Structural design of closely packed horseshoe-shaped sewer linings during installation

The paper describes the results of a numerical parametric study aimed at studying the structural response of closely packed horseshoe-shaped sewer linings. The effect of various restraint conditions which simulate different temporary support systems that may be used by the contractors during installation of the lining, and of different loading configurations which may arise at different stages of grouting the annulus gap between the lining and the sewer, have been thoroughly investigated. Covering the feasible range of geometric, material and loading parameters, comprehensive design curves — based on the allowable stress-limit, deflection-limit and (approximate) buckling criteria are presented.     

Structural sensitivity of circular sewer liners to geometrical imperfections

The impact of geometrical defects of liners on their structural performance has been examined in this article. The major common imperfections, such as gap, ovality and wavy imperfections, have been taken into consideration. In the first step, the influence of separate imperfections is presented. Then, the combination of coinciding defects is examined. The formula for weighted influence of individual defects has been found, based on a wide range of FEM calculations and statistical interpretation. All the examinations performed led to improving the general formula for critical groundwater pressure.     

Behavior and innovative design model on soil pressure at the top of large-diameter buried steel pipes

Existing design models of soil pressure at the top of buried steel pipes are limited to small-diameter pipes. This study aims to investigate the behavior and design model on the soil pressure for large-diameter pipes considering the pipe diameter, diameter-to-thickness ratio, and cover depth. The distribution and size of soil pressure are obtained from finite element models and compared with traditional design models. Sensitivity studies of soil parameters, trench parameters, and friction coefficients are discussed. Furthermore, an innovative design model of soil pressure for large-diameter pipes is proposed. The results indicate that the basic distribution pattern of soil pressure is the “inverted basin”/parabola for large/small-diameter pipes, respectively. Peak soil pressure typically appears in the pleura of pipes with great flexibility and deep cover depth. The modulus and Poisson's ratio of backfill and soil-soil friction coefficient have an influence range of within 10% for soil pressure, while trench parameters have a more significant influence. Prism load is too large at high cover depth, and Marston load is small at low cover depth. The proposed basin model for soil pressure adopts the form of “straight line + parabola” for distribution and “Marston + pleura” load for size, with high accuracy and strong adaptability.     

A retrospective evaluation of the performance of liner systems used to rehabilitate municipal gravity sewers

This paper provides new results gathered as part of a 6-year project funded by the U.S. Environmental Protection Agency (USEPA) to document the in-service performance of trenchless pipe rehabilitation techniques. The results from a pilot study focusing on cured-in-place pipe (CIPP) rehabilitation technologies were previously reported and the research program was extended to allow collection of additional CIPP samples and also to extend the study to other rehabilitation technologies (specifically included in this Phase 2 research were fold-and-form, deform–reform, and sliplining technologies). The establishment of a database to house performance evaluation data for rehabilitation technologies used in the water and wastewater sectors is also described. The additional retrospective data for CIPP and other rehabilitation technologies are reported and an overall assessment of CIPP life cycle performance is provided. The examination of CIPP liners with up to 34 years in service and other rehabilitation technologies with up to 19 years of service has shown that all of the rehabilitation technologies are showing little evidence of deterioration in service. The test results for 18 CIPP samples from nine cities across North America indicate that properly designed and installed CIPP liners should meet and likely exceed the typical 50-year expected design life. For the fold-and-form, deform–reform, and sliplining technologies, there are only two to three samples per rehabilitation technology and hence less can be said about overall performance. Nevertheless, all of the samples tested still met the material property requirements at installations after 14–19 years of service. In summary, the results provide an excellent prognosis for the rehabilitation technologies evaluated.     

Numerical investigation of channel columns with complex stiffeners—part II: parametric study and design

A parametric study of cold-formed steel channel columns with complex stiffeners is performed using finite element analysis. An accurate and reliable finite element model is used for the parametric study in which different sizes of complex stiffeners are investigated. Column strengths predicted by the finite element analysis are compared with the unfactored design column strengths calculated using the American Specification and the Australian/New Zealand Standard for cold-formed steel structures. It is shown that the design strengths obtained from the specification and standard are generally conservative for fixed-ended cold-formed steel channel columns with complex stiffeners for the more slender sections having a plate thickness of 1 mm with the flat flange width to thickness ratio of 57, but unconservative for sections having a plate thickness of 2 mm with the flat flange width to thickness ratio of 27.     

