Abstract
Catastrophic disasters of large-scale framed structures occurred recently
are mainly caused by sudden, extreme external loads such as aircraft collision,
explosion, large seismic excitation, tsunami, big fire, and so on. Dynamic
codes are generally used to investigate such phenomena. However, strong
nonlinearity in the deformation of structures and rapidness of the external
loads often cause instabilities and difficulties in the analyses. Motion
behaviors of non-structural components such as furniture and ceilings in
buildings have also became one of the main targets of investigation to
reduce number of victims in disasters. Under these circumstances, a finite
element code, which can handle large-scale collapse and motion behaviors
of structural and non-structural components of buildings, was developed.
The code was developed with a use of an ASI (Adaptively Shifted Integration)-Gauss
technique. It provides higher computational efficiency than the conventional
code in those problems with strong nonlinearities including phenomena such
as member fracture and elemental contact.
One of the applications of the numerical code was a fire-induced collapse
analysis of a high-rise tower, which was carried out for an investigation
seeking for the true cause of the total collapse of New York World Trade
Center (WTC) towers, which collapsed in 2001. A seismic pounding analysis
was also performed on a simulated model of the Nuevo Leon buildings, in
which two out of the three collapsed completely in the 1985 Mexican earthquake.
The numerical results showed that the difference of natural periods between
the buildings, which was caused by the damages from previous earthquakes,
may have triggered the collision between the north and the center buildings.
Another application of the numerical code was a continuous analysis of
a steel frame building subjected under a seismic excitation followed by
an input of the drag force and buoyant force due to tsunami wave, and finally,
collided with a debris. With a particular structural condition of the building
with no walls under water, the building withstands the tsunami force as
well as the impact force driven by the debris collision. The numerical
code was also applied to a ceiling collapse analysis of a gymnasium under
seismic excitation. It is very important, nowadays, to know the collapse
mechanism of the ceilings since it causes not only the possibility of human
injuries, but may disturb the use of the facilities after earthquakes.
The behaviors of plaster boards near walls and roof top, which drop occasionally
due to detachment of clips and screws, were well simulated. The other numerical
cases include a motion analysis of furniture under seismic excitation.
A sophisticated penalty method was applied, in this case, to realize the
slip and contact motions of furniture with and without casters. The tumbling
motions of furniture were well simulated as a whole in spite of different
conditions of seismic waves.