Finite Element Model

One quarter of RC girder was three-dimensionally modeled for numerical analysis with respect to the two symmetrical axis. Figure 4(a) shows the mesh geometry of the girder, which is finally used for numerical analysis with an appropriate design accuracy investigated here. A geometrical configuration of heavy weight was modeled as the real one. Supporting gigues including load-cells and gigue for protecting the girder from jumping up were also precisely modeled corresponding to the real ones. In this model, axial rebar and stirrup were modeled using beam element having equivalent axial stiffness, cross sectional area and mass with those of real ones. The other were modeled using eight-node and/or six-node solid elements. The mesh geometries for axial rebar and stirrup are shown in Figure 4(b).

Total number of nodal points and elements for the whole structure shown in Figure 4(a) are 13,963 and 12,360, respectively. Number of integration points for solid and beam elements are one and four, respectively. In order to take into account of contact interface between adjoining concrete and a head of heavy weight elements and between adjoining concrete and supporting gigue elements, contact surface elements for those are defined, in which contact force can be estimated by applying penalty methods for those elements but friction between two contact elements were neglected.

A head of heavy weight was set so as to contact the impacting point of the upper surface of RC girder and predetermined impact velocity was applied to all nodal points of the weight model. The

Fig. 4. FE numerical analysis model.

elasto-plastic impact response behavior was analyzed during 400 ms from the beginning of impact to the RC girder reaching steady state. The time increment of numerical analysis has been determined calculating in the LS-DYNA code based on a Courant numerical stability condition and was about

0. 8 ps for all numerical analysis conducted here.