静载下花岗岩破坏的声发射特性研究

在声发射试验系统上,进行了花岗岩声发射实验,获得了静载下花岗岩破坏的声发射规律。结果表明,在加载初期,出现了一定量的声发射信号,声发射计数最大达到2 000,这对应着岩石初始裂纹的闭合段;随着应力继续增大,声发射能量增大量较小,声发射计数逐步增大至峰值,这对应着岩石弹性段;岩石进入损伤阶段后,声发射能量迅速增大,在应力最高点附近,声发射能量达到峰值,而声发射计数却下降至较低值,这种低频大试件往往意味着结构的破坏。     

Numerical simulation on dynamic bending strength of three-graded concrete beam based on meso-mechanics

To study the bending strength of mass concrete under dynamic loading, the pure bending zone of three-graded concrete beam is considered as a three-phase composite composed of matrix, aggregate and interface between them on meso-level. Dynamic constitutive model considering strain-rate strengthening effect and damage softening effect is adopted to describe the cocrete and meso-element's damage. The failure mechanisms of beam under impact loading, triagle wave load, dynamic load coupling with initial static loading were simulated by using displacement-controlled FEM. Furthermore, stress-strain curve of the specimens and their dynamic bending strength were obtained. The results obtained from numerical simulation agreed well with experimental data.     

Acoustic Emission Monitoring of Fatigue Crack Growth in a Slender Web of Bridge Girder

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持续荷载下混凝土的硫酸盐腐蚀研究

研究了普通混凝土和高强混凝土在2．5％,5．0％和10％Na2SO4溶液（质量分数）,以及承受不同应力比（0.25％和50％）弯曲荷载作用下的损伤失效规律、特点．结果表明：混凝土在硫酸盐溶液中腐蚀,其损伤劣化包括初始劣化段、性能改善段和性能劣化段．腐蚀溶液中Na2SO4浓度从2．5％增加到5．0％,混凝土失效时间缩短了25％左右;Na2SO4浓度增加到10％,失效时间缩短了40％．弯曲荷载在腐蚀后期加速混凝土的损伤劣化速度,应力比由0增加到25％,混凝土破坏时间降低15％;应力比增加到50％,其破坏时间降低25％～35％．此外,用SEM、能谱和XRD分析了混凝土在硫酸盐腐蚀作用下的腐蚀产物．     

Damage assessment for buried structures against internal blast load

The soil-structure interaction (SSI) decoupling is applied to simplify buried structure against internal blast load as spring effect. Shear failure, bending failure and combined failure modes are considered based on five transverse velocity profiles for the rigid-plastic structural element. The critical equations for shear and bending failure are derived respectively. Pressureimpulse diagrams are accordingly developed to assess damage of the buried structures against internal blast load. Comparison is done to show influences of soil-structure interaction and shear-to-bending strength ratio of a structural element. A case study is conducted to show the application of damage assessment to a reinforced concrete beam element of buried structure.     

Testing Studies on Rock Failure Modes of Statically Loads Under Dynamic Loading

By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure,two series of experiments on sandstone are earned out to research the failure mode of rock during the course of exploitation of resources in deep.One is under the conditions that the confining pressure is fixed and the axial pressure is changeable.The other is under the conditions that the confining pressure becomes and the axial pressure is fixed.It is found that samples break up evenly after impacting when axial static pressures are low,there is great disparity in size of fragments when axial static pressures are high,and the main bodies of samples after the tests under the combination of dynamic and static loads frequently show the type of V or X.The samples are more close-grained at the elastic stage and impacts make many cracks be generated and developed,as makes samples more crackable.At the initial phase of damage stage,the static pressures make some cracks in the samples which are undeveloped and the impacts' role is similar to that at the elastic stage.At the metaphase or anaphase of damage stage,these cracks in the samples develop adequately and the impacts mainly accelerate samples' failure.The main bodies of samples show the type of V or X after impacting due to the confining pressures' restraining samples' lateral formation at the elastic stage or the initial phase of damage stage,the main bodies of samples have almost formed at the stage loading static pressures and the results after impacting usually are similar to those under the axial pressures tests.     

Numerical Calculation of Concrete Slab Response to Blast Loading

In the present paper, a dynamic plastic damage model for concrete has been employed to estimate responses of a reinforced concrete slab subjected to blast loading. The interaction between the blast wave and the concrete slab is considered in 3D simulation. In the first stage, the initial detonation and blast wave propagation is modelled in 2D simulation before the blast wave reaches the concrete slab, then the results obtained from 2D calculation are remapped to a 3D model. The calculated blast load is compared with that obtained from TM5-1300. Numerical results of the concrete slab response are compared with the explosive test carried out-in the Weapons System Division, Defence Science and Technology Organisation, Department of Defence, Australia.     

