Quantifying the accuracy of numerical collapse predictions for the design of submarine pressure hulls

An overview of current design practices for submarine pressure hulls is presented, along with the results of a survey of the literature that was conducted to determine standard nonlinear numerical modelling practices for those structures. The accuracies of the conventional submarine design formulae (SDF) and nonlinear numerical analyses for predicting pressure hull collapse are estimated by comparing predicted and experimental collapse loads from the literature. The conventional SDF are found to be accurate within approximately 20%, with 95% confidence, for intact pressure hulls. The accuracy of a wide range of nonlinear numerical methods, including axisymmetric finite difference and general shell finite element (FE) models, is found to be within approximately 16% with 95% confidence. The accuracy is found to be within 9% when only higher fidelity general shell FE models are considered. It is shown how the observations taken from the survey could serve as a starting point for establishing modelling guidelines, quantifying the accuracy of nonlinear FE analysis in pressure hull collapse calculations, and introducing this method into a design procedure by way of a partial safety factor.     

Sensitivity Study on Using Different Formulae for Calculating the Temperature of Insulated Steel Members in Natural Fires

The applicability of using different formulae for calculating the temperature of insulated steel members exposed to natural fires which include heating and cooling phases has been investigated. The widely referenced ‘Swedish’ fire curves and measured temperature time curves in real fire tests are adopted to represent different natural fire environments. Parameters including insulation thickness, section factor, and protection material are considered in sensitivity studies. The steel temperatures predicted by different formulae are compared with the numerical results predicted by FEM. Comparatively, the formula given by Chinese Code CECS200 gives best prediction of steel temperatures. Studies also show that the approach adopted by Eurocode 3 for avoiding the negative steel temperature increment at the early heating phase in standard fire should not be used for calculation in natural fires. The formula given by CECS200 is recommended as the most satisfactory formula for the temperature calculation of insulated steel members in natural fires.     

用应力矢量本构模型确定无粘性土的静止土压力系数

 利用将应力矢量的作用效应分解为球应力作用效应和应力比矢量作用效应叠加而建立的应力矢量本构模型,推出了无粘性土静止土压力系数的三个计算公式。验证结果证实了这些公式的适应性。     

Buckling of cylindrical shells under transverse shear

This work concerns with experimental studies on buckling of thin-walled circular cylindrical shells under transverse shear. The buckling loads are also obtained from finite element models, empirical formulae and codes and are compared. Experiments are conducted on 12 models made of stainless steel by rolling and longitudinal seam welding. In situ initial geometric imperfection surveys are carried out. The tests are conducted with and without axial constraint at the point diametrically opposite the loading. Theoretical analyses are carried out using ABAQUS finite element code. Two finite element models considered are: (i) geometry with real imperfection (FES-I) and (ii) critical mode imperfect geometry (FES-II). In the former, the imperfections are imposed at all nodes and in the latter, the imperfection is imposed by renormalizing the eigen mode, using the maximum measured imperfection. General nonlinear option is employed in both the cases for estimating the buckling load. Galletly and Blachut’s expressions, design guidelines of Japan for LMFBR main vessel expressions (empirical formulae), ASME and aerospace structural design codes are used for comparing with experimental loads.The comparisons of experimental, numerical and analytical buckling loads reveal the following. The numerical results are always higher than the experimental values; the percentage difference depends on the wall thickness. FES-II predicts somewhat a lower load than that of the FES-I. The Japanese guidelines predict the lowest load, which is conservative. Experimental loads are lower than that predicted by both ASME and aerospace structural design codes.     

钢-混凝土组合梁在单调荷载下的变形及延性

采用栓钉等柔性抗剪连接件的钢－混凝土组合梁具有良好的延性，是组合梁按简化塑性理论方法设计的前提条件，也是为了保证组合结构在地震作用下具有良好的耗能性能。钢－混凝土简支组合梁的延性在一定的程度上受到剪力连接程度和横向配筋率的影响，本文通过对１２根梁的试验研究和对一些国内外组合梁试验结果的分析，建立了截面屈服曲率和极限曲率及等效塑性铰长度计算公式，根据这些公式得到的组合梁屈服挠度和极限挠度计算值与实测结果吻合良好。试验和分析结果表明，组合梁的延性指标要高于混凝土梁。     

