CN107885947B - Method for weakening ground vibration caused by large-scale structure collapse - Google Patents
Method for weakening ground vibration caused by large-scale structure collapse Download PDFInfo
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- CN107885947B CN107885947B CN201711184986.2A CN201711184986A CN107885947B CN 107885947 B CN107885947 B CN 107885947B CN 201711184986 A CN201711184986 A CN 201711184986A CN 107885947 B CN107885947 B CN 107885947B
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Abstract
The invention provides a method for weakening ground vibration caused by collapse of a large structure, which comprises the following steps: i) determining the ground range of rubble accumulation after the structure collapses; II) providing damping cushions, designing and selecting preliminary physical parameters of the damping cushions, obtaining the compression height of the damping cushions by using fragments and rubbles in the rubble accumulation, and comparing the preliminary physical parameters of the damping cushions with the compressed height to further determine the optimal parameters of the damping cushions; III) arranging the damping cushion determined by the final physical parameters within the ground range of the rubble accumulation. The vibration damping cushion layer has the advantages of strong energy consumption, almost negligible resilience after compression, good durability, low maintenance cost and the like, and can generate a plurality of folds under the action of impact force, so that the vibration of the ground caused by the collapse of a large structure is effectively weakened.
Description
Technical Field
The invention belongs to the technical field of civil engineering, and relates to a method for weakening ground vibration caused by collapse of a large structure.
Background
It is well known that large structures, if collapsed, can cause strong ground vibrations that can be harmful to surrounding structures, equipment and people.
This situation is currently of particular concern in inland nuclear power plants in china. Generally, site selection of an inland nuclear power plant requires consideration of the following factors:
(1) the water cooling system of the nuclear power station is ensured to work normally by being close to a large river to obtain abundant water sources;
(2) dense areas are avoided for population evacuation in the event of a nuclear accident.
In our country, the result of site selection considering the above two factors is that the plant site area is generally narrow. In addition, in consideration of economy, a large-sized reinforced concrete cooling tower having a height of about 200m is generally used as a cooling tower for a nuclear power plant, and is located about 300m from a nuclear island. The investor and the engineer have a fear that once the large cooling tower collapses under the action of an external load, strong ground vibration will be caused. Vibrations will be transmitted to the nuclear island in a very short time, possibly causing a nuclear facility to malfunction, with the risk of inducing a nuclear accident.
To solve the above problems, one of the existing methods is to reduce ground vibration, and among them, the use of a cushion layer laid on the ground surface is an effective damping method. The cushion layer is generally made of soft materials, and when concrete fragments impact the cushion layer, the cushion layer deforms to absorb impact energy, the fragment speed is reduced, and the ground vibration reduction effect is achieved.
The bedding frequently used in the general engineering is fine sand and backfill, however, the two bedding materials have the following defects:
(1) the softness degree is insufficient, and the energy consumption effect is limited;
(2) the durability is insufficient, the steel plate can be hardened after a long time, and the vibration damping effect is reduced;
(3) if it is desired to remain unhardened, additional maintenance work is required.
Disclosure of Invention
In order to overcome the defects of the prior art, the method for weakening the ground vibration caused by the collapse of the large structure is provided, and the vibration damping cushion layer (mainly densely distributed steel pipes in the application) has the advantages of high energy consumption, almost negligible rebound after compression, good durability, low maintenance cost and the like, and can generate a plurality of folds under the action of impact force, so that the ground vibration caused by the collapse of the large structure is effectively weakened.
In order to achieve the above purpose, the solution of the invention is: a method for attenuating ground vibration caused by the collapse of a large structure is provided, which comprises the following steps:
i) determining the ground range of rubble accumulation after the structure collapses;
II) providing damping cushions, designing and selecting preliminary physical parameters of the damping cushions, obtaining the compression height of the damping cushions by using fragments and rubbles in the rubble accumulation, and comparing the preliminary physical parameters of the damping cushions with the compressed height to further determine the optimal parameters of the damping cushions;
III) arranging the damping cushion determined by the final physical parameters within the ground range of the rubble accumulation.
