Bridge pier damage early warning analysis method under flood effect

Abstract

The invention relates to a pier damage early warning analysis method under the action of flood, and solves the technical problems of high disaster recognition cost, low bridge damage recognition precision, untimely early warning and alarming and the like based on monitoring equipment in the existing concrete bridge flood-disaster-resistant technology. According to the method, by means of an established plastic damage simulation model, expensive sensors do not need to be arranged on a bridge structure, only basic information of the bridge structure and flood information such as the flow speed, the water level and the scouring depth are obtained, and damage and failure analysis of the bridge pier structure under the action of different influence factors by the flood action can be studied; structural damage state qualitative analysis and modal integrity damage index quantitative analysis are combined to determine bridge pier structure damage grades and damage failure judgment criteria, and early warning values corresponding to different damage grades of a bridge pier are inverted, so that accurate damage identification and rapid grading early warning of the bridge pier structure under the flood effect are realized. The flood disaster resistance of the bridge structure is improved, safe operation of the bridge is guaranteed, and the service life of the bridge is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of bridge performance analysis, and in particular to a graded early warning analysis method for bridge pier damage under flood action. Background Art

[0002] Bridge water damage is one of the main causes of damage to existing bridges. When a flood peak passes through a bridge, it will quickly scour the foundation, causing the bridge superstructure to collapse, slide, bearings to slide, lower structure to bend or shear, scouring damage, and multiple forms of damage to occur together. Studies have shown that bridge water damage is gradually becoming the main cause of bridge failure worldwide. According to statistics, floods have caused thousands of bridges to suffer varying degrees of damage, resulting in direct economic losses of hundreds of millions of yuan. This shows that floods cause serious damage to the safety and operation of bridges.

[0003] Accurate calculation of flood forces is the basis for analyzing the damage to bridge structures under floods and thus ensuring the safety of bridge structures. A large number of scholars at home and abroad have conducted research on the effects of floods on bridges.

[0004] For example, the master's thesis of Chang'an University, "Static and seismic response analysis of continuous beam bridges after scouring combined with water flow forces during floods", uses numerical simulation methods to analyze the flow field of bridge substructures under the action of water flow during floods. The water flow resistance coefficient obtained by analyzing the water flow force during floods was compared with the standard value, and it was found that the resistance coefficient given in the standard was conservative.

[0005] For example, the paper "The Instantaneous Impact Effect of Floods on Bridge Piers" published in the journal "Highway and Transportation Research and Development" used the numerical simulation software ANSYS-CFX to conduct a fluid-solid coupling transient simulation of the process of floods impacting bridge piers with different cross-sectional forms, clarified the concepts of impact amplification coefficient and impact effect coefficient, and defined the expression of the impact effect coefficient. It analyzed the relationship between the instantaneous impact effect and fluid-solid coupling effect and the flood flow velocity and water height, revealed the reason for the large instantaneous impact response, compared the bypass pressure after the impact with the calculated value in the specification, and suggested that the railway bridge specification should appropriately multiply the water flow force by the amplification factor.

[0006] The above existing methods analyze the resistance of floods through simulation analysis methods, and point out that the flood force in the specifications is conservative and does not consider the pulsation impact effect. The research results lay the foundation for the accurate calculation of flood forces, but it is still necessary to further clarify the precise expression of flood forces with the effects of flood elements.

[0007] In the research on bridge damage and early warning under floods, domestic and foreign scholars have conducted research on the dynamic response and damage early warning of structures under floods through real bridge monitoring and numerical simulation analysis methods.

[0008] For example, the paper "Damage Analysis of Bridge Piers under Rapid Water Flow Based on Concrete Plastic Damage Model" published in the journal "Transportation Research" established a finite element analysis model of bridge piers under water flow pressure based on the concrete plastic damage model, and concluded that the tensile zone of the water-facing surface at the root of the bridge pier is more susceptible to damage under the action of rapid water flow, and proposed the concept of early warning flow rate as a critical indicator for judging bridge pier damage. However, this method does not take flow rate, water level and scouring into account, and only gives the early warning flow rate when the tensile zone of the water-facing surface at the root of the bridge pier is slightly damaged and uses it as the early warning value.

