Service Life Cost Research Articles

ANALYSIS OF ENGINEERING ECONOMICS OF THE NEW ERA COMPARED WITH THE CONVENTIONAL MATERIALS USED IN HVAC DUCT APPLICATION

Selecting suitable materials for air ductwork is essential to ensure efficient airflow distribution and reduce economic costs, as it directly impacts an air conditioning system’s overall performance and functionality. The PVC-coated polyester canvas and foam materials have revolutionized the construction of air ductwork, offering numerous benefits and advantages over conventional materials. For instance, these materials have been successfully used in the construction of air ducts for large commercial buildings, resulting in significant energy savings and improved indoor air quality. Using these new-era materials has design flexibility, durability, energy efficiency, and cost-effectiveness. This research has provided a comprehensive analysis of the economic cost of the new era of air ductwork compared with conventional air ductwork in Thailand, and the thorough assessment of total service life costs has improved on the financial implications of adopting this new technology. The economic analysis of PID ducts reveals their cost-effective excellence compared to other investment types. The benefit-cost ratio of 4.73 and a payback period of 1.48 years show the financial advantages offered by PID ducts. With their affordability, efficiency, and simplicity, PID ducts emerge as the most attractive option for investors seeking long-term profitability and sustainability in construction projects.

A parametric study of concrete runway pavement layers depression under impact load

Introduction. Airport runway pavement is always subjected to considerable impact loads as a result of aircraft landing heavily on the concrete surface. As a result, runway pavements must have adequate strength and durability capability to avoid damage caused by a hard impact, such as surface deflection downward or penetration, because repair works are inconvenient within the operating conditions of the airport and increase the service life cost of the pavement structure. 3DFE research is carried out to identify some beneficial elements in influencing the concrete and base layers deformation of the runway pavement.
 
 Materials and methods. The research developed 3D finite element model from the previews study by using the Explicit Dynamics model using the Ansys workbench. The concrete characteristics such as slab thickness, concrete density, modulus of elasticity, flexural tensile strength, and compressive strength of the runway pavement are tested, while the impactor weight and velocity are chosen and investigated too.
 
 Results. The results included the effect of 4–7 different values for each factor. The depression of the concrete and base layers is presented.
 
 Conclusions. The main conclusion that can be drawn from this work is that flexural tensile strength, compressive strength, and slab thickness have a significant effect on the concrete depression of the runway pavement as well as the impactor weight and velocity.

Service life cost of selected design and repair strategies for concrete structures in chloride exposure: Particular consideration of 12% chromium steel

AbstractCalculation of service life costs allows for a holistic assessment of the cost‐effectiveness of options in design regarding materials and intervention strategies for an infrastructure object. A method is presented in which probabilistic service life modeling and cost calculations are combined. This method is exemplified by two cases of reinforced concrete structures exposed to a chloride‐bearing environment. Two different types of reinforcing steel and several intervention strategies are analyzed. The results show that the method is suitable for decision‐making on the most economical solution. The solution with the lowest initial construction costs does not necessarily result into the lowest service life costs, depending on chloride exposure conditions and the anticipated interventions.

Vrednovanje neakustičnih svojstava zidova za zaštitu od prometne buke

The presented research aims to reduce the uncertainty in the selection of noise wall panel materials, and thus to improve the traffic noise management process in the Republic of Croatia. An evaluation of concrete, metal, wood, and transparent panels is performed to improve the panel material selection procedure in the planning and design of traffic noise walls. Properties of panels made of these four basic materials are studied under the assumption that the acoustic requirements relating to the wall structure have been fully met. Thus, the research focuses on six non-acoustic properties of panels (criteria that must be considered by civil engineers): mechanical resistance and stability, service life, construction, maintenance, and replacement costs, service life costs, and recyclability. These properties are analysed using the publicly available data from secondary sources. The data are systematized and subjected to a multicriteria analysis, which has revealed that concrete panels have the highest (weighted and unweighted) mean score.

