30-11-2012, 01:30 PM
SHAKE TABLE STUDIES ON VARIOUS LABORATORY MODEL
[attachment=41841]
INTRODUCTION
Many of the earthquakes give the little or no warning before occurring and this is the reason why the earthquake engineering is complex. Experimental testing of the structural system is essential for improving knowledge about component and system performance in earthquake. Shaking table test providing important experimental data about critical issue such as the effect of component damage on the system response, collapse mechanisms, residual, deformation, and post earthquake capacity. Even with this facility, most structural system is too large to test at or near full scale.
In many fields, there is great uncertainty as to whether a new design will actually do what is desired. New designs often have unexpected problems. A prototype is often used as part of the product design process to allow engineers and designers the ability to explore design alternatives, test theories and confirm performance prior to starting production of a new product. Engineers use their experience to tailor the prototype according to the specific unknowns still present in the intended design. For example, some prototypes are used to confirm and verify consumer interest in a proposed design whereas other prototypes will attempt to verify the performance or suitability of a specific design approach.
Even with these recent advantages, structural testing has typically been conducted using customized software that is dependent on the configuration and computation procedure for the test method. Investigation on the dynamic behaviors of the large scale civil engineering structures such as buildings and bridges by performing full scale test is very difficult or often practically impossible to be realize due to the size, weight, and cost etc. therefore the behavior of the whole structure is estimated generally based on the test results obtained by using scaled down model.
Most structures are subjected to vibrations. Vibration means to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road. Vibration is occasionally "desirable". For example, the vibration motions of engines, electric motors, or any mechanical device in operation are typically unwanted. There are two types of the vibrations in the structural dynamics;
a) Free vibration
b) Forced vibration
Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. The mechanical system will then vibrate at one or more of its "natural frequency" and damp down to zero.
Forced vibration is when an alternating force or motion is applied to a mechanical system. Examples of this type of vibration include a shaking washing machine due to an imbalance, transportation vibration (caused by truck engine, springs, road, etc.), or the vibration of a building during an earthquake. In forced vibration the frequency of the vibration is the frequency of the force or motion applied, with order of magnitude being dependent on the actual mechanical system. Types of the structural vibration of the system are shown in Figure 1.1.
VIBRATIONAL EQUIPMENT
Vibration measurement instruments and vibration analyzers are used for measuring, displaying and analyzing vibrations. Typically, these instruments comprise of a transducer, data acquisition and either a local display or some sort of output to a computer or another instrument. Vibration measurement instruments and vibration analyzers can have many features, including incorporating features such as totalizing, local or remote display and data recording. They may be stationary or else portable field-type instruments.
Vibration measurement instruments and vibration analyzers can accept a number of different types of transducers, including acceleration, linear velocity, proximity and displacement, rotary velocity and temperature. In addition, many vibration instruments can take generic signal inputs, including voltage, current, frequency and serial inputs. Some of these instruments can even accept wireless data transmissions.
Four main features must be considered when selecting vibration measurement instruments and vibration analyzers: number of channels, accuracy, sampling frequency and ambient conditions. Electrical output options depend on the system being used with the vibration instruments. Common analog options are voltage, current or frequency. Digital output choices are the standard parallel and serial signals. Another option is to use vibration instruments with an output of a change in state of switches or alarms. Two further output options are important to consider. Vibration instruments can often output acceleration, velocity or displacement values as well as standard vibration readings.
Vibration instruments come in different form factors. As mentioned above, they can be stationary or portable. Another slightly different option is a handheld device, meaning that the instrument is actually small enough to operate in one’s hand, as opposed to being a portable device with wheels or a handle. One such device is shown in Fig1.1. the above the device shown is single channel FFT analyzer.
[attachment=41841]
INTRODUCTION
Many of the earthquakes give the little or no warning before occurring and this is the reason why the earthquake engineering is complex. Experimental testing of the structural system is essential for improving knowledge about component and system performance in earthquake. Shaking table test providing important experimental data about critical issue such as the effect of component damage on the system response, collapse mechanisms, residual, deformation, and post earthquake capacity. Even with this facility, most structural system is too large to test at or near full scale.
In many fields, there is great uncertainty as to whether a new design will actually do what is desired. New designs often have unexpected problems. A prototype is often used as part of the product design process to allow engineers and designers the ability to explore design alternatives, test theories and confirm performance prior to starting production of a new product. Engineers use their experience to tailor the prototype according to the specific unknowns still present in the intended design. For example, some prototypes are used to confirm and verify consumer interest in a proposed design whereas other prototypes will attempt to verify the performance or suitability of a specific design approach.
Even with these recent advantages, structural testing has typically been conducted using customized software that is dependent on the configuration and computation procedure for the test method. Investigation on the dynamic behaviors of the large scale civil engineering structures such as buildings and bridges by performing full scale test is very difficult or often practically impossible to be realize due to the size, weight, and cost etc. therefore the behavior of the whole structure is estimated generally based on the test results obtained by using scaled down model.
Most structures are subjected to vibrations. Vibration means to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road. Vibration is occasionally "desirable". For example, the vibration motions of engines, electric motors, or any mechanical device in operation are typically unwanted. There are two types of the vibrations in the structural dynamics;
a) Free vibration
b) Forced vibration
Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring. The mechanical system will then vibrate at one or more of its "natural frequency" and damp down to zero.
Forced vibration is when an alternating force or motion is applied to a mechanical system. Examples of this type of vibration include a shaking washing machine due to an imbalance, transportation vibration (caused by truck engine, springs, road, etc.), or the vibration of a building during an earthquake. In forced vibration the frequency of the vibration is the frequency of the force or motion applied, with order of magnitude being dependent on the actual mechanical system. Types of the structural vibration of the system are shown in Figure 1.1.
VIBRATIONAL EQUIPMENT
Vibration measurement instruments and vibration analyzers are used for measuring, displaying and analyzing vibrations. Typically, these instruments comprise of a transducer, data acquisition and either a local display or some sort of output to a computer or another instrument. Vibration measurement instruments and vibration analyzers can have many features, including incorporating features such as totalizing, local or remote display and data recording. They may be stationary or else portable field-type instruments.
Vibration measurement instruments and vibration analyzers can accept a number of different types of transducers, including acceleration, linear velocity, proximity and displacement, rotary velocity and temperature. In addition, many vibration instruments can take generic signal inputs, including voltage, current, frequency and serial inputs. Some of these instruments can even accept wireless data transmissions.
Four main features must be considered when selecting vibration measurement instruments and vibration analyzers: number of channels, accuracy, sampling frequency and ambient conditions. Electrical output options depend on the system being used with the vibration instruments. Common analog options are voltage, current or frequency. Digital output choices are the standard parallel and serial signals. Another option is to use vibration instruments with an output of a change in state of switches or alarms. Two further output options are important to consider. Vibration instruments can often output acceleration, velocity or displacement values as well as standard vibration readings.
Vibration instruments come in different form factors. As mentioned above, they can be stationary or portable. Another slightly different option is a handheld device, meaning that the instrument is actually small enough to operate in one’s hand, as opposed to being a portable device with wheels or a handle. One such device is shown in Fig1.1. the above the device shown is single channel FFT analyzer.