Preferably, the step ii specifically includes:
a. preliminarily selecting a damping cushion layer with a certain preliminary height;
b. determining two different characteristics of debris when the rubble impacts the ground in step i, one being the debris having the largest volume and the velocity of such debris, the other being the rubble having the largest velocity and the volume of such rubble;
c. through a finite element model, the fragments with the maximum volume and the rubbles with the maximum speed impact the vibration reduction cushion layer, so that the compressed height of the vibration reduction cushion layer is respectively obtained, and the larger value of the two is taken and preliminarily determined as the compressed height of the vibration reduction cushion layer;
d. if the compression height of the vibration-damping cushion layer obtained in the step c is smaller than the initial height of the vibration-damping cushion layer selected in the step a, modifying physical parameters of the vibration-damping cushion layer in the step c;
e. and d, continuously trial-calculating until the compression height of the damping cushion layer obtained in the step d is close to and smaller than the initial height of the damping cushion layer, so as to determine the optimal density of the damping cushion layer.
Preferably, a densely covered steel pipe is selected as the damping cushion layer.
Preferably, the step i specifically includes:
and determining the range of the rubble piled on the ground surface after the structure collapses under the action of various loads in a finite element numerical simulation mode.
Preferably, the load includes an earthquake and a strong wind.
Preferably, the step iii specifically includes:
and the top of the vibration damping cushion layer is sealed by adopting a light felt material, and the top elevation of the cushion layer formed by the vibration damping cushion layer is set to be the same as the adjacent ground elevation.
The method for weakening ground vibration caused by large structure collapse has the advantages that:
(1) the vibration reduction effect is good. Compared with fine sand and backfill, the damping cushion layer has stronger energy consumption capability. The fragments are scattered and submerged in the damping cushion layer, so that the damping effect is better;
(2) the variety selection range is large. By changing different parameters of the damping cushion layer such as steel type, wall thickness, height and the like, the damping cushion layer with different 'soft' degrees can be obtained, and compared with the damping cushion layer, the damping cushion layer has fewer types of fine sand and backfill soil;
(3) the performance is stable. Once construction is finished, the performance of the damping cushion layer is almost unchanged in the following decades, and fine sand and backfill soil are continuously solidified and hardened;
(4) the maintenance cost is low. The damping blankets are almost maintenance free for decades of use, whereas fine sand and backfill require constant maintenance and incur maintenance costs if the performance is to be maintained.
Drawings
FIG. 1 is a diagram of the layout of a vibration damping shim used in the method of the present invention;
FIG. 2 is a view corresponding to FIG. 1 showing the compression deformation of a single steel pipe;
FIG. 3 is a graph of damping shim stress-strain relationship corresponding to FIG. 3;
FIG. 4 is a plan view of the range of arrangement of the vibration damping shim in the practice of the present invention;
fig. 5 is an elevation view showing the range of arrangement of the cushion layer in the practical use of the present invention.
Reference numerals:
a single steel pipe 1, a collapsed structure 2, a vibration damping blanket 3, a vibration affected structure 4.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings.
As shown in figure 1, the steel pipes 1 are cylindrical and are arranged in a regular way to form a damping cushion layer. The damping shim 1 can be seen as a porous material. The porosity of the material is close to 100%, and the material has high compressibility.
As shown in fig. 2, a single steel pipe 1 is compressed and largely deformed to form a plurality of "wrinkles", consuming energy. For example, the damping shim is considered to be a material that has a compressive stress-strain relationship.
As shown in fig. 3, the method can be divided into three stages of a line bouncing segment, a platform segment and a compaction segment. Knowing the physical parameters of the damping shim 1, a corresponding compressive stress-strain relationship can be obtained.