[0009] For example, the prior art patent number CN202111037161.4, an invention patent named "A method for analyzing the vulnerability of concrete bridges to floods considering pier failure modes", gives the probability of bridge collapse under different water flow velocities and water flow depths. By analyzing the vulnerability of the pier failure mode under the action of floods, the water flow velocity at which the pier overturns and collapses, i.e. at the maximum bearing capacity, is determined. This has very important guiding significance for judging the safety performance of the bridge. However, this method does not carry out graded warnings for the different degrees of damage to the piers from damage to collapse.

[0010] For example, the invention patent with the prior art publication number CN118397795A and the name “A graded early warning system and method for inland river bridges” establishes a flood risk prediction model based on the method of machine learning by collecting river data information, preprocessing the water level change rate and flow data, extracting features, and classifying flood risks into different levels, such as low risk, medium risk, high risk, etc. However, this method is for early warning of flood risks, and does not analyze the stress and response of the pier structure under different flood influencing factors, resulting in insufficient accuracy in early warning of pier structure damage.

[0011] Based on the above analysis, it can be seen that the research on bridge pier damage and early warning under the impact of floods is still insufficient, and it is not possible to provide timely and effective early warning for the safety of bridges based on flood disaster information and pier structure damage information. Therefore, conducting research on catastrophic damage and failure of bridge pier structures under floods and proposing an effective early warning analysis method for bridge pier damage under floods are of great theoretical and application significance for ensuring the safe operation of bridges. Summary of the invention

[0012] In order to solve the technical problems existing in the existing concrete bridge flood prevention technology, such as high cost of disaster identification based on monitoring equipment, low accuracy of bridge damage identification, and untimely early warning and alarm. The present invention provides a pier damage classification early warning analysis method under the action of floods. With the help of the established plastic damage simulation model, this method does not need to deploy expensive sensors on the bridge structure. It only obtains bridge information and flood information such as flow rate and water level, and can study the effects of floods on different factors, including the damage and failure analysis of the pier structure under the action of flood velocity, water level and scouring. Combined with the structural damage phenomenon, the damage failure judgment criteria are determined based on the damage index, and the early warning values ​​corresponding to different damage levels of the pier are inverted, so as to realize the accurate identification of the damage of the pier structure under the action of floods and rapid classification early warning, improve the ability of the bridge structure to resist flood disasters, ensure the safe operation of the bridge, and extend the service life of the bridge.

[0013] The technical solution adopted by the present invention is as follows:

[0014] A method for early warning and analyzing bridge pier damage under flood conditions, the method comprising the following steps:

[0015] Step S101: obtaining basic information of the bridge structure to be studied;

[0016] Step S102: Obtaining river channel and flood disaster information at the bridge location, including cross-sectional dimensions of the river channel at the bridge location, riverbed slope, flood flow, flood flow velocity, water level, bridge pier scouring depth, and water flow density;

[0017] Step S103: Based on the river channel and flood disaster information at the bridge location, the horizontal resistance coefficient under the flood is determined by using the calculation formula obtained by the existing fluid-solid coupling and statistical analysis, and the impact load force of the bridge pier under the flood is calculated by using the horizontal resistance coefficient under the flood;

[0018] Step S104: Based on the basic information and the impact load force of the bridge pier under the flood, a simulation model of plastic damage of the bridge pier structure under the flood is established using the MechanicalAPDL command flow in the ANSYS software;

[0019] Step S105: In the plastic damage simulation model, the impact load force of the bridge pier under different floods is applied to the bridge pier structure, and the dynamic response analysis of the bridge pier under different influencing factors such as flood velocity, water level and scouring depth is performed to clarify the influence rules of the dynamic response of the bridge pier including the displacement of the pier top under different influencing factors;

