高強度混凝土之T頭鋼筋錨定行為研究

Anchorage Behavior of T Headed bars within High-Strength Concrete

紀凱甯(Kain-Ning Chi)

指導教授 ： 廖國偉

淡江大學/工學院/土木工程學系碩士班/碩士(2010年)

https://doi.org/10.6846/TKU.2010.00259

摘要

在鋼筋混凝土構件中，現階段鋼筋端部仍普遍使用傳統90o或180o標準彎鉤之錨定特性，以縮短鋼筋直線發展長度，提供載重所需之強度。近幾年T頭鋼筋已漸漸地應用在橋梁及建築結構上，2008年版美國ACI 318設計規範於機械錨定章節中，更針對T頭鋼筋之設計提出建議，其設計規定包括鋼筋強度不得超過420MPa、混凝土強度上限為42MPa、鋼筋淨間距不得少於4db、淨保護層不得少於2db及T頭端板面積必須不可少於5倍鋼筋斷面積。本研究目的欲突破上述規定之適用限制，以擴大T頭端錨之實際應用範圍。
本研究共進行52組梁構件CCT節點試驗及26組拉拔試驗，探討T頭鋼筋在混凝土中之錨定行為與傳力機制。其中研究參數包括鋼筋強度、混凝土強度、T頭端板大小、鋼筋淨間距(4db及1.5db)及圍束條件等，同時也探討T頭鋼筋、直通鋼筋與標準90o及180o彎鉤鋼筋之錨定效應。
試驗結果顯示，鋼筋之T頭錨定確實遠比標準彎鉤錨定提供較佳之錨定性能，其強度約增加15%至50%，且T頭端板越大，錨定強度提升越顯著，本研究顯示，使用3倍T頭端板即可取代標準彎鉤之錨定強度；鋼筋淨間距採用1.5db與4db之試體，其強度表現均獲得相近之結果，故規範規定之鋼筋淨間距，應可適當縮短，但仍須更多的實驗數據加以證實；在混凝土強度參數方面，鋼筋錨定強度隨混凝土強度的增加而提升，但超過56MPa強度後，其上升趨勢漸緩，但部分試體發生強度降低之現象；在圍束效應方面，配置圍束箍筋可有效提升鋼筋端部錨定強度，約提升未圍束試體之10%至30%，隨著圍束鋼筋量的增加，其錨定強度提升越顯著。觀察T頭端部之滑動情形也發現，T頭端板面積越大滑移量越小，約為直通鋼筋端部滑移量的20%，同時圍束鋼筋所提供之圍束效果，也顯示有降低其滑動之趨勢。本研究亦針對試體不同條件，歸納其破壞模式，以提供讀者參考。

關鍵字

機械錨定 ； T頭鋼筋 ； CCT節點 ； 拉拔 ； 90度與180度標準彎鉤 ； 壓桿破壞模式

並列摘要

To ensure the reinforcement concrete structure to reach the design strength, one of the criteria is the bonding behavior between reinforced steel and the concrete. To provide the necessary bonding resistance force, bended-hook steel bar is commonly used in these days. This traditional design usually results in too many reinforced steel in the area of beam –column joint which arises difficulties in construction field. Thus, in this study, we attempt to investigate another technology which is the T plate-ended reinforced steel to examine if it can provide a suitable bonding resistance.
The T plate-ended reinforced steel has been applied in the structures of bridge and building in many other countries. In ACI 318 (2008), the recommendation of T plate-ended reinforced steel used in the building are the strength of steel must be less than 420MPa, the strength of concrete must be less than 42MPa, the clearance between steels must be larger than four times of the diameter of the steel (4db), the lower bounds of the side clearance and the area of T plate-ended is 2db and 4db, respectively. In this study, in order to fully capture the mechanism of anchorage behavior between reinforced steel and concrete, we perform 52 CCT Node tests and 26 pull-out tests.
In the tests, the design parameters are the strength of steel and concrete, size of T plate-ended steel, clearance between steels and the confinement conditions. From the tests, we learn that the T plate-ended steel provide a better bondage effect which is about 15% ~ 50% more than the traditional design. The bigger the T plate-ended steel is, the better the strength of anchorage is. In general, T plate-ended steel with 3db can reach the same design target of the traditional straight reinforced steel. The effect of clearance is not significant. Also, increase the strength of concrete can have a better anchorage performance. However, this trend does not hold when the strength of concrete is over 56MPa. The arrangement of confinement reinforcement can also enhance the integrated strength about 10% ~30%. The closer the confined reinforcement is, the bigger the integrated strength is.
Based on the test results, the bigger the T plate-ended steel is, the smaller the slip of the bar is. The amount of slip is only 20% of the regular reinforcement. Thus, it is concluded that the increase of confinement can enhance the anchorage effect. The tests conducted in this study provide different failure modes which is valuable for further investigation.

並列關鍵字

mechanically anchored ； T headed bars ； CCT Node ； pull-out ； 90o and 180o bended-hook ； strut failure mode

參考文獻

[1].ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary (ACI 318R-08), ”American Concrete Institute, Farmington Hills, 2008.

[4].ACI-ASCE Committee 352, “Recommendations for Design of Beam-Column Joints in Monolithic Reinforced Concrete Structures,” ACI Journal, Proceedings, 2002.

[9].DeVries, R. A., Anchorage of Headed Reinforcement in Concrete, PhD Dissertation, The University of Texas at Austin, Austin, Texas, December 1996.

[10].Bashandy, T. R., Application of Headed Bars in Concrete Members, PhD Dissertation, The University of Texas at Austin, Austin, Texas, December 1996.

[2].土木401-96，「混凝土工程設計規範與解說」，中國土木水利工程學會，臺北 (2007)。