Research results

Aseismic capacity assessment method of existing highway bridge foundations: Studies to prioritize existing bridges for aseismic reinforcement

Cases of Highway bridge damage caused by earthquake
(Top: Bridge pier damage due to the Great Hanshin-Awaji Earthquake;
Bottom: Bridge foundation damage due to the Niigata Earthquake in 1964)

Scenes of piles after the loading experiment (Top: Piles designed according to the design method provided by Specifications for Highway Bridges before the Great Hanshin-Awaji Earthquake; Bottom: Piles designed according to the design method provided by Specifications for Highway Bridges after the Great Hanshin-Awaji Earthquake)
Piles designed in accordance with Specifications for Highway Bridges revised after the Great Hanshin-Awaji Earthquake show less damage

Themes to be approached in this study

At present, there are an enormous number of highway bridge foundations in Japan: approximately 60,000. To effectively reinforce such an enormous number of highway bridge foundations with limited time and budget, we need to set a seismic reinforcement priority for bridges by considering the relationship with highways that are required for recovery activities after earthquakes and the level of foundation damage caused by earthquakes. This study aims to set a seismic reinforcement priority by focusing on the level of foundation damage caused by earthquakes.
There are various factors that affect the damage level when an earthquake occurs. For example, when were Specifications for Highway Bridges applied to the bridge prepared? What is the condition of the ground? What materials were used to make the foundation? What type of foundation was applied? In this study, we analyzed the past experimental results and damage cases and classified earthquake-affected bridge foundation damage into 5 levels by calculating damages as needed. We figured out a simple prediction method to know to which level the foundation belongs based on some of the factors mentioned above (applied Specifications for Highway Bridges , ground materials, foundation type, etc.) without implementing completed calculations.
To safely and efficiently place highways in service, it is essential for bridges to maintain a certain performance without collapsing even if earthquake occurs. To that end, highway bridges are built in accordance with certain technological standards - referred to as the Specifications for Highway Bridges - that provide for design and construction procedures to secure a given level of performance. Specifications for Highway Bridges are revised when new facts related to highway bridge design and construction are discovered or performance required for highway bridges needs to be revised due to a large-scale earthquake. For example, the Hyogo-Ken Nanbu Earthquake in 1995(the Great Hanshin-Awaji Earthquake) was an unprecedented large-scale earthquake. Because of this, bridges were required to be safe even in the event that such a large earthquake were to occur again. The standard specifications were revised to build bridges with higher seismic capacity. On the other hand, some old bridges don't satisfy the seismic capacity required by the present standards. Those bridges need seismic reinforcement.
However, it is difficult to carry out seismic reinforcement for all bridges within a limited budget and period. In these days, the imminent danger of large earthquakes is quite clear and the need for reinforcement is urgent. The Ministry of Land, Infrastructure, Transport, and Tourism started a three-year program on the aseismic reinforcement of bridges on emergency routes from FY2005. This program selects important routes for search and rescue activities or critical material transportation and implements seismic reinforcement to prevent great damage and ensure at least a minimum transportation system. Specifically, the first priority is to prevent bridges related to highways and specified emergency transportation roads from great damage or collapse even if an earthquake of a level similar to the Great Hanshin-Awaji Earthquake were to occur.
Three-year program on the aseismic reinforcement of bridges on emergency routes was completed in FY2007. We think that the reinforcement of foundations will be discussed as the next seismic reinforcement strategy. Therefore, a study to set the seismic reinforcement priority for highway bridges is very important. We will try to further improve the precision of this method.

(Contact : CAESAR)

Frequency of drought in paddy fields in cold regions may increase due to global warming: Prediction from weather predictive values

Figure-1 Outline of the flow to be considered

Figure-2 Change in the future runoff period

Figure-3 Dam water balance calculation method

Figure-4 A-dam future required capacity

Many studies in the agricultural field have predicted that future climate change would not have a serious impact on rice cultivation in Hokkaido. However, these studies are premised on no shortage of irrigation water. On the other hand, studies in the hydrological field predict that the melted snow outflow would occur earlier. For the rice cultivation in a cold and snowy regions like Hokkaido, snow is an important water source. Therefore, it is essential for the future stable food supply in Japan to consider the impact of climate change on the change in snowfall and snow meting time. Given this background, we received weather predictive values from Japan Meteorological Agency and considered the supply and demand of irrigation water in a dam for agricultural use in Hokkaido (Dam A) during the period from 2031 to 2050.
The flow to be considered is shown in Figure 1. We first developed an outflow model from the Dam A to reservoirs and input future temperature and precipitation data (2031 - 2050) to predict the future outflow. We calculated the effective rainfall from the future precipitation data during the irrigation period and worked out the water volume required for paddy fields. We calculated the water balance of the dam based on these values.
Figure-2 shows a comparison of the current value (1991 - 2000) and the future value (2031 - 2051) in terms of the yearly integrated runoff volume. The sharp inclination of the curve around May 1 shows snow melting outflow. Compared to recent years, in the future snow will start melting in March in some years and the snow melting outflow is predicted to start earlier even looking at average values.
In paddy fields, a large amount of water is required for times of soil paddling and rice planting. Presently, these times match those of high river flow rate due to snow melting. Therefore, currently the snow melting is used effectively. However, in the future, snow starts melting earlier, so the water balance of the dam changes. Assuming water usage as shown in Figure 3, we calculated the water balance of the dam during the irrigation period using the irrigation water amount for paddy fields and the outflow from the dam catchment areas, obtaining the result show in Figure 4. The study results suggest that if rice is cultivated in the determined area as shown in the irrigation plan for the next 20 years, the frequent of drought may increase with the current capacity of Dam A. We will proceed with the study on measures for stable irrigation supply making this study as a stepping stone.

(Contact : Irrigation and Drainage Facilities Research Team, CERI)