[0020] Step S106: Calculate the pier frequency using a stress modal analysis method, use the frequency change caused by the stiffness loss after the pier is stressed, i.e., the modal integrity, as a pier structure damage index, and determine the modal integrity change law under different flood flow rates, water levels, and scouring depths;

[0021] Step S107: Based on the variation law of the modal integrity, the relationship between the pier damage and the modal integrity is analyzed, and the qualitative analysis of the structural damage state and the quantitative analysis of the modal integrity damage index are combined to determine the pier structure damage level and the damage failure judgment criterion, and the pier structure damage level is divided based on the calculated modal integrity, where the damage level is divided into intact function, slight damage, moderate damage, severe damage and severe destruction;

[0022] Step S108: Based on the plastic damage simulation model, the warning values ​​corresponding to different damage levels of the piers are inverted, including warning flow velocity, warning water level or warning scour depth, and the warning level is set to level I to level IV according to the damage level of the pier structure, so as to provide different levels of rapid warning for the safe passage of the bridge under the action of floods.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) Reduced the cost of pier damage warning: The present invention does not need to install expensive sensing equipment on the piers, such as displacement, stress or strain sensors, acceleration sensors and their corresponding data acquisition equipment for monitoring the dynamic response of the pier structure. It only uses measured flood information, such as water level, flow velocity and scour depth information, to calculate the flood impact effect as the input of the finite element plastic damage model, thereby conducting structural damage and warning research, combining the measured flood data with simulation calculations, and breaking the barrier of structural damage warning relying on expensive monitoring equipment.

[0025] (2) Improved the recognition accuracy of pier damage warning: The present invention takes into account the most critical flood influencing factors, including flood velocity, water level and scouring depth, and proposes a calculation formula for the resistance coefficient under different pier shapes, which more accurately calculates the flood force under different flood velocities, water levels and scouring depths. The SOLID65 solid unit is used to simulate the pier, abutment and pile structure, the COMBIN14 unit is used to simulate the pile-soil effect and the bearing support effect, and the MASS21 unit is used to simulate the deadweight and traffic load of the upper structure. The plastic constitutive model that can simulate structural cracking damage is used to accurately simulate the dynamic response and damage status of the structure under the action of deadweight and traffic load and the coupling effect of flood impact. Compared with single factor analysis, from the precise calculation of flood force to the establishment of a refined plastic simulation model that takes into account the boundary conditions of scouring depth, it is more in line with the actual situation of the pier structure under the action of floods, and improves the recognition accuracy of damage warning.

[0026] (3) Improved the speed of pier damage warning: The present invention inputs actual flood information into the simulation model and accurately calculates the frequency parameters that characterize the structural dynamic characteristics. Based on the proposed pier modal integrity calculation formula, the damage grade and warning level under different flow rates, water levels and scouring depths can be quickly determined, providing a judgment basis for the detection and maintenance of underwater pier structures, and providing an efficient and convenient early warning analysis method for the safety of pier structures under floods.

[0027] (4) Expanded the scale of pier damage warning: Based on a large number of statistical and simulation analyses, the present invention proposes a classification standard for the damage level of simply supported beam bridges, and divides the pier damage into intact function, slight damage, moderate damage, severe damage, and severe damage according to the proposed different modal integrity value ranges. The warning value and warning level are determined by reversely deducing the flow velocity, water level or scour depth values ​​corresponding to the critical values ​​of different damage levels. The warning level is divided into levels I-IV, and the graded warning can provide more response time for the bridge emergency management department, allowing it to more effectively protect the safety of the bridge structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without exceeding the scope of protection required by the present invention.

