自攻螺钉波峰连接的抗剪性能试验研究

为了满足防水要求,目前我国在蒙皮连接上广泛采用自攻螺钉在压型钢板的波峰处与构件相连的形式.通过对30个波峰连接的自攻螺钉连接件的试验研究,探索波峰连接的抗剪性能,同时比较支承构件(以下简称支承板)板厚不同对连接试件抗剪性能的影响.结果表明,支承板过薄时,对螺钉根部锚固力不足,会导致螺钉在受力过程中倾斜,使试件的抗剪承载力大大增加而刚度降低;支承板越薄,其性能对安装缺陷越敏感;当支承板达到一定厚度,其厚度的变化对试件抗剪承载力影响不大;压型钢板波高越高,试件的抗剪承载力越低;波峰连接的抗剪承载力和抗剪刚度远远低于相同条件下波谷连接的相应性能,连接的抗剪承载力的降低,将较大影响蒙皮体的整体抗剪性能,但与裸骨架相比,此种连接形式仍具有相当的受力蒙皮作用可资利用.     

Combined MVP failure criterion for steel cross-sections

This study determines failure criterion for steel member cross-sections, subjected to combined bending moment M, shear force V, and axial force P (MVP). The principle of maximum plastic strain energy is employed to develop the strain-stress relationship for plastic flow, and the expression for the MVP yield surface of the cross-section. A linear distribution of shear strain over the cross-section is assumed. The influence of plastic deformation on bending moment, shear force and axial force, at full yield of the cross-section, is investigated. Results predicted by the derived MVP failure surface, are compared with those obtained by other studies in the literature. The derived MVP yield surface can serve as a basis to identify the failure of steel members, such as during seismic or progressive-failure analysis of building frameworks.     

An early warning criterion for the prediction of snowmelt-induced soil slope failures in seasonally cold regions

In Hokkaido, Japan, soil slope failures occur frequently during the snow melting season. These slope failures are triggered by the excess amount of water derived from snowmelt and rainfall. For the prediction of snowmelt-induced soil slope failures in seasonally cold regions, an early warning criterion is required. The existing Japanese early warning criteria for sediment disasters, i.e., the relationship between the 60-min cumulative rainfall and the Soil Water Index (SWI), the effective rainfall index etc., consider the influence of rainfall and the time-dependent random moisture of the soil. However, these criteria do not consider the soil moisture contributed by the snowmelt water. In this study, therefore, the applicability of the existing early warning criteria to predict snowmelt-induced soil slope failures is examined. An empirical method to quantify the amount of snowmelt water is presented. Various scenarios of conceptual soil slope failures are studied using numerical simulations under different magnitudes of rainfall and snowmelt water. As a result, a revision is introduced for the SWI and the effective rainfall index, adding the amount of snowmelt water to that of rainfall, and slope failure scenarios are studied. Based on the results, a new early warning criterion, the Effective Precipitation (EP) index, is introduced. It is found that the new failure criterion performs well for the prediction of snowmelt-induced soil slope failures.     

Peeling and diagonal tension failures in steel plated R/C beams

This paper focuses on the design of an experimental investigation motivated by the need to identify various independent modes of failure of steel plated R/C beams. Parameters controlling the various failure modes are identified, and an elaborate testing program confirms existence of peeling failure and flexural failure in addition to isolation of a diagonal tension mode of failure. An expression is proposed to predict ultimate capacity of steel plated R/C beams prone to fail by diagonal tension.     

A criterion for optimal damping design

The design of elements for maximum damping of vibrations in a linear elastic system is described. Single and multiple damping elements of purely viscous, visco-elastic, rigid-plastic, or Coulomb type are treated.A general theorem is developed which equates the optimal impedance (dynamic stiffness) of the damping element to the impedance (elastic plus inertial stiffness) of the linear system at the point at which the element is applied. This theorem provides a criterion which may be used directly to design the elements: Formulae are derived from there to specify the elements and to evaluate their effectiveness and thus indirectly indicate where to locate them.Applications include damping of sway vibrations of tall buildings, and of vibrations in floor systems, vehicles and machines. Noise producing vibrations may be included. In each case, the optimal impedance characteristics of the damping element may be expressed in terms of the impedance characteristics of linear system, e.g. the elastic stiffness of the structure or the mass of the machine, and the frequency of the loading force.     

A new strength criterion for structured soils

Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soils in many aspects, especially in their strength properties. Thus, the influence of soil structure (bonding and fabric) on the mechanical properties of structured soils cannot be correctly described. By analyzing the breakage mechanism of natural soils, the structured soils can be conceptualized as binary medium materials consisting of bonded blocks and weakened bands. On this basis, a new strength criterion is proposed for structured soils. The expressions of the strength criterion on both meridian and deviator planes are given to describe the strength properties of structured soils on these planes. The proposed strength criterion is compared with available test data under conventional and true triaxial stress conditions in the literature. It is observed that the proposed strength criterion agrees well with the test data.     

