Construction preparation and on-site review and inspection: Before jacking, arrange several displacement and centerline observation points on the bridge deck, accurately measure the elevation value and bridge deflection of each point, and keep records to determine the exact jacking height of each point; S2. Clean the bottom surface of the bridge where the lifting support device 2 is bonded and fixed. Use a hard-bristled brush to remove any grease or dirt from the surface, then rinse with tap water. Then, polish the bonding surface, removing 1-2 mm of the surface layer until the new surface is completely exposed. Use oil-free compressed air to blow away any powder or particles, then rinse thoroughly. After the surface is completely dry, wipe it with a clean cotton ball dipped in acetone. S3, applying a structural adhesive layer 1 on the top surface of the jacking support device 2; S4, using a lifting device to lift the lifting support device 2 until the structural adhesive layer 1 contacts the bottom surface of the bridge, and applying appropriate pressure to squeeze the adhesive out of the side seam of the curved top plate 21; S5. Use a spirit level to level the bottom surface of the base plate 23. Then use the filling steel plate layer 4 to fill the space between the bottom surface of the jacking support device 2 and the top surface of the temporary support 3 to support and fix them. Wait for the structural adhesive layer 1 to cure. After curing for 24 hours, the pressure can be removed. After 72 hours, the jacking construction can be carried out. After the structural adhesive layer 1 is completely cured, the jacking equipment can be debugged. S6. Debugging of jacking equipment: The main purpose of trial jacking is to eliminate possible problems of the whole synchronous jacking system, such as oil leakage of oil line joints, insufficient oil pump pressure, etc., and to eliminate possible non-elastic deformation during the jacking process. First, conduct trial jacking. According to the load tonnage of each point displayed on the jacking equipment computer, calculate the actual reaction force value and compare it with the reaction force value of the design drawing. When the error of the comparison value is less than or equal to 10%, continue jacking; when the comparison value is greater than 10%, stop the machine to confirm the cause of the error and confirm the design before continuing jacking. After the trial jacking is completed, check and confirm the synchronization of the jacking equipment. After confirming the synchronization, restore the jacking equipment to the original position and prepare for the bridge jacking operation; S7, bridge jacking operation: start the jacking equipment and run it to S1 to determine the precise jacking height of each point. During the jacking process, manually adjust the thickness of the filling steel plate layer 4 to ensure that the space between the bottom surface of the jacking support device 2 and the top surface of the temporary support 3 is fully filled. Each operator who adjusts the thickness of the filling steel plate layer 4 is equipped with a walkie-talkie and is under the unified command of the jacking person in charge.

[0027] S8. Replace the bridge bearings, remove the old bearings and install new ones; S9. Equipment removal and site cleanup: After the new bearings meet the design requirements, start the jacking equipment to raise the bridge, remove the filling steel plate layer 4, and then control the jacking equipment to return to the original position. During the bridge's descent, the new bearings are assembled. The jacking equipment and temporary bearings 3 are removed. Use an electric hammer to destroy the structural adhesive layer 1 to remove the jacking support device 2. Use a grinder to grind the remaining structural adhesive layer on the bottom of the bridge. If the structural adhesive layer 1 cannot be chiseled off, the curved top plate 21 can be appropriately heated. The structural adhesive used in this project is a Class I adhesive. When the temperature exceeds 65°, the structural adhesive layer 1 will begin to deform thermally. According to the "Standard for the Evaluation of Engineering Structures After Fire" T / CECS252-2019, concrete will not be damaged until it exceeds 280°. Therefore, heating methods can be used to effectively remove the structural adhesive layer 1 without damaging the bridge structure.

[0028] The embodiments of the present invention disclosed above are intended only to illustrate the present invention. The embodiments do not describe all details in detail, nor do they limit the present invention to the specific embodiments described. Numerous modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention.

Claims

1. A bridge bearing replacement device with a curved bottom surface, characterized in that: It comprises a structural adhesive layer (1), multiple pairs of lifting support devices (2), multiple temporary supports (3) and a filling steel plate layer (4); The structural adhesive layer (1) is arranged on the top surface of the jacking support device (2) and is used to fixedly connect the bottom surface of the bridge to the jacking support device (2); The lifting support device (2) is symmetrically arranged on both sides below the bridge, and comprises an arc-shaped top plate (21), a plurality of support plates (22) and a bottom plate (23). The curvature of the arc-shaped top plate (21) matches the curvature of the bottom surface of the bridge. The support plates (22) are vertically arranged, with the top end fixedly connected to the arc-shaped top plate (21) and the bottom end fixedly connected to the bottom plate (23). The bottom surface of the bottom plate (23) is a horizontal flat surface for assembling with the lifting equipment to lift the bridge. The temporary support (3) is placed on the bridge pier, directly below the jacking support device (2), and is used to provide a support site for the jacking support device (2); The filling steel plate layer (4) is arranged between the jacking support device (2) and the temporary support (3) and has an adjustable thickness, and is used to transmit the supporting force.