[0029] Figure 1 It is a flow chart of the method for early warning and analysis of bridge pier damage under flood according to an embodiment of the present invention;

[0030] Figure 2 is the lower structure layout diagram, where Figure 2 (a) Main view, Figure 2 (b) is a side view, Figure 2 (c) is a top view, all units are meters (m);

[0031] Figure 3 Simplified calculation model for pile foundation;

[0032] Figure 4 (a) is a schematic diagram of the large horizontal displacement of the pier top under different flow velocities. Figure 4 (b) is a schematic diagram of the displacement change rate of the pier top under different flow velocities;

[0033] Figure 5 (a) is a schematic diagram of the maximum horizontal displacement of the pier top under different water levels. Figure 5 (b) is a schematic diagram of the displacement change rate of the pier top under different water levels;

[0034] Figure 6 (a) is a schematic diagram of the maximum horizontal displacement of the pier top under different scouring depths. Figure 6 (b) is a schematic diagram of the displacement change rate of the pier top under different scour depths;

[0035] Figure 7 It is a schematic diagram of the first three frequencies of the bridge pier under different flood velocities;

[0036] Figure 8 It is a schematic diagram of the first three frequencies of the bridge pier under different water levels;

[0037] Fig. 9 (a) is a schematic diagram of the first three frequencies of the bridge pier at different scouring depths under low flow velocity; Fig. 9 (b) is a schematic diagram of the first three frequencies of the bridge pier at different scouring depths at flow velocities of 1 m / s, 3 m / s, 5 m / s, 7 m / s, and 10 m / s; DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0039] like Figure 1 As shown, this embodiment provides a pier damage early warning analysis method under flood action, which belongs to the performance analysis method of reinforced concrete piers under flood action, and specifically involves the establishment of nonlinear plastic simulation model, pier dynamic response analysis, pier damage analysis and early warning analysis. The method specifically includes the following steps S101-step S108.

[0040] Step S101: Obtain basic information of the bridge structure to be studied: including bridge span, main beam cross-sectional dimensions, concrete strength, steel yield strength, pier cross-sectional dimensions, pier cross-sectional height, longitudinal reinforcement ratio, stirrup reinforcement ratio, abutment cross-sectional dimensions, number of piles, number of supports, support friction coefficient, distance between main beam and pier, and specific parameters of concrete and steel materials. The specific structural dimensions of a bridge structure obtained in this step are as follows: Figure 2 shown.

[0041] Step S102: Obtain the river channel and flood disaster information at the bridge location. The river channel information at the bridge location includes the cross-sectional dimensions of the river channel at the bridge location, the riverbed slope, and the water flow density. The flood disaster information includes the flood flow, flood flow velocity, water level, bridge pier scouring depth, flood peak flow, and flood duration. The flood flow process line is calculated based on formula (1):

[0042]

[0043] Among them, Q is the flood flow, q0 is the initial flow, q j is the peak flow of the jth flood, τ j is the flood duration of the jth flood, t j is the peak time of the jth flood, α j t j The exponential decay intensity coefficient after time.

[0044] For the trapezoidal section, based on the Xie Cai formula and the Manning formula, according to the influence of the hydraulic gradient of the flood rapid flow and the roughness of the gravel in the mountainous area, the process formula of the water level over time is proposed, as shown in formula (2) and formula (3). Through formula (2) and formula (3), the flood velocity process line can be obtained.

[0045]

[0046] Among them, H is the river water level, H0 is the riverbed bottom elevation, which changes according to the actual modeling situation; n is the Manning roughness coefficient, which can be taken as n = 0.06; Q is the flood flow; a is the river channel width-to-depth ratio; S0 is the riverbed slope, which can be taken as S0 = 0.008; is the time-varying term of flow; g is the gravity coefficient; A is the cross-sectional area of ​​the river.

[0047] In order to analyze the damage status of the structure under different flood influencing factors and then determine the damage judgment criteria, this step requires normalizing the results calculated by the above formula to determine the flood process under the range of maximum flood flow velocity, highest water level and maximum scour depth. When the flow velocity is greater than 10m / s, the dynamic effect of the water flow should be considered, that is, the pulsating impact pressure of the water flow should be considered, and the result after normalization calculation should be multiplied by a dynamic amplification factor of 1.4.

