Bridge energy dissipation raft type pile foundation structure and construction method

Abstract

The invention relates to the field of reservoir area bridge design and construction, in particular to a bridge energy-dissipation raft type pile foundation structure and a construction method, and the bridge energy-dissipation raft type pile foundation structure can effectively achieve shock absorption and isolation of a bearing platform of a bridge and comprises a pile foundation, the bearing platform and a pier which are sequentially arranged from bottom to top, an energy-dissipation cushion layer is fixedly arranged at the bottom of the bearing platform, and the bottom face of the energy-dissipation cushion layer is fixedly connected with the top face of the pile foundation. Friction energy dissipation layers are arranged on the bottom faces of the energy dissipation cushion layers, and the top of the bearing platform is fixedly connected with the bottom of the pier through energy dissipation devices. The method is particularly suitable for construction of bridges arranged in high-intensity fortification areas.

Description

Technical Field

[0001] The invention relates to the field of reservoir area bridge design and construction, in particular to an energy-absorbing raft type pile foundation structure of a bridge and a construction method thereof. Background Art

[0002] For bridges located in the reservoir area and within the reservoir influence area, due to the influence of factors such as reservoir water storage, water level changes, and flood discharge, the foundation design, pier design, management and maintenance of the reservoir area bridge are more complicated than ordinary bridges. If the bridge is built first and then the reservoir is built, the impact of water storage on foundation settlement needs to be considered. If the reservoir is built first and then the bridge is built, the underwater construction of the foundation needs to be considered. When located in an earthquake fortification zone, it is also necessary to consider that the piers will vibrate in the reservoir water environment under the action of an earthquake and have a large additional mass. The impact of siltation also needs to be considered for reservoir area bridges. In addition, for bridges located within the scope of high earthquake fortification intensity areas, that is, bridges located in areas with a seismic fortification intensity of 8 degrees or above, the potential risk of earthquakes is high, so stricter seismic standards must be followed in building design and infrastructure construction.

[0003] For the bridges in the above application scenarios, taking the high-intensity defense zone as an example, if the pile foundation of the bridge is located on a thick covering layer, it is possible that the pile foundation cannot enter the high-strength bearing layer. In this case, under the action of seismic force, the bridge composed of pile foundation, pier, bridge pier and superstructure becomes a vibration of a multi-mass system on a flexible rod. The pier of the bridge is a solid structure determined by the punching and shearing calculation according to the common design form, with large mass and high stiffness. In this multi-mass system, stress concentration is bound to occur, leading to the destruction of the pile top and pier bottom. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a bridge energy-absorbing raft pile foundation structure and a construction method for effectively realizing the vibration reduction and isolation of the bridge pedestal.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a bridge energy-absorbing raft pile foundation structure, including a pile foundation, a cap and a pier arranged in sequence from bottom to top, an energy-absorbing cushion layer is fixedly arranged at the bottom of the cap, the bottom surface of the energy-absorbing cushion layer is fixedly connected to the top surface of the pile foundation, a friction energy-absorbing layer is arranged on the bottom surface of the energy-absorbing cushion layer, and the top of the cap is fixedly connected to the bottom of the pier through an energy absorber. In actual use, the energy-absorbing cushion layer at the bottom of the cap consumes energy by friction with the surrounding soil, especially the soil under the cap, during an earthquake, thereby reducing the damage caused by the mass concentration of the cap. In addition, the energy-absorbing cushion layer also has the effect of sealing the bottom of the cap. The efficiency of construction is improved. Secondly, the energy absorber utilizes the damping characteristics to dissipate the destructive energy under the action of the earthquake, thereby improving the seismic resistance of the cap and the entire building. Compared with the conventional cap structure, the present invention has the advantages of convenient construction, light weight, good force transmission performance, energy-absorbing capacity, and easy repair, especially in the construction of bridges in reservoir areas with high seismic fortification intensity.

