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The probabilistic modelling of deterioration in the time-dependent reliability analysis is a necessary step for developing a risk-based approach to the life cycle management of infrastructure systems. The decisions regarding the time and frequency of inspection, maintenance and replacement are confounded by sampling and temporal uncertainties associated with the deterioration of structural resistance. To account for these uncertainties, probabilistic models of deterioration have been developed under two broad categories, namely the random variable model and stochastic process model. The paper presents a conceptual exposition of these two models and highlights their profound implications to the age-based and condition-based preventive maintenances policies. The proposed stochastic gamma process model of deterioration is more versatile than the random rate model commonly used in the structural reliability literature. [ABSTRACT FROM AUTHOR]

The moment Lyapunov exponents are important characteristic numbers for determining the dynamical stability of stochastic systems. Monte Carlo simulations are complement to the approximate analytical methods in the determination of the moment Lyapunov exponents. They also provide criteria on assessing how accurate the approximate analytical methods are. For stochastic dynamical systems described by Itô stochastic differential equations, the solutions are diffusion processes and their variances may increase with time of simulation. Due to the large variances of the solutions and round-off errors, bias errors in the simulation of momemt Lyapunov exponents are significant in the cases of improper numerical approaches. The improved estimation for some systems is presented in this paper. [ABSTRACT FROM AUTHOR]

Centering on worldwidly present urban areas, there have been many high-rise landmark buildings constructed in recent years. It is recognized that reinforced concrete has merit over steel frame construction in high-rise buildings, such as less sway in high winds, better human life protection in case of accidental heavy damage, better noise resistance. The use of high-strength concrete is rising, not only for pillars, in high-rise buildings. The paper points out on the need of classifying the HP-HSC for the different requested characteristic that materials have to exhibit on different structural elements of a complex structure. Among types of concrete, which binds together characteristics of High Strength Concrete (HSC) and High Performance Concrete (HPC), particular reference is made to Limestone Concrete (LSC). Existing literature provides data on self-levelling, high performance, rapid hardening concrete, able to reach in few days the standard of HPC (Kelham, 1998; Montgomery et al., 1998; Nehdi et al., 1998. In particular the technology here referred for limestone concrete is not the usual one, but it makes reference to a mix design, characterized by an industrially produced limestone aggregates, with total absence of Silica Fume or any other addition of pozzolanic material or accelerating admixture (Cangiano, 2005; Cangiano et al., 2004. The paper points out the significance of Limestone Concrete, as High Performance Concrete, application, starting from the following key construction requirements: in large public works with characteristic of very high durability, the choice of a technical solution it is not at all dependent on the construction cost only. In fact in this work, life service and safety performances, that slightly increase the construction costs, are of paramount importance. Starting from this key assumption, new materials, and in particular new concretes, may be able to notably cut life service and safety costs, considerably improving the performance/cost ratio of the selected solution, due to the large cut of maintenance costs. The paper wants to briefly explain the state of the art and the today frontier which lead to the material basic choices in structural design of high-rise buildings. In particular the paper refers to a comprehensive campaign of tests, in a starting-up phase, shared among different university and private laboratories in Italy, which aims to draw Guide Lines for different specific uses of Limestone Concrete, as HPC, in different structures typologies and environmental conditions. [ABSTRACT FROM AUTHOR]

The comparative merits of hand and automated upper and lower bound techniques for the collapse load estimation of reinforced concrete slabs are examined. Examples, drawn from both theoretical and practical design work, are used to show that both hand and automated upper bound yield line techniques can produce significant, unsafe errors. Automated lower bound solutions, however, are shown to consistently provide safe estimates that are not unduly conservative, provided appropriate formulations are adopted. As long as the engineer is willing to dispense with the crutch of a yield line pattern, it is therefore contended that, whilst Heraclitus may be correct in that both the upper and the lower bound roads can lead to one and the same collapse load, the lower bound road gets you there, certainly more safely, and usually quicker, as the Traditional Song suggests. [ABSTRACT FROM AUTHOR]

