Naiyu Wang

Reliability-Based Evaluation of Flexural Members Strengthened with Externally Bonded Fiber-Reinforced Polymer Composites

Structural applications of carbon fiber-reinforced polymer (FRP) composites in civil infrastructure rehabilitation projects are receiving increasing interest due primarily to their high strength-weight ratio, resistance to aggressive environments, and other favorable properties that can be used to advantage in civil projects. Structural design and evaluation in civil engineering applications are distinguished by their reliance on codes of practice and on advanced analysis in lieu of component testing. The current lack of supporting codes, standards, and other regulatory guidance is a barrier to the implementation of high-performance FRP materials in civil construction. Experience over the past three decades in developing probability-based limit state design criteria for common construction materials points the way forward for making similar advances in guidelines for design and evaluation of structural components and systems that employ FRP composite materials. This paper summarizes some of the available tools and supporting databases that can be used to develop reliability-based guidelines for design and evaluation of FRP composites in civil construction and illustrates their application with several practical examples involving strengthening reinforced concrete flexural members.

Bridge Rating Using System Reliability Assessment. I: Assessment and Verification by Load Testing

Condition assessment and safety verification of existing bridges and decisions as to whether a bridge requires posting currently are addressed through analysis, load testing, or a combination of these methods. The rating process is described in AASHTO’s Manual for Bridge Evaluation, which permits ratings to be determined by allowable stress, load factor, or load and resistance factor methods, the latter of which is keyed to AASHTO LRFD Bridge Design Specifications. These three rating methods may lead to differently rated capacities and posting limits for the same bridge, a situation that has serious implications with regard to public safety and the economic well-being of communities that may be affected by bridge postings or closures. This paper is the first of two papers that summarize a research program to develop improvements to the current bridge rating process using structural reliability methods. This paper appraises current bridge rating methods and summarizes a coordinated program of analysis and ...

A risk de-aggregation framework that relates community resilience goals to building performance objectives

Abstract Resilience is often regarded as an attribute of communities rather than of individual buildings, bridges, and other civil infrastructure facilities. Previous research to support development of resilient infrastructure has considered, for the most part, actions and policies to achieve resilience objectives at the community level. While it is clear that a community cannot be resilient without resilient individual facilities, few attempts have been made to relate the performance criteria for individual facilities to community resilience goals in a quantitative manner. This paper presents a method for relating risk-informed performance criteria for individual buildings exposed to extreme hazards to broader community resilience objectives and illustrates the application of the method to two residential building inventories. The paper demonstrates the feasibility of de-aggregating community resilience goals to obtain design performance objectives for individual facilities and thereby relating community goals to requirements in codes and standards that govern design of buildings and other structures.

The Centerville Virtual Community: a fully integrated decision model of interacting physical and social infrastructure systems

Abstract Enhancing community resilience in the future will require new interdisciplinary systems-based approaches that depend on many disciplines, including engineering, social and economic, and information sciences. The National Institute of Standards and Technology awarded the Center for Risk-Based Community Resilience Planning to Colorado State University and nine other universities in 2015, with the overarching goal of establishing the measurement science for community resilience assessment. The Centerville Virtual Community Testbed is aimed at enabling fundamental resilience assessment algorithms to be initiated, developed, and coded in a preliminary form, and tested before the refined measurement methods and supporting data classifications and databases necessary for a more complete assessment have fully matured. This paper introduces the Centerville Testbed, defining the physical infrastructure within the community, natural hazards to which it is exposed, and the population demographics necessary to assess potential post-disaster impacts on the population, local economy, and public services that are described in detail in the companion papers of this Special Issue.

Building portfolio fragility functions to support scalable community resilience assessment

Abstract Community resilience planning, risk mitigation, and recovery optimization must assume a system perspective at the level of the overall community built environment. While engineers can quantify the performance of individual buildings and facilities, such information must be aggregated to reflect the vulnerability of the building portfolio as a whole to support resilience-based decisions at the community level. This study presents a methodology for building portfolio analysis that relates the performance of individual buildings exposed to natural hazards to the overall performance of a building portfolio. We introduce the concept of building portfolio fragility function (BPFF), defined as the probability that a building portfolio, as an aggregated system, fails to achieve prescribed performance objectives conditioned on scenario hazards, to characterize the vulnerability of a building portfolio and to directly inform resilience-driven decisions at the community level. The paper concludes with an illustration of the development of BPFFs to the Centerville community.

