A Survey of Bridge Practitioners to Relate Damage to Closure

The Pacific Earthquake Engineering Research (PEER) Center's second-generation performance-based earthquake engineering (PBEE) methodology is intended in part to model highway bridge performance in terms of collapse, closure, repair duration, speed or load limitations, and possibly other performance measures. Some of these are difficult to model, particularly closure decisions where the engineering evidence of safety is inconclusive and must be supplemented by the inspector's judgment. This paper presents results of a limited, initial survey of department of transportation (DOT) engineers' beliefs about the relationship between physical damage and closure. The initial survey addresses a common class of reinforced-concrete bridges. The author and others developed and administered to a select, nationwide group of DOT engineers a one-page, multiple-choice survey form with expert self-rating, asking the engineers to relate ten damage measures (DM) to four closure levels. The DMs include approach settlement, offsets at abutments and expansion joints, flexural and shear cracks in beams, columns, shear keys, and backwalls. The performance levels considered are: leave open, close briefly for quick repairs, close for an extended period, and reduce speed. The survey results are analyzed to produce a number of preliminary relationships between damage and post-earthquake decisions by inspectors, relationships that can be used in probabilistic seismic performance evaluation in PEER's developing PBEE methodology. This preliminary test of a survey form also yielded insight into a number of desirable improvements for a second round of survey, possibly to be administered via the Internet early in 2004

Simplified PBEE to Estimate Economic Seismic Risk for Buildings

A seismic risk assessment is often performed on behalf of a buyer of large commercial buildings in seismically active regions. One outcome of the assessment is that a probable maximum loss (PML) is computed. PML is of limited use to real-estate investors as it has no place in a standard financial analysis and reflects too long a planning period for what-if scenarios. We introduce an alternative to PML called probable frequent loss (PFL), defined as the mean loss resulting from an economic-basis earthquake such as shaking with 10% exceedance probability in 5 years. PFL is approximately related to expected annualized loss (EAL) through a site economic hazard coefficient (H) introduced here. PFL and EAL offer three advantages over PML: (1) meaningful planning period; (2) applicability in financial analysis (making seismic risk a potential market force); and (3) can be estimated by a rigorous but simplified PBEE method that relies on a single linear structural analysis. We illustrate using 15 example buildings, including a 7-story nonductile reinforced-concrete moment-frame building in Van Nuys, CA and 14 buildings from the CUREE-Caltech Woodframe Project

Uncertainty Propagation and Feature Selection for Loss Estimation in Performance-based Earthquake Engineering

This report presents a new methodology, called moment matching, of propagating the uncertainties in estimating repair costs of a building due to future earthquake excitation, which is required, for example, when assessing a design in performance-based earthquake engineering. Besides excitation uncertainties, other uncertain model variables are considered, including uncertainties in the structural model parameters and in the capacity and repair costs of structural and non-structural components. Using the first few moments of these uncertain variables, moment matching requires only a few well-chosen point estimates to propagate the uncertainties to estimate the first few moments of the repair costs with high accuracy. Furthermore, the use of moment matching to estimate the exceedance probability of the repair costs is also addressed. These examples illustrate that the moment-matching approach is quite general; for example, it can be applied to any decision variable in performance-based earthquake engineering. Two buildings are chosen as illustrative examples to demonstrate the use of moment matching, a hypothetical three-story shear building and a real seven-story hotel building. For these two examples, the assembly-based vulnerability approach is employed when calculating repair costs. It is shown that the moment-matching technique is much more accurate than the well-known First-Order-Second-Moment approach when propagating the first two moments, while the resulting computational cost is of the same order. The repair-cost moments and exceedance probability estimated by the moment-matching technique are also compared with those by Monte Carlo simulation. It is concluded that as long as the order of the moment matching is sufficient, the comparison is satisfactory. Furthermore, the amount of computation for moment matching scales only linearly with the number of uncertain input variables. Last but not least, a procedure for feature selection is presented and illustrated for the second example. The conclusion is that the most important uncertain input variables among the many influencing the uncertainty in future repair costs are, in order of importance, ground-motion spectral acceleration, component capacity, ground-motion details and unit repair costs

