Essay: Dynamic performance of the shaking table

1.1 General
It is the fact that if we working with any instrument we have to know about its performance and permissible values of inputs may be off any kind in terms of loads , excitations etc. in this case we are actually analyzing the structural and instrumental performance of our shake table. To define its permissible values we have to perform some tests on it under characteristic loading condition. The shaking table is analyzed for their frequencies and movement amplitudes that are obtained in accordance with the mass that is excited in the platform.
Dynamic testing in small-scale models always performed a very important role in the Understanding of dynamic loads in structures, it is the important to understand many of the concepts involved in experimental analysis in structures, namely in the testing of small-scale models. It is in the context of dynamic testing of structures, developed their shaking table that in this thesis will be the main subject of study. The main objective of this work is to Characterization of the Shake table, to introduce improvements in the system and to suggest future interventions in the table. The shaking table is analyzed for their frequencies and amplitudes that are obtained in accordance with the mass that is excited in the platform and without mass.
A complete understanding of the shaking table capacities, will allow a more accurate performance of the dynamic testing in small-scale models. In this work, is executed the dynamic testing, of a small-scale steel framed structure and spring mass model when it is excited with the shaking table. In this study a portable models, servo motor driven arrangement of table, controller and one-dimensional earthquake simulator is manufactured.
The goal of this work is the characterization the instrumental and structural limitations of the shake table. Tests performed by shake tables are popular in areas of earthquake engineering, structural dynamics, testing of smart materials, actuators, and sensors. One of the interesting points of the current manufacture comes from the fact that servo motors and controller devices that are newly being used in shaking tables.Most of the modern seismic codes in the world are essentially Prescriptive, which means they are based on a set of prescribed requirements for Design of buildings that are expected to result in structures that can attain certain performance levels, mostly life safety, during an earthquake event.
The exact performance of such structures under an actual earthquake is unknown because of the inherent uncertainties in the level of ground shaking and material and structural behaviour. As such, performance can vary between structures designed based on the same prescriptive requirements and under the same seismic hazard levels.
However for the life safety performance level, which is one of the key target levels in most modern seismic codes, such damage is to be expected and often considered to be acceptable, under the maximum considered seismic event. The life safety performance level targeted in most current codes has been considered to be non-reflective of the needs of modern societies where the economical losses during downtime of the business due to damage to structures or the damage to the contents of the structures can be far more than the construction costs of the structure itself.
The actual seismic behaviour of structural components and systems, and development of analytical models to more accurately predict the seismic response of different structures in terms of specific physical parameters known as performance indicators.
 Elementary Parts of Vibrating System
A Vibrating system is consists of a spring mass or inertia (a means for storing kinetic energy), and a damper (a means by which energy is gradually lost). An undamped vibrating system involves the transfer of its potential energy to kinetic energy and kinetic energy to potential energy, alternatively. In a damped vibrating system, some energy is dissipated in each cycle of vibration and should be replaced by an external source if a steady state of vibration is to be maintained.
 Continuous Systems and Discrete System
The most of the mechanical and structural systems can be described using a finite number of degrees of freedom. However, there are some systems, especially those include continuous elastic members; have an infinite number of degree of freedom. Most mechanical and structural systems have elastic (deformable) elements or components as members and hence have an infinite number of degrees of freedom. Systems which have a finite number of degrees of freedom are known as discrete or lumped parameter systems, and those systems with an infinite number of degrees of freedom are called continuous or distributed systems.
 Free vibration of single degree of freedom system.
The free vibration force just act for a moment in free vibration the body at first is given as initial displacement and the force is withdrawn. The body starts vibrating and continues the motion of its own accord. No external force acts on the body further to keep it in motion. On free vibration the object is not under the influence of any kind of outside force. The frequency of free vibration is known as free frequency. The most basic mechanical system is the single degree of freedom system, which is characterized by the fact that its motion is described by a single variable or coordinates. Such a model is often used as an approximation for a generally more complex system Excitations can be broadly divided into two types, initial excitations and externally applied forces the behaviour of a system characterized by the motion caused by these excitations is called as the system response. The motion is generally described by displacements
Example — pendulum vibration it is free vibration.
