what does a shaking table do

gold shaking table

gold shaking table

A Gold Shaking Table are basically low-capacity machines used as last step in the gold upgrading process. Theshakingtable is a thin film, shear flow process equipment, that separatesparticlegrains of its feed material based on thedifferences in their specific gravity, density, size and shape. Mineral rich particles, from light to heavy and fine to coarse will be sorted by net effective weight. Finely crushed or ground ore material goes as feed mixed with water to form a pulp (mud) andfed as slurry of an average about 2025% of solids by weight onto the highest point of the table deck. The gold tables deck hasa reciprocal movement along its main axis that is given using a vibrator or an eccentric head motion. The table surface is manufactured and fitted with several tapered strips called riffles or grooves, often made with of yellow pine (way back in time that is), low-density polythene or aluminum surfacing.Shaking tables and other thin film separating plant recover finely divided gold under conditions of subcritical laminar and supercritical laminar regimes of flow, which may occur only where there is a very thin depth of fluid.

Agold shaking tables riffles taper downwards in elevation in the direction the gold (and all heavies), precious metals concentrate discharge end of the table. This facilitates the ease with which mineral particles can move transversal to the tables axis or shaker-line, therefore helpingseparation over the complete tablelength. Riffle heights and pattern designs are selected based on the desired and required duty/function expected.

Preparing several size fractions for tabling is usually achieved in a hydrosizer. Ifgold is present in both coarse and finely divided sizings at least three, or perhapsfour separate size fractions must be treated, each under a different set of operatingconditions. Tables operate most efficiently with a closely sized feed. The slurry fansout across a smooth section of the surface until it reaches the riffles. The lighterand very fine particles are washed over the riffles and moved along the riffles by thereciprocating motion imparted to the deck while the heavier particles are held back. The concentrates of heavy mineral and gold are discharged over the end of thedeck. Tailings are washed over the lower edge and a middlings fraction is taken offbetween the lower edge of the concentrate strip and the higher edge of the tailingstrip.

Wash water usage is dependent upon the particle diameter and varies from aslow as 0.7 m/t/h of solids for slime decks, up to 56 m/t/h for coarse solidsseparation. Coarse fractions are usually treated at feed rates of up to 1 t/h using approximately 15 to 20 mm stroke lengths at around 280 rpm (Wilfley table data). Thestroke lengths of finer fractions are reduced to 915 mm with increased speeds ofup to 325 rpm but, because of the corresponding lower film, thickness capacitiesmay fall to around 0.25 t/h. The inclination of the deck is adjusted during operationusing a hand-operated tilting device. It is important following each adjustment toallow the table operation to settle down before making a fresh adjustment. The correct inclination is reached when the ribbon of concentrates is clearly defined andremains steady.

The extreme sensitivity of water depths and corresponding current depths to obtain F = 1, and the use of stationary tables as primary concentrating units, was probably the main reason for the consistently low (R.E. 6065%) gold recoveries of early dredgers. For such table types, the fluid forces are applied to the stream-beds as a whole and ripples form, which keep the sand in orbital motion and provide for the denser particles to sink to the bed. Deposition is most favoured by anti-dune conditions produced by free-surface flow at or near the supercritical state. Such bed forms are in phase with the water surface and are produced in the rapid flow conditions of Froude Number F = 1. In this state of flow, the bed forms of the upper flow regime are stable. Below F = 1 the flow is tranquil and shear forces are reduced. In reviewing recovery distributions of certaindredgers it wasnoted that some coarse gold reported with the tailing after passing through two stages of tabling and that fine gold did not concentrate noticeably down the line.

I consider the gold shaker table to be a shaking sluice box OR self cleaning sluice as they both essentially are classifiers used as heavy gold concentrating devices. Apart from nuggets; generally the valuable minerals like heavy precious metals like platinumandpalladium thatcan berecovered by tables and sluices, are found in one size range (generally the finest) and the waste minerals in another. On agold sluice, large particles (gravel) travel by sliding and rolling over the riffles, with finer particles travelling by saltation. Sand travels by a combination of modes described earlier with some saltation over the riffles.Very fine particles are maintained in suspension by turbulent and inter-particle collision.

Riffles function properly only if in the space between them and the slurry is sufficiently live (turbulent) to reject the lighter particles, but not so lively that the gold cannot settle. On a gold shaker table, those particles are allowed to settle as they will get transported to the other end by the vibrating/shaking back-and-forth motion. Lower grade, light pieces, will be able to escape the table a the riffles becomes shorter along the tables length.Once the particle has started to move, the coefficient of friction changes to a dynamic coefficient of friction. In fact, because the fluid push on the particles is larger at the top of the particle than at the bottom, the particle rolls, largely according to the shape of the particle and according to the speed. At low speeds, the effective friction is the relatively large coefficient of dynamic sliding friction, and at high speeds it is the lower coefficient of rolling friction. The change probably takes place partly continuously and partly discontinuously. As a first approximation, the dynamic coefficient of friction may, however, be regarded as constant.

In a sluice box, the settling of heavy minerals between the riffles requires frequent stirring to prevent the riffle spaces from blinding. This also disturbs the gold, which then moves progressively down-sluice. Frequent clean-ups are needed to avoid excessive loss. Boxes may be used in parallel to avoid loss of production time. One box is kept in operation while cleaning up in the other.

Effect of Deck Roughness: The foregoing analysis is based on the postulate that the deck is perfectly smooth. If the deck is rough, i.e., if it has at its surface some recesses capable of partly shielding fine particles from the rub of the fluid, the slope required to move the particles by either rolling or sliding will be increased. At the same time such an effect, while present also for large particles, may be so much smaller for them as to be imperceptible. The relationship of critical angle to size obtained above will therefore not hold for rough surfaces. The problem is analytically complex and it is nevertheless a problem that might well be explored further if a full insight is desired into the mechanism of flowing-film concentration.

Adjustments are provided in all tables for the amount of wash water, the cross tilt, the speed, and the length of the stroke. The speed of the table ranges usually from 180 to 270 strokes per minute, and the strokes are from 1/2 to 1 1/2 long.

Variations in character of feed require variations in operation. The operators duty is to take care of them by adjusting the tilt, the wash water, and the position of the splitters that control discharge of table into concentrate, middling, and tailing launders. One man may look after 10 to 100 tables, depending upon the regularity of the feed and the difficulty of the task assigned to the table.

A coarse feed can be treated in larger amounts than a fine feed. It would seem that the treatable tonnage increases at least as the square of the average size (theory indicates that it increases as the cube of the particle size).

A roughing operation is preferably conducted on a fully riffled deck. These decks have a greater capacity because the particles are treated throughout the deck in the form of a teetering suspension many particles deep instead of as a restive layer one particle deep. Such decks do not provide flowing-film concentration but some sort of jigging. On the other hand, a cleaning operation is preferably performed on a partly riffled deck.

It is clear that minerals of different specific gravity must be present the greater the spread in specific gravity between minerals, the greater the capacity since that sort of condition permits crowding without considerable penalty.

The effect of locked particles on capacity of tables should also be recognized. These particles behave in a fashion intermediate between that of pure particles of their constituent minerals. It is as if a three-product separation were sought in which one of the products would guide-in specific gravity between the two other.

Table capacity may be as high as 200 tons per 24 hr. on a fully riffled deck 4 by 12 ft. treating minus 3-mm. sulphide ore having a specific gravity of about 3.0 (roughing duty), or 500 tons per 24 hr. But table capacity may be as low as 5 tons per 24 hr., or even less, for fine ore (minus 0.3 mm.) if there is only a small specific-gravity differential between minerals.

Operating a shaking table is cheap as power requirement per table are typically low. Most of the energy is expended to move the deck, which must therefore be as light as is consistent with rigidity. Laboratory gold shaking table testingreport.

There are a few steps that need to be taken in order to get yourgold shaker table to work efficiently. The first step that aspiring gold miners must take would be to make sure that all four corners of the table are level from forward to back. It is very important to anchor the bolts so that the shaking of the gold goes to the table and not through the frame. After you begin running your table, you may need to adjust your table from side to side to maintain an even flow of materials on both sides of the table.