This paper presents an experimental approach for the development of new bridge restrainer system using laminated fiber reinforced rubber (LFRR). After Kobe earthquake on January 1995, the design concept for the bridge restrainer has been revised so that the bridge should install the shock absorber which may be prevented from falling down due to earthquake shock. However, the shock absorbing system for the bridge restrainer has been required to satisfy the two performance requirements of high energy absorption and reduction of impact load. To this end, the laminated fiber reinforced rubber was developed to apply to the new bridge restrainer system as a shock absorber. In this study, the three kinds of tests of static compression, rapid speed loading and weight dropping impact for the LFRR specimen were first performed in order to investigate the efficiency of LFRR as a shock absorber. Then, the rubber-rolled pin was also developed as a new bridge restrainer system from the viewpoints of impact load reduction and high energy absorption. [ABSTRACT FROM AUTHOR]

Transparent glass constructions are being used more and more often in the construction industry using up-to-date carrying systems. The progress in this field is determined by the methods to couple glass systems and transparent substructures in a durable manner while keeping the dimensions of the substructures as small as possible. Experimental investigations have shown that carrying glass-hybrid beams are possible and that there are appropriate adhesive and surface pre-treatment substances available on the market to connect glass and plastic in an orderly manner. [ABSTRACT FROM AUTHOR]

This paper introduces amodel for optimizing and visualizing infrastructuremaintenance programs of multiple-distributed sites. Two unique aspects of the model are discussed in the paper: the underlying Geographic Information System (GIS); and the powerful scheduling engine that optimizes execution plans. The GIS system stores and represents two main levels of information about the scattered sites involved in a construction/maintenance program. The first level pertains to pre-planning data such as resources, locations, optional estimates, and work constraints. This information is then used by the scheduling engine to generate an optimum schedule, and accordingly, a second layer of GIS information is generated containing activities' start and finish dates and the assigned crews. This layer of information is then used by the GIS system to visualize the crews' work assignments in a legiblemanner. An implementation program BAL is presented on an example application to illustrate the benefits of using GIS to supportmunicipalities and owner/contractor organizations administering large number of infrastructure assets, such as buildings, highways, and bridges, etc. [ABSTRACT FROM AUTHOR]

Risk management, as it relates to construction, is vital to the successful undertaking and completion of any construction project. One way to effectively manage project's risks is to develop more reliable means of identifying the most critical risks and the associated effective response methods. Research studies have extensively addressed this aspect of risk management. However, a small fraction of this research focused on identification of the critical risks encountering contractors working in the construction industry of developing countries, and few tackled identifying the risk mitigation measures employed in such an industry by domestic, international, and multinational contractors. This paper presents a comprehensive methodology that addresses the risk identification and response methods for developing countries represented by Egypt. The paper is based mainly on the approaches used by large contractors either domestic or international. The investigation, via a comprehensive questionnaire survey, tries to identify the most critical and significant risks that face the contractors working in the Egyptian construction industry and their associated effectively employed risk mitigation/elimination measures. Twenty-nine (29) construction project risks are classified into six (6) main categories according to their type and hundred and forty (140 risk) mitigation/elimination measures are introduced to overcome the impact of risks under each of these risk categories. According to the collected data and the results of the statistical analysis procedures employed, the most critical risk encountered by the contractors working in the Egyptian construction industry are: 1)the financial inability of the client; 2)the improper management of construction projects; 3)inflation and interest rates; 4)in-house cash shortage; and 5)Foreign exchange and convertibility. 101 risk response methods were found to be effective from the 140 methods introduced. The most commonly used risk response method was the risk reduction technique. [ABSTRACT FROM AUTHOR]

The level of automation technology and processes control, within the construction sector, faces unique challenges if it is to catch up with automotive and aerospace applications. The construction industry has problems relating to health and safety, environmental legislation and traditional methods of procurement. These are compounded by diminishing skills in the labour force. One way to address these issues is by increased automation and integration of design, modelling and process control. Digital Fabrication has demonstrated the feasibility of the integration of design and component production on a large scale. Freeform Construction builds on Digital Fabrication by integrating the control of final material deposition. This paper reports on recent meetings held with industrialists to gauge their perceptions of the technology and encourage discourse to identify both applications and opportunities for the wider research community. Examples of digital fabrication in construction are discussed. Freeform Construction is defined and potential applications are presented. An example of physical model generation from construction CAD software is described. [ABSTRACT FROM AUTHOR]

