JP6238043B2 - Simple calculation method of residual deformation during liquefaction of soil-structure system - Google Patents

Description

  The present invention relates to a simple method for calculating residual deformation during liquefaction of a ground-structure system. In order to set an appropriate input value, a simple trial analysis can be performed to obtain an analysis result close to an actual phenomenon. The present invention relates to a simple method for calculating residual deformation during liquefaction of a ground-structure system.

  Conventionally, a seismic design work has been performed to create an analysis model that integrates the ground and the structure by a design method such as the finite element method, and analyze the deformation behavior of the ground and the structure due to ground liquefaction (Patent Literature) 1, Non-Patent Document 1, Non-Patent Document 2). In the design work using this analysis model, it takes time and labor to create an analysis model, and input data such as soil parameters is insufficient, and it may not be possible to perform high-precision analysis using a complex analysis model. There are many.

  The ground / structure deformation prediction method described in Patent Document 1 can input ground motion input data into a 3D analysis model developed by the applicant and reproduce ground deformation behavior associated with the occurrence of an earthquake with high accuracy. It is an invention of analysis software. In order to obtain a rough deformation state (residual deformation) of the ground after liquefaction in the actual design work, a design method using such high-precision analysis software is disclosed in Patent Document 1. There is also a need for an analysis method that can obtain an approximate analysis result with a simple analysis model rather than a large-scale and time-consuming analysis model as shown.

For example, when performing analysis (for example, two-dimensional finite element method analysis) to easily determine the residual deformation of the ground or structure after liquefaction, as a model for analysis after liquefaction, the ground elasticity of the ground element is reduced. Assuming a body, static weight analysis is performed to obtain residual deformation of ground and structures. At this time, in order to properly set the ground characteristics after liquefaction, it is important to properly set two input values of ground rigidity and Poisson's ratio. The ground rigidity in a state where the rigidity is reduced at this time is a graph disclosed in the past design guidelines (Non-patent Document 2) and research results (Non-Patent Document 3, Non-Patent Document 4) (for example, FIG. 3, FIG. 4, Referring to FIG. 5), it is known that a predetermined rigidity reduction rate can be taken into account, or can be set based on the FL value and the maximum shear strain γ _max . In the following description of the embodiments, when referring to the graphs disclosed in the above-mentioned non-patent documents (specifically, the following list), they are simply referred to as “Document 1”.

Japanese Patent No. 4640671

Susumu Yasuda et al., “ALID Study Group”, [online], April 5, 2010, Introduction of 2D Liquefaction Flow Analysis Program ALID / Win, [Search April 1, 2013], Internet <http: // www.jibansoft.com/alid_lab.htm> Edited by Architectural Institute of Japan, “Guidelines for Basic Design of Architectural Architecture”, Published by Architectural Institute of Japan, October 2001, pp.61-72 Taiyoshi Noriyoshi and three others, “Effects of shear history during repeated loading on flow characteristics after liquefaction”, Symposium on fluidity and permanent deformation of ground and soil structures during earthquake, Geotechnical Society, 1998, pp . 325, 328, Ishihara, K, andYoshimine.M .: “Evaluation of settlements in sand deposits following liquefaction during earthquakes, SOILS & FOUNDATIONS, Vol.32, No.1, pp.173-188, 1992 (4)

  However, with respect to the Poisson's ratio ν, which is another input value, there has conventionally been no appropriate setting method and an empirical input value has been used. Therefore, it cannot be said that the reliability of the ground subsidence amount and the inclination amount of the structure obtained as the analysis result is high.

  Considering the liquefaction state from the viewpoint of phenomenon, when a soft sandy layer liquefies during an earthquake, the excess pore water pressure increases and the sandy layer becomes nearly liquid. Under such an assumption, the Poisson's ratio ν is considered to be a value very close to 0.5 (for example, 0.499...). At this time, the deformation of the sandy layer is a non-drainage / equal volume condition. In this case, a structure such as a building or a soil structure such as embankment is constructed on the sandy layer to be analyzed, as in the analysis model shown in FIG. 1 (mesh is omitted for explanation). In this example, the structure sinks due to its own weight, as shown in Fig. 2 (2). At this time, since the analysis is performed under an equal volume condition, the surrounding ground is raised by the sinking ground volume integral. It will result in a mode. This analysis result is different from the actual structure subsidence and ground deformation. That is, the ground around the structure also actually subsides due to the dissipation of excess pore water pressure after liquefaction (similar to consolidation subsidence).

