CN114186460A - Risk analysis method under bridge earthquake-scour disaster coupling effect - Google Patents
Risk analysis method under bridge earthquake-scour disaster coupling effect Download PDFInfo
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Abstract
The invention discloses a method for analyzing the risk of a bridge under the coupling action of earthquake and scour disasters, which comprises the following steps: establishing a nonlinear dynamic numerical analysis model under the earthquake action of a bridge structure system, and solving to obtain the dynamic response of the structure system; establishing vulnerability curves of components and structures under the action of an earthquake and vulnerability curved surfaces under the action of earthquake-scour coupling, and establishing average annual failure probability under the action of an earthquake disaster and combined average annual failure probability under the action of earthquake-scour coupling; and determining the reasonable design scouring depth and load coefficient under the action of earthquake-scouring coupling. According to the method, the earthquake-scour disaster coupling effect is considered by adopting a probability statistics idea, the nonlinear factors in a bridge structure system and the nonlinear effect of the earthquake-scour coupling effect are fully considered, the neglect of the edge effect in disaster combination analysis is effectively avoided, and the risk analysis under the bridge earthquake-scour disaster coupling effect is realized.
Description
Technical Field
The invention relates to the technical field of bridge engineering disaster prevention and reduction, in particular to a method for analyzing dangerousness under the coupling action of bridge earthquake-scour disasters.
Background
In recent years, with the global climate change aggravating, various natural disasters frequently occur, and the collapse of the bridge structure is in an increasing trend. The flood disaster causes great threat to the bridge safety due to high frequency. The scouring action of flood disasters on the bridge foundation greatly destroys the enclosing and supporting action of surrounding soil layers on the foundation, thereby influencing the stability of the bridge. In earthquake high-intensity areas, the scouring action of rivers can influence the anti-seismic performance of bridges. Along with the increase of the scouring depth, the bearing platform and the pile foundation are gradually exposed, the enclosing effect of the original soil layer on the foundation is reduced, and the structure tends to be unstable. Along with the reduction of the depth of the enclosing soil layer, the free length of the pile foundation is increased, the inherent period of the structure is changed, and the earthquake action is changed accordingly.
The earthquake resistance of the bridge after scouring action can be accurately evaluated, so that the efficiency of personnel evacuation and personnel material conveying in post-disaster rescue can be effectively improved. The earthquake damage of the past times shows that disaster relief personnel and materials cannot reach the center of a disaster area in time due to the damage of bridge facilities, and huge personnel and property loss is brought to the country, so that the significance of accurately evaluating the earthquake resistance of the bridge under the earthquake-scouring disaster coupling action is great.
In the current domestic and foreign earthquake resistance standard, the fixed end of a pier is generally used as a general scouring line or a foundation top surface when horizontal earthquake force is calculated. However, in practical situations, because the influence of different scour depths on the bridge foundation is not fully studied, simply using the fixed end as a scour line may underestimate the horizontal seismic effect and increase the risk of bridge failure.
At present, bridge design develops from a deterministic design theory to a probabilistic/reliable design theory, and the load and resistance coefficient design specification and the reliable degree theory depending on the load and resistance coefficient design specification gradually become a research hotspot in recent years. Although the existing domestic and foreign specifications consider the ultimate design states of natural disaster conditions such as earthquake, ship collision, vehicle collision, floating ice load and the like, most of the existing domestic and foreign specifications only study the load coefficient under the action of a single disaster, and no clear regulation is made on how earthquake and scouring are combined.
Disclosure of Invention
Technical problem to be solved
In order to solve the defects of the prior art, the invention mainly aims to provide a method for analyzing the risk under the coupling action of the bridge earthquake and the scour disaster, so as to determine the scour load coefficient under the coupling disaster action, effectively avoid neglecting the edge effect in disaster combination analysis and realize the risk analysis under the coupling action of the bridge earthquake and the scour disaster.
