Bridge energy dissipation raft pile foundation structure and construction method

Abstract

The present application relates to the field of reservoir bridge design and construction, and more particularly to a bridge energy dissipation raft pile foundation structure and construction method for effectively realizing the cushion shock absorption and isolation of a bridge, comprising a pile foundation, a cushion and a pier arranged in sequence from bottom to top, a bottom of the cushion being fixedly provided with an energy dissipation cushion layer, a bottom surface of the energy dissipation cushion layer being fixedly connected with a top surface of the pile foundation, the bottom surface of the energy dissipation cushion layer being provided with a friction energy dissipation layer, and a top of the cushion being fixedly connected with a bottom of the pier through an energy dissipator. The present application is particularly suitable for the construction of a bridge arranged in a high-intensity seismic fortification zone.

Description

Technical Field

[0001] This invention relates to the field of bridge design and construction in reservoir areas, and in particular to a bridge energy-dissipating raft foundation structure and construction method. Background Technology

[0002] For bridges located within the reservoir area or its influence zone, the design, pier design, and maintenance are more complex than those of ordinary bridges due to factors such as reservoir impoundment, water level changes, and flood discharge. If the bridge is built before the reservoir, the impact of water impoundment on foundation settlement must be considered. If the reservoir is built before the bridge, the underwater construction of the foundation must be addressed. When located in a seismic fortification zone, the vibration of the piers under seismic loads in the reservoir water environment must be considered, resulting in significant added mass. The impact of siltation must also be taken into account. Furthermore, for bridges located in areas with high seismic intensity (i.e., areas with a seismic fortification intensity of 8 degrees or higher), the potential seismic risk is high, therefore, stricter seismic standards must be followed in architectural design and infrastructure construction.

[0003] For bridges in the aforementioned application scenarios, taking high-intensity seismic fortification zones as an example, if the bridge's pile foundations are located on a deep overburden layer, the pile foundations may not be able to penetrate the high-strength bearing layer. In this case, under the action of seismic forces, the bridge, consisting of pile foundations, abutments, piers, and superstructure, becomes a multi-mass system vibrating on a flexible rod. Furthermore, the bridge abutment, according to common design practices, is a solid structure determined based on punching and shear calculations, possessing large mass and high stiffness. In this multi-mass system, stress concentration is inevitable, leading to failure at 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-dissipating raft foundation structure and construction method that can effectively realize bridge abutment vibration reduction and isolation.

[0005] The technical solution adopted by this invention to solve its technical problem is: a bridge energy-dissipating raft-type pile foundation structure, including pile foundations, a pile cap, and piers arranged sequentially from bottom to top. An energy-dissipating cushion layer is fixedly installed at the bottom of the pile cap, and the bottom surface of the energy-dissipating cushion layer is fixedly connected to the top surface of the pile foundation. A friction energy-dissipating layer is provided on the bottom surface of the energy-dissipating cushion layer. The top of the pile cap is fixedly connected to the bottom of the pier through an energy dissipator. In actual use, the energy-dissipating cushion layer at the bottom of the pile cap dissipates energy through friction with the surrounding soil, especially the soil under the pile cap, during an earthquake, reducing damage caused by the concentration of the pile cap's mass. In addition, the energy-dissipating cushion layer also has the effect of sealing the bottom of the pile cap, improving construction efficiency. Secondly, the energy dissipator utilizes damping characteristics to dissipate the destructive energy under seismic action, improving the seismic performance of the pile cap and the overall structure. Compared with conventional pile cap structures, this invention has the advantages of convenient construction, light weight, good force transmission performance, energy dissipation capacity, and easy repair, especially in the construction of bridges in reservoir areas with high seismic fortification intensity.

[0006] As one embodiment of the foundation, the following scheme can be selected: the foundation includes an outer frame and longitudinal and transverse beams, which extend horizontally and are located within the outer frame. An energy-dissipating cushion layer is placed below the beams. This beam-structured foundation reduces weight, and the gaps between the beams allow for quick repair of any damage, facilitating future maintenance. Specifically, ECC (Extended Concrete Cemented Concrete) can be used at the beam joints, while the remaining parts can be made of ordinary concrete or precast with ECC. Using ECC at the joints significantly improves joint toughness and overall resistance. Furthermore, the beam-structured foundation features an adjustable stiffness design, meaning the foundation is no longer a single, punching-shear resistant entity. Because the foundation and energy-dissipating cushion layer form a raft structure, settlement is reduced and more uniform. Simultaneously, the foundation and piles can be jointly adjusted for consistent stiffness, achieving a coordinated stiffness ratio. During an earthquake, the beams can crack, allowing the foundation to further absorb seismic energy, thus reducing earthquake damage. Generally, the outer frame 21 of the foundation can be chosen to be a rectangular structure or an octagonal structure.

