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METHOD
DEM is used in this study. The DEM is a numerical analysis method that can compute the position of
each element by solving the equation of motion step by step. All elements are assumed to be rigid.
Each element has a spring and dashpot in its normal and tangential direction. When it comes in contact
with others (Fig.3.1), the contact force is generated by the connected springs and dashpots. By solving
the equations of motions for all elements step by step, the behaviors of all elements can be traced. The
forces applying to the element are the external force (/,,/.) and the total sum of contact forces
between elements (F x1 F z J e ). The element acceleration is obtained as follows:
/m
I m
(3.1)
(3.3)
(3-2)
where m is the element mass, and I 9 is the inertia moments around the center of the gravity.
From the above equations, the velocity and the displacement of the next time step is calculated as:
uT-A/
Ar (3.4)
(3.5)
where Ar is the time interval of the computation.
ANALYTICAL MODEL
Modeling of the structure
The analyzed structure model is a two-story house as shown in Fig.4.1. Both the height and the width
are 10m. The structure consists of four columns, two ceiling beams and a roof. The roof and the ceiling
beam are connected by three support beams. In this study, we deal with wooden houses. All elements
are 10cm width. The mass and inertia moments of all elements are calculated from the density of
Japanese cypress (0.34g/cm 3 ).
In usual DEM, elements affect only contact force each other because joint elements are not considered.
But elements of real structures are connected at joints and behave as a continuum until joints are