利用初流量法分析有自由面渗流问题之改进

在利用初流量法分析带有自由面的渗流问题时,常因采用高斯积分点作为结点初流量计算判断依据所带来的误差而令解出现振荡。为了减低这一因素的影响及提高计算的效率,针对常用的 4 结点平面单元和 8 结点 6 平面三维单元的自由面方程进行分析,提出采用坐标变换和等参变换等技术来改造结点初流量的计算,并建议按自由面穿越单元之状况引用分部积分,使其积分上、下限符合高斯积分法的格式化要求,从而可利用高斯积分法求出精确的结点初流量,而精确的结点初流量则有助于改善解的振荡及提高计算结果的精度。通过一矩形均质坝实例分析,表明该方法的稳定性和收敛性良好。     

A new method for the design of tall buildings: The mit design method

A new method for the design of tall and super-tall buildings is presented in this paper. The method is based on transforming the stiffness properties of the building to equivalent beam properties. The equivalent beam is allowed to deform both in bending and shear to capture the true behavior of the building. The method is a stiffness based approach that later requires checks for strength. This is quite appropriate since the design of tall and super-tall buildings is governed by stiffness and not by strength. Knowing the load and assuming a desired shape of the beam, the required shear and bending rigidities of the beam can be calculated. The method is robust and easy to apply, and is particularly suited for space truss systems. The simplicity and efficiency of the method are illustrated with an example.     

纵向焊接铝合金柱设计方法研究

大多数结构用铝合金通常要经过热处理或加工硬化以得到比退火状态更高的力学性能。这种合金焊接后,焊接热会使焊缝附近局部区域(称为热影响区HAZ)强度降低。而对于钢结构,由于其热导率比铝材小得多,因此只有高强钢才可能产生强度降低的热影响区,而且其强度的降低没有铝合金显著,热影响区宽度也比铝合金小得多。这将使焊接铝合金柱的设计变得更为复杂。由于我国目前还没有关于铝合金结构的设计规范,为此本文通过试验研究及对已有试验数据的分析,并参考国外规范,提出了纵向焊接铝合金柱设计方法的建议,并将计算结果与试验结果进行比较,两者吻合较好,从而验证了建议设计公式的适用性。     

Engineering method of predicting structure settlement with allowance for primary and secondary bed consolidation

The possibility of separating the consolidation of a loaded saturated bed into the phases of the prevailing effect of the seepage and viscous resistances of the soil is substantiated by the dependence of primary deformations on the duration of the seepage phase. A simple method of calculating the settlements of structures and the time required for dispersal of excess pore pressure and the stabilization of soil deformations is developed on the basis of the indicated concept and familiar laws governing the occurrence of various phases. Procedures are proposed for calculation of soil parameters and determination of correlation relationships for their approximate assignment with respect to indicators of the soil's physical properties. Computed results are compared with data derived from field observations for a bed with a layer of weak saturated clayey soil. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 2–6, September–October, 1996.     

基于渗流分析的膨润土力学状态计算方法

提出一种渗流分析和力学计算相结合的方法来分析膨润土在吸水膨胀过程中的力学状态.首先,通过渗流分析获得土体中的饱和度分布;其次,根据饱和度与膨胀力之间的关系求得膨胀力的分布;最后,将膨胀力作为初始应力带入模型,进行力学计算.对两组膨润土进行注水试验,并测量膨润土土压力的变化.将计算的结果和试验测量数据进行对比,以检验提出的计算方法的精确性.对比结果表明,计算结果与试验测量结果数值吻合较好.得出结论：利用渗流分析与力学计算相结合的计算方法计算力膨润土在吸水过程中的力学状态分布具有可行性.     

