Aligned carbon nanotube based ultrasonic microtransducers for durability monitoring in civil engineering

Structural health monitoring of porous materials such as concrete is becoming a major component in our resource-limited economy, as it conditions durable exploitation of existing facilities. Durability in porous materials depends on nanoscale features which need to be monitored in situ with nanometric resolution. To address this problem, we put forward an approach based on the development of a new nanosensor, namely a capacitive micrometric ultrasonic transducer whose vibrating membrane is made of aligned single-walled carbon nanotubes (SWNT). Such sensors are meant to be embedded in large numbers within a porous material in order to provide information on its durability by monitoring in situ neighboring individual micropores. In the present paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated well-aligned, ultra-thin, dense SWNT membranes that show above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz.     

Environmental durability of adhesively bonded FRP/steel joints in civil engineering applications: State of the art

Over the past three decades, the strengthening and repair of existing civil engineering structures using FRP laminates has attracted a great deal of attention. With the advances in polymer science, adhesive bonding has become a common joining technology in these applications. Despite numerous studies that address the short-term behaviour of adhesively bonded FRP/steel joints, uncertainty with respect to long-term performance still remains. This knowledge gap is regarded as a critical barrier, hindering the widespread application of FRPs to strengthen and retrofit steel structures. This paper presents the state of the art in terms of the durability of FRP/steel joints used in civil engineering applications. Important influential factors relating to the durability of adhesively bonded joints are reviewed and different damage mechanisms are discussed. Moreover, related investigations of the combined environmental durability of these joints are critically reviewed and the findings are presented. The paper concludes with a discussion to motivate future research topics, while it is emphasised that the generalisation of the available results is questionable.     

Strain gauge installation in a civil engineering site

Installurion of resistance strain gauges is described for field tests under conditions of high humidity and in water in the intake area of a water power plant in New Zealand.     

Automated manufacture of composites: handling,measurement of properties and lay-up simulations

This paper presents some issues relevant to the automated manufacture of low-cost composites. The process of cutting fabric panels from broadcloth and assembling individual pieces had its origins in the clothing industry. The paper investigates the advances made, and the problems encountered in clothing automation projects during the 1980s, with a view to adopting some of the relevant techniques for composites manufacture. Laminate materials, either in the form of prepregs or dry fabrics, exhibit highly non-linear and large deformation behaviour. Hence, a key step towards full-scale automation is the accurate prediction of handling and subsequent processing behaviour of the preforms, with the aid of numerical simulations. The paper describes some automated test methods for measuring the non-linear material properties, required as constitutive properties for simulations. Because of the variety and variability of the preform mechanical properties, rapid and accurate measurements are necessary. A commercial robot has been adopted to conduct a series of tests on dry laminate materials. The tests include intra-ply shear, transverse compression, tension, bending and inter-ply shear. Process simulations such as laying-up, fabric folding and draping have been conducted, based on the measured properties.     

An experimental investigation on the low velocity impact response of composite plates repaired by VARIM and hand lay-up processes

This paper presents results of an experimental investigation on the impact response of repaired and unrepaired glass/epoxy composite plates. Repaired samples were prepared by two different manufacturing methods; vacuum assisted resin infusion process and hand lay-up technique. In order to compare impact response of the repaired and unrepaired samples a number of single impact tests were performed under various impact energies. Damage process of the samples is analyzed from cross-examining load–deflection curves and damaged specimens. From the visual inspection, for the impacted side of the samples, it is noted that the main damage modes for repaired samples are matrix and fiber cracks around point of impact and delaminations while severe matrix cracks expanded through fiber directions are the dominant damage mode for unrepaired samples. At the back surfaces, delaminations and fiber–matrix debonding oriented in the fiber directions are observed for unrepaired samples. However, for repaired samples the fiber fractures through repair line as well as the delaminations become dominant modes. For a reasoning justification in discussing impact test results, interlaminar fracture toughness (Mode I and Mode II) and flexural tests for repaired and non-repaired samples were also conducted.     

Toward a probabilistic design of reinforced concrete durability: application to a marine environment

This work aims to propose a complete design methodology for concrete durability problems based on a probabilistic method including an original chloride diffusion modelling compatible with the new performance-based approaches. This is illustrated by the study of a concrete immersed in sea water. The physical and chemical processes that lead to the corrosion of the concrete reinforcement bars are presented first. A chloride penetration model based on Fick’s second law is proposed. Next, the durability modelling parameters chosen among the durability indicators (Baroghel-Bouny, Concrete design for structures with predefined service life—durability control with respect to reinforcement corrosion and alkali–silica reaction, 2004; Alexander et al., Mater Struct 41:921–936, 2008) are assessed. They depend on the concrete formulation and the chemical composition of the cement. These indicators are characterized by their statistical distributions, which are realistically specified from a wide literature review. The whole probabilistic modelling is included in a Bayesian network so that it can be easily updated to include new experimental data. The evaluation of the time dependant corrosion risk is estimated for two types of cement: CEM I and CEM I with silica fume. The result shows the effect on the Lind–Hasofer reliability index of the type of cement, the concrete quality and the design options. The quality is integrated through the mean value and the standard deviation of the modelling parameters. The method could be used either directly for cover design or for semi-probabilistic design code calibration.     