As shown in fig. 4 and 5, the embodiment takes the falling and touching type vibration of the large cooling tower in the land-based nuclear power station as an example to explain that the application adopting the vibration damping cushion layer as the cushion layer can significantly reduce the ground vibration caused by the falling of the large structure. In the figure, the collapsed structure 2 is a cooling tower, the damping pad 3, and the structure 4 affected by vibration is a nearby containment. The vibrations of which cannot exceed a certain limit value, otherwise the safe operation of the nuclear facilities is affected, with the risk of inducing nuclear accidents.
The concrete steps that the damping cushion layer is adopted as the cushion layer to weaken the ground vibration caused by the collapse of the large-scale structure comprise:
(1) the ground area of rubble accumulation after the structure 2 collapses is determined. The range needs to be determined by numerical simulations of structural collapse, with external loads typically considered including earthquakes and strong winds.
(2) The method for determining the physical parameters of the damping cushion layer 1 specifically comprises the following steps:
firstly, determining the height of a damping cushion layer 1, wherein the height is 1 to 2 meters generally;
secondly, determining two characteristic fragments when the rubble impacts the ground in the step (1), wherein one is the fragment with the maximum volume and the speed thereof, and the other is the rubble with the maximum speed and the volume thereof;
and thirdly, preliminarily selecting various physical parameters of the damping cushion layer 1, such as steel material parameters and geometric parameters of the steel pipe 1. And establishing a 'fragment-damping cushion layer' finite element model, and respectively impacting the damping cushion layer 1 by using the fragment with the maximum volume and the speed thereof, and the fragment with the maximum speed and the volume thereof to respectively obtain the compression height of the damping cushion layer 1. Taking the larger value of the two as the compression height of the damping cushion layer obtained in the step;
and fourthly, if the compression height of the damping cushion layer 1 obtained in the third step is obviously smaller than the height of the damping cushion layer 1 determined in the first step, modifying the physical parameters of the damping cushion layer 1 in the third step (such as reducing the wall thickness of a steel pipe) to enable the damping cushion layer 1 to become softer, and recalculating the third step. And (4) continuously trial-calculating until the compression height of the damping cushion layer obtained in the third step is close to but slightly smaller than the height of the damping cushion layer. At this moment, the damping cushion layer 1 has a good energy consumption damping effect. Meanwhile, the vibration damping pad layer 1 is economically preferable in view of its full use.
(3) The damping blanket 1 is arranged in the ground area where rubble is piled up. The top of the damping cushion layer 1 is sealed by adopting light-weight felt materials, so that the personnel can be prevented from falling, and the safety effect is achieved. The top elevation of the damping shim 3 is the same as the adjacent ground elevation.
The following is one example of the verification listed in this example:
as is known, the hyperbola of a reinforced concrete cooling tower has a tower height of 185m and a distance of 74m from the bottom of a strut to the central axis of the cooling tower. The foundation is medium-stroke sandy slate, and the shear wave speed is 1406 m/s. The bottom of the cooling tower column is separated from the surface of the foundation and artificially synthesized RG1.60 seismic waves are applied to the bottom of the column. When the horizontal acceleration peak value of the seismic waves reaches 0.6g and the vertical acceleration peak value reaches 0.4g, the cooling tower collapses, specifically, the connecting part of the tower barrel and the support is damaged, and the tower barrel impacts the ground in a relatively complete posture.
And respectively calculating the existence of the damping cushion layer 3 on the surface of the foundation to evaluate the damping effect of the damping cushion layer 3. The damping cushion layer is arranged in a circular area with the center of a circle at the intersection point of the central axis of the cooling tower and the ground and the radius of 120m, and the height of the damping cushion layer is 1.4 m. The outer diameter of the steel pipe is 850mm, the wall thickness is 20mm, and the steel pipe is Q345 steel. The collapsed fragments hit the cushion 1 with a maximum compression height of 0.94 m.