A gold shaker table contains a water access point where you can fill it with clean water, which can be seen right under the control area. Alternatively you can directly fill the tank of the shaker table with clean water. The water access point allows you to connect a clean water system through a garden hose. The valve that is right behind the tank is then turned off and the pump system is not running during the process of running fresh water. When clean washing water is distributed at the top of the table at right angles, particles are moved diagonally across the deck and separate from each other according to their size and density. During the fast shaking process, you will gradually begin to see the separation of materials. For example, when you have dirt and rocks that contain materials like lead, sulfides and gold, because of the varying weights of these different materials, you will see these materials venture off in different directions on the shaker table. The lead and the sulfides will be carried over to the right side of the table while the pure gold will be carried over to the far left side of the table.

There is one term to remember when professional gold miners describe the actions of a gold shaker table. When professional gold miners say that small particles of gold are being carried through the grooves, they are referring to the ripples that you can plainly see on the shaker table. When they say that there is an overflow of materials like Black Pyrrhotite, White Quartz, silver and gold on the grooves, then this is a good thing.

When materials are washed by the clean water they are supposed to drop into 3 hoppers/launders underneath the table. There is a centre launderthat will gather the purest portions of gold while the two outside launders will gather some gold, though not as much.

It is crucial to remember to plug the cable of your shaker table into a GFCI (Ground Fault Circuit Interrupter) outlet. Most shaker tables will not work if they are plugged into any other kind of outlet.

In aPercussion Gold Shaker Table,the work of keeping the pulp in a state of agitation, done by the rakes or brushes in the German and Cornish buddies described above, is affected by sudden blows or bumps imparted sideways or endways to the table. The table is made of wood or sheet metal, the surface being either smooth or riffled.

End-bump tables are hung by chains or in some similar manner, so as to be capable of limited movement, and receive a number of blows delivered on the upper end. These blows are given by cams acting through rods, or else the table is pushed forward against the action of strong springs by cams on a revolving shaft, and then being suddenly released is thrown back violently by the springs against a fixed horizontal beam. The movement of the pulp depends on the inertia of the particles, which are thrown backward up the inclined table by the blow given to the table, the amount of movement varying with their mass, and depending, therefore, both on their size and density. The vibrations produced by the percussion also perform the work of the rakes in destroying the cohesion between the particles, and a stream of water washes them down. The result is that the larger and heavier particles may be made to travel up the table in the direction in which theyare thrown by the blow, by regulating the quantity of water, while the smaller and lighter particles are carried down. These machines yield only two classes of material, headings and tailings. One such machine, the Gilpin County Gilt Edge Concentrator was devised in Colorado, and has displaced the blanket sluices atalmost all the mills at Blackhawk. It consists (Fig. 46) essentially of a cast-iron or copper table, 7 feet long and 3 feet wide, divided into two equal sections by a 4-inch square bumping-beam. The table has raised edges, and its inclination is about 4 inches in 5 feet at its lower end, the remaining 1 feet at the head having a somewhat steeper grade. The table is hung by iron rods to an iron frame, the length of the rods being altered by screw threads, so as to regulate the inclination to the required amount. A shaft with double cams, A, making 65 revolutions per minute, enables 130 blows per minute to be given to the table in the following manner; onbeing released by the cam, the table is forced forward by the strong spring, B, so that its head strikes against the solid beam,C, which is firmly united to the rest of the frame.

The pulp coming from the copper plates is fed on to the table near its upper end by a distributing box, D, and is spread out and kept in agitation by the rapid blows. Thesulphides settle to the bottom of the pulp, and are thrown forward by the shock, and eventually discharged over the head of the table at the left hand of the figure, while the gangue is carried down by the water and discharged at the other end. One machine is enough to concentrate the pulp from five stamps. If the table consists of amalgamated copper plates, it is of some use for catching free gold also, treating about 8 cwts. of ore per hour. This machine is not so effective in saving slimed pyrites as the Wilfley table or the vanners.

Gold shaker tables are environmentally friendly (chemical free) for recovering pure gold as they can play an important part in reducing the use of mercury by gold miners. With gold shaker tables miners dont need to resort to mercury amalgamation or cyanide to recover gold. The filter will constantly need to be removed and cleaned as it will get dirty even after using the table a few times.

Miners can design and construct a basic shaking table out of cheap materials that are affordable in local stores, including a drive mechanism that contains bicycle gears, chains and rubber bands that are made from car tire inner tubes. The drive mechanism for a gold shaker table can be a hand crank or it can contain parts of a motorcycle frame and engine. If one prefers to use a motor for his or her table, either an electric motor or a motor that runs on diesel fuel would be the ideal options.

It is important to keep in mind that there is no one specific way to create your own gold shaker table system. Many professional gold mining organizations will create tables of different shapes and sizes to cater to the needs of their customers. Some shaker table systems will feature machines that can crush hard rocks, which are referred to as jaw crushers. The speeds of shaker table systems will vary as they can shake from hundreds to thousands of pounds of materials per hour.

development of the shaking table and array system technology in china

development of the shaking table and array system technology in china

Chun-hua Gao, Xiao-bo Yuan, "Development of the Shaking Table and Array System Technology in China", Advances in Civil Engineering, vol. 2019, Article ID 8167684, 10 pages, 2019. https://doi.org/10.1155/2019/8167684

Shaking table is important experimental equipment to carry out antiseismic research. Research, conclusion, comparison, and analysis concerning the developmental history, constructional situation, performance index, control algorithm, and experimental technique of the internal shaking table were reviewed and compared. Such functional parameters as internal shaking tables table-board size, bearing capacity, working frequency, and maximum acceleration were given. Shaking tables constructional status quo and developmental trend were concluded. The advantages and disadvantages of different control algorithms were contrastively analyzed. Typical shaking table test, array system tests, and experimental simulation materials were induced and contrasted. Internal existing shaking table and array system tests structural type, reduced scale, and model-material selection were provided. Analysis and exposition about the developmental tendency of shaking tables enlargement, multiple shaking tables array, full digitalization, and network control were made. The developmental direction, comparison of technical features, and relevant research status quo of shaking table with high-performance were offered. The result can be reference for domestic or overseas shaking tables design and type selection, control technique, and research on experimental technique.

At present, the structural seismic research methods include the pseudostatic test, pseudodynamic test, and shaking table test. The test method of the shaking table test can recreate the structural response and seismic oscillation in the lab accurately and reproduce the whole process of seismic oscillation effect or artificial effect in real time. The development of shaking table provides an accurate and effective way to study structural elastic-plastic seismic response [13].

Japan and the United States are the first two countries to establish shaking tables in the world. And, China initially built a shaking table in 1960 [1] when Institute of Engineering Mechanics, Chinese Academy of Sciences, built one-way horizontal vibration [47] with a specimen size of 12m3.3m. So far in China, there are a lot of shaking tables [1]; some were made in China, some were systematically remodeled from imported parts, and some were totally imported. In recent years, many scholars [8, 9] and Wang et al. [2] conducted abundant research on the development and control technology of Chinas shaking tables and also got some research achievements. However, such results are mostly summaries of the test technologies or control technologies of shaking table [10], while there are few summaries concerning the construction history and usage of domestic shaking tables. This paper makes a comprehensive summary of the development and application of domestic shaking tables and array test technologies in terms of the development, control technology, test application, and development trend of shaking table and array system based on current collected information, so as to provide some reference and basis for the construction and development of domestic shaking table.

The development of shaking table in China came relatively late [1, 3, 1114]. It can be roughly divided into four stages. In 1960s, the mechanical shaking table was the main stream with a working frequency of 1Hz40Hz, of which the characteristics of the specimens in low segment are difficult to be controlled [2, 10, 11]. Electrohydraulic shaking table was then rapidly developed with its high frequency. In 1966, departments of machinery and electronics collaborated with each other to build Chinas first exclusive shaking table for national system of defense in three years [2, 10, 13]. Thereafter, many domestic colleges and universities as well as scientific research institutes also begun to conduct researches. For example, Tongji University brought in the 4m4m two-horizontal dimensional identically dynamic electrohydraulic shaking table developed by American MTS, which has been transformed into three- to six-degree-of-freedom identically dynamic shaking table [1]. At the beginning of the 70s, the research on shaking table in China was continuously carried out and quickly developed. Our country also started to develop one-way electrohydraulic servo shaking table but rarely hooked into multiaxis shaking table [1520]. And, foreign shaking tables were introduced only when the test was demanding, so the introduction quantity of shaking tables was sharply decreased. Domestic institutes that conduct researches on shaking table mainly include China Academy of Building Research, Xian Jiaotong University, HIT (Harbin Institute of Technology), Institute of Engineering Mechanics, and Tianshui Hongshan Testing Machine Co., Ltd. [21, 22]. The shaking table construction situation in China is shown in Table 1.

