實尺寸三層樓自復位斜撐構架含滑動消能樓版之振動台試驗

Abstract

本研究討論以不同水平裝置連接樓版及構架之滑動消能樓版系統與不滿足美國鋼結構耐震設計規範AISC 341-22中等韌性斷面之銲接箱型鋼柱於振動台試驗中之耐震性能，製作實尺寸三層樓斜撐構架，兩支箱型柱之寬厚比皆為27.4，不滿足中等韌性斷面之要求，材料使用SN490B。試體樓版採用鋼筋混凝土預鑄樓版，安裝於構架上後不須現場灌漿，樓版與構架間在四個階段試驗中分別以自復位彈簧裝置、摩擦裝置與自復位彈簧裝置、水平夾型挫屈支撐與自復位彈簧裝置、高勁度及高強度的T型桿件連接，以模擬不同滑動樓版系統與傳統固接樓版構架。振動台輸入震波為2022池上地震EYUL測站的東西向加速度紀錄，試驗由中小規模地震並逐次增加強度，試驗中最大振動台面加速度達0.57 g。 實驗結果顯示，在設計地震下，前三階段的樓版皆已開始有相對構架的位移，其中又以沒有安裝額外消能裝置的第一階段有最顯著相對第四階段的構架反應降低，且在最大考量地震下，RFL側位移相對第四階段有高達58%的側位移下降和39%的一樓剪力折減；第二和第三階段則分別於樓版作用後開始有對應的構架反應降低，並在1.4倍最大考量地震下，在RFL構架位移折減量則分別有36%和16%，一樓剪力則有23%和10%的下降。顯示滑動消能樓版系統在樓版開始作用後，帶動消能裝置作用，有降低構架位移與地震下之側向力，進而達到提升結構耐震能力之作用。在第四階段Test 10一樓最大層間變角達2.4%，柱底皆發展至Mpc，最大軸力達0.30 Py，試驗後柱底無局部挫屈，柱底彎矩遲滯迴圈上也無強度衰減的現象，顯示AISC 341-22對斜撐構架柱桿件的寬厚比要求，在初始軸力約0.1 Py的情況下，要求過於保守。 本研究亦提出三種夾型挫屈束制支撐核心減弱之樣式，在動靜態的反覆載重試驗結果都顯示該設計以減弱消能段強度的方式保護核心兩端，確實可延緩因外頂壓力造成試體軸拉力比值急遽上升現象的發生，避免整體破壞模式發生。

This study discusses the seismic performance of a sliding slab system connecting the frame and slabs with different devices, and welded box steel columns with width-to-thichness ratio not satisfying the moderately ductile requirement of AISC 341-22. A full-scale three-story braced frame was constructed, with a width-to-thickness ratio of 27.4 for both box columns, not meeting the requirements for moderately ductile sections, using SN490B. The slabs were precast reinforced concrete slabs, installed on the frame without onsite grouting. Four phases of tests were conducted using different devices connecting the slabs and frame: with self-centering spring devices, friction devices with self-centering spring devices, horizontal buckling-restrained braces with self-centering spring devices, and high stiffness and strength T-members respectively, simulating different sliding slab systems and traditional frame with rigidly connected slabs. The input ground motion of the shaking table was the east-west acceleration record from the EYUL station of the 2022 ChiShang earthquake, with seismic intensities incrementally increased from moderate to large earthquakes, reaching a maximum table acceleration of 0.57 g. Experimental results showed that under design basis earthquake, the slabs of first three phases began displacing relative to the frame. Phase 1, without additional energy dissipating devices, exhibited the most significant reduction in frame response relative to the Phase 4. Under maximum considered earthquake, the relative floor lateral displacement of RFL decreased by up to 58%, and shear at first story reduced by 39%. Phase 2 and 3 also showed corresponding reductions in frame response after slabs slide, with reductions in RFL displacement of 36% and 16%, and reductions in shear at first story of 23% and 10% respectively, at 1.4 times the maximum considered earthquake. This demonstrates that the sliding slab system, triggers the action of energy dissipating devices when the slabs start sliding, and reduce frame displacement and lateral forces under earthquake, thereby enhancing structural seismic resilience. In test 10 of phase 4 showed a maximum interstory drift angle of 0.024 rad at the first story, columns developing Mpc at bases, and maximum axial force reaching 0.30 Py. There were no local buckling at column bases after testing, and no strength degradation observed in the hysteresis loops, indicating that the width-to-thickness ratio requirements for braced frame columns in AISC 341-22 are overly conservative under initial axial force around 0.1 Py. The study also proposes three styles of perforated core buckling-restrained braces, with results from dynamic and static cyclic loading tests showing that this design effectively reduces the strength of dissipating segments to protect both ends of the core, thus delaying the rapid increase in ratio of the maximum compression force to the maximum tension force and preventing global failure modes from occurring.