RU2700833C1 - Seismic platform - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction, in particular to devices for performing model tests of building structures and their bases, taking dynamic loads, and can be used to assess deformations of structures, their foundations and soil bases during construction in seismically hazardous areas, or perceiving dynamic loads of another kind (explosions, vibration, etc.). Disclosed is seismic platform containing device for arrangement of model of tested element of structure or building and facility for generating dynamic loads. Facility for arrangement of the model of the tested element of the structure or building is made in the form of a ground tray, in the form of a box, which base is made in the form of a rigid frame and is equipped with a baffle plate. At that, base is arranged on rigid guides of fixed support with possibility of reciprocating movement on them and is spring-loaded on the side opposite to baffle plate. Means of forming dynamic loads is made as a striker, in the form of a metal box hingedly suspended on the bands, on the support frame with the possibility of its contact with the butt end with the baffle plate. On the additional frame there arranged is the striker removal device from the equilibrium position, made with possibility of its engagement-disengagement with the striker. Besides, device for removal of striker from equilibrium position comprises system of polyspast and trigger mechanism.

EFFECT: creation of dynamic oscillations of the whole system (movable tray filled with soil, with model of structure installed on soil).

1 cl, 3 dwg

Description

The invention relates to the field of construction, in particular to devices for conducting model tests of building structures and their bases, perceiving dynamic loads and can be used to assess the deformation of structures, their foundations and soil bases during construction in seismically dangerous areas, or perceiving dynamic loads of a different kind (explosions, vibration, etc.).

A well-known stand for modeling the seismic effects of the earthquake on the model of structures. The stand consists of a base, to the racks of which, using a pivot-swivel mechanism with a clamp, a frame is mounted with a rigidly fixed shock mechanism with a drive and a seismic platform, with a shock absorption system and a work table fixed to the seismic platform also using a swivel-rotary mechanism with a clamp. Sensors and objects under investigation are installed on the table (see RU No. 2024955, MPKG09B 25/00, 1994).

The disadvantage of this installation is the inability to simulate the compressibility of the base soil, since the tested design model is rigidly attached to the seismic platform.

Also known is a seismic platform containing a means for accommodating a model of a tested element of a structure or building, a means of generating dynamic loads (see RU No. 2617568, IPC G01M 7/00, 2015). The platform is mounted on supports made of coil springs, which are mounted on an additional gasket plate, which, in turn, rests on the foundation through horizontal compliant supports and is connected to the wall and the foundation through hydraulic drives. As a result, this solution provides the possibility of generating three-dimensional damped oscillations.

The disadvantage of the above solution is the representation of the soil foundation of the structure in the form of bonds of finite stiffness (springs), which leads to errors in modeling.

The problem to which the invention is directed, is to expand the modeling capabilities of structures that perceive dynamic loads by simulating the dynamic vibrations of the base of the structure in the soil tray.

The technical result consists in creating dynamic vibrations of the entire system (a movable tray filled with soil, with a model of the structure installed on the ground).

To solve the problem, a seismic platform containing means for placing the model of the tested building element or building, means for generating dynamic loads, characterized in that the means for placing the model of the tested building element or building is made in the form of a soil tray, in the form of a box, the base of which is made in in the form of a rigid frame and is equipped with a chipper, while the base is placed on the rigid guides of the fixed support, with the possibility of reciprocating movement along them, and suppressed from the side opposite to the chipper, in addition, the dynamic load generating means is made as a striker, in the form of a metal box pivotally suspended on strands, on a support frame with the possibility of its end contacting with the chipper, and on the additional frame there is a means of diverting the striker from the equilibrium position, made with the possibility of its engagement-disengagement with the striker. In addition, the means of diverting the striker from the equilibrium position contains a chain hoist and a trigger mechanism.

The compliance with the criterion of "novelty" is evidenced by a comparative analysis of the essential features of the analogue and prototype and the essential features of the proposed technical solution.

Distinctive features of the claims solve the following functional tasks.

The signs "... the means for placing the model of the tested element of the structure or building is made in the form of a soil tray, in the form of a box, the base of which is made in the form of a rigid frame and equipped with a chipper ..." provide the possibility of placing a model of a building or structure in the tray with the ground containing them and shock impact on him.

The sign "... the base is placed on the rigid guides of the fixed support, with the possibility of reciprocating movement on them ..." provides the possibility of horizontal displacements of the soil tray during impact on it.

