本文選題：膠合木曲梁 + 濕度變化　； 參考：《哈爾濱工業(yè)大學(xué)》2015年博士論文

【摘要】：膠合木(Glulam)是一種最常見的工程木產(chǎn)品(Engineered Wood Product),既保留了木材的天然紋理又具有良好的力學(xué)性能,因此廣泛應(yīng)用于木結(jié)構(gòu)建筑中,且往往采用弧形受彎構(gòu)件的形式(曲梁)。由于木材的橫紋抗拉強(qiáng)度很低,膠合木曲梁在荷載作用下產(chǎn)生的橫紋拉應(yīng)力會導(dǎo)致橫紋受拉破壞。在正常使用過程中,膠合木構(gòu)件周圍環(huán)境空氣相對濕度會因氣候變化和人類活動等影響而變化,吸濕和解吸過程使膠合木構(gòu)件內(nèi)部含水率不均勻分布導(dǎo)致梁內(nèi)各點(diǎn)干縮濕脹變形不同,從而產(chǎn)生濕度應(yīng)力。當(dāng)膠合木曲梁受荷載和濕度變化的共同作用時,荷載產(chǎn)生的橫紋拉應(yīng)力與濕度橫紋拉應(yīng)力疊加,會降低膠合木曲梁的承載力。因此,開展?jié)穸茸兓秃奢d共同作用下膠合木曲梁的長期性能研究具有理論意義與實用價值。本文先對足尺東北落葉松膠合木曲梁進(jìn)行了三分點(diǎn)加載抗彎試驗,驗證了膠合木曲梁發(fā)生橫紋受拉脆性破壞的破壞模式,并獲得了由該破壞模式?jīng)Q定的膠合木曲梁短期承載力,為長期承載試驗提供了依據(jù)。然后在人工氣候?qū)嶒炇覂?nèi)開展了膠合木曲梁環(huán)境濕度變化和荷載聯(lián)合作用下的長期承載試驗Ⅰ和長期承載試驗Ⅱ,試驗結(jié)果表明環(huán)境濕度變化引起的濕度應(yīng)力與荷載應(yīng)力疊加造成曲梁長期承載力下降明顯。為獲得有限元分析所需的材料參數(shù),還開展了東北落葉松木材的Ⅰ型、Ⅱ型斷裂韌性試驗和橫紋抗拉強(qiáng)度、順紋抗壓強(qiáng)度、順紋抗剪強(qiáng)度及彈性常數(shù)試驗。建立了考慮木材熱脹冷縮、濕脹干縮、粘彈性蠕變、機(jī)械吸附蠕變、破壞模式、各向異性損傷和荷載持續(xù)時間效應(yīng)的本構(gòu)關(guān)系模型。采用簡化的Luikov傳熱模型和Fick第二定律分別建立了溫度和水分傳輸方程。采用Kelvin鏈模型描述木材的粘彈性蠕變,并采用與含水率變化率相關(guān)的機(jī)械吸附柔度矩陣來描述木材機(jī)械吸附蠕變。在木材三個材料主方向上建立了相互獨(dú)立的強(qiáng)度準(zhǔn)則,并引入9個損傷因子來描述木材的應(yīng)變軟化,從而實現(xiàn)了木材受拉或受剪發(fā)生脆性斷裂、受壓發(fā)生塑性變形的模擬。利用Fortran語言開發(fā)了用戶材料子程序UMAT,實現(xiàn)了所建立的木材本構(gòu)關(guān)系模型在有限元軟件ABAQUS中的嵌入。采用ABAQUS建立了膠合木曲梁有限元模型,計算分析了膠合木曲梁短期承載力試驗和長期承載試驗,揭示了在試驗的溫、濕度條件下,濕度應(yīng)力的幅值及分布規(guī)律,并實現(xiàn)了荷載和環(huán)境濕度變化共同作用下膠合木曲梁橫紋受拉破壞的模擬并較準(zhǔn)確地預(yù)測了破壞發(fā)生的時間。還基于線彈性斷裂力學(xué)理論,建立了木材的開裂準(zhǔn)則和裂紋擴(kuò)展準(zhǔn)則,采用擴(kuò)展有限元法(Extended Finite Element Method)模擬了膠合木曲梁在荷載作用下橫紋受拉破壞時裂紋的產(chǎn)生和擴(kuò)展過程。提出采用濕度橫紋應(yīng)力積分來綜合度量濕度橫紋應(yīng)力的大小和作用范圍。以含水率影響深度來表示環(huán)境相對濕度變化導(dǎo)致梁內(nèi)含水率劇烈變化的影響范圍和含水率波動的衰減。通過有限元參數(shù)分析研究了膠合木曲梁橫截面寬度、相對濕度變化周期、幅值和循環(huán)次數(shù)對濕度橫紋應(yīng)力的影響規(guī)律。提出了等效濕度橫紋應(yīng)力的概念,并提出了濕度橫紋應(yīng)力與荷載產(chǎn)生的橫紋應(yīng)力疊加的簡化方法判斷荷載和濕度變化共同作用下膠合木曲梁是否橫紋受拉破壞的方法。分析了中國典型氣候區(qū)代表性城市的年相對濕度變化產(chǎn)生的濕度橫紋應(yīng)力的幅值和變化規(guī)律,為在我國各典型氣候類型區(qū)內(nèi)考慮濕度應(yīng)力影響的膠合木曲梁設(shè)計提供了參考。
[Abstract]:Glulam is one of the most common engineering wood products (Engineered Wood Product), which not only preserves the natural texture of wood but also has good mechanical properties. Therefore, it is widely used in wood structure and often used in the form of curved flexural members (curved beams). The tensile strength of the wood is very low, and the laminated beam is loaded. In normal use, the relative humidity of ambient air in the surrounding environment changes due to the influence of climate change and human activity during the normal operation. The moisture absorption and desorption process the uneven distribution of water content in the glued wood components, resulting in the different dry shrinkage and swelling deformation of each point in the beam. When the curved beam of the glued wood is subjected to the joint action of load and humidity, the stress of the transverse tensile stress and the tensile stress of the humidity will be superimposed, which will reduce the bearing capacity of the curved beam of the glued wood. Therefore, it is of theoretical and practical value to study the long-term performance of the curved beam of the glued wood under the joint action of humidity and load. In this paper, a three point loading anti bending test was carried out on the full scale northeastern Larix Larix glued beam, which verified the failure mode of the tensile brittleness of the glued Liang Fasheng cross pattern, and obtained the short-term bearing capacity of the laminated wood curved beam determined by the failure mode, which provided the basis for the long-term bearing test. Then it was opened in the artificial climate