New RCS系統梁柱接頭之設計

Abstract

複合框架系統中，以鋼筋混凝土（RC）柱和鋼（S）梁組成的系統被稱為RCS系統。RCS系統結合了RC柱固有的勁度和經濟性，以及鋼梁的輕自重和長跨能力。RCS系統的初步研究和開發始於1980年代的美國和日本。RCS系統發展的關鍵在於梁柱接頭細節的設計。然而，現有文獻中的接頭細節主要是為了適應具有常規變形鋼筋（規定降伏應力至多490 MPa）和普通強度混凝土（抗壓強度低於55 MPa）的RC柱而開發的。為了在高層建築中達到最佳結構效率，RC柱需要高強度混凝土（抗壓強度超過70 MPa）和高強度鋼筋（規定降伏應力為550-690 MPa）。此外，現有文獻只探討了對於方形RC柱的同心鋼梁RCS接頭。建築需求往往需要非同心布置的梁和柱，並且具有多種截面形狀。

因此，在本研究中，設計了不同類型的New RCS梁柱接頭。“New”的概念是指在RC柱中使用高強度變形鋼筋（屈服應力為550-690 MPa）和高強度混凝土（抗壓強度超過70 MPa）。研究開發了四大類型的New RCS接頭，分別是： 1. 方形截面RC柱的經典貫通梁型接頭， 2. 方形截面RC柱的貫通柱型偏心接頭， 3. 圓形截面RC柱的貫通梁型接頭， 4. 圓形截面RC柱的貫通柱型和貫通隔板型接頭。

設計並實驗測試了總共11個大型梁柱子裝配試件，以評估接頭的行為。實驗結果證實了所提議的接頭細節的有效性。除了具有問題的螺栓網焊法蘭拼接細節的試件外，所有測試的梁柱子裝配試件均顯示出優秀的抗震行為。

除了上述New RCS接頭細節的開發，本研究還重點重新檢查了RCS接頭的承載行為。過去的多次實驗報告指出，現有文獻中的經典承載強度預測方程可能高估了接頭的承載強度。因此，本研究測試了兩個以柱軸向載荷為變量的外部貫通梁型New RCS 接頭，以評估承載行為。隨後，詳細的分析模型被設計用於考慮軸向載荷影響下的接頭承載強度估算。該模型能夠可靠地估算當前和先前研究中測試的試件的接頭承載強度。

本研究的結果表明，現有RCS設計指南將最大鋼筋降伏應力限制在490 MPa的規定，可以通過適當修改限制接頭內縱向鋼筋滑移的最小節點深度要求，安全地延長至690 MPa。此外，研究還表明，可以利用RCS節點鋼組件提供的額外約束，安全地降低現有設計指南要求的接頭約束體積比。總結來說，本研究中開發的接頭細節為結構設計師在比例設計複合New RCS系統方面提供了更多靈活性，所有簡化的接頭設計分析程序都可以無縫地整合到現有的國際設計指南中。。

Composite moment frame structural systems with Reinforced Concrete (RC) columns and Steel (S) beams are popularly known as RCS systems. These composite RCS systems combine the inherent stiffness and economy of RC columns with the light-weight and long-spanning capability of steel beams. The initial research and development of RCS systems began in the 1980s in the US and Japan. The key to the development of RCS system is the design of beam-column joint detail. However, the joint details available in the existing literature were developed primarily for RC columns having conventional deformed bars with a specified yield stress up to 490 MPa and normal-strength concrete (compressive strength <55 MPa). To achieve optimal structural efficiency for high-rise construction, RC columns require high-strength concrete (compressive strength exceeding 70 MPa) and high-strength reinforcement (specified yield stress of 550-690 MPa). Additionally, existing literature only explores RCS joints with concentrically framing steel beams for square RC columns. Architectural demands, however, often necessitate eccentrically framing beams and columns with a variety of cross-sectional shapes.

Thus, in this research, different types of New RCS beam-column joints were designed. The term “New” refers to the use of high-strength deformed bars (yield stress of 550-690 MPa) along with high-strength concrete (compressive strength > 70 MPa) in RC Columns. The research developed four major sub-categories of New RCS joints which are: I. Classical through-beam type joints for RC columns with square cross-section, II. Through-column type eccentric joints for RC columns with square cross-section, III. Through-beam type joints for RC columns with circular cross-section, and IV. Through-column and through-diaphragm type joints for RC columns with circular cross-section. A total of 11 large-scale beam-column subassembly specimens were designed and experimentally tested to evaluate the behaviour of joints. The experimental results were used to verify the efficacy of proposed joint details. All tested beam-column subassembly specimens except those featuring the problematic bolted web-welded flange splice detail, demonstrated excellent seismic behaviour.

In addition to development of New RCS joint details mentioned above, the research also focuses on re-examining the bearing behaviour of RCS joints. Multiple experiments in the past have reported that the classical bearing strength prediction equations available in the literature can overestimate the joint bearing strength. Hence, in this research, two exterior through-beam type New RCS joints were tested with axial load in the column as the varying parameter; to evaluate the bearing behaviour. Thereafter, a detailed analytical model has been devised to estimate the joint bearing strength considering the influence axial load. The proposed model was able to provide reliable estimates joint bearing strength for the specimens tested in the current and previous studies.

The findings of this study, indicate that limitation set by existing RCS design guidelines, to restrict the maximum reinforcement yield stress to 490 MPa can be safely extended to 690 MPa, by appropriately modifying the minimum joint depth requirement provision which is meant to limit the slip of longitudinal reinforcement in the joint. Further, the study also indicates that the volumetric ratio of joint confinement can be safely reduced from the existing design guideline requirement, by taking advantage of the additional confinement provided by the steel components of RCS joint. In summary, the joint details developed in this study provide more flexibility to the structural designer in proportioning composite New RCS systems, and all the simplified analytical procedures devised to design the joints can be seamlessly integrated to the existing international design guidelines.