A double-cylindrical caisson is to create a wide calm water region in deep sea around Japan. The cylindrical wall is subjected to wave forces, impact forces by a ship and so on. Static loading tests are carried out to investigate the strength and the crack properties of reinforced concrete and prestressed concrete cylindrical walls with many rectangular openings. Four specimens are manufactured. A concentrated load is applied from outside at the center of two specimens by a longing jack. For the other two specimens, uniform distributed loads are applied from inside by water pressures through a rubber bag.
　On the basis of the test results, it is made clear that the influence by the openings is small on the mechanical properties of the cylindrical wall, when suitable reinforcement is supplied.