| 摘要: | 本研究主要是研究New RC梁有斜向鋼筋設置，相較於無斜向鋼筋設置，其耐震性能差異。其中RC梁有斜向鋼筋設置，主要是參考紐西蘭規範NZS3101-2006[2]中，有關防止梁塑性鉸區受震中可能產生與梁向垂直之滑移剪力(Sliding shear)裂紋破壞而訂定之斜向鋼筋設計。因此本研究繼游凱翔[25]研究，因該研究結果乃利用T頭鋼筋進行塑鉸外移設計，有成功產生塑性鉸轉移，但有產生滑移剪力裂紋破壞跡象，故考量配置斜向鋼筋防止滑移剪力破壞。
試驗規劃乃製作兩座懸臂梁試體，矩形斷面為270mm×550mm，使用#10與#8 SD690螺紋節為梁主筋，#3 SD790竹節鋼筋作為梁橫向箍筋，混凝土設計強度f_c^′=60MPa。其中，第一座HB-T0為2.0m之原型懸臂梁，於梁內有配置#8-SD690斜向筋，第二座HB-T550為2.2m塑鉸外移550mm懸臂梁，於梁內配置#5-SD790斜向筋，皆為抑制滑移剪力發生。
試驗結果顯示，HB-T0因配置斜向筋，使試體強度於DR=8%後才開始衰退，相較於無斜向筋之原型梁，遲滯迴圈圖較為飽滿，明顯改善試體循環性能;HB-T550因於梁端配置超額鋼筋，成功使塑鉸轉移至梁區，且因斜向筋設計方式為從柱面開始彎折，交叉範圍遍佈塑鉸區，因此於實驗最終塑鉸區未產生剪力斜向裂縫破壞，亦未產生滑移剪力破壞，相較於無斜向筋有塑鉸外移梁之遲滯迴圈圖，HB-T550並未產生明顯束縮作用(Pinching)，故斜向鋼筋對梁抗震能力及防止斜向剪力或垂直滑移剪力破壞有明顯效果。
本文亦研究先前計畫與相關文獻試體測試數據結果，NZS 3101判斷產生滑移剪力破壞可能性之經驗公式，較不適用於短跨梁(a/d<2.5)，乃因其主要以斜壓桿或剪張破壞為主;而長跨梁(a/d≥2.5)於試驗過程，結構受到反覆荷載因相互交錯之撓曲裂縫與對角剪力裂縫作用下，在塑鉸區有潛在滑移剪力裂縫，應考慮滑移剪力設計。於實務面，當梁加入斜向鋼筋，應注意現場實際鋼筋配置是否可行。;This study is mainly to discuss the difference between the seismic performance of the New RC beams with diagonal reinforcement, and that without the diagonal reinforcement. The RC beams with diagonal reinforcement are designed to the New Zealand code NZS3101-2006[2] to prevent the beams in the plastic hinge zone from the failure of the sliding shear crack. Therefore, this study continues to Kai-xiang You [25] research on the hinge relocation design by using T-headed bars. The main conclusion is that the T-headed bars as extra reinforcement can successfully relocate the plastic hinge zone from the column face to a distance away from the face, but the final failure mode of sliding shear occurred.
A experimental work is also carried out in the study. Two cantilever beam specimens, named HB-T0 and HB-T550, with rectangular cross-section 270mm×550mm are produced. #10 and #8 SD690 as the main reinforcement, #3 SD790 as the transverse reinforcement, and design concrete strength f_c^′=60MPa are used. The prototype beam HB-T0 is a 2.0m long cantilever beam having #8-SD690 diagonal reinforcement. The beam HB-T550 is a 2.2m long cantilever beam with hinge relocating 550mm from the column face. The beam arranged #5-SD790 diagonal reinforcement in the potential plastic hinge zone.
The test results show that, due to the configuration of diagonal reinforcement, HB-T0 began to fail after the DR=8%. Compared with the beams without diagonal reinforcement, the beams with diagonal reinforcement presented a better seismic performance. HB-T550 also showed better seismic behavior in comparison with the beams with hinge relocation, but no diagonal reinforcement set up. Therefore, no shear diagonal crack failure or sliding shear failure was founded in HB-T550 at the end of the test. That is, HB-T550 did not produce obvious pinching, compared with the hysteresis loop of the beam having plastic hinge relocation without diagonal reinforcement, so diagonal reinforcement has the benefit of the seismic resistance on preventing the failure of diagonal shear or vertical sliding shear from occurring.
This article also collected the test data of the previous researches. The results showed that NZS 3101 empirical formula for determining the possibility of sliding shear failure is less suitable application than the short-span beams (a/d<2.5) because of their main failure mode occurred in the diagonal strut compression or shear-tension failure. However, NZS3101 empirical formula can be used for the long-span beams (a/d≥2.5), because these beams were subjected to reverse loads to cause the potential sliding shear cracks to happen in the plastic hinge zone. Thus the check of sliding shear failure is suggested to be considered. In practical situations, when the beam is added with diagonal reinforcement, it should be noted whether the reinforcement configuration in the site is feasible. |