Simplified Estimation of Economic Seismic Risk for Buildings

A seismic risk assessment is often performed on behalf of a buyer of commercial buildings in seismically active regions. One outcome of the assessment is that a probable maximum loss (PML) is computed. PML is of limited use to real-estate investors as it has no place in a standard financial analysis and reflects too long a planning period. We introduce an alternative to PML called probable frequent loss (PFL), defined as the mean loss resulting from shaking with 10% exceedance probability in 5 years. PFL is approximately related to expected annualized loss (EAL) through a site economic hazard coefficient (H) introduced here. PFL and EAL offer three advantages over PML: (1) meaningful planning period; (2) applicability in financial analysis (making seismic risk a potential market force); and (3) can be estimated using a single linear structural analysis, via a simplified method called linear assembly-based vulnerability (LABV) that is presented in this work. We also present a simple decision-analysis framework for real-estate investments in seismic regions, accounting for risk aversion. We show that market risk overwhelms uncertainty in seismic risk, allowing one to consider only expected consequences in seismic risk. We illustrate using 15 buildings, including a 7-story nonductile reinforced-concrete moment-frame building in Van Nuys, California, and 14 buildings from the CUREE-Caltech Woodframe Project

Sensitivity of Building Loss Estimates to Major Uncertain Variables

This paper examines the question of which sources of uncertainty most strongly affect the repair cost of a building in a future earthquake. Uncertainties examined here include spectral acceleration, ground-motion details, mass, damping, structural force-deformation behavior, building-component fragility, contractor costs, and the contractor's overhead and profit. We measure the variation (or swing) of the repair cost when each basic input variable except one is taken at its median value, and the remaining variable is taken at its 10th and at its 90th percentile. We perform this study using a 1960s highrise nonductile reinforced-concrete moment-frame building. Repair costs are estimated using the assembly-based vulnerability (ABV) method. We find that the top three contributors to uncertainty are assembly capacity (the structural response at which a component exceeds some damage state), shaking intensity (measured here in terms of damped elastic spectral acceleration, Sa), and details of the ground motion with a given Sa

Cost-Effectiveness of Stronger Woodframe Buildings

We examine the cost-effectiveness of improvements in woodframe buildings. These include retrofits, redesign measures, and improved quality in 19 hypothetical woodframe dwellings. We estimated cost-effectiveness for each improvement and each zip code in California. The dwellings were designed under the CUREE-Caltech Woodframe Project. Costs and seismic vulnerability were determined on a component-by-component basis using the Assembly Based Vulnerability method, within a nonlinear time-history structural-analysis framework and using full-size test specimen data. Probabilistic site hazard was calculated by zip code, considering site soil classification, and integrated with vulnerability to determine expected annualized repair cost. The approach provides insight into uncertainty of loss at varying shaking levels. We calculated present value of benefit to determine cost-effectiveness in terms of benefit-cost ratio (BCR). We find that one retrofit exhibits BCRs as high as 8, and is in excess of 1 in half of California zip codes. Four retrofit or redesign measures are cost-effective in at least some locations. Higher quality is estimated to save thousands of dollars per house. Results are illustrated by maps for the Los Angeles and San Francisco regions and are available for every zip code in California

An X-ray absorption spectroscopic study at the mercury LIII edge on phenylmercury(II) oxygen species

The X-ray absorption spectra of the reference and model compounds HgCl2, PhHgCl, PhHgOAc and [(PhHg)2OH][BF4].H2O have been analysed in both the XANES and EXAFS regions, and the technique was extended to determine the structures of (PhHg)2O, PhHgOH, and the basic salts PhHgOH.PhHgNO3 and PhHgOH.(PhHg)2SO4, which were previously structurally uncharacterised. Results indicate that (PhHg)2O is a molecular species with Hg-O-Hg 135°, while PhHgOH contains the [(PhHg)2OH]+ cation and is better formulated as [(PhHg)2OH]OH. The same cation is also featured in the two basic salts. Electrospray mass spectral studies of PhHgOH in aqueous solutions show that [PhHgOH2]+, [(PhHg)2OH]+ and [(PhHg)3O]+ co-exist in solution in a pH-dependent equilibrium