[0007] As one embodiment of the friction energy dissipation layer, the following scheme can be selected: the friction energy dissipation layer includes a corrugated energy dissipation layer, the surface of which has a uniform corrugated shape, and the corrugated energy dissipation layer is arranged in the horizontal direction. The corrugated energy dissipation layer allows the bearing platform on it to slide relatively within a small range during an earthquake, thereby effectively dissipating frictional energy and reducing earthquake damage. Similarly, the following scheme can also be selected: the friction energy dissipation layer includes a deep groove ribbed energy dissipation layer, the surface of which has a structure with alternating bosses and grooves, and the bosses extend downward in the vertical direction.

[0008] To ensure a stable installation of the energy dissipator, a top plate can be added to the top of the foundation, with the bottom of the energy dissipator mounted on the top plate.

[0009] The construction method for bridge energy-dissipating raft foundation includes the following steps: a) Pile foundation design and construction: Based on the vertical bearing capacity, the pile diameter and pile length are initially determined. Then, finite element analysis is performed in the overall structural model to adjust the pile diameter and pile length. The number of piles corresponding to each pier cap is less than or equal to three. Subsequently, the pile foundation is set in a deep overburden layer. b) Construction of pier cap and energy-dissipating cushion layer: First, the outer frame of the pier cap is constructed. Then, the outer frame of the pier cap is sunk above the pile foundation. After it is sunk into place, it is connected to the steel cofferdam. Then, water is pumped out and the bottom is cleaned. Next, the energy-dissipating cushion layer is poured to seal the bottom of the pier cap. Then, steel bars are tied inside the outer frame of the pier cap to complete the pouring of the longitudinal and transverse beams. Then, the top slab is poured on the top surface of the longitudinal and transverse beams and pier reinforcement bars connected to the piers are set. c) Construction of piers: Energy dissipators are set on the top slab, and piers are set on the energy dissipators. The outer ring of the pier also serves as a cofferdam, with slots provided for connection to the upper steel cofferdam. Combined with a bedding layer as a sealing layer, it achieves self-cofferdam functionality. Furthermore, it can be utilized for repairing damage.

[0010] Furthermore, in step b, the longitudinal and transverse beams are cast using the ECC casting process. The ECC casting process has excellent toughness, reducing damage to the joints under seismic loading, and excellent fluidity, enabling self-compactment without the need for vibration.

[0011] The beneficial effects of this invention are as follows: First, the pier cap effectively dissipates the destructive energy under seismic action through the energy-dissipating pad layer at the bottom and the energy dissipator at the top, reducing the destructive force borne by the pier cap and thus lowering the risk of pier cap damage. Second, the internal longitudinal and transverse beam structure of the pier cap allows for rapid repair of pier cap damage. Furthermore, the cracking of the longitudinal and transverse beams allows the pier cap to further absorb seismic energy, thereby reducing seismic damage. Third, by optimizing the specific structure of the friction energy-dissipating layer, the effect of friction energy dissipation is improved, further reducing seismic damage. This invention is particularly suitable for the construction of bridges located in high-intensity seismic fortification zones. Attached Figure Description

[0012] Figure 1 This 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 This is a schematic diagram of the wavy shape of the friction energy dissipation layer of the present invention.

[0014] Figure 3 This is a schematic diagram of the friction energy dissipation layer of the present invention being a shallow sloping rib shape.

[0015] Figure 4 This is a schematic diagram of the friction energy dissipation layer of the present invention being a deep groove rib shape.

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

[0017] Figure 6 This is a schematic diagram of the octagonal structure of the support frame of the present invention.

[0018] The following are marked in the diagram: pier 1, abutment 2, abutment outer frame 21, longitudinal and transverse beams 22, top plate installation area 23, energy dissipation cushion layer 3, corrugated energy dissipation layer 31, shallow slope ribbed energy dissipation layer 32, deep trench ribbed energy dissipation layer 33, pile foundation 4, reservoir water 5, thick overburden layer 6, water level 7. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] like Figures 1 to 6 The diagram illustrates an embodiment of an energy-dissipating raft foundation structure for bridges. At the bottom of the structure is pile foundation 4, with an energy-dissipating cushion layer 3 atop it. The energy-dissipating cushion layer 3 is located at the bottom of the pier cap 2. Pile foundation 4, energy-dissipating cushion layer 3, and pier cap 2 are housed within a deep overburden layer 6. A top plate is installed in the top plate mounting area 23 above the pier cap 2. Existing energy dissipators are installed on top of the top plate and fixedly connected to the bottom of the pier 1 via the energy dissipators. The pier 1 is located within the reservoir water 5.

