CN112926118A - Transformer substation engineering deep foundation soil-structure cooperative analysis method - Google Patents
Transformer substation engineering deep foundation soil-structure cooperative analysis method Download PDFInfo
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Abstract
The invention provides a transformer substation engineering deep foundation soil-structure collaborative analysis method which comprises pile-raft foundation finite element collaborative analysis and seismic response analysis, wherein the finite element collaborative analysis comprises pile-raft foundation design, three-dimensional finite element modeling, pile-raft scheme design and pile-raft stress analysis; the seismic response analysis includes finite element modeling, seismic simulation scheme design, and response analysis. The cooperative analysis method provided by the invention simulates the stress condition and the seismic reaction condition of the transformer substation foundation under different schemes by means of finite element analysis software, and can select the optimal scheme for construction according to geological conditions.
Description
Technical Field
The invention belongs to the technical field of finite element analysis, and particularly relates to a transformer substation engineering deep foundation soil-structure collaborative analysis method.
Background
The electric power system is an important lifeline project for guaranteeing normal life and production activities of people. A substation is an important electrical facility in an electrical power system that transforms voltage, receives and distributes electrical energy, controls the flow of electrical power, and regulates voltage. Buildings in a transformer substation mainly comprise a master control communication building, a production comprehensive building, a distribution room, a capacitor room and the like, and are generally provided with primary equipment such as a transformer, a high-voltage circuit breaker, a bus, a capacitor, an electric reactor and the like, and secondary equipment such as a relay protection device, a measurement and control device, a metering device, an automation system and the like.
In order to ensure the normal operation of the transformer substation and the good connection of pipelines and have strict requirements on the total settlement and the uneven settlement of the transformer substation foundation, raft foundations, pile foundations or piled raft foundations are often adopted. The settlement and bearing characteristics of the pile foundation are influenced by various factors such as soil layer distribution, pile forming mode, pile length and pile spacing. Pile foundation settlement is calculated by adopting an equivalent effect layer summation method and combining an angular point method according to a standard method, the nonlinearity and the elastoplasticity of a soil body are ignored, and the interaction and the three-dimensional space effect among an upper load, a raft plate, a pile foundation and the soil body are not considered. For the complex conditions of uneven stratum distribution and related upper load-piled raft foundation-foundation interaction, better pile length design parameters are difficult to obtain by simplifying more methods.
The theoretical research on the seismic performance of the transformer substation structure in China is lagged, and the reliability and the safety of the current transformer substation structure design are low. In the design of a transformer substation, in order to ensure that the deformation of a foundation meets requirements, raft foundations and pile foundations are often adopted. At present, research results considering dynamic interaction of foundation-pile foundation-superstructure have been few, but related research aiming at the structure of a transformer substation has not been common yet.
Disclosure of Invention
The purpose of the invention is as follows: based on the existing transformer substation foundation analysis technology, a transformer substation engineering deep foundation soil-structure collaborative analysis method and a manufacturing method thereof are provided.
A transformer substation engineering deep foundation soil-structure collaborative analysis method is characterized in that finite element simulation analysis is carried out on a foundation structure of a transformer substation to determine the design scheme and the seismic strength of a piled raft foundation structure, and the method comprises the steps of finite element collaborative analysis and seismic reaction analysis of the piled raft foundation.
Preferably, the finite element cooperative analysis of the piled raft foundation comprises the following steps
Designing a piled raft foundation: selecting a proper pile-raft combination according to the actual construction position of the transformer substation and combining with the land condition;
three-dimensional finite element modeling: establishing a three-dimensional finite element model according to the pile-raft structure and the stratum distribution;
pile raft scheme design: designing different pile foundation lengths to fully simulate the influence of different pile lengths on the working condition;
analyzing the stress of the pile raft: and (4) performing simulation analysis on the stress condition of the pile raft structure, and selecting an optimal scheme.
Preferably, the three-dimensional finite element modeling comprises embedded pile elements, geometric models and material parameters.
Preferably, the analysis of the stress of the pile and raft comprises raft settlement, foundation settlement and pile foundation stress.
Preferably, the seismic response analysis comprises the steps of:
finite element modeling: establishing a finite element model based on a stratum boundary and geological characteristics aiming at the geotechnical terrain where the transformer substation is located;
designing a seismic simulation scheme: designing different simulation schemes according to different pile lengths and seismic wave forms so as to fully simulate the response condition of the structure;
response analysis: and selecting an optimal scheme according to the response condition of the pile foundation structure to the seismic waves.
