實尺寸中空鋼筋混凝土梁扭力實驗

Experiment on Full-size Hollow Reinforced Concrete Beams Subjected to Pure Torsion

林俊呈(Jyun-Cheng Lin)

指導教授 ： 鄭全桓

國立暨南國際大學/科技學院/土木工程學系/碩士(2013年)

https://doi.org/10.6837/NCNU.2013.00279

摘要

本論文描述五組不同斷面尺寸、混凝土強度及鋼筋量之中空鋼筋混凝土(reinforced concrete, RC)梁試體純扭力試驗試驗結果與比較。
以往的混凝土扭力試驗多使用鋼構件夾具傳遞扭轉力矩，類似的裝置其鋼構件夾具和混凝土試體之間的微小滑移量很難消除，對小扭轉角量測可能造成可觀的誤差。本試驗使用與以往實驗不同的方法裝置，及較大的試體斷面尺寸。試體梁3.5 m 長測試區內配置中空RC梁之設計鋼筋量，在測試區左右兩端加強區，則設計了較厚之壁厚、並配置較密集箍筋，以確保最後的破壞發生於中央測試區內。全部試體，包括縱向主梁、十字型橫梁、和RC block，使用預拌混凝土一體澆置。實驗量測包括開裂點在內的全程扭矩、扭轉角、剪力流有效厚度 、鋼筋和混凝土表面應變、及試體縱向伸長等。本文由實驗結果討論本實驗使用裝置及方法對於量測長度、小扭轉角量測及消除試體縱向伸長束制之成效，並且比較T_cr及theta_cr、扭矩-扭轉角曲線、剪力流有效厚度、鋼筋應變、混凝土表面斜向應變之實驗結果與理論及公式預測值之間的差異。
本研究所使用之實驗裝置及方法於量測小扭轉角及開裂扭轉角量測相當成功，並可有效消除試體梁縱向伸長束制。實驗結果顯示，扭轉角量測長度應包含整個破壞區域，否則可能得到較小的單位扭轉角。此外，試體D075a和C065a之實驗扭矩-扭轉角曲線與分析曲線相當一致。

關鍵字

鋼筋混凝土 ； 扭力 ； 實驗 ； 梁 ； 扭矩 ； 扭轉角

並列摘要

This thesis describes the experiment of five hollow reinforced concrete (RC) beam specimens subjected to pure torsion, and compares the test results with .
Previous torsion tests of concrete beams often used metal components to clamp the concrete beam specimen while exerting a twisting torque. This type of apparatus could have gaps and slips between the clamping metal components and the concrete specimen, introducing errors into the small deformation measurement. This study used a monolithic transverse RC beam to convey a twisting torque without gaps to the twist end of the longitudinal test beam, and constructed a monolithic RC block at the fixed end. Pre-tensioning forces were used to fasten the RC blocks of the specimens to the underlying steel seat and to the strong floor, thus producing a slippage-free mechanism for the fixed end. The test apparatus also incorporated devices to eliminate any constraints on the longitudinal elongation of the test beams. Seven quantities were experimentally determined for each of the specimens through continuous measurement, using various measuring lengths.
The test results show that the test apparatus is rather efficient in determining small twists, and that the initial branches of the obtained torque-twist curves exhibit a high degree of linearity. The results also demonstrate that a measuring length should be long enough to incorporate the entire failure region, but should not be too long as too much length can cause the twist angles to be underestimated. Furthermore, the experimental values of the shear flow zone thickness reduce drastically around the cracking and remain relatively constant after cracking. The obtained elongation-twist curves are smooth when the measuring length covers the entire failure region, but otherwise have abrupt turns due to drastic losses of measured twist angles. The experimental torque-twist curves of specimens D075a and C065a agree reasonably well with the analytical curves.

並列關鍵字

Reinforced concrete ； torsion ； experiment ； beam ； torque ； twist

參考文獻

ACI Committee 318 (2008), “Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary,” American Concrete Institute, Farming Hills, Mich., pp.465.

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Fang, I.-K. and Shiau, J.-K.(2004), “Torsional Behavior of Normal- and High- Strength Concrete Beams,” ACI Structural Journal, Vol. 101, No. 3, 2004, pp. 304-313.

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