1. Dept. of Civil Engineering, Kunsan National Univ., Gunsan, Korea.
2. Renewable Energy Research Institute, Dept. of Civil Engineering, Kunsan National Univ., Gunsan, Korea.
3. Dept. of Civil and Environmental Engineering, Kunsan National Univ., Gunsan, Korea.
4. Renewable Energy Research Institute, Kunsan National Univ., Gunsan, Korea.