Entrepreneurial universities June 7, 2007
Posted by dionsiringo in Indonesiana, opinion.add a comment
In the spirit of the slogan “2006, The Indonesian Year for Science”, it worth asking the question how much our scientific communities have contributed to the economy. With the current 0.3 percent of national GDP invested in research and technology, some might argue that it is too soon to ask for such a contribution. But while increasing national investment in research is vital, it is also essential to measure how much economic growth has — and will — emanate from these knowledge investments. New strategies should be developed to avoid the pitfall of the so-called “European paradox”; the conjecture that while European countries have consistently been leading players with top levels of scientific output, they lag behind in the ability to convert this knowledge into wealth-generating power.
During the New Order government of the 1980s and 1990s Indonesia experienced a similar kind of European paradox, only on a smaller scale. Back then, the promotion of high technology was initiated from the top, on the assumption this technology would automatically function as the accelerator of economic growth..
System identification of suspension bridge using ambient response May 28, 2007
Posted by dionsiringo in Bridge Engineering, Jembatan Suspensi, Structural Monitoring, Vibration.add a comment
Performance of a suspension bridge under wind, seismic and other live loads depends upon its structural properties such as mass, stiffness and damping and their distribution. Although these properties can be modeled using sophisticated analytical models, the real behaviors of the bridge remain to be verified from a full-scale vibration test. The fullscale vibration test would facilitate identification of dynamic characteristics (e.g. natural frequency, damping ratio and mode shape), whose quantities serve as the basis for validating and/or updating analytical models of the structure, as well as providing the actual structural properties and boundary conditions. Furthermore, frequent measurements and analysis of these characteristics will facilitate the evaluation of structural safety and health monitoring.
There are two most common techniques for vibration test of a bridge, namely, the measured-input test and the ambient vibration test. In the measured-input tests, the structure is excited by artificial means using large inertial shakers or drop weights. Measured input excitation is usually applied at a single location where the force input to the structure can be monitored. The tests with measured inputs are usually conducted on small- or moderate-span bridges. The results are generally sufficient for modal identification since the inputs can be well defined and the excitations can be optimized to the response of vibration modes of interest. However, the test features that require extensive instrumentations and disruption of traffic have made frequent tests less favorable. Furthermore, in the case of large and flexible bridges (such as cable-stayed and suspension bridges), where the natural frequencies of the predominant modes are closely spaced within the frequency range 0–1 Hz, the controlled use of specific exciters to obtain significant levels of response is often difficult and costly. In such cases, ambient vibration becomes the only practical means of exciting the structure. This type of test makes use of ambient environment effects such as wind, traffic load, and environmental load as excitation force.
Seismic Monitoring of Cable-Stayed Bridge May 10, 2007
Posted by dionsiringo in Bridge Engineering, Earthquake, Jembatan Cable-stayed, Structural Monitoring.add a comment
Strong motion data acquired from instrumented bridges during seismic events provides an excellent opportunity to gain insight into the behaviour of bridges and performance of their components. Using system identification, modal parameters of bridges can be estimated and the performance during various level of earthquake can be studied. In this study dynamic behaviour of Yokohama-Bay Cable-Stayed Bridge is investigated using seismic response recorded from six earthquakes. Modal parameters of the structure are estimated using system realization of state–space model.
The realization method used here is based on the system realization using information matrix (SRIM), which makes use of the correlations between earthquake input and output data to identify the coefficient matrices of state–space model. Identification results from six earthquakes show that the system identification can be used to capture global behaviour of the bridge by estimating modal parameters and also to explain local behaviour of its component such as performance of link-bearing connections during earthquake.
Dynamic characteristics of a curved cable-stayed bridge April 29, 2007
Posted by dionsiringo in Bridge Engineering, Earthquake, Jembatan Cable-stayed, Structural Monitoring, Vibration.add a comment
An assessment of dynamic characteristics of the 455 m Katsushika–Harp curved cable-stayed bridge is presented. Dynamics characteristics such as natural frequencies, mode shapes and modal damping ratios are obtained from seismic response of the bridge by employing a time-domain multi-input multi-output (MIMO) system identification (SI) technique. The technique makes use of base motions and superstructure accelerations as pairs of inputs–outputs to realize the coefficients of state-space system matrices. The SI results indicate the occurrence of many closely spaced modal frequencies with spatially complicated mode shapes. Fourteen global modes in the ranges of 0.45–2.5 Hz were identified, in which the girder motion dominated most of the modes. The tower modes were associated with girder modes and were characterized by the lowly-damped motion. Using identification results from six earthquakes, the effects of earthquake amplitude on modal damping ratios were observed.
Revitalizing disaster management April 29, 2007
Posted by dionsiringo in Disaster Mitigation, Indonesiana, opinion.add a comment
It seems every story about Indonesia recently involves a disaster. With alarming speed, we have replaced such countries as the Philippines, Nepal and Bangladesh as the most disaster-prone nation in the world. Indonesia, however, is not alone in facing natural disasters. Globally, the number of environmental calamities is rising, mostly owing to an increase in floods.
