Steel–concrete–steel sandwich system in Arctic offshore structure: Materials, experiments, and design

The gravity based structure (GBS) with external Steel–Concrete–Steel (SCS) sandwich ice-resistant wall has been developed for the Arctic oil and gas drilling. This paper firstly reported the experimental studies on the mechanical properties of steel and concretes under Arctic low temperature. With the test data, design equations were developed to incorporate the influences of the low temperature on these mechanical properties. Two types of Arctic GBS structure with flower-conical SCS sandwich shell type and plate type of ice-resistant wall have been developed for the Arctic offshore structure. Besides the studies on the materials, two SCS sandwich prototype shells and plates were, respectively, prepared and tested under patch loading that simulated the localized ice-contact pressure. The structural behaviors of the SCS sandwich structure under patch loading were reported and discussions were made on the influences of different parameters on the structural behavior of the structure. Analytical models were developed to predict the punching shear resistances of the SCS sandwich structure through modifying the code provisions. The accuracies of the developed analytical models were checked through validations against 27 tests in the literature. Corresponding design procedures on resistances of SCS sandwich structure were recommended based on these discussions and validations.

Influence of inclination angle of plate on friction, stick-slip and transfer layer-A study of magnesium pin sliding against steel plate

In this study, sliding experiments were conducted using pure magnesium pins against steel plates using an inclined pin-on-plate sliding tester. The inclination angle of the plate was varied in the tests and for each inclination angle, the pins were slid both perpendicular and parallel to the unidirectional grinding marks direction under both dry and lubricated conditions. SEM was used to study morphology of the transfer layer formed on the plates. Surface roughness of plates was measured using an optical profilometer. Results showed that the friction, amplitude of stick-slip motion and transfer layer formation significantly depend on both inclination angle and grinding marks direction of the plates. These variations could be attributed to the changes in the level of plowing friction taking place at the asperity level during sliding.

Studies on friction and formation of transfer layer when Al-4Mg alloy pins slid at various numbers of cycles on steel plates of different surface texture

In the present investigation, various kinds of textures, namely, unidirectional, 8-ground, and random were attained on the die surfaces. Roughness of the textures was varied using different grits of emery papers or polishing powders. Then pins made of Al-4Mg alloys were slid against steel plates at various numbers of cycles, namely 1, 2, 6, 10 and 20 under both dry and lubricated conditions using an inclined pin-on-plate sliding tester. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. Surface roughness parameters of the plate were measured using an optical profilometer. It was observed that the coefficient of friction and formation of transfer layer during the first few cycles depend on the die surface textures under both dry and lubricated conditions. It was also observed that under lubricated condition, the coefficient of friction decreases with number of cycles for all kinds of textures. However, under dry condition, it ecreases for unidirectional and 8-ground surfaces while for random surfaces it increases with number of cycles

CFRP strengthened CFST columns under vehicular impact

Concrete filled steel tubular (CFST) columns are increasingly used in bridge piers and high-rise buildings due to their excellent axial load bearing capacity. These columns may experience severe damage or failure due to transverse impact of vehicle collisions. In this study, numerical investigation is carried out to evaluate the effect of carbon fibre reinforced polymer (CFRP) strengthening CFST columns under vehicular impact. The CFRP composites damage mechanisms are simulated to account four different failure criteria. The cohesive elements are introduced as interface element to properly simulate the adhesively bonded regime. Simplified vehicle model is also developed to represent real vehicle behaviour. The FE analysis results show that externally bonded CFRP composites improve the impact resistance capacity compared to bare CFST column.

Fire resistance of light gauge steel frame wall systems lined with gypsum plasterboards

Light gauge steel frame (LSF) wall systems are increasingly used in residential and commercial buildings as load bearing and non-load bearing elements. Conventionally, the fire resistance ratings of such building elements are determined using approximate prescriptive methods based on limited standard fire tests. However, recent studies have shown that in some instances real building fire time-temperature curves could be more severe than the standard fire curve, in terms of maximum temperature and rate of temperature rise. This has caused problems for safe evacuation and rescue activities, and in some instances has also lead to the collapse of buildings earlier than the prescribed fire resistance. Therefore a detailed research study into the performance of LSF wall systems under both standard fire and realistic fire conditions was undertaken using full scale fire tests to understand the fire performance of different LSF wall configurations. Both load bearing and non-load bearing full scale fire tests were performed on LSF walls configurations which included single layer, double layer, externally insulated wall panels made up of different steel sections and thicknesses of gypsum plasterboards. The non-load bearing fire test results were utilized to understand the factors affecting the fire resistance of LSF walls, while loading bearing fire test results led to development of simplified methods to predict the fire resistance ratings of load bearing LSF walls exposed to both standard and realistic design fires. This paper presents the results of full scale experimental study and highlights the effects of standard and realistic fire conditions on fire performance of LSF walls.