[0006] As an embodiment of the cap, the following scheme can be selected: the cap includes a cap frame and longitudinal and transverse beams, the longitudinal and transverse beams are extended along the horizontal plane, the longitudinal and transverse beams are arranged in the cap frame, and the energy dissipation cushion layer is arranged under the longitudinal and transverse beams. The cap of the longitudinal and transverse beam structure reduces the mass, and there is a gap between the beams, so that the damage of the cap has the conditions for quick repair, which is convenient for later repair. Among them, ECC cast-in-place can be used at the nodes of the longitudinal and transverse beams, and the remaining parts are ordinary concrete or ECC prefabricated. The use of ECC at the nodes can greatly improve the toughness and overall resistance of the nodes. In addition, the cap of the longitudinal and transverse beam structure has a structural foundation with adjustable stiffness design, and the cap is no longer an entity that resists impact and shear. Since the cap and the energy dissipation cushion layer form a raft structure, the settlement can be reduced and the settlement can be more uniform. At the same time, the cap and the pile foundation can jointly adjust the stiffness to be consistent, thereby achieving stiffness ratio coordination. When an earthquake comes, the cap can further absorb the energy of the earthquake by cracking the longitudinal and transverse beams, thereby reducing earthquake damage. Generally, the support frame 21 can be selected to be a rectangular structure or an octagonal structure.

[0007] As an embodiment of the friction energy dissipation layer, the following scheme can be selected: the friction energy dissipation layer includes a wavy energy dissipation layer, the surface of the wavy energy dissipation layer is a uniform wavy shape, and the wavy energy dissipation layer is arranged in the horizontal direction. The wavy energy dissipation layer can make the pedestal on it slide relatively in a small range when an earthquake occurs, thereby effectively consuming friction energy and reducing earthquake damage. Similarly, the following scheme can also be selected: the friction energy dissipation layer includes a deep groove rib-shaped energy dissipation layer, the surface of the deep groove rib-shaped energy dissipation layer is a structure in which bosses and grooves are alternately arranged, and the bosses are arranged to extend downward in the vertical direction.

[0008] In order to stably set up the energy absorber, a top plate can be added on the top of the pedestal, and the bottom of the energy absorber is set on the top plate.

[0009] The energy-absorbing raft pile foundation construction method of a bridge comprises the following steps: a. pile foundation design and construction: according to the vertical bearing capacity, the pile diameter and pile length are initially planned, and then the finite element analysis is performed in the overall structural model, and then the pile diameter and pile length of the pile foundation are adjusted, and the number of pile diameters of the pile foundation corresponding to each pedestal is less than or equal to three; then, the pile foundation is set in a thick covering layer; b. construction of the pedestal and energy-absorbing cushion layer: first, the pedestal outer frame is made, and then the pedestal outer frame is sunk above the pile foundation, and after sinking into place, it is connected with the steel cofferdam, and then water is pumped out and the bottom is cleaned; next, the energy-absorbing cushion layer is poured to seal the bottom of the pedestal; then, steel bars are tied in the pedestal outer frame to complete the casting of the longitudinal and transverse beams, and then the top plate is cast on the top surface of the longitudinal and transverse beams and the pier dowel bars connected to the piers are set; c. construction of the piers: an energy absorber is set on the top plate, and the piers are set on the energy absorber. The outer ring of the cap also serves as a cofferdam, with a slot left between it and the upper steel cofferdam, and combined with the cushion layer as the bottom cover, it realizes self-cofferdam. It can also be used when repairing damage.

[0010] Furthermore, in step b, the casting method of the longitudinal and transverse beams is an ECC casting process. The ECC casting process has good toughness, reduces the damage of the nodes under earthquake action, has good fluidity, and can achieve self-compacting without vibration.

[0011] The beneficial effects of the present invention are: 1. The pedestal effectively dissipates the destructive energy under the action of the earthquake through the energy-absorbing cushion layer at the bottom of the pedestal and the energy absorber at the top of the pedestal, thereby reducing the destructive force borne by the pedestal and further reducing the risk of damage to the pedestal. 2. The longitudinal and transverse beam structures are adopted inside the pedestal, so that the damage to the pedestal can be quickly repaired. At the same time, the longitudinal and transverse beams can be cracked to allow the pedestal to further absorb the energy of the earthquake, thereby reducing the damage caused by the earthquake. 3. By optimizing the specific structure of the friction energy-absorbing layer, the effect of friction energy absorption is improved, and the damage caused by the earthquake is further reduced. The present invention is particularly suitable for the construction of bridges located in high-intensity defense areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of an embodiment of the support platform and related structures above and below the support platform of the present invention.

