碳纤维片材加固含裂缝砼梁的弯曲破坏分析

借鉴复合材料力学的分析方法,建立一种分层剪滞模型,并结合线弹性断裂力学的能量法,研究了碳纤维薄板加固含裂缝素砼梁和钢筋增强砼梁的四点弯曲破坏问题,求得的破坏荷载大多与试验较吻合,为此类构件的弯曲破坏分析提供了一种新的研究途径和方法.     

既有网格结构损伤检测与模拟方法研究进展

网格结构在使用过程中会产生不同程度的损伤,损伤的累积会导致结构承载性能的降低甚至倒塌.基于现有研究成果,首先阐明了结构损伤检测过程中样本选取方法的研究进展与不足,指出了概率抽样方法的合理性与局限性;在结构损伤的参数化表征方面,总结了基于损伤力学与断裂力学等研究方法的成果,指出了不同方法在应用过程中面临的问题;在结构损伤...     

Imperfections in steel girder webs with and without perforations under patch loading

In this paper, the problem of stability of web plates with imperfections, subjected to patch load, is studied. The aim is to give some insights about the best way to take into account real imperfections in non-linear stability analyses of plates with and without perforations. In this context, the study is developed on the basis of the measured imperfections or numerically deriving the deformed model (theoretical imperfections). The influence of the patch load length, out-of-plane imperfection amplitude, dimension and position of the hole on stability behaviour and buckling strength are studied comparing some theoretical deformed configurations corresponding to different modal shapes. The results obtained with a three-dimensional model of the whole real beam with stiffeners, with experimentally measured imperfections, and each corresponding single web panel are compared and discussed obtaining some insights about the accuracy of the simplified (and conservative) model of the single panel.The main insights of this work are as follows. The deformed shape, corresponding to the first buckling mode, can be assumed as the initial configuration of the panels with and without holes to study post-critical behaviour until ultimate condition. The shape of the imperfection does not severely change the critical buckling stress. A longer patch load reduces the ultimate stress in the panel. An initial imperfection amplitude of less than 1% of the height of the panel does not reduce the ultimate load by more than about 5%.     

壳体结构形态的量化重构——基于建筑参数化设计技术与结构力学的协同机制

复杂形态与结构体系之间所存在的数学逻辑与力学法则之间的偏差,构成了当今国际建筑参数化设计深化研究与面向现实实施的困境与挑战。因此,实现数字化复杂形态与结构力学逻辑的有机统一构成了该研究的初衷与最终目标。从结构工程学的角度出发,以双曲抛物面壳体为实验对象,提出了“结构原型——力学机制——力与形数字重构——验算与优化”的实验方法与创作思路,并通过圆形、三角形、菱形与编织状四种反映力学机制的肌理形式的量化试验与数据分析,论证了该技术路线的可行性与有效性,并最终形成一种从结构原型到多样性形态重塑的创新建筑设计模式。文中着力于如何利用与发掘潜在的结构力学机制,指出了复杂空间形态的创作如何结合结构力学的关键点,可为现时建筑参数化设计的现实运用与纵深研究提供实证参考与理论线索。     

Modelling and analysis of time-dependent behaviour of historical masonry under high stress levels

Masonry which is subjected to high, sustained stress levels can suffer from long-term damage accumulations. This type of stress-induced damage interacts with other long-term phenomena, such as deterioration and fatigue. In this work, the time-dependent damage which is caused by elevated stress levels is analysed and modelled. A one-dimensional rheological model, which was calibrated on the results of an extensive experimental test campaign, is extended to a three-dimensional version. The time-dependent constitutive relations are implemented in a finite element code. The issues of triaxial stresses and mesh-dependency are addressed. In a first application, the model is used to simulate the long-term behaviour of a masonry tower. Secondly, the effects of time-dependent stress redistributions on the long-term stability of three-leaf masonry are investigated.     

含不连续面巷道的动力破坏过程数值分析

利用新近开发的动态版岩石破裂过程分析系统RFPA2D模拟了动力扰动下含不连续面巷道的破坏过程,从细观角度分析了不同宽度不连续面的岩石巷道在动力扰动下破坏的规律,并和未含不连续面巷道结构的相应情况进行比较,探讨了含不连续面巷道结构在动载荷作用下的力学特性,结果表明不连续面对应力波衰减作用明显,对巷道的稳定与破坏影响较大.     

Rock brittleness indices and their applications to different fields of rock engineering:A review

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst proneness.As such,it is of high practical value to correctly evaluate rock brittleness.However,the definition and measurement method of rock brittleness have been very diverse and not yet been standardized.In this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly discussed.The development and role of rock brittleness in different fields of rock engineering are also studied.Eighty brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are discussed.The results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock brittleness.On the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness.It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness.This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.     

