高強度鋼纖維混凝土外部梁柱接頭剪力強度與反復側推行為研究

Shear Strength and Cyclic Behavior of High Strength Steel Fiber Reinforced Concrete Exterior Beam-Column Joints

張凱越(Kai-Yueh Chang)

指導教授 ： 廖文正

國立臺灣大學/工學院/土木工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703794

摘要

隨著建築技術提升，對建築材料之強度需求也越來越高，日本New RC Project使用高強度材料以縮減構件尺寸及節省材料用量。然而相較於普通強度混凝土，高強度混凝土達極限強度後強度驟降，設計時應將此脆性破壞納入考量，故ACI 318-14要求使用高強度混凝土 (f_c^'≥70MPa)時，需配置更多橫向鋼筋維持柱構件韌性。
特殊抗彎構架中梁柱接頭為重要傳力單元，在設計時皆以緊密箍筋配置確保其具足夠韌性；惟梁柱接頭中已有柱及梁主筋之交會，實務上再綁紮緊密橫向鋼筋常會出現鋼筋過密施工困難的問題。此一施工問題，在構件尺寸較小、要求配置較傳統RC結構更多橫向鋼筋的New RC結構系統中，將更為困難。
本研究重點在於探討添加鋼纖維於高強度混凝土外部梁柱接頭中，完全或部分取代橫向鋼筋，其耐震能力的表現，並進一步評估其接頭剪力強度及量化圍束能力。
實驗計畫設計了兩支實尺寸之外部梁柱接頭，接頭區皆澆置體積取代率1.5%之高強度鋼纖維混凝土，在分別為低軸力比及高軸力下進行反復側推試驗。其中低軸力試體以接頭發生剪力破壞進行設計，以評估其接頭剪力強度；高軸力試體依柱構件以韌性比量化鋼纖維取代橫向鋼筋之圍束效益回歸公式進行設計，藉以印證該設計式於接頭中之適用性。低軸力試體試驗結果顯示高強度鋼纖維接頭即便無配置任何橫向鋼筋，其抗剪容量是規範設計值之1.9倍；且雖然為接頭剪力破壞，接頭外觀仍相當完整，並符合ACI 374耐震性能規範中合格接頭之各項要求。高軸力試體試驗結果確認柱構件之韌性比回歸公式可用於設計梁柱接頭，於高軸力下鋼纖維能取代75%之橫向鋼筋量。此研究顯示將高強度鋼纖維混凝土應用於梁柱接頭上，不論是抗剪能力或是損傷容限，皆有良好表現；且不論在剪力強度評估或是鋼纖維取代橫向圍束鋼筋，都有設計公式可供直接應用。
關鍵字: 鋼纖維、外部梁柱接頭、New RC、韌性比、剪力強度

關鍵字

鋼纖維 ； 外部梁柱接頭 ； New RC ； 韌性比 ； 剪力強度

並列摘要

The New RC Project conducted by Japan in 1988 mainly used high strength materials to reduce the section sizes of members and to save the consumption of materials. However, the brittle nature of high strength concrete should be considered compared to ductile response of normal strength concrete. Therefore, ACI 318-14 requires denser transverse reinforcement while using high strength concrete (f_c^'≥70MPa) in column members to assure its toughness.
For special moment frames, beam-column joint is a key element to transfer shear and moment forces. Nevertheless, beam-column is an intersection of longitudinal reinforcement of beams and columns along with transverse reinforcement of columns. The heavy reinforcement arrangement may result in construction difficulty and poor construction quality. This issue could be severer in New RC members since their section sizes are smaller. Addition of steel fiber in beam column joints may be an alternative to transverse reinforcement since its validity has been verified in columns.
This study investigates the seismic performances of high strength fiber reinforced exterior beam-column joints. Estimation of shear strengths and quatification of confinement efficiency are also discussed.
Two full-scale high strength fiber reinforced exterior beam-column joints with 1.5% volume fraction steel fibers were subjected cyclic loading under low and high axial loading levels respectively. The high axial load specimen was designed to verify the fiber confinement efficiency in terms of toughness ratio. The test results show not only toughness ratio can properly quantify fiber confinement efficiency in beam-column joints, but 75% of transverse reinforcement can be eliminated owing to steel fibers under high axial loading. The other specimen was designed to obtain its shear capacity under low axial loading level by joint shear failure. The test results show that its shear strength is 1.91 times of that suggested in ACI 318, even there is no any transverse reinforcement in the joint. The specimen ends up with shear failure, but it still can keep the good shape and satisfy all the criterions of a qualified beam-column joints required in ACI 374. In summary, application of high strength fiber reinforced concrete in New RC beam-column joints offers opportunities to significantly simplify the design and construction work, while ensuring adequate ductility and damage tolerance.
Keywords: Steel fiber, Exterior beam-column joint, New RC, Toughness ratio, Shear strength.

並列關鍵字

Steel Fiber ； Exterior Beam-Column Joint ； New RC ； Toughness Ratio ； Shear Strength

參考文獻

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