[0013] Figure 2 It is a schematic diagram showing that the friction energy dissipation layer of the present invention is wavy.

[0014] Figure 3 It is a schematic diagram showing that the friction energy dissipation layer of the present invention is in the shape of shallow slope ribs.

[0015] Figure 4 It is a schematic diagram showing that the friction energy dissipation layer of the present invention is in the shape of deep groove ribs.

[0016] Figure 5 It is a schematic diagram of a rectangular structure of the outer frame of the support platform of the present invention.

[0017] Figure 6 It is a schematic diagram of an octagonal structure of the outer frame of the support platform of the present invention.

[0018] Marked in the figure are: pier 1, abutment 2, abutment outer frame 21, longitudinal and transverse beams 22, top plate installation area 23, energy absorption cushion layer 3, wavy energy absorption layer 31, shallow slope rib-shaped energy absorption layer 32, deep groove rib-shaped energy absorption layer 33, pile foundation 4, reservoir water 5, thick covering layer 6, water level 7. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0020] like Figures 1 to 6 The embodiment of the energy-absorbing raft pile foundation structure of the bridge is shown. The pile foundation 4 is located at the bottom of the structure, and the energy-absorbing cushion layer 3 is arranged on the top of the pile foundation 4, and the energy-absorbing cushion layer 3 is arranged at the bottom of the cap 2. The pile foundation 4, the energy-absorbing cushion layer 3 and the cap 2 are arranged in a thick covering layer 6. The top plate installation area 23 above the cap 2 is provided with a top plate, and the top of the top plate can be provided with an existing energy absorber, which is fixedly connected to the bottom of the pier 1 through the energy absorber, and the pier 1 is arranged in the reservoir water 5.

[0021] As the core of the improvement, the cap 2, such as Figure 5 and Figure 6 As shown, the outer frame 21 of the support 2 is a rectangular structure or an octagonal structure. The outer frame 21 of the support is provided with longitudinal and transverse beams 22 formed by vertically intersecting transverse beams and longitudinal beams, and the longitudinal and transverse beams 22 are extended along the horizontal plane. Figure 2 , Figure 3 and Figure 4 As shown, the bottom surface shapes of the energy-absorbing cushion layer 3 of the cap 2 are respectively a wave-shaped energy-absorbing layer 31, a shallow slope rib-shaped energy-absorbing layer 32 and a deep groove rib-shaped energy-absorbing layer 33. The above three bottom surface shapes of the energy-absorbing cushion layer 3 are all used to increase the friction between the energy-absorbing cushion layer 3 and the surrounding soil, and reduce the damage to the cap 2 caused by earthquakes. Steel bars can be arranged in the energy-absorbing cushion layer 3, and the reinforcement is calculated with reference to the bottom plate of the raft foundation. Considering that the cap 2 also has a bottom plate, it can be configured based on the calculated reinforcement amount multiplied by a coefficient of 0.6.

[0022] In actual design, the outer frame 21 of the pedestal needs to be designed according to the equal stiffness principle based on the upper structure load and pile foundation design of the outer frame 21 of the pedestal, that is, the pedestal 2 is included in the pile foundation 4, and the combined line stiffness is equal to or approximately equal to (the difference is not greater than 15%) the combined line stiffness after the pedestal 2 is included in the pier 1, so as to determine the size of the outer frame 21 of the pedestal, that is, to determine the height, width and wall thickness of the outer frame 21 of the pedestal and the proportion of the internal longitudinal and transverse beams 22. The outer frame 21 of the pedestal can be prefabricated to form a structure similar to a concrete cofferdam. A slot for the steel cofferdam is reserved around the top of the outer frame 21 to facilitate the plug-in and pull-out installation of the steel cofferdam.