Income over service life cost – Estimation of individual profitability of dairy cows at time of death reveals farm-specific economic trade-offs

Managing a dairy farm requires a farm- and cow-specific assessment of the required resources and the revenues obtained from the production process. Due to scientific and practical reasons, the various types of data from a farm, e.g., economic and biologic data, commonly lack connectivity and compatibility at animal level. This means that the economic impacts associated with differences in rearing, productivity and culling as well as the economic values of cow-individual service lives often remain hidden under average figures. This work is based on a two-fold hypothesis: (1) large differences in cow profitability exist between farms but also between individual cows within one farm, and (2) knowledge about the farm-specific economic impact of service life characteristics provides new options for action. In this article, a farm-specific full-cost calculation that links routine herd management data and key economic figures gained from business sheets of the farm's dairy branch is introduced. The new methodology for the calculation of individual income over service life cost was exemplarily tested on a sample of 4,962 culled cows from 32 German dairy farms. Median income over service life cost of culled cows was negative for 19 farms (59%) and varied largely between farms (-€3,502 to €3,323). Within a given economic situation, i.e., cows of the same farm, the number of lactations was identified as the major lever to cow profitability for most farms, followed by the individual milk yield level and the number of days in milk at culling during last lactation. This indicates that the economic sustainability of the farm is inherently linked to the ability of cows to cope with their environment. The vastly different monetary value associated with, e.g., productivity and longevity parameters and the heterogeneity in the ranking of their effect sizes between farms also show that the economic impacts of herd characteristics are highly farm-specific. Evaluation of the overall lifetime profitability of culled cows along with identification of economically poor farm-specific herd characteristics can help to pinpoint problems, optimize herd management, and prioritize investment necessities.

Aircraft Maintenance: Structural Health Monitoring Influence on Costs and Practices

AbstractThe structural health monitoring (SHM) represents an evolution of the traditional way to design and maintain mechanical structures. SHM systems allow to continuously (or discretely) monitor the structural integrity of an asset, not waiting for the planned check. This result implies an important reduction of inspection time and guarantees an improvement of service life cost of the structural components, but how and how much this cost can be influenced is still an open issue. This research addresses the identification of previous studies that dealt with this topic. A systematic literature review (SLR) is carried out with the aim of investigating the current SHM state‐of‐the art in the aircraft industry in order to point out the main advantages deriving from the application of these technologies and the existing gaps and limitations. Three database (Scopus, Web of science and Google Scholar) are used for selecting peer‐reviewed papers that address with evidence the changes in maintenance practices resulting from the use of SHM. The analysis proves the differences between the traditional programmed maintenance and the innovative predictive approach based on SHM information in terms of interval inspection policy and costs. Moreover, the technical limits that do not allow to totally exploit the potential strength of SHM are outlined.

Predictive information and maintenance optimization based on decision theory: a case study considering a welded joint in an offshore wind turbine support structure

Predictive information and maintenance optimization for deteriorating structures is concerned with scheduling (a) the collection of information by inspection and monitoring and (b) maintenance actions such as repair, replacement, and retrofitting based on updated predictions of the future condition of the structural system. In this article, we consider the problem of jointly identifying—at the beginning of the service life—the optimal inspection time and repair strategy for a generic welded joint in a generic offshore wind turbine structure subject to fatigue. The optimization is performed based on different types of decision analyses including value of information analyses to quantify the expected service life cost encompassing inspection, repair, and fatigue damage for all relevant combinations of inspection time, repair method, and repair time. Based on the analysis of the expected service life cost, the optimal inspection time, repair method, and repair time are identified. Possible repair methods for a welded joint in an offshore environment include welding and grinding, for which detailed models are formulated and utilized to update the joint’s fatigue performance. The decision analyses reveal that an inspection should be scheduled approximately at mid-service life of the welded joint. A repair should be performed in the same year after an indication and measurement of a fatigue crack given an optimal inspection scheduling. This article concludes with a discussion on the results obtained from the decision and value of information analyses.

