锚杆系统动测信号的特征分析

利用实验室锚杆模型试验所测得的信号,采用现代信号处理技术对信号进行时频分析,得到具体、精确的信号特征。信号的短时傅立叶变换可在相平面表达信号的强度大小,并且杆底反射信号比较明显,但不能反映缺陷处的反射信号。另外,锚杆缺陷越多,反射信号的能量也越大。通过Wigner-Ville分布计算和分析,可得到信号的能量在时间和频率中的分布情况,不同损伤的锚杆的反射能量是不同的。通过与完整锚杆信号相比较可以发现信号变化的大致位置及变化的程度。小波分析提供了更多关于锚杆锚固质量的特征信息,更适合于处理锚杆系统有损伤情况下动测波形的识别。     

冻土–桩动力相互作用模型试验系统研制

桩基础是冻土区大型结构物的主要基础型式，但目前学者对冻土环境中桩基动力特性的研究甚少。在比较分析国内外在该领域研究现状的基础上，设计了一套冻土–桩动力相互作用模型试验系统，主要包括动力加载系统性能参数的确定与设计、模型试验箱的设计与制冷效果分析、加载工作架的设计及其与试验箱的拼接等。试验结果表明，所设计的试验系统能为试验提供所需的冻土环境，结构牢固，能较好地模拟分析冻土–桩动力性能，此外该试验系统还可应用于其他冻土问题的试验研究。     

Genetic programming for predictions of effectiveness of rolling dynamic compaction with dynamic cone penetrometer test results

Rolling dynamic compaction(RDC),which employs non-circular module towed behind a tractor,is an innovative soil compaction method that has proven to be successful in many ground improvement applications.RDC involves repeatedly delivering high-energy impact blows onto the ground surface,which improves soil density and thus soil strength and stiffness.However,there exists a lack of methods to predict the effectiveness of RDC in different ground conditions,which has become a major obstacle to its adoption.For this,in this context,a prediction model is developed based on linear genetic programming(LGP),which is one of the common approaches in application of artificial intelligence for nonlinear forecasting.The model is based on in situ density-related data in terms of dynamic cone penetrometer(DCP)results obtained from several projects that have employed the 4-sided,8-t impact roller(BH-1300).It is shown that the model is accurate and reliable over a range of soil types.Furthermore,a series of parametric studies confirms its robustness in generalizing data.In addition,the results of the comparative study indicate that the optimal LGP model has a better predictive performance than the existing artificial neural network(ANN)model developed earlier by the authors.     

端锚式锚杆-围岩耦合流变模型研究

针对端锚式锚杆-围岩结构体在长时条件下支护作用的演化机制,建立了端锚式锚杆-隧洞围岩耦合作用的结构模型。进行了结构模型的基本假设：①圆形隧洞;②深埋;③各向等压原岩应力;④均质且各向同性黏弹性围岩模型;⑤一维黏弹性锚杆模型;⑥锚杆对围岩作用力整体为面力。基于基本假设建立了端锚式锚杆-围岩耦合流变理论模型。假设围岩和锚杆均为Maxwell模型时,求解了圆形隧洞围岩应力和位移的径向分布随时间变化的解析解,获得了锚杆轴力随时间演变的理论公式。基于锚杆（索）流变模型,进行了FLAC^3D数值模拟软件的二次开发;并通过数值模拟与理论计算的对比分析验证了理论模型的合理性,分析了端锚式锚杆-围岩耦合流变规律及其影响因素。该模型对于研究地下隧洞的流变力学行为,分析锚固支护结构的长期稳定性,指导工程支护设计具有重要的基础理论价值。     

航空货运站波浪型螺栓球网架施工

介绍采用滑移脚手架安装螺栓球网架的施工方法 ,提出质量控制及施工实践中的几点体会     

Development of a dynamic model for estimating the food web transfer of chemicals in small aquatic ecosystems

A dynamic combined fate and food web model was developed to estimate the food web transfer of chemicals in small aquatic ecosystems (i.e. ponds). A novel feature of the modeling approach is that aquatic macrophytes (submerged aquatic vegetation) were included in the fate model and were also a food item in the food web model. The paper aims to investigate whether macrophytes are effective at mitigating chemical exposure and to compare the modeling approach developed here with previous modeling approaches recommended in the European Union (EU) guideline for risk assessment of pesticides. The model was used to estimate bioaccumulation of three hypothetical chemicals of varying hydrophobicity in a pond food web comprising 11 species. Three different macrophyte biomass densities were simulated in the model experiments to determine the influence of macrophytes on fate and bioaccumulation. Macrophytes were shown to have a significant effect on the fate and food web transfer of highly hydrophobic compounds with log K_OW > = 5. Modeled peak concentrations in biota were highest for the scenarios with the lowest macrophyte biomass density. The distribution and food web transfer of the hypothetical compound with the lowest hydrophobicity (log K_OW = 3) was not affected by the inclusion of aquatic macrophytes in the pond environment. For the three different hypothetical chemicals and at all macrophyte biomass densities, the maximum predicted concentrations in the top predator in the food web model were at least one order of magnitude lower than the values estimated using methods suggested in EU guidelines. The EU guideline thus provides a highly conservative estimate of risk. In our opinion, and subject to further model evaluation, a realistic assessment of dynamic food web transfer and risk can be obtained using the model presented here.     

