【作者】 宋敏；

【导师】 闫晓鹏； 王志勇；

【作者基本信息】 太原理工大学 ， 力学， 2018， 硕士

【摘要】 混凝土作为一种多相复合材料,其各组成部分的物理特性均不同,且骨料与砂浆之间的结合面应力分析复杂,给混凝土内部断裂机理的研究带来很大困难。混凝土材料由于其良好的保温性、抗压性等特点被广泛应用于工程领域,在建筑工程中使用已达百余年。而混凝土自身存在的缺陷、微孔洞等损伤在外界载荷作用下生成新的裂纹,导致建筑物出现裂缝和断裂面,给国防工程、工业建筑、桥梁等带来巨大隐患,造成国民经济重大财产损失和人员伤亡。在混凝土基体中引入的钢筋可以有效抑制其在受到破坏时裂纹的产生与扩展,而钢筋与混凝土接触面的受力分析依然是研究热点。钢筋和混凝土两种材料均具有不同程度的应变率效应,在不同的冲击速度下,梁的破坏模式会随着冲击速度的变化以及配筋率的不同而发生改变。钢筋混凝土结构在突发情况下受到爆炸、冲击等非设计荷载时的应力分析日益受到学者们和工程师们的广泛关注。开展钢筋混凝土结构的抗冲击性能以及动态加载下的破坏模式研究十分必要。本文通过三点弯曲动态实验和数值模拟研究了含有预制裂纹的少筋梁在不同冲击高度下的结构响应以及梁的破坏模式。主要工作如下:人工浇筑了含有预制裂纹的少筋梁试件,利用DHR-9401落锤式冲击试验机对混凝土梁试件进行冲击试验,并结合DIC进行高速摄像追踪,分析了四种不同冲击高度下梁的变形以及破坏模式。通过对比不同冲击高度下试件的承载力、混凝土预制裂纹尖端处起裂应变、钢筋应变的变化趋势来分析梁的抗承载能力以及梁的破坏模式随冲击高度的变化。实验结果表明,冲击高度大于60mm时梁的破坏模式发生改变;随着冲击高度的提高,梁表面的宏观裂纹更加清晰;对比不同冲击速度下的钢筋应变发现,钢筋应变逐渐趋于稳定,说明冲击速度增大时钢筋对于提高混凝土的抗拉性能以及阻裂作用逐渐减弱。在ABAQUS有限元分析软件中,基于混凝土的损伤断裂模型和钢筋的三折线模型进行数值模拟分析。通过与实验结果中的最大冲击力、第一峰值响应时间进行对比,验证了模型的有效性。基于本文模型对其他实验建模并与试验结果对比发现,冲击力、跨中挠度时程曲线的实验结果与模拟结果吻合较好;随着冲击速度的提高,梁的破坏模式从弯拉破坏逐渐转变为剪切破坏,表明模型具有一定的普适性。在此研究基础上,通过改变有限元模型中钢筋横截面积来改变梁配筋率,探讨了不同冲击速度下配筋率对于梁承载能力、抗变形能力、破坏模式的影响。模拟结果表明,随着混凝土梁配筋率的减小,冲击速度的提高,梁从弯曲破坏逐渐转变为剪切破坏。更多还原

【Abstract】 As a multi-phase composite,the difference of physical characteristics of each component and the complex stress analysis of the aggregate and the mortar in the concrete,making it difficult to study the fracture mechanism of the concrete.Concrete have been widely used in engineering field for over 100 years due to the good thermal insulation and compression resistance.Under the external loading,new cracks generated from the existing defects,microporous holes and other damage in concrete result in large cracks of the building,which causes huge dangers to the national defense engineering,industrial buildings and bridges,and brings property losses for the national economy.The steel bar in the concrete matrix inhibits the produce and expansion for the cracks effectively when the concrete structure is damaged.Besides,the stress analysis of the contact surface between the steel bar and concrete is still a hot issue these years.Because of the strain rate effect,the failuremode of reinforced concrete beams changes as the increase of the impact velocity and change of the ratio of reinforcement.The stress analysis of reinforced concrete structures under unexpected conditions,such as explosion,impact and other non-design loads,has been widely concerned by scholars and engineers.It is very necessary to study the impact resistance of reinforced concrete structures and the failure modes under dynamic loading.In this paper,three point bending dynamic experiment and numerical simulation for the beam with prefabricated cracks under different heights were carried out to study the structural response and the failure mode of the beam.The main works are as follows:The specimens with prefabricated cracks were artificially constructed,and the impact test of concrete beams was carried out by the DHR-9401 impact test machine,and the high-speed video tracking was carried out with DIC.The deformation and failure modes of the beams under four different impact heights were analyzed.By comparing the bearing capacity of the specimen,the change of the crack strain at the tip of the precast concrete and the strain of the steel bar,the resistance bearing capacity and the change of the failure mode of the beam were analyzed.The experimental results show that the failure mode of the beam is changed when the impact height is greater than 60 mm,and the macro crack on the surface of the beam becomes clearer.At the same time,the time curves for the impact forces show a different trend of shockdevelopment.And the strain of the steel bar gradually tends to the stable value,which shows the effect on tensile strength and crack resistance of concrete is gradually weakened.Based on the ABAQUS software,the damage and fracture model of concrete and the trilinear model of steel bar were introduced to carry out numerical simulation analysis.Compared with the maximum of impact force and the response time,the validity of the model was verified.Compared with the other experimental results,the time curves for the impact force and the mid span deflection were in good agreement with the simulation results.The failure mode of the beam gradually changes from the bending failure to the shear failure as the increase of the impact velocities,which proves that the model has a certain universality.On the basis of this model,the cross section area of the steel bar in the finite element model are changed to change the reinforcement ratio of the beam.And then the influence of the reinforcement ratio on the bearing capacity,the resistance to deformation and the failure mode of the beam under different impact speeds is discussed.The simulation results show that with the decrease of the reinforcement ratio and the increase of impact speed,the fracture mode of beam gradually changes from bending failure to shear failure.更多还原