A design method for seismically isolated bridges with abutment restraint

Seismic isolation is a commonly used technique for protecting new and existing bridges. It usually consists of introducing isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake action. This paper deals with partially restrained seismically isolated continuous bridges, which are a particular class of isolated bridges whose transverse motion is restrained at the abutments.In this study a method is proposed for the preliminary design of these systems, which can be applied to both new and existing bridges. The dynamic problem is described in a variational form in order to obtain a simplified solution based on a pre-fixed transverse deformed shape of the deck. The objective of the design procedure is to control the internal actions on the piers by means of an appropriate configuration of the isolation bearings. Simple formulas for estimating the forces transmitted to the abutments and the superstructure transverse curvature demand are also derived, which account for the contribution of higher modes of vibration.Validation studies are undertaken for different bridge configurations, in order to assess the ability of the simplified method to control the force demand at the piers.     

堤坝非稳定渗流观测资料分析方法

堤坝在实际运行中由于上游水位的不断变化,渗流状态是非稳定渗流。由于其边界条件复杂多变,参数很难确定,使得非稳定渗流的求解变得非常困难。在目前观测资料渗流分析中,仍采用稳定渗流方法。应用非稳定渗流理论,借鉴目前简单边界已有的结果,提出了一个新的非稳定渗流近似计算模型。利用已有测压管观测资料,求出非稳定渗流的半经验半理论公式的近似解,并进一步求出测压管水位在上游水位逐日变化的情况下,测压管水位日变化量的计算方法。用此方法计算了实例,与观测结果符合良好,计算值与实测值误差很小,一般仅几厘米,成果理想。求出近似的位势值,比较不同年份位势的变化,可作为工程防渗能力变化及防渗能力的评价指标,用于评价工程防渗状态的变化,应用于大坝安全监测评价中。     

某高等级公路桥头路基预抛高新方法

首先对桥头跳车现象作了概述,以某高等级公路改建工程为例,分析了桥头跳车的原因,对预抛高值的计算进行了探讨,并指出该工程根据专业单位沉降监测计算的预抛高值,采用直接抬高搭板尾枕梁,用宕渣进行抛高,节省了大量工程费用,该方法可推广应用。     

A design method for flaming fire detection

The scientific basis of a design method for the detection of flaming fires is reviewed. The equations required to calculate detector spacings are included and the selection of appropriate design input parameters is discussed. Limitations of the method and areas for further research are identified. The design method has been implemented and proposed for inclusion in NFPA Standard 72E-1984 as Appendix C by the 72E-M Committee. Center for Fire Safety Studies Worcester Polytechnic Institute     

有自由面非稳定渗流分析的改进截止负压法

截止负压法是求解有自由面渗流问题较为有效的算法之一。针对其算法特点,结合渗流本质,指出该算法的不足之处在于只引用了单参数的罚函数,从而造成自由面附近区域的渗流计算不够精确。为此,提出了引用双参数罚函数的改进截止负压法,改进后的算法更能准确地考虑单元的部分饱和非饱和作用,精确地计算单元结点外力或者结点不平衡力,进而提高计算精度和收敛速度。最后,将改进算法用于求解有自由面非稳定渗流问题,编制了相应的有限元分析程序,并通过算例进行验证。     

初始孔压非均布考虑起始比降的一维固结解

研究了考虑起始比降的一维固结问题,获得了初始孔压非均布条件下考虑起始比降的一维固结解答,并与已有文献解答进行了对比,讨论了考虑起始比降后土体的一维固结特性。计算分析表明,当初始孔压降小于起始比降时,渗流并不会在整个土层中瞬间发生,而是逐渐向下发展的,起始比降越大,渗流边界移动速度越慢;固结结束时,土体中的孔隙水压力并不会完全消散,且起始比降越大,残余孔隙水压力越大。与不考虑起始比降不同,均质地基平均固结度按沉降定义和按孔压定义是不同的,随着起始比降的增大,按沉降定义的固结度随之增大,而按孔压定义的固结度则随之减小。     