Underground utility services play an essential role in sustaining urban life. The majority of these utility services are delivered through pipeline networks, which are mostly buried underground and are interconnected through other urban systems to distribute or collect basic sustainable needs such as treated water, waste water, gas, communication, and power. Deterioration of underground infrastructure systems occurs due to ineffective maintenance management practices. Because new installation can be very costly and disruptive, the best course of action is to maintain the present infrastructure in a more effective way to maximize life span and prevent catastrophic failures. The accurate evaluation of current underground infrastructure must be done before any crucial decisions including lifecycle, rehabilitation and replacement intervals, and appropriate remedial methods can be made. Unfortunately, traditional technologies and management approaches have been limited by the use of insufficient data in the evaluation of the structural integrity of an aged infrastructure. This paper describes the testing, development, and application of a novel assessment technology, which combines in-pipe Ground Penetrating Radar (GPR) with Digital Scanning and Evaluation Technology (DSET) robotics to collect accurate information about the condition of the inside wall of concrete sewer pipes. A case study applying this innovative technology to sections of large diameter PVC-lined concrete pipe in the City of Phoenix is presented. The study and adoption of innovative pipeline assessment methods provide better information to improve the decision-making process, thereby making economical decisions to optimize resources in more efficient ways. [ABSTRACT FROM AUTHOR]

This paper presents a practical approach for maintenance optimization of a network of aging highway bridge decks that integrates a stochastic deterioration model based on Bogdanoff's cumulative damage theory with an effective multi-objective optimization approach. The multi-objective maintenance optimization takes into account all relevant objectives, such as improving bridge deck condition, minimizing maintenance costs, and minimizing traffic disruption and associated user costs. The consideration of these three objectives enables to take full advantage of the available bridge inspection data and implicitly lead towards the minimization of the risk of failure due to bridge deck deterioration and maintenance activities. A multi-objective optimality index is proposed as an optimality criterion for priority ranking of the deficient bridge decks for maintenance. The obtained optimal maintenance project prioritization strategy achieves a satisfactory trade-off or compromise between the selected relevant and competing optimization objectives. The proposed approach is illustrated on a small network of ten bridge deck projects that are optimized for maintenance. [ABSTRACT FROM AUTHOR]

Probabilistic assessment of the ductility demand and reliability analysis were carried out for bilinear hysteretic SDOF systems. The assessment considered two sets of strong ground motion records, and was focused on the evaluation of the mean and the coefficient of variation of the ductility demand for a given value of the normalized yield strength. The results indicate that the ductility demand could be modeled as a Frechet (Extreme value type II) variate. Based on the obtained results, empirical equations were provided to predict the mean of the ductility demand for bilinear SDOF systems of different natural vibration periods, damping ratios, and ratios of the post yield stiffness to the initial stiffness. The numerical results show that the coefficient of variation (cov) of the ductility demand can go as high as to about 1.0 depending on the characteristics of the structure. Also, a simple approach was given to estimate the probability of incipient damage and the probability of incipient collapse using the developed probabilistic characterization of the ductility demand. The approach, which could be suitable for carrying out design code calibration analysis, is illustrated numerically. [ABSTRACT FROM AUTHOR]