Optimization of Inspection Period in Natural Stone Claddings

In condition-based maintenance plans, the schedule of inspections is an important step. Condition-based actions are performed according to prescribed condition criteria (i.e., condition, cost, availability, among other factors), and the main purpose of inspections is to evaluate the façade’s condition and plan its correction in order to reduce the risk of failure of the cladding. Therefore, the main goal of this study is to implement multi-objective optimization to understand whether there is an optimal time interval for performing the inspections. For that purpose, a Petri-net condition maintenance model is used to assess the influence of different maintenance plans on the overall degradation of natural stone claddings. In this model, the maintenance activities can only be performed after an inspection has been carried out. The definition of the best maintenance policy results in a conflict of objectives. Owners/managers seek to achieve a maintenance strategy that minimizes service life costs and maintain the cladding in a safe and minimal degradation condition. Multi-objective optimization procedures are capable of considering several conflicting objectives. In this paper, the objective functions considered are minimization of the service life costs, maximization of the efficiency index, maximization of the service life, and minimization of the total number of replacements over the time horizon.

Bridge design for inspection and maintenance – a UK and US perspective

Over the past few decades, engineers working in design offices have become much better at designing for constructability. The use of the design and build form of procurement has, in many ways, been instrumental in this change. The use of accelerated bridge construction in the USA, although primarily a method of reducing traffic impact, has also helped engineers become better at designing for constructability. However, it can be argued that engineers have not made the same progress in designing bridges to make future inspections and maintenance easier. In fact, unless an employer's requirements for inspection and maintenance are clearly prescribed in detail in the contract, then the design and build form of procurement is perhaps the least advantageous when considering the service life of a structure. Over the lifespan of a bridge, the service life costs, including inspection and maintenance, can account for a significant percentage of the lifecycle costs of the bridge. Therefore, the importance of not only ensuring that an adequately funded proper inspection and maintenance regime is established but also that sufficient attention is paid to the provision of inspection and maintenance during the design stage cannot be overstated. This paper examines and compares current practice in the UK and USA and considers ways of improving the design process to assist the future inspection and maintenance of bridges.

Design Implications towards Inspection Reduction of Large Scale Structures

Operational management is a key contributor in life cycle costs, especially for large scale assets which are in most times complex in structural hierarchy and with a large nominal service life. Decisions on the operational management may concern the number of inspections or maintenance strategies which may allow full utilization of structural capacity or sacrifice residual life in order to avoid an unscheduled intervention. Design of such assets is often governed by design standards which offer the designer the flexibility to take certain decisions that may affect the CAPEX to OPEX ratio such as that of building a more robust structure which may eliminate the need for costly inspection operations. This paper is investigating this approach, taking the example of offshore wind turbine support structures as the reference case, and examines the relevant provisions of the DNV-Os-J101 Standard with respect to the design implications that such a decision may have to the overall life-cycle cost of the structure. Assessment of the structural properties under different design conditions is evaluated through a combination of detailed cost model and an iterative optimization algorithm. The approach which is followed and documented, can be applicable to other complex structural systems for decision making through evaluation of service life costs.

Investigation of the effect of the quality of inspection techniques on the optimal inspection interval for structures

Quantitative data from inspections are necessary to determine the state of a deteriorating structure and to identify the optimal maintenance strategy for the remaining life of the structure. This article presents the development of a two-stage inspection based maintenance management framework, which provides the owner/manager of a structure with a decision tool to optimise the service life costs of a structure. The two stages of an inspection are considered here, detection of defects present and sizing of detected defects. Using this framework, the optimal inspection interval for this study, based on the minimisation of the service life costs, is determined and the effect of inspection quality of the two techniques is studied. By modelling the detection and sizing stage of an inspection separately, the optimum combination of techniques can be determined.