[0021] As the core of the improvement, the foundation 2, such as Figure 5 and Figure 6 As shown, the outer frame 21 of the foundation 2 is a rectangular or octagonal structure. Inside the outer frame 21, longitudinal and transverse beams 22, composed of intersecting horizontal and vertical beams, are installed, extending horizontally. Figure 2 , Figure 3 and Figure 4 As shown, the bottom shapes of the energy-dissipating cushion layer 3 of the foundation 2 are corrugated energy-dissipating layer 31, shallow sloping ribbed energy-dissipating layer 32, and deep groove ribbed energy-dissipating layer 33, respectively. All three bottom shapes of the energy-dissipating cushion layer 3 are designed to increase the friction between the energy-dissipating cushion layer 3 and the surrounding soil, reducing earthquake damage to the foundation 2. Reinforcing steel can be installed within the energy-dissipating cushion layer 3, with reinforcement calculations referring to those for the raft foundation's base slab. Considering that the foundation 2 also has a base slab, the calculated reinforcement amount can be multiplied by a coefficient of 0.6 to determine the required reinforcement.

[0022] In actual design, the outer frame 21 of the pier cap needs to be designed according to the principle of equal stiffness, based on the load of the superstructure and the pile foundation design. This means that the combined linear stiffness of the pier cap 2 (including the pile foundation 4) should be equal to or approximately equal to (with a difference of no more than 15%) the combined linear stiffness of the pier cap 2 (including the pier 1). This determines the dimensions of the outer frame 21, including its height, width, wall thickness, and the proportion of the internal longitudinal and transverse beams 22. The outer frame 21 can be prefabricated, forming a structure similar to a concrete cofferdam. A slot for a steel cofferdam is pre-drilled around the top of the outer frame 21 for easy insertion and removal of the steel cofferdam.

[0023] Regarding the longitudinal and transverse beams 22, the transverse and longitudinal beams intersect perpendicularly to form a beam grid. The longitudinal and transverse beams 22 can be precast, with the intersections cast in-situ. For materials, if precast, conventional concrete can be used, while ECC (electro-concrete composite) can be used for the joint areas. ECC has excellent toughness, reducing damage to the joints under seismic loads, and excellent fluidity, allowing for self-compacting without vibration. The internal forces of the longitudinal and transverse beams 22 can be calculated using finite element modeling, and reinforcement should be designed according to the reinforced concrete member principle. Crack width should be controlled to no more than 0.15mm. The proportion of the longitudinal and transverse beams 22, as mentioned earlier, needs to be calculated based on the principle of equal stiffness. The space reserved within the longitudinal and transverse beams 22 facilitates subsequent formwork and casting after damage to the beams 22, or allows the existing structure to be used as a template, with reinforcing steel inserted, to form a solid structure.

[0024] The energy-dissipating cushion layer 3 serves two purposes. First, it facilitates the formwork construction of the foundation 2. The outer ring of the foundation 2 has a cofferdam-like structure, and the energy-dissipating cushion layer 3 acts as a sealing layer, connecting to the steel cofferdam on top to facilitate underwater construction. The second purpose of the energy-dissipating cushion layer 3 is to dissipate energy through friction with the surrounding soil, especially the soil beneath the foundation, during earthquakes, mitigating earthquake damage caused by the concentrated mass of the foundation 2. Therefore, the shape of the energy-dissipating cushion layer 3 requires specialized design, calculated and reinforced according to raft foundation principles.

[0025] Regarding the energy dissipation connection between the pier cap 2 and the bridge pier 1, an energy dissipation connection can be made at the position corresponding to the top plate at the bottom of the bridge pier 1. The energy dissipation connection can be a reinforced concrete rib beam or a pre-embedded steel plate, and the bridge pier and the top plate can be connected by a finished energy dissipator.

[0026] To reduce and eliminate stress concentration caused by abrupt changes in stiffness, the design of pier 1, abutment 2, and pile foundation 4 should be considered holistically. First, based on the vertical bearing capacity, the pile diameter and length of pile foundation 4 are initially determined. Then, a high-order finite element analysis considering multiple coupled factors such as pile-soil-structure-water-seismic motion is conducted in the overall structural model. This involves adjustments to the structure of abutment 2 and pile foundation 4. Generally, the pile diameter of pile foundation 4 should not be excessive; no more than three diameters are allowed for the same abutment 2 or the same bridge. The pile length can be adjusted based on the principle that the settlement after single-pile bearing is basically consistent, and then the strength is verified in the seismic analysis. Regarding the construction method of abutment 2, the outer frame 21 is prefabricated and constructed like a cofferdam, lowered into position, and sealed with an energy-dissipating cushion layer 3. Then, using the slots at the top of the outer frame, a steel sheet pile cofferdam is used to raise the height, water is pumped out, and the internal longitudinal and transverse beams 22 are constructed. After the longitudinal and transverse beams 22 are hoisted into place, the ECC nodes are poured. The top slab is then poured. Reserve the reinforcing bars for pier 1. Construct pier 1 above the water surface and remove the steel sheet pile cofferdam.