The work frequency of electrohydraulic shaking table in the early stage of our country was about 50Hz. At present, at home and abroad, the work frequency of high-thrust shaking table with over 50t can reach more than 1000Hz. For instance, the work frequency of Y2T.10c shaking table developed by 303 Research Institute of China Aviation Industry Corporation is as high as 1000Hz, and the wide band random vibration control precision is 2.0dB [23] within the frequency range of 20Hz1000Hz.

In 2006, Beijing University of Technology built a nine-sub-building block array system with a size of 1m1m, which along with the original 3m3m single-array system composed the 10-subarray system, which can be used to constitute testing systems with any several subarray systems and many optional positions; at the end of 2006, Institute of Electro-Hydraulic Servo Simulation and Test System of Harbin Institute of Technology (HIT) developed successfully the first domestic multiaxis independent intellectual property rights (the hydraulic vibration test system with shaking table system is shown in Figure 1) and got identification, which changed the history of depending on importing shaking tables [24]. In 2012, Jiangsu Suzhou Dongling Vibration Test Instrument Co., Ltd. successfully developed the worlds largest single electromagnetic shaking table test system (http://www.cnki.net/kcms/detail/11.2068.TU.20130124.1608.001.html) with a thrust of 50 tons.

With the 9-subarray system of Beijing University of Technology as an example, this paper introduces the construction situation of shaking table array system. In 2003, The State University of New York built the first set of two-subarray systems. In the same year, the University of Nevada-Reno built the three-subarray system with three movable two-direction shaking tables. The size of the table and the maximum bearing capacity of the shaking table are introduced. The array system (shown in Figure 3) is suitable for experimental research on spindly space structure.

In 2004, Chongqing Jiaotong Institute of our country completed the constitution of the two-subarray system with a specimen size of 6m3m, of which one is fixed and the other is movable (shown in Figure 4). And, in 2008, National Key Laboratory of Bridge Dynamics was established.

In 2011, Beijing University of Technology began to prepare to construct nine-subarray system (shown in Figure 5) and has built 12 sets of actuator building block array systems till 2006, which was increased to 16 sets in 2009 and is now the array system with the largest number of single-array system in the world. Each single shaking table is composed by mesa, 5 connecting rods, a vibrator, and a base. The array system can be made into various combinations by 16 sets of vibrators and connecting rods to conduct varied shaking table array tests with different layouts and forms. The performance indicators of nine-subarray system are shown in Table 2. The system uses four piston pumps to offer oil. The rated oil supply pressure of the seismic simulated shaking table system is the same as the maximum oil supply pressure. In addition to 4 oil pumps, the system also has energy storage to supplement the oil supply when the oil supply of the oil supply pump is insufficient.

There are two main types of traditional shaking table control technology: one is PID control based on displacement control and the other is three-parameter feedback control (also known as the three-state feedback control) synthesized by the displacement, velocity, and acceleration [25]. It is essential for feedback theory to adjust the system after making the right measurement and comparison. In 1950, the PID control method mainly composed of unit P proportion, integral unit I, and differential unit D was developed. The traditional PID control method is simple in control algorithm, good in stability, and high in reliability and thus has been widely applied in the practical engineering. The PID control method is especially suitable for deterministic control system. Yet, as the target signal of shaking table is acceleration signal, high-frequency control performance is poorer when the displacement PID control is adopted, while the mesa cannot be located if acceleration PID is used. Meanwhile, in the process of control, nonlinear behavior exists in every specimen; thus, the effect of traditional PID control is not ideal due to the large waveform distortion [24, 2629]. As the structure sets higher requirement for control accuracy, three-parameter feedback control synthesized by the displacement, velocity, and acceleration was put forward in 1970s (the control principle is shown in Figure 6), which makes up for the narrow frequency band and the inability to realize acceleration control of single displacement control. Acceleration feedback can improve the system damping, and velocity feedback can improve the oil column resonance frequency. Adopting the displacement to control low frequency, speed to control midfrequency, and acceleration to control high frequency plays an important role in improving the dynamic behavior and bandwidth of the system. The introduction of three-parameter control technology greatly improved the playback accuracy of seismic time history, but due to the complexity of transfer function in the system, the correlation of input and output waveform is still not high. Power spectrum emersion control algorithm modifies drive spectrum utilizing system impedance and the deviation of the reference spectrum and the control spectrum, so as to get a relative high consistency of response spectrum and reference spectrum of the system [30, 31]. Power spectrum retrieval principle diagram is shown in Figure 7. This method belongs to the nonparametric method, which has nothing to do with any model parameters. But the matching degree of estimated power spectral density and real power spectral density is very low, so it is an estimation method with low resolution.

Another kind of the parametric estimation method, using the parameterized model, can give a much higher frequency resolution than period gram methods. The power spectrum control method based on the parameter model has high resolution and can improve the system control convergence speed and power spectrum estimation precision, yet it is sensitive to noise with higher computation requirements. Therefore, in the vibration test control, it has not reached practical stage [32].

The traditional control algorithm is based on the linear model of vibration table and specimen [33], and the parameters in the process of test are assumed unchanged, but the actual test object is very complex. The components experience elastic-plastic phase and then the failure stage in the process of the test, and the parameters that were assumed to be unchanged turn out to have been changed in the process of test. The change of the parameters influences the accuracy of the input seismic signal, which is the biggest defect in the traditional control technology. From the 1970s to 80s, intelligent control is a new theory and technology with strong control ability and great fault tolerance. The introduction of the adaptive control improved the robustness and control precision of the system, such as adaptive harmonic control theory (AHC), adaptive inverse function control theory (AIC), and the minimum control algorithm (MCS) [34]. At present, the fuzzy control algorithm of the structure control attracted the attention of more and more scholars with its advantages of powerful knowledge expression ability, simple operational method, and the adoption of fuzzy language to describe the dynamic characteristics of the system. As early as 1996, some scholars abroad has carried out the induction and comparison of structural seismic control methods and summarized the advantages and disadvantages of various control methods, particularly expounding that the fuzzy control and neural network control algorithm could better solve the problem of nonlinear. The application of domestic intelligent control algorithm in the engineering structure control is relatively late. In 2000, Ou [29] and other scholars proposed the control algorithm which can realize fuzzy control according to the control rules and fuzzy subset, which greatly improved the practicability and efficiency of fuzzy control algorithm.

Most of the fuzzy control rules are established based on experience, leading to great difficulty in structure control. In view of this, Wang and Ou [35], in 2001, put forward the method of extraction, optimization, and generation of fuzzy control rules with the basis of structural vibration fuzzy modeling and genetic algorithm. Qu and Qiu [36] came up with a kind of active feed forward control method based on adaptive fuzzy logic system method, which better solved the nonlinear control problems of reference signal and external interference in the feedforward control. Wang [30] for flexible structure completed the application of the fuzzy PID control method in the structural vibration and conducted the active control experimental verification of beam vibration.

The efficiency of fuzzy control depends on the selection of function parameters and the establishment of the fuzzy control rules. Therefore, the adaptive fuzzy control is of great research significance for the nonlinear structure system. Because of the functions of self-adaptation and self-study of artificial neural network, the application of neural network in seismic control in civil engineering began in the 60s, which adopts a simple neural network controller to control the movement of the inverted pendulum, and achieved good effect. In 2003, Mo and Sun [31] implemented numerical simulation of active vibration control on the beam vibration control model by using genetic algorithm with the minimum energy storage structure as the goal, compared with the exhaustive method, and achieved good control effect. Chen and Gu [37] carried out simulation research on the application of frequency adaptive control algorithm based on the least square method in the domain of vibration control, and the simulation got the damping effect of about 50db. Li and Mao [38] achieved evolutionary adaptive filtering algorithm with strong instantaneity and applied it into the vibration control of structures to conduct simulation calculation based on genetic algorithm and moving least mean square algorithm of transient step, and the simulation obtained the damping effect of about 30db.

