Calculation of reinforced concrete beam reliability on operation stage by crack length criterion

The mechanical (structural) reliability of a building, safety of people and continuity of the technological processes in buildings and structures depend on the reliability of the bearing structures on operation stage, including reinforced concrete beams. One of the measures to provide safety and reliability is the probability of no-failure operation of structural elements or systems of elements. For reliability calculation the Russian State Standard recommends to apply probability and statistical methods when possessing enough data on variability of the controlled parameters in the mathematical model of the limit state, in particular, when the amount of data allows conducting its statistical analysis. In the current time there appear the works pointing, that the future advancing of calculation methods for building structures requires the wide use of reliability theory. The article describes the methods for calculating the reliability of a reinforced concrete beam according to the criterion of crack length with the limited statistical information about controlled parameters. The authors illustrate the application of the theory of evidence to determine the statistical mathematical expectation of reliability in the presence of a subset of reliability intervals. Each design case is followed by numerical examples. The article underlines the importance of applying fracture mechanics for the further development of the methods of calculation of reinforced concrete structures

Last Glacial Maximum records in permafrost of the East Siberian Arctic

Palaeontological proxy data and cryolithological information from Siberian Arctic permafrost preserves records of late Quaternary climate and environmental conditions in West Beringia and their variability which results from interglacial-glacial and interstadial-stadial dynamics. To date, the Last Glacial Maximum (LGM) period has been rather poorly represented in East Siberian permafrost records. Here, we present pollen, sediment, and ground-ice stable water isotope data obtained from coastal exposures on Bol'shoy Lyakhovsky Island (New Siberian Archipelago, Arctic Ocean) that mirror the coldest conditions during the Sartan period between about 26 and 22 ka BP, using pollen and sediment data for summer conditions and stable water isotope data for winter conditions. The pollen record revealed a cold tundra-steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice-wedges data indicate extremely cold winter temperatures with mean values of delta O-18 of about -37 parts per thousand, delta D of about -290 parts per thousand. Combined with available regional LGM permafrost records that extend from the Taymyr Peninsula in the west to the Yana River lowland in the east, the new data set from Bol'shoy Lyakhovsky Island indicate that the regional appearance of LGM conditions depended on atmospheric circulation patterns that were influenced by the extent of the Northern Hemisphere glaciation. (C) 2011 Elsevier Ltd. All rights reserved