Preferably, the finite element modeling includes dynamic boundary, geometric model and meshing and material parameters.
Preferably, the response analysis includes field response analysis, structural response analysis, pile length response analysis, and seismic peak and waveform impact analysis.
The invention has the beneficial effects that: the invention takes the pile-raft foundation engineering of the transformer substation as the background, considers the condition of non-uniform distribution of the bearing stratum, and carries out the pile-raft foundation cooperative analysis under the condition of non-uniform stratum distribution by establishing a three-dimensional finite element model, thereby providing reference for the pile length optimization design based on settlement deformation control under similar working conditions. Starting from a coupling system of a transformer substation pile foundation-raft plate-distribution building structure, establishing a pile-raft-soil-basement-superstructure three-dimensional finite element power interaction integral model, and analyzing the power response and the seismic performance of the system under the action of different seismic levels and different seismic waves by considering the elastic-plastic property and the small strain characteristic of a soil body.
Drawings
Fig. 1 is a flow chart of finite element cooperative analysis of a piled raft foundation;
FIG. 2 is a flow chart of seismic response analysis;
fig. 3 is a schematic plan view of a pile foundation;
FIG. 4 is a schematic view of an embedded beam element;
FIG. 5 is a schematic diagram of a three-dimensional geometric model of a stratum and a pile raft structure;
FIG. 6 is a schematic diagram of a pile length variation simulation scheme;
fig. 7 is a raft plate cross-section settlement curve;
FIG. 8 is a sectional view of a foundation settlement cloud;
FIG. 9 is a pile foundation axial force distribution diagram;
FIG. 10 is a pile foundation side friction resistance profile;
FIG. 11 is a schematic view of a geometric model of formation distribution;
FIG. 12 is a diagram illustrating HSS model hysteresis behavior;
FIG. 13 is a horizontal acceleration response spectrum of a surface measurement point;
FIG. 14 is a graph of roof and floor power spectra;
FIG. 15 is a time course curve of horizontal displacement of a roof measuring point;
FIG. 16 is a graph of pile tip axial force time course;
FIG. 17 is a graph of the time course of the pile top toy;
FIG. 18 is a graph of roof vibration time course;
FIG. 19 is a graph of the horizontal acceleration time course of the roof at different seismic levels;
FIG. 20 is a graph of the time course of the horizontal acceleration of the lower base plate at different seismic levels;
FIG. 21 is a graph of horizontal acceleration time course of the downstairs with the same magnitude of seismic waves at different locations;
FIG. 22 is a graph of the horizontal acceleration time course of the bottom plate under the same magnitude of seismic waves with different seismic waves;
figure 23 is a graph of the same gathered down-roof PSA curves for different seismic waves.
Detailed Description
The present invention is further illustrated by the following specific examples.
Example (b):
the landform type of the area where the site of the proposed transformer substation is located belongs to the salinized coastal plain in the northeast of China, the terrain is low-lying, flat and wide, the area slowly inclines from the northwest to the southeast, the site area is a salt pond at present, and accumulated water is stored in the salt pond.
The field stratum is totally new system landform alluvial by the fourth system
Terrestrial allusion to swamp phase deposition
And the upper update of the systematic alluvial product
The formed silt, silty clay and silt layer. From the viewpoint of geotechnical engineering properties, the stratum revealed in the field has large variation and difference in the vertical direction. Therefore, the engineering geological unit layer is divided into 8 large engineering geological unit layers according to the characteristics of the engineering geological unit layer, including silty clay, silty sand, silty clay, silty soil, silty sand, silty clay, silty sand and silty soil. The physical and mechanical parameters of the soil body are shown in the table 1.
TABLE 1 physical and mechanical parameters of rock and soil mass
Pile-raft foundation design
The distribution equipment building is designed by adopting a cast-in-place flat-plate raft type foundation, the thickness of a raft plate is 0.8m, the foundation is positioned on the second powdery clay layer, a pile foundation is arranged under the raft plate, a pile end bearing layer is composed of silt and silt, and a limit end resistance standard value q is a limit end resistance standard valuepk was 3000 kPa and 2000 kPa, respectively, and the standard values of the limiting side resistances are shown in Table 1.
