混凝土構架破壞機制之預測

The prediction of the fracture mechanism for RC portal frame

王文宏(Weng-Hone Wang)

指導教授 ： 陳清泉

國立臺灣大學/工學院/土木工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201600827

摘要

本論文研究係對於混凝土結構物之破壞機制作研究、分析及探討，除由實驗室試驗外，尚依據材料力學及塑性力學之觀念，對於結構物裂縫之產生、延伸及最後導致破壞之機制作分析及推導及證明工作。更運用有限元素分析程式SAP於混凝土圓柱試體作應力、主應力及應變能分析，以獲得裂縫之延展及破壞之數學證明，並運用HHT分析法分析結構物破壞前後之特徵值改變狀況作結構物安全評估。本論文研究工作除對混凝土圓柱試體劈裂破壞模式作探討外，另對於一層樓兩跨度結構物作實尺寸試驗，以探討混凝土結構物之破壞機制。
混凝土圓柱試體進行劈裂試驗時，其達到破壞時裂縫分佈之型式，依ASTM C496認知，裂縫發生於沿平行試體受力直徑方向上，試體元素力學行為平行受力直徑方向上承受壓力，垂直方向上承受拉力，其破壞機制為壓拉破壞。本研究除對圓柱試體進行劈裂試驗以觀察裂縫機制之發展模式，並藉重彈性理論分析平行及垂直方向直徑上應力分佈，再輔以有限元素法分析試體剖面能量分佈狀態，探討等應力線及等能量線梯度方向分佈，再藉以建立劈裂試驗破壞機制之模式。
另一層樓兩跨度結構物上藉由感測器上量得之位移、速度、加速度等歷時資料，可分為振動台試驗Seismic Table Test(STT)、振動台試驗前、後之White Noise(WN1、WN2)、反力牆施加循環載重前後之微振試驗Ambient Test1(AT1、AT2)等不同環境影響下，運用希爾伯特(Hilbert-Huang Transform,HHT)等方法將時間域轉移至頻率域之影響，以評估比較不同環境影響階段下，結構物頻率、相位角、勁度、阻尼改變情形，作為建立評估結構物安全評估之方法。
經由混凝土元素網狀切割，製作等應力線、等能量線梯度方向分佈，分析得最大主應力梯度方向先產生拉力裂縫、延伸及裂縫核心擴大外，再加上最小主應力梯度方向之較高壓應力形成壓拱破壞機制。等單位應變能梯度方向亦分為較小之最大主應力形成等單位應變能及較大之最小主應力形成等單位應變能，其分析結果與壓拱破壞機制亦具同樣原理及效果。
藉由HHT分析法，可將傳統僅應用於穩定且線性之頻率域分析亦可適用於非穩定及非線性頻率域分析，並利用存在於自然界之雜訊濾除，配合正交化及平坦化處理能量譜，可獲得結構物破懷前、後之主頻衰減，另分析反力牆各遲滯迴圈之加載線性勁度、缷載線性勁度、單位應變能、阻尼比可評估結構物之耐震效能，並提供於安全評估、減振設施所需提供之功效。
混凝土結構物之破壞預測於現今地震頻繁及較為大眾重視之情形，欲經由本結構物破壞機制之研究，建立可行之破壞機制之預測、模式，以作為結構物安全評估之判斷準則。

關鍵字

等應力線 ； 等能量線 ； 壓拱 ； 希爾伯特

並列摘要

This thesis studies were produced by the department for the failure pattern of concrete structures, analysis and discussion, except by laboratory tests, but still based on the concept of material mechanics and plastic mechanics. The structure for the generation of cracks, stretch and the final failure pattern are derived, analyzed and proven. The finite element analysis program, SAP, is adopted by cylindrical concrete splitting test to attain stress, principal stress and strain energy that can be analyzed to obtain cracks stretch and mathematical proof of failure pattern. The HHT method is also adopted by analysis the change situation of the structure characteristic value before and after the failure pattern of the structure for structural safety was assessed. In this paper, the research work in addition to splitting failure pattern of the cylindrical concrete splitting test specimen for discussion, the one floor, two-span structures for real-scale tests to investigate the failure pattern of concrete structures.
When the cylindrical concrete splitting test was be done, the crack distribution of the failure pattern along the parallel loading diameter of the cylindrical concrete specimen according to ASTM C496 was recognized. Because the cylindrical concrete element is compression parallel to the diameter of the cylindrical concrete and tension perpendicular to the diameter of the cylindrical concrete, the combination of the mechanics behavior lead to the failure pattern of compression and tension. In this study, in addition to the cylindrical concrete splitting test was be done to investigate the development situation of fracture pattern, the analysis of the elastic analysis by the stress distribution parallel and perpendicular to the direction of the diameter, and the finite element method analyzed energy distribution, stress, etc of the test specimen cross-section are also finished. The failure pattern of cylindrical concrete splitting test is gained with the gradient direction of equal principal stress and equal energy distribution line.
The historic data of displacement, velocity and acceleration is attained by setting sensors on the one floor and two bays concrete structure. The analysis data is gained from before and after seismic table test, white noise(WN1、WN2), seismic table test, and before and after reaction wall test, ambient test1(AT1、AT2). The structure principal frequent, phase angle, stiffness, and damping ratio changes in different stages of environmental influence can be searched by the HHT method is adopted to transform the time domain to the frequent domain. As described above, the safety estimation of the structure can be done.
The gradient direction of the equal maximum principal stress, the equal minimum principal stress and equal unit strain energy that analyzed by cutting the concrete network elements, the cracks happen, stretch, and form the tension crack core from the gradient of the maximum principal stress on which the higher tension stress is distributed, then finally the compression arch is formed along the gradient of the minimum principal stress on which the higher compression stress is distributed. The gradient directions of equal unit strain energy stored in the concrete structure include two parts of unit stain energy formed according to the maximum principal stress and the minimum principal stress. The analysis results from the gradients of equal strain energy are the same as the theorem and effect of the compression arch.
In addition to the traditional stead and linear analysis, and the promotion non-stead and nonlinear analysis in the frequent domain are adapted according to the HHT method, and the white noise existed in the natural environment is filtered by dealing with the energy spectrum with concepts of orthogonal and flattening, the promotion non-stead and nonlinear analysis in the frequent domain is finished. According to the results of the HHT method, the principal stress of concrete structure attenuate between before and after of the concrete structure failure pattern happen. The effects of seismic resistance to the concrete structure are gained and estimated from the analysis of Hysteresis loop of reaction wall about the loading linear stiffness, unloading linear stiffness, the unit strain energy and damping ratio, and the safety estimate of the concrete structure and functions of the concrete structure arranged with damper can be reached.
The prediction about the failure pattern of the concrete structure is already important state to the much more earthquakes existed in our environment. According to the failure pattern research of the concrete structure by establishing the feasible prediction and model of the failure pattern, the safety estimate of the concrete structure can be used.

並列關鍵字

equal stress line ； equal energy line ； compression arch ； Hubert-Huang Transform

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