鋼纖維混凝土外部梁柱接頭剪力強度評估與設計建議

Evaluation of Shear Strength and Design Procedure of Steel Fiber Reinforced Concrete Exterior Beam-Column Joints

曾鈺軒(Yu-Hsuan Tseng)

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/NTU201701145

摘要

梁柱接頭在耐震構架中扮演極為重要的角色，若接頭受到嚴重破壞，構架整體的耐震行為將會大受影響。而梁柱接頭在承受地震力時，會有高剪力傳入接頭中，因此，規範建議在接頭處配置緊密箍筋以避免接頭處發生剪力破壞且確保接頭有足夠的圍束，但配置緊密箍筋卻造成綁紮不易、澆置品質不佳等施工問題。
然而，實驗指出，在接頭處使用鋼纖維混凝土可以減少箍筋的使用量，因為鋼纖維混凝土具有高拉力強度且具有很好的韌性能力。但是，鋼纖維使用量跟箍筋配置量之間的取代關係一直都沒有被明確地量化，造成鋼纖維混凝土一直無法被廣為應用。
本研究從剪力強度以及圍束下手，致力於提出鋼纖維混凝土外部梁柱接頭之設計建議。首先，本研究建立了一個外部梁柱接頭資料庫，並以軟化壓拉桿模型及半經驗公式模型為基礎，提出一個適用於計算鋼纖維混凝土外部梁柱接頭之剪力強度模型，而此模型亦可用於評估接頭之破壞模式。另一方面，分析資料庫試體的圍束值後，本研究找出了圍束的下限值。此外，從資料庫分析中，本研究亦評估了規範要求的設計準則之適用性。綜合剪力模型、圍束下限值以及適用之設計準則，本研究最後提出一個適用於鋼纖維混凝土外部梁柱接頭之設計建議，並以一實例去比較與ACI 318-14設計規範之間的差異。

關鍵字

梁柱接頭 ； 鋼纖維混凝土 ； 剪力強度 ； 圍束 ； 剪力模型 ； 設計建議

並列摘要

A beam-column joint takes an important role in the force transferring mechanism in a moment resisting frame. Thus, severe damage within a joint panel may cause deterioration in overall seismic performance of the frame. As a joint is subjected to high shear strength, code recommendations suggest to arrange closely-spaced hoop transverse reinforcement to either prevent joints from shear failure or provide joints with enough confinement, which leads congested joints and results in difficult construction works. However, with high tensile strength and good toughness behavior, applying steel fiber concrete in joint panels is expected to reduce the amount of transverse reinforcement. Besides, steel fiber reinforced concrete (SFRC) joints were tested to be of higher energy absorption and ductile behaviors. However, due to the unclear replacement between steel fibers and transverse reinforcement, a SFRC joint is of limitation to be designed.
In this research, a design procedure for SFRC exterior joints is proposed based on the aspects of shear strength and confinement. At first, predictive shear strength models based on the softened strut-and-tie theory are developed to predict the shear strength of SFRC exterior joints. Besides, a database of exterior beam-column joints, both with or without steel fiber concrete in joint panels, is constructed in order to evaluate the accuracies of predictions of shear strength. Moreover, the limit of confinement and the adequacy of the existing design criteria are assessed from the analysis of database. At last, with the observations, a design procedure for SFRC exterior joints is proposed.
In additional, a SFRC joint is designed by following the proposed procedure, and is also demonstrated to be of good seismic performance by an experimental test [42] with applying steel fiber concrete in joint panel and similar arrangement of reinforcement. Also, from the case study, it is investigated that with applying 1.5% volume fraction of steel fibers, the shear strength is at most 40% enhanced, and the requirement of transverse reinforcement is at least 30% decreased.

並列關鍵字

beam-column joint ； steel fiber concrete ； shear strength ； confinement ； shear model ； design method

參考文獻

[18] Guo, C.H (2011). Seismic Performance of High-Strength Reinforced Concrete Beam-Column Joints. Master's Thesis, National Yunlin University of Science and Technology, Yunlin, Taiwan.

[25] Ji, Y.C (2013). Database Construction and Parameter Analysis of Reinforced Concrete Beam-Column Connections. Master's Thesis, National Yunlin University of Science and Technology, Yunlin, Taiwan.

[2] ACI-ASCE Committee 352 (2002), Recommendations for Design of Beam-Column Connections in Monolithic Reinforced Concrete Structures. American Concrete Institute, Farmington Hills.

[3] American Concrete Institute (2014). Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (318R-14), Farmington Hills, MI.

[5] Architectural Institute of Japan (1988). Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings based on Ultimate Strength Concept (draft) and Commentary. Architectural Institute of Japan.