Invisible elastic bolt model concept for finite element analysis of bolted connections

In accurate numerical modeling of bolted connections challenges are introduced due to the complexities encountered in meshing and providing non-conforming mesh for the exact modeling of bolt assemblages which may undermine the monotonic convergence in the solution algorithms. Thus, an elastic invisible bolt model is introduced to represent the bolt’s effect in the finite element modeling of bolted connections. The proposed algorithm assigns three degrees-of-freedoms (DOF) to each bolt’s end that include; one translational, in the bolt axial direction, and two rotational. Constraints are introduced for the DOF of the nodes in contact with the bolt head (or nut) such that they are permitted to move in the normal direction of the bolt based on the bolt elongation and end rotations. This introduces a variable-sized element stiffness matrix for the elements in contact with bolt ends. This bolt model is implemented in a general purpose cyclic plasticity-based finite element computer program, capable of predicting energy dissipation of bolted surfaces. Finally, the proposed algorithm is validated using a benchmark case and a sensitivity study on a hypothetical connection to ensure that the expected trend in energy dissipation is observed when geometric variables are varied.     

A model for the dynamic response of a cooling coil

The purpose of this study is to develop and evaluate simulation models for the dynamic performance of dry and wet cooling coils. The energy consumed by a building air conditioning system is directly related to that in the cooling coil. A dry-area model without consideration of condensation is established with three energy equations, and a wet-area model is developed based on a mass balance equation for moist air and three energy equations for the air, tube/fin, and working fluid. The derivatives with respect to the time variable are approximated using an explicit method, and the upwind approximation is used for the spatial variables. The results of the dry-area model show good agreement with those for the effectiveness method and the dynamic responses have reasonable physical meaning. The wet-area model is first compared to the dry-area model, and then the wet conditions are applied. A new factor called the mass transfer efficiency as a parallel to the total fin efficiency is introduced in the mass balance equation for the wet-area model to produce consistent results. The dynamic responses for several practical operations related to changing inlet conditions are reported. Comparisons indicate that the model predictions show good agreement with experimental data.     

锚杆支护技术发展现状与展望

对现有锚杆支护技术进行了介绍,分析了锚杆支护技术的支护机理、支护特点和存在的问题,对我国现阶段锚杆支护技术的发展现状进行了归纳总结,同时对未来锚杆支护的发展提出建议。     

混凝土无对拉螺栓模板加固工艺研究及应用

结合工程实例,介绍了汽轮发电机基础施工采用的大模板且混凝土无对拉螺栓的模板加固工艺,分别就支撑系统设计及施工过程控制措施作了说明,以期推广无对拉螺栓加固工艺的应用。     

Application of artificial neural networks for predicting the impact of rolling dynamic compaction using dynamic cone penetrometer test results

Rolling dynamic compaction (RDC), which involves the towing of a noncircular module, is now widespread and accepted among many other soil compaction methods. However, to date, there is no accurate method for reliable prediction of the densification of soil and the extent of ground improvement by means of RDC. This study presents the application of artificial neural networks (ANNs) for a priori prediction of the effectiveness of RDC. The models are trained with in situ dynamic cone penetration (DCP) test data obtained from previous civil projects associated with the 4-sided impact roller. The predictions from the ANN models are in good agreement with the measured field data, as indicated by the model correlation coefficient of approximately 0.8. It is concluded that the ANN models developed in this study can be successfully employed to provide more accurate prediction of the performance of the RDC on a range of soil types.     

Assessing subgrade strength using an instrumented dynamic cone penetrometer

Subgrade strength is an important aspect to be considered when designing unsurfaced roads and working platforms for pavement structures. Furthermore, dynamic cone penetration tests are used to characterize the subgrade strength. However, the results of dynamic cone penetration tests, including the penetration depth per blow, can be affected by transferred energy and the verticality of the cone penetrometer. The objective of this paper is to characterize the subgrade strength using an instrumented dynamic cone penetrometer (DCP). The instrumented DCP includes a load cell and an accelerometer, located on the cone tip, and measures the dynamic responses of force and velocity over elapsed time. Weathered soil is compacted with three different dry unit weights in a square-shaped container for lab-scale dynamic cone penetration tests. Using instrumented and standard DCPs, several dynamic cone penetration tests are performed, and the dynamic cone penetration index (DCPI) is recorded along the depth profiles. Based on the dynamic responses at the cone tip of the instrumented DCP and the principles of energy conservation, the dynamic cone resistance is suggested as a new strength index. The experimental results show that the dynamic cone resistance increases with the depth of the instrumented DCP, providing a reliable subgrade strength profile in the soil. In addition, the correlation between the DCPI obtained from the instrumented DCP and the dynamic cone resistance suggests that the dynamic cone resistance is more sensitive than the DCPI for stiff soil. Based on the correlation values of the dynamic cone resistance obtained from the instrumented DCP, the internal friction angle and California bearing ratio values can be estimated with a high degree of reliability. This study demonstrates that use of the instrumented DCP may be a promising in situ testing method for the reliable characterization of subgrade strength.     