A sign indicating that the base is "spring loaded from the side opposite the bump" provides the possibility of oscillatory movements of the base in the horizontal plane.

A sign indicating that the "means of forming dynamic loads made like a firing pin" provides the possibility of impact on the soil tray.

A sign indicating that the soil tray is made “in the form of a metal box pivotally suspended on the strands, on a support frame with the possibility of its end contacting with the chipper”, provides a variation in the weight of the striker and a variation in the speed of movement of the striker, while simplifying the mechanism of putting the striker in motion.

The sign indicating that "on the additional frame is placed a means of diverting the striker from the equilibrium position, made with the possibility of its engagement-disengaging from the striker" ensures the striker is diverted from the equilibrium position and, thereby, giving it the possibility of impact on the soil tray.

A sign indicating that “the means of diverting the striker from the equilibrium position contains a chain hoist and a trigger mechanism” reveals a possible design of the means for generating dynamic loads allowing the striker to be brought to its initial position, in which, when the striker is reset, the required impact force is provided to create oscillations of the desired frequency.

The claimed solution is illustrated by drawings, where figure 1 shows a side view of the device; figure 2 shows a top view of the device; figure 3 shows the design scheme of the device.

The drawings show the base 1, soil tray 2, soil 3, frame 4, wheels 5, bottom 6 of frame 4, springs 7, fixed support 8, bump 9, firing pin 10, metal frame 11, dynamic vibration sensors 12, structure model 13, displacement sensors 14, additional metal frame 15.

The seismic platform is mounted on a fixed base 1. The base is a metal frame consisting of guide elements (rails) fastened to the transverse connecting elements. Soil tray 2, filled with soil 3, is made as a container containing a metal frame, sheathed with sheet steel. A model of structure 13 is installed on the ground 3. The lower part of the soil tray 2 is made in the form of a frame 4, equipped with wheels 5 (three on each side) mounted on the outside of the bottom 6 of the frame 4, with the possibility of rotation. On one side of the frame 4 is attached through the springs 7 to a fixed support 8. On the opposite side of the frame 4 there is a fender 9 (recruited from profiled metal), which will be hit by the hammer 10. The hammer 10 is made of metal rod elements and a small metal box and fastens to a metal frame 11 with the help of cords (flexible rods). In addition, dynamic vibration sensors 12, a model of a structure 13, and the number of displacement sensors 14 required by the test conditions that record the model’s displacements in the plane of the load and / or strain gauge sensors for fixing stresses in the model of the structure 13 are shown.

To divert the striker 10 from the equilibrium position, an additional metal frame 15 is installed, to which the chain hoist and the trigger mechanism (not shown) are attached.

To provide the possibility of modeling the dynamic load on the model of the structure 13 installed in the tray 2 with soil 3 in the form of damped oscillations of the required frequency, simulating a real seismic effect, the stiffness of the springs 7 is preliminarily determined.

In this case, the required oscillation frequency is provided by the stiffness of the springs based on the following considerations.

The fundamental natural frequency ω of a single-mass system is defined as

where k is the stiffness of the support; m is the mass.

As a result:

наиболее вероятных землетрясений в данном районе суммарная жесткость пружин k экспериментальной установки, обеспечивающая заданный диапазон собственных колебаний, равна:With the known weight of the Q system of the soil tray and the known carrier frequency range

the most likely earthquakes in a given area, the total spring stiffness k of the experimental setup, providing a given range of natural vibrations, is equal to:

where g = 9.81 m / s ² is the acceleration of gravity.

For example, for the weight of the system Q = 30 kN and at the carrier frequency of the most likely earthquakes in the Primorye and the Sea of Japan, ω is from 0.7 to 2.2 Hz (Okamoto S. Seismic resistance of engineering structures. - M .: Stroyizdat, 1980 - 342с. ) the total stiffness of the springs will be:

Further, taking a shock is absolutely elastic, according to the law of conservation of momentum:

- масса бойка; М - масса лотка; V_л - скорость лотка; V_б – скорость бойка до удара;

- скорость бойка после удара; можно вычислить скорость движения лотка и скорость движения бойка.Where

- mass striker; M is the mass of the tray; V _l - the speed of the tray; V _b - striker speed before impact;

- speed striker after impact; you can calculate the speed of the tray and the speed of the striker.