A new analysis of the strength of some simple fillet welded connections

The strength of some simple fillet welded connections is investigated. The connections considered are those made using (a) tension fillet welds, (b) shear fillet welds, and (c) a combination of types (a) and (b), the welds having equal leg lengths. The strength of the welds is determined as a function of the weld geometry and the ultimate tensile strength of the weld metal by considering the forces acting on the welds. The sets of forces for which the welds are analysed are not the actual ones present but they are ‘equivalent’ to the actual forces. The effect of longitudinal residual stresses, which are locked into the weld metal when the weld is deposited, is allowed for. The predictions of the various strength formulae developed are compared with experimental results published by other workers and agreement between the theoretical and experimental results is found to be reasonable. The strength formulae turn out to be so simple that they could easily be used in design. The effect of unequal leg lengths on the strength of the welds is investigated and it is shown that the strength of tension fillet welds is markedly affected by the shape of the weld cross-section. The way in which the proposed method can be applied to more complex loading conditions is described and an example is given to show that the predictions of the method are in reasonable agreement with experimental results.     

Tests and design of concrete-filled elliptical hollow section stub columns

Similar to concrete-filled tubular columns, void-filling of elliptical hollow sections (EHS) will produce increased strength, stiffness, energy absorption and fire resistance. Stub column tests on unfilled EHS were performed first. Discussions are made on the equivalent diameters in the literature for deriving the yield slenderness limit. An equivalent rectangular hollow sections (RHS) is proposed to derive such a limit for EHS sections in axial compression. An experimental investigation has also been carried out on the behaviour of concrete-filled EHS stub columns. Both normal concrete and self consolidating concrete (SCC) were used in the testing program. Different loading methods were investigated; e.g., loading through steel alone, loading through concrete alone and loading through the whole cross-section. This paper is based on experimental data on carbon steel EHS with an aspect ratio of 2, which is also the only product type currently produced. The load carrying capacity is compared with that predicted using EC4 and CAN/CSA-S16. Proposed design formulae are given.     

Tests and calculations for hollow structural steel (HSS) stub columns filled with self-consolidating concrete (SCC)

The behaviour of self-consolidating concrete (SCC) filled hollow structural steel (HSS) stub columns subjected to an axial load was investigated experimentally. A total of 50 specimens were tested. The main parameters varied in the tests are: (1) sectional types: circular and square; (2) steel yielding strength: from 282 to 404 MPa; and (3) tube diameter or width to wall thickness ratio (D/t or B/t): from 30 to 134.A mechanics model is developed in this paper for concrete-filled HSS stub columns. A unified theory is described whereby a confinement factor (ξ) is introduced to describe the composite action of the steel tube and the filled concrete. The predicted load versus deformation relationship was in good agreement with test results. The theoretical model was used to investigate the influence of important parameters that determine the ultimate strength of the composite columns. The parametric and experimental studies provide information for the development of formulae for the calculation of the ultimate strength and the axial load versus axial strain curves of the composite columns. Comparisons are made with predicted stub column strengths using the existing codes, such as ACI-1999, AISC-LRFD-1999, AIJ-1997, BS5400-1979 and EC4-1994.     

Prediction of compressed air leakage from tunnels

Adoption of a tunnel pressure, and the required volume of air to maintain that pressure, are currently based on judgment or empirical formulae. The risks associated with leakage of air from tunnels are not addressed by these methods. Such risks include surface settlement, uplift of structures, and development of air paths to other structures and excavations. A principal reason for these shortfalls is that the path and zone of influence of the air leakage cannot be predicted. In view of the paucity of scientific guidance for predicting these, a numerical model has been developed that simulates the consequences of using compressed air in soils. The model uses the program ABAQUS in an iterative scheme by updating the data for subsequent steps until convergence is reached and the final steady-state equilibrium is obtained. This model is compared to available empirical methods for a simple two-dimensional case.     

