Lateral-Torsional buckling of end-restrained beams

The influence of semi-rigid joint action on the behaviour and strength of laterally unsupported beams has been investigated using a finite element approach. The ultimate strength analysis allows for the effects of initial deflections, residual stresses and the gradual development of yielded zones. Connection behaviour is modelled with a multi-linear representation of in-plane moment-rotation (M-φ) behaviour. The validity of the program has been verified by checking against both analytical and experimental results. A parametric study has been conducted to assess both the importance of end-restraint effects and the sensitivity of the beam's strength to variations in the main problem variables. Studies of the spread of yield have been employed to explain the various phenomena observed. The results have been used as the basis for an assessment of the methods used to allow for end restraint in the new UK steelwork code.     

A shakedown limit calculation method for geogrid reinforced soils under moving loads

A method to calculate the elastic shakedown limit of transportation systems (e.g. pavements and railways) supported by geogrid reinforced soils is presented. For the first time, lower-bound shakedown theory is combined with a strength-based geogrid simulation approach, resulting in a rapid method to quantify the benefit of geogrids on the elastic shakedown limit. It allows decoupling of elastic stress generation and shakedown calculations, meaning it is straightforward to implement, and requires minimal computational effort. Therefore it presents a useful tool to optimise geogrid design for transportation structures such as highway pavements and railways. To show the capability of the method, shakedown limits are calculated for a variety of geogrid configurations using elastic stresses induced by a moving Hertz load. The effect of geogrid depth, soil cohesion, soil friction angle and loading type (normal versus tangential) are investigated for reinforced and non-reinforced soils. It is found that the optimum depth is sensitive to the soil strength properties. Regarding loading, it is shown that for highly tangential loads, shallower geogrids are effective, while for loads with a minimal tangential component, deeper geogrids are effective.     

在交变荷载作用下钢筋砼连续梁、框架的安定分析

本文论述了安定定理的基本概念。对三根钢筋砼连续梁和三榀钢筋砼门架进行交变荷载试验表明,试验结果与理论安定分析是一致的,从而初步证明了安定定理同样适用于钢筋砼结构。 理论分析和试验都表明,交变荷载比同样大小的简单加载情形更为不利。考虑交变荷载作用,按安定极限状态进行设计,可获得确切的可靠度和一定的经济效果。     

Pore Pressure and Viscous Shear Stress Distribution Due to Water Flow within Asphalt Pore Structure

Abstract:   There has been a concentrated effort in modeling fluid flow in asphalt pavements, and most of the existing work has been limited to evaluation of directional permeabilities. The effects of other phenomena, such as development of flow-induced pore pressure and viscous shear stress distributions at the pore–solid interfaces, on moisture damage in an asphalt pore structure have not been fully understood. A three-dimensional (3D) numerical fluid flow model was developed using the lattice Boltzmann (LB) method to simulate water flow within the pore structures of various hot mix asphalt (HMA) pavements . In this article, an in-depth analysis of variations of pore pressures and viscous shear stresses caused by water flow within the 3D pore structure of different HMA specimens is provided. The relationship between the pore geometry and the pore water pressure and viscous shear stresses were studied. Pore pressures and viscous shear stresses were computed after 3D fluid flow simulations conducted within the real pore structures of numerous HMA specimens. X-ray computed tomography (CT) was used to acquire 3D pore structures of HMA specimens, and the obtained images were input into the LB model. The results indicated that the pore water pressure gradient is highly nonlinear within the pore structure of HMA pavements, as opposed to a linear gradient commonly observed in homogeneous pore structures (e.g., granular soils). The viscous shear stresses were observed to be the largest at the constrictions located at the mid-depth of the specimens. Furthermore, a one-to-one relationship was observed between the reduction in the pore area and viscous shear stresses developed during the water flow .     

海洋平台地基的极限分析与安定性分析

应用以Melan静力型安定定理为基础的弹塑性有限元数值方法，对海洋平台地基进行了变值加载条件下的安定性分析，同时，为便于比较，进行了静力极限分析。通过对海洋平台地基在各种荷载分量共同作用下的安定性分析，得到了地基在不同荷载组合模式下的安定荷载包络图。由此根据海洋结构上外载的可能变化模式可以确定地基的最可能失稳形式，从而评价复杂变值荷载作用下地基的稳定性。     

Thermo-hygro-mechanical modelling of self-induced stresses during the service life of RC structures