To solve the limit bearing capacity of shaking table for large structure test, scholars from all over the world conducted a wide variety of researches. The combination of substructure technique and shaking table test is an effective way to solve this problem [39]. Hybrid vibration test divides the structure into test substructure and numerical substructure. Test substructure is the complex part in experiment on shaking table, while numerical substructure is the simple part to carry out numerically simulation. Test substructure can carry out full-scale or large-scale model test, avoiding the influence of the size limit of shaking table with large-scale structure, and thus was widely used in the study of the engineering seismic test. The domestic researchers Chen and Bai [33] implemented preliminary exploration into structural seismic hybrid test technique on account of the condensation technology. In 2008, Chen and Bai [33] also embarked on the hybrid vibration test on the hybrid structural system of commercial and residential buildings, of which the bottom commercial district was put into a full-scale experiment on shaking table and other parts were involved in numerical simulation.

In 2007, Mr. Wu Bin from Harbin Institute of Technology applied the center difference method into the change of the acceleration calculation formula in hybrid real-time test which takes consideration of the quality of test substructure and analyzed the stability of the algorithm. The test results show that the stability of the center difference method in real-time substructure application is poorer than that of the standardized center difference method. Such scholars as Yang [40] in the same year made the numerical simulation analysis on the shaking test substructure test, and the analysis results show that the integral step change is sensitive to the influence of experimental stability. At the same time, he verified the validity of the theoretical research results.

In recent years, the structural styles of shaking table test research were developed from masonry structure, frame structure, tube structure to bridge structure, structures with the consideration of some isolation and damping measures, and structural foundation interaction experiment. The application of shaking table tests on the structure seismic resistance made it possible to establish structure nonlinear model with various structural styles [2]. Many shaking table tests have been carried out in recent years in China, which, according to the testing purpose, can be roughly divided into three categories: the first type is to determine structural earthquake-resistance performance as the test purpose; the second type is to determine the dynamic characteristics of structure, obtain such dynamic parameters as the natural vibration period and damping of structure, seek for weak parts of the structure damage, and provide the basis for super high-rise and supergage designs; the third type is to verify the applicability of certain measure or design theory in the structure. This paper drew a conclusion of typical shaking table tests in recent years in terms of building types, model dimensions, and so on (shown in Table 3).

Shaking table experiment diversifies the structural styles in experiment, makes it possible to establish the nonlinear damage model, and provides a reliable basis for all kinds of structures to establish the corresponding destruction specification. But large span structure tests on bridges, pipes, aqueduct, transmission lines, and so on may produce traveling wave effect under the action of earthquake due to large span, and a single shaking table will not be able to simulate the real response of the whole structure under seismic action. Array system can better solve these problems. For example, the State University of New York-Buffalo did damper damping effect research on Greek Antiliweng Bridge using 2-subarray system; conducted shaking table array test research on two continuous steel plate girder bridge and concrete girder bridge by using the 3-subarray system of University of Nevada. Many domestic scholars also carried out shaking table array test research on different structures of array systems. For instance, in 2008, Gao Wenjun made shaking table array test research of organic glass model on Chongqing Chaotianmen Bridge with the 2-subarray system of Chongqing Traffic Academy; conducted a multipoint shaking table array test research on concrete-filled steel tubes arch bridge with the 9-subarray system in Beijing University of Technology.

According to the size of mesa, shaking tables can be divided into large, medium, and small ones; in general, specimen size less than 2m2m for the small, 6m6m for the medium, and over 10m10m for the large. Due to the size limitation of a small seismic simulation vibration table, it can only do small-scale tests, and there is a certain gap with the prototype test. In the seismic simulation vibration table test of scale model, all parameters are required to meet the similarity principle, but it is difficult to do in practical engineering. For some important structures, especially the important parts of large structures, to accurately reflect the dynamic characteristics of the structure, within the permitted scope of the condition of capital, it is necessary to increase the specimen size and the maximum load as much as possible to eliminate the size effect of the model, so the large full-scale test must be the development trend of shaking table. China Academy of Building Research developed a shaking table with a mesa dimension of 6.1m6.1m and the maximum model load of 80t.

Due to the great investment, high maintenance cost, and test fees as well as long production cycle of large-scale shaking table, infinite increase in size of shaking table is obviously unreasonable, and likewise, it is not possible to fully meet the actual requirements only by increasing the size of shaking table. For large-span structure tests on bridges, pipes, aqueduct, transmission line, and so on array systems composed of many sets of small shaking table can be adopted. Shaking table array can either conduct a single test or make seismic resistance test on the structure of large-scale, multidimensional, multipoint ground motion input with varied combinations according to various needs. Therefore, the array system composed of many sets of small shaking tables must be the development trend of shaking table.

In terms of control mode, power spectral density control was mostly adopted before 1975. After 1975, Huang Haohua and other scholars used the time-history playback control to finish the seismic wave control research in a broad band. In the mid-1990s, digital control and analog control are widely used in the shaking table control, of which digital control is mainly applied in the system signal and compensation and the analog control is the basis for the control, whose control mode is complicated in operation with too much manual adjustment. After 1990s, Fang Zhong and other scholars developed a full digital control technology which has been widely used in the hydraulic servo control system with the rapid development of digital technology. Other than the valve control device and feedback sensor which adopt analog circuits, the rest utilize digital software to fulfill implementation. This control method can make up for some flaws in the analog control with simple test operation, being able to improve the accuracy, reliability, and stability of the system. Full digital control is the inevitable development trend of hydraulic servo system control.

With the appearance of slender and shaped structures and the application of new materials in building engineering, the seismic test methods of structures are put forward with higher and higher requirements. To meet the requirements of actual engineering and seismic research, scholars from all over the world are active in exploration and attempt and put forward some new testing methods. In recent years, countries around the world greatly invest in seismic research. From 2000 to 2004, the United States Science Foundation Committee spent eighty million dollars of research funding on the NEES plan; Europe established a collaborative research system European Network to Reduce Earthquake Risk (ENSRM); South Korea established a virtual structure laboratory using grid technology, which includes the wind tunnel, the shaking table, and other scientific research equipment. Furthermore, Internet ISEE Earthquake Engineering Simulation System in Taiwan of China was the earthquake engineering research platform developed by National Earthquake Engineering Research Center of Taiwan, China, with the Internet. The platform not only allows several laboratories to interconnect each other to implement large-scale shaking table test but also permits different laboratory researchers around the world to observe the test simultaneously and synchronously.

In China, Hunan University firstly put forward the structure network synergy test research and cooperated with Vision Technology Co., Ltd in 2000 to develop the network structure laboratory (NetSLab is shown in Figure 8). The main module and interface are shown in Figure 8. Thereafter, Hunan University cooperated with Harbin Institute of Technology to accomplish secondary development to establish the network collaborative hybrid test system and conducted a structure remote collaborative test along with Tsinghua University, Harbin Institute of Technology. Three domestic universities firstly completed remote collaboration pseudodynamic test, which is shown in Figure 9.

This paper drew a conclusion of the construction, history, and status quo as well as application and research of shaking table and array. The main conclusions are as follows:(i)On account of factors of actual application demand and economy, the size of the shaking table is between 1m and Xm, among which 3m6m are the majority. For large span structures such as bridges and pipes many sets of small array mode of vibration table can be used.(ii)Shaking table mesa acceleration and speed are about and 80cm/s, respectively. Through statistics, the remarkable frequency of previous ground motion records is mainly within 0.1Hz30Hz, and the frequency range of medium shaking table should be in 0Hz50Hz according to the requirements of the similar rule. Moreover, tests with special requirements need to be above 100Hz.(iii)With the appearance of slender and shaped structures and the application of new materials in building engineering, the seismic test methods of structures are put forward with higher and higher requirements.