The pile type adopts prefabricated reinforced concrete square piles, the cross section size of each pile is 0.4m multiplied by 0.4m, the effective pile length is 19m, and the grid type arrangement of the piles is shown in figure 3, wherein the pile spacing is 1.8-2.4 m, and 757 piles are arranged. The vertical ultimate bearing capacity of the single pile is 2000 kN, and the characteristic value R of the vertical bearing capacity of the single pile is designeda＝1 000kN。
Three-dimensional finite element modeling
Embedded pile unit
Embedded beams have been developed to describe the interaction of piles, anchors or bolts with their surrounding soil or rock. The interaction of the embedded beam perimeter and bottom is described by the embedded interface elements. The pile, anchor or bolt is considered as a beam that can be passed through the volume unit in any direction at any location, as in fig. 4, and due to the presence of the beam unit, three additional nodes are introduced in the volume unit.
Pile-soil interaction comprises side friction resistance and end resistance, and the side friction and pile end force exertion magnitude is determined by pile-soil relative displacement. Although the embedded pile unit itself has no volume, the pile perimeter is assumed to be an elastic region in which no plastic behavior occurs. The size of the spring zone depends on the (equivalent) diameter of the embedded pile input, so that the embedded pile behaves like a volumetric pile. But the Embedded pile cannot take the pile driving effect into account, and the simulated pile-soil interaction occurs on the pile axis, rather than the interaction of the cylindrical side surface of the elastic region around the pile and the surrounding soil.
Geometric model
And (3) according to the actual stratum distribution and the arrangement condition of the raft plates and the pile foundations, adopting PLAAXIS 3D to establish a non-uniform stratum pile raft foundation three-dimensional model, as shown in figure 5. In PLAAXIS 3D, non-uniformly distributed formations are built from actual borehole plan placement and borehole histograms.
Parameters of the material
The rock-soil body is simulated by a small strain soil hardening model (HSS), the HSS model comprises more than ten input parameters, conventional weight gamma, strength parameter cohesive force c ', internal friction angle phi' and shear expansion angle psi, and a rigidity parameter consolidation test reference tangent modulus is required to be input
Triaxial drainage shear test reference secant modulus
Reference loading and unloading modulus of triaxial drainage shear test
Stiffness stress level dependent power exponent m, and two small strain parameters, i.e. reference initial modulus of small strain stiffness test
And the shear strain gamma corresponding to the decay of the secant shear modulus to 70% of the initial shear modulus0.7. The strength parameters are the same as those of a Moire-Coulomb model, the rigidity parameters and the small strain parameters can be obtained through indoor tests, and can be determined according to the compression modulus values provided by the conventional geotechnical tests in combination with empirical relations in the absence of test data.
Pile raft scheme design
In order to research the influence of pile length change on foundation settlement under the condition of non-uniformly distributed strata, better pile length design parameters are obtained, and simulation analysis of variable pile length and multiple working conditions is carried out. The following four simulation schemes are designed:
in the scheme 1, the pile length is determined according to the fluctuation condition of a bearing stratum, the pile end is embedded into the bearing stratum by 1m (about 2.5 times of the pile diameter), and the pile length is different from 29m to 14m from left to right, as shown in fig. 6 (a);
in the scheme 2, on the basis of the scheme 1, the long pile is shortened by 2m, the short pile is lengthened by 1.5m, and the pile length is different from 27m to 15.5m from left to right, as shown in fig. 6 (b);
in the scheme 3, on the basis of the scheme 2, the long pile is shortened by 5m, the short pile is lengthened by 4m, and the pile length is different from 22m to 19.5m from left to right, as shown in fig. 6 (c);
in case 4, the pile length is equal to 19m with reference to the uniform stratum condition, as shown in fig. 6 (d).
Raft plate stress analysis
Raft sedimentation
The raft cross-sectional deformation curves were exported as shown in fig. 7.