Folding of a plastic fibre under combined shear and compression

Large deflection of an elastic–plastic, nonlinear strain-hardening clamped-sliding beam subjected to a combined compression and shear load is solved analytically. The solution requires only numerical evaluation of integrals. Analytical expressions for applied force, deflection, bending moment, and strain energy are obtained. Numerical examples are given for a single stainless steel fibre of the hybrid stainless steel assembly (HSSA). The contact condition of the beam with end platens is determined. It is shown that the normalized effective crush distance ranges from 0.85 to 1.00, and depends only on loading angles and material hardening exponents. The crushing load has a maximum for the case with a small material hardening exponent and a small loading angle. It is found that no plastic unloading will occur before the beam contacts with the end platens. Finite element simulations are performed to verify the accuracy of the analytical solution, and a rather good agreement is obtained.     

Design of rectangular industrial duct plates subjected to out-of-plane pressure considering nonlinear large deformations

Large industrial steel ducts are often rectangular and are built-up of stiffened plates. The plates along with stiffeners act to resist the pressure loads and transfer these loads to the supports. Parallel wide flange steel profiles, usually beams, are used as transverse stiffeners that are spaced perpendicular to the longitudinal axis of duct. The design process involves determining the load carrying capacity and deflection of the plate based on the plate thickness and the spacing between stiffeners. The current analysis and design method for industrial ducts is based on the elastic large deflection plate theory using standard tables.A nonlinear finite element parametric study was conducted on dimensionless parameters to investigate the behavior of laterally loaded long plates. Through-thickness yielding of the plate and formation of partial plastic hinges at the ends is allowed. The results are presented in terms of a proposed dimensionless Normalized Load Factor (NLF) representing the applied pressure, the Normalized Deflection Factor (NDF) representing the out-of-plane deflection and the Normalized Maximum Stress Factor (NMSF) representing the maximum stresses induced in the plates. Design equations for deflection and stresses of plates are established with the aid of Bezier curves. A simple design procedure allowing for large deflection and partial yielding of edges is proposed. A limiting value for pressure has been found where it becomes irrelevant to check deflection. Results show that the proposed design procedure is simple and can lead to economic plate thicknesses and spacing of stiffeners in industrial ducts in ambient temperatures.     

An economic loss model for failure of sewer pipelines

Estimating the costs of failure for sewer pipelines is usually accompanied with uncertainties because of the difficulty in capturing the relationship between the physical and economical characteristics of failed pipelines. To reduce such uncertainties economic loss models are usually used to evaluate the consequences of failure. This paper presents a methodology to estimate economic loss as a result of sewer pipelines’ failure using cost benefit analysis approach. Costs of sewer pipelines’ failure in addition to costs resulting from avoiding such failures are identified and analysed. To validate the proposed methodology, actual costs from a real failure incident were compared with the proposed model outputs. The model could estimate the direct and indirect costs with a deviation ranging between 10–12% and 22–30%, respectively. By implementing the proposed methodology on two case studies, it was found that the indirect costs as a result of sewer pipelines’ failure represent a significant portion ranging between 89 and 94% of the total costs of failure. Also, it was found that costs related to environment, delays to work and traffic disruptions contribute by 12–35% to the indirect costs.     

Local buckling curves for the design of FRP profiles

Local buckling in FRP profiles is analyzed. Some experimental results in compression and bending, where local buckling of the flanges in compression occurred, are described and the critical stresses are summarized. A numerical model by the finite element method (FEM) is introduced and validated by comparison of the numerical results with the experimental ones. This finite element model is applied for a wide parametric analysis in order to individuate a buckling curve for the local buckling of the flange. An analytical expression of the buckling curve is developed, taking into consideration the orthotropy of the material, in which the restraint action of the web on the flange is explicitly introduced as a function of the geometrical and mechanical data of the section sub-components. The reliability of the proposed curve as a design tool is confirmed by comparison with the experimental results.     