硬石膏岩膨胀特性试验及隧道抗膨胀衬砌设计

石膏质岩的膨胀机理复杂,膨胀时间漫长,其膨胀力对隧道支护结构破坏性极强。本文采用室内试验方法研究了硬石膏岩的膨胀力学特性,得出膨胀应力-应变曲线为凹形函数,膨胀应变-时间曲线为“S”型函数, 膨胀应力-时间曲线为指数型函数等规律。基于试验结果提出了可考虑时间效应的硬石膏岩膨胀变形计算公式,进而建立硬石膏岩隧道围岩膨胀变形、膨胀应力及时间的关系,用以描述隧道修建过程中膨胀应力应变的动态变化。并提出一种新型石膏质岩隧道抗膨胀衬砌设计,从主动和被动两个方面减缓石膏岩遇水致膨胀对衬砌结构的影响,为类似工程提供借鉴与思考。     

Geosynthetic-reinforced soils above voids: Observation and prediction of soil arching

The assumption with the biggest impact on the design of geosynthetic-reinforced soils above voids is the presence and degree of soil arching, which affects the predicted applied stress on the geosynthetic. A series of centrifuge tests were conducted to investigate the soil arching in geosynthetic-reinforced soils with measurements of the soil stresses and observation of soil and geosynthetic deformation used to infer the arching behaviour. Detailed analysis of the results showed that arching significantly reduces the stress at the base of the soil when a void forms; this mechanism is due to stress redistributions and not the formation of a physical arch as suggested in some models. A new method to reliably predict this reduction is proposed by calculating the coefficient of lateral stress on vertical failure planes based on the observations of a continuous convex arc of major principal strains above the void, and the assumption that this is indicative of the stress behaviour.     

基于损伤理论的预应力混凝土冻融破坏研究

损伤力学提供了一种分析疲劳演化、估算疲劳寿命的有效方法.混凝土冻融破坏是一种低周疲劳损伤,可以利用损伤力学理论进行分析.试验利用损伤力学中疲劳损伤的基本原理对预应力混凝土在冻融循环作用下的损伤与失效过程进行了分析,在比较几种低周疲劳损伤理论的基础上,利用混凝土冻融前后动弹性模量变化的规律建立了预应力混凝土冻融破坏模型.并根据试验结果对模型进行了评价.结果表明在相同冻融循环次数下,随着应力水平的提高,混凝土抗冻能力是提高的;随着冻融的继续进行,应变趋向于定值,此时混凝土不再能承受应力作用而失效破坏.     

Experimental and Numerical Study on Buckling Behavior of a Rigidly Stiffened Plate with Tee Ribs

In the bridge structures, stiffened plates are usually designed as rigidly stiffened when the orthotropic steel box girder is used as the main load-bearing structure. Therefore, the buckling mode of stiffened plates is plate buckling which occurs in subpanel supported by stiffeners. The orthotropic steel box girder is used as the main girder for Egongyan Rail Special Bridge, which is a self-anchored suspension bridge. Plates of the steel girder are rigidly stiffened with unequal spacing open ribs, and the most slender stiffened plate is the mid web stiffened with Tee ribs. In order to ensure the safety of the bridge, the buckling behavior of the web and orthotropic steel box girder under axial compression, including ultimate strength, post-buckling behavior and failure modes, should be clearly investigated by experimental and numerical methods. The design, loading and testing methods of the 1:4 scale model of the orthotropic steel box girder are introduced in detail firstly. The orthotropic steel box girder and the stiffened web finite element (FE) models are validated by the test results, and the effects of residual stress and the magnitude of geometric imperfections are discussed roughly. Based on the validated web FE model, a detailed parametric study is performed to systematically investigate the effects of residual stress and geometric imperfections on buckling behavior of the web. The effect of shapes of geometric imperfections discussed is highlighted. Through tracing stress states, the failure modes of stiffened plate are in agreement with the experimental phenomenon to some extent. Results show that shapes of geometric imperfections have significantly influenced post-buckling behavior and failure modes of the web, but slightly affected the ultimate strength. It is advised that residual stress and geometric imperfections should be controlled to make full use of excellent performance of steel materials.     