[0023] As for the longitudinal and transverse beams 22, the transverse beams and the longitudinal beams intersect vertically to form a beam grid. The longitudinal and transverse beams 22 can be prefabricated, and the intersection of the longitudinal and transverse beams 22 can be cast in place. In terms of materials used, if prefabricated, conventional concrete can be used, and ECC cast-in-place can be used in the node area. ECC has good toughness, which reduces the damage to the nodes under the action of earthquakes, has good fluidity, and can achieve self-compacting without vibration. The calculation of the longitudinal and transverse beams 22 can use finite element modeling to calculate the internal forces, and the reinforcement is carried out according to the reinforced concrete components. The crack width is controlled to be no more than 0.15mm. The proportion of the longitudinal and transverse beams 22, as mentioned above, needs to be calculated according to the principle of equal stiffness. The space reserved in the longitudinal and transverse beams 22 is convenient for the subsequent formwork casting after the longitudinal and transverse beams 22 are damaged, or the existing structure is used as a template, steel bars are placed, and cast into a solid.

[0024] The energy dissipation cushion 3 has two functions. One is to facilitate the formwork construction of the cap 2. The outer ring of the cap 2 is a structure similar to a cofferdam. The energy dissipation cushion 3 plays the role of bottom sealing, and is combined with the steel cofferdam on it to facilitate underwater construction. The second function of the energy dissipation cushion 3 is to dissipate energy through friction with the surrounding soil, especially the soil under the cap, during an earthquake, to reduce the earthquake damage caused by the mass concentration of the cap 2. Therefore, the shape of the energy dissipation cushion 3 needs to be specially designed, and calculated and reinforced according to the raft slab.

[0025] In terms of the energy-absorbing connection between the abutment 2 and the pier 1, an energy-absorbing connection can be realized at the position of the bottom of the pier 1 corresponding to the top plate. The energy-absorbing connection has a reinforced concrete rib beam type or a pre-embedded steel plate, and the pier and the top plate are connected with a finished energy absorber.

[0026] In order to reduce and eliminate the stress concentration caused by the sudden change of stiffness, the design of the pier 1, the cap 2 and the pile foundation 4 should be considered in a coordinated and integrated manner. First, according to the vertical bearing capacity, the pile diameter and pile length of the pile foundation 4 are initially planned. Then, it is arranged in the overall structural model, and a high-order finite element analysis considering the coupling of multiple factors such as pile-soil-structure-water-seismic vibration is carried out. During this period, the adjustment of the cap 2 structure and the adjustment of the pile foundation 4 will be involved. Generally speaking, the pile diameter of the pile foundation 4 should not be too much, and there should be no more than three types for the same cap 2 or the same bridge. The pile length can be adjusted based on the principle that the settlement after the single pile is basically the same, and then the strength is verified in the seismic analysis. In terms of the construction method of the cap 2, the outer frame 21 of the cap is prefabricated, constructed like a cofferdam, lowered to the position, and the bottom is cast with the energy-absorbing cushion layer 3. Then, the top slot of the outer frame is used to raise the cofferdam with steel sheet piles, pump water, and construct the internal longitudinal and transverse beams 22. After the longitudinal and transverse beams 22 are hoisted in place, the node ECC is cast. The top plate is cast. Reserve the dowel bars for Pier 1. When Pier 1 is out of water, remove the steel sheet pile cofferdam.

[0027] The height of the pedestal 2, the size of the longitudinal and transverse beams 22, and the reinforcement all need to be determined by the coupled linkage finite element analysis considering the pile-soil-structure-reservoir water, and can be determined iteratively by considering the pile foundation parameters in conjunction. When repairing the pedestal 2, the formwork can be supported in the empty space, reinforcement can be arranged, and ECC can be poured. It is also possible to fill the empty space directly after reinforcement. The top plate thickness and reinforcement are determined based on the connection strength and the punching shear force calculation of pier 1. Generally, stiffening ribs can also be set at the connection between the top plate and pier 1 to increase the connection effect. For those with higher seismic requirements, energy absorbers can also be set here to avoid premature damage to the connection between pier 1 and pedestal 2 during an earthquake.