A failure criterion for transversely isotropic rocks

In this paper, a new failure criterion for the transversely isotropic rocks is presented. The new criterion is based on two distinct failure modes; one is the sliding mode where the failure is caused by sliding along the discontinuity, and the other is the non-sliding mode where the failure is controlled by the rock material and is not dependent on discontinuity. This failure criterion is defined with seven material parameters. The physical meanings of, and the procedures for determining, these parameters are described. Both the original Jaeger criterion and the extended Jaeger criterion are shown to be special cases of the proposed criterion. The accuracy and applicability of the proposed failure criterion are examined using the published experimental data. The data used cover various types of transversely isotropic rocks, different orientation angels and confining pressures. The predicted strength behaviors of the transversely isotropic rocks agree well with the experimental data from various investigators. The accuracy and applicability of the proposed empirical failure criterion are demonstrated in this paper.     

A Unified Strength criterion for rock material

A non-linear Unified Strength criterion for rock material is presented. It is the development of the Unified Strength Theory (in: M. Jono, T. Inoue (Eds.), Mechanical Behaviour of Materials-VI (ICM-6), Pergamon, Oxford, 1991, pp. 841–846) and the modification of the Hoek–Brown strength criterion (Underground Excavations in Rock, The Institution of Mining and Metallurgy, London, 1980). The effect of intermediate principal stress on rock strength is considered in the non-linear Unified Strength criterion. The Hoek–Brown criterion is a single-shear strength criterion that forms the lower bound, and the non-linear twin-shear strength criterion forms the upper bound in the deviatoric plane. All the failure criteria ranging from the Hoek–Brown criterion (lower bound) and the non-linear twin-shear criterion (upper bound) and a series of criteria ranging between these two bounds may be introduced by the non-linear Unified Strength criterion. The theory can also be generalized to rock mass strength.     

矩形钢管混凝土受弯构件材料本构关系与失效判据研究

为了正确评估矩形钢管混凝土(CFST)受弯构件的承载力,提出钢管和核心混凝土材料本构关系的修正模型,建立CFST受弯构件的承载力失效判据。首先,考虑受拉区钢管双轴受拉有利应力状态及受压区钢管双轴拉压不利应力状态,并基于矩形CFST轴压短柱试验数据库,通过回归分析建立约束混凝土峰值应力表达式,在此基础上建立矩形钢管混凝土材料本构关系的修正模型。其次,基于构件承载能力极限状态,并合理考虑受拉区钢管的应变强化段,提出矩形CFST受弯构件的承载力失效判据。最后依据纤维模型法和试验数据库对比分析CFST受弯构件的不同材料本构关系和失效判据的精度及适用性。结果表明,所建立的CFST构件材料本构关系和承载力失效判据能够更加准确地反映矩形CFST构件的抗弯能力,具有更高的计算精度和广泛的适用性。     

Evaluation of a strain monitoring system for existing steel railway bridges

The old steel bridges that integrate the existing railway lines are structures built with materials that are no longer used and whose knowledge has being lost over the years, often presenting severe problems of deterioration and subjected to loading environments very different from those for which they were designed. In this context, adequate strain monitoring is a crucial tool in supporting the behavior characterization and safety assessment of these structures.This article presents and discusses the monitoring systems installed in the Trezói Bridge, within a research project aimed at developing and applying procedures for evaluation of the structural integrity of steel railway bridges. The field observations of the structural behavior were accomplished by using two different types of sensors: electric and fiber optic strain sensors. The electric monitoring system was designed and installed on the bridge to supply the experimental data for the research project, while the fiber optic monitoring system was firstly applied to evaluate the reliability of the former and to check its efficiency, and secondly to provide some redundancy of the measurements at critical locations. The obtained results are analyzed to characterize the bridge behavior and the capabilities and limitations of both types of sensors to acquire the relevant data for the bridge service condition and fatigue assessment are discussed, namely in what concerns the ability to accurately capture the static and dynamic components of the structural response and the frequency content of interest.     

