高強度鋼纖維混凝土版之壓桿行為實驗研究

Experimental Investigation on Isolated Strut Behavior of High Strength Steel Fiber Reinforced Concrete Panels

郭珈均(Chia-Chun Kuo)

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(2019年)

https://doi.org/10.6342/NTU201902816

摘要

近年來高樓結構需求提升，各國陸續發展高強度混凝土材料，且台灣在高強度材料的使用也日漸普及(例如台灣NEW RC計畫)，然而，高強度混凝土達極限強度後常伴隨產生脆性破壞疑慮。台灣地震活動頻繁，結構物必須擁有足夠之耐震能力，此外，結構中存在許多載重不連續區及幾何不連續區，其破壞模式通常為脆性之剪力破壞，為避免高剪力作用下導致試體產生脆性破壞，設計時常保守採大量剪力箍筋圍束混凝土，但過度加密的剪力箍筋將導致施工困難。
根據多項研究顯示，透過添加鋼纖維於混凝土中，可明顯提升混凝土材料之韌性，且透過額外橋接效應有效抑制混凝土裂縫生成，並取代部分橫向鋼筋的角色，同時解決高剪力脆性破壞及箍筋綁紮過密的施工問題。本研究著重於探討高強度鋼纖維混凝土使用於構件不連續區之力學行為，並期望提出鋼纖維混凝土瓶狀壓拉桿之設計建議。
本研究採鋼纖維體積取代率(0%、0.75%及1.5%)及鋼筋配置位置作為設計參數，製作24座長、寬、高尺寸分別為90cm×90cm×10cm的高強度混凝土及高強度鋼纖維混凝土平版試體，並進行直壓試驗。實驗結果顯示，隨鋼纖維體積取代率的提高，可使試體由脆性之劈裂破壞轉變為混凝土壓桿擠碎破壞，有效增加試體韌性，且添加鋼纖維之高強度混凝土試體，可提升平版試體極限強度達40%以上。另透過分析不同鋼纖維體積取代率試體之壓桿擴散角度及試體鋼筋應變ε_s，以有效混凝土面積之型式提出鋼纖維於瓶狀壓拉桿模型內之拉桿貢獻，分析結果顯示，相較於一般混凝土平版試體，鋼纖維體積取代率0.75%及1.5%之平版試體可分別提升2.2倍及2.9倍的鋼纖維混凝土拉桿強度、40%及50%的有效面積。綜上所述，添加鋼纖維於混凝土中除可取代部分橫向鋼筋提供混凝土橫向拉力，亦可有效提升試體強度、韌性及圍束能力。

關鍵字

鋼纖維 ； 平版 ； 高強度混凝土 ； 壓拉桿

並列摘要

In recent years, the demand of high-rising structures increases, so development and application of high strength materials have been facilitated either in research and practice. The Taiwan New RC Project using high strength concrete along with high strength rebars to reduce the member section sizes and save materials consumption have been conducted since 2009. However, the brittle failure modes owning to the nature of high strength concrete could be a major concern.
In Taiwan, which locates on Pacific Ring of Fire, structures need to have sufficient seismic capacity. In addition, there are many load discontinue regions and many geometric discontinue regions (D-regions) in structures. The failures of these regions are usually caused by shear accompanying with sudden and brittle failure patterns. In order to ensure strength and ductility of structure members, higher transverse reinforcement ratio is required. However, dense transverse reinforcement arrangement will lead to construction difficulty.
According to many experiment results, adding steel fiber in concrete can notably enhance ductility, tensile strength, shear strength and damage tolerance of concrete and prevent cover spalling in the early stage. Fibers can be an effective alternative to transverse reinforcements to solve the congestion problem. The objective of the study is to investigate the isolated strut behavior of high strength steel fiber reinforced concrete panels for further development of bottle-shaped strut-and tie model.
The experimental program involves 24 panels fabricated with different volume fractions of steel fiber (0%, 0.75%, 1.5%) and different transverse reinforcement location. The test results show that the failure mode can be transferred from splitting failure to strut failure by adding 0.75% and 1.5% volume fraction of steel fibers. The ultimate shear strength can be increased more than 40% with addition of fibers. Moreover, by analyzing the strut-spreading angle of the specimens and the strain of transverse reinforcements, it showed that the tensile strength of concrete in ties can be increased by 2.2 times and 2.9 times by adding 0.75% and 1.5% fibers, compared to concrete without fiber, respectively. Furthermore, the effective concrete area can be increased by 40% and 50% by adding 0.75% and 1.5% fibers, compared to concrete without fiber, respectively. In summary, the addition of steel fiber can replace the transverse reinforcements to provide tensile strength in the concrete, and can also effectively enhance the strength, ductility and ability of confinement of the specimens.

並列關鍵字

steel fiber ； panel ； high strength concrete ； strut-and-tie model ； isolated strut

參考文獻

[1] Aoyama, H., 1992, “Development of Advanced Reinforced Concrete Buildings with High-Strength and High-Quality Materials,” Earthquake Engineering Tenth World Conference, Rotterdam.

[2] Alwan, J. M., Naaman, A. E., and Guerrero, P., 1999, “Effect of Mechanical Clamping on the Pull-out Response of Hooked Steel Fibers Embedded in Cementitious Composites,” Concrete Science and Engineering, Vol. 1, No. 1, pp. 15-25.

[3] ACI Committee, 318, 2014, “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary,” American Concrete Institute.

[4] Arabzadeh, A., Aghayari, R., and Rahai, A. R., 2012, “A New Model for Predicting the Effective Strength in Reinforced Concrete Bottle-Shaped Struts,” International Journal of Civil Engineering, Vol. 10, No. 4.

[5] Bencardino, F., Rizzuti, L., Spadea, G., and Swamy, R., 2008,” Stress-Strain Behavior of Steel Fiber-Reinforced Concrete in Compression,” Journal of Materials in Civil Engineering, ASCE, Vol. 20.