【摘要】：寒區(qū)的隧道、大壩及橋梁等混凝土結(jié)構(gòu)會(huì)經(jīng)歷荷載歷史與凍融循環(huán)作用,同時(shí)動(dòng)力荷載作用對(duì)這些結(jié)構(gòu)的安全性和穩(wěn)定性有著重要的影響。本文開(kāi)展了180個(gè)混凝土棱柱體試件分別經(jīng)歷疲勞荷載、凍融循環(huán)、先疲勞后凍融以及先凍融后疲勞等四種模式作用后的單軸動(dòng)態(tài)抗壓試驗(yàn),系統(tǒng)研究了疲勞荷載和凍融循環(huán)單一因素作用、疲勞與凍融雙重因素作用對(duì)混凝土動(dòng)態(tài)力學(xué)性能的影響,同時(shí)分析了疲勞與凍融不同作用次序下混凝土的微觀形貌和損傷演化機(jī)理。主要成果如下:(1)研究了單因素作用后混凝土動(dòng)態(tài)特性,包括疲勞荷載、凍融循環(huán)作用后混凝土動(dòng)態(tài)特性。首先,開(kāi)展了受疲勞混凝土單軸動(dòng)態(tài)抗壓試驗(yàn),研究了疲勞次數(shù)和應(yīng)變率對(duì)混凝土強(qiáng)度和變形性能的影響。結(jié)果表明抗壓強(qiáng)度和峰值應(yīng)變均隨疲勞次數(shù)增加呈先增后減的趨勢(shì);隨著應(yīng)變率的增加,抗壓強(qiáng)度增大,而峰值應(yīng)變減小。其次,開(kāi)展了受凍融混凝土單軸動(dòng)態(tài)抗壓試驗(yàn),分析了混凝土抗壓強(qiáng)度、峰值應(yīng)變與凍融次數(shù)、應(yīng)變率的關(guān)系,提出考慮應(yīng)變率和凍融次數(shù)影響的混凝土應(yīng)力-應(yīng)變曲線(xiàn)模型,結(jié)果表明抗壓強(qiáng)度隨應(yīng)變率的增大均明顯增加,而峰值應(yīng)變呈減小的趨勢(shì);隨著凍融次數(shù)的增加,抗壓強(qiáng)度均有所降低,降低幅度最大達(dá)7.46%,而峰值應(yīng)變逐漸增大。(2)研究了疲勞與凍融雙重因素作用后混凝土動(dòng)態(tài)特性,包括先疲勞后凍融以及先凍融后疲勞作用下混凝土動(dòng)態(tài)特性。首先,開(kāi)展了先疲勞后凍融作用模式下混凝土動(dòng)態(tài)抗壓特性試驗(yàn),探討了疲勞次數(shù)以及凍融次數(shù)對(duì)混凝土動(dòng)態(tài)力學(xué)性能的影響規(guī)律。結(jié)果表明先疲勞后凍融作用下混凝土的強(qiáng)度損失大于在疲勞單一作用下的損失,強(qiáng)度隨疲勞次數(shù)、凍融次數(shù)的增加均呈減小的趨勢(shì),隨應(yīng)變率的增大均明顯增大,相比未經(jīng)損傷的混凝土靜態(tài)強(qiáng)度,強(qiáng)度降低最大可達(dá)10MPa。其次,開(kāi)展了先凍融后疲勞作用模式下混凝土動(dòng)態(tài)抗壓特性試驗(yàn)研究,基于試驗(yàn)結(jié)果,分析了凍融次數(shù)、疲勞次數(shù)和應(yīng)變率對(duì)混凝土抗壓強(qiáng)度、峰值應(yīng)變和應(yīng)力-應(yīng)變曲線(xiàn)的影響,結(jié)果表明先凍融后疲勞作用下的混凝土具有明顯率效應(yīng),較少的疲勞荷載次數(shù)對(duì)混凝土的凍融損傷具有緩解作用。(3)探討了疲勞與凍融作用的先后次序?qū)炷羷?dòng)態(tài)特性的影響,引入疊加效應(yīng)變量Kc對(duì)疲勞與凍融損傷疊加效應(yīng)進(jìn)行表征,結(jié)果表明先疲勞后凍融作用模式下,疲勞荷載與凍融循環(huán)聯(lián)合作用均為正效應(yīng),先疲勞后凍融作用模式導(dǎo)致強(qiáng)度的損失大于同一應(yīng)變率下先凍融后疲勞作用模式。采用掃描電子顯微鏡對(duì)混凝土損傷后的微觀形貌進(jìn)行觀察分析,從微觀角度揭示了疲勞與凍融不同次序作用下混凝土損傷劣化的機(jī)理。
[Abstract]:Concrete structures such as tunnels, dams and bridges in cold regions will undergo load history and freeze-thaw cycles, and dynamic loads will have an important impact on the safety and stability of these structures. In this paper, the uniaxial dynamic compression tests of 180 concrete prisms subjected to fatigue loading, freeze-thaw cycle, first fatigue, freeze-thaw and first freeze-thaw after fatigue were carried out respectively. The effects of fatigue load and freeze-thaw cycle on the dynamic mechanical properties of concrete are systematically studied. At the same time, the microstructure and damage evolution mechanism of concrete under different action order of fatigue and freeze-thaw are analyzed. The main results are as follows: (1) the dynamic characteristics of concrete after single factor action, including fatigue load and freeze-thaw cycle, are studied. First, the uniaxial dynamic compressive tests of fatigue concrete are carried out, and the effects of fatigue times and strain rates on the strength and deformation properties of concrete are studied. The results show that the compressive strength and peak strain increase