The role of modelling in structural fire engineering design

This paper discusses structural fire engineering modelling, and how modelling techniques have allowed practicing engineers to learn lessons about global structural fire performance. Some of these lessons have been adopted in the design of new buildings, and some are also being fed-back into the design process to improve structural performance in fire and mitigate known structural vulnerabilities. The complexity of this modelling has permitted structures to be designed and lessons to be learned about whole frame behaviour in response to fire. This paper examines how the lessons learned from finite element modelling may be further disseminated to the structural engineering community through the creation of full frame design guidance. The benefits of this would be to improve the delivery of structural fire safety by increasing the impact of the discipline across structural engineering, while facilitating and encouraging the use of more in-depth structural fire models as appropriate.     

Design and shape optimization of a new type of hollow concrete masonry block using the finite element method

This study describes the development of a new type of hollow concrete masonry block unit in order to minimize its weight based on topological optimization and design of experiments (DOE). This key factor is the most important parameter in human and robotic block handling in masonry construction, due to the traditionally heavy weight of the blocks. With this aim, it was necessary to use the finite element method (FEM) to calculate the compressive resistance of the different concrete block designs and then to choose the optimum hollow block from the handling and structural points of view. The nonlinearity in this problem is due to the material behaviour of the concrete. In this way a combined mathematical model (Drucker-Praguer and Willam-Warnke material models) for concrete was implemented and solved using the FEM. The numerical results of the candidate blocks give rise to new solutions in masonry construction through the adequate redesign of the blocks. These new block designs are lighter, keeping the structural resistance and improving the block handling. Finally, conclusions of the study are given.     

异型楼板结构分析

本文采用有限元分析方法,对工程实例中三块异型板采用不同厚度时的受力状态进行比较,为异型板的设计提供依据。     

Large diameter shafts for underground infrastructure

The technique of large diameter shafts for deep excavations was analysed in terms of its basic construction elements, reported literature cases and design methods. The effects of the construction sequence and the geological deposition on the behaviour of the shaft was analysed using 3D finite element models. Induced stresses and displacements on the soil mass were investigated. Three methods to assess the stability of the shaft lining were presented and employed as a post-processing stage of analysis of the models. The results indicated a major influence of the height of the vertical excavation stages on the shaft behaviour, markedly on the induced settlements. The lining analysis also demonstrated the effects of the vertical excavation stages and how different safety assessment methods can produce significantly different results.     

Aerobic transformations of organic matters in sewer wastewater,a case study of Milan,Italy

Today, we know that not only the sewers carry urban wastewater, but also act as chemical and biological reactors, in which both organic and inorganic substances undergo significant transformations. This article describes a study on the western part of the sewer system of the city of Milan. The hydraulic model of the sewer system was coupled with the chemical and dynamic biological model to assess the extent of the degradation of organic matter in the network. The hydraulic and biological models were calibrated with real data obtained at the entrance of the wastewater treatment plant (WWTP) ‘Milan South’ and assuming standard values of daily per capita loads of COD and BOD₅.     

Non-linear analysis of unbolted base plates by the FEM and experimental validation

Unbolted base plates are often used in civil engineering as structural connections in storage racks construction. The aim of this work is to describe the development of a numerical model to simulate accurately the connection between columns and foundation in metallic structures, which constitute any frame in automated storage systems. In this way, the bending stiffness of the column can be modeled in the analysis of these structures, in order to approach the real behavior in service, and these values can be included in linear beams of structural analysis programs, such as ESCAL3D [del Coz Diaz JJ, Ordieres Mere B, Siare Dominguez FJ, Bello García A, Felgueros Fernández D. J Constr Res 1998; 46:273–5]. In this study, a non-linear structural behavior of the model occurs due to the changing status of the contact surfaces and point-to-point contacts, the geometric non-linearities of the model and the material non-linearities, such as plasticity and surface friction. The finite element method is a general technique for numerical solution of differential and integral equations in science and engineering. Thus the finite element approach has been carried out in two phases. Firstly, a pre-buckling analysis has been accomplished and secondly, the above-mentioned non-linear analysis has been performed, updating the geometry of the finite element model to the deformed configuration for the first mode buckling. A total of four load cases were analyzed, with different compressive load and imposed lateral displacement. In order to validate the results some experimental models were tested to compare with the numerical model, so that a good agreement and better correlations were obtained between both.     

