Thermal,moisture and microbiological boundary conditions of slab-on-ground structures in cold climate

Coarse-grained fill or drainage layers beneath heated slab-on-ground structures are warm and moist throughout the year. According to the in situ measurements, the relative humidity of the fill layer is high at RH ≈100%$\approx 100\%$. High relative humidity of the fill layer is not a sign of an un-functional drainage or capillary break layer, but a natural boundary condition for a slab structure adjacent to the moist subsoil. Due to the favourable conditions, microbe growth is very common in fill layers. Fungal or bacterial growth, in general, was detected in 98% of the test specimens taken beneath the ground slabs of heated buildings. Indicator species, either fungal or bacterial, were detected in 79% of the specimens. Yet, no moisture damage related to the ground floors was ever detected or recorded in the test buildings. The high microbe concentration in the fill layer beneath ground slabs is not a sign of moisture damage, but a natural state of the moist and warm fill layer.     

Bending and stretching actions in shallow domes. Part 2. A comparative study of various boundary conditions

In this, the second of the two-part series of articles on the interaction o bending and stretching effects in shallow axisymmetric shells, this interaction is examined by means of the two-surface shell theory, with particular reference to the influence of boundary conditions.     

Consistent boundary conditions for flows within the atmospheric boundary layer

In computational wind engineering the neutrally stable atmospheric boundary layer (ABL) is often simulated using the standard k-ε model. The application of boundary conditions that are inconsistent with the profiles used at the inflow boundary causes streamwise gradients in the solution and prevents the simulation of a horizontally homogeneous boundary layer. In the present work these problems are overcome by applying a simple extension of the shear stress boundary condition at the top of the domain and by using one-dimensional models to generate inflow profiles in equilibrium with the ground boundary condition. This procedure allows the impact of the inconsistent boundary conditions to be quantitatively assessed. It is shown that inconsistent boundary conditions at the top of the domain result in erroneous streamwise gradients throughout the domain. These errors are reduced by enlarging the domain in the vertical direction but are not removed. The errors are also found in simulations with idealised and real topography included in the domain. A brief discussion of the impact of the errors on simulations of wind energy projects is given.     

边界条件对网壳结构稳定性的影响分析

利用ANSYS软件,从周边刚性支座、周边铰支座、12点支承刚性支座及12点铰支座等方面分析了边界条件变化对网壳结构稳定性的影响,并结合实际的工程设计,给出了合理的建议。     

Probabilistic force calculations for structures in ice-covered seas

Ice ridges are expected to govern the design of conical structures in the arctic offshore against sliding forces and to affect the design of gravity or pile structures against overturning moments. Given that the mechanics of sea ice and the degree of consolidation and failure mode of ice ridges against a particular structure geometry are specified, there will still be uncertainty as to the size, shape and number of ridges that may impact a structure placed in these areas. The situation is analogous to designing against storm waves. The concern in both cases is with the probability of exceedance (risk) of rare events that approach the design strength of a surface-piercing structure founded on the seafloor.This paper describes a procedure for calculating the probability distribution of ice forces on a structure. A Monte Carlo approach is taken, together with ice mechanics, to convert information on structure geometry, structure location, and ice conditions at the location into a probability distribution for the force that will be imposed on the structure over a specified time period. The probability calculation is comprehensive in the sense that it can accommodate information on ice movement, ridge spacing, ridge geometry, etc. A comprehensive calculation gives the best estimate of risk under the assumptions made, and provides a framework for making prompt use of additional data as it is gathered. The data gathering effort itself can be focused by determining those environmental parameters to which the design ice force is most sensitive at acceptable risk levels.     

扁球壳结构的塑性极限分析

本文在文献基础上,分析了矩形底扁壳结构的塑性极限状态.利用机动法分别求出了等矢高方形底、不等矢高矩形底扁球壳的内力和极限荷载,并给出了计算实例.     

浅埋地下结构耐震时程分析法最优持时研究

为研究持时对地下结构耐震时程分析结果的影响,选取II类和III类工程场地中典型的两层三跨地铁车站为原型,以基岩场地地震动均值反应谱为目标谱,构造了6种典型持时的耐震加速度时程曲线作为输入。通过将耐震分析结果与增量动力分析基准结果对比表明,耐震加速度时程曲线的持时对分析结果影响显著。根据目标时间点与地震动能量指标阿里亚斯强度值的变化规律,给出了最优目标时间点的确定公式并进行验证。由研究结果可知,对于II和III类工程场地,耐震时程曲线较优持时分别为30s和45s;给出的目标时间点的确定公式对上述两类场地中的地下结构抗震性能评价具有一定适用性,当构造的耐震时程曲线在目标时间区段内的能量值与实际地震动的能量值较为接近时,耐震时程分析结果最为精确。     

First order vs. second order reliability analysis of series structures

The paper presents an extension of the first order reliability method for computation of failure probabilities. The improvement is achieved by a better approximation to the limit state surface. The analysis is demonstrated for individual failure modes and for series structures. The results obtained are very close to ‘exact’ results obtained by simulation. The method is seen as a supplement to first order reliability methods for special cases. It is not meant to completely replace these methods.     