Reliability can be considered as a rational evaluation criterion in assessment of bridge structures. The traditional element-based approach to bridge design and evaluation does not allow for consideration of interaction between the components that form a structural system and, therefore, it can be conservative. Safety of the structural system also depends on the degree of redundancy (load sharing) and ductility. As a result, it has been observed that the load carrying capacity of the whole structure can be much larger than what is determined by the design of individual components. Therefore, this paper is focused on the system behavior. The objective is to formulate a limit state function for the whole bridge, identify the load and resistance parameters, and develop an analysis procedure to assess the reliability of the bridge as a structural system. The major steps of the procedure include selection of representative structures, formulation of limit state functions, development of load and resistance models, development of the reliability analysis method, reliability analysis of selected bridges, and formulation of recommendations for practical bridge assessment. The live load is considered in form of a design truck. The analysis is performed for different values of span length, truck position (transverse and longitudinal), number of vehicles on the bridge (multiple presence), girder spacing, and stiffness of structural members (slab and girders). For each combination of these parameters, the bridge resistance is determined in terms of the weight of a truck (or trucks) causing an unacceptable deflection or instability of the considered bridge. The reliabilities are also calculated for individual components (girders) and compared to system reliabilities of the bridge. The resulting system reliability can serve as a tool in the development of a rational bridge design and evaluation procedure. [ABSTRACT FROM AUTHOR]

A methodology of enhanced computational efficiency is presented for continuum topology optimization of sparse structural systems. Such systems are characterized by the structural material occupying only a small fraction of the structure's envelope volume. When modeled within a continuum mechanics and topology optimization framework such structures require models of very high refinement which is computationally very expensive. The methodology presented herein to deal with this issue is based on the idea of starting with a relatively coarse mesh of low refinement and employing a sequence of meshes featuring progressively greater degrees of uniform refinement. One starts by solving for an initial approximation to the final material layout on the coarse mesh. This design is then projected onto the next finer mesh in the sequence, and the material layout optimization process is continued. The material layout design from the second mesh can then be projected onto the third mesh for additional refinement, and so forth. The process terminates when an optimal design of sufficient sparsity, and sufficient mesh resolution is achieved. Within the proposed methodology, additional computational efficiency is realized by using a design-dependent analysis problem reduction technique. As one proceeds toward sparse optimal designs, very large regions of the structural model will be devoid of any structural material and hence can be excluded from the structural analysis problem resulting in great computational efficiency. The validity and performance characteristics of the proposed methodology are demonstrated on three different problems, two involving design of sparse structures for buckling stability, and the third involving design of a hinge-free gripper compliant mechanism. [ABSTRACT FROM AUTHOR]

This paper presents a consistent approach for the optimal seismic design of added viscous damping in framed structures. The approach presented is appropriate for use in elastic as well as yielding frames. The sum of added damping is chosen as the objective function and the performance of the structure, under the excitation of an ensemble of deterministic ground motion records, is constrained. The performance of the structure is measured by the maximal inter-story drifts in both the linear and nonlinear cases. The nonlinear case however, uses an additional performance measure of the normalized hysteretic energy of the plastic hinges Gradients of the performance measures are first derived to enable the use of an appropriate first order optimization scheme. Moreover, an efficient selection scheme enables the consideration of only a few records rather than the whole ensemble, hence making the optimization process efficient in terms of the computational effort. [ABSTRACT FROM AUTHOR]

A computer-automated design and optimization process for pile foundations with rigid concrete slabs is presented. Optimality Criteria methodology is used to provide optimal pile designs. A threedimensional optimization computer program has been developed that designs a foundation system with an optimal number of piles, geometric layout, pile orientation, batter, and size for a given structure subjected to multiple load cases. The optimization procedure controls displacements while reducing the overall weight of the pile foundation design. A new method for optimizing weightless variables, such as batter, was also created. Thus, the challenges of optimizing variables that indirectly affect the weight of the pile foundation can still be designed to create weight savings. In one example, the total volume of the steel piles is reduced from 61,920 in3 to 49,570 in3 by optimizing only the pile sizes. Furthermore, the weight is reduced again by simultaneously optimizing each pile group's size coupled with the weightless variable, batter. [ABSTRACT FROM AUTHOR]