2. The bridge bearing replacement device with a curved bottom surface according to claim 1, characterized in that: The structural adhesive layer (1) is a steel-bonding structural adhesive layer.

3. The bridge support replacement device with a curved bottom surface according to claim 1 is characterized in that: The arc-shaped top plate (21), the plurality of support plates (22) and the bottom plate (23) are all steel plates.

4. The bridge bearing replacement device with a curved bottom surface according to claim 1 is characterized in that: The plurality of support plates (22) are arranged vertically and cross-sectionally with each other, and the cross sections of the plurality of support plates (22) are in the shape of grid lines.

5. The bridge bearing replacement device with a curved bottom surface according to claim 1 is characterized in that: The temporary support (3) includes a supporting cylinder (31) and a plurality of I-beams (32), wherein the plurality of I-beams (32) are evenly arranged along the circumference of the cylindrical surface of the supporting cylinder (31), the supporting cylinder (31) is vertically arranged, the waist plate of the I-beam (32) is vertically arranged and faces the axial direction of the supporting cylinder (31), the bottom surface of the I-beam (32) and the bottom surface of the supporting cylinder (31) are located in the same horizontal plane, and one end of the I-beam (32) is vertically provided with an arc-shaped notch and is fixedly connected to the cylindrical surface of the supporting cylinder (31).

6. The bridge bearing replacement device with a curved bottom surface according to claim 5, characterized in that: The temporary support (3) further comprises a plurality of bolts, a plurality of nuts and a plurality of strip plates (33) corresponding to the I-beams (32) one by one. The plurality of strip plates (33) are all vertically arranged and evenly arranged along the circumference of the cylindrical surface of the supporting cylinder (31). The side edges of the strip plates (33) are fixedly connected to the cylindrical surface of the supporting cylinder (31). The plate surface of the strip plates (33) is tightly fitted with the waist plate of the I-beam (32). A plurality of through holes are provided through the strip plates (3) and the waist plate of the I-beam (3). The bolts are assembled with the nuts after passing through the through holes.

7. The bridge bearing replacement device with a curved bottom surface according to claim 6, characterized in that: There are four I-beams (32), four through holes, and sixteen bolts and nuts.

8. A method for replacing a bridge bearing with a curved bottom surface, characterized in that: Using the bridge bearing replacement device with a curved bottom surface as described in any one of claims 1 to 7 comprises the following steps: S1. Construction preparation and on-site review and inspection: Before jacking, arrange several displacement and centerline observation points on the bridge deck, accurately measure the elevation value and bridge deflection of each point, and keep records to determine the exact jacking height of each point; S2, cleaning the bottom surface of the bridge for bonding and fixing the jacking support device (2); S3, applying a structural adhesive layer (1) on the top surface of the jacking support device (2); S4, using a lifting device to lift the lifting support device (2) until the structural adhesive layer (1) contacts the bottom surface of the bridge, and applying appropriate pressure to squeeze the adhesive out of the side seam of the curved top plate (21); S5. Use a level to level the bottom surface of the base plate (23), then use a filling steel plate layer (4) to fill and support the space between the bottom surface of the jacking support device (2) and the top surface of the temporary support (3), and wait for the structural adhesive layer (1) to solidify. After the structural adhesive layer (1) solidifies, debug the jacking equipment; S6. Debugging of jacking equipment: First, conduct a trial jacking. According to the load tonnage at each point displayed on the jacking equipment computer, calculate the actual reaction force value and compare it with the reaction force value in the design drawing. If the comparison value error is less than or equal to 10%, continue jacking. If the comparison value is greater than 10%, stop the machine to confirm the cause of the error and confirm it with the design before continuing jacking. After the trial jacking is completed, check and confirm the synchronization of the jacking equipment. After confirming synchronization, restore the jacking equipment to the original position and prepare for the bridge jacking operation. S7, bridge jacking operation: start the jacking equipment and run it to S1 to determine the precise jacking height of each point. During the jacking process, manually adjust the thickness of the filling steel plate layer (4) to ensure that the space between the bottom surface of the jacking support device (2) and the top surface of the temporary support (3) is fully filled; S8. Replace the bridge bearings, remove the old bearings and install new ones; S9. Equipment removal and site cleaning: After the new bearings meet the design requirements, start the jacking equipment to lift the bridge, remove the filling steel plate layer (4), and then control the jacking equipment to fall back to the original position. During the bridge's descent, the new bearings are assembled. Remove the jacking equipment and temporary bearings (3), use an electric hammer to destroy the structural adhesive layer (1), remove the jacking support device (2), and use a grinder to grind the remaining structural adhesive layer on the bottom surface of the bridge.

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