first and then decrease with the increase of fatigue times, and increase with the increase of strain rate, while the peak strain decreases with the increase of strain rate. Secondly, the uniaxial dynamic compression test of freeze-thawed concrete is carried out, and the relationship between compressive strength, peak strain and freeze-thaw times, strain rate is analyzed, and the stress-strain curve model of concrete considering the influence of strain rate and freeze-thaw number is put forward. The results show that the compressive strength increases obviously with the increase of strain rate, while the peak strain decreases, and the compressive strength decreases with the increase of freeze-thaw times. The maximum reduction range is 7.46, while the peak strain increases gradually. (2) the dynamic characteristics of concrete after fatigue and freeze-thaw are studied, including first fatigue and freeze-thaw after fatigue. Firstly, the dynamic compressive properties of concrete under the mode of first fatigue and freeze-thaw are tested, and the effects of fatigue times and freeze-thaw times on the dynamic mechanical properties of concrete are discussed. The results show that the strength loss of concrete under first fatigue and freeze-thaw is larger than that under single fatigue, and the strength decreases with the increase of fatigue times and freeze-thaw times, and increases obviously with the increase of strain rate. Compared with the static strength of undamaged concrete, the maximum reduction of strength can be up to 10 MPA. Secondly, the dynamic compressive behavior of concrete under the mode of freeze-thaw and fatigue is studied. Based on the test results, the influence of freeze-thaw times, fatigue times and strain rate on the compressive strength of concrete is analyzed. The effect of peak strain and stress-strain curve shows that concrete under freeze-thaw and fatigue has obvious rate effect. Less fatigue loads can alleviate the freeze-thaw damage of concrete. (3) the influence of the order of fatigue and freeze-thaw action on the dynamic characteristics of concrete is discussed. The superposition effect variable Kc is introduced to characterize the superposition effect of fatigue and freeze-thaw damage. The results show that the combined effect of fatigue load and freeze-thaw cycle is positive under the mode of first fatigue and freeze-thaw. The strength loss caused by the first fatigue and then freeze-thaw action mode is greater than that under the same strain rate. The microstructure of concrete after damage was observed and analyzed by scanning electron microscope (SEM), and the mechanism of damage deterioration of concrete under different order of fatigue and freeze-thaw was revealed from the microcosmic point of view.
【學(xué)位授予單位】：煙臺(tái)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TU528

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本文編號(hào)：2206061