| 摘要: | 過去針對鋼筋混凝土抗彎矩構架中梁柱接頭的轉角變形容量在相關規範並無明確告知。然而對於過去一系列的梁柱接頭研究已證實，在符合規範的配置條件下，均可提供至少4%弧度層間位移角的變形容量。本研究係透過改變擴頭鋼筋與擴頭鋼筋耐震錨定伸展長度，對於外柱梁柱接頭觀察其轉角性能優劣，綜合內柱梁柱接頭試體一併探討梁柱接頭轉角變形需求為何？
本研究共進行9組梁柱接頭受反覆載重試驗，其中7組為外柱梁柱接頭，2組為內柱梁柱接頭。外柱梁柱接頭試驗梁縱向主筋設計長度基於先前研究成果(簡育淇，2023)所建議之彎鉤鋼筋與擴頭鋼筋耐震受拉伸展長度公式所配置。除此之外，也針對梁柱接頭梁構件有、無配置繫筋與柱構件接頭交會區域有、無配置繫筋對於試體整體破壞模式與耐震性能的影響。內柱梁柱接頭試驗之柱深配置則符合現行美國ACI 318-19規範中梁縱向鋼筋貫穿接頭區域的最小柱深限制(26d_b)，比較先前研究成果(廖柏州 2017，劉志國 2019)所建議之內柱梁柱接頭握裹滑移模型所計算出的柱深長度，觀察在不同的混凝土設計強度條件下，兩者試體的破壞模式與性能進行比較。
試驗結果顯示，當外柱梁柱接頭梁主筋錨定伸展長度採用f_y/(65√(f_c^′ )) d_b(in, psi)，無論以彎鉤鋼筋或擴頭鋼筋錨定，當梁縱向鋼筋間距為2.5d_b時，皆可提供試體發展至少5%弧度之層間位移角的變形容量，且4%弧度變形之第2或3圈強度衰減低於3%。此外本研究也顯示擴頭鋼筋錨定長度可再縮短0.8倍長度至f_y/(81√(f_c^′ )) d_b(in, psi)，仍未發生錨定失敗的情形。而在相同的配置下，梁構件是否配置繫筋對於整體破壞模式與變形性能無明顯差異，但接頭交會區域未配置柱繫筋的影響十分顯著。就最終試體破壞模式來而言，交會區有配置柱繫筋的破壞模式為梁塑鉸破壞，儘管未配置柱繫筋的破壞模式本研究評定為梁降伏後接頭剪力破壞，試體發展至4%弧度層間位移角時仍保有其一定的耐震性能。
內柱梁柱接頭試驗結果則顯示當試體採用較低之混凝土強度(42 MPa)與鋼筋強度等級為SD 550W進行設計時，ACI 318-19所規定之最小柱深26d_b可能導致梁主筋在梁柱接頭內產生握裹滑移之現象，同時當試體採用高強度混凝土(70 MPa)配置時，整體內柱梁柱接頭試體最終破壞模式則順利發展為梁塑鉸破壞。顯示出當梁主筋貫穿梁柱接頭內部時，應合理考慮混凝土強度影響，建議合理制定混凝土強度之最小柱深設計公式，以提供梁柱接頭交會區足夠之握裹容量，使梁構件能有效發揮撓曲塑鉸藉此消散地震能量。
;In the past, there has been no clear guidance in the relevant codes regarding the rotational deformation capacity of beam-column joints in reinforced concrete moment-resisting frames. However, a series of past studies on beam-column joints has confirmed that, under code-compliant configurations, they can provide a deformation capacity of at least 4% inter-story drift ratio. This study aims to observe the performance of exterior beam-column joints by varying the use of headed reinforcement bars and the seismic anchorage development length of these bars. Additionally, it explores the rotational deformation demands on beam-column joints, including those for interior beam-column joints.
This study involved a total of nine beam-column joint specimens subjected to cyclic loading tests, with seven specimens being exterior beam-column joints and two specimens being interior beam-column joints. The longitudinal reinforcement length in the exterior beam-column joint tests was designed based on the formula for seismic tensile development length of hooked and headed reinforcement bars recommended by previous research (Jian, 2023). Moreover, the study investigated the effects of the presence or absence of transverse reinforcement in beam components and in the joint intersection region of column components on the overall failure mode and seismic performance of the specimens. The column depth configuration in the interior beam-column joint tests complied with the minimum column depth requirement for longitudinal beam reinforcement passing through the joint region as specified in the current American ACI 318-19 code (26d_b). The results were compared with the column depths calculated using the bond-slip model for interior beam-column joints recommended by previous research (Liao, 2017; Liu, 2019), observing the failure modes and performance of the specimens under different concrete strength conditions.
The test results indicated that when the anchorage development length of the beam′s main reinforcement in the exterior beam-column joints was f_y/(65√(f_c^′ )) d_b (in, psi), both hooked and headed reinforcements could provide a deformation capacity of at least 5% inter-story drift angle, with longitudinal beam reinforcement spacing at 2.5d_b, and the strength degradation at the 2nd or 3rd cycle of 4% drift ratio was less than 3%. Furthermore, the study showed that the anchorage length for headed reinforcement could be further reduced by 0.8 times to f_y/(81√(f_c^′ )) d_b (in, psi) without resulting in anchorage failure. Under the same configuration, the presence or absence of transverse reinforcement in beam components did not significantly affect the overall failure mode and deformation performance, but the impact of the absence of column transverse reinforcement in the joint intersection region was quite significant. Regarding the final failure mode of the specimens, the failure mode for specimens with transverse reinforcement in the joint region was beam plastic hinge failure, while for those without column transverse reinforcement, the failure mode was joint shear failure after beam yielding. The specimens still retained a certain level of seismic performance at 4% inter-story drift ratio.
The test results of the interior beam-column joint tests indicated that when the specimens were designed with lower concrete strength (42 MPa) and reinforcement strength grade of SD 550W, the minimum column depth of 26d_b specified by ACI 318-19 could lead to bond-slip phenomena of the beam main reinforcement within the beam-column joint. Additionally, when the specimens were configured with high-strength concrete (70 MPa), the final failure mode of the interior beam-column joint specimens successfully developed into beam plastic hinge failure. This suggests that when longitudinal beam reinforcement passes through the beam-column joint, the influence of concrete strength should be reasonably considered. It is recommended to establish a reasonable design formula for the minimum column depth based on concrete strength to provide sufficient bond capacity in the beam-column joint region, allowing beam components to effectively develop flexural plastic hinges to dissipate seismic energy. |