Numerical Calculation of Concrete Slab Response to Blast Loading

In the present paper, a dynamic plastic damage model for concrete has been employed to estimate responses of a reinforced concrete slab subjected to blast loading. The interaction between the blast wave and the concrete slab is considered in 3D simulation. In the first stage, the initial detonation and blast wave propagation is modelled in 2D simulation before the blast wave reaches the concrete slab, then the results obtained from 2D calculation are remapped to a 3D model. The calculated blast load is compared with that obtained from TM5-1300. Numerical results of the concrete slab response are compared with the explosive test carried out- in the Weapons System Division, Defence Science and Technology Organisation, Department of Defence, Australia.     

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.     

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA.The multi-material Eulerian and Lagrangian coupling algorithm was adopted.A fluid-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground,multiple ALE element for simulating air and TNT explosive material.Numerical simulations of the blast pressure wave propagation,structural dynamic responses and deformation,and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed.The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure.The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation.The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic deformation subjected to intensive blast waves,and columns lost carrying capacity,subsequently leading to the collapse of the whole structure.The approach coupling influence between structural deformation and fluid load well simulated the progressive collapse process of structures,and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.     

钛合金板裂纹损伤声发射源的信号特征分析

针对钛合金损伤在役监测需要,提出了采用声发射实时动态监测技术.利用有限元分析方法,通过建立钛合金板结构模型,并对其中不同类型、不同上升时间与不同传导距离的裂纹源开展研究,利用小波方法和频散曲线分析声发射源的特征频率与模态.仿真实验结果表明,在设定适当的上升时间与传导距离时,不同类型的声发射源有着不同的特征频率与模态,根...     

高应力比下路用水泥混凝土疲劳可靠度量化分析(英文)

为获得路用水泥混凝土在高应力比作用下其疲劳可靠度的变化规律,首先推导了包括混凝土疲劳寿命在内的单调随机变量的概率密度,然后推导了 Miner 与 Chaboche-Zhao 疲劳损伤模型的概率密度. 借助室内疲劳试验结果,获得这 2 种模型的疲劳损伤概率密度函数. 最后,将荷载作用次数代入上述函数,从而获得水泥混凝土疲劳可靠度随荷载作用次数的变化规律. 结果表明: 随着荷载作用次数的增加,相同应力比下,疲劳可靠度从 100%逐渐衰减为 0%; 无论何种应力比,在荷载作用初期,疲劳可靠度均有一个较为稳定的阶段; 随着应力比的增加,该稳定阶段逐渐缩短,且可靠度为 0%时对应的荷载作用次数也减小; 在可靠度衰减阶段,对于相同荷载作用次数,应力比越高,则混凝土可靠度越低; 此外,Miner 疲劳损伤模型比Chaboche-Zhao 疲劳损伤模型偏安全.     

Statistical algorithm for damage detection of concrete beams based on piezoelectric smart aggregate

The functional piezoelectric ceramic smart aggregate(SA) sensors and actuators,based on piezoelectric ceramic materials such as lead zirconium titanate(PZT),were embedded into the reinforced concrete beams with three-point bending under static loading for purposes of damage detection.The SA actuators generated the desired sine sweep excitation signals online and the SA sensors received and detected real-time signals before and after damage.The wavelet analysis and statistical characteristics about damage signals were used as a signal processing and analysis tool to extract the optimal damage information and establish a statistical damage detection algorithm.The damage index-based wavelet analysis and damage probability-based probability and statistics were proposed by PZT wavebased theory and active health monitoring technology.The results showed that the existence of cracks inside largely attenuated the amplitude of active monitoring signal after the damage of beam and the attenuation was related to the severity degree of damage.The innovative statistical algorithm of damage pattern detection based PZT-SA can effectively determine damage probability and damage degree,and provide a prediction for the critical damage location of reinforced concrete structures.The developed method can be utilized for the structural health comprehensive monitoring and damage detection on line of various large-scale concrete structures.     