基于土拱效应的墙背非极限主动土压力

根据平移模式下的微元滑裂体水平面上的剪力为零的条件和土拱效应,获得受填土内摩擦角和墙土摩擦角影响的非极限滑裂面倾角和非极限主动土压力系数,其中,非极限填土内摩擦角和墙土摩擦角是墙体位移的函数。根据非极限水平微元滑裂体的静力平衡,得到平移模式下考虑土拱效应和位移影响的非极限主动土压力计算式。参数影响分析表明:非极限滑裂面倾角和非极限主动土压力系数均随非极限墙土摩擦角的增大而增大;非极限主动土压力系数和非极限主动土压力均随侧向位移比的增大而减小;非极限主动土压力分别随着非极限填土内摩擦角、非极限墙土摩擦角的增大而减小。理论值及试验值的对比结果显示:相较于其他方法,本文方法的非极限主动土压力理论值与试验值吻合更好。     

等向强化–软化Drucker-Prager材料强度参数演化

Drucker-Prager屈服准则中压力相关系数α和黏聚剪切强度k的实测结果少有报道。根据同一组致密砂岩三轴压缩试验,同时测试Mohr-Coulomb准则中的内摩擦角φ和黏聚力c以及Drucker-Prager准则中的压力相关系数α和黏聚剪切强度k。测试结果显示,描述岩石内摩擦性质的参数φ和α随着塑性变形的增长而增长,但是增长速率逐渐减小;描述岩石胶结性质的参数c和k在岩石初始屈服后会先上升至峰值,然后随着塑性变形的增长从峰值逐渐下降。同时,从5种常用的Mohr-Coulomb准则与Drucker-Prager准则转换关系中,通过同一组三轴压缩试验结果寻找到吻合程度最高的换算关系。Drucker-Prager材料强度参数的变化将来可应用到岩土类材料的数值计算中来模拟材料的强化和软化性质,同时也可以为Mohr-Coulomb准则参数与Drucker-Prager准则参数转换提供一定参考。     

钢-混凝土组合梁截面组合抗剪性能的试验研究

对4根密实截面钢-混凝土组合梁的组合抗剪性能进行了试验研究。试件全部采用简支,跨中两点对称单调静力加载,考虑抗剪连接程度及正负弯矩的影响。试验结果表明,组合梁负弯矩区的界面滑移规律与正弯矩区的不同,其大小对组合梁的抗剪承载能力影响较小。不论混凝土翼板是处于组合梁截面的受压区还是受拉区,其对组合梁截面的抗剪承载能力均有明显的贡献,目前规范仅计算钢梁腹板的抗剪作用偏于保守。按叠加法建立了计算组合梁抗剪承载能力的计算式,计算值与实测值吻合良好。     

基于广义SMP准则的软基路堤临界填土高度研究

针对路堤填土自重作用下的平面应变天然软土地基,基于能合理反映中间主应力效应的广义SMP准则,同时考虑地基软土的侧压力系数和固结程度,建立了软土地基临界荷载与路堤临界填土高度的解析公式,并给出公式适用条件,最后结合M–C准则解答探讨了各参数的影响特性。经与文献结果比较,验证了解析公式的正确性及所给公式适用条件的必要性。参数分析表明:固结度、侧压力系数、黏聚力及内摩擦角对路堤临界填土高度的影响均很显著,不应盲目选定固结度为0或100%进行计算;M–C准则的结果偏保守,考虑中间主应力所得解答的最小侧压力系数更小、公式适用范围更广;应原位测定地基软土的真实侧压力系数,并充分考虑其抗剪强度参数的变异性。     

Numerical simulation of pressure changes in closed chamber fires

Pressure rising in closed chamber fires will be studied numerically in this paper with Computational Fluid Dynamics (CFD). The Fire Dynamics Simulator (FDS) developed at the National Institute of Standards and Technology (NIST) in USA is taken as the simulation tool. Experiments on closed chamber fires were reported in the literature by the Defence Research Establishment (FoA) in Sweden. Scenarios similar to those in that experimental study were taken as examples for simulation. Air flow pattern, pressure and temperature distribution are predicted. Functional analysis is used to compare predicted values with experiments. This gives some indication on how good CFD can be when applied for studying closed chamber fires. It is observed that input heat release rate to FDS is a key point. Predicted results on air velocities, temperature and pressure agree reasonably well with experimental results. Care should be taken in applying the fast reaction mixture fraction combustion model for simulating under-ventilated fires.     