[0027] The height of pier cap 2, the dimensions of longitudinal and transverse beams 22, and their reinforcement all need to be determined through a coupled finite element analysis considering the pile-soil-structure-reservoir water system. Furthermore, iterative determination can be achieved by considering pile foundation parameters in conjunction with the analysis. During the repair of pier cap 2, formwork can be erected in the empty spaces, reinforcement can be added, and ECC (Electronic Cavity Concrete) can be poured. Alternatively, the empty spaces can be filled directly after reinforcement. The thickness and reinforcement of the top slab are determined based on connection strength and punching shear force calculations for pier 1. Generally, stiffening ribs can be added at the connection between the top slab and pier 1 to enhance the connection effect. For applications with higher seismic resistance requirements, energy dissipators can be installed at this location to prevent premature failure of the connection between pier 1 and pier cap 2 during earthquakes.

[0028] When constructing pier cap 2, a method similar to adding a caisson to a raft foundation can be used. During construction, the outer ring is constructed first, typically prefabricated on the shore, then sunk, connecting to the upper steel cofferdam before reaching its final position. Dewatering and bottom cleaning are then completed. Next, the energy-dissipating cushion layer 3 is constructed, its reinforcement is tied, and it is poured, completely sealing the bottom. Then, formwork is installed, reinforcement is tied, and longitudinal and transverse beams 22 are poured. The top slab is then poured, pier reinforcement bars are installed, and finally, the construction of pier 1 is completed.

Claims

1. A bridge energy-dissipating raft foundation structure, comprising, from bottom to top, pile foundations (4), pile caps (2), and piers (1), characterized in that: A heat dissipation cushion layer (3) is fixedly installed at the bottom of the pile cap (2). The bottom surface of the heat dissipation cushion layer (3) is fixedly connected to the top surface of the pile foundation (4). A friction heat dissipation layer is installed on the bottom surface of the heat dissipation cushion layer (3). The top of the pile cap (2) is fixedly connected to the bottom of the pier (1) through a heat dissipator. The foundation (2) includes a foundation frame (21) and longitudinal and transverse beams (22). The longitudinal and transverse beams (22) extend along the horizontal plane and are located inside the foundation frame (21). The energy-absorbing cushion layer (3) is located below the longitudinal and transverse beams (22). The foundation (2) absorbs the energy of the earthquake by cracking the longitudinal and transverse beams (22). The friction energy dissipation layer includes a wave-shaped energy dissipation layer (31), the surface of which is a uniform wave shape, and the wave-shaped energy dissipation layer is set along the horizontal direction; Alternatively, the friction energy dissipation layer may include a deep groove rib energy dissipation layer (33), the surface of which is a structure with alternating bosses and grooves, the bosses extending downward in the vertical direction.

2. The bridge energy-dissipating raft foundation structure as described in claim 1, characterized in that: The outer frame of the foundation (21) is a rectangular or octagonal structure.

3. The bridge energy-dissipating raft foundation structure as described in claim 1 or 2, characterized in that: The base (2) includes a top plate set on the top, and the bottom of the energy dissipator is set on the top plate.

4. A construction method for bridge energy-dissipating raft foundation, including the bridge energy-dissipating raft foundation structure as described in claim 3, characterized in that, Includes the following steps: a. Design and construction of pile foundation (4): Based on the vertical bearing capacity, the pile diameter and pile length are initially planned. Then, finite element analysis is performed in the overall structural model to adjust the pile diameter and pile length of the pile foundation (4). The number of pile diameters of the pile foundation (4) corresponding to each pile cap (2) is less than or equal to three. Then, the pile foundation (4) is set in the deep overburden layer (6). b. Construction of the foundation (2) and energy dissipation cushion (3): First, the outer frame (21) of the foundation is made, and then the outer frame (21) of the foundation is sunk to the top of the pile foundation (4). After it is sunk to the bottom, it is connected to the steel cofferdam. Then, the water is pumped out and the bottom is cleaned. Next, the energy dissipation cushion (3) is poured to seal the bottom of the foundation (2). Then, the steel bars are tied in the outer frame (21) of the foundation to complete the pouring of the longitudinal and transverse beams (22). Then, the top plate is poured on the top surface of the longitudinal and transverse beams (22) and the pier dowels connected to the pier (1) are set. c. Construction of pier (1): Install energy dissipators on the top slab and install pier (1) on the energy dissipators.

5. The bridge energy-dissipating raft foundation construction method as described in claim 4, characterized in that: In step b, the casting method for the longitudinal and transverse beams (22) is the ECC casting process.

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