动力荷载作用下固体材料本构模型研究的进展

在地震、爆炸、冲击等动力荷载作用下,材料的力学特性与准静态荷载作用下有本质的区别。在建筑结构抗震、抗爆设计规范中,常采用增大材料屈服强度（或极限强度）的方法来考虑材料的应变率效应,但是,该方法分析结果与实际情况有较大差别,所以,在对结构进行抗震、抗爆和抗冲击分析时,必须采用考虑应变率效应的本构模型。本文综述了国内外关于应变率（时间）效应有关的固体材料动态本构模型,对每种模型进行了简要分析,指出了其使用范围和优缺点,并根据现有的钢与混凝土材料的动力试验结果,提出了建立固体材料动态本构模型时应考虑的主要问题,对建筑结构的抗震、抗爆和抗冲击分析研究具有指导意义。     

动载作用下圆形巷道锚杆支护结构破坏机理研究

将冲击应力波进行合理简化,建立平面P波与圆形锚固巷道相互作用简化模型。结合算例,通过分析深部围岩径向应力、巷道表面切向应力、巷道表面径向位移以及深部围岩与巷道表面径向位移差等代表性指标,确定了重点支护位置,推导了重点支护位置的锚杆受力机制并提出了相应破坏类型及判据。结果表明:迎波侧与侧向位置是重点支护位置。迎波侧锚杆总应力是静载轴应力、锚杆振动的动应力和动载下围岩变形引起的附加应力的叠加,强冲击下迎波侧支护结构的破坏类型为单次瞬间摧垮破坏,围岩受压破裂,锚杆松动失去加固作用;循环弱冲击下的破坏类型为循环累积损伤破坏,受压围岩逐渐损伤致裂,锚杆反复受压、受拉直至松动,这进一步加剧围岩的损伤破裂,当承载拱强度降低到一定值后,一次小冲击就能诱发巷道冲击破坏。侧向位置锚杆总应力是静载轴应力、动载下围岩变形引起的附加应力的叠加,锚杆始终受拉,在强冲击下可能发生拉断破坏。通过相似模拟试验,较好地验证了理论分析结果,表明理论分析结果对工程实践具有一定的指导意义。     

裂隙岩体弹塑性损伤本构模型及其加锚计算(英文)

根据裂隙岩体的弹塑性损伤变形机制，建立了断续多裂隙岩体在初始损伤、损伤演化和塑性损伤变形状态下的三维弹塑性损伤本构关系。在此基础上，建立了空间损伤岩锚柱单元模型，模拟锚杆对断续裂隙岩体的支护效果。最后，将建立的模型应用于三峡船闸高边坡，进行了边坡加锚裂隙岩体三维非线性有限元计算，获得了较为满意的结果。     

Application of wave equation theory to improve dynamic cone penetration test for shallow soil characterisation

Among the geotechnical in situ tests,the dynamic penetration test(DPT)is commonly used around the world.However,DPT remains a rough technique and provides only one failure parameter:blow count or cone resistance.This paper presents an improvement of the dynamic cone penetration test(DCPT)for soil characterisation based on the wave equation theory.Implemented on an instrumented lightweight dynamic penetrometer driving with variable energy,the main process of the test involves the separation and reconstruction of the waves propagating in the rods after each blow and provides a dynamic cone load-penetration(DCLT)curve.An analytical methodology is used to analyse this curve and to estimate additional strength and deformation parameters of the soil:dynamic and pseudo-static cone resistances,deformation modulus and wave velocity.Tests carried out in the laboratory on different specimens(wood,concrete,sand and clay)in an experimental sand pit and in the field demonstrated that the resulting DCLT curve is reproducible,sensitive and reliable to the test conditions(rod length,driving energy,etc.)as well as to the soil properties(nature,density,etc.).Obtained results also showed that the method based on shock polar analysis makes it possible to evaluate mechanical impedance and wave velocity of soils,as demonstrated by the comparisons with cone penetration test(CPT)and shear wave velocity measurements made in the field.This technique improves the method and interpretation of DPT and provides reliable data for shallow foundation design.     

Automatic control of the activated sludge process—I. Development of a simplified dynamic model

A set of simplified dynamic models was developed for the activated sludge process (primary settler, biological reactor, and final settler). The models incorporate variable gains, variable time constants, and fixed dead times. Because the parameters may be easily evaluated on site, the models will be particularly useful for process analysis, control system design, and automatic control of a particular plant. Two different cases were studied; one for a plant in which the steady state concentration of suspended solids in the final effluent is directly proportional to the mixed liquor suspended solids, and one in which it is inversely proportional. Due to this difference in steady state gains the final performance of the system is quite different for the two cases although the dynamics are very similar. Therefore, care should be taken in characterizing the final settler.