2016美濃地震之街屋耐震需求評估及其於初步評估之應用

Abstract

街屋耐震初步評估常見作法以垂直構材量和總樓地板面積之比值(柱量比)與樓層數做為評估參數，求取耐震容量(capacity)，規範475年回歸期設計反應譜之地表最大加速度0.4S_DS做為耐震需求(demand)，評估結構是否需進行補強。地震發生後，可利用測站實際地震動強度，推估結構物所在點之地震動強度，作為耐震需求進行初步評估。透過實際結構震損情況與初評結果相比，可驗證耐震容量計算及初評方式的可靠度。 2016年2月6日南台灣發生芮氏規模6.6的美濃地震，震後國家地震工程研究中心與普渡大學合作，至災情嚴重的台南市進行現場勘查並整理成震損資料庫，同時以實際PGA值評估街屋地震動大小並進行初步評估，發現部分輕微震損街屋評估結果較保守，可能造成補強較不經濟。本研究以現有適用於台灣之水平向地震動模型為基礎，針對美濃地震之地震動特性，以速度脈衝週期(T_p)及測站-斷層最短距離(R_rup)兩自變數進行兩階段迴歸修正，提出一適用於美濃地震的地震動中值模型。利用實際觀測值輔以中值模型，分別以譜加速度和最大地表加速度為評估目標，提出兩種街屋耐震容量的估算方法，應用於初步評估中，並討論各方法之準確度與可行性。最後利用美濃地震所造成台南地區各地不同程度的地震動大小及相對應之街屋震損資料，擬合街屋之易損性曲線。

Before earthquake happening, seismic capacity of a low-rise RC building can be preliminary evaluated by the ratio of column section area to floor area of the building. The seismic demand shall be determined by 0.4S_DS based on seismic code, which S_DS is short-term design horizontal acceleration coefficient. The preliminary seismic assessment provide a pre-screening of seismic capacity and the retrofit standard. After earthquake happening, seismic demand of the street house can be evaluated by real acceleration records. Then, the reliability of the assessmet for seismic capacity can be confirmed through the accuracy of seismic preliminary assessment. On 6 Faburary 2016, Meinong Earthquake with ML 6.4 attacked the south part of Taiwan. After the Meinong earthquake, a reconnaissance team composed of Purdue university and National Center for Research on Earthquake Engineering (NCREE) collected buildings data in the strong ground motion area, Tainan, amd conducted preliminary assessment based on peak ground acceleration recorded in the earthquake. However, some of the buildings with minor or slight damage have a result of less than 1, demonstrating that the results of the preliminary assessment are conservative. In order to have more accurate prediction of ground motion for Meinong earthquake, this study used the pulse period (T_p) and the closest distance to fault (R_rup) to conduct two-step regression which can modify horizontal ground motion model for crust earthquake and subduction earthquake in Taiwan. Propose two method to predict the spectral acceleration and peak groud acceleration of street houses by using this ground motion model. Then, apply the seismic demand to preliminary assessment and discuss the accuracy and feasibility. Lastly, conduct the fragility curve which representing the probability of exceeding a given seismic demand for Meinong earthquake.