From the overall and section distribution characteristics of raft sedimentation deformation and the pile length arrangement condition of each scheme, the lower pile foundation of the raft in the scheme 1 is long at the left and short at the right, the pile end is embedded into a bearing layer by 1m, the maximum pile length at the left is 29m, the minimum pile length at the right is 14m, the difference of the pile lengths at the left end and the right end is 15m, the sedimentation distribution of the corresponding raft is most uneven and has the distribution characteristics of small left and large right, and the differential sedimentation at the left side and the right side of the raft is 15.13 mm; scheme 2 the difference of pile lengths on the left side and the right side of the raft is reduced by 3.5m compared with scheme 1, but still reaches 11.5m, the settlement of the raft is shown to be large on the left and small on the right, and the difference settlement on the two sides of the raft is still large and reaches 13.70 mm; scheme 3, the pile length arrangement under the raft is further adjusted, the maximum and minimum pile length difference is reduced to 2.5m, at the moment, the sedimentation of the raft is relatively uniform, the sedimentation distribution of the raft is also adjusted to be the typical disc-shaped sedimentation distribution characteristics with large middle and small periphery, and the maximum differential sedimentation of the raft is reduced to 9.45 mm; scheme 4 is directly arranged according to equal pile length, and due to the non-uniformity of the distribution of the pile end bearing force layer, the sedimentation distribution characteristics of the raft are opposite to those of scheme 1 and scheme 2, and the raft is shown to be large at the left and small at the right, and the maximum differential sedimentation is 12.57 mm.
Along with the change of the pile length arrangement of each scheme, the pile length at the lower left side of the raft from the scheme 1 to the scheme 4 is gradually shortened, the pile length at the right side is gradually increased, the maximum sedimentation value of the raft is changed along with the pile length, the position where the maximum sedimentation of the raft occurs is gradually transferred from the right side of the raft to the middle of the raft and even to the left side of the raft, and the sedimentation distribution of the raft is also represented by two different distribution characteristics of asymmetric distribution and disc-shaped distribution. The sedimentation deformation distribution relative difference of the raft plates under each scheme can be displayed more clearly, and the scheme 3 is obviously superior to other schemes, the maximum sedimentation value and the differential sedimentation of the raft plates are minimum, and the sedimentation distribution of the raft plates is relatively more uniform.
Foundation settlement
As can be seen from fig. 7, the sedimentation distribution characteristics along the transverse direction of the raft under each scheme are basically consistent and are distributed approximately symmetrically. Here, the settlement deformation of the longitudinal section of the stratum is mainly output along the longitudinal direction of the raft, as shown in fig. 8.
The pile length of the scheme 1 and the scheme 2 is left long and right short, although the top surface burial depth of the right bearing stratum is shallow relative to the left side, the right side of the foundation is higher than the left side obviously due to the short pile length on the right side, and the settlement deformation difference of the longitudinal section of the foundation under the raft is large. The pile length of the scheme 4 is equal, but the buried depth of the left supporting layer is relatively large, the buried depth of the right supporting layer is relatively shallow, and the stratum distribution is uneven, so that the left side of the foundation is higher than the right side of the foundation in the condition of equal pile length, but the deformation distribution condition of the foundation of the scheme 4 is more uniform than that of the scheme 1 and the scheme 2. Compared with other schemes, the foundation deformation of the scheme 3 is much more uniform, which shows that the pile length arrangement, the stratum distribution and the upper load reach a better balance state at the moment.
Pile foundation stress
In order to observe the stress of the pile body and the development of the side frictional resistance of the pile, 4 corner piles (P1, P2, P4 and P5) and a center pile (P3) in the figure 3 are selected, and the distribution of the axial force and the side frictional resistance of the pile body along the length of the pile is extracted, as shown in figures 9 and 10.
As can be seen from fig. 9: the axial force distribution of 5 piles is gradually attenuated from the pile top downwards, except for P1, the axial force attenuation rate of each pile in the depth range of 10-15 m below the pile top is slow, the axial force of the pile body below 15m is fast reduced, and the numerical value of the axial force and the change condition of the axial force along the pile body are different along with the difference of the pile length, the soil around the pile, the soil property at the pile end and the position of the pile. The angle piles P1, P2, P4 and P5 are respectively arranged at the corners of the two longitudinal ends of the raft, the pile length of the angle piles changes along with different calculation schemes, and accordingly, the pile body axial force distribution also changes along with the change of the pile length, which is characterized in that the longer the pile length is, the smaller the pile top axial force extreme value is relatively, and conversely, the shorter the pile length is, the larger the pile top axial force extreme value is, namely, the load shared by the pile top is relatively larger at the moment, and the corresponding pile top (raft) is also higher in settlement.