Current practices of structural design in reinforced concrete (RC) structures usually account for stresses caused by phenomena such as heat of hydration and drying shrinkage in a quite simplified manner. The present paper aims to evaluate the consequences of explicitly considering self-induced stresses, which actually vary significantly within structural cross-sections, combined with stresses caused by external loads. The used numerical framework involves the explicit calculation of the temperature field in concrete, with proper account for the heat of hydration of cement. Simultaneously, the moisture field in concrete is computed in order to ascertain the relative humidity changes in the pore structure caused by drying, and the inherent shrinkage strains. Stress calculations are made with due consideration of the evolution of mechanical properties of concrete as a function of the equivalent age, as well as relevant phenomena like creep, concrete cracking and influence of reinforcement. Two separate groups of numerical applications are presented, checking influence of the self-induced stresses: a unrestrained concrete prism usually used for shrinkage measurement, and concrete slabs subjected to external loads. Particularly for the second set of applications, the obtained results (with explicit consideration of the differential effects of self-induced stresses) are compared, in terms of cracking loads and crack propagation, to those that would be obtained by using the simplified design approach based on considering uniform shrinkage fields in concrete. It is found that the behaviour of both formulations is quite similar after crack stabilization, but may be quite distinct in the crack propagation phase.     

Analytical Method for thin-walled members in general bending and torsion

The classical theory of thin-walled members has been applied extensively in practice. Since the theory was based on the assumption of no shear deformation, it is unable to reflect some of the important phenomena such as shear lag in structures.In mixed variational principles, both stresses and displacements are taken as variables, and they create equal possibilities to yield good results both in stresses and in displacement. Based on a mixed variational principle and introducing the co-ordinate functions in the cross-section, a mixed variational method has been presented.¹ Following this method, the method of solution for thin-walled members of open cross-sections in general bending and torsion is derived in this paper. This method is more general than the classical one and can be applied to members with rows of openings. It can also be applied to problems involving tension, bending and torsion actions, and simple analytical solutions in closed form can be obtained. Both warping and shear lag phenomena can be dealt with.     

降低CFRP板加固梁界面应力集中方法的研究

粘接技术作为传统的焊接、铆接、螺栓连接等技术的替代已经被广泛地应用于土木工程中。为减少粘接层的应力集中,采用端部为楔形的CFRP板及保留板端溢出的胶水为工程中常用的方法。通过有限元对一般板端、板端楔形、板端反楔形及板端溢胶等情况进行了界面应力分析。结果显示,由于梁与胶层界面端部奇异点的影响,胶层底部和顶部的最大界面应力有很大差别;而板端溢胶能降低奇异点处的剪应力和正应力集中,并且使得应力的分布更平缓,这也造成板端溢胶情况的裂缝开展不在奇异点,而在溢出胶的斜面;板端正、反楔形均能降低应力集中,而反楔形的效果要好于正楔形;板端溢胶降低正应力的效果要好于板端楔形,但板端反楔形对降低剪应力的效果则要好于板端溢胶。这些结论与搭接头研究的结果一致,但加固梁的最大界面应力减小幅度要远小于搭接头。     

Analyses of the effect of seismic behavior of shallow tunnels in liquefiable grounds

Many studies have focused on the effects of earthquake loading on the forces and displacements of underground structures. As part of the analysis of these forces and displacements, seismic loading effects are considered when designing underground structures, and so the equations are measured under small strains. Thus, the real results in surrounding tunnels and underground structures cannot be expressed by applying these equations when large strains due to some phenomena such as liquefaction occur. In other words, the mechanism of underground structure seismic behavior has not been fully recognized, and despite the presence of several studies that have been conducted already, many others are still needed. So the present study strives to assess the effect of liquefaction on shield tunnels.     

Ground behaviour and rock mass composition in underground excavations

Underground excavations like tunnels, caverns shafts, are located in a vast variety of rock mass and ground conditions with different modes of behaviour. The paper describes the main parameters and features determining the behaviour of the ground surrounding an underground excavation, namely: (1) the ground conditions (rock mass, stresses and water) and (2) the project related features, (size and shape of the opening and excavation method). Based on this a simple, qualitative division of the rock masses is presented, which together with the influence of stresses, ground water and dimension of the excavation, is used to find the probable behaviour. This may help the user to select appropriate rock engineering tool(s) for the geotechnical design as has been described by the two authors in an earlier paper.     

