A Finite Element Approach to Analyze Large-Scale Collapse Behaviors of Buildings and Motion Behaviors of Non-Structural Components


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.