Fatigue capacity of cold-formed steel roof battens under cyclic wind uplift loads

Steel roofs made of thin cold-formed steel roof claddings and battens are widely used in low-rise residential and industrial buildings all around the world. However, they suffer from premature localised pull-through failures in the batten to rafter connections during high wind events. A recent study proposed a suitable design equation for the pull-through failures of thin steel roof battens. However, it was limited to static wind uplift loading. In contrast, most cyclone/storm events produce cyclic wind uplift forces on roofs for a significantly long period, thus causing premature fatigue pull-through failures at lower loads. Therefore, a series of constant amplitude cyclic load tests was conducted on small and full scale roof panels made of a commonly used industrial roof batten to develop their S-N curves. A series of multi-level cyclic tests, including the recently introduced low-high-low (LHL) fatigue loading test, was also undertaken to simulate a design cyclone. Using the S-N curves, the static pull-through design capacity equation was modified to include the effects of fatigue. Applicability of Miner’s rule was evaluated in order to predict the fatigue damage caused by multi-level cyclic tests such as the LHL test, and suitable modifications were made. The combined use of the modified Miner’s law and the S-N curve of roof battens will allow a conservative estimation of the fatigue design capacity of roof battens without conducting the LHL tests simulating a design cyclone. This paper presents the details of this study, and the results.

Influence of electroslag refining on the hot ductility of AISI 4340 steel in torsion

Electroslag refining is a useful remelting process by which clean steels can be produced for sophisticated applications. In this investigation, AISI 4340 steel has been electroslag refined and the improvement in its hot ductility has been assessed using hot torsion tests; electroslag refining has improved the hot ductility considerably. The temperature at which peak ductility is obtained has also increased — from 1473 K in the unrefined steel to 1573 K in ESR steel. Results indicate that it should be possible to subject the ESR ingot to much higher strains per unit operation during industrial hot working processes such as forging, which would result in a considerable saving of power. The improvement in hot ductility in ESR steel has been attributed primarily to the removal of non-metallic inclusions and the reduction in sulphur content. From the apparent activation energy estimated from the hot torsion data, the dynamic recrystallization process is identified as the mechanism controlling the rate of hot deformation.

Theoretical investigations of the two-bond proton-carbon-13 coupling constants. Angular variations of the couplings involving carboxyl carbon

A formulation has been developed using perturbation theory to evaluate the π-contribution to the nuclear spin coupling constants involving nuclei at least one of which is an unsaturated center. This fromulation accounts for the π-contribution in terms of the core polarization and one-center exchange at the π-center. The formulation developed together with the Dirac vector model and Penney-Dirac bond-order formalisms was employed to calculate the geminal (two-bond) proton coupling constants of carboxyl carbons in α-disubstituted acetic acids. The calculated coupling constants were found to have an orientational dependence. The results of the calculation are in good agreement with the experimental values.

Valence bond analysis of the Kondo chain Hamiltonian

Accurate extrapolations for the ground state energy per site of the one - dimensional Kondo chain system is obtained from exact finite system calculations carried out employing a valence bond scheme. An analysis of the ground state wave function indicates that the localized spin is quenched for all nonzero values of the Kondo exchange constant in one dimension.