Detection of DNA damage in haemocytes of Mytilus galloprovincialis in the coastal ecosystems of Kastela and Trogir bays, Croatia

Coastal waters are burdened with different contaminants of anthropogenic origin due to intensive urbanisation and economical development. Bays, semi-enclosed areas with limited water renewal ability, are particularly endangered by contaminant inputs. Kastela Bay (Dalmatia, Eastern Adriatic) has earlier been identified as an area loaded with diffuse sources of pollution, including genotoxic agents. However, there is lack of data on the effects of these contaminants on the local marine fauna. The aim of this study was to assess genotoxic impacts in Kastela Bay and the neighbouring Trogir Bay using the micronucleus test and Comet assay with mussel (Mytilus galloprovincialis) haemocytes. Native and caged mussels were included in the studies. Our results confirmed that mussels in Kastela and Trogir Bays are affected by genotoxic contaminants. In addition to mussels from the most known polluted site (Vranjic), there was evidence for genotoxic effects in mussels collected at other locations. The response in the micronucleus test and the Comet assay differed somewhat between sites, the latter apparently being more sensitive, but the two methods complement each other and it is therefore desirable to use them both in monitoring the impacts of genotoxic pollution in coastal waters.     

A 3-D study of the effects of thermomechanical loads on fracture slip in enhanced geothermal reservoirs

Heat extraction from enhanced geothermal systems (EGS) can greatly affect the behavior of joints and other discontinuities in the reservoir. Fracture permeability can change in response to fluid injection/extraction, rock cooling, variations of stress field, and mineral dissolution/precipitation. The reduction in effective stress caused by pore pressure increase can cause the slippage of discontinuities, thus inducing seismicity. Studies have shown that thermal stresses generated by cold water injection have a similar effect. In order to assess the influence of thermal stresses on fracture opening and slippage, a 3-D coupled heat extraction/thermal stress/elastic displacement discontinuity model is used in this study. The effects of each mechanism on fracture slip is estimated with particular reference to the Coso geothermal field. The results indicate that under typical field conditions, a substantial increase in fracture slip is observed when thermal stresses are taken into account. The temporal evolution of the thermal stresses suggests that the rock mass deformation will not cease upon stoppage of water injection, which can be a cause of delayed seismic activity.     

What We Argue About When We Argue About Regionalism

A new debate emerged in the 1990s about regional solutions to urban problems. The debate has been carried out overwhelmingly within a welfare economics framework that stresses the economic costs and benefits of regional governance structures. Unlike earlier debates about regional reforms, the new regionalists emphasize not just that more collaborative regional governance structures will improve local services but that they will enhance the competitiveness of regions in the global economy as well. The article surveys the evidence on two propositions put forth by the new regionalists: 1) whether fragmented regional governance harms economic growth; and 2) whether suburbs are dependent on cities for their economic well‐being. Neither proposition is well supported by research and even if they were, the author concludes, this would not necessarily persuade citizens to support regional reforms. Research on the economic effects of regional governance needs to be supplemented with research on its political effects. The article concludes by examining the effects of regional governance structures on three core American political values.     

Effects of in situ stress measurement uncertainties on assessment of predicted seismic activity and risk associated with a hypothetical industrial-scale geologic CO_2 sequestration operation

Carbon capture and storage(CCS) in geologic formations has been recognized as a promising option for reducing carbon dioxide(CO_2) emissions from large stationary sources.However,the pressure buildup inside the storage formation can potentially induce slip along preexisting faults,which could lead to felt seismic ground motion and also provide pathways for brine/CO_2 leakage into shallow drinking water aquifers.To assess the geomechanical stability of faults,it is of crucial importance to know the in situ state of stress.In situ stress measurements can provide some information on the stresses acting on faults but with considerable uncertainties.In this paper,we investigate how such uncertainties,as defined by the variation of stress measurements obtained within the study area,could influence the assessment of the geomechanical stability of faults and the characteristics of potential injection-induced seismic events.Our modeling study is based on a hypothetical industrial-scale carbon sequestration project assumed to be located in the Southern San Joaquin Basin in California,USA.We assess the stability on the major(25 km long) fault that bounds the sequestration site and is subjected to significant reservoir pressure changes as a result of 50 years of CO_2 injection.We present a series of geomechanical simulations in which the resolved stresses on the fault were varied over ranges of values corresponding to various stress measurements performed around the study area.The simulation results are analyzed by a statistical approach.Our main results are that the variations in resolved stresses as defined by the range of stress measurements had a negligible effect on the prediction of the seismic risk(maximum magnitude),but an important effect on the timing,the seismicity rate(number of seismic events) and the location of seismic activity.     

