Since a resonance curve of non-linear structure depends on magnitude of exciting force, vibration tests of such structure must be carried out keeping the amplitude of exciting force constant even though its frequency is changed. However, the most of vibration exciters with eccentric masses can not keep its force constant without once stopping the machine operation, when the frequency is altered. To overcome such inconvenience, the authers made a new vibration exciter with four eccentric masses whose relative position is controlled with special gear system during the machine operation. Therefore, it can maintain the constant amplitude of generating force without stopping the machine operation. The main specifications are as below.

Maximum force　　　　　　　　　　:2.5ton
Frequency range　　　　　　　　　 :0.3-3.0Hz
Direction of force　　　　　　　　　:Horizontal
Weight of an eccentric mass　　:480.8kg
Weight of mechanical part　　　　:6.193ton

　This vibration exciter was successfully used for vibration tests of large model piers with steel pipe piles in Shimizu Port in 1964.