Drydock Service Life Cost Reduction by Use of Finite Element Analysis

AbstractMilitary Standard 1625 (SH) is currently the principal governing document for certification of floating drydocks which service US Navy ships. In order to maintain their certification, drydock owners must periodically document, evaluate, and repair corroded structural elements according to this standard's specifications. This evaluation and repair process is frequently cost‐prohibitive for some docks that have sustained significant corrosion. As an alternative, a finite element analysis (FEA) may be performed to isolate areas that require repair to maintain the safe operating capacity of the vessel. First, a finite element model of the drydock is created based on corrosion data from ultrasonic testing (UT). The corroded model is then analyzed to evaluate the global strength of the drydock and to isolate specific areas of corrosion that require repair. By isolating structurally critical areas, unnecessary repairs otherwise required, may be avoided. This process may result in considerable cost savings for drydock owners. In addition, wastage rates from historic ultrasonic survey data may be used to predict future corrosion. This paper will summarize the FEA conducted of the floating drydock ADEPT, a US Navy‐owned dock that is leased by Gulf Copper Ship Repair Inc. of Corpus Christi, TX. During the drydock's service life, significant corrosion has developed throughout the vessel's structure. Ultrasonic surveys were conducted to document the existing levels of corrosion and MAESTRO, a FEA program developed by Proteus Engineering, was used to develop a finite element model of the vessel based on the scantlings reported from the surveys. MAESTRO was then used to perform a FEA to isolate areas that require repair. Additionally, results from this analysis were used to calculate wastage rates and predict future corrosion. The FEA was then modified to analyze the future condition of the vessel in order to evaluate the need for future repairs.

Life Cycle Costing of Interior Materials for Florida's Schools

This paper describes a collaborative research project that expands an otherwise limited Service Life Cycle Cost (SLCC) evaluation of interior materials for Florida's educational facilities. The participatory research strategy involved a wide range of community representatives and academic scholars with different expertise: architecture, interior design, building construction, and civil engineering plus a variety of facilities users. The resulting SLCC evaluation produced a decision making tool that school officials could use to make informed decisions about building construction and renovation. The SLCC method differs from the AIA life cycle assessment [LCA] guidelines by utilizing input from the community of stakeholders to create an accurate and in–depth understanding of the LCA “product use phase.” By combining data from observation of users’ behavior with published information regarding interior materials, the research suggests that a majority of building costs are incurred after the initial capital expenditure for construction. The selection of interior materials, based solely on low initial cost, often results in service life costs that exceed the cost benefit of the initial purchase. The research provides evidence that interior materials have a more significant impact on the life cycle costs of educational facilities than other building materials.

Codified Risk-Based Inspection Planning

Simplified methods are described for reliability- and risk-based inspection planning of steel structures. The methods simplify the practical aspects of identifying inspection plans complying both with specific requirements to the maximum acceptable annual probability of structural collapse and member failure and at the same time minimizing overall total service life costs. Generic inspections plans can then be established for representative fatigue sensitive details in terms of characteristics such as FDF (Fatigue Design Factor), detail type, RSR (Reserve Strength Ratio) given fatigue failure and inspection/repair techniques. Generic inspection plans can be used for design of new structures as well as for requalification of existing structures. In this paper it is described how generic inspection plans can be used for codification purposes in connection with inspection planning of steel structures.

Silicone Rubber—A Perspective

Abstract Silicone rubber began as a polydimethylsiloxane elastomer vulcanized by benzoyl peroxide. Today, 33 years after its discovery, silicone rubber is a line of products of widely different compositions and vulcanized by many different systems. Our knowledge of the rubber is far better than it was but it is by no means complete. Applications are many, but in general, they are in vital areas where extreme environmental conditions will not permit the use of any other material. Service life cost is usually lower than for other rubbers, despite higher initial cost. Uses in surgery fulfill a unique role in saving lives or improving the quality of life for many. Dr. R. R. McGregor said of the field of silicones, in general, “What had been started as a search for further knowledge proved to be the groundwork for technological advances that have proved helpful to industry, and in so doing, have contributed to improving our standard of living”. What he said of silicones as a whole, certainly applies to silicone rubber, and I have been happy to have contributed to the knowledge of silicone rubber and to have been a part of these advances which, in addition, contribute to our physical wellbeing by their use in the human body. These remarks are not in any way an epitaph for silicone rubber, but rather, they are the opening words in a book of growing usefulness for silicone rubber for us all. The adventure has just begun.