CN-122021422-A - High-sand-content mountain torrent bridge damage assessment method based on water-sand power-finite element coupling

Abstract

The invention discloses a method for evaluating the damage of a mountain torrent bridge with high sand content based on water sand power-finite element coupling, which comprises the following steps of 1, establishing a water sand hydrodynamic simulation model; step 2, calculating load time course acting on the bridge, step 3, building a bridge finite element model, step 4, calculating damage evaluation indexes, and step 5, determining damage grade and evaluating results. The method realizes time-course coupling analysis of the water-sand dynamic model and the finite element model, accurately simulates the time-varying characteristic of the mountain torrent load and the accumulated effect of structural response, comprehensively considers the special action mechanism of the mountain torrent with high sand content, remarkably improves load calculation precision, establishes a multi-dimensional damage evaluation index system comprising displacement, strength and stability, can comprehensively identify various damage modes, provides a damage grade division standard based on multi-index comprehensive judgment, realizes scientific conversion from quantitative evaluation to qualitative grading, and provides clear basis for engineering decision.

Inventors

• SUN MINGYU
• LIU RONGHUA
• WANG TENGFEI
• LIU XIAOWAN
• DOU YANHONG
• LIU QI

Assignees

• 中国水利水电科学研究院

Dates

Publication Date

20260512

Application Date

20260122

Claims (5)

