本文選題：疲勞 + 殘余應(yīng)變　； 參考：《重慶交通大學(xué)》2014年博士論文

【摘要】：混凝土橋梁往往不可避免地存在某些細(xì)小結(jié)構(gòu)缺陷，這些缺陷大多以微觀裂紋形式出現(xiàn)，在長時(shí)間的結(jié)構(gòu)服役期內(nèi)，由于環(huán)境的侵蝕、材料的老化及自然災(zāi)害，加之交通荷載的反復(fù)疲勞作用，因這些細(xì)小缺陷引起的疲勞損傷不斷累積，導(dǎo)致橋梁結(jié)構(gòu)整體抵抗自然災(zāi)害，甚至正常服役荷載的能力逐漸下降。限于研究手段和測試技術(shù)，以往的橋梁結(jié)構(gòu)疲勞分析只能局限于構(gòu)件或細(xì)節(jié)表面已出現(xiàn)肉眼可見的疲勞裂紋，距離疲勞損傷早期（裂紋萌生）的發(fā)現(xiàn)和分析尚有很大差距。近年來，橋梁長期監(jiān)測技術(shù)取得了較大進(jìn)展，如何充分利用橋梁在線營運(yùn)監(jiān)測的手段和技術(shù)優(yōu)勢，盡早發(fā)現(xiàn)疲勞損傷和跟蹤其損傷累積演化過程，是橋梁界值得探索的課題。目前，在該領(lǐng)域還沒有較為系統(tǒng)的研究成果。鑒于此，本文利用斷裂與損傷力學(xué)的相關(guān)理論與知識，從研究鋼筋混凝土橋梁的疲勞裂紋擴(kuò)展規(guī)律出發(fā)，獲取能表征疲勞損傷的特征因子，同時(shí)，在大量實(shí)時(shí)監(jiān)測數(shù)據(jù)的基礎(chǔ)上，，挖掘出疲勞特征參量，從而實(shí)現(xiàn)對服役混凝土橋梁疲勞損傷的安全狀態(tài)評估。論文的主要研究內(nèi)容和結(jié)論如下： ①通過對鋼筋混凝土材料的裂紋擴(kuò)展機(jī)理分析，在恢復(fù)力模型的基礎(chǔ)上，提出了融入殘余應(yīng)力影響因子的修正Paris公式，并進(jìn)行了數(shù)值計(jì)算分析。分析結(jié)果表明：考慮殘余應(yīng)力影響之后的作用效果明顯不同于未考慮的情況，其對裂紋擴(kuò)展影響較大，更符合實(shí)際。 ②根據(jù)混凝土疲勞損傷微觀機(jī)理分析，結(jié)合疲勞裂紋穩(wěn)定擴(kuò)展與不穩(wěn)定擴(kuò)展這兩個(gè)斷裂判據(jù)，在相應(yīng)假設(shè)的基礎(chǔ)上，獲取了殘余應(yīng)變的計(jì)算模型；同時(shí)，為了使該模型的適用范圍更廣，尤其是對服役的鋼筋混凝土橋梁，對其進(jìn)行了實(shí)時(shí)殘余應(yīng)變計(jì)算模型的研究。經(jīng)驗(yàn)證，該模型能滿足實(shí)際情況需求，且不受加載歷程的影響；此外，通過累積殘余應(yīng)變的多少來劃分疲勞損傷狀況等級，實(shí)現(xiàn)了混凝土橋梁的實(shí)時(shí)疲勞安全狀況評估。 ③通過對鋼筋混凝土梁的非線性數(shù)值模擬分析，獲取了循環(huán)荷載作用下梁在不同階段的發(fā)展變化狀況，特別是塑性變形情況。同時(shí)，根據(jù)鋼筋混凝土梁在單級和多級荷載作用下的疲勞試驗(yàn)，發(fā)現(xiàn)融入殘余應(yīng)力影響的應(yīng)力強(qiáng)度因子較常規(guī)的應(yīng)力強(qiáng)度因子能更好的表達(dá)出裂紋的擴(kuò)展速率；此外，利用已提出的殘余應(yīng)變計(jì)算模型，計(jì)算出的殘余應(yīng)變與實(shí)測的殘余應(yīng)變初期吻合良好，后期略高于實(shí)測值，可見，利用殘余應(yīng)變評估循環(huán)荷載作用下服役橋梁結(jié)構(gòu)的疲勞安全狀況可行，且偏于安全。 ④為了有效剔除監(jiān)測數(shù)據(jù)中的異常信息，壓縮減小數(shù)據(jù)量，以小波分析為手段，根據(jù)監(jiān)測數(shù)據(jù)呈周期性變化的特點(diǎn)，提供了標(biāo)準(zhǔn)循環(huán)塊（以天為周期）的獲取方法；此外，兼顧疲勞安全狀況評估對循環(huán)特征參數(shù)（峰值imax及其對應(yīng)的循環(huán)次數(shù)ni）的需求，在遵循計(jì)數(shù)原則的基礎(chǔ)上，借鑒已有計(jì)數(shù)方法，提出了改進(jìn)的跨均值峰值計(jì)數(shù)法，并針對實(shí)際的監(jiān)測數(shù)據(jù)進(jìn)行了應(yīng)用分析。 ⑤選取已構(gòu)建健康監(jiān)測系統(tǒng)的典型混凝土連續(xù)剛構(gòu)橋—龍河大橋?yàn)橐劳�，利用其�?shí)時(shí)監(jiān)測數(shù)據(jù)，提取出當(dāng)前疲勞特征參數(shù)（峰值imax及其對應(yīng)的循環(huán)次數(shù)ni），同時(shí)，借助殘余應(yīng)變計(jì)算模型，獲取了龍河大橋典型截面相關(guān)位置目前的殘余應(yīng)變量值。該殘余應(yīng)變量值非常小，表明目前龍河大橋的疲勞安全狀況良好，這與大橋?qū)嶋H安全狀況相符�？梢姡跉堄鄳�(yīng)變的評估模式達(dá)到了進(jìn)行服役橋梁疲勞安全狀況分析的目的。
[Abstract]:Some small structural defects are unavoidable in concrete bridges. Most of these defects appear in the form of micro cracks. During the long period of structural service, the fatigue damage caused by these tiny defects accumulates continuously because of the erosion of the environment, the aging and natural disasters of the materials, and the repeated fatigue of the traffic loads. As a whole, the bridge structure resists natural disasters, and even the ability of normal service load gradually decreases. Limited to the research means and test techniques, the previous fatigue analysis of bridge structures can only be limited to the visible fatigue cracks visible on the surface of the component or the detail surface, and the discovery and analysis of the early fatigue damage (crack initiation) is still very bad. In recent years, the long-term monitoring technology of bridge has made great progress. How to make full use of the means and technical advantages of bridge on-line operation monitoring, to find the fatigue damage and track the cumulative damage process of damage as soon as possible is a subject worth exploring in the bridge circle. At present, there are no more systematic research results in this field. Based on the theory and knowledge of fracture and damage mechanics, the characteristic factors that can characterize fatigue damage are obtained from the study of fatigue crack propagation of reinforced concrete bridges. At the same time, on the basis of a large number of real-time monitoring data, the fatigue characteristic parameters are excavated, so as to realize the safety assessment of fatigue damage of service concrete bridges. The main contents and conclusions of the paper are as follows:
(1) through the analysis of the crack propagation mechanism of reinforced concrete material, on the basis of the restoring force model, a modified Paris formula is put forward to integrate the influence factors of residual stress, and the numerical analysis is carried out. The results show that the effect of the residual stress is obviously different from that of the non considered. It is more effective and more practical.
Secondly, based on the analysis of the microscopic mechanism of the fatigue damage of concrete, combining the two fracture criteria of fatigue crack stability expansion and unstable expansion, the calculation model of residual strain is obtained on the basis of the corresponding hypothesis. At the same time, in order to make the application of the model more wide, especially for the reinforced concrete bridge serving in service, the model has been carried out in real time. The model of residual strain calculation is studied. It is proved that the model can meet the actual requirement and is not affected by the loading process. In addition, the fatigue damage status is divided by the amount of accumulated residual strain, and the real time fatigue safety assessment of concrete bridges is realized.
(3) through the nonlinear numerical simulation analysis of reinforced concrete beams, the development and change of the beam in different stages are obtained, especially the plastic deformation condition. At the same time, according to the fatigue test of the reinforced concrete beam under the single and multistage loads, it is found that the stress intensity factor which is integrated with the residual stress is more conventional. The stress intensity factor can better express the propagation rate of the crack. In addition, the residual strain calculated by the proposed residual strain calculation model is in good agreement with the measured residual strain at the beginning, and the later period is slightly higher than the measured value. It can be seen that the residual strain is used to evaluate the fatigue safety of the bridge structure under cyclic loading. It is feasible and partial to safety.
(4) in order to effectively eliminate the abnormal information in the monitoring data and reduce the amount of data, the method of wavelet analysis, according to the characteristics of the periodic changes of the monitoring data, provides a method for obtaining the standard circulation block (the day as a cycle). In addition, the cyclic characteristic parameters (peak IMAX and its corresponding cycle times) are evaluated by the fatigue safety assessment. On the basis of counting the counting principle and using the existing counting method, the improved cross mean peak counting method is put forward on the basis of counting the counting principle, and the application analysis of the actual monitoring data is carried out in the light of the counting principle.
5. Based on the typical concrete continuous rigid frame bridge, the long river bridge, which has been constructed, the current fatigue characteristic parameters (peak IMAX and its corresponding cycle times Ni) are extracted by using the actual monitoring data. At the same time, the residual strain is obtained by the residual strain calculation model, and the residual stress of the typical section of the typical section of the long river bridge is obtained. The value of the residual strain is very small, which indicates that the fatigue safety of the long river bridge is good, which is in line with the actual safety condition of the bridge. It is obvious that the evaluation model based on the residual strain has achieved the purpose of analyzing the fatigue safety of the bridge.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：U448.33

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本文編號：1978260