钢筋混凝土简支梁桥耐久性指标的确定

通过对钢筋混凝土简支梁桥耐久性劣化的主要原因分析,给出了钢筋混凝土结构寿命评估的准则,提出了钢筋混凝土简支梁桥耐久性指标,以期为桥梁耐久性的设计和评估提供依据。     

A generalized three-dimensional failure criterion for rock masses

The smooth convex generalized failure function, which represents 1/6 part of envelope in the deviatoric plane, is proposed. The proposed function relies on four shape parameters (Ls, a, b and c), in which two parameters (a and b) are dependent on the others. The parameter L s is called extension ratio. The proposed failure function could be incorporated with any two-dimensional (2D) failure criteria to make it a three-dimensional (3D) version. In this paper, a mathematical formulation for incorporation of Hoek-Brown failure criterion with the proposed function is presented. The Hoek-Brown failure criterion is the most suited 2D failure criterion for geomaterials. Two types of analyses for best-fitting solution of published true tri-axial test data were made by considering (1) constant extension ratio and (2) variable extension ratio. The shape and strength parameters for different types of rocks have been determined by best-fitting the published true tri-axial test data for both the analyses. It is observed from the best-fitting solution by considering uniform extension ratio (Ls) that shape constants have a correlation with Hoek-Brown strength parameters. Thus, only two parameters (σc and m) are needed for representing the 3D failure criterion for intact rock. The statistical expression between shape and Hoek-Brown strength parameters is given. In the second analysis, when considering varying extension ratio, another parameter fis introduced. The modified extension ratio is related to f and extension ratio. The results at minimum mean misfit for all the nine rocks indicate that the range of f varies from 0.7 to 1.0. It is found that mean misfit by considering varying extension ratio is lower than that in the first analysis. But it requires three parameters. A statistical expression between f and Hoek-Brown strength parameters has been established. Though coefficient of correlation is not reasonable, we may eliminate it as an extra parameter. At the end of the paper, a methodology has also been given for its application to isotropic jointed rock mass, so that it can be implemented in a numerical code for stability analysis of jointed rock mass structures.     

一种横观各向同性沉积岩的失效准则

通过定义初始屈服函数及由试验测定沉积岩的参数,提出了一般应力条件下岩石材料的失效准则,给出了该准则的数学表达式,对两种典型横观各向同性岩石强度特性的模拟结果表明,该准则能较好地反映沉积岩类材料在一般应力条件下的强度变化规律。     

A three-stage full-range stress–strain inversion for stainless steel alloys as an explicit function of temperature

Presented in this paper is a new explicit full-range stress–strain inversion for stainless steel alloys which expresses the stress as an explicit function of strain and temperature. The relation utilizes an approximation of the closed form inversion of a highly accurate three-stage stress–strain relation recently obtained from a modified version of the Ramberg–Osgood equation. The inversion which is obtained by making a generalized rational function assumption on the fractional deviation of the actual stress–strain curve from an idealized linear elastic behavior is applicable both to tensile and compressive stresses. The temperature dependence is then accounted for by using modified mechanical properties which are functions of temperature. The paper also presents a new direct temperature dependent stress–strain relation based on material properties at normal temperature. While previous studies use temperature dependent material properties to account for the effect of temperature on the stress–strain relation, this paper proposes explicit formulation based on the material properties at normal temperatures. The explicit temperature dependence is introduced by modifying the form of the stress–strain relation which includes a factor with an appropriate temperature dependent function. The validity of the temperature-dependent expression is tested over a wide range of material parameters and a wide range of temperatures. It is demonstrated that the proposed expression is both qualitatively and quantitatively in excellent agreement with the fully iterated numerical solution of the full-range temperature-dependent stress–strain relation at moderate and high temperatures.     

A new fracture criterion for peridynamic and dual-horizon peridynamics

A new fracture criterion based on the crack opening displacement for peridynamic (PD) and dual-horizon peridynamics (DH-PD) is proposed. When the relative deformation of the PD bond between the particles reaches the critical crack tip opening displacement of the fracture mechanics, we assume that the bond force vanishes. A new damage rule similar to the local damage rule in conventional PD is introduced to simulate fracture. The new formulation is developed for a linear elastic solid though the extension to nonlinear materials is straightforward. The performance of the new fracture criterion is demonstrated by four examples, i.e. a bilateral crack problem, double parallel crack, monoclinic crack and the double inclined crack. The results are compared to experimental data and the results obtained by other computational methods.     

考虑T应力的最大周向应变断裂准则研究

岩石的裂纹扩展问题需要确定所采用的断裂准则。为克服最大周向应力准则与材料参数以及平面应力和平面应变无关的不足,该文基于最大周向应变准则思想,推导既包含裂纹尖端r1/2奇异应力项,又考虑非奇异项的应变型断裂准则。通过在KII中考虑摩擦的影响作用,进而实现不同摩擦系数条件下裂纹的起裂角度和起裂强度的研究。运用文中所提出的断裂准则,分别研究含单裂纹的无限板在双轴拉伸和双轴压缩两种条件下的断裂特征,进一步揭示泊松比、侧压系数、摩擦系数等材料参数对裂纹扩展的影响作用,计算结果与相应的试验及理论结果具有较好的一致性。     

一个用于预测金属板材断裂的损伤破坏准则

基于连续介质损伤力学 ,提出了描述金属板材塑性损伤的演变方程 ,并依此得到了一个用于预测金属板材断裂破坏的简单准则 .其中特别考虑了剪切机制和剪切应力在金属薄板损伤发展和最终破坏过程中的作用 ,同时也引入了材料微观损伤对材料机械性能的影响 .提出的损伤演变规律 ,可近似表征金属薄板在成型过程中损伤的发展变化 ,计算得出的损伤曲线与有关实验曲线比较吻合 .给出的损伤破坏准则 ,可直接用于预测金属板材的断裂极限应变