陈宗基讲座：岩石流变力学及其工程应用研究的若干进展

讨论岩石流变力学及其工程应用研究近年来的若干进展，主要内容包括：对岩石工程流变学问题的综述性介绍、软岩和节理裂隙发育岩体的流变试验研究、流变模型辨识与参数估计、流变力学手段在收敛约束法及隧道结构设计优化中的应用、高地应力隧洞围岩非线性流变及其对洞室衬护的力学效应，以及岩石流变损伤与断裂研究。此外，还对土力学与土工流变方面的一些进展作了简要介绍，并就今后岩土工程流变研究的展望阐述了一点认识。     

从埃菲尔铁塔看结构艺术的表现

从埃菲尔铁塔外观形式的角度对埃菲尔铁塔的设计进行了详细的介绍。并进一步从力学和结构的角度分析了铁塔的设计思想。在此基础上。将结构艺术的思想引入桥梁、塔架等大型结构工程。认为形式的设计是为了控制应力而非创造空间。另外。仅仅显示出结构与表现结构并不是一回事。结构的表现应当清楚地展现荷载的传递与构件的连接。优秀的设计应该将力学与美学结合起来。在结构艺术的层次上力求创新,达到力与美完美结合的境界。     

浅析火灾后钢筋混凝土加固措施及行业现状

本文提出了火灾后钢筋混凝土结构损伤等级,在此基础上,简要分析了几种火灾后结构的加固措施,提出其优缺点及适用范围;分析了行业现状,为理论研究和工程实际应用提供参考。     

Theoretical study of failure in composite pressure vessels subjected to low-velocity impact and internal pressure

A theoretical solution is aimed to be developed in this research for predicting the failure in internally pressurized composite pressure vessels exposed to low-velocity impact. Both in-plane and out-of-plane failure modes are taken into account simultaneously and thus all components of the stress and strain fields are derived. For this purpose, layer-wise theory is employed in a composite cylinder under internal pressure and low-velocity impact. Obtained stress/strain components are fed into appropriate failure criteria for investigating the occurrence of failure. In case of experiencing any in-plane failure mode, the evolution of damage is modeled using progressive damage modeling in the context of continuum damage mechanics. Namely, mechanical properties of failed ply are degraded and stress analysis is performed on the updated status of the model. In the event of delamination occurrence, the solution is terminated. The obtained results are validated with available experimental observations in open literature. It is observed that the sequence of in-plane failure and delamination varies by increasing the impact energy.     

Effect of size and orientation of a centrally located dent on the ultimate strength of a thin square steel plate under axial compression

Thin steel plates are widely used in many structural applications because of its high load carrying capacity with less weight. The load carrying capacity of thin plates mainly depends on the imperfections present in them. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the ultimate strength of a thin square plate with a centrally located dent is studied using nonlinear static finite-element analysis, under uni-axial compressive loading with simply supported boundary conditions.     

孔径变形法测试地应力弹性模量参数选取分析

 随着大型水电工程和地下空间工程建设的发展,势必会加大研究岩体的应力测量技术及应力对工程岩体、工程建设的影响。以黄登水电站坝区岩体地应力测量为背景,通过岩芯围压试验、室内岩块压缩变形试验等方法测试弹性模量,其测试成果在各种试验中有很大的不同,因此采用岩石损伤力学、高围压下岩体特性等理论对该现象进行分析;同时,根据卸荷岩体特性对地应力测试中应力解除过程进行分析,确定扩容对地应力测试的影响。研究结果表明,随着围压的增加,岩体弹性模量可能出现正增长关系,主要原因是岩体裂隙的压紧导致结构的致密;岩体在卸荷的情况下会出现一定程度的扩容;同时,机械振动势必也加大扩容对于变形的影响。考虑上述因素,提出黄登水电站地应力测试中弹性模量的选取原则,该方法可为类似工程提供一定的参考价值。     

考虑结构缺陷敏感性影响的单层空间网格结构形态优化研究

自由曲面单层空间网格结构以总应变能为优化目标时,优化后的结构以轴向应变能为主而弯曲应变能极小,结构承载能力较高;但在考虑初始几何缺陷影响后,其承载力会大幅下降,结构对初始几何缺陷异常敏感,经过形态优化后的结构实际承载力并不高。为此,提出以结构弯曲应变能比例作为约束条件的单层网格结构形态优化方法。该方法通过控制优化终止时结构内部弯曲应变能比例,调节结构弯曲应变能和总应变能比例关系,降低优化后结构对初始几何缺陷的敏感性,可得到考虑初始几何缺陷后仍具有较高承载力的结构形态。自由曲面单层空间网格结构数值算例表明,优化后结构在考虑初始几何缺陷后,其承载力相比传统优化方法有较大提高,证明了所提方法的可行性。     

单轴压缩下混合片麻岩脆性破坏特征分析

岩石单轴压缩变形试验是地下工程勘察中的基本力学试验。本文根据混合片麻岩单轴压缩变形试验的峰前应力—应变曲线,把其破坏过程分为裂纹闭合阶段、线弹性变形阶段、裂纹稳定扩展阶段和裂纹非稳定扩展阶段,并采用滑点回归分析技术得到了混合片麻岩各阶段裂纹临界应力值,即:裂纹闭合应力为23MPa,裂纹起裂应力为45MPa,裂纹损伤应力为86MPa,最后进行了单轴压缩下混合片麻岩脆性破坏过程细观模拟分析,为工程支护设计和围岩破坏机理分析提供参考。