laboratory. The long-term bearing test I and long-term bearing test II under the combined action of ambient humidity and load on the curved beam of the laminated wood are shown. The results show that the superposition of the humidity stress and the load stress caused by the change of the ambient humidity causes the long bearing capacity of the curved beam to decrease obviously. Ye Song wood type I, type II fracture toughness test and tensile strength, CIS compression strength, CIS shear strength and elastic constant test. The constitutive relation model, which consider wood thermal expansion and shrinkage, wet expansion shrinkage, viscoelastic creep, mechanical adsorption creep, failure mode, anisotropic damage and load duration effect, is established. The temperature and moisture transfer equations are established by the Luikov heat transfer model and the second law of Fick. The viscoelastic creep of wood is described by the Kelvin chain model, and the mechanical adsorption flexibility matrix is used to describe the mechanical adsorption creep of wood. The independent strength of the three wood materials is established in the main direction of wood material. 9 damage factors are introduced to describe the strain softening of wood, thus the simulation of brittle fracture and plastic deformation of wood subjected to tension or shear can be realized. The user material subroutine UMAT is developed by Fortran language, and the embedded wood constitutive relation model is embedded in the finite element software ABAQUS. ABAQU S established the finite element model of glued wood curved beam, calculated and analyzed the short term bearing capacity test and long-term bearing test of the glued beam, revealed the amplitude and distribution of the humidity stress under the temperature and humidity conditions of the test, and realized the simulation of the tensile failure of the cross grain of the laminated wood under the joint action of load and the change of ambient humidity. The time of failure is predicted. Based on the theory of linear elastic fracture mechanics, the Cracking Criterion and crack propagation criterion of wood are established. The crack initiation and expansion process is simulated by the extended finite element method (Extended Finite Element Method). The grain stress integral is used to measure the size of the stress of the RH and the range of action. The influence depth of water content is used to indicate the influence of the change of the relative humidity of the environment and the attenuation of the fluctuation of water content in the beam. The width of cross section of the curved beam and the period of relative humidity change are studied by the finite element parameter analysis. The influence of the amplitude and the number of cycles on the stress of the RH is proposed. The concept of the equivalent humidity transverse stress is put forward, and a simplified method of superposition of the transverse stress of the RH stress and the load is put forward to judge whether the tensile failure of the curved beams of the glued wood under the action of the load and the humidity changes. The typical gas of China is analyzed. The amplitude and change law of humidity transverse stress produced by the change of relative humidity in the representative city of the weather district provides a reference for the design of laminated beam of glued wood considering the influence of humidity stress in the typical climate types of our country.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TU366.3

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