Study on the Maintenance of an RC Bridge Wall Rail Affected by Frost and Salt Damage
Figure 1: An actual an RC bridge wall rail
Figure 2: Damage broken down by type
(click to enlarge)
Figure 3: Damage found from
the RC bridge wall rail
(click to enlarge)
Figure 4: Experiment on
an RC bridge wall rail
(click to enlarge)
1.What is an RC Bridge Wall Rail?
Concrete guard rails on bridges (hereinafter: "RC bridge wall rails")(Figure 1) have several purposes:(1) preventing vehicles in accidents from entering the opposing lane or from running off the road, (2) minimizing the effects of collisions on vehicles and (3) redirecting vehicles in collisions to the right driving direction. Therefore, it is vital to understand the deterioration of wall rails and, if necessary, to repair and strengthen the structure such as to achieve the perfomance requirements.
2. Investigation on the Deformation of an RC Bridge Wall Rail
Japan is widely distributed with cold snowy regions, from the Hokkaido District in the north to the mountainous areas of the Chugoku District in the south. Concrete structures in such regions, including RC bridge wall rails, are exposed to severe climate conditions; thus, they incur damage from frost (concrete collapse due to repeated freezing and thawing of water in the concrete) and/or salt (corrosion of the steel rebar inside the concrete due to the spraying of de-icing agents). This study investigated the external appearance of RC bridge wall rails, toward examining them for deformation caused by frost and salt damage. Roughly 40% of all RC bridge wall rails installed on the 389 bridges in Hokkaido were found to be deformed. At over 20 years after construction, 60% of those wall rails were found to have exposed reinforcing bars, which proves that the structure has deteriorated.
3. Experiment on Deteriorated RC Bridge Wall Rails
We conducted investigations and experiments on RC bridge wall rails that were installed in Hokkaido about 40 years ago (Figure 3). This series of investigations and experiments clarified how frost and salt damage change the properties of concrete and reinforcing bars, as well how much such change affects the performance of the structure. For example, we extracted an RC beam from an RC bridge wall rail, and determined how the beam fails when loaded (Figure 4).
Towards securing the safety of RC bridge wall rails, we will propose a deterioration index that will help to determine when repair and strengthening are necessary.
(Contact: Materials Research Team, Civil Engineering Research Institute for Cold Region (CERI))
A Study on the Evaluation of In-river Barriers Using Biotelemetry
Photo-1. Radio waves from an
EMG transmitter being received
Photo-2. A masu salmon (male)
attached with a EMG transmitter
Photo-3. Antennas installed in a fishway,
a PIT tag and a smolt attached with
a PIT tag (click to enlarge)
1. Biotelemetry Defined
Biotelemetry is a powerful survey method to understand the behaviors of various organisms that have not been identified fully. In this method, a small-size transmitter attached to an organism serves as a powerful tool for data about the behaviors, physiology and habitats as well as for surveying their ecology.
In recent years, because of the miniaturization and performance improvement of equipment for telemetry, this method has come to be widely used. In Europe and the United States, biotelemetry has been used in the study of various organisms such as whales, turtles, migratory birds and fish. Biotelemetry is being used in a wide variety of investigations in Japan as well, and is increasingly utilized in the study of various organisms.
2. Study utilizing biotelemetry
Our team is conducting a study on the evaluation of in-river barriers by tracking the behaviors of salmonid fish such as chum salmon and masu salmon by using biotelemetry. Salmonid fish are known to have the migration behavior between the seas and rivers to spawn eggs and grow; they migrate upstream rivers to spawn in autumn and migrate downstream to the sea to grow in spring. However, the presence of headworks or dams on rivers, constructed to irrigate farmland, prevents the migration of fish and are frequently associated with extirpation or extinction of fish species. In order to aid the fish migration, it is necessary to build facilities that bypass in-river barriers in order for fish to successfully migrate upstream and downstream. This path for the fish is called a "fishway." Fishways, which have a history longer than fifty years in Japan, have been installed in many places throughout the country.
Traditionally, fishway functionality has been evaluated with numerical values such as flow velocity, water height and other factors. However, very few studies have been conducted on the evaluation of a fishway with consideration for the ecology of the fish. For example, whether the fish can migrate upstream the fishway with minimal energy consumption or whether the fish can pass through the fishway in a short period of time. Biotelemetry is an effective method for understanding upstream-migration behavior of fish in a fishway. In addition, this method enables the evaluation of in-river barriers, including fishways, to be conducted with consideration for how they affect the migratory fish behavior.
3. Two types of biotelemetry equipment
In the evaluation of fishway functionality, EMG transmitters (Electromyogram: 5.3cm in length and 18g in weight) are attached for measuring the migration speed of chum salmon and masu salmon. By using this transmitter, the electrodes of which are embedded in the fish muscle, it becomes possible to determine whether the tail fin of a fish is moving fast or slow. The swimming speed of a fish, in meters per second, can be calculated by analyzing the data obtained from the transmitter.
Since the smolt, that immature fish of masu salmon returning to the sea in spring are about 10 centimeters long, it is impossible to attach a large transmitter like an EMG to them. Instead, a PIT tag (Passive Integrated Transponder Tag, 1cm in length and 0.1g in weight) is attached to the smolt. PIT tags are designed to provide data that enables the identification of the date and time of passage of individual fish when they pass the location of any antenna.
Thus, depending on what information is needed or according to the fish size, the appropriate equipment can be selected from among various types of biotelemetry equipment that have several functions.
(Contact: Watershed Environmental Engineering Research Team, Civil Engineering Research Institute for Cold Region (CERI))