An investigation of bond formation in the weakly bound first excited 1Σ and lowest 3Σ states of HeH+

The role of the electronic kinetic energy and its Cartesian components is examined during the formation of the first excited 1�£ and the lowest 3�£ states of HeH+ employing wavefunctions of multi-configuration type with basis orbitals in elliptic coordinates. Results show that the bond formation in these states is preceded primarily by a charge transfer from H to He+ rather than by polarisation of the H-orbital by He+

Study of Friction and Transfer Layer Formation in Copper-Steel Tribo-System: Role of Surface Texture and Roughness Parameters

In the present investigation, experiments were conducted on a tribological couple-copper pin against steel plate-using an inclined pin-on-plate sliding tester to understand the role of surface texture and roughness parameters of the plate on the coefficient friction and transfer layer formation. Two surface characteristics of the steel plates-roughness and texture-were varied in the tests. It was observed that the transfer layer formation and the coefficient of friction along with its two components, namely, the adhesion and plowing, are controlled by the surface texture of the plate. The plowing component of friction was highest for the surface texture that promotes plane strain conditions while it was lowest for the texture that favors plane stress conditions at the interface. Dimensionless quantifiable roughness parameters were formulated to describe the degree of plowing and hence the plane strain/stress type deformations taking place at the asperity level.

Influence of heat-treatment on the strength and fracture-behavior of fe-12cr-6al ferritic stainless-steel

The changes in the tensile properties and fracture mode brought about by heat treatment of Fe-12Cr-6Al ferritic stainless steel have been studied. A favourable combination of high strength and good ductility is obtained by heating the material at 1370 K for 2 h followed by a water quench. The high-temperature treatment results in carbide dissolution as well as an increase in the grain size. The mechanism of strengthening has been evaluated from the apparent activation energy (28 kJ mol–1) and is identified to be the unpinning of dislocations from the atmosphere of carbon atoms. As the heat-treatment temperature is increased, the fracture behaviour changes from ductile to brittle mode and this is related to the changes in grain size and friction stress.

A study on the nature of the compound layer formed during the ion nitriding of En40B steel

Commercial-grade En40B steel has been ion nitrided in the temperature range 475–550°C in a 25%N2–75%H2 gas mixture. The nature of the compound layer formed was studied by the X-ray diffraction technique and optical metallography. It was observed that the structure of the compound layer gradually transforms from a predominantly epsilon (Porson) nitride to a predominantly γ′ nitride structure with increasing treatment time. Optical metallography studies on sections orthogonal to the nitrided surface showed that, after about 5 h of treatment, the thickness of the compound layer decreases with further increase in treatment time.

Thin-Walled Timber Structures

Due to their efficiency, lightweight, ease of erection and low cost, steel and aluminium thin-walled structures have become very popular in the construction industry over the past few decades. Applications include roof and wall systems (purlins and girts), storage racks, and composite concrete and steel slabs. The effectiveness of these structures lies in the cross-sectional shape of the profiles which enhances their strength by controlling the three fundamental buckling modes: local, distortional, and global. However, despite the attractiveness of these structures, steel and aluminium are greenhouse gas intensive materials and do not produce sustainable structural products. This paper presents an investigation performed at the Griffith School of Engineering, Griffith University, which shows manufacturing these types of profiles in timber is possible. Short composite thinwalled timber Cee-sections (500 mm long) were fabricated by gluing together thin softwood (Araucaria cunninghamii) veneers (1 mm thick). Two types of Ceesections were considered, one with a web stiffener to increase the local buckling capacity of the profile and one without. The profiles were tested in compression and the test results are presented and discussed in the paper in terms of structural behaviour and performance. Further research directions are proposed in order to provide efficient and lightweight sustainable structural products to the timber industry. © RILEM 2014.

Experimental and numerical investigation of the behaviour of CFRP strengthened CHS beams subjected to bending

This paper presents the results of an experimental and numerical program to investigate the circular hollow section (CHS) beams, strengthened using Carbon Fibre Reinforced Polymer (CFRP) sheets. The circular hollow shaped steel beams bonded with different CFRP layer orientations were tested under four-point bending. The mid-span deflection, service load and failure load were recorded. The LHL (where L, first inner longitudinal layer, H, second hoop layer and L, third outer longitudinal layer) and LLH (where L, first inner longitudinal layer, L, second longitudinal layer and H, third outer hoop layer) layer oriented strengthened beams perform slightly better than HHL (where H, first inner hoop layer, H, second hoop layer and L, third outer longitudinal layer) layer oriented strengthened beams. The LHL and LLH layer oriented treated beams showed very similar structural behaviour. Numerical analyses were then conducted on the CFRP strengthened steel CHS beams. The validity of the models has been assessed by comparing the failure loads and mid-span deflections. The effects of various parameters such as bond length, section types, tensile modulus of CFRP, adhesive layer thickness and adhesive types have been studied.