Quantifying Material Uncertainty in Seismic Evaluations of Reinforced Concrete Bridge Column Structures.

In seismic performance evaluations, the force-deformation response of a structure is typically assessed using a deterministic analytical model, and inherent uncertainty is often neglected. For reinforced concrete structures, a source of uncertainty is variability in the mechanical properties of reinforcing steel and concrete (that is, material uncertainty). This paper presents an analytical investigation to quantify the impact of the statistical variability in mechanical properties of ASTM A706 Grade 60, 80, and 100 reinforcing steel and normalweight concrete on the seismic response of reinforced concrete bridge columns. The effects on the drift response, expressed by the coefficient of variation (COV), range between COV values of 0.1 for low-to-moderate ductility demands (that is, drift ratio < 5%), and 0.3 for larger ductility demands. The COV of the force demand is lower, ranging between 0.05 and 0.1. Overall, the study shows that material uncertainty can be incorporated in seismic performance assessments through a few additional analyses.

Review of Seismic Risk Mitigation Policies in Earthquake-Prone Countries: Lessons for Earthquake Resilience in the United States.

This article reviews the current state of practice in seismic risk mitigation, focusing on policies in ten of the most earthquake-prone countries around the world. In particular, the review compares policies to retrofit existing buildings and mechanisms for financing seismic risk mitigation, within the context of seismic risk and design standards for each country. The goal of the review is to identify policy best practices that may be useful for national and local governments that are interested in improving their earthquake resilience. The result is a set of best practice recommendations that are organized conceptually around key stages of the seismic retrofit process: (1) risk assessment; (2) knowledge transfer; (3) setting targets; (4) implementation; and (5) monitoring. While these lessons may be valuable to any earthquake-prone country, the recommendations are framed with particular attention to the United States where seismic risk mitigation is primarily the responsibility of local governments.

Motivators and impediments to seismic retrofit implementation for wood-frame soft-story buildings: A case study in California.

Motivating property owners to mitigate seismic risks for existing buildings is a major challenge for many earthquake-prone regions. This article identifies primary factors that may affect the adoption of seismic retrofit by owners of commercial and residential buildings, assesses the influence of economic, social, regulatory, and individual factors on retrofit implementation in three California cities, and discusses potential approaches to promoting seismic retrofits. Data for three retrofit programs are utilized to create predictive models for retrofit probability. The results suggest that retrofit probability for multifamily residential buildings may increase with building height, median housing value, educational attainment, and population density in the neighborhood, but may decrease with building age, building size, land value, and housing vacancy rate in the neighborhood. The retrofit decision for commercial buildings is strongly correlated with the number of stories and rooms, land value, vacancy rate, and population density, while the retrofit decision for residential buildings is highly associated with building age, number of rooms, land value, median housing value, median contract rent, and educational attainment. Overall, promoting seismic retrofits requires careful consideration of different motivators and impediments to owner's retrofit actions for commercial and residential buildings, and for older, taller, larger buildings, which tend to be more vulnerable but are associated with higher retrofit costs. In addition, neighborhood characteristics including median housing value and vacancy rate may be strong indicators of the retrofit probability among building clusters.

The Total Costs of Seismic Retrofits: State of the Art.

This article presents the current state-of-practice with respect to quantifying the total cost to retrofit an existing building. In particular, we combine quantitative, qualitative, and heuristic data to provide a taxonomy for understanding the direct and indirect costs associated with seismic risk mitigation. Much of the literature to date has focused on estimating structural retrofit costs, the costs of retrofitting the structural elements of a building. In contrast, there is very little research or data on the remaining cost components of the total cost. We propose using structural cost as the foundation for approximating the remaining cost components and the total cost itself. To validate our findings, we compare the proposed approximations with actual cost estimates developed by engineering professionals.

A Predictive Modeling Approach to Estimating Seismic Retrofit Costs.

This paper presents a methodology for estimating seismic retrofit costs from historical data. In particular, historical retrofit cost data from FEMA 156 is used to build a generalized linear model (GLM) to predict retrofit costs as a function of building characteristics. While not as accurate as an engineering professional's estimate, this methodology is easy to apply to generate quick estimates and is especially useful for decision makers with large building portfolios. Moreover, the predictive modeling approach provides a measure of uncertainty in terms of prediction error. The paper uses prediction error to compare different modeling choices, including the choice of distribution for costs. Finally, the proposed retrofit cost model is implemented to estimate the cost to retrofit a portfolio of federal buildings. The application illustrates how the choice of distribution affects cost estimates.

Social and Economic Components of Resilient Multi-Hazard Building Design.

In 2017, U.S. damages from natural hazard events exceeded $300B, suggesting that current targets for building performance do not sufficiently mitigate loss. The significant costs borne by individuals, insurers, and government do not include impacts from social disruption, displacement, and subsequent economic and livelihood effects. In 2016, Congress mandated the National Institute of Standards and Technology (NIST) develop a report (NIST SP 1224) describing the research needs, implementation activities, and engineering principles necessary to improve the performance of residential and commercial buildings subjected to natural hazards. An Immediate Occupancy Performance Objective (IOPO) could help preserve building and social functions post event, minimizing physical, social, and economic disaster. The stakeholder-informed NIST report sets forth items needed for multi-hazard building design that can support enhanced resilience decision-making. This paper highlights the social and economic considerations that require additional research, particularly with regard to feasibility and potential impacts from an IOPO. These topics must be considered prior to and throughout the IOPO technical development and community implementation processes to ensure better outcomes after natural hazard events.