As can be seen from fig. 10, in general, the side frictional resistance is weak in the depth range from below the pile top to 10-15 m, and the side frictional resistance of the pile below 15m is rapidly increased, which corresponds to the law that the axial force of the pile body slowly attenuates along the depth and then rapidly attenuates below the depth of 15m as shown in fig. 9. According to the distribution condition of soil layers, the compactness of the soil body within the depth range of 10m below the pile top is relatively low, the shear strength and the compression modulus are not high, the limit side resistance is small, and the side frictional resistance of the pile is not good in exertion. The silt layer and the silt layer in the deep part are taken as pile end holding layers, the constraint effect on the pile is large, the limit side resistance is relatively high, the pile length in the corresponding area is large at the moment, and the raft sedimentation is relatively small.
Small knot
Finite element analysis results show that with the change of pile length arrangement of different areas under the raft in 4 schemes, the sedimentation distribution form, the maximum sedimentation value and the position where the maximum sedimentation value appears of the raft correspondingly change, wherein scheme 3 is obviously superior to other 3 schemes, the maximum sedimentation value and the differential sedimentation value of the raft are relatively minimum, the sedimentation distribution of the raft is relatively uniform and is in disc-shaped distribution, the pile length of each area is adapted to the soil layer distribution at the moment, the effect of well adjusting the sedimentation of the raft and the foundation is achieved, and the sedimentation of the raft of other 3 schemes is in asymmetric distribution.
Substation seismic response analysis
Finite element modeling
Dynamic boundary
For the x-direction damper, the normal and tangential stress components that are transferred from the free-field cells to the main grid are as follows.
Where ρ is the material density, VpAnd VsRespectively compressional wave velocity and shearThe speed of the wave is controlled by the speed of the wave,
and
particle velocities in the main grid and free field cells, C, respectively1And C2To correct for the relaxation coefficient of the absorption effect. When the compressional wave is only perpendicular to the boundary, then C1＝C2＝1。
The equivalent stress component at the flexible substrate boundary is given by:
in the formula (I), the compound is shown in the specification,
and
representing upward and downward mass point velocities, which can be considered displacements in the flexible base unit and the primary mesh, respectively. If the relaxation coefficient C1And C2Equal to 1, the flexible substrate boundary will work properly.
The peak acceleration and the frequency spectrum characteristic of the seismic waves have important influence on the structural dynamic response, the excellent frequencies of the seismic waves are different, the reactions of the structural objects with different periods are different, and if the frequency of the seismic waves is close to the natural vibration frequency of the structural objects, the resonance effect can occur. To account for these effects, three seismic motion inputs were chosen, namely, the U.S. Ugland seismic waves, Kobe waves, and Taft waves in 1990.
Geometric model and meshing
The whole superstructure-basement-piled raft foundation-stratum three-dimensional finite element model built by using PLAAXIS 3D is shown in figure 11.
The model rock-soil body adopts 10-node tetrahedral units to divide the grids, the floor slab, the raft and the side wall adopt 6-node plate unit simulation, the structural column adopts 3-node beam unit simulation, and the pile foundation adopts 3-node embedded pile unit simulation.
In the seismic analysis, only seismic motion along the x direction is considered, seismic motion load is applied to the bottom boundary of the model along the x direction, a flexible bottom boundary is arranged, free field boundaries are arranged on two sides of the model in the x direction, and normal constraint is arranged on two side boundaries of the model in the y direction.
Parameters of the material
The rock-soil body is simulated by a small strain soil hardening model (HSS). Under the condition of power, the soil body is subjected to cyclic shear loading, and shows both nonlinear behavior and energy dissipation behavior to form a hysteresis loop. The earthquake action can cause small strain in the soil body, and the soil body shows high shear rigidity G0When the amplitude of the shear strain gamma is increased to aggravate the energy consumption, the soil shear stiffness G is reduced.
The stress correlation of the soil body in the HSS model is represented by the following formula
Wherein the initial shear stiffness G0Is a function of the parameters such as effective stress, strength parameters (c and phi) and m, and is related to the type of soil; p is a radical ofrefIs the reference confining pressure.
The typical hysteretic behavior of the soil is shown in figure 12. Initial tangent and secant stiffness and maximum shear stiffness G of initial loading curve0And (5) the consistency is achieved. As the shear strain increases, the stiffness decays. When the loading direction is reversed, the rigidity is changed from the same G0Go out and then go down to the next load reversal. The stress-strain relationship is as follows
τ＝Gs·γ
Wherein G issSecant modulus.
The local hysteretic damping ratio is obtained by:
in the formula, EDWhich is representative of the energy dissipated,the (a + B region) is given by the hysteresis loop containment region. ESIs the energy build-up at maximum shear strain (B + C region). The damping ratio ξ is applied until the material behavior retains elasticity and the shear modulus decays with strain. The model parameters can be verified according to field measured data and indoor test results.
