This paper proposes an estimation method of the impact force acting on ceiling safety nets in consideration of the distance between ceiling and safety nets. The proposed method utilizes the balance of the potential energy of the falling objects including ceiling boards and the strain energy stored in safety nets or wire ropes after their deformation, in order to obtain the maximum displacement of the safety nets or wire ropes. The structures targeted by the proposed method can be categorized into two types: 1) safety nets or wire ropes solely lying in one way, and 2) safety nets and wire ropes which interact with each other in two dimensions. The collapse patterns of ceiling considered in this paper are the one that can be treated as concentrated load and the one that can be treated as uniformly distributed load.
The results obtained in this study are as follows:
(1) It has been confirmed that the finite element analyses can reproduce the result of the static loading experiment in sufficient accuracy, in which the load-displacement relation of the ceiling safety nets has nonlinear characteristic.
(2) The impact force acting on safety nets or wire ropes solely lying in one way can be estimated as the vertical reaction force by adapting the maximum displacement on the relation of the vertical force and the displacement. Due to the difficulty originating from the geometrical nonlinearity, the vertical force-displacement relation and the horizontal force of the distributed load are obtained by finite element analyses, whereas those of the concentrated load are obtained by theory.
(3) The impact force acting on safety nets and wire ropes which interact with each other in two dimensions can be estimated as done in the above case. The maximum displacement of the structure is calculated by adding the maximum displacement of each structural element.
The proposed method has been applied to some examples to examine the influence of the distance between ceiling and safety nets on the impact force. It has been concluded by the results obtained through these examples that the distance between ceiling and safety nets seriously affects the impact force and should be considered in estimation.