  As a countermeasure for matching this analysis result with the actual situation, a method of superimposing the amount of settlement at each node position by consolidation analysis on the analysis result at each node of the analysis model shown in FIG. However, this consolidation analysis needs to be analyzed from moment to moment in combination with the amount of excess pore water pressure generated during an earthquake and the assumption of its dissipation, and the analysis is complicated and laborious. Therefore, it cannot be said that it is an easy-to-use design method from the viewpoint of the practice of simple design as described above. Also, in linear weight analysis, using a value that is reduced without ground as the Poisson's ratio ν has no physical meaning in the amount of settlement. Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art and propose a design method for setting the Poisson's ratio ν used for linear gravity analysis after ground liquefaction by an appropriate method. -To construct a method that can easily evaluate the residual deformation during liquefaction of a structural system.

  According to the present invention, through a simple liquefaction determination calculation based on the existing design guideline, deformation due to ground rigidity reduction due to liquefaction and consolidation deformation due to dissipation of excess pore water pressure can be performed only by linear weight analysis. Residual deformation considering both can be obtained easily. Thereby, there exists an effect that the amount of ground subsidence and inclination including a structure can be evaluated appropriately and simply.

To achieve the above object, the present invention is the residual deformation after liquefaction occurs during an earthquake of ground and structures to be analyzed, there a simple calculation method by a computer determined by linear self-weight analysis by the finite element method element model And calculating the settlement amount δv of the one-dimensional horizontal ground model after liquefaction based on the horizontal displacement Dcy value of the ground surface, and the relationship between the correction N value in the element of each ground layer to be analyzed. Calculates the ground stiffness after liquefaction from the maximum shear strain value γ _max, and uses the ground stiffness and the initial Poisson's ratio ν as input values for the linear weight analysis by the finite element method using the ground and the structure as an element model A step of calculating the subsidence amount δr in the distant ground at, and comparing the δv and δr, under the condition of (ν + Δν) <0.5,
When δv <δr, ν is the input value (ν + Δν)
When δv> δr, ν is an input value (ν−Δν)
And the linear weight analysis is repeated until the difference between δv and δr is equal to or less than a preset threshold, that is, δv ≒ δr, and the difference Δν is used. The step of determining the residual deformation of the ground or structure to be analyzed in the element model is performed.

  As the settlement amount δr at the far ground, it is preferable to use the settlement amount at the side boundary node that is not affected by the behavior of the structure of the analysis model.

The maximum shear strain value γ _max of each element to be analyzed may not be derived from the relationship with the corrected N value, but may be calculated from the effective stress analysis result using the applied shear stress. In this case, a more accurate value can be obtained.

The schematic analysis model figure shown about the method of the residual deformation | transformation simple calculation method (linear weight analysis) at the time of the liquefaction of the ground-structure system by this invention. The analysis flow figure which showed one Embodiment of the analysis flow in the residual deformation | transformation simple calculation method at the time of the liquefaction of the ground-structure system by this invention. The calculation graph of the limit residual shear strain (gamma) _max used in the analysis process of this invention (an addition to the table of literature 2 publication). The graph published in the literature 3 which showed the relationship between the maximum shear strain at the time of an earthquake, and the rigidity fall rate after liquefaction. The graph published in the literature 4 which showed the relationship between the maximum shear strain (gamma) _max at the time of an earthquake, and the volume strain (epsilon) _v of each element after liquefaction. The graph as described in the past literature which showed the relationship between FL value and the rigidity fall rate after liquefaction.

  Hereinafter, the following embodiment will be described with reference to the accompanying drawings as an embodiment for carrying out the method for easily calculating the residual deformation during liquefaction of the ground-structure system of the present invention.

[Basic analysis]
A method for analyzing the deformation state after liquefaction occurs in the target ground will be described. The analysis method is based on a finite element method (FEM) linear weight analysis performed by a computer. A feature of the present invention is to propose a method for setting an appropriate Poisson's ratio ν as an analysis input value. The analysis flow of linear weight analysis performed based on the input value will be described below. FIG. 2 is an analysis flow diagram showing a schematic procedure of a series of linear weight analysis from setting of each input value to obtaining residual deformation performed by the computer.

First, assuming the ground surface maximum acceleration α _max of the target ground, input shear stress as an external force, input density of the target ground, N value, and particle size distribution are set. Based on these, the maximum shear strain γ _max of each layer is obtained from the graph of FIG. 3 (added to the chart shown in Reference 2). Similarly, from the repeated shear strain γ _cy , a D _cy value (horizontal displacement amount due to liquefaction) is set with reference to the publication chart of Reference 2, and the settlement amount of the target ground horizontal ground is obtained from the value. This subsidence phenomenon is considered to be a subsidence corresponding to volumetric strain due to dissipation of excess pore water pressure, and corresponds to a consolidation component.