[0048] Step S103: Based on the basic information of the bridge to be studied obtained in step S101 and the flood information calculated in step S102, the horizontal resistance coefficient under the flood (including the horizontal resistance coefficient of the rectangular bridge pier C D矩 and the horizontal resistance coefficient C of the circular pier D圆 ) and the force of flood on bridge piers (i.e. the impact load force on bridge piers under flood) F D :

[0049]

[0050] C D矩 =-0.0001V 2 +0.0026V+1.3366 (5)

[0051] C D圆 =-0.00008V2 -0.001V+0.6448 (6)

[0052]

[0053] Among them, F D is the water flow resistance, ρ is the water flow density, V is the water flow velocity, C D矩 and C D圆 are the horizontal resistance coefficients of rectangular and circular piers, respectively, A1 is the area of ​​the bridge perpendicular to or parallel to the water flow direction, and A2 is the unit flow cross-sectional area. The above formulas (4) to (7) are the calculation formulas obtained by using existing fluid-structure coupling and statistical analysis.

[0054] Step S104: Based on the basic information of the bridge structure obtained in step S101 and the flood force on the bridge pier calculated in step S103, a simulation model of plastic damage of the bridge pier structure under the action of flood is established using the MechanicalAPDL command flow in the ANSYS software.

[0055] In this step, the concrete material uses the kinematic hardening constitutive model (MKIN) command to input the concrete compressive stress-strain constitutive model to simulate a more realistic concrete damage model. The tensile steel bar material uses the bilinear isotropic hardening model (BISO) for the steel bar constitutive relationship. The SOLID65 unit is used to simulate the piers, abutments and piles, the COMBIN14 unit simulates the pile-soil interaction and the bearing support, and the MASS21 unit simulates the superstructure deadweight and traffic load. The boundary conditions are set as the pile bottom consolidation and the pile foundation is subject to soil spring constraints of different stiffness. The spring stiffness value can be calculated according to the "Highway Bridge and Culvert Foundation Design Code" (JTG3363-2019). The simplified calculation model of the pile foundation is as follows: Figure 3 As shown, the numbers 1, 2, ..., N on the right side of the figure represent the pile foundation soil springs at different depths.

[0056] Step S105: In the established plastic damage simulation model, different flood forces on the bridge piers are loaded onto the bridge pier structure, and the dynamic response analysis of the bridge piers under different influencing factors such as flow velocity, water level height and scouring depth is carried out to clarify the influence rules of the dynamic response of the bridge piers including the pier top displacement under different influencing factors.

[0057] This step considers the cumulative effect of the flood process on the response of the bridge piers and analyzes the dynamic response of the bridge piers under different influencing factors, including the analysis of the influence of flow velocity, water level height, and scouring depth on the maximum horizontal displacement response of the pier top.

[0058] Influence of flow velocity on dynamic response of bridge piers: Select the value range of flood flow velocity as 0-14m / s, calculate the horizontal force of the corresponding bridge piers, and simulate the dynamic response of the bridge piers under different flood flow velocities based on the simulation model in step S104. The maximum horizontal displacement of the pier top and the rate of change of the pier top displacement are as follows: Figure 4 shown.

[0059] The influence of water level on the dynamic response of bridge piers: The water level corresponding to the same flood velocity of 1m / s is selected in the range of 0-13m, and the changes in the maximum horizontal displacement of the pier top and the rate of change of the pier top displacement under different water levels are analyzed. Figure 5 shown.

[0060] The influence of scouring depth on the dynamic response of bridge piers: Starting from the bottom of the pier, different scouring depth conditions of 0-20.5m are set. The maximum horizontal displacement of the pier top and the change rate of the pier top displacement under different scouring depths are calculated as follows: Figure 6 shown.

[0061] Step S106: The pier frequency is calculated using a stress modal analysis method, and the frequency change caused by the stiffness loss after the pier is stressed, i.e., the modal integrity, is used as a pier structure damage index to determine the modal integrity change pattern of the pier under different flood velocities, water levels, and scouring depths.