Uncertainty management in a process environment

Abstract

Software systems are developed by software projects. A software project generally associates with a process (software development process). A software project's process can be managed by process‐centered software engineering environments (PSEEs). In other words, PSEEs facilitate monitoring software projects. When a software project is being executed, many details may be uncertain in the early phases of the project. Therefore, managing uncertainty of a project's process becomes necessary. We identified existing approaches that can manage process uncertainty. Nevertheless, existing approaches suffer from drawbacks such as resource wasting. We thus propose two new approaches, which are pre‐defined semantics and incremental process program development. The former approach prevents duplicating the same code in a process program and the latter handles both predictable and unpredictable process uncertainty. This paper primarily presents the new approaches.     

Product design in a concurrent engineering environment: an optimization approach

In this paper an optimization approach to the design of products in a concurrent engineering environment is explored. A five-step algorithm containing attribute-based utility values is utilized which allows for the incorporation of concurrent engineering design attributes in the objective function. Two integer programming models are presented. Model 1 considers module/part interactions; however, it does not consider the interactions among various part options making up a product. Model 2 considers both interactions and also results in groups of part options that can be designed and manufactured together. In each step of the optimization process, the design of a pad assembly of a braking system is considered and explained.     

Theory and application of ground freezing in civil engineering

The mechanical behavior of frozen soil is described with respect to failure conditions and related to the influence of time and temperature. It is shown how these data are used in analytical and numerical design procedures. In a similar way the thermal calculation for the build-up of a frozen soil body is described and the necessary data on thermal soil properties are given. The paper also contains case histories, and a few details of the practical application of the ground freezing technique is discussed.     

Risk assessment for civil engineering facilities: critical overview and discussion

The present paper should be seen as a basis for discussion of important aspects of risk analysis and assessment, as well as attempting to describe risk assessment in accordance with the present state of the art. Risk assessment is thus presented in an overview form from the viewpoint of being a means for decision-making and thus within the formal framework of decision theory. First the motivation for risk analysis is given and the theoretical basis together with the practical aspects, methodologies and techniques for the implementation of risk assessment in civil engineering applications are explained and discussed. The paper furthermore addresses the problems associated with risk acceptance criteria, risk aversion and value of human life and attempts to provide suggestions for the rational treatment of these aspects. Finally a number of problem areas are highlighted and the needs for further education, research and dissemination are stressed.     

Concurrent engineering in a high variety label printing environment

Here an attempt is made to use the principles of concurrent engineering in high variety label printing industry. The existing approach to label printing in the company is basically what is known as serial engineering approach. This approach leads to serious problems of high levels of work-in-process and increased requirements of cutter capacity. We attempt to make a case for the application of concurrent engineering by introducing the multifunctional team concept at the design stage which helps reduce WIP inventory as well as the cutting capacity requirements. For this purpose we develop a heuristic algorithm. The concurrent engineering approach and the algorithm are illustrated by an example.     

Managing a deteriorating process in a batch production environment

When manufacturing processes have a tendency to deteriorate over time and begin producing defective products, there is always a trade-off between the cost and/or rework time that is associated with such defectives and the amount of time that is spent inspecting and restoring the process. Although a considerable amount of attention has been devoted to this trade-off as it is found in high-volume, repetitive manufacturing, we study it in a job shop environment. In particular, we study the way in which inter-job setups affect the inspection policy. After modeling the problem as one of maximizing the throughput of defective-free jobs, we describe a simple algorithm which identifies optimal inspection intervals.     

FBG智能传感器及其在土木工程中的应用研究

光纤光栅传感器已经越来越得到土木工程界的认可,并应用到了实际工程.针对大型土木工程结构长期健康监测的变形监测需要,在光纤光栅传输理论的基础上,分析了光纤光栅应变与温度传感特性以及光纤光栅应变传感的温度补偿原理和方法;研制开发出满足工程应用的光纤光栅封装传感器、FRP-OFBG复合智能筋、光纤光栅智能拉索;此外,考虑传感器开发和工程应用的需要,研究了光纤光栅应变传感的界面传递机理和误差修正.最后,建立了光纤光栅智能监测系统,并成功地将光纤光栅传感器应用到实际桥梁结构的施工与运营监测.     

Compression behaviour of non-industrial materials in civil engineering by three scale experiments: the case of rammed earth

In order to give an example of a scientific approach adapted to non-industrial materials, we chose to study a structural element: a load-bearing building wall made of rammed earth material. Rammed earth construction is an ancient technique which is attracting renewed interest throughout the world today. Although rammed earth is currently regarded as a promising material in the construction sector in the context of sustainable development, it is still difficult to quantify its durability, as well as its thermal and mechanical performances, which discourages people from using it. This paper is devoted to the study of the last problem. Three different scales were studied. The first is the scale of in-situ walls. Dynamic measurements were carried out on site to determine the Eigen frequencies of the walls. The elastic modulus was determined from the frequencies measured by using a finite element model. The second is the scale of a representative volume element (RVE). Rammed earth RVE samples with dimensions similar to those of the walls on site were manufactured and tested in the laboratory. Finally, at the last scale, called the micro-mechanical scale, tests were performed on equivalent compressed earth blocks (CEBs), which can replace the rammed earth RVE samples to facilitate laboratory tests.     

N silicon solar cells emitters realized using phosphoric acid as doping source in a spray process

The spray technique is used to realize the n⁺ emitter from phosphoric acid H₃PO₄ as a doping source. Emulsions have been prepared using several organic solvents. It was found that H₃PO₄:2-butanol mixture provides the most uniform deposited layer. The sheet resistance and the n⁺ profile were measured with a four point probe and the Hall profiling, respectively. The variety of emitters obtained are characterized by a sheet resistance ranging from 10 to 86 Ω/□ and a junction depth of about 0.2 to 0.7 μm which can be adequate for emitters in a polycrystalline silicon solar cell process.