On the other hand, the ground stiffness is calculated from the γ _{max according} to the graph of FIG. Using this ground stiffness value and initially assumed Poisson's ratio ν (= 0.490), two-dimensional or three-dimensional FEM linear weight analysis is performed. The ground side boundary of the analysis model at this time is preferably set sufficiently far from the structure, and is set to a range up to the extent that the settlement distribution on the ground surface is uniform. In this case, the analysis result of the far ground as the analysis result can be regarded as free ground that is not affected by the structure. Therefore, the value of the Poisson's ratio ν is determined so that the subsidence amount Δr of the far ground matches the subsidence amount Δv of the horizontal free ground (one-dimensional ground). For this purpose, linear self-weight analysis is performed by a trial in which the value of Poisson's ratio ν is changed. That is, ν of the first analysis is set to 0.490, and the settlement amount δr of the far ground in the analysis model is compared with the settlement amount δv of the one-dimensional (1D) horizontal ground. If δr> δv, The initial Poisson's ratio ν is increased to a value close to 0.5 (ν + Δν), and if it is smaller, ν is decreased (ν−Δν). The difference Δν at that time is preferably set to about 0.001 to 0.005. The condition that the settlement amount δr of the distant ground matches the settlement amount δv of the horizontal free ground (one-dimensional ground) is set so that the difference between δr and δv is less than a predetermined threshold value, and is repeated until the result is obtained. Perform the operation. Since the series of trial analysis described above is linear weight analysis, it is very simple and requires a short calculation time. Therefore, it is possible to easily calculate the integrated settlement amount of the ground-structure system, the inclination angle of the structure, and the like.

  Hereinafter, if there is another analysis result in the analysis target ground, an optional analysis that can obtain a more accurate result by using the analysis result is also possible. The contents will be briefly described below.

[Option analysis (1)]
If there is a ground response analysis result of the target ground, it is possible to predict the residual deformation using the applied shear stress τ instead of the ground surface acceleration α _max assumed in the basic analysis described above, and taking into account the effects of differences in the input seismic waveform Can do.

[Option analysis (2)]
If there is an effective stress analysis result based on a one-dimensional ground model of the target ground, the accuracy can be further improved by using γ _max of each element. For example, by using the graph of FIG. 5 (table shown in Reference 4), the volumetric strain ε _v of each element after liquefaction is obtained from the maximum shear strain γ _max of each element of the effective stress analysis result to calculate the consolidation settlement amount. be able to.

[Option analysis (3)]
Furthermore, using the graph (FIG. 6) showing the relationship between the FL value and the rigidity reduction rate after liquefaction, which is applied in the “two-dimensional liquefaction flow analysis program ALID / Win” disclosed in Document 1. It is also possible to calculate the ground stiffness after liquefaction (the rate of decrease in ground stiffness).

  In addition, this invention is not limited to the Example mentioned above, A various change within the range shown to each claim is possible. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

δr Subsidence amount of distant ground δv Subsidence amount of horizontal ground

Claims (3)

Residual deformation after liquefaction occurs during an earthquake of ground and structures to be analyzed, the computer is a simple calculation method for obtaining the linear self-weight analysis by the finite element method element model,
Calculating the settlement amount δv of the one-dimensional horizontal ground model after liquefaction based on the ground surface horizontal displacement Dcy value;
The ground stiffness after liquefaction is calculated from the maximum shear strain value γ _max set based on the relationship with the corrected N value in the element of each ground layer to be analyzed, and the ground stiffness and the initial Poisson's ratio ν are used as input values. Calculating a subsidence amount δr in a distant ground in a linear weight analysis by a finite element method using the ground and structure as an element model;
Compare δv and δr, and under the condition of (ν + Δν) <0.5,
When δv <δr, ν is the input value (ν + Δν)
When δv> δr, ν is an input value (ν−Δν)
The linear weight analysis is repeated until the difference between δv and δr is equal to or less than a preset threshold, that is, δv ≒ δr,
A step of determining a residual deformation of a ground or a structure to be analyzed in the element model based on the result of the repeated calculation. A method for simply calculating a residual deformation during liquefaction of a ground-structure system. Subsidence δr at the distant ground uses subsidence at the side boundary nodes of the element model that is not affected by the behavior of the structure of the element model, soil according to claim 1 - Structural System For simple calculation of residual deformation during liquefaction. The method for easily calculating a residual deformation at the time of liquefaction of a ground-structure system according to claim 1, wherein the maximum shear strain value γ _max of each element to be analyzed is calculated from an effective stress analysis result using an acting shear stress. .

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