In HSS model, soil stiffness parameters
According to the following steps: 1: (3-5) value and small strain parameter gamma0.7Taking 0.0001 to 0.0003,
is taken as
2 times of[25]. The soil strength parameters are the same as in the Mohr-Coulomb model, see Table 1.
Simulation scheme
And designing 7 simulation schemes in total, and analyzing the dynamic response of the soil and the structure under the conditions of existence of the structure, different pile lengths, different seismic waves, different seismic peak acceleration and the like. In the calculation process, monitoring points are arranged at the center, the side edges and the angular points of the bottom of the basic raft so as to analyze the dynamic response of the basic raft.
Activating a structural model, wherein the pile length is 19m, calculating for 10s by adopting Uppland seismic waves and the seismic dynamic acceleration peak value is 0.2 g;
in the scheme 4, on the basis of the scheme 2, the earthquake motion peak acceleration is increased to 0.4 g;
in the scheme 5, on the basis of the scheme 2, the earthquake motion peak acceleration is increased to 0.6 g;
in case 7, in addition to case 2, the same acceleration of 0.2g is converted by using the Taft wave.
Analysis of results
Site response analysis
Under the same input seismic action, horizontal acceleration response spectrums of the earth surface points at distances of 1m, 25m and 50m are respectively output to the model of the scheme 1 and the model of the scheme 2, as shown in fig. 13. It can be seen that the response spectra of the surface points close to the structure (fig. 13(a)) are similar in both cases, the maximum acceleration response of the free field is generally higher than that of the added structure, the acceleration response is larger when the inherent period of the field and the structure is 0.15-0.6 s, wherein the excellent period corresponding to the maximum response of the field is about 0.4 s; the reaction spectra of a ground surface point (figure 13(b)) 25m away from the structure are greatly different under two conditions, the acceleration reaction of the ground surface point is the largest when the period of the free field is 0.2-0.3 s, the acceleration reaction of the ground surface point is the largest when the structure is added and the period is 0.08-0.2 s, the maximum horizontal acceleration in the range of 0.01-0.2 s is higher than that of the free field, and the maximum horizontal acceleration is lower than that of the free field when the period is more than 0.2 s; the surface point 50m from the structure (fig. 13(c)), the maximum horizontal acceleration response at this point after the structure is added is generally higher than in the case of the free field. Generally, after the combined action of the structure, the pile foundation and the soil body is considered, the horizontal acceleration response spectrum of the ground surface and the free field generate obvious difference, the difference is different along with the distance from the structure, the horizontal acceleration response of the ground surface point 25m away from the structure is the largest, the horizontal acceleration response of the ground surface point 1m away from the structure is the smallest, and the horizontal acceleration response of the ground surface point 50m away from the structure is the smallest.
Structural response analysis
The survey point spectrogram was output by fast fourier transform, as shown in fig. 14. It can be seen that the maximum amplitude frequency of the monitoring points of the roof and the bottom plate of the structure is in the range of 2-4 Hz. From the time course curve of the displacement of the roof measuring point shown in fig. 15, the natural vibration period of the structure is about 0.567s (corresponding to the frequency of 1.765 Hz). Scheme 2, the length of the pile is 19m, and the pile end enters a silt layer. And outputting time-course curves of the axial force and the bending moment of the pile top measuring point of the center pile, as shown in fig. 16 and 17, the total variation range of the axial force and the bending moment is small and is within 3%.
Pile length impact analysis
The time course of the horizontal acceleration of the roof measuring point under the pile length schemes of the scheme 3 and the scheme 2 is shown in a figure 18, and the peak value of the vibration acceleration of the structure is slightly reduced after the pile length is shortened by 6m (the scheme 3). The analysis is that compared with the soil body, the pile has larger rigidity and smaller damping, the long pile scheme is equivalent to reinforcing a deeper soil layer, the comprehensive rigidity is improved, and the pile end of the long pile extends into a silt layer, so that the long pile has a favorable effect on the transmission of earthquake motion to an upper structure. Therefore, from a structural seismic point of view, the longer the pile length is, the better, which also indicates the necessity of conducting seismic analysis in the pile foundation design in consideration of the foundation-soil-structure interaction.