[0062] In ANSYS software, modal analysis includes stress-free structural modal analysis and stress modal analysis. When the stiffness matrix [K] of the system includes the stress stiffness matrix, it is a stress modal analysis. When the stress modal analysis method is used to calculate the pier frequency, the unit stress stiffness matrix is ​​saved by opening the command "SSTIF,ON" before solving, and superimposed with the structural stiffness matrix during the static analysis process, so that the unit stress stiffness matrix participates in the iterative calculation. After obtaining the static analysis, re-enter the solver and obtain the modal analysis solution.

[0063] First, the modal integrity of the pier is calculated according to the pier frequency calculation theory. The calculation formula is:

[0064]

[0065] Among them, ξ i is the modal integrity of the pier, f i (x) is the i-th modal frequency corresponding to the damaged pier obtained in step S104, F i (x) is the i-th modal frequency of the undamaged pier.

[0066] Secondly, the effects of different flood velocities, water levels and scouring depths on the modal integrity of bridge piers are analyzed.

[0067] Influence of flow velocity on modal integrity of bridge piers: Based on the simulation model in step S104, the range of flood flow velocity is selected as 0-14 m / s, and stress modal analysis is carried out to obtain the first three frequencies of the bridge piers under different flood flow velocities. Figure 7 shown.

[0068] The influence of water level on the modal integrity of bridge piers: The water level corresponding to the same flood velocity of 1m / s is selected in the range of 0-13m. Through stress modal analysis, the first three frequencies of the bridge piers at different water levels are obtained as follows: Figure 8 shown.

[0069] The influence of scouring depth on the modal integrity of bridge piers: Starting from the bottom of the pier, different scouring depth conditions of 0-20.5m were set. Based on the stress modal analysis, the first three frequencies of the bridge piers at different scouring depths under low, medium and high flow velocities were obtained. Fig. 9 shown.

[0070] Step S107: Based on the variation law of modal integrity, the relationship between pier damage and modal integrity is analyzed, and the qualitative analysis of the structural damage state and the quantitative analysis of the modal integrity damage index are combined to determine the pier structure damage level and damage failure judgment criteria, as shown in Table 1. Based on this criterion and the modal integrity calculated in step S106, the damage level of the pier under the action of flood is divided into five levels: functionally intact, slightly damaged, moderately damaged, severely damaged, and severely damaged.

[0071] Table 1 Damage levels and damage failure criteria for pier structures

[0072]

[0073] Step S108: Based on the plastic damage simulation model, the warning values ​​corresponding to different damage levels of the pier are inverted, including the warning flow velocity, the warning water level or the warning scouring depth, and the warning level is set from level I to level IV according to the damage level of the pier structure, so as to provide different levels of rapid warning for the safe passage of the bridge under the action of floods. The warning flow velocity, water level or scouring depth are inverted for different damage levels under the action of floods, so as to determine the warning level: from the intact function of the pier to slight damage is level I warning; from slight damage to moderate damage to the pier is level II warning; from moderate damage to severe damage to the pier is level III warning; and serious damage to the pier is level IV warning.

[0074] Combining steps S107 and S108, the pier damage grades and graded warning results for different flood velocities, water levels and scouring depths are listed in Tables 2 to 5.

[0075] Assuming that the fixed water level is 12m, different flow rate conditions are set from 1m / s to 14m / s, and the impact of scouring is not considered, the modal integrity under different flow rates is explored, and the damage level and warning level under different flow rates are shown in Table 2. It can be seen from Table 2 that the level I and level II warning flow rates are 9m / s and 11m / s respectively.

[0076] Table 2 Damage levels at different flow rates at the same water level

[0077]

[0078]

[0079] Taking the flood velocity as 10m / s, setting different water level conditions of 1m-13m, and not considering the impact of scouring, the damage grade and warning level of the bridge pier at different water levels are shown in Table 3. It can be seen from the table that the level I warning water level is 11m.

[0080] Table 3 Damage levels at different water levels at the same flow rate

[0081]

[0082]

[0083] The damage grade and warning level at different scour depths under low flow velocity (1m / s) and high flow velocity (10m / s) conditions are shown in Tables 4 and 5. It can be seen from the table that under the low flow velocity V = 1m / s condition, the warning scour depths of level I, level II and level III are 3.5m, 8.5m and 12.5m respectively, while under the high flow velocity V = 10m / s condition, the warning scour depths of level I, level II, level III and level IV are 0m, 2.5m, 4.5m and 8.5m respectively.

