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.trackback
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.
What is a cable. It is a part of a bridge
The cables are the structural part of the structure. They carry the girder load (gravity and traffic loads) and transferring them to the supports (i.e. pylon and tower).
Salam kenal.
TMD (Tuned Mass Damper) nya besar ya.
Bentuk flaps untuk suppress Vortex Induced Vibration nya seperti apa ya.
Apakah Tacoma Bridge yg baru di Seattle juga pakai TMD & flaps.
Kalo ada fotonya lebih menarik lagi.
Tks.
Ind
Pada Okutama Bridge flaps tidak digunakan dengan alasan estetis, sebagai gantinya dipakai TMD utk menekan kemungkinan VIV. Pada New Tacoma Bridge (opened 2007) main girdernya terbuat dari space truss jadi VIV tidak menjadi concern, apalagi kekakuan torsionalnya cukup tinggi.
VIV countermeasures diperlukan pada jembatan dgn box girder, countermeasure-nya bisa menggunakan fairings, flaps atau TMD.