 Force vibration
A vibration in which the force remains present in the system while vibrating. When a periodic disturbing force keeps the body in vibration throughout its entire period of motion, such vibration is said to be a forced vibration is said to be a forced vibration. The frequency of vibration of the body is saw as the free of the applied force. Force vibration is the vibration which is caused due to external force applied on the studying or material respectively.
When an external periodic force is applied on a body whose natural period is different from the period of force then the body is made to vibrate with a frequency equal to that of the externally impressed force.
Example — drilling machine vibration of depends on a force outside.
1.2 Rayleigh’s Method generalized single degree of freedom system distributed elasticity
We are concentrated our efforts in obtaining the response to dynamic loads of structure modeled by the simple oscillator, that is, structure which may be analyzed as a damped or undamped spring mass system. Which a structural system consisting of multiple interconnected rigid bodies or having distributed mass and elasticity can still are modeled as a one degree of freedom system.
This method for approximating the analysis of a system with an infinite number of degrees of freedom with a single degree of freedom consider the cantilever beam, the physical properties of the beam are the flexural stiffness and its mass per unit of length.
1.3 F.R.F (frequency response function)
The FRF (frequency response function) is the measure of any system output spectrum in response to an input signal. A linear system such as an SDOF or an MDOF, when subjected to sinusoidal excitation will respond sinusoid ally at the same frequency and at specific amplitude that is characteristic to the frequency of excitation. The phase difference b/w the response and the excitation will vary with frequency. The characteristics of a system that describe its response to excitation as the function of frequency is the frequency response function. It is defined as the ratio of the output to the input as a function of frequency. Accelerometer measures the vibration levels at several points on the structure and signal analyzer computes the FRF.
1.4 Objective of the present work
• To produce a detailed characterization to a common specification, of the dynamic performance of the shaking table.
• Finding the structural properties of models using shake table.
• To analyze the parameters of shake table namely acceleration under characteristic loading condition.
• To identify the advantages and Disadvantages in the present shake table
1.5 Outline of thesis
• Is a presentation of previous studies of free vibration techniques, and force vibration to measure natural frequency of materials models this includes theoretical and experimental investigations done by other investigators.
• Is an experimental procedure and methodology.
• Describes experimental investigation.
• Performance of the shake table without load and with load.
• Presents a description of Impact hammer test and shake table tests is also included.
• The experimental results and analysis presented in details. The study of the results in terms of the parameters is also presented.
1.6 Scope of the work
To achieve the above objectives, the scope of this work for the project generally involves the following:
• To build up the experiment test rig for testing
• To catch the signals of vibration using accelerometer and FFT analyzer to obtain the natural frequency of Single storey building steel frame and spring mass models varying the parameters like thickness ,different materials different and height etc. and for the fundamental natural frequency.
• To compare the natural frequencies of different material according the different parameters like their Thickness, Material, and Height.
• To apply the free and forced vibration on the structure and the analysis of single storey and spring mass models beam of different materials by impact hammer and shake table tests using a FFT analyzer.
Selected study
 H H Yoo, et.al (1967)
• Vibration analysis of rotating beam
The study of the vibration analysis of a rotating cantilever beam is an important and peculiar subject of study in the mechanical engineering. There are many engineering examples which can be idealized as rotating cantilever beams such as turbine blades or turbo engine blades and helicopter blades. the proper design of the structures their vibration characteristics which are natural frequencies and mode shapes should be well identified study. Compared to the experimental and vibration characteristics of non rotating structures those of rotating structures often vary significantly. The variation results from the stretching induced by the centrifugal inertia force due to the rotational motion. The stretching causes the increment of the bending stiffness of the structure which naturally results in the variation of natural frequencies and mode shapes. The equations of motion of a rotating cantilever beam are derived based on a new dynamic modelling method. With the coupling effect ignored the analysis results are consistent with the results obtained by conventional modelling method. A modal formulation method is also introduced in this study to calculate the tuned angular speed of a rotating beam at which resonance occurs of the study.