Delamination of sandwich columns is studied using a relatively simple cohesive layer model. The model is described in some detail and is incorporated as a user supplied element (UEL) in a finite element package. The model is shown to predict accurately the test results of delamination of a facing sheet of a sandwich member. The accuracy of the model is seen to be superior to a model previously proposed by the authors, which predicts an earlier termination of crack growth. The UEL model is applied to a sandwich column investigated by earlier investigators — a column that is relatively stout (ratio of length (L) to depth (d) ≈ 7.3) and has stiff facing sheets (ratio of depth d to the thickness (h) of facings ≈ 15). The model is able to capture the onset of delamination buckling, sudden delamination growth at nearly constant compression, stable delamination growth and reaching of a limit point of the load carrying capacity. A slender sandwich column with relatively thin facings (L/d ≈ 15, d/h ≈ 40) is next considered. It indicates that overall bending tends to inhibit delamination growth under quasistatic loading as it tends to keep the delaminated surfaces in contact. [ABSTRACT FROM AUTHOR]

Any construction project that is completed on-time at the lowest total cost requires the consideration of logistics processes and economics. This study investigates the cost implications of moving and transforming materials in various materials network configurations associated with popular prefabrication construction methods. Efforts focus on the trade-offs that exist among contract-to-completion times, transportation costs, and assembly costs for the alternative construction methods. The findings suggest that the competitive advantage of prefabrication methods can be enhanced through an optimal combination of reduced construction times as well as the number, distance, and configurations of materials and sub-assembly shipments. [ABSTRACT FROM AUTHOR]

At the conceptual stage of the design process where only a partial specification for a design is available and due to fuzzy nature of information at this stage it is difficult to program every design requirements. Experience has shown that evolutionary computation EC, (particularly the genetic algorithm) to be an effective decision support tool for conceptual design. To make EC useful in this stage of the design it needs strong human interaction and guidance to lead the search in discrete regions of the search space to explore and discover more appropriate design concepts. Humans are extremely good at perceptual evaluation of designs according to criteria that are extremely hard to program (Eckert et al., 1999). As a result, they can provide useful fitness evaluation for interactive evolutionary systems. They can also include personal preferences to lead the search and exploration to a preferred direction. This kind of interaction is extremely important to satisfy design/client requirements, particularly at the conceptual stage of the design process. This paper introduces a novel approach which demonstrates that interactive use of evolutionary computation, assisted by visualisation tools, leads to a human-led search. A system which support human-led search and it is based on an interactive visualisation clustered genetic algorithm, developed by Packham and coworkers (Packham, 2003; Packham and Denham, 2003; Packham et al., 2004; Rafiq et al., 2004), is introduced and its application on an example of a multi-disciplinary decision making process is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, applications of crystal plasticity theory to the numerical modelling of large strain plasticity phenomena are considered. In particular, instabilities and localized deformation phenomena for face-centred cubic (FCC) and body-centred cubic (BCC) polycrystals subjected to various deformation modes are investigated. In-house finite element analyses based on a rate-dependent crystal plasticity model have been developed to simulate the large strain behaviour for sheet specimens subjected to plane strain and plane stress deformation modes. In the formulation, the plastic deformation of an individual crystal is assumed to be due to crystallographic slip and simulations are performed using two approaches. In the first approach, each material point in the finite element analysis is considered to be a polycrystalline aggregate having a large number of FCC or BCC grains, and the Taylor theory of crystal plasticity is adopted to model the behaviour of the polycrystal. In the second approach, each grain is represented individually using one or more finite elements, and the constitutive response within each element is given by the single crystal constitutive model. Both approaches account for initial textures, as well as texture evolution during large plastic deformations. The numerical analyses incorporate parallel computing features. The results of simulations for the above-mentioned deformation modes are discussed, and in certain cases comparisons are made with experimental results for rolled aluminum sheet alloys and for draw quality steels. [ABSTRACT FROM AUTHOR]

We derive here equivalent self-adjoint systems for conservative systems of the second kind. Existence of the symmetrized systems confirms that certain conservative systems of the second kind behave as a true conservative system. In this way, study of stability can be carried out on the symmetrized system. In general, it is easier to study a self-adjoint system than a nonself-adjoint system. For the conservative system of the second kind, including the Pflüger column, we also presented a lower bound self-adjoint system. For a linear conservative gyroscopic system, we gave a zero parameter sufficient condition for instability and one for stability. The criteria depend only on the characteristics of the system. For a simple 2-DOF system, the present criteria yield the exact solutions. [ABSTRACT FROM AUTHOR]