(II) technical scheme
In order to achieve the purpose, the invention provides a method for analyzing the risk under the coupling action of bridge earthquake-scour disasters, which comprises the following steps:
constructing a nonlinear dynamic numerical analysis model under the seismic action of a bridge structure system according to the bridge structure system 1 and the seismic excitation 2, and solving the nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system to obtain the dynamic response of the structure system;
under a given scouring depth, fitting the performance state of the structural member and the dynamic response of the structural system to obtain an ability demand ratio model I with seismic intensity as a variable, and establishing a vulnerability curve equation 4 under the given scouring depth;
according to a vulnerability curve equation 4 and an earthquake risk probability density equation 7 under a given scouring depth, establishing an average annual failure probability model 8 under the action of the given scouring depth and earthquake disasters, and calculating average annual failure probability values under different scouring depths to obtain a scouring depth-failure probability curve equation 9;
under different scouring depths, fitting the performance state of the structural member and the dynamic response of the structural system to obtain a capability demand ratio model II taking seismic oscillation strength and the scouring depth as variables, and establishing a vulnerability curved surface equation 6 under different scouring depths;
according to the vulnerability curved surface equation 6, the earthquake risk probability density equation 7 and the scouring risk probability density equation 10 under different scouring depths, a combined average annual failure probability model 11 under the action of earthquake-scouring coupled disasters is established, the average annual failure probability value is obtained through calculation, and the scouring depth obtained in a scouring depth-failure probability curve equation 9 is a reasonable scouring depth 12; and
and taking the ratio of the reasonable scouring depth 12 to the designed scouring depth 14 as a scouring load coefficient 13 under the earthquake-scouring disaster coupling action.
In the above scheme, in the step of constructing the nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system according to the bridge structure system 1 and the seismic excitation 2, the main beam 1-1, the pier 1-2, the pile 1-3, the pile-soil interaction 1-4, the support 1-5, the cable tower 1-6 and the cable bearing system 1-7 in the bridge structure are used as members of the bridge structure system 1 for simulation, wherein: the bridge structure system 1 is simulated by adopting a finite element method, the main beam 1-1, the pier column 1-2 and the cable tower 1-6 are simulated by adopting a beam-column element, the pile-soil interaction 1-4 and the support 1-5 are simulated by adopting a system consisting of mass, springs and dampers, and the cable bearing system is simulated by adopting a truss element.
In the scheme, the performance state of the structural member is determined by the performance states of the main beam 1-1, the pier stud 1-2, the pile 1-3, the support 1-5, the cable tower 1-6 and the cable bearing system 1-7.
In the scheme, the performance state of the main beam 1-1 is determined by the yield bending moment and the curvature of the section; the performance state of the pier stud 1-2, the performance state of the pile 1-3 and the performance state of the cable tower 1-6 are determined by the ductility of section curvature and the drift rate of each component; the performance state of the support 1-5 is determined using support shear strain.
In the above scheme, the expressions of the capability requirement ratio model I using the seismic intensity as a variable and the capability requirement ratio model II using the seismic intensity and the scour depth as variables are respectively:
μd＝g(IM)
μdh＝g(IM，h)
in the formula, mudIs a capability demand ratio model I, mu with seismic intensity as a variabledhIn order to obtain the capacity demand ratio model II taking the earthquake motion intensity and the scouring depth as variables, g is a polynomial equation, IM is the earthquake motion intensity, and h is the scouring depth.
In the above scheme, the expressions of the vulnerability curve equation 4 under the given scouring depth and the vulnerability curve equation 6 under the different scouring depths are as follows:
in the formula, PdFor a given washout depth the vulnerability curve equation 4, PdhEquation 6 of the vulnerability curved surface under different scouring depths, phi is a standard normal distribution function, sigmadVariance, σ, in the model I for the ratio of energy requirements with seismic oscillation intensity as a variabledhThe variance in model II is compared to the capability requirement using seismic intensity and scour depth as variables.
In the above scheme, the probability density equation 7 of the earthquake risk is expressed by the probability that the intensity of earthquake motion occurring under a certain field condition is greater than the pre-estimated earthquake motion intensity, and the expression manner is as follows:
in the formula, i is seismic intensity, and the relation between i and the seismic intensity IM is as follows:
IM＝10(ilg2-0.01) (3-2)
in the above scheme, the average annual failure probability model 8 under the given scour depth and earthquake disaster is a joint probability of a probability density equation of structural earthquake damage failure probability and earthquake risk, and the expression mode is as follows:
in the above scheme, the scour risk probability density equation 10 conforms to a lognormal distribution, and the expression manner thereof is:
in the formula, eta is the logarithmic mean value of the scouring depth; xi is the logarithmic standard deviation of the scouring depth;
the joint average annual failure probability model 11 under the action of the earthquake-scour coupling disaster is a joint probability of structural earthquake damage failure probability, probability density of earthquake risk and scour depth risk, and the expression mode is as follows:
in the above scheme, the ratio of the reasonable scour depth 12 to the designed scour depth 14 is used as the scour load coefficient 13 under the earthquake-scour disaster coupling effect, and the expression mode is as follows:
in the formula, HxFor reasonable scouring depth, H, calculated from joint probability densitydTo design the depth of the flush.