The ponding problem on flat steel roof grids

Due to several reasons, a flat steel roof grid of industrial or commercial single-story buildings may be very flexible in the vertical direction. Due to its flexibility, a ponding effect can take place. The rainwater fills the space created by vertical deflection of the roof grid and this space increases under the gradually accumulated rainwater until equilibrium is reached.Ponding may be full or partial, and it is a self exciting phenomenon that can lead to grid instability. The problem is strongly non-linear, since the rainwater distribution on the roof grid in not known a priori.A closed form response to particular ponding cases and a simple grid geometry is achieved. Moreover, a non-linear finite element technique is presented in order to study the small/large deflection solution to the ponding problem of a complex flat steel roof grid.Finally, several steel roof grids are examined in order to illustrate the effect of precambering, grid dimensions and vertical flexibility on the ponding effect. The practical significance of a large deflection analysis for practical situations is also elucidated.     

Numerical investigation into the composite behaviour of over-deformed segmental tunnel linings strengthened by bonding steel plates

Bonding steel plate has been used as a strengthening approach to repair disrupted segmental lining of operational tunnels. This paper introduces numerical investigation into the composite behaviour of the initially deformed segmental tunnel linings strengthened by bonding steel plates using finite element modelling. Cohesive zone modelling was used to simulate the interface bonding behaviour between the segmental linings and steel plates. The full history of the tunnel behaviour before and after strengthening were simulated, where the segmental tunnel lining is initially loaded to create some deformation, then after bonding steel plate, the strengthened tunnel is reloaded until failure occurs. By comparing the results with experimental data from the literature, the proposed model was proved to be capable of simulating the strengthened lining behaviour and able to capture the strengthening failure process in terms of the interface debonding. Subsequently, the segmental lining response and interface shear stress distribution and propagation were analysed to interpret the interaction and failure mechanism of the steel plate strengthened segmental linings. The influence of the initial deformation and the steel plate thickness were investigated and discussed in terms of the strengthened stiffness and capacity. It has been found that the interface shear stress concentration occurred at the positions of the segment joints, where bond damage first initiated. The ultimate failure of the steel plate strengthening happened suddenly once a local debonding zone close to the segmental joint was formed. In addition, the predicted results indicate that a delay in strengthening would result in an increase in strengthened capacity but a decrease in strengthened stiffness. By using thicker steel plates, the strengthened stiffness was improved, while the strengthened capacity could be improved only if the thickness was relatively thin.     

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.     

深圳大运中心体育场钢屋盖设计难点与分析

深圳大运中心体育场钢屋盖采用单层折面空间网格结构,最大悬挑跨度68.4m,用20个球铰支座支撑,具有稳定问题突出、多项技术超规范设计特点.为了结构安全、经济,并具有良好抗风、抗震性能,通过计算分析,研究了结构找形和增设肩谷环梁前后的整体结构动力及静力性能、支座反力等.结果表明:结构体系稳定、安全;悬挑挠度限值的确定经济...     

超高龙门吊安装塔架结构系统的非线性静力分析

大型龙门吊安装塔架系统是应用于重型龙门吊安装过程中的一种索杆混合结构体系。在水平力作用下 ,体系非线性效应显著。为了比较全面的解决大型龙门吊安装塔架的非线性静力问题 ,文中给出了龙门吊安装塔架静力分析的经典力学法和非线性有限元法。前者首先建立了轴压悬臂柱的平衡微分方程 ,再联立纤绳方程 ,求解了柱顶位移和纤绳内力 ;后者通过一种非线性直线单元 ,建立了混合体系的增量平衡方程。最后分别用两种分析方法验算了体系横风、纵向顺风 ,两种工况 ,并比较了二者的柱顶位移和纤绳张力。结果表明 ,两种方法都是可靠的