Optimizing the design of timber components under decay and climate variations

International audienceThe durability of timber structures can be affected by the isolated or combined actions of loading, moisture content, temperature, biological activity, etc. This work focuses on the optimal design of new timber structures subjected to deterioration. Since the deterioration processes and the structural behavior of timber structures are complex, nowadays the deterioration models are not able to account for all influencing factors. Consequently, this study is based on an empirical model that was derived based in-lab experimental studies for the decay growth of brown rot in pine sapwood under variant climate conditions. Such a model is divided into two processes: (i) activation process and (ii) mass loss process. On the other hand, there are significant uncertainties involved in the problem. The uncertainties inherent to materials properties, models and climate are considered throughout a time-dependent reliability based-design optimization (TD-RBDO) approach. The TD-RBDO aims to ensure a target reliability level during the operational life. This approach is applied to design optimization of a new timber component subjected to different French climates. The performance of the optimized solution is compared with a traditional cross-section designed according to the Eurocode 5 in terms of safety. The overall results indicate that an optimized solution ensures a target reliability level during the whole structural lifetime

Climate Change Risk for Irish Timber Power Pole Networks

The latest IPCC report states that warming of the climate system is unequivocal, and this warming may lead to increased risk of breakdown of infrastructure networks due to extreme weather. Before appropriate action can be taken for power infrastructure in this regard, we must first understand existing risk, and then try to predict potential climate related changes in risk. The work described in this paper examines both existing vulnerability, and potential future vulnerability, for a notional network of Irish timber power poles. These power pole networks represent important critical infrastructure assets, both nationally, and internationally. There are currently approximately two million timber power poles in service in Ireland, five million timber power poles in service in Australia, worth over $10 billion, and approximately 200 million treated power poles in service in the United States. The impacts of climate change on Irish power poles will be examined herein using a Monte-Carlo event-based sequential model, which incorporates structural reliability, deterioration, climatic effects and network maintenance. The hazards of interest are storm winds and timber decay - both of which may worsen due to a changing climate.The authors would like to acknowledge the financial support of the Irish Environmental Protection Agency who funded this research. The authors would also like to acknowledge Fergus Sweeney and Kevin OConnor, of the Irish Electricity Supply Board, for their invaluable expertise and support in developing appropriate model parameters

System-level Maintenance Optimization for Power Distribution Systems Subjected to Hurricanes

Overhead electric power distribution systems are vulnerable to extensive damage due to hurricanes. Most of the damage is caused by the failure of distribution poles, which are mostly wood poles. As a natural material, wood is susceptible to strength deterioration over time due to decay. As such, utility companies carry out preventive maintenance actions to minimize the likelihood of failure of the poles due to decay and extreme events (hurricanes). Due to the scarcity of resources for maintenance, an optimization approach to maintenance planning is necessary. Most utilities consider minimizing maintenance cost as the objective in their wood pole maintenance planning. However, due to increasing demand for higher system reliability, the consideration of cost alone in maintenance optimization is not adequate. This paper presents a maintenance optimization framework for power distribution systems under hurricane hazard considering system performance as the objective. Two maintenance strategies are explored: periodic chemical treatment and the use of fiber reinforced polymer (FRP). The distribution system of a virtual city assumed to be located in Florida is used to demonstrate the framework

RISK-BASED ASSESSMENT AND STRENGTHENING OF ELECTRIC POWER SYSTEMS SUBJECTED TO NATURAL HAZARDS

Modern economic and social activities are dependent on a complex network of infrastructure systems that are highly interdependent. Electric power systems form the backbone of such complex network as most civil infrastructure systems cannot function properly without reliable power supply. Electric power systems are vulnerable to extensive damage due to natural hazards, as evident in recent hazard events. Hurricanes, earthquakes, floods, tornados and other natural hazards have caused billions of dollars in direct losses due to damage to power systems and indirect losses due to power outages, as well as social disruption. There is, therefore, a need for a comprehensive framework to assess and mitigate the risk posed by natural hazards to electric power systems. Electric power systems rely on various components that work together to deliver power from generating units to customers. Consequently, any reliable risk assessment methodology needs to take into account how the different components interact. This requires a system-level risk assessment approach. This research presents a framework for system-level risk assessment and management for electric power systems subjected to natural hazards. Specifically, risk due to hurricanes and earthquakes, as well as the combined effect of both is considered. The framework incorporates a topological-based system reliability model, probabilistic and scenario-based hazard analysis, climate change modeling, component vulnerability, component importance measure, multi-hazard risk assessment, and cost analysis. Several risk mitigation strategies are proposed; their efficiency and cost-effectiveness are studied. The developed framework is intended to assist utility companies and other stakeholders in making a risk-informed decision regarding short- and long-term investment in natural hazard risk mitigation for electric power systems. The framework can be used to identify certain parts of the system to strengthen, compare the efficiency and cost-effectiveness of various risk mitigation strategies using life-cycle cost analysis, compare risks posed by different natural hazards, and prioritize investment in the face of limited resources

Reliability assessment of power pole infrastructure incorporating deterioration and network maintenance

There is considerable investment in timber utility poles worldwide, and there is a need to examine the structural reliability and probability based management optimisation of these power distribution infrastructure elements. The work presented in this paper builds on the existing studies in this area through assessment of both treated and untreated timber power poles, with the effects of deterioration and network maintenance incorporated in the analysis. This more realistic assessment approach, with deterioration and maintenance considered, was achieved using event-based Monte Carlo simulation. The output from the probabilistic model is used to illustrate the importance of considering network maintenance in the time-dependent structural reliability assessment of timber power poles. Under wind load, treated and untreated poles designed and maintained in accordance with existing Australian standards were found to have similar failure rates. However, untreated pole networks required approximately twice as many maintenance based pole replacements to sustain the same level of reliability. The effect of four different network maintenance strategies on infrastructure performance was also investigated herein. This assessment highlighted the fact that slight alterations to network maintenance practices can lead to significant changes in performance of timber power pole networks

Reliability and sustainability of wood poles in the electrical power distribution network

Abstract: The reliability and sustainability of wood poles in the electrical power distribution network is of vital importance, as it directly affects the entire power system network connected to them. Wood poles support power line conductors and carry electrical equipment in order for electricity to be transmitted and distributed safely from the power company to consumers. One of the main challenges faced by electrical power distribution companies is the failure of wood poles on the distribution networks. Some of the identified problems when wood utility poles fail in the electrical power distribution network include loss of profit, unsafe households and damage of machinery. Looking at the South African electrical power distribution network from ten years back until now, it is evident that wood poles are crucial for the system and that the need for reliable and sustainable wood utility poles has grown tremendously in this period...M.Phil. (Engineering Management