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研究生:蕭志坤
研究生(外文):Jyh-Kun Shiau
論文名稱:普通及高強度混凝土梁於扭矩作用下之剪力流厚度研究
論文名稱(外文):Shear Flow Zone in Torsion of Reinforced Normal and High-Strength Concrete Beams
指導教授:方一匡方一匡引用關係
指導教授(外文):I-Kuang Fang
學位類別:博士
校院名稱:國立成功大學
系所名稱:土木工程學系碩博士班
學門:工程學門
學類:土木工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:英文
論文頁數:169
中文關鍵詞:扭矩剪力流厚度
外文關鍵詞:torsionshear flow zone
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ACI 318-95規範對於扭力設計已改採薄管類比空間桁架之觀念,將實心與空心斷面之混凝土構件均模擬為剪力流薄管,其中剪力流管壁之厚度 為一重要因素。本文旨在探討高強度混凝土梁及普通強度混凝土梁在扭力作用下之強度及變形行為,並依據斜彎曲理論及薄管空間桁架類比模式之觀念,以理論及試驗詮釋管壁厚度之物理意義,據此提出一理論分析模式來預測鋼筋混凝土梁的扭矩及變形。本研究共測試22根斷面尺寸為350 × 500 mm之高強度及普通強度混凝土梁,依量測梁受扭力作用時試體表面之應變及彎曲程度推求扭力作用下之壓力區厚度,並探討該厚度對鋼筋混凝土梁抗扭矩行為之影響。
研究結果顯示:高強度混凝土( )試體之極限扭矩強度、開裂前及開裂後之扭轉勁度分別約為普通強度混凝土( )試體之1.25、2.0及1.4倍。對於高強度混凝土梁而言,依ACI 318-02規範所求得之極限扭矩強度值約為實測值的90 %。而薄管類比理論中之剪力流有效厚度將隨著混凝土抗壓強度之提高而減小,且隨著鋼筋量之增加而增厚。
經理論及試驗印證,根據薄管理論所得之管壁厚度約等於斜彎曲理論中壓剪區之深度,依該厚度所求得試體長邊之混凝土承壓應力均較短邊大,其最大壓應力約為ACI規範容許值的1.5倍。本研究建立之預測模式可預測斷面長、短邊之厚度及斜壓應力,並可進一步推算45度斜裂縫上之剪應力。在預測強度與變形方面,經與試驗值比較,得到良好之預測效果。
The torsion design provisions based on the thin-walled tube analogy for reinforced concrete members had been adopted in the ACI 318-95 Code, in which, the solid and hollow sections were idealized as a thin-walled tube, and the torsional capacity of a section was directly related to the effective wall thickness . This paper investigated the torsional strength and behavior of high and normal-strength concrete beams under pure torsion. An analytical model was developed which combines the basic concepts of skew-bending theory and thin-walled tube analogy for predicting the torsional strength and deformations of rectangular sections. The physical meaning of was experimentally validated. Twenty-two beam specimens made of normal and high-strength concrete, having a cross section of 350 × 500 mm, were tested under pure torsion and measured the surface strain and corresponding curvature of the concrete struts to find the effective wall thickness .
Test results showed that the ultimate strength, uncracked and cracked torsional stiffness in HSC beams were about 1.25, 2.0 and 1.4 times of those in NSC beams. For HSC beams, the calculated ultimate strength according to ACI 318-02 Code was about 0.9 times of the experiments. The effective wall thickness increased as the amount of torsional reinforcement increased, and decreased as the compressive strength of concrete in the thin-walled tube analogy.
The effective wall thickness was analytically and experimentally validated as the compression zone in the skew-bending theory. According to the calculated thickness, the maximum compressive stress in longer sides was greater than that in shorter sides, which was about 1.5 times of that allowed in the ACI 318-02 Code. The proposed analytical model can predict very accurately the torsional responses, including the effective wall thickness and the corresponding compressive stresses as well as the shear stresses at 45-degree concrete struts.
Acknowledgments………………………………………………I
Table of Contents……………………………………………II
Figures List…………………………………………………VI
Tables List…………………………………………………X
English Abstract…………………………………………XII
Chinese Abstract…………………………………………XIV
1. INTRODUCTION………………………………………1
1.1General………………………………………………………1
1.2Review of Torsion Theories and Design Provisions………3
1.3Research Significance………………………………………13
2. EXPERIMENTAL PROGRAMME.…………………….14
2.1Specimen Details…….……………………………..………14
2.2Materials Propoties……………..……..….…………….20
2.3Test Setup and Instrumentations….………….…………….23
2.4Test Procedure.…….………………………….……………30
2.5Measuring and Derivation for Effective Wall Thickness..…31
3. EXPERIMENTAL RESULTS AND DISCUSSION…...36
3.1Torsional Behavior of Normal and High-Strength
Concrete Beams………………………..………….………36
3.1.1General Behavior………………………….…..……39
3.1.2Torsional Stiffness………………………….………52
3.1.3Comparison of Test Ultimate Strength with
Model Predictions……..……………….……………55
3.1.4Effect of Concrete Strength on Ultimate Strength…...61
3.1.5Angle of Compression Diagonals………….……….63
3.1.6Summary……………………………………………68
3.2Thickness of Shear Flow Zone in Torsion….……...……..…70
3.2.1Torsional Characteristics of Solid and Hollow
Sections……………………………….………..……70
3.2.2Examination on Ultimate Strength Using
Experimental Wall Thickness………..…….……….77
3.2.3Comparisons of Design and Experimental Wall
Thickness………………………………….…………78
3.2.4Effect of Amount of Reinforcement…………………82
3.2.5Effect of Compressive Strength of Concrete…..……84
3.2.6Crushing Strength of Concrete Diagonals……….…..88
3.2.7Summary………………………………..….………93
3.3Physical Meaning of Shear Flow Zone in the
Thin-Walled Tube Analogy………………….……………..95
3.3.1Link Between Skew-Bending Theory and
Thin-Walled Tube Analogy……………...…………96
3.3.2Experimental Verification………………………….110
3.3.3Thickness of Compression Zone in Longer and
Shorter Sides…………………………….…………112
3.3.4Compressive Strength in 45-Degree Concrete
Struts……..……………………………….……….116
3.3.5Shear Stress at Crack Surfaces………….…………119
3.3.6Summary………………………………..…………121
4. ANALYTICAL MODEL ………………….….….……124
4.1Description of the Model…………………..……………125
4.2Method of Solution……………..…………..……………136
4.3Comparisons of Analytical with Test Results…....……140
4.4Mode of Failure……………..……..…………..…….……146
4.5Shear Stresses at Diagonal Cracks……….………..……148
4.6Summary…………………………..……………..……..151
5. CONCLUSIONS AND RECOMMENDATIONS
FOR FUTURE WORK……………….………………152
5.1Conclusions……………..……………….……………...152
5.2Recommendations for Future Work…..……….…………156
REFERENCES………………..…………………..……….157
NOTATION……………………….……………..………..163
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