[0084] Table 4 Modal integrity of the substructure in low velocity state (V = 1 m / s)

[0085]

[0086]

[0087] Table 5 Modal integrity of the lower structure in high velocity state (V = 10 m / s)

[0088]

[0089] The pier damage early warning analysis method under flood action proposed by the present invention takes into account the response and failure model of pier shear under flood impact, and can give the degree of damage of the bridge under flood action according to the design parameters of the bridge, water flow velocity, water flow depth and scouring depth, and then can determine the early warning value of structural damage through numerical indicators such as water level height, flow velocity, scouring depth, etc. when the damage begins to accumulate, providing a judgment basis for the detection and maintenance of underwater pier structures, and filling the technical gap of the existing technology that lacks concrete bridge damage mechanism and failure mode and early warning analysis that considers the failure mode of piers. The present invention provides a method scheme for early warning analysis of bridge damage and failure under flood action, which is helpful for rapid and accurate flood damage assessment and failure judgment of concrete bridges, and can provide early graded early warning for flood disasters.

[0090] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0091] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for early warning analysis of bridge pier damage under flood conditions, characterized in that: The following steps are involved: Step S101: obtaining basic information of the bridge structure to be studied; Step S102: Obtaining river channel and flood disaster information at the bridge location, including cross-sectional dimensions of the river channel at the bridge location, riverbed slope, flood flow, flood flow velocity, water level, bridge pier scouring depth, and water flow density; Step S103: Based on the river channel and flood disaster information at the bridge location, the horizontal resistance coefficient under the flood is determined by using the calculation formula obtained by the existing fluid-solid coupling and statistical analysis, and the impact load force of the bridge pier under the flood is calculated by using the horizontal resistance coefficient under the flood; Step S104: Based on the basic information and the impact load force of the bridge pier under the flood, a simulation model of plastic damage of the bridge pier structure under the flood is established using the MechanicalAPDL command flow in the ANSYS software; Step S105: In the plastic damage simulation model, the impact load force of the bridge pier under different floods is applied to the bridge pier structure, and the dynamic response analysis of the bridge pier under different influencing factors such as flood velocity, water level and scouring depth is performed, and the influence rules of the pier dynamic response including the pier top displacement under different influencing factors are analyzed; Step S106: Calculate the pier frequency using a stress modal analysis method, use the frequency change caused by the stiffness loss after the pier is stressed, i.e., the modal integrity, as a pier structure damage index, and determine the modal integrity change law under different flood flow rates, water levels, and scouring depths; Step S107: Based on the variation law of the modal integrity, the relationship between the pier damage and the modal integrity is analyzed, and the qualitative analysis of the structural damage state and the quantitative analysis of the modal integrity damage index are combined to determine the pier structure damage level and the damage failure judgment criterion, and the pier structure damage level is divided based on the calculated modal integrity, where the damage level is divided into intact function, slight damage, moderate damage, severe damage and severe destruction; Step S108: Based on the plastic damage simulation model, the warning values ​​corresponding to different damage levels of the piers are inverted, including warning flow velocity, warning water level or warning scour depth, and the warning level is set to level I to level IV according to the damage level of the pier structure, so as to provide different levels of rapid warning for the safe passage of the bridge under the action of floods.

2. The method for early warning and analysis of bridge pier damage under flooding according to claim 1 is characterized in that: The basic information of the bridge structure includes bridge span, main beam cross-sectional dimensions, concrete strength, steel bar yield strength, pier cross-sectional dimensions, pier cross-sectional height, longitudinal reinforcement ratio, stirrup reinforcement ratio, abutment cross-sectional dimensions, number of piles, number of supports, support friction coefficient, and distance between main beam and pier.