The authors acknowledge the support from the Science and Technology Breakthrough Project of the Science and Technology Department of Henan Province ( 9), the Key Scientific Research Projects in He Nan Province (No. 18B560009), and Nanhu Scholars Program for Young Scholars of XYNU in China. The authors thank Xin Yang Normal University School of Architecture and Civil Engineering Laboratory and would also like to thank teachers and students of the team for collecting data.

Copyright 2019 Chun-hua Gao and Xiao-bo Yuan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

shaking table | gravity separator - mineral processing

shaking table | gravity separator - mineral processing

Shaking tables are one of the oldest gravity separators in the mineral processing industry, capable of handling minerals and coal of 0-2mm.Shaking tables are rectangular-shaped tables with riffled decks across which a film of water flows. The mechanical drive imparts motion along the long axis of the table, perpendicular to the flow of the water. The water carries the particles of the feed in slurry across the riffles in a fluid film. This causes the fine, high density particles to fall into beds behind the riffles as the coarse, low-density particles are carried in the quickly-moving film. The action of the table is such that particles move with the bed towards the discharge end until the end of the table stroke, at which point the table rapidly moves backwards and the particles momentum propels them still forward.

The capacity of the shaking table is about 0.5 t/h. 1.5-2TPH depending on the particle size of the process. In chromite processing and dressing industry, it is usually dozens of shaking table series or parallel installation to deal with excess tons. Therefore, the required installation space, equipment control difficulties due to the increased number of installations and the need for more automated processes have brought new challenges to the process design.

1. Big channel frame, very strong steel base structure( other companies use small channel frame)2. Polypropylene materials feeding chute and collection chute.(other companies dont have )3. Heighten steel stand,making it more convenient when feeding materials.4. Add cover for belt wheel5. Use top quality fiberglass deck,more wear-resisting6. Has various grooves on the table for your choice. We will recommend the best grooves to you according to your gold size.

what is the shaking table? | recyclinginside

what is the shaking table? | recyclinginside

The shaking table, also known as gravity separation, has different relative movements against gravitational forces, depending on factors such as weight, particle size, and shape by taking advantage of the density differences between mineral particles.

Shaking tables are rectangular-shaped tables with ribbed decks with a water film flowing on them. Water flowing along the long axis of the table slurries the fed sample. Low-density particles are transported in the fast-moving film, causing fine, high-density particles to fall into the beds behind rifles. With the rapid backward movement of the table, the particles gain a forward movement thanks to momentum, so each structure is separated from the other. Separation performance in shaking tables is directly related to particle size distribution.

Therefore, the narrower the grain size of the material, the better the separation performance. Wilfley and Gemini type shaking tables appear with different models in the recovery of precious metals, in gold mines, and in electronic waste recycling processes.

The shaking table used in the beneficiation of the mine field has the feature of separating precious and rare metals, especially in the structure of complex electronic wastes, from glass fiber and other plastic structures according to the density difference.

It is divided into three as concentrate, intermediate, and residue. In the chemical process, metals in concentrates and intermediates can be obtained more easily with high purity, while the residue, which is thought to be plastic and its derivatives, can be evaluated in another recycling process.

Proses Makina Company has minimized the leaks that may occur in the physical process with the innovations it made in the shaking table in addition to the chemical solutions it offers in mining and recycling. We continue to provide the needs of our customers in this adventure that we set out with the vision of zero loss!

Proses Makina is producing plants for refining and recycling systems. Thus, precious metals and rare metals attainable from e-waste, catalytic converter/spent catalyst, jewellery and mining fields. Catalytic converters contain PGMs and it's possible to recovery as Platinum, Palladium, Rhodium. Also e-waste has a precious metals and our e-waste recovery ...

shaking table tests on earthquake response characterization of a complex museum isolated structure in high intensity area

shaking table tests on earthquake response characterization of a complex museum isolated structure in high intensity area

Wenguang Liu, Chuan Qin, Yang Liu, Wenfu He, Qiaorong Yang, "Shaking Table Tests on Earthquake Response Characterization of a Complex Museum Isolated Structure in High Intensity Area", Shock and Vibration, vol. 2016, Article ID 7974090, 23 pages, 2016. https://doi.org/10.1155/2016/7974090

Owing to special functional requirements of museum, such as great space and story height for exhibitions, large floor slab openings in plan and long span truss in elevation are becoming increasingly considered in museum design, which leads to challenges to structural safety. The aseismic performance of an isolated museum structure in high earthquake intensity regions was thus studied because of its complexity and irregularity. In order to observe the seismic characteristics and verify isolation effect, shaking table tests of a 1/30-scale structural model with and without base isolation bearings have been carried out under minor, moderate, and major earthquakes. The experimental results show that isolated structure dynamic characteristics and isolation effect are stable and storey peak acceleration responses of superstructure are less than that of fixed structure. Storey drifts of isolated structure meet required limits stipulated in Chinese design code and torsion responses of the bearings are not remarkable. It is suggested that seismic performances of complex museum structures have been effectively improved with isolation in use.

Seismic isolation using lead rubber bearings (LRBs) has been recognized as one of the most effective approaches to protect vulnerable buildings (e.g., historical buildings, hospitals, and computer facilities) from strong earthquakes. In the past decades, numerical analyses and experimental studies conducted by many researchers [1, 2] have shown the effectiveness of seismic isolation. Actual evaluations also demonstrate the superior performance of isolated structures subjected to destructive seismic events in Northridge, USA (in 1994), and Kobe, Japan (in 1995) [36].

Museum is a kind of special functional public building, and its structural aseismic performances are always reduced by unique and complicated architectural design, such as large openings in floor slabs and long span truss in elevation. Structural safeties of these complex buildings are unable to realize by conventional structural design, especially in high earthquake intensity regions. The adoption of isolation could be an alternative choice for museums being capable of satisfying particular architectural functionality and structural aseismic requirements [7, 8].

To examine the effectiveness of isolation for complicate museum, shaking table test is reliable choice, which has been increasingly used to study the dynamic responses of different types of structures in these decades [912]. Iiba et al. studied 3-dimensional shaking table tests on a full-scale, two-storey house model with rubber bearing system, sliding system, and rolling system, respectively [13]. Lu et al. investigated shaking table tests on building models with a new system that combined the sliding and layered rubber bearing [14]. The effects of damping in various laminated rubber bearings on the seismic response of a 1/8 scale isolated test structure were investigated through shaking table tests [15]. The diameter of a lead plug was progressively increased so that a maximum isolator damping ratio of 24% was achieved. Dolce et al. assessed the effectiveness of four identical 1/3.3-scale, two-dimensional, reinforced concrete (RC) frames, with rubber-based, steel-based, shape memory alloy-based and hybrid in an extensive program of shaking table tests [16, 17]. Rawlinson et al. studied a passive gap damper to provide additional damping for isolation bearings, through numerical analysis and shaking table tests [18].

As an important parameter in the shaking table tests, the scale factors of test model and prototype structure also have been studied by many researchers. Takaoka et al. ascertained the ultimate behavior of slender base-isolated steel framed buildings in response to buckling fracture in laminated rubber bearings based on 1/9 scaled model shaking table tests [19]. Kikuchi et al. conducted earthquake simulation tests of a 1/2.5-scale model of an existing base-isolated, three-story reinforced concrete building [20], and Hwang and Hsu conducted uniaxial, biaxial, and triaxle shaking table tests to study the seismic response of a 1/2.5-scale three-story base-isolated steel structure [21]. The analytical and experimental results of a 1/3 scaled model of a reinforced concrete soft single storey structure mounted on natural rubber-based isolators and subjected to uniaxial seismic motion were investigated [22].

In recent studies, the aspect ratio effects on isolated structures have also been analyzed using shaking table tests. Chung et al. evaluated the effectiveness of base isolation systems for low-rise structure against severe seismic loads through the shaking table tests [23]. Miyama and Masuda conducted a shaking table test on high-aspect-ratio models of base-isolated buildings [24]. He et al. compared the seismic responses of large and small aspect ratio isolated buildings using a 1/30 scaled isolated model [25].