1. 1. A method for evaluating the damage of a mountain torrent bridge with high sand content based on water-sand power-finite element coupling, which is characterized by comprising the following steps: Step 1, establishing a water-sand hydrodynamic force simulation model, namely acquiring topographic data, land utilization data, historical rainfall data and sediment characteristic parameters of a target river basin, establishing the water-sand hydrodynamic force simulation model based on a shallow water equation and a sediment transport equation, wherein the shallow water equation comprises a water flow continuous equation and a water flow momentum equation; Step 2, calculating load time courses acting on the bridge, namely acquiring bridge foundation data comprising geometric dimensions, material characteristics and pile foundation depth, extracting water depth, flow velocity and sediment concentration time course data at the position of the bridge based on the output result of the water-sediment hydrodynamic simulation model, and calculating various load time courses acting on the bridge structure, wherein the load time courses comprise hydrostatic pressure, hydrodynamic pressure, sediment acting force, total horizontal load and total horizontal load acting point height; the calculation formula of the hydrostatic pressure is as follows: (5) wherein: Is hydrostatic pressure in kN; is the density of water body, h (t) is the depth of water at the bridge position, and the unit is B is the width of the pier body, and the unit is ; The calculation formula of the dynamic water pressure is as follows: (6) wherein: The dynamic water pressure is given by kN; Taking a round pier of 0.7 and a rectangular pier of 1.4 as resistance coefficients; Is the effective water-facing area, the unit is ; 、 Respectively at bridge positions 、 Directional flow velocity in units of ; The calculation formula of the sediment acting force is as follows: (7) Wherein: (8) (9) wherein: the unit is kN for acting force of sediment; The static pressure increment is given by kN; The unit is kN for the power impact force; Is the density of the mixed fluid; is the sediment concentration; the collision coefficient is determined according to the shape of the bridge pier, the diameter of a round or oval pier is 0.1-0.15, the diameter of a rectangular pier is 0.25-0.3, and the diameter of a pointed pier is 0.05-0.1; Taking 2650 kg/m3 as the sediment density; The calculation formula of the total horizontal load is as follows: (10) wherein: Is the total horizontal load in kN; the calculation formula of the total horizontal load action height is as follows: (11) wherein: The height of the action point of the total horizontal load is m; the height of the action point of hydrostatic pressure; the height of the action point is the action point of the dynamic water pressure and the sediment impact force; Step 3, building a bridge finite element model, namely building the bridge finite element model according to the acquired bridge foundation data, and extracting finite element analysis results, including a displacement result, an internal force result, a stress result and a support counter force; the displacement result comprises the horizontal displacement of the pier top node Vertical displacement The internal force result comprises pier bottom section bending moment Pier bottom shear force Pier bottom axial force The stress result comprises the maximum compressive stress of the concrete Stress of steel bar The support counter force comprises vertical counter force of each support , I is a support variable, and m is the number of supports; Calculating damage evaluation indexes, namely calculating damage indexes at each moment based on a finite element output result and load information, wherein the damage indexes comprise displacement indexes, strength indexes and stability indexes; The displacement index comprises a pier top displacement angle The calculation formula is as follows: (12) wherein H is pier height; the strength index comprises a section bearing force ratio Stress ratio of concrete Stress ratio of steel bar ; The calculation formula of the section bearing force ratio is as follows: (13) wherein: the ultimate bending moment bearing capacity is calculated according to the design Specification of reinforced concrete and prestressed concrete bridge and culvert of highway (JTG 3362); The calculation formula of the concrete stress ratio is as follows: (14) wherein: The concrete axle center compressive strength design value is determined according to the concrete strength grade in unit MPa according to the design Specification of reinforced concrete and prestressed concrete bridge and culvert of highway (JTG 3362); The calculation formula of the steel bar stress ratio is as follows: (15) wherein: is designed to be the tensile strength of the steel bar, and is taken by the unit MPa and HRB400 steel bar MPa; The stability index includes a roll stability factor Minimum support reaction force ; The calculation formula of the overturning stability coefficient is as follows: (16) (17) (18) wherein: the overturning stability coefficient is dimensionless; Is anti-overturning moment, and is in units of kN.m; g is the self weight of the upper structure and the unit kN; the unit m is the horizontal distance from the gravity center of the upper structure to the pier bottom overturning point; The unit is kN for pier bottom axial force; the calculation formula of the minimum support counter force is as follows: (19) When (when) When the support is empty, the support is indicated to be empty; Step 5, determining the damage level and evaluating the result, namely firstly judging the instantaneous damage level, namely determining the instantaneous damage level corresponding to each index according to the judging standard according to each index value at the moment t; then, the damage level is comprehensively judged, namely, the most unfavorable principle is adopted, and the maximum value of the instantaneous damage level corresponding to each index at the moment t is taken as the damage level at the moment : (20) Finally, determining the final damage level, namely, taking the maximum value of the damage level at all moments as the final damage level in the whole time range of the flood process : (21) According to the final level of destruction And evaluating the safety state of the bridge and providing corresponding engineering treatment suggestions.
2. 2. The method for evaluating the damage of the mountain torrent bridge with high sand content based on water-sand power-finite element coupling according to claim 1, wherein the water flow continuous equation in the step 1 is as follows: (1) the water flow equation is: (2) (3) The sediment transport equation is as follows: Considering that the mountain torrent sediment has wide grading characteristic, the sediment is divided into the particle sizes Particle size group [ ] ) Respectively establishing sediment transport equations of each particle size group: (4) wherein: Is the depth of water, unit ; 、 Respectively is 、 Directional flow velocity in units of ; Gravitational acceleration; is the elevation of the river bed, unit 、 Respectively is 、 Directional bed surface shear stress, unit Ρ is the water density in units ; Is the first The sediment concentration in the particle size group is dimensionless; 、 respectively the first Particle size fraction scouring and fouling rate, unit 。
3. 3. The method for evaluating the damage of the mountain torrent bridge with high sand content based on water-sand power-finite element coupling according to claim 2, wherein the specific process of setting parameters and solving the established water-sand-water power simulation model in the step 1 is as follows: (1) Dividing a calculation area and grids, namely determining the calculation area according to a target drainage basin range, performing space dispersion by adopting unstructured triangular grids or structured rectangular grids, determining the grid size according to the terrain complexity and calculation accuracy requirements, and taking 5-20 m; (2) Setting the roughness parameters, namely determining the coefficient of the Manning roughness according to the land utilization type The main groove is 0.03-0.05, the beach is 0.05-0.08, and the building area is 0.08-0.15; (3) Grouping the particle size of the sediment: determining representative particle size of each particle size group according to river basin sediment characteristics Is divided into clay Mm, silt Mm, fine sand Mm, gravel Mm) group; (4) The boundary condition setting, namely inputting an inflow process line which is deduced based on actual measurement or design rainfall process into an upstream boundary, and setting a water level boundary or a free outflow boundary according to actual conditions by a downstream boundary; (5) Setting simulation time length, namely covering the whole process from rising to falling of flood; and then obtaining the space-time distribution of each physical quantity under the mountain torrent condition of different reproduction periods by solving an equation set through the numerical values, wherein the space-time distribution comprises water depth, flow velocity and sediment concentration.
4. 4. The method for evaluating the damage of the mountain torrent bridge with high sand content based on water-sand power-finite element coupling according to claim 1, wherein the specific process of establishing the bridge finite element model in the step 3 comprises the following steps: (1) Establishing a bridge numerical model by adopting commercial finite element software: The girder comprises girder units, wherein the girder units define section characteristics and prestress; the bridge pier is a fiber beam unit or a solid unit, and reinforcing bars are considered; pile foundation, wherein the beam unit is matched with a soil spring; The support is a nonlinear connection unit and defines friction and detachment characteristics-a material structure, wherein the concrete adopts a nonlinear model considering cracking and crushing, and the reinforcing steel bar adopts a bilinear elastoplastic model; (2) Model input parameter setting: geometric parameters, namely bridge span L, pier height H, pier diameter D or pier width B and wall thickness; The material parameters are concrete strength grades C30-C50 and reinforcing steel bar HRB400; load input, namely inputting the load calculated in the step 2 According to the action height Applied to the bridge pier; Boundary conditions, namely pier bottom consolidation or considering pile-soil interaction; (3) Analysis settings: Analysis type, namely nonlinear time course analysis; Step size: Determining according to the load change rate, and taking 10-60 seconds; Total duration t e [0, t f ] covering the complete flood process, wherein Is the total duration of the flood process; Solving the problem that the structure is opened and greatly deformed, and the P-delta effect is considered, wherein the P-delta effect refers to an additional bending moment effect generated by a vertical load on the structure after the structure generates lateral displacement under the action of horizontal load; The finite element analysis result is specifically that finite element software automatically calculates the structural response of each time step by solving a structural dynamics equation according to the input load time course and the structural model.
5. 5. The method for evaluating the damage of the mountain torrent bridge with high sand content based on water-sand power-finite element coupling according to claim 1, wherein the determination criteria in the step 5 are specifically: For pier top displacement angle When (when) Class I when Class II when Class III when Stage IV; Bearing ratio to cross section When (when) Class I when Class II when Class III when Stage IV; Stress ratio for concrete When (when) Class I when Class II when Class III when Stage IV; For the stress ratio of the steel bar When (when) Class I when Class II when Class III when Stage IV; stability coefficient to capsizing When (when) Class I when Class II when Class III when Stage IV; For minimum abutment reaction force When (when) Class I when Class IV.