Seismic peak and waveform impact analysis
As shown in fig. 19 and 20, which are acceleration time courses of the top of the structure and the bottom of the basement when the same seismic wave and different seismic wave input peak values are respectively shown, it can be seen that as the input seismic wave peak value increases, the horizontal acceleration peak value of the top of the structure also increases, and is not obvious enough for the bottom of the basement. Meanwhile, the horizontal acceleration time courses of the top of the structure and the bottom plate of the basement under the same seismic peak of different seismic waves are output, as shown in fig. 21 and 20. It can be seen that the peak acceleration differs from seismic wave to seismic wave, whether the structure is top or bottom, but the peak acceleration is the same. It can be seen from fig. 23 that the excellent period difference of the horizontal acceleration response of the structural roof caused by different seismic waves is not large, but the maximum horizontal acceleration response of the roof caused by the Kobe waves at the periods of 0.01 to 0.15s and 0.4 to 1.15s is obviously higher than the cases of the input Upland waves and the Taft waves. This is because even though the peak acceleration is the same, the spectral characteristics of different seismic waves are different, which results in differences in structural dynamic response characteristics. Therefore, the design of the transformer substation pile foundation should be subjected to auxiliary checking calculation through earthquake time course analysis considering soil-structure interaction as much as possible so as to more accurately evaluate the structural earthquake response performance under a specific pile foundation scheme.
Summary of the invention
In the aspect of earthquake-resistant design, three-dimensional finite element power time course analysis considering pile-soil-structure interaction can be used for obtaining that most transformer substation buildings are low-rise structures, the self-vibration period is short, the self-vibration period is close to the excellent period of a site, and the resonance problem needs to be concerned; the characteristics of pile length and pile end bearing layer have certain influence on the anti-seismic performance of the structure, and the longer the pile is, the better the anti-seismic performance of the structure is; the structural dynamic response varies with the intensity of the earth vibration and the frequency spectrum characteristic.
In general, in consideration of the field geological conditions and the complexity of the foundation-structure static-dynamic interaction in the actual engineering, in the static-dynamic design calculation of the pile foundation of the transformer substation, besides a standard method, a three-dimensional finite element method is preferably adopted to establish a foundation-structure static analysis and dynamic analysis integral numerical model reflecting the actual engineering conditions, the soil body mechanical properties and the soil structure interaction under the static-dynamic condition are reasonably considered, and auxiliary checking calculation is provided for determining a reasonable design scheme of the pile foundation.
Claims (7)
1. A transformer substation engineering deep foundation soil-structure collaborative analysis method is characterized by comprising the following steps: and carrying out finite element simulation analysis on the foundation structure of the transformer substation to determine the design scheme and the seismic strength of the piled raft foundation structure, wherein the finite element cooperation analysis and the seismic reaction analysis are carried out on the piled raft foundation.
2. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 1, is characterized in that: the finite element cooperative analysis of the piled raft foundation comprises the following steps
Designing a piled raft foundation: selecting a proper pile-raft combination according to the actual construction position of the transformer substation and combining with the land condition;
three-dimensional finite element modeling: establishing a three-dimensional finite element model according to the pile-raft structure and the stratum distribution;
pile raft scheme design: designing different pile foundation lengths to fully simulate the influence of different pile lengths on the working condition;
analyzing the stress of the pile raft: and (4) performing simulation analysis on the stress condition of the pile raft structure, and selecting an optimal scheme.
3. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 2, is characterized in that: the three-dimensional finite element modeling comprises an embedded pile unit, a geometric model and material parameters.
4. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 2, is characterized in that: and the pile raft stress analysis comprises raft settlement, foundation settlement and pile foundation stress.
5. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 1, is characterized in that: the seismic response analysis comprises the following steps:
finite element modeling: establishing a finite element model based on a stratum boundary and geological characteristics aiming at the geotechnical terrain where the transformer substation is located;
designing a seismic simulation scheme: designing different simulation schemes according to different pile lengths and seismic wave forms so as to fully simulate the response condition of the structure;
response analysis: and selecting an optimal scheme according to the response condition of the pile foundation structure to the seismic waves.
6. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 5, is characterized in that: the finite element modeling comprises dynamic boundary, geometric model, mesh division and material parameters.
7. The transformer substation engineering deep foundation soil-structure collaborative analysis method according to claim 5, is characterized in that: the response analysis comprises field response analysis, structural response analysis, pile length response analysis and earthquake peak value and waveform influence analysis.
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