Failure and size effect for notched and unnotched concrete beams

Modelling failure in geomaterials, concrete or other quasi‐brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three‐point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral‐type non‐local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd.     

A four elements porous model to estimate the strength of unsaturated soils

One of the most prevalent relationships for effective stresses on unsaturated soils was proposed by Bishop in the middle of the last century. However, only recently Bishop’s effective stress equation has been implemented in various constitutive models for unsaturated soils. These models have the advantage of naturally including the hydro-mechanical coupling that has been experimentally observed on these materials. Unfortunately, the problem of properly evaluating Bishop’s parameter χ still remains unsolved. This paper presents the results of a solid-porous model used to determine the value of Bishop’s parameter χ and evaluate the strength of unsaturated soils. These theoretical results are compared with a series of triaxial test performed on a silty sand subjected to different suctions in wet and dry paths. These comparisons show that the porous model proposed herein can be used to estimate the strength of unsaturated soils for both the wetting and the drying paths.     

The Southern Westerlies during the last glacial maximum in PMIP2 simulations

The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales. Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO₂. The position, intensity, and associated climatology of the southern westerlies during the last glacial maximum (LGM), however, is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM than at present with a clear decrease in precipitation south of 40°S over the oceans. We identify important differences in precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over NW Patagonia.     

The effect of habitat and environmental history on otolith chemistry of barramundi Lates calcarifer in estuarine populations of a regulated tropical river

We examine the microchemistry of otoliths of cohorts of a fished population of the large catadromous fish, barramundi Lates calcarifer from the estuary of a large tropical river. Barramundi from the estuary of the large, heavily regulated Fitzroy River, north-eastern Australia were analysed by making transects of ⁸⁷Sr/⁸⁶Sr isotope and trace metal/Ca ratios from the core to the outer edge. Firstly, we examined the Sr/Ca, Ba/Ca, Mg/Ca and Mn/Ca and ⁸⁷Sr/⁸⁶Sr isotope ratios in otoliths of barramundi tagged in either freshwater or estuarine habitats that were caught by the commercial fishery in the estuary. We used ⁸⁷Sr/⁸⁶Sr isotope ratios to identify periods of freshwater residency and assess whether trace metal/Ca ratios varied between habitats. Only Sr/Ca consistently varied between known periods of estuarine or freshwater residency. The relationships between trace metal/Ca and river flow, salinity, temperature were examined in fish tagged and recaptured in the estuary. We found weak and inconsistent patterns in relationships between these variables in the majority of fish. These results suggest that both individual movement history within the estuary and the scale of environmental monitoring were reducing our ability to detect any patterns. Finally, we examined fish in the estuary from two dominant age cohorts (4 and 7 year old) before and after a large flood in 2003 to ascertain if the flood had enabled fish from freshwater habitats to migrate to the estuary. There was no difference in the proportion of fish in the estuary that had accessed freshwater after the flood. Instead, we found that larger individuals with of each age cohort were more likely to have spent a period in freshwater. This highlights the need to maintain freshwater flows in rivers. About half the fish examined had accessed freshwater habitats before capture. Of these, all had spent at least their first two months in marine salinity waters before entering freshwater and some did not enter freshwater until four years of age. This contrasts with the results of several previous studies in other parts of the range that found that access to freshwater swamps by larval barramundi was important for enhanced population productivity and recruitment.     

Geographical object–oriented databases—a case study

ABSTRACT

An Australian standard for Spatial Data Transfer modelled on the draft American standard is likely to be introduced in 1993. The spatial data model is not accommodated by existing DBMS such as relational systems. Using this model as an example, the suitability of object–oriented database systems for geographical databases is demonstrated. Some initial performance figures obtained with the ONTOS system on an example database are given.     

CMIP3 projected changes in the annual cycle of the South American Monsoon

Nine models from the Coupled Model Intercomparison Project version 3 dataset are employed to examine projected changes in the South American Monsoon System annual cycle by comparing the 20th Century and SRES A2 scenarios. The following hypotheses are examined: (1) the warm season climate responses in the Southeast, Continental South Atlantic Convergence Zone (CSACZ) and Monsoon regions are related by regional circulation and moisture transport changes which, in turn, must be consistent with robust large-scale changes in the climate system, and (2) an increased threshold for convection in a warmer world may affect the timing of warm season rains. The present analysis reaffirms that the Southeast region is likely to experience increased precipitation through the warm season. Additional results exhibit more uncertainty due to large inter-model variance and disagreement in the A2 scenarios. Nevertheless several statistically significant results are found. In the Monsoon and to a lesser extent in the CSACZ region, the multi-model median suggests reduced precipitation during spring (Sep–Nov). These continental precipitation changes are accompanied by a southward shift of the maximum precipitation in the South Atlantic Convergence Zone. Changes in circulation include a poleward displaced South Atlantic Anticyclone (SAAC) and enhanced moisture transport associated with a strengthened northerly low level flow east of the Andes during spring. Moisture transport divergence calculations indicate unchanged divergence in the Monsoon region during spring and increased convergence in the Southeast throughout the warm season. The circulation and moisture transport changes suggest the increased precipitation in the Southeast during spring may be related to changes in the SALLJ and SAAC, which both enhance moisture transport to the Southeast. The seasonally dry Monsoon region is further affected by an increased threshold for convection in the warmer, more humid and stable climate of the 21st century, which combined with the circulation changes may weaken the onset of the rainy season. Although there is substantial variability among the models, and the results are represented by small changes compared with the multi-model variance, their statistical significance combined with their consistency with expected robust large scale changes provides a measure of confidence in otherwise tentative results. Further testing of the relationships presented here will be required to fully understand projected changes in the South American Monsoon.     

The Loncopué Trough: A Cenozoic basin produced by extension in the southern Central Andes

The Loncopué Trough is located in the hinterland Andean zone between 36°30′ and 39°S. It constitutes a topographic low bounded by normal faults and filled by lavas and sediments less than 5 Ma old. Reprocessed seismic lines show wedge-like depocenters up to 1700 m deep associated with high-angle faults, correlated with the 27–17 Ma Cura Mallín basin deposits, and buried beneath Pliocene to Quaternary successions and Late Miocene foreland sequences. The southern Central Andes seem to have been under extension in the hinterland zone some 27 Ma ago and again at approximately 5 Ma ago. This last extensional period could have been the product of slab steepening after a shallow subduction cycle in the area, although other alternatives are discussed. Orogenic wedge topography, altered by the first extensional stage in the area, was recovered through Late Miocene inversion, and was associated with foreland sequences. However, since the last extension (<5 Ma) the Andes have not recovered their characteristic contractional behavior that controlled past orogenic growth.