Sinchuan Earthquake felt in Vietnam May 29, 2008
Posted by dionsiringo in Bridge Engineering, Earthquake, Jembatan Cable-stayed, Teknik Sipil.add a comment
The May 12 2008 Sinchuan earthquake was felt in northern area of Vietnam. Today we received the records from the instrumented Bai Chay Cable-Stayed in Ha Long Bay, about 1,154 km from the earthquake epicenter. The bridge experienced moderate shaking (acceleration RMS of 3.2 cm/s2) at the top of the 95m tower that caused 5 cm of displacement. The Bai-Chay Bridge is currently the world’s longest center span for the single-plan Cable Stayed Bridge (435 m). It is designed by the Japan Bridge & Structure Institute Inc, Pacific Consultants Int Tokyo, and constructed by Shimizu Corp and Sumitomo Mitsui Const. Co.Ltd. The bridge was just opened to traffic in December 2006
Okutama Cable-Stayed Bridge : TMD for supression of Vortex-Induced Vibration April 3, 2008
Posted by dionsiringo in Bridge Engineering, Jembatan Cable-stayed, Teknik Sipil, Vibration, mechanical vibration, visit.4 comments
The Okutama Cable-stayed Bridge
Recently I had a very rare opportunity to go inside a cable-stayed bridge girder. The bridge is the Okutama Bridge, a single pylon cable-stayed bridge located at the Okutama area west part of Tokyo. The span length is 160 + 105 meter and the girder width is 12 m. The A-shape tower is made of steel reinforced concrete . The main girder is composed of double-span continuous steel double-box girder. Bridge construction was completed in 1996 and has become a part of the Okutama-Ohme Line in west part of Tokyo ever since.
We went inside the bridge following a group of Korean engineers, who are interested in the Tuned Mass Damper (TMD) system installed in this bridge. Unlike any other bridges that have TMD installed on the towers, in this bridge the TMD was installed on the girder.
The main reason for TMD installation is to suppress the Vortex-Induced Vibration (VIV) in vertical direction of the grider. As mentioned in the paper published by the designer and owner of the bridge, wind tunnel test of the current design girder revealed that vortex-induced vibration in vertical and torsional direction were evident under the wind velocity of 10 and 45 m/s, respectively. Both types of vibration had caused vertical amplitudes that were higher than the permissible one.
Tuned Mass Damper (0.8 ton of mass), main spring (white coil),and adjustable cantilever arm (in the middle)
In order to suppress the vibration, two measures were considered, one is aerodynamic measures by increasing aerodynamic damping using flaps, and the other is by mechanical measures such as installing a tuned-mass damper. The aerodynamic measure was abandoned for aesthetic and pedestrian safety precautions reasons, the TMD measure was selected instead.
Eight units of TMD were installed inside the girder, where each consists of mass (0.8 ton), springs (two of them: main and supporting springs) and a cylinder type of oil damper. The main spring, which has a form of coil, is connected to the mass by steel cantilever. Due to limited space inside the girder, the natural frequency of TMD is controlled by changing the position of the mass through an internal adjusting mechanism.
The bridge and its vibration control system are very impressive. In fact, it is the first girder VIV controlled bridge in Japan. However, when we visited the site, I was quite surprise to see that not so many passerby or vehicles crossing the bridge.
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.
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.
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.