(III) advantageous effects
Compared with the prior art, the method for analyzing the dangerousness of the bridge under the coupling action of earthquake and scour disasters has the following beneficial effects:
1. according to the method for analyzing the risk under the bridge earthquake-scour disaster coupling effect, the earthquake-scour disaster coupling effect is considered by adopting a probability statistics idea, nonlinear factors in a bridge structure system and nonlinear effects of the earthquake-scour coupling effect are fully considered, the scour load coefficient under the coupling disaster effect can be finally determined, the neglect of edge effects in disaster combination analysis is effectively avoided, and the risk analysis under the bridge earthquake-scour disaster coupling effect is realized.
2. According to the method for analyzing the risk under the bridge earthquake-scour disaster coupling effect, the earthquake-scour disaster coupling effect is considered by adopting a probability statistics idea, the ratio of the reasonable scour depth to the designed scour depth is used as the scour load coefficient under the earthquake-scour disaster coupling effect, the concept is clear, scientific and reasonable, the method accords with the actual state of the bridge under the earthquake-scour disaster coupling effect, an effective method is provided for risk analysis and load combination coefficient determination under the bridge earthquake-scour disaster coupling effect, and the method is beneficial to wide application in the technical field of bridge engineering disaster prevention and reduction.
Drawings
Fig. 1 is a flowchart of a method for risk analysis under the coupling effect of bridge earthquake-scour disasters, which is implemented according to the present invention.
FIG. 2 is a schematic diagram of a typical bridge construction system numerical calculation model under seismic-scour coupling in accordance with the present invention.
FIG. 3 is a graph of vulnerability at a given flush depth implemented in accordance with the present invention.
FIG. 4 is a seismic risk probability density curve implemented in accordance with the invention.
FIG. 5 is a graph of a given flush depth and seismic-flush coupling failure probability, implemented in accordance with the present invention.
FIG. 6 is a graph of a seismic-scour coupled vulnerability surface.
FIG. 7 is a graph of the probability density of scour hazards.
In the drawings, the reference numbers: 1-1 main beam, 1-2 pier stud, 1-3 piles, 1-4 pile-soil interaction, 1-5 support, 1-6 cable tower and 1-7 cable bearing system.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
According to the method for analyzing the dangerousness under the bridge earthquake-scour disaster coupling effect, the earthquake-scour disaster coupling effect is considered by adopting a probability statistics idea, firstly, a nonlinear dynamic numerical analysis model under the earthquake effect of a bridge structure system is established, and the dynamic response of the structure system is obtained through numerical solution; secondly, establishing vulnerability curves of the components and the structures under the action of the earthquake and vulnerability curved surfaces under the action of earthquake-scour coupling, and establishing average annual failure probability under the action of the earthquake disaster and combined average annual failure probability under the action of the earthquake-scour coupling disaster by combining a probability density equation of earthquake hazard and a scour depth risk curve; and finally, determining the reasonable design scouring depth under the earthquake-scouring coupling action, and taking the ratio of the reasonable scouring depth to the design scouring depth as a scouring load coefficient under the earthquake-scouring disaster coupling action.