[0028] When constructing the cap 2, a method similar to adding a caisson to the raft foundation can be used. During construction, the outer ring is made first, usually prefabricated on the shore, and then sunk. After connecting to the upper steel cofferdam, it sinks into place. Then complete the pumping and bottom cleaning. Then set the energy-absorbing cushion 3 structure, tie the energy-absorbing cushion 3 steel bars, cast the energy-absorbing cushion 3, and completely seal the bottom. Then set the formwork, tie the steel bars, and cast the longitudinal and transverse beams 22. Then cast the top plate, set the pier dowel bars, and finally complete the construction of the pier 1.

Claims

1. A bridge energy dissipation raft pile foundation structure, comprising a pile foundation (4), a cap (2) and a bridge pier (1) arranged in sequence from bottom to top, characterized in that: An energy-absorbing cushion layer (3) is fixedly arranged at the bottom of the cap (2); the bottom surface of the energy-absorbing cushion layer (3) is fixedly connected to the top surface of the pile foundation (4); a friction energy-absorbing layer is arranged on the bottom surface of the energy-absorbing cushion layer (3); and the top of the cap (2) is fixedly connected to the bottom of the pier (1) via an energy absorber.

2. The energy dissipation raft pile foundation structure for a bridge according to claim 1, characterized in that: The support platform (2) comprises a support platform outer frame (21) and longitudinal and transverse beams (22), wherein the longitudinal and transverse beams (22) are arranged to extend along a horizontal plane direction, the longitudinal and transverse beams (22) are arranged in the support platform outer frame (21), and the energy dissipation cushion layer (3) is arranged below the longitudinal and transverse beams (22).

3. The energy dissipation raft pile foundation structure for a bridge according to claim 1, characterized in that: The support platform outer frame (21) is a rectangular structure or an octagonal structure.

4. The energy dissipating raft pile foundation structure for a bridge according to any one of claims 1 to 3, characterized in that: The friction energy dissipation layer comprises a wavy energy dissipation layer (31), the surface of the wavy energy dissipation layer (31) is in a uniform wavy shape, and the wavy energy dissipation layer is arranged in a horizontal direction.

5. The energy dissipating raft pile foundation structure for a bridge according to any one of claims 1 to 3, characterized in that: The friction energy dissipation layer comprises a deep groove rib-shaped energy dissipation layer (33). The surface of the deep groove rib-shaped energy dissipation layer (33) is a structure in which bosses and grooves are alternately arranged, and the bosses are arranged to extend downward in the vertical direction.

6. The energy dissipating raft pile foundation structure for a bridge according to any one of claims 1 to 3, characterized in that: The support platform (2) comprises a top plate arranged on the top, and the bottom of the energy dissipator is arranged on the top plate.

7. A method for constructing a bridge energy dissipation raft pile foundation, comprising the bridge energy dissipation raft pile foundation structure according to any one of claims 1 to 6, characterized in that: The steps include: a. Design and construction of pile foundation (4): initially design the pile diameter and pile length according to the vertical bearing capacity, then perform finite element analysis in the overall structural model, and then adjust the pile diameter and pile length of the pile foundation (4), so that the number of pile diameters of the pile foundation (4) corresponding to each cap (2) is less than or equal to three; then, set the pile foundation (4) in the deep covering layer (6); b. Construction of the cap (2) and the energy-absorbing cushion layer (3): First, the cap outer frame (21) is manufactured, and then the cap outer frame (21) is sunk to the top of the pile foundation (4). After the cap outer frame (21) is sunk to the right position, it is connected to the steel cofferdam, and then the water is pumped out and the bottom is cleaned; next, the energy-absorbing cushion layer (3) is poured to seal the bottom of the cap (2); then, steel bars are tied inside the cap outer frame (21) to complete the casting of the longitudinal and transverse beams (22), and then the top plate is cast on the top surface of the longitudinal and transverse beams (22) and pier dowel bars connected to the piers (1) are set; c. Construction of the bridge pier (1): an energy absorber is arranged on the top plate, and the bridge pier (1) is arranged on the energy absorber.

8. The bridge energy dissipation raft pile foundation construction method according to claim 7, characterized in that: In step b, the casting method of the longitudinal and transverse beams (22) is the ECC casting process.

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