某水库运行初期渗流量“异常”机理研究

目前为止,我国修建了许多水库,或以防洪、防凌、减淤为目的,或以供水、灌溉、发电为目的,又或多种用途兼而有之,除害兴利,对我国现代化建设有着举足轻重的意义。文中利用某水库水位与渗流量的数据,结合研究区的水文地质条件,定性分析该水库运行初期渗流量出现"异常"的可能原因。然后,运用脉冲响应函数(IRFA)分析方法,定量分析该水库水位和渗流量的关系。最终,确定该水库运行初期渗流量的"异常"其实质是一种渗流量变化滞后于库水位变化的现象。合理解释了该水库运行初期渗流量出现"异常"的原因,为进一步做好水库防渗工作提供了科学依据。     

A method for the design of longwall gateroad roof support

A longwall gateroad roof support design method for roadway development and panel extraction is demonstrated. It is a hybrid numerical and empirical method called gateroad roof support model (GRSM), where specification of roof support comes from charts or equations. GRSM defines suggested roof support densities by linking a rock-mass classification with an index of mining-induced stress, using a large empirical database of Bowen Basin mining experience. Inherent in the development of GRSM is a rock-mass classification scheme applicable to coal measure strata. Coal mine roof rating (CMRR) is an established and robust coal industry standard, while the geological strength index (GSI) may also be used to determine rock-mass geomechanical properties. An elastic three-dimensional numerical model was established to calculate an index of mining induced stress, for both roadway development and longwall retreat. Equations to calculate stress index derived from the numerical modelling have been developed. An industry standard method of quantifying roof support is adopted as a base template (GRSUP). The statistical analyses indicated that an improved quantification of installed support can be gained by simple modifications to the standard formulation of GRSUP. The position of the mathematically determined stable/failed boundary in the design charts can be changed depending on design criteria and specified risk.     

肋环型索穹顶初始预应力分布的快速计算法

肋环型索穹顶是美国工程师Geiger根据Fuller的张拉整体结构思想开发的一种新型预张力结构，并最早应用在汉城奥运会的体操馆和击剑馆。考虑到该结构是一种轴对称结构，本文提出了确定初始预应力分布的快速计算法．该法从平面径向桁架节点平衡关系入手，推导了不设和设有内拉环的肋环型索穹顶预应力杆内力一般性的计算公式．对特定参数的索穹顶结构还给出了内力计算用表．通过本文提供的分析方法、计算公式和内力计算用表，可方便快速的确定肋环型索穹顶结构的初始预应力分布，为该类结构的进一步设计和力学性能分析提供基础．     

A fracture-mechanics-based design method for SFRC tunnel linings

The current design provision on the estimation of the load carrying capacity of steel-fiber-reinforced concrete (SFRC) tunnel lining is briefly introduced. The design method is based on the concept of fracture mechanics of concrete. Existence of a crack and transmitted stress by fibers are considered in the estimation of the maximum resultant forces of the critical cross section. In this study, the validity of the current design method is verified, and the possible improvements of the design method are proposed. It is shown that the crack length at the maximum load depends on the specimen size and the fiber property. The source of the size effect which appears between a small specimen for the material test and the actual lining is the dependence of the crack lenght at the peak on the specimen size. The dependence of the critical crack length on the fiber property is not considered in the current design. It should be taken into account for the quality control of the fibers. Methods to determine the tensile strength carried by fibers and to estimate sectional capacities with various thickness of the lining and different kinds and volume fractions of fibers are proposed.     

A Bayesian method for establishing fatigue design curves

From a reliability viewpoint, the simple conventional procedure for establishing design S−N curves from laboratory fatigue test data suffers from two important limitations. Firstly, the calculated fatigue reliability on the design curve only reflects the observed “physical” uncertainty associated with the fatigue process itself. “Statistical” uncertainties, connected with estimating the parameters of the fatigue model, are not considered. Secondly, it is not possible to account for fatigue run-outs (non-failures) in a rational manner.A new procedure, based on Bayesian statistical inference, is presented which is capable of handling both the above problems. Its use is illustrated via the analysis of some typical fatigue data sets and a number of general points arising from the results are discussed.