System identification applied to long-span cable-supported bridges using seismic records October 20, 2007
Posted by dionsiringo in Bridge Engineering, Earthquake Engineering, Jembatan Cable-stayed, Jembatan Suspensi, Structural Monitoring.add a comment
The recent growing interest in bridge assessment and monitoring has led to the instrumentation of many bridges in Japan, especially the long-span cable-supported ones. Since most part of Japan is located on a seismically active area, these permanent instrumentation installations provide high-quality seismic records every time an earthquake occurs. Such records are essential to gain insights into real behavior of bridges and to evaluate the adequacy of bridge seismic design codes.
The work reported here presents case studies of the application of multiple-input multiple-output (MIMO) SI to three long-span bridges in the Tokyo Bay area. The methodology used in this tudy is based on the System Realization using Information Matrix (SRIM) , which utilizes correlations between input–output data for realization of a state-space model and estimation of modal parameters. To provide a comprehensive discussion, this paper includes: (1) a brief explanation of the SI method, (2) numerical verification using a benchmark cable-stayed bridge, (3) application of the SI to the Yokohama Bay Bridge, Rainbow Bridge, and Tsurumi Fairway Bridge using the records from the Chuetsu-Niigata earthquake, and (4) evaluation of identification results.
Monitoring of bridges and transportation infrastructures using vibration techniques July 15, 2007
Posted by dionsiringo in Bridge Engineering, Jembatan Cable-stayed, Jembatan Suspensi, Structural Monitoring, Vibration, proceeding.1 comment so far
The rapid growth of Japanese economy during the 1960’s intensified construction of bridges and transportation infrastructures system to meet the expansion of industrial activities. Since then, the total infrastructure stocks have accumulated considerably. These include development of national railway line and the highway networks that are still continuing until now. In twenty years from now, the bridges constructed around seventies will be more than fifty years old. Without proper maintenance they will be deteriorating and degradating in function. It is anticipated that by the year 2020 the number of aging road bridges will constitute half of the total road bridge networks. Consequently, even though Japan has been long considered as a country that is active in new construction of infrastructures, maintenance has becoming an increasingly important issue nowadays.
Maintenance, however, is not only the issue for aging bridges and transportation infrastructures but also for the newly constructed ones. In order to maintain infrastructure condition continuously, comprehensive monitoring systems have been introduced at the beginning at its service life. Many newly constructed bridges especially the long-span ones are now being closely monitored. They are instrumented with embedded sensors that allow continuous –and in some cases, online monitoring. For smaller scale bridges, the monitoring process constitutes routine inspection using portable sensors. A routine inspection or an overall monitoring of bridge after certain severe natural environmental condition such as earthquake provides a tool to evaluate structures condition and to detect possible structural defects. For this purpose, the vibration based SHM is considered superior to other non-destructive assessment methods due to its characteristics that allow for global system monitoring as well as detection of local structural defects determined from changes in the vibration characteristics.
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.
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.