To achieve accurate seismic performances of isolated structure, some full-scale isolated models are used by researchers in the shaking table tests. Kasai et al. studied realistic 3D shaking table tests of full-scale building specimens utilizing the new schemes to assess performance of the building with passive control and base isolation schemes [26]. A 5-story steel moment frame building was tested at E-Defense in August 2011 with three different support configurations: a triple friction pendulum isolation system and lead rubber bearings in combination with cross linear bearings and in the fixed-base condition [27]. A base-isolated 2-story specimen for shaking table tests was first designed and cyclic tests of laminated rubber bearings and UH dampers implemented in the base isolating systems were carried out [28].

Besides common civil buildings, isolation bearings are also used to protect other constructions, such as industry facilities, liquid storage tanks, and some public buildings [29]. A five-storied, bench-mark model isolated with rubber bearings was studied for various earthquakes, and the varying efficiency of the isolation system was demonstrated [30, 31]. Paulson et al. examined the experimental results of the effectiveness of base isolators for reducing the seismic demands of a one-fourth scaled model of a masonry structure [32]. Sato et al. conducted a series of shaking table tests using a reduced scale model of a demonstration fast breeder reactor plant with three types of base isolation system [33]. Shaking table tests were performed using a small-scale arch model supported by the base isolation [34]. Tomaevi et al. investigated the efficiency of improving the seismic resistance of old masonry buildings by means of seismic isolation and confining the structure with CFRP laminate trips by using shaking table tests [35].

Shaking table test has become a powerful tool for researchers and designers to examine the dynamic performance of isolation systems of high-aspect-ratio buildings, irregular structures, and some crucial constructions. These years, growing amount of complex structures have been built in high intensity area, and their seismic safeties under severe earthquakes are hard to satisfy according to conventional structural design. As a functional public building, museums aseismic behaviors are always reduced by its large openings in floor slabs and long span truss in elevation. It is necessary for these complex structures taking shaking table tests to verify safety of conventional structural design and examine the effectiveness of isolation design. The objective of this paper is to assess seismic behaviors of such a seismically isolated museum structure called New Yunnan Provincial Museum, which has been attacked by Ludian earthquake in 2014. Brief introduction and primary achievements of the test has been summarized in [36], and more details and complete test analysis are shown in this paper.

The paper presents a shaking table test on a 1/30-scale model of 7-storey concrete-steel isolated structure with irregularities in both plan and elevation. A series of simulated ground motions, such as El Centro 1940, Tangshan 1976, Northridge 1940, and an artificial record, were included in test seismic loads. Dynamic properties, such as accelerations, displacements, and torsion responses, of the model were measured during the test.

New Yunnan Provincial Museum structure (as shown in Figure 1) is a 7-storey concrete-steel structure with a 104m by 104m floor plan and 37.4m in total height. As shown in Figure 3, the large span atrium of 40m 40m dimensions is placed in first three layers. Above the large span atrium, steel truss ceiling is designed at the height between 4th and 5th floor, and three layers of steel suspensions are slung under it as exhibition room of historical relics. The steel truss ceiling and suspension system together mean the so-called Treasures fill the house, which has a negative impact on seismic behavior of the museum structure.

There are three structure forms employed in the prototype structure: concrete filled steel tubular (CFST) in underground and first four layers, reinforced concrete (RC) in fifth layer, and steel truss in Treasures fill the house, as shown in Table 1. Sketches and details of their structural member sections could be achieved in Figure 2 and Table 2. Mechanical properties of steel and concrete materials used in prototype building are listed in Table 2.

According to the Chinese Code for Seismic Design of Buildings (CSDB, GB 50011-2010) [37], the site category of New Yunnan Provincial Museum is set II and its classification of design earthquake is the second set. Due to the seismic intensity 8 for the museum structural analyses and design, the peak accelerations (PGAs) corresponding to earthquakes of minor, moderate, and major levels are specified to be 0.07g, 0.2g, and 0.4g, respectively.

According to the Chinese Code for Seismic Design of Buildings (CSDB) and Chinese Technical Specification for Concrete Structures of Tall Buildings (JGJ3-2010) [38], three irregular characteristics of the building are summarized as follows.

(1) As shown in Figure 3, a large floor slab opening in plan is designed as atrium in the museum. The minimum effective widths of floor slabs in first three layers are only 38.7% and 37.2% of total width of diaphragm in the N-S and E-W directions, which are far less than the limit value 50% required in CSDB. The minimum values of the fifth floor and roof are only 13.8% and 27.6% in each direction. These irregular characteristics are classified as diaphragm discontinuity according to CSDB.

(2) In structural design, several frame columns at axes H and D are only located in first four layers and no upward extension to fifth and roof layer. Column underpin is used to transfer lateral internal forces to lower layers. These irregular characteristics are classified as discontinuity in vertical anti-lateral-force members in CSDB.

(3) As the navy blue parts shown in Figure 3, cantilever slabs are designed for much more exhibition space. The peripheral cantilever slabs and beams from the underground 1st floor to the 4th floor are about 6m and cantilever spans of 4m around atrium are placed from the second floor to the fourth floor. As shown in Figures 4 and 5, another 8m cantilever landscape platform at the second story is set in the atrium. These large cantilevers in design are classified as large cantilever components in the Chinese Technical Specification for Concrete Structures of Tall Buildings.

It is unable for the museum conventional design to satisfy the standard requirements, especially build in high intensity area. Adverse effects of these irregular characteristics on structure seismic performance also have been proved by numerical analysis for conventional structural design. Given the irregularities and complexity of the structure, isolation system is applied to improve seismic behavior of the museum under severe earthquake.

Compared to several isolation plans, lead rubber bearings and normal rubber bearings are chosen in the museum isolation system to protect superstructures. Total weight of the museum is 1069087kN, and 166 bearings are placed between 2nd and 1st layer to support it. Details of isolation bearings in prototype structure are shown in Table 3.

The shaking table tests were conducted in the State Key Laboratory for Disaster Reduction in Civil Engineering at Tongji University. The shaking table used in this test has a table dimension of 4m by 4m, and the maximum payload is 250kN. Its maximum accelerations in longitudinal, transverse, and vertical directions are 1.2g, 0.8g, and 0.7g, respectively. Detailed parameters of this facility are present in [39].

Test model materials including microaggregate concrete, fine wires, and red copper were used to construct structure model. As shown in Table 4, red copper was used to simulate steel structural members due to its low elastic modulus and similar yielding properties to steel. Microaggregate concrete with fine wires was chosen to construct concrete slabs and RC beam and column members. Fine copper tubes were used to simulate steel braces and steel trusses, and short steel strands were selected to simulate the links of suspension layers and steel trusses. Each suspension layer was fixed on the structural floor.

According to the dynamic similitude theory, there are three independent controlling scaling factors, and other subordinate scaling factors are derived from them. The purpose of the museum shaking table test is to examine seismic responses of test model with and without isolation bearings, and the use of large scale model in test is the best way to grasp seismic performance of isolated structure. However, it is often practically impossible to conduct testing at full scale and at the proper conditions of loading and history of motion. Given the bearing capacity and the size of the shaking table, the dimension scaling factor () in the model was chosen to be 1/30, and the model was built with a height of 1.860. The dimension scaling factor could well meet test code (JG J101-96 Specification of Testing Methods for Earthquake Resistant Building) [40]. The elastic scaling factor , which was first designed and finally determined according to the test results of material properties, was 0.25. Thirdly, the acceleration scaling factor was set to be 1.888. All the scaling factors used in the test were derived and are listed in Table 5 [19, 41]. To satisfy similitude relationships, artificial masses (steel plates and concrete blocks) were evenly distributed on the model at each floor, as shown in Figure 7 and Table 6.

Based on general principle of dynamic similarity, isolation period scaling factor () iswhere is period scaling factor, is stress scaling factor, and is time scaling factor. Therefore, the period scale factor is determined to be 0.133 (see Table 4), which can meet (1). The velocity scaling factor is [42]When (1) is substituted in (2), (2) can be rewritten as

According to the test results of model materials, the elastic scaling factor and stress scaling factor were both determined to be 1/4. Considering requirements of the same stress-strain curves and = 1/4, the strain scaling factor was set to be 1 [43]. Then, the velocity scaling factor in the model should be 0.251 due to (3).

