Now showing 1 - 6 of 6
  • Publication
    Variations of safety factors for bridges over their lifetime considering changing live load definitions
    Design of long lasting structures would require insights from the past. In this regard, design of future long-life bridges and the assessment of current ageing bridges can particularly benefit from understanding the evolution of safety over lifetime. This is an important issue since there has been an evolution of design live loads over the lifetime of such bridges in the past and such changes in definition can influence the computed estimates of safety; while the true state of the structure remains the function of the site-specific live loads. Considering the limitations around instrumenting individual bridges, it is important to investigate the variations of such computed estimates over their lifetime. Previous studies around this problem have focused on the changes in terms of reliability indices over time and life-cycle costs due to degradation. However, the key change in safety estimates for owners of bridges based on changes in live load definitions will be reflected in terms of safety factors, which remain a key index for taking commercial and safety intervention decisions for a bridge stock. This paper presents the variation in safety factors of representative slab, beam and prestressed bridges for changing live load definitions and compares it with corresponding changes in reliability index parameter importance factors for the life-cycle of such bridges. The work provides an insight to how future changes in anticipated changes in live loading definitions can influence safety factors and provides guidance around better built bridges for the future.
      174
  • Publication
    The Influence of Flexible Towers on the Dynamics of Offshore Wind Turbine Gravity Base Structures
    With offshore wind turbines increasing in size, there is increasing interest in non-traditional support structures. New concepts include lightweight and flexible fiberglass composite towers that have potential benefits over traditional stiff steel towers. The aim of this paper was to assess how the combination of a more flexible wind turbine tower with an offshore concrete gravity base foundation would affect the dynamic response of the structure. The results focus on how the dynamic amplification factors (DAFs) change with varying levels of foundation stiffness during an extreme event (50 year return period extreme event).
      257
  • Publication
    Reliability index and parameter importance for bridge traffic loading definition changes
    With the continued evolution of traffic loading specifications, safety classifications of bridge structures are subject to change, independent of the actual condition of the structures at that point in time. As investment decisions are often based on these safety classifications, a reclassification of safety level due to changing of traffic load definitions can lead to misinterpretation of the actual state of the structure, and thus lead to a misallocation of resources. Should a reclassification of safety occur after a change in traffic load specification, the question as to whether modern design codes are producing more or less robust bridges than previous design codes is raised. To investigate this, three bridge structures were assessed for evolving definitions of traffic load. Using deterministic and probabilistic methods, critical limit-states were assessed and the associated reliability indices and parametric sensitivity factors were determined and compared across various code specifications. This comparison allowed for the evaluation as to how the evolution of traffic load over time influences the computed safety of bridge structures.
      309Scopus© Citations 5
  • Publication
    Effects of increasing design traffic load on performance and life-cycle cost of bridges
    (CRC Press - Taylor & Francis Group, 2016-06-07) ; ; ;
    Due to the onerous and expensive nature of preventative and essential maintenance of existing bridge infrastructure, it is prudent to look into methods of improving life-cycle safety and cost of newly constructed bridges at the design phase. In an effort to achieve economy in material quantities and initial cost, the structural capacity of these bridges is often at the required minimum target level. This paper investigates the effects that increased design traffic loading have on the initial construction cost and whether that could be balanced by a reduced requirement for financial intervention in the mid to later stages of the bridge’s design-life. This is achieved by conducting a life-cycle performance and cost assessment on a reinforced concrete slab bridge that is designed to increasing standard traffic loads.
      153
  • Publication
    Reliability index and parameter importance for bridge traffic loading definition changes
    With the continued evolution of traffic loading specifications, safety classifications of bridge structures are subject to change, independent of the actual condition of the structures at that point in time. As investment decisions are often based on these safety classifications, a reclassification of safety level due to changing of traffic load definitions can lead to misinterpretation of the actual state of the structure, and thus lead to a misallocation of resources. Should a reclassification of safety occur after a change in traffic load specification, the question as to whether modern design codes are producing more or less robust bridges than previous design codes is raised. To investigate this, three bridge structures were assessed for evolving definitions of traffic load. Using deterministic and probabilistic methods, critical limit states were assessed and the associated reliability indices and parametric sensitivity factors were determined and compared across various code specifications. This comparison allowed for an evaluation of how the evolution of traffic load over time influences the computed safety of bridge structures.
      395Scopus© Citations 5
  • Publication
    Optimization of composite material tower for offshore wind turbine structures
    The focus of this study was to investigate the application of lightweight fiber reinforced composite materials in the construction of offshore wind turbine support structures. A composite tower design suitable for the NREL 5 MW reference wind turbine is presented. The design is based on the most automated and low cost composite manufacturing methods (pultrusion and filament winding) and the conclusions of this study may not be applicable for offshore structures using different composite material construction techniques. The mass of the tower was minimized using gradient based optimization approach. The cost of a composite tower was calculated and levelized cost of energy (LCOE) projections are discussed in comparison with the existing steel tower cost. The study determined that while the composite tower is technically feasible and has a lower mass than a comparable steel tower, uncertainty remains in how it compares economically in terms of LCOE.
      681Scopus© Citations 24