Study on Ultimate Behavior of Building with Imbalance Strength due to Yielding or Buckling Subjected to Severe Earthquake

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When a building reaches collapse with a severe earthquake, it is often that the building finally produces deformation accompanied with torsion. In a current structural design, the possibility of torsion behavior to be occurred by eccentricity of mass and stiffness is considered. On the other hand, torsion behavior may be induced by imbalance of strength caused by yielding or buckling. At first, dynamic behavior of spatial steel frame whose braces are buckled subjected to severe earthquake is numerically investigated in this study. Even if brace of a certain plane of structure buckled, that of other plane did sequentially and immediately, and therefore the torsion behavior was hardly observed.Next static and dynamic behaviors of spatial steel frame without brace are analyzed numerically. In static push-over analysis, it is shown that a formation of collapse mechanism in a certain plane of structure induce a twisting behavior of overall frame. However, if the stiffness of horizontal plane of floor is ensured sufficiently, such a difficult situation is not caused. In dynamic analysis, it is illustrated that the effect of inertia produces good results, unless spatial frame is originally imbalance.Therefore it is not necessary to be concerned that severe torsion behavior may be induced by imbalance of strength caused by yielding or buckling in the building structure with good balance of mass and stiffness originally.