Referring to fig. 1 and 2, fig. 1 is a flowchart illustrating a method for risk analysis under a bridge earthquake-scour disaster coupling effect according to an embodiment of the present invention, and fig. 2 is a schematic diagram illustrating a typical bridge structure system numerical calculation model under an earthquake-scour coupling effect according to an embodiment of the present invention, where the method includes:
step 1: constructing a nonlinear dynamic numerical analysis model under the seismic action of a bridge structure system according to the bridge structure system 1 and the seismic excitation 2, and solving the nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system to obtain the dynamic response of the structure system;
step 2: under a given scouring depth, fitting the performance state of the structural member and the dynamic response of the structural system to obtain an ability demand ratio model I with seismic intensity as a variable, and establishing a vulnerability curve equation 4 under the given scouring depth;
and step 3: according to a vulnerability curve equation 4 and an earthquake risk probability density equation 7 under a given scouring depth, establishing an average annual failure probability model 8 under the action of the given scouring depth and earthquake disasters, and calculating average annual failure probability values under different scouring depths to obtain a scouring depth-failure probability curve equation 9;
and 4, step 4: under different scouring depths, fitting the performance state of the structural member and the dynamic response of the structural system to obtain a capability demand ratio model II taking seismic oscillation strength and the scouring depth as variables, and establishing a vulnerability curved surface equation 6 under different scouring depths;
and 5: according to the vulnerability curved surface equation 6, the earthquake risk probability density equation 7 and the scouring risk probability density equation 10 under different scouring depths, a combined average annual failure probability model 11 under the action of earthquake-scouring coupled disasters is established, the average annual failure probability value is obtained through calculation, and the scouring depth obtained in a scouring depth-failure probability curve equation 9 is a reasonable scouring depth 12;
step 6: and taking the ratio of the reasonable scouring depth 12 to the designed scouring depth 14 as a scouring load coefficient 13 under the earthquake-scouring disaster coupling action.
According to the embodiment of the invention, the step 1 of constructing the nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system according to the bridge structure system 1 and the seismic excitation 2 is to simulate the main beam 1-1, the pier 1-2, the pile 1-3, the pile-soil interaction 1-4, the support 1-5, the cable tower 1-6 and the cable bearing system 1-7 in the bridge structure as the components of the bridge structure system 1, wherein: the bridge structure system 1 is simulated by adopting a finite element method, the main beam 1-1, the pier column 1-2 and the cable tower 1-6 are simulated by adopting a beam-column element, the pile-soil interaction 1-4 and the support 1-5 are simulated by adopting a system consisting of mass, springs and dampers, and the cable bearing system is simulated by adopting a truss element. And further solving a nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system to obtain the dynamic response of the structure system.
And then, determining the performance state of the structural component according to the solved dynamic response of the structural system. According to the embodiment of the invention, the performance state of the structural component in the step 2 is determined by the performance states of the main beam 1-1, the pier stud 1-2, the pile 1-3, the support 1-5, the cable tower 1-6 and the cable bearing system 1-7. Wherein: the performance state of the main beam 1-1 is determined by the cross-section yield bending moment and curvature; the performance state of the pier stud 1-2, the performance state of the pile 1-3 and the performance state of the cable tower 1-6 are determined by the ductility of section curvature and the drift rate of each component; the performance state of the support 1-5 is determined using support shear strain.
And then, under the given scouring depth, fitting the performance state of the structural member and the dynamic response of the structural system to obtain a capacity demand ratio model I with the seismic intensity as a variable, and establishing a vulnerability curve equation 4 under the given scouring depth. Or, under different scouring depths, fitting the performance state of the structural component and the dynamic response of the structural system to obtain a capability demand ratio model II with the seismic intensity and the scouring depth as variables, and establishing a vulnerability curved surface equation 6 under different scouring depths.
According to the embodiment of the invention, the expressions of the capability demand ratio model I taking the seismic intensity as a variable in the step 2 and the capability demand ratio model II taking the seismic intensity and the scour depth as variables in the step 4 are respectively as follows:
μd＝g(IM)
μdh＝g(IM，h)
in the formula, mudIs a capability demand ratio model I, mu with seismic intensity as a variabledhIn order to obtain the capacity demand ratio model II taking the earthquake motion intensity and the scouring depth as variables, g is a polynomial equation, IM is the earthquake motion intensity, and h is the scouring depth.
According to the embodiment of the present invention, the vulnerability curve equation 4 at the given scouring depth in step 2 and the vulnerability surface equation 6 at different scouring depths in step 4 are expressed in the following manner:
in the formula, PdFor a given washout depth the vulnerability curve equation 4, PdhEquation 6 of the vulnerability curved surface under different scouring depths, phi is a standard normal distribution function, sigmadVariance, σ, in the model I for the ratio of energy requirements with seismic oscillation intensity as a variabledhThe variance in model II is compared to the capability requirement using seismic intensity and scour depth as variables.