And determining the direction with the strongest ground vertical vibration acceleration according to the calculation result. Then, on the surface of the foundation, 3 measuring points are taken along the direction, and the measuring points are respectively 200m, 300m and 400m away from the central axis of the cooling tower. The peak values of the accelerations at the above measurement points are shown in Table 1. Therefore, the damping cushion 3 can effectively reduce the ground vibration.
TABLE 1 acceleration Peak value of each measuring point
Note: the number in brackets indicates the percentage of the peak decrease in acceleration after setting the shim.
The embodiments described above are intended to facilitate one of ordinary skill in the art in understanding and using the present invention. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (5)
1. A method of attenuating ground vibration caused by a large structure collapse, comprising the steps of:
i) determining the ground range of rubble accumulation after the structure collapses;
II) providing damping cushions, designing and selecting preliminary physical parameters of the damping cushions, obtaining the compression height of the damping cushions by using fragments and rubbles in the rubble accumulation, and comparing the preliminary physical parameters of the damping cushions with the compressed height to further determine the optimal parameters of the damping cushions;
III) arranging the damping cushion determined by the final physical parameters within the ground range of the rubble accumulation;
the step II specifically comprises the following steps:
a. preliminarily selecting a damping cushion layer with a certain preliminary height;
b. determining the different characteristics of the two fragments when the rubble hits the ground in step I, one is the velocity of the fragment with the largest volume, and the other is the volume of rubble with the largest velocity;
c. through a finite element model, the fragments with the maximum volume and the rubbles with the maximum speed impact the vibration reduction cushion layer, so that the compressed height of the vibration reduction cushion layer is respectively obtained, and the larger value of the two is taken and preliminarily determined as the compressed height of the vibration reduction cushion layer;
d. if the compression height of the vibration-damping cushion obtained in the step c is significantly smaller than the preliminary height of the vibration-damping cushion selected in the step a, modifying physical parameters of the vibration-damping cushion in the step c;
e. and d, continuously trial-calculating until the compression height of the damping cushion layer obtained in the step d is close to and slightly smaller than the initial height of the damping cushion layer, so as to determine the optimal density of the damping cushion layer.
2. The method of claim 1, wherein a densely packed steel tube is selected as the damping blanket.
3. The method according to claim 1, wherein step i comprises in particular:
and determining the range of the rubble accumulated on the ground surface after the structure collapses under the action of various loads in a finite element numerical simulation mode.
4. The method of claim 3, wherein: the loads include earthquakes and strong winds.
5. The method according to claim 1, characterized in that said step iii comprises in particular:
and the top of the vibration damping cushion layer is sealed by adopting a light felt material, and the top elevation of the cushion layer formed by the vibration damping cushion layer is set to be the same as the adjacent ground elevation.
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| CN201711184986.2A CN107885947B (en) | 2017-11-23 | 2017-11-23 | Method for weakening ground vibration caused by large-scale structure collapse |
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| CN201711184986.2A CN107885947B (en) | 2017-11-23 | 2017-11-23 | Method for weakening ground vibration caused by large-scale structure collapse |
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| JP2012087506A (en) * | 2010-10-18 | 2012-05-10 | Tokyo Seiko Co Ltd | Rock lump falling prevention device |
| CN101967888A (en) * | 2010-10-20 | 2011-02-09 | 江苏江中集团有限公司 | Multidirectional multi-fold blasting method for high-rise building with frame-shear structure |
| JP2012112106A (en) * | 2010-11-22 | 2012-06-14 | Taisei Corp | Vibration isolation structure |
| CN104034547A (en) * | 2014-06-19 | 2014-09-10 | 同济大学 | Support release device for simulating component failure in structural collapse test |
| CN106407548A (en) * | 2016-09-13 | 2017-02-15 | 同济大学 | Anti-collapse optimization design method of reinforced concrete shear wall structure |
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Non-Patent Citations (3)
| Title |
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| Mitigation of Ground Vibration due to Collapse of a Large-Scale Cooling Tower with Novel Application of Materials as Cushions;Lin F, Zhong Q H等;《Shock and Vibration》;20171025;1-14 * |
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