For the period of 1994-2003, the International Council for Science found floods were the most common natural hazard, making up 33 percent of disasters. Storms were next at 23 percent, epidemics at 15.2 percent, droughts at 15 percent and earthquakes at 7 percent. The remaining disasters included tsunamis, landslides and volcanic eruptions. Hazards related to extreme weather conditions occurred most frequently and often affected the largest areas.
In disaster science, the paradigm is now shifting from knowing that rivers flood to understanding how a flood can cause so much damage. Human beings, not nature, are the cause of disaster losses. It is unrealistic to think that we can engineer the earth to stop disasters, but it is possible to adjust human behavior to reduce their risk.
Indonesia has long recognized the importance of having a disaster management organization….read complete article
Laser Doppler Vibrometer for Damage Detection April 29, 2007
Posted by dionsiringo in Structural Monitoring, Vibration, mechanical vibration.add a comment
The paper presents a study on the application of a laser Doppler vibrometer (LDV) for structural health monitoring using ambient vibration. The work covers three important issues namely, data acquisition, system identification, and structural damage detection. A two-laser system is employed for data acquisition using ambient response of the structure. Modal parameters are estimated by the eigensystem realization algorithm, after first deriving the impulse response functions from both laser responses using the Natural Excitation Technique.
In damage detection, a new matrix-updating-based method is proposed. The essential feature of this method is the non-iterative solving technique of inverse problem, which allows damage to be located and quantified by employing the modal parameters obtained before and after damage. Numerical simulation and laboratory-scaled experiments using bolted lap joint plate demonstrate that the proposed technique can detect locations and magnitude of damage with incomplete modal information.
Living with and learning from earthquake April 29, 2007
Posted by dionsiringo in Disaster Mitigation, Earthquake, Indonesiana, opinion.add a comment
The two major earthquakes that have struck Indonesia recently caused damage beyond imagination. In 2004 the Aceh earthquake triggered the largest tsunami in modern history. Last month’s quake in Yogyakarta may be not as huge in magnitude as other great historic earthquakes, but the area affected was extensive. The casualties from these two disasters were staggering, and this should remind everyone how earthquake-prone Indonesia is.
Since the devastating San Francisco earthquake of 1906, anti-earthquake engineering techniques have continuously improved…
Minimizing the danger, damage of landslides April 12, 2007
Posted by dionsiringo in Disaster Mitigation, Indonesiana, opinion.add a comment
Every year during the rainy season landslides pose a serious threat to many who live in mountainous areas of Java, Sumatra and several other islands. This year, we have already witnessed two tragic disasters caused by large scale landslides. Heavy rainfall combined with the misuse of land has triggered massive gravitational movements of debris and mud.
The recent toll from the landslides in Jember and Banjarnegara were particularly severe and tragic. However, even though these types of disaster continue to increase in terms of frequency and seriousness, little has been done to prevent, or even, mitigate the possibility.
There is a tendency to focus only on addressing immediate problems rather than anticipating new ones. To make matters worse, many people still merely put this disaster down to an “Act of God”, while in fact prevention of the landslide hazard is both scientifically possible and feasible.
Health Monitoring of Instrumented Bridges (Lessons learned) March 30, 2007
Posted by dionsiringo in Bridge Engineering, Jembatan Cable-stayed, Jembatan Suspensi, Structural Monitoring.add a comment
A great number of long-span bridges were constructed in Japan in the past decades. These bridges, especially the cable-supported ones, are expensive to inspect and maintain. They have long service periods of over 100 years, during which they inevitably suffer from environmental long-term loads effects such as fatigue, material deterioration and other extreme load effects. Governments, bridge authorities, as well as scientists and engineers, are now very much concerned with the issues of health, durability, and safety of these major bridges in a long-term service period. Structural health monitoring (SHM), therefore, becomes an increasingly important, and more concerted efforts are now being devoted to enhance our understanding in implementation of both monitoring technologies and methodologies.
The process of instrumentation, measurement and analysis of bridge response are essential parts of health monitoring. The importance of bridge SHM has been emphasized especially after the 1995 Kobe earthquake. As we know, prior to the 1995 Hyogo-ken Nanbu (Kobe) earthquake, many longspan bridges including the Honshu-Shikoku bridges were designed and constructed using the specified ground motions that were far smaller than the near-field ground motions experienced during Kobe earthquake. To anticipate similar ground motions as experienced in Kobe the bridge seismic design code was later revised. And accordingly the seismic retrofit program of existing bridges has also started.
In the context of retrofitting and evaluation of performance of the existing bridges, instrumentation and monitoring system play important roles. Fortunately, most long-span bridges were instrumented with sensor system that captures bridge responses to various types of motion such as ambient, traffic and earthquakes. Using these responses and by applying a proper analysis, the real performance of a bridge can be evaluated.