Flexural Behaviour of High－Strength Steel Fiber－Reinforced Concrete Beams

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预应力混凝土连续箱梁有限元损伤分析(英文)

为了确定预应力混凝土箱粱的极限承载能力,进行了预应力混凝土连续箱梁的破坏性试验,提出一种有限元损伤分析方法模拟箱梁结构行为.基于实体退化壳单元对箱梁进行模拟,并考虑了结构材料的非线性效应.由于预应力混凝土箱梁中通常存在大量曲线预应力钢筋,提出一种组合单元,并用该单元模拟箱梁中的预应力钢筋,该方法可使结构分析时单元数量大大降低.试验结果和理论分析对比表明:提出的方法能够有效地用于预应力混凝土连续箱梁的破坏性试验计算分析中;研究的旧桥依然存在较大的极限承载能力.     

一种新的可用于混凝土疲劳研究的非线性累积损伤模型

研究混凝土疲劳问题的主要困难之一，就是混凝土疲劳损伤的累积速度与不同强度循环荷载的作用次序有关，且是非线性的。但通常 的一些非线性损伤模型却不能反映荷载作用次序的影响，为了解决此问题和混凝土结构在长期不稳定循环荷载作用下的疲劳问题，我们在Miner线性累积损伤模型的基础上提出了一个新的非线性累积损伤模型，通过两个 疲劳损伤实例的计算证明了该模型不仅能够反映出不同强度应力水平先后作用次序对疲劳损伤演变情况的影响，而且保留了Miner模型概念明确，使用方便的优点，当通过试验得到一组有关曲线之后，不稳定循环荷载作用的混凝土疲劳累积损伤计算将变得异常简单，极便于在工程设计中采用。     

钢筋增强ECC梁受弯性能的试验及数值研究(英文)

为了研究钢筋增强ECC梁受弯性能,进行了钢筋增强ECC梁和普通钢筋混凝土梁受弯的对比研究.结果表明,相比普通钢筋混凝土梁,钢筋增强ECC梁的受弯承载力和延性分别提高了24.8%和187.76%,并且在梁中用ECC代替混凝土可有效延缓裂缝的发展.此外,采用简化的ECC本构模型对钢筋增强ECC及混凝土梁的受弯性能进行了非线性有限元分析,模拟结果与试验结果吻合较好,在服役期间钢筋增强ECC梁的裂缝可以控制在0.4 mm以下.ECC材料的使用可明显提高梁的抗弯承载力、变形能力、延性等受弯性能.     

剪跨比对BFRP筋混凝土梁抗剪性能影响的研究

玄武岩纤维具有优异的耐腐蚀性能,采用玄武岩纤维材料（BFRP）筋代替钢筋是一种解决钢筋锈蚀问题的潜在方法。通过6根试验梁,研究不同剪跨比下BFRP筋混凝土粱的抗剪性能。试验表明,BFRP筋混凝土梁呈脆性破坏,破坏位置集中在分配梁加载点附近;随着剪跨比的减小,斜截面初裂荷载逐渐提高,且逐渐接近于极限荷载;混凝土梁开裂前,挠度增长缓慢,开裂后增长较快,表现为荷载-挠度曲线呈折现变化。     

Cyclic behavior test of a new double-arch steel gate

A new double-arch structure for the gate used as tidal barrage and sluice was adopted in Caoe River Dam in China. It was a spatial structure made up of the right arch, the invert arch, the chord, etc., and was designed to bear bilateral loads. To research the cyclic behavior of the new double-arch structure, a scale-model cyclic test was conducted. First, the test setup and test method were presented in detail, and according to the test results, the cyclic behavior and failure characteristics of this structure were discussed. Then by analyzing the test cyclic envelope curve, it was found the curve was divided into three stages: the elastic stage, the local plastic stage and the failure stage at the local yield point and structural yield point. The gate model has local yield strength and structural yield strength, with both their values being bigger than that of the designing load. Therefore, the gate is safe enough for the projects. At last, dynamic property of the gate was analyzed considering additional mass of the water. It was found that the tidal bore shock would not cause resonance vibration of the gate.     

Numerical Simulation of Response of SRC Columns Subjected to Blast Loading

The dynamic characteristics and failure modes of steel reinforced concrete (SRC) columns subjected to blast loading are complicated because of the transient stress wave in the SRC columns and the interaction between steel and concrete. This paper presents a numerical simulation of the response of SRC columns subjected to blast loading using hydrocode LS-DYNA. In the numerical model, a sophisticate concrete material model (the Concrete Damage Model) is employed with consideration of the strain rate effect and the damage accumulation. An erosion technique is adopted to model the spalling process of concrete. The possible failure modes of SRC columns are evaluated. It is observed that the failure of SRC columns subjected to blast load can generally be classified into three modes, namely, a direct failure in concrete body due to the stress wave, a transverse shear failure near the support sections due to the high shear force, and a flexural failure pertaining to large local and global deformation of the reinforcing steel.