Seismic analysis and design
１．Rational seismic reinforcement of long span cable-stayed bridges using seismic isolation technology – Higashi-Kobe Bridge-
- We conducted seismic reinforcement design for large earthquakes for the Higashi-Kobe Bridge (5 span continuous steel cable-stayed bridge, bridge length 885 m, center span 485 m, support type: all free) among the long span bridges of the Hanshin Expressway. As a result of simulation using advanced seismic response analysis technology on an analysis model of the whole bridge, the main girder displacement (direction of the bridge axis) in the case of a large-scale earthquake reached 2 m. It was confirmed that the horizontal displacement in the direction of the bridge axis could be drastically reduced by making use of new seismic isolation technology called vertical sandwich type ultrahigh damping laminated rubber damper + cable structure that can handle the large displacement and reaction forces.
By using the vertical sandwich type, the laminated rubber deforms smoothly, and by using 16.7 m cable on both sides, it is possible to absorb upward, downward, left and right eccentricity deviation due to the major displacement of the main girder. In order to maximize the effect of the damper from the viewpoint of ease of installation, economy, etc., we repeatedly examined the performance confirmation experiments and the optimization of the rubber shape and realized rational seismic reinforcement making full use of the new seismic isolation technology. Also, in actual construction, the damper is installed with high precision, such as cable tension management and sag amount management. Visitors who participated the site tour were so impressed for this installation.
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- Introduced initial pre-stress (2000 kN) to reduce cable sag and improve cable effectiveness
- Adopted aluminum – magnesium metal spraying for rubber damper parts, ensuring long term corrosion protection performance
- Completed seismic retrofit without losing the beautiful appearance of the Higashi-Kobe Bridge
- 【Reference】
2010 Japan Society of Civil Engineers Prize Engineering Prize (I Group)
Japan Society of Civil Engineers
Rational seismic reinforcement of long span cable-stayed bridges using seismic isolation technology – Higashi-Kobe Bridge and Tenbozan Bridge
Winners: Hanshin Expressway Company Limited., Sho-Bond Corporation, Hitachi Zosen Corporation, Kawakin Core-Tech Co., Ltd., Sogo Engineering Consultants, Co., Ltd., Nippon Engineering Consultants Co., Ltd.
2．Seismic reinforcement project for Harbor Highway bridges considering seismic performance grade
- We created a seismic reinforcement plan for the six major bridges on the Kobe Port Harbor Highway, such as Kobe Bridge (length 319 m), steel semi-through 3 span double deck arch bridge and Nadahama Bridge (length 400 m), steel 5 span continuous V leg rigid frame bridge. In order to develop reasonable seismic measures in terms of structure, workability, economic efficiency, maintenance and management, we implemented seismic reinforcement design with individually set seismic performance grades (required performance) based on the function and role of each bridge.
We used specific target bridges that had experienced The South Hyogo prefecture Earthquake in 1995 where we could use the data (ground, damage, recovery record, etc.) at that time to effectively set the limit state and prioritize restoration, narrowing down the damage tolerance locations and the reinforcement locations in a clear-cut performance design. Based on the new adoption of performance design that separates importance according to the purpose of the bridge in the bridge seismic reinforcement plan, shortening the construction period without long-term traffic restrictions (construction period: about 1 year), and the high degree of contribution to the region from the viewpoint of economic efficiency, etc., this achievement was highly regarded and was awarded the 2010 Engineering Prize of the Kansai Branch of the Japan Society of Civil Engineers.
- In the design, we implemented calculation of the design seismic motion, an evaluation of the seismic performance, a survey of the seismic reinforcement method, detailed design and completion of the construction, in parallel with the committee operation. In order to achieve the purpose of implementing a new performance design, we have discuss with the committee professors many times and received their valued and polite opinions. Rather than carrying out extensive reinforcement with a simple model, we used complex nonlinear dynamic analysis of the whole bridge considering the buckling phenomenon peculiar to steel members, and advanced analytical techniques such as incorporating FEM shell elements in part. In this way, we were able to realize reasonable seismic reinforcement measures by designing the performance so as to satisfy the required performance set for each bridge and each member by raising the response accuracy at the time of an earthquake, and we feel that this will become a pillar of future performance design.
- 【Reference】
2010 Japan Society of Civil Engineers Kansai Branch Engineering Prize
2010 Japan Society of Civil Engineers Kansai Branch Engineering Prizes
Seismic reinforcement project for Harbor Highway bridges considering seismic performance grade
Winner: Kobe City Port General Administration, Nippon Engineering Consultants Co., Ltd. Osaka Branch Office, CTI Engineering Co., Ltd. Osaka Head Office, Sho-Bond Corporation Kinki Branch Office
３．Technology development to anticipate the era of “performance design”
- We are also boldly taking on the challenge of developing technologies to solve problems found on site. For example, in order to reduce temporary construction costs associated with seismic reinforcement windings on river piers, we began development of a girder collision method from around 1998. Through our work, we developed the idea that the movement of the piers could be restrained and windings in the river could be avoided if the resistance of the abutment could be properly considered in terms of the behavior of the entire bridge at the time of an earthquake. Initially it was not possible to model the abutment part, so adoption was not accepted from clients or the Public Works Research Institute since it was premature. However, over 7 years of research we repeatedly studied the validity of the modeling of the abutment part, and also acquired a patent for an NE girder collision method, and we now have a track record of close to 100 bridges. In the verification, observations of local and actual factors such as damage to the abutment part due to girder collision in the 1999 Taiwan Chi-chi Earthquake, the 2004 Niigata Chuetsu Earthquake, and the 2016 Kumamoto Earthquake are also utilized well.
- Besides, we verified ideas inspired by the actual behavior of bridges, such as the restraining pipe method using the existing member applied to the seismic reinforcement design of the steel through arch bridge, by simulation and experiment using advanced analytical techniques. Therefore, these examples applied in practice are so-called “performance design” and we are convinced that they will become a cornerstone of our future technical capabilities.
- 【Reference】
NE girder collision method (track record: about 100 bridges)
◎Seismic reinforcement method for bridges and telescopic device used for the method
(Patent No. 4477556 · Date of registration: March 19, 2010)