 J.S Hwang, et.al (1987)
• The system characteristics and performance of a shaking table
In this paper the dynamic performance of the shaking table assessed by comparing the result introduce by two separate input programme signals, measure acceleration and displacement of a know earth quake record. The system characteristics of the earth quake of the ground motion simulation facility at the state university of New York at Buffalo are described in this paper. The simulation of the buffalo shaking table which has a three variable control system is examined ground motion this system can have both acceleration and displacement as input program source in this research good fidelity of simulation of the shaking table is established. Using this shake table there is no need to be a concerned with the channel arrangement in inelastic structural test where hysteresis curves are required consequently, the dissipated energy s estimated by the area of the hysteresis curves should be reasonable reliable. The simulation ground motion ability is for using the acceleration trace as the input program source this technique is only an extrapolation of the desired exciting level based on a lower level test it should not be automatically assumed to yield superior results than using the displacement input in all cases. In this shake table using the compensation technique the system model is not uniquely determined because it depends on specific test specimen and gain setting, much significant change on test specimen model. Furthermore there is no well established process for choosing the optimal peak value of the time history of the noise especially for a very small level of excitations.
 P.G.Carydis, et.al (1996)
• Comparative Assessment of Shaking Table.
In this research the result of an extensive comparative study of four large capacities shaking tables are described, one, three and six degree of freedom shaking table has been studies and their dynamic characteristics identified. This paper presents a characterization of the shake table study. The purpose and methodology of the tests are explained and the main conclusions are discussed, a very good match of the required acceleration, velocity and displacement time histories was achieved for both rigid and flexible payloads once sufficiently complex control algorithms were used the importance of defining the critical criteria for any time history matching and the requirement for careful adjustment of the shaking table control hardware is also describe the paper. Shaking table provides a test facility that will continue to be important is dynamic and seismic testing fields. This has proved to be a highly successful and valuable exercise and has resulted in improved performance at all four facilities. This programme of test has also given each of the research groups a greater understanding of their own shaking table.standard programme in this research, to produce a detailed characterization to a common specification, of the dynamic performance of the four shaking tables. To identify strengths and weaknesses and possible enhancements for the entire shake table. To compare, validate and verify existing signal generation, control and data processing software at each site, based on a common specification. Produce a standard set of calibration tests and procedures. To develop an adaptable database system and appropriate access software, are used in this research common to all sites, to facilitate data exchange. Establish arrangement for sharing skills and experiences with the aim of developing efficient
 Masanori IIBA, et.al (2000)
• Test on performance of isolators for houses subjected to three dimensional earthquake motions.
In this paper the test performance characteristics of the newly developed isolators, the outline of the tests and the latest results obtained from the experimental data-processing are presented.. Verification of isolators and base-isolated houses behavior under recorded earthquake ground motions has been one of the most important objectives of the project. In order to realize that, 3-dimensional shaking table tests on different types of base isolation systems and on a full-scale, two-story base-isolated house model were conducted. Tests were performed on a large-scale three-dimensional shaking table recently installed at the Public Work Research Institute of Ministry of Construction [PWRI, 1997]. This shaking table is specially designed for simulating earthquake ground motions of the same intensity as those ones recorded during the Northridge Earthquake of January 17, 1994 or Kobe Earthquake of January 17, 1995. the good performance of seismically isolated structures during this earthquake have persuaded structural engineers, isolator makers and housing construction companies to undertake a cooperative research project to investigate the possibility of introducing seismically isolated structures in Japan’s private housing sector. Verification of isolators and base-isolated houses behavior under 3-directional recorded earthquake ground motions has been one of the most important objectives of the project. In order to realize that, 3dimensional shaking table tests on different types of base isolation systems and on a full-scale, two-story base-isolated house model were conducted.
 Rogerio BAIRRAO, et.al (2000)
• Testing of Civil Engineering structures-The Linec 3D simulator experience
The use of shaking tables for the assessment of the dynamic and seismic behavior of civil engineering structures is effective since the sixties. At the beginning, shaking tables had important limitations concerning the power available and they have been used to study the dynamic characteristics (natural frequencies and mode shapes) of small models behaving essentially in the linear range. Meanwhile, bigger and more powerful shaking tables have been put in operation allowing for the adoption of lower scaling factors and therefore involving very important dynamic forces. Nowadays a significant amount of research using shaking tables can be found in the literature. This research has been oriented mainly for the ultimate behavior of steel and RC building structures, structural elements (with a clear emphasis on rc and masonry walls, rc frames with infill’s and dissipating devices) and global models of structures at smaller scales. Shaking tables are nowadays a valuable tool for the seismic behavior assessment of civil engineering structures. The main purpose of this paper is to present some aspects of the recent experience obtained throughout the accomplishment of several series of tests (on different types of structures) which were achieved using the new LNEC 3D earthquake simulator. It should be mentioned that the tests results are not presented, as the emphasis is focused on the main issues found in order to perform the tests as close as possible both to the nature occurrences and the structural behavior.