3. The method for early warning and analysis of bridge pier damage under flood according to claim 1 is characterized in that: The specific calculation formula for the flood flow is: Among them, Q is the flood flow, q0 is the initial flow, q j is the peak flow of the jth flood, τ j is the flood duration of the jth flood, t j is the peak time of the jth flood, α j t j Exponential decay intensity coefficient after time; For the trapezoidal section, based on the Xie Cai formula and the Manning formula, according to the influence of the hydraulic gradient of the flood rapid flow and the roughness of the gravel in the mountainous area, the water level process formula over time is proposed, as shown in formula (2) and formula (3): Among them, H is the river water level, H0 is the riverbed bottom elevation; n is the Manning roughness coefficient; Q is the flood flow; a is the river channel width-to-depth ratio; S0 is the riverbed slope; is the time-varying term of flow; g is the gravity coefficient; A is the cross-sectional area of ​​the river.

4. The method for early warning and analysis of bridge pier damage under flood according to claim 1 is characterized in that: The calculation of the impact load force of the bridge pier under the flood is shown in formula (4) to formula (7). When the flow velocity is greater than 10m / s, the result is multiplied by the dynamic amplification factor of 1.4: C D矩 =-0.0001V 2 +0.0026V+1.3366 (5) C D圆 =-0.00008V 2 -0.001V+0.6448 (6) Among them, F D is the water flow resistance, ρ is the water flow density, V is the water flow velocity, C D矩 and C D圆 are the horizontal resistance coefficients of rectangular and circular piers respectively, A1 is the area of ​​the bridge perpendicular to or parallel to the water flow direction, and A2 is the unit flow cross-sectional area.

5. The method for early warning and analysis of bridge pier damage under flooding according to claim 1 is characterized in that: When establishing the plastic damage simulation model, the concrete material adopts the kinematic hardening constitutive model (MKIN) command to input the concrete compressive stress-strain constitutive relationship, the tensile steel bar material adopts the bilinear isotropic hardening model (BISO) steel bar constitutive relationship, the SOLID65 unit is used to simulate the piers, abutments and piles, the COMBIN14 unit is used to simulate the pile-soil effect and the bearing support effect, the MASS21 unit is used to simulate the deadweight of the superstructure and the traffic load, and the boundary conditions are set as the pile bottom is consolidated and the pile foundation is subjected to soil spring constraints of different stiffness.

6. The method for early warning and analysis of bridge pier damage under flood according to claim 1 is characterized in that: When the stress modal analysis method is used to calculate the pier frequency in step 106, the command "SSTIF,ON" is opened before solving to save the unit stress stiffness matrix, and it is superimposed with the structural stiffness matrix during the static analysis process so that the unit stress stiffness matrix participates in the iterative calculation. After obtaining the static analysis, re-enter the solver and obtain the modal analysis solution.

7. The method for early warning and analysis of bridge pier damage under flood according to claim 1 is characterized in that: The modal integrity calculation formula is: Among them, ξ i is the modal integrity of the pier, f i (x) is the i-th modal frequency corresponding to the damaged pier, F i (x) is the i-th modal frequency of the undamaged pier.

8. The method for early warning and analysis of bridge pier damage under flooding according to claim 1 is characterized in that: The damage level and damage failure judgment criteria of the pier structure are as follows: i When the value range of is (0.9,1], the damage level is functionally intact; when the modal integrity ξ i When the value range of is (0.7,0.9], the damage level is mild damage; when the modal integrity ξ i When the value range of is (0.5,0.7], the damage level is moderate damage; when the modal integrity ξ i When the value range of is (0.3,0.5], the damage level is severe damage; when the modal integrity ξ i When the value range of is [0,0.3], the damage level is severe damage.

9. The method for early warning and analysis of bridge pier damage under flood according to claim 1, characterized in that: The warning levels I to IV respectively represent: Level I means the bridge pier is in good function but slightly damaged; Level II means the bridge pier is slightly damaged to moderately damaged; Level III means the bridge pier is moderately damaged to severely damaged; and Level IV means the bridge pier is severely damaged.

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