Artificial neural networks and their application to assessment of ultimate strength of plates with pitting corrosion

The potential for the structural capability degrading effects of both corrosion and fatigue induced cracks are of profound importance and must be both fully understood and reflected in vessel's inspection and maintenance programme. Corrosion has been studied and quantified by many researchers, however its effect on structural integrity is still subject to uncertainty, particularly with regards to localized corrosion. The present study is focused on assessing the effects of localized pitting corrosion on the ultimate strength of unstiffened plates. Over 265 non-linear finite-element analyses of panels with various locations and sizes of pitting corrosion have been carried out. The results indicate that the length, breadth and depth of pit corrosion have weakening effects on the ultimate strength of the plates while plate slenderness has only marginal effect on strength reduction. Transverse location of pit corrosion is also an important factor determining the amount of strength reduction. When corrosion spreads transversely on both edges, it has the most deteriorating effect on strength. In addition, artificial neural network (ANN) method is applied to derive a formula to predict ultimate strength reduction of locally corroded plates. It is found out that the proposed formulae can accurately predict the ultimate strength of locally corroded plates under uniaxial in-plane compression.     

Earthquake effects on the Anatolian Motorway, Turkey

On 12 November 1999, the Anatolian earthquake in Turkey damaged a partially completed motorway viaduct. The viaduct, which is some 2.3 km long, passes over the Düzce Fault as the route starts its ascent into the Turkish plateau. The Düzce Fault is a northern offshoot of the main North Anatolian Fault (NAF) Zone, and cuts the viaduct at an acute angle of 15 degrees. Movements along the NAF have been identified as the prime cause of the earthquake. Alternatives to a viaduct crossing had been considered in the feasibility stage, but were ruled out because of the rugged landslide-influenced terrain and requirements for an even motorway ascent grade. The relative displacement of around 120 equally spaced piers identified the nature of the ground displacements and gave an indication as to the likely areas of foundation damage. This article examines the damage caused to the viaduct during the earthquake.     

Experimental study of a sloping float breakwater

The aim of this study was to evaluate the performance of a sloping float (or inclined pontoon) breakwater with respect to expected wave climate for protection of small commercial vessels and yatch marinas. A two-dimensional model study was carried out for regular waves in intermediate water depths. The experimental results showed that the transmission coefficient was relatively insensitive to wave height and that it consistently increased as the wave period decreased. The performance of this type of breakwater was found to be promising for intermediate water depths.     

Meiofaunal Colonization of Artificial Substrates in an Estuarine Embayment

Abstract. Artificial substrates were used to investigate the cryptic meiofauna of a Louisiana estuary. Three types of collectors were used as artificial habitats in colonization studies. Mesh collectors (composed of a plastic thread, approximately 74 m long, woven into a pad) and bottle brushes (with approximately 4400 plastic bristles per brush, each 2.5 mm long) were colonized equally well by meiofauna; Hester-Dendy plates with less structural complexity were colonized at a slower rate, especially by copepods. Nematodes and harpacticoid copepods were always the two most abundant meiofaunal taxa collected. Mesh collectors were retrieved in July and December after a 2-week colonization period to examine seasonal trends. Starting in December, a long-term colonization study was also performed to determine if an equilibrium abundance could be achieved; artificial substrates were collected after 2, 4 and 8 weeks. Meiofauna achieved high abundances (means ranged from 1000 – 20,000 individuals per collector) on artificial substrates regardless of season, and abundance was related to supply, water flow and capture efficiency of the substrates as well as behavior of the meiofauna. Copepod species diversity was low (6 species were observed in July and 11 in December). Diversity and evenness were significantly different between July and December, and among the three collections in the long-term study. The copepod species assemblage qualitatively differed between July and December. Our data suggest that an abundant and dynamic but understudied meiofaunal assemblage is present in this estuarine embayment. This assemblage is not associated with macroalgae but rather related to presence of hard substrates and seasonally abundant filamentous microalgae.     

Analysis of faulting in porous sandstones

Faults in porous sandstones occur in three forms: deformation bands about 1-mm thick and tens of m long and across which offsets are a few mm; zones of deformation bands constituted of many closely spaced deformation bands across which offsets are a few cm or dm; and slip surfaces, that is, distinct surfaces within zones of deformation bands across which offsets are a few m to a few tens of m. Deformation bands represent highly localized deformation; analogous localization within a field of homogeneous deformation is theoretically possible in inelastic materials with certain ranges of constitutive parameters. Crushing and consolidation of sandstone within a band cause the material there to become stiffer than the surrounding porous sandstone. A zone of deformation bands behaves mesoscopically much as a stiff inclusion in a soft matrix. According to the constitutive model assumed to investigate the formation of deformation bands, an instability can develop, and strain increments within the zone of deformation bands can become boundlessly large when the far-field stresses reach critical values. This instability is here associated with the formation of slip surfaces.     

The cyclic behaviour of soils and effects of geotechnical factors in microzonation

Geotechnical site conditions that can be very different due to changes in thickness and properties of soil layers, depth of bedrock and water table are among the main factors controlling earthquake characteristics on the ground surface. Soil layers subjected to cyclic stresses may lead to degradation of stress–strain and shear strength properties. The laboratory tests were conducted to evaluate the changes in the stress–strain and shear strength characteristics in terms of threshold cyclic shear stresses and cyclic yield stress. The effects of local site conditions are assessed based on geotechnical site conditions and earthquake source characteristics.