 S. K. Prasad, et.al (2004)
• Test in earthquake geotechnical engineering.
EARTHQUAKE geotechnical engineering in India has received tremendous boost after the Gujarat earthquake of 2001. Earthquakes are not uncommon, but the damage suffered during earthquakes is on the rise because of the population growth, overcrowding of civil engineering facilities in urban areas and improper understanding of ground behavior among many. Developments in earthquake geotechnical engineering which include understanding ground behavior during shaking, effects of earthquake on geotechnical facilities, site amplification studies, etc. have also shown tremendous progress. Research in earthquake geotechnical engineering has shown considerable development in the recent past. We focus here on developments of model testing in earthquake geotechnical engineering. Two aspects of model testing are given importance, namely manual shaking table and laminar box. Design, development, calibration and performance of these equipments are described. Model testing is the essential requirement of earthquake geotechnical engineering that helps in understanding the behavior of geotechnical facilities and their performance during earthquake. Manual shaking table developed very economically can be used as an alternative to a more sophisticated shaking table. Laminar box is a sophisticated container which can enhance the accuracy in assessing the ground behavior. Some of the important calibration techniques necessary are also discussed.
 Abdolhossein Fallahi, et.al (2004)
• Test on an SDOF model steel structure using target earthquake
This paper present the According to recommendation of the Japan Road Bridges Code , it is better to employ some 3 acceleration records, and use average of the corresponding responses in seismic check, which is based on the fact that expected earthquake ground motions on a specific site would be different with each other considering different characteristics of earthquakes, and that earthquake inputs are uncertain even with the present knowledge and it does not appear easy to predict forthcoming events precisely both in time and frequency contents. the using NS component of acceleration record with peak acceleration (PA) of 818 cm/s2 observed by Japan Meteorological Agency (JMA) in the 1995 Kobe earthquake as target earthquake, a critical earthquake which causes greater response on a 1:8 SDOF model steel structure accompanied with a damper was simulated and shaking table test was carried out. Through static experiment nonlinear as bilinear parameters of the model were determined and used in the simulation process. By free vibration test the natural period (0.2 s) of the model was confirmed and the damping ratio (2%) was determined. The simulation was conducted by the product of artificial wave generated from modified power spectral density (PSD) function and envelope function at consecutive time intervals of target. The modification was performed by amplifying the PSD graph of target at each time interval in a specified width corresponding to the structural response and reducing it in the other parts in which the areas under the PSD-frequency diagrams in the original and modified ones to be same.
 Seung-Eock Kim, et.al (2005)
• Test of a two-story unbraced steel frame
The seug-eock had experimental work test of a two storey unbraced steel framed structure in the past many experiments were conducted for steel frames subjected to static loads to provide experimental results for the verification of second-order inelastic static analysis techniques. This paper presents some shaking table tests for a one-bay, two-story steel frame under simulated earthquake loading. The test frame was designed to be capable of showing the second-order inelastic behavior under the earthquake loads and to avoid lateral torsion buckling of a single member. The descriptions of test specimen, instruments, set-up procedures, and results are presented. A comparison of the results obtained from experiment and numerical analysis using beam element model of the ABAQUS program is provided. The experiment aims to clarify the inelastic behavior of steel frames subjected to earthquake load and its results can be used to verify the validity of second-order inelastic dynamic analysis techniques of steel frames. Kim and Kang [9] performed an ultimate strength large-scale testing to account for local buckling father-dimensional, one-bay, two-story steel frame subjected to proportional loads.
 O. Ozcelik1 et al. (2007)
• Experimental characterization, modeling and identification of the shake table system.
