Available space near shore area was exhausted by rapid industrialization and concentration of population toward the cities. Furthermore, reclamation techniques have no longer merits technically and economically as well as in view of environmental conservation. Therefore it is necessary to find a new technology, such as Very Large Floating Structures(VLFS), which can provide pleasant ocean space.
If VLFS technology is developed, we can get the various ocean spaces such as harbor facilities, airport facilities, leisure and sports facilities. but, that technology should be technically safe and economic.
The additional moment occurs because the superstructures of VLFS are influenced by wave loads instead of earthquake loads. In order to reduce the additional moment, this study used the semi-rigid connections which lie between fully rigid and pinned. If the semi-rigid connections are used for superstructures of VLFS, the moment of beams can be reduced and more economical construction will be possible.
This study aims to show the effect of wave loads on structure and the efficiency of the semi-rigid connections due to wave loads by analyzing the time history responses. The dynamic behaviors of the rigid frame are compared with those of the semi-rigid frame considering of static loads, wave loads and combination loads for 4-bay 3 and 8-story frames. To analyze the responses of the semi-rigid frame, the amplitude and period of wave loads are varied. Two models such as the spring and the substitute bar are used to represent the semi-rigid connections. Wave loads have 13 seconds period and 22.63cm amplitude, and the semi-rigid connection type is a steel tubular column with square external-diaphragm connections.
The conclusions of this study are as follows.
1. The additional moment responses due to wave loads increase 33% in the rigid frame, 26% in the spring model and 31% in the substitute bar model. The additional moments occupy 20%～25% of the whole responses for superstructures on VLFS. The results show that the additional moment due to wave loads should be examined for the design of superstructures on VLFS.
2. As the semi-rigid connections are applied as a whole for the frame, the maximum moments are reduced by about 30～45% compared to those of the rigid frame. If the semi-rigid connections are applied partially for the frame, the maximum moments increase. That is the reason why the reduced moments of beams in the semi-rigid regions are transferred to beams of the rigid regions.
3. As the amplitude of wave loads is varied, the additional moments of the semi-rigid frame change smaller than those of the rigid frame. The additional moments of the semi-rigid frame due to period variations change also smaller than those of the rigid frame. The results show that the system of superstructures is designed economically by using the semi-rigid connections.
4. In case of the lateral displacement responses, the effects due to static loads are very little and the effects due to wave loads are dominant. As the stories of superstructures are higher, the lateral displacement responses by the semi-rigid connections increase. In case of the lateral acceleration responses, the maximum accelerations of the whole semi-rigid frame are reduced by 25% but, those of the partial semi-rigid frame are increased by 7%.