Equation (4) contains three unknowns: the striker speed before the strike, the striker speed and the tray speed after the strike. The solution of the equation will determine the unknown speeds:

- the speed of the tray, which allows you to calculate the impact force, which must be applied to shift it and ensure the necessary and calculated above the oscillation frequency;

- the initial speed of the striker.

For a given mass of the striker and its known speed, the calculation can determine the height of the load h and the angle of deviation of the connection α, on which the striker is fixed, from the vertical.

First of all, you can find the speed of the tray after the collision. To do this, we calculate the compression energy of the spring. The energy of movement of the tray should be greater than or equal to the energy of compression of the spring, therefore, the first term from the right side of equation (4) can be equated to the value of the energy required to compress the spring.

According to the law of conservation of momentum with an absolutely elastic impact, the energy required to compress the spring:

where k is the stiffness of the spring; x-compression of the spring, m

From expression (6) we get the speed of the tray:

Further, it is necessary to calculate the value of the energy that will be required to shift the tray with mass M. Such energy will be equal to work A, to overcome the displacement.

where s is the amount of displacement, m; F _sdv is the force required to overcome the friction and shear forces of the tray with mass M. This force is equal to the product of the weight of the moved tray by the coefficient of resistance to movement - ω. For a steel wheel on a rail, it ranges from 0.001 to 0.002.

Then

Equating the work (energy) for shifting the tray to the first term of equation (4), you can get the speed that you need to set the tray to shift.

As a result, we get two values of the speed of the tray: the first is the minimum required to compress the spring; the second is the minimum necessary to shift the tray. For further calculations, the tray speed equal to the sum of the calculated speeds is taken.

Since the collision of the striker with the chute is short-term, the displacement of the chute at this moment is negligible, and the elastic force does not arise at the moment of collision. Consequently, the total momentum of the tray and hammer during the collision is preserved:

Equation (4) and equation (12) are a system of equations. The equations can be transformed as follows, respectively:

By solving the system of equations, several expressions can be obtained to find the necessary velocities.

Dividing equality (13) by equality (14), we obtain the expression:

, и подставив в уравнение 14 получим:From equation (15) we express

, and substituting in equation 14 we get:

получим выражение для скорости лотка в зависимости от начальной скорости бойка:Expressing from the formula (17)

we get the expression for the speed of the tray depending on the initial speed of the striker:

From the same expression we express the initial speed of the striker

The height of the load h (Fig.3):

Deflection Angle:

where L is the length of the suspension; α is the angle of deviation of the cargo.

Similarly, given the height of the load, you can vice versa, determine the required mass of the striker.

The seismic platform works as follows.

Prior to testing, taking into account the above considerations, the required spring stiffness 7 is determined, the striker 10 mass is set, and the height or angle of the striker starting position are calculated.

Next, soil 3 is loaded into the soil tray 2. The model of the structure 13 is installed and the number of dynamic vibration sensors 12 required by the test conditions can be installed. If necessary, displacement sensors 14 can be installed to record the movements of the model of the structure 13 in the plane of the load and / or strain gauges for fixing stresses in the model of the structure. In the striker 10 to give the necessary mass, lay the appropriate load. Next, the firing pin 10 is diverted from the equilibrium position to the initial position and reset. When the striker 10 hits the bump 9 of the soil tray 2, the soil tray vibrates the required frequency in the horizontal direction. If necessary, the readings of the sensors of dynamic vibrations 12, displacement and sensors 14 showing the voltage in the tested model of the structure 13 are recorded.

Then everything repeats.

Claims (2)

1. A seismic platform containing means for accommodating a model of a test element of a structure or building, a means of generating dynamic loads, characterized in that the means for placing a model of a test element of a structure or building is made in the form of a soil tray, in the form of a box, the base of which is made in the form of a rigid frame and equipped with a chipper, while the base is placed on the rigid guides of the fixed support, with the possibility of reciprocating movement along them, and is spring loaded from the side, false bump, in addition, the means of forming dynamic loads is made like a striker, in the form of a metal box pivotally suspended on strands, on a support frame with the possibility of contacting it with the end face of the striker, and on the additional frame there is a means of diverting the striker from the equilibrium position, made with the possibility of its engagement-disengagement with the striker. 2. The seismic platform according to claim 1, characterized in that the means for diverting the striker from the equilibrium position comprises a chain hoist and a trigger mechanism.

Images