Appropriate boundary conditions for computational wind engineering models revisited

At the first Computational Wind Engineering conference in 1992 “Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model” were proposed. In this paper it is shown that these conditions can be directly derived by treating the onset flow as a horizontally homogeneous turbulent surface layer, with the flow being driven by a shear stress at the top boundary. This approach is extended to provide the inlet profiles and boundary conditions appropriate for modelling the flow using the standard k-ε, RNG k-ε, Wilcox k-ω and LRR QI turbulence models. Means for their application within the commercial CFD code CFX 12.0 are given. It is shown that within the flow the various turbulence model constants set the effective value of von Kármán's constant, which does vary slightly between models. The discrepancy between the turbulence level set by the standard turbulence model constants and that observed in the atmosphere is discussed. Problems with excessive turbulence generation near the ground and the over-prediction of stagnation pressures are discussed and possible solutions proposed.     

Vibration and buckling of plates with mixed boundary conditions

This paper deals with the vibration or buckling of thin plates with either mixed boundary conditions or discontinuous boundary conditions using the spline element method.

To demonstrate the accuracy of the method, several examples are solved, and results are compared with those obtained by other numerical methods. The effects of partial rotational constraints and angles of skew on frequencies and buckling loads of isotropic skew plates are also investigated.     

Limit analysis in stability calculations of reinforced soil structures

Stability analyses of reinforced soil structures are traditionally based on limit equilibrium calculations. Results from such analyses are sometimes ambiguous because of different assumptions made in addition to the limit state. It is shown in this paper that these ambiguities can be removed if the kinematic approach of limit analysis is used, in which a rigorous bound to the required strength of reinforcement is sought. The required strength of reinforcement is the strength needed to maintain stability of the structure. Since limit analysis leads to a rigorous bound on the reinforcement strength, limit loads, or a safety factor, the geometry of the failure mechanisms considered can be optimized, so that the best bound is obtained (a solution closest to the exact solution). A dual formulation of kinematic limit analysis is possible in terms of limit force equilibrium, but the former is preferable since the kinematics of collapse mechanisms appeals to engineering intuition more than the distribution of forces does.     

New inflow boundary conditions for modelling the neutral equilibrium atmospheric boundary layer in computational wind engineering

Modelling neutral equilibrium atmospheric boundary layers (ABL) in CFD is an important aspect in computational wind engineering (CWE) applications. In this paper, new inflow boundary conditions are introduced from the viewpoint that these boundary conditions should satisfy the turbulence model employed. The new set of inflow turbulence boundary conditions is an approximate solution to the standard k-ε model transport equations. The capability of these boundary conditions to produce an equilibrium ABL is demonstrated by performing numerical simulations in an empty domain. The new inflow turbulence boundary conditions in this paper support future practical applications in CWE and future research in modelling equilibrium ABLs.     

浅层地下建筑围护结构传热模拟的一种新方法

地下建筑围护结构传热量模拟，是实现热湿环境系统动态模拟的基础课题。通过对浅层地下结构进行简化，并根据空调系统实际运行特点，建立了传热过程的数学模型。用气象模型产生作用于工程的地面空气温度，用线上求解技术实现传热过程的动态模拟。并通过两个实际工程的同步实测与模拟，确认了模拟模型的有效性和可行性。     

Determining the boundary conditions by estimating RDOFs CMS for piping system

It is difficult to obtain boundary conditioners for air conditioner piping system by FE model. An estimating rotational degree of freedoms (RDOFs) component mode synthesis (CMS) method is presented and used to determine the boundary conditions. This paper presents the method to determine the boundary conditions of the piping system from experimental data. A piping system of the air conditioner is carried out as an example using MSC. Nastran, and the comparisons between the results and the experimental ones show the achievements.     

Geomechanics in analysis and design of shallow underground structures (characteristics and problems)

The inclusion, in the journal "Soil Mechanics and Foundation Engineering," of the section "Underground Structures" reflects the interest of the engineering circles in the problems of design and development of projects in the underground space. In the section, material is published on construction of underground structures in the industrial, transport, energy, and other fields. Taking into account the traditional profile of the Journal and the professional interests of the greater mass of its readers, it is proposed to devote maximum attention in the future to material relating to geotechnical problems that arise during construction of shallow structures in the underground space of cities and industrial installations.The complex and multilevel nature of the technical problem of effective and ecologically sound development of the underground space calls for participation of specialists working in different fields of the applied and fundamental sciences. Hence, we will welcome proposals for new architectural-planning solutions for underground structures, methods for their reconstruction and engineering protection, and solutions of engineering-geologic, ecologic, and other problems relating to underground construction. One of the most important places in this connection should be assigned to geomechanical problems, whose correct formulation and solution is determined by reliable analysis and design of the underground structures as well as of the overground structures that interact with them. The opening article of this section is devoted to the characteristics of such problems.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 24–27, May–June, 1992.     

DQEM for large deformation analysis of structures with discontinuity conditions and initial displacements

A nonlinear mathematical model of the large deformation analysis of beams with discontinuity conditions and initial displacements is first formulized by the arc coordinates. The differential quadrature element method (DQEM) is applied to discretize the nonlinear mathematical model, and an effective method of applying DQEM to analyse the large deformation of structures with discontinuity conditions of multivariables is presented. A set of DQEM discretization equations are obtained. Then, the Newton–Raphson method is used to solve the system of nonlinear algebraic equations. As applications, some numerical examples in engineering are presented, which include the large deformation analysis of beams, frames, piles with elastic joints. The obtained results are compared with those in the existing literatures. The numerical results show that the model and the method presented in this paper may be widely applied to solve the problems of large deformation of structures with discontinuity conditions in engineering; also the method has the advantages of little amount in computation, good stability and convergence and so on.