Description

High-sand-content mountain torrent bridge damage assessment method based on water-sand power-finite element coupling Technical Field The invention belongs to the technical field of disaster prevention and reduction engineering, and particularly relates to a method for evaluating the damage of a mountain torrent bridge with high sand content based on water-sand power-finite element coupling. Background In recent years, under the influence of global climate change, extreme rainfall events occur frequently, and mountain torrent disasters have become one of the main natural disasters threatening the security of mountain infrastructure. The mountain floods have the characteristics of strong burst, fast flow speed and high sand content, and the damage to the bridge structure is often catastrophic. The bridge is used as a key node of a traffic network, and the safety of the bridge under the action of mountain floods is directly related to the smoothness of a post-disaster rescue channel and regional economic loss. The existing bridge flood loss assessment method mainly has the following defects: (1) Most methods only consider the hydrostatic pressure, and neglect the special dynamic action of high flow velocity and strong impact characteristics of the mountain torrents on the bridge structure; (2) Most methods only consider the effect of clear water, neglect the special high sandiness of mountain torrents, and cannot accurately evaluate the acting force of wide-grading sediment on bridge structures; (3) The probability analysis of the response of the bridge structure is lacking, the influence of uncertainty factors such as material parameters, geometric dimensions, boundary conditions and the like on the bridge damage cannot be fully considered, and the damage probability of the bridge under the action of torrential floods with different intensities cannot be accurately reflected; (4) The existing method mostly adopts an empirical formula or a simplified model, and is difficult to reflect the complex mechanical mechanism of the mountain torrent-bridge interaction; (5) The existing method is difficult to give the damage probability of the bridge under the effect of the mountain floods with different intensities, and cannot provide a probabilistic evaluation result for risk decision. Therefore, there is a need to develop a loss evaluation method that comprehensively considers the characteristics of the torrential flood, the response of the bridge structure and the damage probability, so as to improve the accuracy and the scientificity of the torrential flood disaster risk evaluation. Disclosure of Invention The invention aims to provide a high-sand-content mountain torrent bridge damage evaluation method based on water-sand power-finite element coupling, which realizes accurate evaluation of bridge damage level by coupling a water-sand-water power model and a finite element model. In order to achieve the above purpose, the present invention provides the following technical solutions: the invention discloses a method for evaluating the damage of a mountain torrent bridge with high sand content based on water sand power-finite element coupling, which comprises the following steps: Step 1, establishing a water-sand hydrodynamic force simulation model, namely acquiring topographic data, land utilization data, historical rainfall data and sediment characteristic parameters of a target river basin, establishing the water-sand hydrodynamic force simulation model based on a shallow water equation and a sediment transport equation, wherein the shallow water equation comprises a water flow continuous equation and a water flow momentum equation; Step 2, calculating load time courses acting on the bridge, namely acquiring bridge foundation data comprising geometric dimensions, material characteristics and pile foundation depth, extracting water depth, flow velocity and sediment concentration time course data at the position of the bridge based on the output result of the water-sediment hydrodynamic simulation model, and calculating various load time courses acting on the bridge structure, wherein the load time courses comprise hydrostatic pressure, hydrodynamic pressure, sediment acting force, total horizontal load and total horizontal load acting point height; the calculation formula of the hydrostatic pressure is as follows: (5) wherein: Is hydrostatic pressure in kN; is the density of water body, h (t) is the depth of water at the bridge position, and the unit is B is the width of the pier body, and the unit is; The calculation formula of the dynamic water pressure is as follows: (6) wherein: The dynamic water pressure is given by kN; Taking a round pier of 0.7 and a rectangular pier of 1.4 as resistance coefficients; Is the effective water-facing area, the unit is ;、Respectively at bridge positions、Directional flow velocity in units of; The calculation formula of the sediment acting force is as follows: (7) Wherein: (8