According to an embodiment of the present invention, the probability density equation 7 of the earthquake risk in step 5 is expressed by the probability that the intensity of earthquake motion occurring under the determined field condition is greater than the pre-estimated earthquake motion intensity, and is expressed by:
in the formula, i is seismic intensity, and the relation between i and the seismic intensity IM is as follows:
IM＝10(ilg2-0.01) (3-2)
according to the embodiment of the invention, the average annual failure probability model 8 under the action of given scouring depth and earthquake disaster in the step 3 is the joint probability of the probability density equation of the structural earthquake damage failure probability and earthquake risk, and the expression mode is as follows:
according to the embodiment of the present invention, the scour risk probability density equation 10 in step 5 conforms to a log normal distribution, and the expression manner is as follows:
in the formula, eta is the logarithmic mean value of the scouring depth; ξ is the logarithmic standard deviation of the scour depth.
According to the embodiment of the invention, the joint average annual failure probability model 11 under the action of the earthquake-scour coupling disaster in the step 5 is a joint probability of structural earthquake damage failure probability, probability density of earthquake risk and scour depth risk, and the expression mode is as follows:
according to the embodiment of the invention, the ratio of the reasonable scour depth 12 to the design scour depth 14 is used as the scour load coefficient 13 under the seismic-scour disaster coupling effect in step 6, and the expression mode is as follows:
in the formula, HxRationalization obtained for joint probability density calculationDepth of erosion, HdTo design the depth of the flush.
The method provided by the invention considers the combination of earthquake-scour two disaster coupling effects by adopting a probability-based method, can consider the nonlinear factors in a bridge structure system and the nonlinear effect of the earthquake-scour coupling effects, effectively avoids neglecting the edge effect in disaster combination, and provides an effective method for risk analysis and load combination coefficient determination under the bridge earthquake-scour disaster coupling effect.
Examples
The present invention will be described below by taking a bridge as an example as shown in fig. 2.
A nonlinear dynamic analysis model of the bridge structure is established, wherein the main beam, the pier column and the cable tower are simulated by adopting a beam column unit, the pile-soil interaction and the support are simulated by adopting a system consisting of a mass, a spring and a damper, and the stay cable is simulated by adopting a truss unit, as shown in fig. 2. By adjusting parameters in the pile-soil interaction model, different scouring depths are realized, the dynamic response of the bridge structure under different scouring depths is solved numerically, the vulnerability curves under different scouring depths are established, the vulnerability curves under different scouring depths refer to a formula 2-1, and the corresponding curves are shown in fig. 3.
As shown in fig. 4, an average annual failure probability model under the action of the given scouring depth and the earthquake disaster is established according to the vulnerability curves and the earthquake risk probability density curves under different scouring depths, and the average annual failure probability model refers to a formula 4-1 to calculate an average annual failure probability value under the given scouring depth, so as to obtain a scouring depth-failure probability curve, which is shown in fig. 5.
According to a vulnerability curved surface (formula 2-2, a corresponding curve is shown in figure 6), an earthquake risk probability density curve and a scour risk probability density curve (shown in figure 7) considering scour-earthquake coupling, a combined average annual failure probability model under the action of earthquake-scour coupling disasters is established, the combined average annual failure probability model refers to the formula 6-1, and an average annual failure probability value is calculated and obtained, and is shown in figure 5.
In the flush depth-failure probability curve shown in FIG. 5, the flush depth (H)x) For reasonable scour depth, the scour load coefficient can be calculated by equation 7-1.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for analyzing risks under the coupling effect of bridge earthquake-scour disasters is characterized by comprising the following steps:
constructing a nonlinear dynamic numerical analysis model under the seismic action of a bridge structure system according to the bridge structure system (1) and the seismic excitation (2), and solving the nonlinear dynamic numerical analysis model under the seismic action of the bridge structure system to obtain the dynamic response of the structure system;
under a given scouring depth, fitting the performance state of the structural member and the dynamic response of the structural system to obtain an ability demand ratio model I with seismic intensity as a variable, and establishing a vulnerability curve equation (4) under the given scouring depth;
according to a vulnerability curve equation (4) and an earthquake risk probability density equation (7) under a given scouring depth, an average annual failure probability model (8) under the action of the given scouring depth and the earthquake disaster is established, average annual failure probability values under different scouring depths are calculated, and a scouring depth-failure probability curve equation (9) is obtained;
under different scouring depths, fitting the performance state of the structural component and the dynamic response of the structural system to obtain a capability demand ratio model II taking seismic intensity and the scouring depth as variables, and establishing a vulnerability curved surface equation (6) under different scouring depths;
according to the vulnerability curved surface equation (6), the earthquake risk probability density equation (7) and the scouring risk probability density equation (10) under different scouring depths, a combined average annual failure probability model (11) under the action of earthquake-scouring coupled disasters is established, the average annual failure probability value is obtained through calculation, and the scouring depth obtained in the scouring depth-failure probability curve equation (9) is a reasonable scouring depth (12);
and taking the ratio of the reasonable scouring depth (12) to the designed scouring depth (14) as a scouring load coefficient (13) under the coupling action of earthquake-scouring disasters.