Resilience-based post-disaster recovery strategies for road-bridge networks

Abstract This paper presents a novel resilience-based framework to optimise the scheduling of the post-disaster recovery actions for road-bridge transportation networks. The methodology systematically incorporates network topology, redundancy, traffic flow, damage level and available resources into the stochastic processes of network post-hazard recovery strategy optimisation. Two metrics are proposed for measuring rapidity and efficiency of the network recovery: total recovery time (TRT) and the skew of the recovery trajectory (SRT). The TRT is the time required for the network to be restored to its pre-hazard functionality level, while the SRT is a metric defined for the first time in this study to capture the characteristics of the recovery trajectory that relates to the efficiency of those restoration strategies considered. Based on this two-dimensional metric, a restoration scheduling method is proposed for optimal post-disaster recovery planning for bridge-road transportation networks. To illustrate the proposed methodology, a genetic algorithm is used to solve the restoration schedule optimisation problem for a hypothetical bridge network with 30 nodes and 37 bridges subjected to a scenario seismic event. A sensitivity study using this network illustrates the impact of the resourcefulness of a community and its time-dependent commitment of resources on the network recovery time and trajectory.

Disaggregating community resilience objectives to achieve building performance goals

Resilience is often regarded as an attribute of communities rather than of individual buildings, bridges and other civil infrastructure facilities. Previous research to support resilient infrastructure has considered, for the most part, actions and policies to achieve resilience objectives at the community level. While it is clear that a community cannot be resilient without resilient individual facilities, few attempts have been made to relate the performance criteria for individual facilities to community resilience goals in a quantitative manner. This paper presents a method for relating riskinformed performance criteria for individual buildings exposed to extreme hazards to broader community resilience objectives and illustrates the application of the method to two residential building inventories. The paper demonstrates the feasibility of disaggregating broader community resilience goals to obtain performance objective of individual facilities.

Reliability-based framework for determination of fitness for service of corroding metal pipes

Steel pipelines, whether buried in the ground or exposed to the atmosphere, are susceptible to corrosion, which may impact their structural integrity. Pipeline failures can be catastrophic, especially for pipelines that transport hazardous materials. Maintenance actions, however, are often deferred following detection of localized corrosion due to operational requirements and financial constraints. Consequently, pipeline owners are often confronted with decisions as to whether a corroded pipe is still fit for service with an acceptable reliability or what is the remaining service life of the pipe before it poses a serious threat to public safety. The methodology presented in this paper to predict remaining service life of pressurized steel pipelines can be used to support decisions related to continued safe pipe operation and optimal pipe inspection intervals and maintenance schedules.

LRFD Approach to CFRP Renewal of Prestressed Concrete Cylinder Pipes

Carbon fiber reinforced polymer (CFRP) composites are being used increasingly for renewal of prestressed concrete cylinder pipe (PCCP), due primarily to its easy and speed of installation requiring no excavation of the pipe. Experience in developing probability-based limit states design (PBLSD) criteria for common construction materials points the way forward for making similar advances in guidelines for design and evaluation of PCCP renewal using CFRP composite materials. This paper is aimed at providing technical basis to support such a standard development. The paper reports progress made on developing the PBLSD approach for CFRP renewal of PCCP. Reliability tools and supporting databases that are available for developing the load and resistance design (LRFD) criteria are summarized. A set of load combinations for underground pipe design that are consistent with the modern probability-based load modeling concepts are proposed. The LRFD design formats for pipe strength limit states are presented in a relatively simple, practical and familiar form to facilitate the implementation of CFRP composites in concrete pipeline renewal practices.

The Impact of Climate Change on Resilience of Communities Vulnerable to Riverine Flooding

Riverine flooding due to intense precipitation or snowmelt is one of the most devastating natural hazards in the United States in terms of annual damages and economic losses to the built environment and social impacts on communities. Flood inundation mapping, where the likely depths of extreme floods are placed on a map of the community, is important for evaluating flood risks and for enhancing community resilience. However, the Flood Insurance Rate Maps developed by the Federal Emergency Management Agency are not adequate for the evolving needs for community resilience assessment and decision-making over the next century, during which climate change effects are likely to be significant. In this study, we develop a flood hazard modeling framework to support community resilience assessment. This framework couples a hydrological model, which simulates the hydrological processes in a community at a coarser resolution using measured and/or remote sensed precipitation, with a hydraulic analysis module, which computes localized flood depths, velocities and inundated areas at a finer spatial resolution. The Wolf River Basin in Shelby County, Tennessee, which includes the city of Memphis, is used as a testbed to calibrate and validate this coupled model using precipitation and streamflow data obtained from gauge stations operated by the US Geological Survey and to illustrate the potential impacts of climate change in the 21st Century on civil infrastructure, revealing that such impacts are non-negligible but are manageable by proper engineering.