| 摘要: | 現行規範中，對彎鉤鋼筋錨定彎轉半徑已有明文限制，但在實務設計中，若梁構件使用較大號數的鋼筋，且上下層主筋配置均超過一層，則梁柱交會區常面臨鋼筋碰撞與壅塞問題，特別是外柱接頭範圍更難避免。以擴頭鋼筋取代傳統彎鉤方式，不僅可有效提升錨定性能，更大幅改善接頭區的施工性。此外，目前規範對於機械續接器於塑鉸區的配置存在實務應用上的爭議。
本研究共設計並進行8組外柱梁柱接頭受反覆載重試驗。探討主筋錨定方式（彎鉤與擴頭）、續接形式（傳統搭接與灌漿螺紋套筒續接器）、梁繫筋配置、擴頭灌漿與否、鋼筋強度與伸展長度等變數對接頭耐震性能之影響。實驗中驗證修正後之接頭剪力容量定義，將有效剪力面積設為「錨定主筋伸展長度+125 mm」，並據以計算剪力需求容量比 V_jh⁄V_n ，用以判別接頭破壞模式，並與實際破壞觀察結果對照分析。
試驗結果顯示，擴頭鋼筋相較於傳統彎鉤，在相同伸展長度下具更佳之錨定穩定性，未出現滑移裂縫；而彎鉤設計試體則普遍出現沿主筋方向滑移徵象，導致強度提前衰減。採用本研究建議之剪力面積定義，所得剪力比與實際破壞模式具良好對應性，建議當 V_jh⁄(V_n>1.15)時，接頭破壞風險明顯提升，應強化接頭剪力圍束設計。試體BCJ3C未設梁繫筋但採雙層箍筋，仍順利發展梁端塑性鉸，顯示在錨定與剪力拘束足夠前提下，繫筋配置可予簡化。試體BCJ3與BCJ3G伸展長度相同但軸力不同，其破壞模式亦隨軸力大小改變，突顯軸力對破壞型態具顯著影響。此外，續接試體BCJ4證實續接器配置於塑鉸區並不阻礙撓曲延性發展，BCJ6則因伸展長度不足導致接頭剪力破壞，與續接器本身無直接關聯。本研究不僅驗證擴頭鋼筋與續接器應用於外柱接頭之可行性，亦提出剪力需求容量比與破壞模式之對應準則，並對軸力與構造細節對行為影響加以量化分析。研究結果可供未來高強度鋼筋梁柱接頭設計、施工細部處理及耐震性能評估之參考。
;Current design codes specify the minimum bend diameter for hooked bars; however, in practical applications, especially when large-diameter reinforcement and multiple layers of top and bottom bars are used in beam-column joints, reinforcement congestion frequently occurs. This issue is particularly severe in exterior joints, where spatial limitations make bar placement and concrete casting more challenging. Replacing traditional hooked bars with headed bars not only enhances anchorage performance but also significantly improves construction feasibility in congested joint zones. Meanwhile, existing design codes provide no explicit restrictions on the use of mechanical splices within plastic hinge regions, leading to uncertainties in practical implementation.
This study conducted cyclic loading tests on eight full-scale exterior reinforced concrete beam-column joint specimens to investigate the effects of various design parameters on seismic performance. Variables included anchorage type (hooked vs. headed bars), bar splicing method (lap splice vs. grouted sleeve coupler), presence of beam transverse reinforcement, head grout placement, bar strength and diameter, and bar extension length. A revised definition for joint shear capacity was also proposed, using an effective joint shear area defined as “bar extension length + 125 mm.” The shear demand-to-capacity ratio V_jh⁄V_n was then calculated and compared with observed failure modes.
Test results indicate that headed bars provided superior anchorage stability compared to hooked bars under the same extension length, with no visible slip cracks observed. In contrast, specimens with hooked bars exhibited significant slip-related cracking along bar paths, leading to early strength degradation. The proposed shear area definition yielded a shear ratio that corresponded well with observed failure mechanisms. Specimens with V_jh⁄(V_n>1.10)were prone to joint shear failure, suggesting the need for enhanced shear confinement. Specimen BCJ3C, without beam transverse reinforcement but with double-layer stirrups, still developed a ductile beam plastic hinge, suggesting that beam ties may be simplified if anchorage and confinement are sufficient. Comparison between BCJ3 and BCJ3G (with identical bar extensions but different axial loads) highlighted the significant role of axial load levels in influencing failure modes. Additionally, specimen BCJ4 confirmed that mechanical splices placed within the plastic hinge region did not hinder flexural hinge formation, while BCJ6, which experienced joint shear failure, did so primarily due to insufficient bar extension rather than the use of splices.
This study confirms the feasibility of using headed bars and mechanical splices in exterior beam-column joints and proposes a shear ratio-based criterion for predicting failure modes. The influence of axial load and detailed configurations on joint performance was also quantitatively assessed. The findings provide valuable guidance for the design, detailing, and seismic performance evaluation of RC beam-column joints using high-strength reinforcement. |