2. The method according to claim 1, characterized in that in the step of constructing a nonlinear dynamical numerical analysis model of the bridge structure system under seismic action from the bridge structure system (1) and seismic excitation (2), the girders (1-1), the piers (1-2), the piles (1-3), the pile-soil interactions (1-4), the supports (1-5), the pylons (1-6), and the cable bearing system (1-7) in the bridge structure are simulated as members of the bridge structure system (1), wherein:
the bridge structure system (1) is simulated by a finite element method, the main beam (1-1), the pier column (1-2) and the cable tower (1-6) are simulated by beam-column elements, the pile-soil interaction (1-4) and the support (1-5) are simulated by a system consisting of mass, springs and dampers, and the cable bearing system is simulated by a truss element.
3. Method according to claim 2, characterized in that the performance status of the structural elements is determined by the performance status of main girders (1-1), piers (1-2), piles (1-3), supports (1-5), pylons (1-6), cable bearing systems (1-7).
4. The method of claim 3,
the performance state of the main beam (1-1) is determined by the cross-section yield bending moment and curvature;
the performance state of the pier column (1-2), the performance state of the pile (1-3) and the performance state of the cable tower (1-6) are determined by the ductility of section curvature and the drift rate of each component;
the performance state of the support (1-5) is determined by the support shear strain.
5. The method according to claim 1, wherein the expressions of the seismic intensity-variant energy demand ratio model I and the seismic intensity-and scour depth-variant energy demand ratio model II are respectively:
μd＝g(IM)
μdh＝g(IM，h)
in the formula, mudIs a capability demand ratio model I, mu with seismic intensity as a variabledhIn order to obtain the capacity demand ratio model II taking the earthquake motion intensity and the scouring depth as variables, g is a polynomial equation, IM is the earthquake motion intensity, and h is the scouring depth.
6. The method according to claim 1, wherein the vulnerability curve equation (4) at the given scour depth and the vulnerability surface equation (6) at the different scour depths are expressed as:
in the formula, PdFor the vulnerability Curve equation (4), P, at a given depth of scourdhIs a surface equation (6) of vulnerability under different scouring depths, phi is a standard normal distribution function, sigmadVariance, σ, in the model I for the ratio of energy requirements with seismic oscillation intensity as a variabledhThe variance in model II is compared to the capability requirement using seismic intensity and scour depth as variables.
7. The method according to claim 1, characterized in that the probability density equation (7) of the earthquake risk is expressed by the probability that the intensity of earthquake motion occurring under certain field conditions is greater than the pre-estimated intensity of earthquake motion, expressed as:
in the formula, i is seismic intensity, and the relation between i and the seismic intensity IM is as follows:
IM＝10(ilg2-0.01) (3-2)
8. the method according to claim 1, characterized in that the model (8) of the mean annual failure probability under the action of seismic disasters at a given scour depth is the joint probability of the probability density equation for structural seismic damage failure probability and seismic risk expressed as:
9. the method of claim 1,
the scouring danger probability density equation (10) conforms to lognormal distribution, and the expression mode is as follows:
in the formula, eta is the logarithmic mean value of the scouring depth; xi is the logarithmic standard deviation of the scouring depth;
the joint average annual failure probability model (11) under the action of the earthquake-scour coupling disaster is a joint probability of structural earthquake damage failure probability, probability density of earthquake risk and scour depth risk, and the expression mode is as follows:
10. the method according to claim 1, characterized in that the ratio of the reasonable scour depth (12) to the design scour depth (14) is used as a scour load coefficient (13) under seismic-scour disaster coupling, expressed as:
in the formula, HxFor reasonable scouring depth, H, calculated from joint probability densityaTo design the depth of the flush.
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