Permanent deformation models for a granular material used in road pavements

This paper analyses the permanent deformation performance of an unbound granular material that has been subjected to repeated triaxial loads. The study focuses on the evolution of the cumulative strain and includes a classification of the specimens according to the shakedown concept. This was done by fitting models that express the cumulative strain to cyclic loads and stress level. The predictions of the models were not absolutely perfect. The results with the granular material were not satisfactory enough to warrant their use in a low traffic road pavement section in Galicia (Spain).     

上海地铁车站混凝土结构的温度干缩应力分析

简要论述了混凝土干缩变形及分析方法 ,通过有限元的仿真计算 ,较为准确地模拟地铁地下车站混凝土框架结构的实际施工情况 ,计算和分析了地下车站混凝土结构的温度干缩应力 ,在一定程度上揭示了混凝土结构由温度徐变及干缩应力引起的裂缝成因。     

部分预应力混凝土梁裂缝闭合应力及闭合弯矩的简化计算

根据国内已有的试验研究成果，对部分预应力混凝土梁裂缝闭合时的闭合应力和闭合弯矩的计算方法进行了进一步研究。根据已搜集到的试验资料，通过回归分析，得出了统一的裂缝闭合应力的计算公式，用该公式求得的闭合应力与试验结果符合良好。在此基础上，还对闭合应力取常数时的闭合弯矩进行了验算比较，验算结果表明，对于有粘结及无粘结部分预应力混凝土梁，当闭合应力分别取1N／mm^2及2N／mm^2时，闭合弯矩的计算值与试验值也符合较好。     

Experimental investigation on the accumulated strain of coarse-grained soil reinforced by geogrid under high-cycle cyclic loading

In this study, a series of cyclic triaxial tests were conducted to study the accumulated strain of coarse-grained soil reinforced with geogrids, and the effect of the number of geogrid layers, confining pressure and cyclic stress amplitude was investigated in detail. The test results show that the final accumulated axial strain of the soils reinforced with geogrids is less than that without reinforcement, and less accumulated axial strain is generated for the specimens with more geogrid layers under identical cyclic loading. The results also show that a higher confining pressure or a lower cyclic stress amplitude yields less accumulated axial strain for the reinforced soils. Furthermore, the plastic shakedown limits are determined by the criterion proposed by Chen et al. It indicates that the plastic shakedown limit increases significantly when one layer of geogrid is incorporated into the specimen and then tends to level off with a continuous increase in the number of geogrid layers. Moreover, a higher confining pressure yields a higher plastic shakedown limit for the soils reinforced with geogrid. The results demonstrated that the use of geogrid can be an effective method to reduce the accumulated deformation of subgrade filling materials under high-cycle traffic loading.     

Column curves for elliptical hollow section members

A thermo-mechanical finite element analysis model is developed to predict residual stress patterns in hot-rolled sections. The model is first verified against experimental measurements for residual stresses reported for I-sections reported in the literature. The method is then used to predict residual stresses in elliptical hollow sections. A sensitivity analysis is then conducted to assess the influence of various input parameters of the model on the predicted residual stress patterns. The effects of cross-section geometric parameters on the residual stress distribution are then investigated.A series of column curves is generated providing the compressive capacity of a column as a function of slenderness. The column curves are generated based on a) elasto-plastic geometrically nonlinear analyses, b) including the effect of residual stresses as predicted from thermo-mechanical analyses and c) incorporating initial geometric out-of straightness according to the fundamental buckling mode as predicted from an elastic buckling eigen value analysis. Generated column curves are then compared to those in current design codes. A best fit for the numeric results obtained is conducted to cast them in a format similar to that in the current codes.     

Optimisation of the shear stress transfer in structural bonded assemblies using a curved bonded joint geometry

Structural adhesive bonding is coming into increasing use in civil engineering either for strengthening operations involving the adhesive bonding of external reinforcements or to replace traditional assembly techniques in new structures. However adhesive bonding induces stress concentrations at the edges of the joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the assembly. These studies are all, therefore, concerned with optimizing shear stress transfer in adhesively bonded joints. This paper investigates the role of the hydrostatic pressure on the ultimate capacities of common civil engineering adhesives. This led us to investigate a new joint geometry, the “curved” bonded joint that naturally creates compressive stresses on the edge of the joint. Initially, classical modelling is conducted to determine how the geometry affects the stresses in the joint. Then, fracture mechanics is used to investigate crack propagation. After this theoretical modelling, several experimental investigations are presented. These are quasi-static tests which compare classical shear lap joints to curved joints. The experimental results are then exploited using the modelling described before. Additional testing is currently in progress, but the curved bonded joint seems to hold good prospects and a patent has been filed.