FE analysis of time-dependent behavior of tunneling in squeezing ground using two different creep models

Ground movement and contact pressure on the lining of Stillwater Tunnel (Utah, USA) were investigated. Axisymmetirc finite element analysis was used in the analysis. Power law and hyperbolic creep models were used to model ground squeezing and to show the differences in the results between the two models. Creep parameters for the two models were evaluated based on the experimental creep and strength tests that were performed by other investigators on the gouge materials encountered along the tunnel axis through the heavily sheared and fault zones of the Red Pine shale. The results of the analysis which include normalized inward movement at the tunnel crown, normalized radial ground convergence with depth, and lining-ground contact pressure were compared with the results that were measured along the tunnel axis by other investigators. The results of the analysis show that lining pressure and deformation can be predicted well from the use of power law creep model if the delay time before lining erection is considered.     

地基土工实验数据的随机-模糊统计原理及方法

将模糊数学及随机统计理论相结合，给出了地基土工实验数据的随机-模糊统计原理，导出了一系列计算公式，证明了随机统计公式是本文导出的随机-模糊统计公式的一种特例，算例验证了本文提出的统计方法的正确可行性。计算结果表明，随机-模糊统计方法更切合实际并优于传统的方法。     

Equivalent Mohr–Coulomb and generalized Hoek–Brown strength parameters for supported axisymmetric tunnels in plastic or brittle rock

The evaluation of equivalent Mohr–Coulomb (M–C) strength parameters to the prototype Hoek–Brown (H–B) ones for tunnels has been tackled in different ways for many years. The extension of the H–B criterion to the generalized one has made the challenge even greater. Most of the latest methods did not account for the effect of the support pressure and none gave formulae for equivalent parameters of supported or brittle rock. Here, an almost exact explicit solution for the evaluation of the critical pressure, of a tunnel in a rock mass satisfying the generalized H–B criterion, is initially investigated. Then, formulae are derived for the evaluation of equivalent parameters, of either elastoplastic or elastic–brittle plastic rock. They are based either on a best fitting procedure of the two envelopes or on the equation of selected responses of the models. Supported tunnels in equivalent M–C rock masses are then validated against those excavated in the prototype H–B rock masses.     

Wind-tunnel-wall constraint on two-dimensional rectangular-section prisms

The effect of wall constraint on rectangular-section prisms is investigated experimentally in a low-turbulence wind tunnel up to a blockage ratio of 0.25. The depth to width ratio ($\text{d}\text{h}$) of the sections varies from 0.5 to 5.0.It is shown that the effect of confinement on the mean surface pressure on the models is not uniform in the streamwise direction and therefore cannot be regarded as an increase in the effective dynamic pressure estimated from drag or base pressure measurements as assumed by some investigators. The current bluff-body blockage correction formulae are found to be inadequate for correcting the drag and base pressure for these sections, particularly at large blockage ratios. A new equation, which is a modification of Maskell's equation and includes a shape factor to allow for the depth of the rectangular section, yields satisfactorily corrected drag and base pressure. Due to the large depth of the sections in the stream direction, corrections to the pressure distribution around them for blockage using this equation, are not very satisfactory. The correction for the Strouhal number using the new equation is valid up to $\text{d}\text{h}\text{= 3.0}$.     

Numerical studies on atrium smoke movement and control with validation by field tests

Many computer fire models were developed in the literature with the rapid advancement of information technology. With the possibility of implementing engineering performance-based fire codes, fire models are used frequently in hazard assessment. Among the different approaches, fire field models using the technique of computational fluid dynamics (CFD) are widely used. The approach takes the advantage of predicting the fire environment in a ‘microscopic’ picture. Air flow pattern, pressure and temperature contours can be predicted. However, it is not easy to validate the CFD predicted results. Most of the field models are only validated by some experiments not specially designed for such purpose. There are very few studies on comparison with field measurements in actual sites. Whether those models are suitable for use are queried, leading to challenges. In this paper, the CFD tool fire dynamics simulator developed at the National Institute of Standards and Technology in USA will be applied to study atrium fires. Smoke layer interface height and air temperatures inside the atrium are simulated. The experimental data on atrium hot smoke tests carried out recently was used. CFD results predicted can be validated by comparing with the experimental results.     

浅圆仓贮料压力计算公式

给出一组大直径浅圆仓贮料侧压力的计算公式 ,并推导或解释之。此组公式已被中华人民共和国国家标准《钢筋混凝土筒仓设计规范》(GB 5 0 0 77 2 0 0 3)采用。