Almost large-panel buildings in Japan have been executed with the filled-joint system so far; however the claims on leaking of rain having been repeated recently, the development of a new type of joint is expected.

We have given an effort to the investigation on open joints for several years. Some experiments with joint models of plastics or in concrete have been carried out, for the purpose of grasping the actual state of rain water penetrating into joints and obtaining any basic informations for a systematic joint design. The tests with transparent plastics, making us possible to visualize the behaviour of rain water, were particularly advantageous for the above purpose.

This field of research has just begun in Japan, and further investigations will be continued.