Theoretically, if (or >1) [42] and , low-strength and high-elastic modulus material will be needed, which is practically impossible to realize. Although yield strength of lead is related to loading cycle, velocity, and temperature, it is hard to satisfy the requirements for velocity scaling factor in practice.

Moreover, due to the small size of the bearings in test, no remarkable reduction of the yield force was observed with the cyclic deformation increases, which should be much more remarkable for large size bearings [44, 45].

The base-isolated museum structure with a 4m by 4m floor plan for shaking table tests is shown in Figures 6 and 7. The overview and structural components of Treasures fill the house in model are shown in Figure 8. A rigid base plate was constructed as the basement of the base-fixed structure model, ignoring the interaction of the soil and the prototype structure. The total weight of model is 198.78kN and details of each layer are shown in Table 2.

The bearings (as shown in Figure 9) used in the isolated model were placed below the base plate, and the period of isolated structure was estimated as 0.542s (see Table 8). According to the dimension scale factor, the diameter of scaled bearing in test model should be 33.33mm while maximum diameter of prototype bearing is 1000mm, but this small isolator is unstable and hard to fabricate.

For reasonable bearings used in test model, dynamic similitude of isolation performance was proposed to keep design parameters of isolation layer, such as horizontal stiffness and yielding force, to be consistent with the bearings in prototype model. Considering similitude law, nine lead rubber bearings with 100mm diameter were designed in the isolated model, which could well simulate the performance and deformation requirements of the prototype bearings. Major properties of the base isolators are shown in Tables 7 and 8.

Three types of sensors, including accelerometers, displacement transducers, and 3-directional force sensors, were installed on the model so that both the global and bearing responses could be measured. Totally, there were 39 piezoelectric acceleration sensors including 23 laboratory shaking table system sensors and 16 external acceleration sensors used to monitor the acceleration responses of test model. The acceleration sensors were located on the shaking table, isolation layer, and each storey of superstructure and steel truss. 15ASM drawing displacement sensors with ranges of 0~375mm were located on the isolation layer and each storey of superstructure. Seven 3-directional force sensors including three ESM-100kN type sensors and four YBY type pressure sensors were employed to measure mechanism properties of bearings and analyze horizontal hysteresis performance and vertical force. Distributions of some accelerometers and 3-directional force sensors are shown in Figure 10.

The New Yunnan Provincial Museum was located in the city of Kunming, Yunnan Province. According to the CSDB, the site soil in this city belongs to type III, which is an important factor for selecting earthquake waves in dynamic tests. Considering the definition of type III site soil in the CSDB, the overlaying thickness of the site is no less than 50m, and average velocity of shear wave in the soil layer is between 150m/s and 250m/s. Then three different ground motions (as shown in Table 9) and one artificial wave were selected as input accelerations to the test: (a) the El Centro ground motion (designated as EL) from the California Imperial Valley Earthquake on 18 May 1940, which has been extensively used in Chinese design practice for the major level; (b) LWD-DEL AMO ground motion (designated as LWD) obtained from the 1994 Northridge Earthquake in USA; (c) Tianjin ground motion (designated as TJ) obtained from 1974 Tangshan Earthquake in China; (d) the Kunming artificial wave (ART). As shown in Figure 11, the ART wave fits the design spectra well and the other three earthquake waves decrease remarkably in the long period section, while the structural period of isolated prototype museum is 4.026s. Considering the adverse effect of long period earthquake waves to isolated structure, the ART wave is used to verify isolation effectiveness and ensure the safety of isolated museum structure.

Details of the waves attacked the test model in the tests are also important parameters for shaking table tests. Figure 12 shows the time histories and the corresponding Fourier amplitude spectra of the four scaled input motions measured from the shaking table. As shown in Figure 12, the predominant frequencies of scaled waves are 15.66, 18.75, 5.61, and 14.86Hz. For the dominant period of isolated test model is 0.542s, much more components of the ART wave close to this period could be seen in Figure 12 and greater seismic responses were achieved accordingly in the following test results of isolated model with the ART wave input.

According to the CSDB, three earthquake input levels, including minor, moderate, and major earthquakes, should be considered in shaking table tests. As Kunming belongs to the seismic zone of intensity 8, the peak ground accelerations (PGAs) for isolated structure design corresponding to the three different levels are specified as 0.132g, 0.378g, and 0.755g, respectively. In the seismic response analysis for the prototype structure with and without isolation, seismic-reduced factor (max ratio of structures storey shear forces with and without isolation) is less than 0.4, and the superstructure supported by isolation bearings could be designed as intensity 7 due to the CSDB. The peak ground accelerations (PGAs) for superstructure corresponding to the three input levels are specified as 0.092g, 0.264g, and 0.581g, respectively. There were unidirectional and three-dimensional inputs used in the shaking table tests. As stipulated for three-dimensional inputs by CSDB, the PGA ratio of the principal direction to the other direction should be 1:0.85:0.65.

The objective of the white noise excitation tests is to measure the dynamic properties of the model structure and investigate the variations of dynamic characteristics of model structures with and without isolation. A total of 74 cases were conducted in test, and a summary of the inputs used for each case is presented in Tables 10 and 11.

Before and after each test phase, as mentioned in Section 3.5, white noise signal was input to the model structure and its dynamic performance information was recorded by sensors. Comparisons of initial natural frequency values measured in white noise cases for the isolated structure and base-fixed structure are presented in Table 12. The first two modes of the isolated structure are of translation in directions and with the same initial natural periods of 0.257s. The third mode is of torsion with an initial natural period of 0.235s. For fixed model, the first three vibration modes frequencies are 0.118s, 0.101s, and 0.091s, the same as isolated model of translation in directions x and y and the torsional mode.

The variations of average frequency (variation of frequency = (frequency after shaking table tests original frequency)/original frequency) values for each mode have been also listed in Table 12. The average variation values for the isolated structure are 0%, 1.0%, and 1.2% after the minor, moderate, and major level earthquake inputs, which indicates that the isolated model definitely remains in elastic without any damage under minor earthquake and with a little damage under moderate and major level. This is also consistent with the ordinary assumption of elastic state under minor earthquakes.

For the fixed model, the average variation values are 3.4%, 7.60%, and 20.60% after the minor, moderate, and major level earthquake inputs. Although the natural frequency of base-fixed structure decreased a little after minor earthquake, it was still much more than that of the isolated structure under moderate and major earthquake. The base-fixed structure has even more serious damage than the isolated structure after major earthquake. Besides, the first torsion frequency of the isolated structure is 4.25Hz after different levels earthquake input. However, the values for the base-fixed structure are 10.97Hz, 10.26Hz, and 7.08Hz after minor 7, moderate 7, and major 7 tests, implying that serve damage has taken place in the model due to the reduction of torsion stiffness.

Acceleration responses were measured directly by mounted accelerometers on the model. The acceleration amplification factor (AAF) which is usually defined as the ratio of the peak value of floor accelerations response to the PGA of input waves is used to evaluate acceleration vibration amplification effects at different floor of the New Yunnan Provincial Museum structure with and without isolation bearings.

The profiles of acceleration amplification factor (AAF) for the isolated model (ISO) and fixed model (FIX) are shown in Figures 13, 14, and 15, where the AAF envelop values of each case are used. Compared with the fixed structure, the maximum AAFs for the isolated structure under three level ground motions are all less than 1 for both horizontal dimensions, implying the effectiveness of the isolation system. For the vertical response, it is clear that the acceleration differences of isolated and fixed models are little with minor earthquake input and becoming increasingly significant with earthquake loads arise.

The storey distributions for the isolated structure are close to a linear characteristic, and whip effects have been effectively controlled. With arising of seismic inputs, the decreases of superstructure acceleration responses are increasingly obvious. Figures 16 and 17 show the acceleration time histories of roof and the corresponding Fourier amplitude spectra of the isolated structure (ISO) and fixed structure (FIX) under major earthquakes. It is clearly shown in Figure 17 that isolation bearings filter out vast vibrations of building structure in the wide short period regions and only amplify few vibrations in the specified long period regions because of filtering effect. The results can explain the reduction effect of absolute acceleration of base-isolated structure.

