The 1st year of the COVID-19 epidemic in Estonia: a population-based nationwide sequential/consecutive cross-sectional study.

OBJECTIVES: The objective of this study was to assess the population prevalence of SARS-CoV-2 and changes in the prevalence in the adult general population in Estonia during the 1st year of COVID-19 epidemic. STUDY DESIGN: This was a population-based nationwide sequential/consecutive cross-sectional study. METHODS: Using standardised methodology (population-based, random stratified sampling), 11 cross-sectional studies were conducted from April 2020 to February 2021. Data from nasopharyngeal testing and questionnaires were used to estimate the SARS-CoV-2 RNA prevalence and factors associated with test positivity. RESULTS: Between April 23, 2020, and February 2, 2021, results were available from 34,915 individuals and 27,870 samples from 11 consecutive studies. The percentage of people testing positive for SARS-CoV-2 decreased from 0.27% (95% confidence interval [CI] = 0.10%-0.59%) in April to 0.04% (95% CI = 0.00%-0.22%) by the end of May and remained very low (0.01%, 95% CI = 0.00%-0.17%) until the end of August, followed by an increase since November (0.37%, 95% CI = 0.18%-0.68%) that escalated to 2.69% (95% CI = 2.08%-2.69%) in January 2021. In addition to substantial change in time, an increasing number of household members (for one additional odds ratio [OR] = 1.15, 95% CI = 1.02-1.29), reporting current symptoms of COVID-19 (OR = 2.21, 95% CI = 1.59-3.09) and completing questionnaire in the Russian language (OR 1.85, 95% CI 1.15-2.99) were associated with increased odds for SARS-CoV-2 RNA positivity. CONCLUSIONS: SARS-CoV-2 population prevalence needs to be carefully monitored as vaccine programmes are rolled out to inform containment decisions.

Sensitivity of response of isolated bridges to modeling and design parameters : A case study

The concept of base isolations in bridges implies that structural components should experience limited inelastic behavior associated only with minor damage. Most isolation systems are designed to eliminate altogether inelastic behavior. The estimation uncertainties during the design process of the future ground motions, associated with the uncertainties involved in the constructed practice, leave the possibility that the entire system will ecperience inelastic behavior with permanent deformations and damage.(AU)

Implications of spatial variation of ground motion on the seismic response of bridges : Case study

Linear and non-linear analytical studies were conducted for evaluating the performance of the southbound separatin and overhead bridge at the SR14/15 interchange during the Northridge earthquake of January 17, 1994. The analyses are focused on potential implications of the spatial variability of ground motion on the collapse of the structure. The influences of vertical ground motion, soil-structure interaction and non-linear contact effects at the expansion joints and abutments, are also examined. The parameter studies help to determine some of the causes of collapse and offer insight on the complex seismic behavior of long multi-span concrete bridges. (AU)