【摘要】：混凝土作為一種建筑材料,已被廣泛應(yīng)用了一百多年。關(guān)于其斷裂與破壞的研究一直是熱點(diǎn)�；炷淋浕緲�(gòu)曲線描述了斷裂過(guò)程區(qū)的特性,是很多混凝土斷裂模型的基礎(chǔ),尤其是在有限元程序模擬混凝土非線性性能的時(shí)候,軟化曲線與混凝土抗拉強(qiáng)度以及斷裂能是必要的輸入?yún)?shù),因此準(zhǔn)確且方便的得出軟化曲線,對(duì)混凝土斷裂的研究是十分重要的。本文根據(jù)某混凝土試件基本力學(xué)試驗(yàn)及斷裂能試驗(yàn)的相關(guān)資料,即混凝土三點(diǎn)彎曲梁試驗(yàn)所測(cè)得的荷載一裂縫口張開(kāi)位移(P-CMOD)曲線,建立一種全自動(dòng)化的確定混凝土軟化曲線的反演求解過(guò)程。該方法的主要流程如下:首先假定混凝土軟化曲線是雙線性,創(chuàng)新性的將建模、擬合以及優(yōu)化結(jié)合,使模擬的P-CMOP曲線與三點(diǎn)彎曲梁斷裂試驗(yàn)測(cè)得的P-CMOD試驗(yàn)曲線高度擬合來(lái)確定相應(yīng)的斷裂參數(shù)。其優(yōu)勢(shì)在于方便、精確的對(duì)軟化曲線進(jìn)行求解。通過(guò)分析用反演法求解得出的混凝土雙線型軟化曲線得出以下結(jié)論:(1)用反演法得到的不同尺寸的混凝土三點(diǎn)彎曲梁試件的斷裂能各不相同。說(shuō)明即使同級(jí)配、同批次澆筑的混凝土試件,由于混凝土骨料分布的隨機(jī)性,以及混凝土材料本身的非均質(zhì)性,都會(huì)使得反演得出的不同尺寸混凝土試件的斷裂能完全不同,且在一定的范圍內(nèi)波動(dòng)。(2)雙線性軟化曲線的形狀與試件尺寸有關(guān),其中轉(zhuǎn)折點(diǎn)處的縱坐標(biāo)隨試件尺寸的增大而增大,而轉(zhuǎn)折點(diǎn)處的橫坐標(biāo)隨試件尺寸的增大而減小。(3)數(shù)值模擬時(shí),網(wǎng)格劃分的疏密程度影響著反演計(jì)算過(guò)程的快慢;罰剛度Knn的取值影響著P-CMOD曲線荷載峰值及曲線的光滑程度。(4)w_1值影響P-CMOD曲線峰值的大小,σ1/f1與wc值共同影響P-CMOD曲線后半段的高低。本文采用在昆明理工大學(xué)水工樓現(xiàn)場(chǎng)完成的一組三點(diǎn)彎曲梁試驗(yàn)測(cè)得的P-CMOD曲線,根據(jù)文中提出的反演分析法求得該混凝土試件的雙線性軟化曲線,從而證明該方法具有通用性。本文將理論知識(shí)用于分析解決工程中的實(shí)際問(wèn)題,對(duì)工程建設(shè)具有重要的指導(dǎo)意義。
[Abstract]:As a kind of building material, concrete has been widely used for more than 100 years. The research on fracture and failure has always been a hot topic. The softening constitutive curve of concrete describes the characteristics of fracture process zone, which is the basis of many concrete fracture models, especially when the finite element program is used to simulate the nonlinear behavior of concrete. Softening curve, tensile strength and fracture energy of concrete are necessary input parameters, so it is very important to get the softening curve accurately and conveniently, and it is very important to study the fracture of concrete. Based on the basic mechanical test and fracture energy test of a concrete specimen, the load-crack opening displacement (P-CMOD) curve obtained from the three-point bending beam test of concrete is described in this paper. A fully automatic inversion process for determining the softening curve of concrete is established. The main flow of this method is as follows: firstly, assuming that the softening curve of concrete is bilinear, the innovative combination of modeling, fitting and optimization, The height of the simulated P-CMOP curve and the P-CMOD test curve obtained by the three-point bending beam fracture test were fitted to determine the corresponding fracture parameters. Its advantage is that it is convenient and accurate to solve the softening curve. By analyzing the double line softening curves of concrete obtained by inverse method, the following conclusions are drawn: (1) the fracture energy of concrete specimens with different sizes obtained by inversion method for three-point bending beams is different. It shows that even with the same gradation, the same batch of concrete specimens, because of the randomness of concrete aggregate distribution and the heterogeneity of concrete material itself, the fracture energy of concrete specimens of different sizes obtained by inversion will be completely different. (2) the shape of bilinear softening curve is related to the size of the specimen, in which the vertical coordinate at the turning point increases with the increase of the specimen size. The horizontal coordinates at the turning point decrease with the increase of specimen size. (3) in numerical simulation, the density of mesh division affects the speed of inversion calculation. The value of penalty stiffness Knn affects the peak load of P-CMOD curve and the smoothness of P-CMOD curve. (4) the value of W / S affects the magnitude of peak value of P-CMOD curve, 蟽 1/f1 and wc value affect the level of the latter half of P-CMOD curve. In this paper, the bilinear softening curve of the concrete specimen is obtained by using the P-CMOD curve measured by a set of three-point bending beam tests completed in the hydraulic building of Kunming University of Technology, and the inversion analysis method proposed in this paper is used to obtain the bilinear softening curve of the concrete specimen. It is proved that the method is universal. In this paper, theoretical knowledge is used to analyze and solve practical problems in engineering, which is of great significance to engineering construction.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TV431

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