Creating Fragility Functions for Performance-Based Earthquake Engineering

The Applied Technology Council is adapting PEER's performance-based earthquake engineering methodology to professional practice. The methodology's damage-analysis stage uses fragility functions to calculate the probability of damage to facility components given the force, deformation, or other engineering demand parameter (EDP) to which each is subjected. This paper introduces a set of procedures for creating fragility functions from various kinds of data: (A) actual EDP at which each specimen failed; (B) bounding EDP, in which some specimens failed and one knows the EDP to which each specimen was subjected; (C) capable EDP, where specimen EDPs are known but no specimens failed; (D) derived, where fragility functions are produced analytically; (E) expert opinion; and (U) updating, in which one improves an existing fragility function using new observations. Methods C, E, and U are all introduced here for the first time. A companion document offers additional procedures and more examples

Occurrence of Kelvin-Helmholtz Billows in Sea-breeze Circulations

Centred at the interface between the sea-breeze and the return flow aloft, Kelvin-Helmholtz billows (KHB) are an important feature of the turbulent structure of some sea-breeze circulations (SBCs). In other SBCs, there are no prominent KHBs observed. Factors governing the appearance of billows are determined from a database of 139 sea breezes, constructed from two years of summertime surface observations at a site on the south coast of England. Post-frontal oscillations occur in the surface data for some SBCs and are interpreted as indicating possible KHBs aloft. The SBCs are formed under a wide range of synoptic conditions, enabling various measures of possible billow occurrence to be related to properties of the large-scale, ambient flow. Consistent with laboratory experiments of density currents, KHBs are suppressed for propagation into a head wind and enhanced with a tail wind. They are also found to be enhanced for stronger ambient wind speeds, while large-scale coast-parallel flow is effective in suppressing the billows

New instabilities of de Sitter spacetimes

We construct an instanton describing the pair production of non-Kaluza Klein bubbles of nothing in higher odd dimensional de Sitter spaces. In addition to showing that higher dimensional de Sitter spaces have a nonzero probability to become topologically nontrivial, this process provides direct evidence for the association of entropy with cosmological horizons and that non-Kaluza Klein bubbles of nothing are a necessary ingredient in string theory or any other consistent quantum theory of gravity in higher dimensions.Comment: 19 pages, 1 figur

Effect of ENSO phase on large-scale snow water equivalent distribution in a GCM

Understanding links between the El Nino-Southern Oscillation (ENSO) and snow would be useful for seasonal forecasting, but also for understanding natural variability and interpreting climate change predictions. Here, a 545-year run of the general circulation model HadCM3, with prescribed external forcings and fixed greenhouse gas concentrations, is used to explore the impact of ENSO on snow water equivalent (SWE) anomalies. In North America, positive ENSO events reduce the mean SWE and skew the distribution towards lower values, and vice versa during negative ENSO events. This is associated with a dipole SWE anomaly structure, with anomalies of opposite sign centered in western Canada and the central United States. In Eurasia, warm episodes lead to a more positively skewed distribution and the mean SWE is raised. Again, the opposite effect is seen during cold episodes. In Eurasia the largest anomalies are concentrated in the Himalayas. These correlations with February SWE distribution are seen to exist from the previous June-July-August (JJA) ENSO index onwards, and are weakly detected in 50-year subsections of the control run, but only a shifted North American response can be detected in the anaylsis of 40 years of ERA40 reanalysis data. The ENSO signal in SWE from the long run could still contribute to regional predictions although it would be a weak indicator onl

The cyclical behavior of state employment during the postwar period

This study documents a substantial decline in employment volatility at business-cycle frequencies over the postwar period using state-industry level data. The distribution of total employment volatilities at the state level has become less disperse over time, and mean volatility has fallen. Similar results are obtained using employment data on one-digit sectors across states: all sectors have seen a decline in employment volatility over the postwar period, and state-sectors are more alike in terms of volatility levels. A key source of the decline in volatility appears to be widespread (across states and industries) decreases in the size of shocks hitting employment levels. Shifts in the demographic factors, and industrial structures of state economies have had little or no impact. Neither have inter-state employment shifts, such as migrations from the Frostbelt to the Sunbelt. The sources of the smaller employment shocks are unclear, although the evidence points to macroeconomic phenomena.Employment (Economic theory)

Private Crop Insurers and the Reinsurance Fund Allocation Decision

This research investigates the strategic behavior of private crop insurance firms reinsured by the USDA through the Standard Reinsurance Agreement. This arrangement allows the private firm to strategically allocate individual policies into different risk sharing arrangements. Thus, firm earnings are conditioned upon accurately forecasting policy loss experience. Our analysis begins with models investigating the characteristics explaining the placement of policies into the assigned risk fund. Then a simulation model of the SRA is used to compare the post-SRA returns of actual firm allocations to two alternative allocation strategies based on aggregate models and a policy-level econometric forecasting model.Risk, insurance, reinsurance, logit, policy

On the stability of employment growth: a postwar view from the U.S. states.

In 1952, the average quarterly volatility of U.S. state employment growth stood at 1.5 percent. By 1995, employment growth volatility came in at just under 0.5 percent. While all states shared in the decline, some states declined much more dramatically than others. We analyze aspects of this decline using new data covering industry employment by state during the postwar period. Estimates from a pooled cross-section/time-series model corrected for spatial dependence indicate that fluctuations in state-specific and aggregate variables have both played an important role in explaining volatility trends. However, state-level differences in responses to aggregate shocks account for less of the postwar fluctuations in employment growth volatility than do state-specific forces.Employment (Economic theory)