For architectural aesthetics and large exhibition space of the museum, the Treasures fill the house system composed of steel trusses and suspension layers hanging below was designed in the atrium. As an additional system of the whole structure, it arises construction clearance and reduces cross-section of steel beam at same time.

For structural design, it is essential to analyze the seismic responses of this suspension system because of its weakening in lateral stiffness. The distributions of Treasures fill the house AAFs under the three level earthquakes are presented in Figures 18, 19, and 20. As shown, the maximum AAF values for the base-fixed structure are almost 12 times of those for isolated structure, and obvious isolation effects for the Treasures fill the house could be achieved. It is clear that AAFs in the x direction are much larger than that in y direction due to difference of lateral stiffness for base-fixed structure, and the variations are much smaller of isolated structure. With increasing of input earthquake level, AAF differences between isolated and fixed structures vary little for each horizontal direction. In general, the acceleration responses could be reduced by about 80% and 78% in directions x and y, respectively. For vertical direction, no obvious differences of two models could be achieved with minor earthquake input, and AAFs of isolated model are much less than that of fixed structure under moderate and major earthquake. The acceleration responses of the steel truss and the suspension layer could be effectively reduced by isolation bearings.

The max displacement responses of isolated model with different intensity earthquakes input are shown in Figures 21, 22, and 23. Seismic vibrations are mainly dissipated by plastic deformations of LRBs and that is why deformations of superstructure are relatively much smaller. The isolated model mainly oscillates under its first modal shape due to isolation effect. With increase of input earthquakes, deformations of isolation layer arise remarkably, in order to meet the requirement of bearings plastic deformation to dissipate input seismic energy. For different earthquake waves, isolation displacement responses of TJ and ART waves are much larger than that of EL and LWD waves under three level earthquakes; that is due to the much more long period components in wave TJ and ART, as shown in Figure 17.

The peak interstorey drift ratios (defined as the ratio of the peak interstorey drift and storey height) for isolated and fixed structures subjected to three level excitations are plotted in Figure 24, which is a crucial factor to assess structural damage. As specified in the CSDB, the limit value of elastic story drift for structure under minor earthquake is 1/550, and the limit value of elastoplastic story drift under major earthquake is 1/100.

In the test, the input earthquake level for isolated model was designed as intensity 8 and the earthquake for fixed model was designed as intensity 7 according to the CSDB. As shown, the interstorey drift ratios of isolated model are still less than that of fixed model, which are much more obvious with moderate and major earthquake input. With minor earthquake input, the storey drift ratios of both models are much less than the elastic limit value, which indicates that both models are in elastic condition and no damage happened. As input earthquake increases, the differences of storey drift ratios become much more notable. For major earthquake, the storey drift ratios of both models are still less than the elastoplastic limit value and no severe damage occurred in the structure. It could be found that, under major earthquake, the storey drift ratio of isolated model is still less than the limit value of elastic story drift, and the isolation effect is remarkable.

A series of bearing force-displacement curves under different level intensity ground motions are shown in Figure 25. For each earthquake wave, bearing hysteresis curves become full with seismic input level arising. As shown, isolation bearings work well and seismic energy is fully absorbed. It is found that hysteresis curves of waves TJ and ART are much larger than that of waves EL and LWD, and that is mainly because of more long period components in the former two waves, as mentioned above.

As shown in Table 13, with minor, moderate, and major earthquake inputs, the average torsional angles of isolation layer are, respectively, 1/6215, 1/4208, and 1/3016 in direction and 1/5700, 1/2389, and 1/1482 in direction , which indicates that the isolated model mainly oscillates with its first mode, and the torsional responses are not significant. The isolation design of the museum is stable to support superstructure.

Shaking table tests for the New Yunnan Provincial Museum with and without base isolators were conducted and the model was subjected to earthquake actions representing minor, moderate, and major earthquakes for a region of moderate seismicity, with basic seismic intensity at the 8 degrees. From the test results the following conclusions can be drawn:(1)The interstorey drift ratios of isolated structure are all less than the elastic and elastoplastic limits specified in the CSDB. The museum isolated model remains in elastic state without any damage occurring under minor earthquake and no severe damage happened with major earthquake input.(2)Compared with the test results of isolated and base-fixed structures, significant differences are experimentally observed in the acceleration and story drift responses. The acceleration amplification factors (AAFs) for the isolated structure under three level ground motions are all less than 1. Acceleration responses of the Treasures fill the house, composed of steel truss and suspension system, are effectively reduced by isolation bearings.(3)The isolation bearings exhibit full hysteretic curves and the input seismic energy is well dissipated. The efficiency of the isolation system varies with different earthquakes, which is better for high-frequency waves such as EL wave. Base isolation provides outstanding seismic performances for this complex museum structure under different level earthquakes.

The writers gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant nos. 51478257, 51308331, and 51508414), Natural Science Foundation of Shanghai (Grant no. 15ZR1416200), and Research Fund for the Doctoral Program of Higher Education of China (Grant no. 20 4).

Copyright 2016 Wenguang Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

how to brace a shaky table | home guides | sf gate

how to brace a shaky table | home guides | sf gate

Everyone has had the experience of setting a full cup of hot coffee or tea on a kitchen or restaurant table only to have the beverage spill when the table shakes, rattles and rolls. This happens because the table legs are loose or different lengths or the floor is uneven, resulting in a wobbly table.

When the floor is at fault, the solution that first comes to mind is to put something like a folded napkin or a piece of cardboard under the leg that doesn't reach the floor, and while this might work, it's just a temporary solution. In fact, physics tells us that there's a better, more permanent solution that's even easier than shimming the leg. Of course, if the legs are loose, Family Handyman reminds you that you have to tighten them, and if they're not the same length, you need to install table wobble-stoppers.

The repair strategy for a table that wobbles because the floor is uneven comes from Oliver Knill of Harvard University, so perhaps it is rocket science. All you have to do is rotate the table until it stops wobbling. Yep, that simple technique has been proven by mathematicians using complex geometry and algebra, and the proof is known (no joke) as the Wobbly Table Theorem. For this fix to be successful, all four legs have to be the same length.

Here's how it works: Three legs of the table must always be in contact with the floor no matter what, or the table would fall over. If you rotate the table through 90 degrees keeping all three legs on the floor and the middle one stationary, the fourth leg must come in contact with the floor at some point, and the table will stop wobbling. If you don't believe the mathematician at Harvard, you'll probably have to test this for yourself but don't be surprised when you find that it happens as predicted. It's math!

Sometimes, the cause of a wobbly table isn't an uneven floor but the table legs themselves. They're loose, and if you want the table to stop wobbling, you have to tighten them. For this, you'll need an adjustable wrench, and it's a lot easier to do if you turn the table upside down. If the floor isn't carpeted, you'll want to lay down some newspaper so you don't scratch the finish on the tabletop, and if it's a large table, you'll need help turning it over.

Most tables have corner blocks for the table legs, and there is usually a single large bolt securing each leg to the corner block. If the table is wobbling, it's because these nuts are loose, and you can verify this by turning one of the nuts; you'll probably be able to do it by hand. You can see the loose nuts, and you have the wrench in your hand, so you know what to do next: tighten all the nuts securely to stabilize the table legs, turn the table upright and voila no wobble.

A more technical name for wobble-stoppers is leg equalizers, but whatever you call them, they're what you need if the table legs are different lengths. Most wobble-stoppers consist of a sleeve that you insert into a predrilled hole on the bottom of the leg and a glider attached to a bolt that screws into the sleeve. The gliders are usually smooth plastic, and that's a bonus because they won't scratch the floor when you move the table.

To install wobble-stoppers, turn over the table and drill holes for the sleeves using a drill bit with the same diameter as the sleeves. Tap a sleeve into each hole using a hammer and then insert the glider bolt and screw the glider clockwise as far as it will go. When you've installed all four, turn the table upright, note which leg is not in contact with the ground and unscrew the glider until it touches the floor.

Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at such sites as Hunker.com, SFGate and HomeSteady.

Related Equipments