WORST EARTHQUAKE INPUT DIRECTION OF CRITICAL DOUBLE IMPULSE FOR IRREGULAR SHAPED BUILDING STRUCTURE

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  • 不整形立体構造物を対象とした極限的ダブルインパルスの最悪地震動入力方向
  • フセイケイ リッタイ コウゾウブツ オ タイショウ ト シタ キョクゲンテキ ダブルインパルス ノ サイアク ジシンドウ ニュウリョク ホウコウ

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Abstract

<p> The seismic responses of three-dimensional irregular shaped building structures depend on the input direction of earthquake ground motions, and the earthquake input direction has to be considered in the structural design of the irregular shaped buildings. However, it is difficult to predict the earthquake ground motions input into the specific irregular shaped building structure. Therefore, it is necessary to evaluate the input direction that maximizes the seismic response, and the seismic resistance of the irregular shaped building structures have to be confirmed by calculating the responses under earthquake ground motions in the direction that maximizes the earthquake responses. In this paper, the input direction of the earthquake ground motion that maximizes the earthquake responses is defined as the worst earthquake input direction. On the other hand, the characteristic of the earthquake ground motion at the site of the building structure is also difficult to predict, and the input direction that maximizes the earthquake response depends on the earthquake ground motion characteristics including predominant period and waveform. Hence, the critical earthquake ground motion, that maximizes the earthquake response, has to be evaluated for each input direction, and it is necessary to calculate the worst input direction of the earthquake ground motion considering the critical earthquake ground motion for each input direction.</p><p> After Northridge earthquake in 1994, Hyogo-ken Nanbu earthquake in 1995 and 2016 Kumamoto earthquake, many structural damages were reported due to near-fault ground motions including fling-step and forward-directivity inputs. The fling-step inputs were observed in Kumamoto earthquake, and its accelerations were characterized by the one-cycle sinusoidal wave in the previous papers.</p><p> In this paper, double impulse input is introduced in order to represent fling-step near-fault input under ground motions. The evaluation method of the worst input direction of the critical double impulse, which maximizes the total input energy, is proposed for the irregular shaped building structure. The critical timing that maximizes the total input energy for arbitrary input direction is the timing when the sum of the restoring force and damping force of the first floor in the input direction becomes zero. On the other hand, the total input energy by the double impulse with arbitrary time interval can be expressed as the sine-wave function of the input direction angle, and the worst input direction of the double impulse can be obtained analytically.</p><p> The situation when the critical double impulse inputs into the irregular shaped building structure in the worst direction is defined as the worst-case situation in this paper. The total input energy of the building in the worst-case situation can be calculated by using the critical timing and worst input direction, and the optimum viscous damper placement is obtained which minimizes the total input energy in the worst-case situation. The validity of the proposed optimum viscous damper placement is checked by calculating the total input energy by changing the input direction angle.</p>

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