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.