This paper presented the experimental characterization of the shake table and the propose a simple conceptual mathematic model for the mechanical components of the NEESUCSD large high performance outdoor shaking table and focuses on the identification of the parameters of the model by using an extensive set of experimental data. Finding the displacement, Acceleration, and Velocity of the present work. The effectiveness of the proposed conceptual models verified through a comparison of analytical results with the experimental results for various tests conducted on the system. An identification approach based on the measured hysteresis response is used to determine the fundamental model parameters including the effective horizontal mass, effective horizontal stiffness of the table, and the coefficient of the classical coulomb friction and viscous damping element representing the various dissipative forces in the system. Physics based model of the entire mechanical, hydraulic, and electronic system. Although the parameters of the model considered herein have been identified by using the response during periodic sinusoidal and triangular excitations, it has been shown that the resulting model is also capable of representing the more common shake table tests involving earthquake ground motions and white noise excitations.
 Dr. S. Chandrasekaran, et.al (2007)
• Horizontal Shaking table
This study described mechanism of the horizontal shake table. The Table was designed in-house by Dr S. Chandrasekaran and Dr. P.K.Singh; fabricated & commissioned by Milenium Technologies (I) Pvt. Ltd, Bangalore, under the braces of Special Assistance Programmer Project funded by University Grants Commission. It is a unidirectional shake table operates only in horizontal direction. The motion is simple harmonic and works in the principle of crank mechanism, converting the rotary motion of the motor to linear motion of the Table. It comprises of few important components namely: i) Sliding Table; ii) Driving mechanism; ) control panel. The whole mechanism of the Shake Table is designed to make the working simple and less electronic controlled; rather the motion is made as mechanically controlled. The idea behind is that it can be easy overhauled/repaired using the existing technical knowhow of the Lab staff. While conventional imported Shake Tables shall cost very high, this in-house designed Table costs 1/5th of that price and also cater to the on-going research and post-graduate teaching of the Dept.
 C. S. Sanghvi , et.al (2012)
• DEVELOPMENT OF LOW COST SHAKE TABLES
In this paper “development in the field of earthquake engineering, experimental study is required” To study the effects of earthquake, laboratory facilities are needed. The development has reached to a stage where earthquake simulation is achieved in laboratory. Shake table is used to provide earthquake simulation and to test the prototype and scaled model of the structure. In order to reproduce actual earthquake data, a six-degree of freedom electro-hydraulic shaking table is essential. They are very expensive and require high maintenance and operational costs. There exists a need to developed suitable teaching and learning aids to augment the classroom teaching. One of the most effective ways to achieve this is to develop simple experimental setup with suitable shake table. Development of shake table for the Earthquake Engineering laboratory to test models is a challenge the law cost shake table. Single translation (horizontal) degree of freedom shaking tables is useful for laboratory testing to study behavior of structural models. From this perspective, low cost uni-axial shaking tables were designed & fabricated at L.D College of Engineering. These low cost shake tables will be used to study behavior of structure through models under harmonic as well as random excitation.
Shake tables prepared by L.D College of Engineering (L.D.C.E) are Uni-axial Electro-mechanical Shaking tables. These shaking tables are assembly of various steel sections that forms a table on which a plate is supported. The movement of this plate is considered as shaking of ground due to earthquake. The term Uni-axial means movement in one horizontal direction only.
 Hakim BECHTOULA, et al (2014).
• Performance and overview of the new 6 DOF Shaking Table.
This research paper had activity of laboratory will include the development of experimental research in field of earthquake engineering, dynamic qualification test of industrial equipment; conduct a collaborative research project with and international institutions. This laboratory is located at Algiers ant it is composed of a six degree of freedom shaking table of 6.1×6.1m, a reaction wall of 13x15m and a strong floor of 13x32m. In this laboratory is equipped with an advanced hydraulic distribution system, a series of high performance actuators are used and 128-channel data acquisition system and two high-capacity bridge cranes of 10 and 32t. The shaking table is capable of simulating earthquake events and other ground vibration with displacements of ±150 mm and ±250mm in the horizontal directions and ±100mm in the vertical direction. Accelerations of ±1.0 g for horizontal directions and ±0.8 g for vertical direction are possible with maximum test specimens of 60tons. Performances of the shaking table were checked using 4 specimens. It was observed that the achieved and the target performance envelope are in good agreement for all frequencies of operation. The error in peak value between achieved and target signal did not exceed in the worst case 1% in displacement control and 2% in acceleration control. This result indicates that the CGS shaking table is performing to its design specifications criteria. The dynamic testing facility can be used reliably for the type of experiments that it was designed for.