以鋼纖維混凝土簡化BRB與RC構架接合之實驗設計與研究

Abstract

挫屈束制支撐(Buckling Restrained Brace, BRB)具備優異的勁度與消能能力， 能在拉壓雙向均發展至降伏而不產生挫屈，並透過穩定的塑性變形有效消散能量。 目前 BRB 應用於鋼構系統已相當普遍，然其與鋼筋混凝土(RC)構架接合之應 用則較不常見，主因為鋼構與 RC 間之接合施工介面較為複雜。過往將 BRB 直 接接合於梁柱構件時，可能導致以下缺點:梁柱開合效應造成接合板挫屈與焊道破 壞、接合區剛性增加導致結構振動週期下降進而提高地震力需求、剛性接合板傳遞 彎矩至 BRB 使其易產生降伏破壞，以及接合區對柱造成損傷進而影響 BRB 消 能行為等問題。 鋼纖維摻入混凝土後，除可提升混凝土之韌性、圍束能力與剪力強度，亦能透 過多重裂縫效應減少破壞過程中的瞬間剝落，維持構件整體性。有鑑於此，本研究 嘗試將 BRB 僅接合於 RC 梁構件，搭配預埋鐵件與鋼纖維混凝土使用，以強化 接合區剪力強度，進而改善因 BRB 集中載重所造成的彎矩與剪力需求提升問題。 本研究設計一座含 BRB 之 RC 子構架，於接合區域使用鋼纖維混凝土進行 簡化設計，使用體積取代率 Vf 為 1.5%之鋼纖維混凝土，並透過反覆載重試驗探討 其可行性。最終將提出一套適用於此類構架接合之簡化設計流程。 實驗結果顯示，本研究之破壞模式為 BRB 破壞主控，符合本研究之設計;由 於實驗系統制動器出力問題，導致柱之塑鉸較梁先早發生。於加載層間變位 3%以 前，梁非接合區域發展較接合區域較多之撓曲裂縫，於 0.5%層間變位時 BRB 降伏 並開始消能。於層間變位 5%時 BRB 發生破壞，實驗終止。試驗結果顯示預埋鐵 件和接合板能在 BRB 破壞時仍保持完整不破壞，符合實驗之設計邏輯，惟 RC 接 頭區域產生剪力破壞，因此建議在接頭部分多配置剪力鋼筋以提升剪力強度。

Buckling Restrained Braces (BRBs) exhibit excellent stiffness and energy dissipation capacity, capable of yielding in both tension and compression without buckling, thereby dissipating seismic energy through stable plastic deformation. While BRBs have been widely adopted in steel structures, their application in reinforced concrete (RC) frames remains limited, primarily due to the complexities associated with the steel–RC connection interface. Previous studies have shown that directly connecting BRBs to RC beam–column joints may induce several issues, including gusset plate buckling and weld failure due to frame action, increased joint stiffness that shortens structural period and raises seismic demand, unintended moment transfer to BRBs, and damage to RC columns that compromises the BRB’s energy dissipation performance. Incorporating steel fibers into concrete enhances its toughness, confinement, and shear strength, while also reducing spalling through multiple fine cracks, thereby preserving member integrity. Based on this, the present study investigates a connection strategy where BRBs are anchored solely to RC beams using embedded steel plates and steel fiber reinforced concrete (SFRC) to strengthen the shear capacity of the joint and alleviate the increased moment and shear demand caused by concentrated BRB forces. A simplified RC subassembly specimen with BRB connections was designed, in which the connection region employed SFRC with a fiber volume fraction (Vf) of 1.5%. A cyclic loading test was conducted to evaluate the feasibility of the proposed design. The study ultimately proposes a simplified design approach for such BRB-to-RC beam connections. Experimental results indicate that the failure mode was governed by BRB fracture, consistent with the design intent. Due to actuator force imbalance in the test setup, plastic hinging occurred in the RC column prior to the beam. Before reaching a 3% interstory drift, more flexural cracks developed outside the connection region than within, demonstrating the effectiveness of the plastic hinge control design. The BRB yielded at 0.5% drift and fractured at 5% drift, leading to test termination. The embedded steel plates and gusset connections remained intact throughout, validating the proposed connection approach. However, shear failure occurred in the RC joint region, suggesting that additional transverse reinforcement should be provided to enhance shear strength in future designs.