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Collaborating Authors
Results
Development of SCS Sandwich Composite Shell for Arctic Caissons
Marshall, P.W. (Department of Civil and Environmental Engineering, National University of Singapore) | Sohel, K.M.A. (Department of Civil and Environmental Engineering, National University of Singapore) | Liew, J.Y. Richard (Department of Civil and Environmental Engineering, National University of Singapore) | Jiabao, Yan (Department of Civil and Environmental Engineering, National University of Singapore) | Palmer, A. (Department of Civil and Environmental Engineering, National University of Singapore) | Choo, Y.S. (Department of Civil and Environmental Engineering, National University of Singapore)
Abstract There is a wide range of offshore structures which may be constructed byeither steel or concrete materials to be used in the arctic region, such assteel tower platforms, caisson-retained islands, shallow-water gravity-basecaisson, jack-up structures, bottom-founded deep-water structures, floatingstructures, well protectors, seafloor templates and breakwaters. One commonfeature of these structures is that they must be able to resist the highlateral forces from the floating ice and transmit these forces to thefoundation. This study explores the use of Steel-Concrete-Steel (SCS) curvedsandwich system for arctic caisson structures. SCS sandwich system, whichcombines the beneficial effects of steel and concrete materials, has promisingbenefits over conventional plates and stiffeners design and heavily reinforcedconcrete design because of their high strength-to-steel weight ratio and highresistance to contact and impact loads. Shear connectors have been proposed toprovide bonding between the external steel plates and high-performancecementitious core materials. Finite element analyses and large-scale testresults showed that SCS sandwich panels without mechanical bond enhancement arevulnerable to interfacial shear failure and impairment of structural integritywhen subject to shrinkage and thermal strains, accidental loads, and impact. The proposed SCS sandwich system features mass-produced mechanical shearenhancement and/or cross-ties. It can reduce structure complexity, particularlyin the number of weld joints which are prone to fatigue, hence increasingservice life, cutting down the cost of fabrication, and reducing the manpowercost to operate, inspect, and maintain the structure in the long run. Considering local ice load, the punching shear and shell bending strength ofthe SCS sandwich composite shell is studied experimentally. Test results showedthat the SCS sandwich panels, which are designed using the ISO ice load, arecapable of resisting the localized contact and punching loads causedthereby.
- Europe (0.94)
- North America > United States > Texas (0.28)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government (0.68)
- North America > United States > Alaska > Arctic Ocean (0.89)
- North America > Canada (0.89)
ABSTRACT Difficult geo-mining conditions of a deep seated coal pillars limit the scope of conventional semi-mechanised depillaring process, mainly due to their slow rate of extraction. Application of a fully mechanized depillaring process has resulted faster rate of extraction resulting improvement in safety along with production and productivity of the depillaring faces. Out of six mechanized depillaring practices in India, the three successful ones of Anjan Hill, Jhanjra and Pinoura Mines do not belong to deep cover (<200m). While the Tandsi depillaring is practiced at nearly 260m depth of cover and achieved intermediate results. The deepest practiced mechanised depillaring panel in the county is CMP-1of VK7 at 377m of cover. This depillaring encountered massive collapse (before main fall), which adversely affected the pace of mechanisation for pillar extraction operation at higher depth in the country. Actual cause of the problem is still being investigated and is found difficult to be concluded. However, as per core analysis results, a good understanding of the nature of overlying strata might have guided the approach for a better pattern of the pillar extraction and the chance of failure might have been arrested. After realizing this fact, a depillaring operation in the neighboring panel 26 of the mine was successfully conducted. Here, the menace of dynamic loading due to competent overlying strata could successfully be encountered through management of the natural support only. The sixth mechanised depillaring face is successfully being practiced at GDK 11 Incline at around 310m of cover. Again, here application of available knowledge of the site conditions helped in successful completion of mechanised depillaring operation in couple of panels. Field investigations through underground instrumentation and monitoring showed distinct natures and amount of stress re-distribution for shallow and deep cover of the depillaring. The prominence of periodic nature of face loading at shallow cover got reduced during depillaring of a deep coal seam. Pillars around extraction line encountered, almost, continuous loading after first major fall during pillar extraction from deep seated coal seams.
- Asia > India (0.50)
- North America > United States (0.47)
ABSTRACT We generalize our view of a bonded-particle model (BPM) to consist of a base material (of rigid grains joined by deformable and breakable cement at grain-grain contacts) to which larger-scale joints can be added and whose mechanical behavior is simulated by the distinct-element method using the two- and three-dimensional discontinuum programs PFC2D and PFC3D. The micromechanical processes that control brittle fracture and thus, should inform any micromechanical model, are summarized. The rich variety of microstructural models that can be produced by the bonded-particle modeling methodology are described and classified with respect to their microstructural and larger-scale features. These models provide a wide range of rock behaviors that encompass both compact and porous rock at both an intact and rock-mass scale, and examples are provided of how BPMs are being used to model rock at these scales. The examples include an intact anisotropic material that may swell and contract in response to changes in saturation, the behavior of two alternative BPMs that can match both the uniaxial and tensile strengths of compact rock and the embedding of an intact BPM within a larger continuum model to study fracturing around a gold-mine stope in quartzite.
- North America > United States (1.00)
- Europe (1.00)
- Asia (0.67)
- North America > Canada (0.67)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.92)
- Geology > Mineral (0.88)
ABSTRACT Failure in rocks is attributed to crack initiation and coalescence processes upon loading. Crack behavior study, which has been extensively conducted in various rock types containing artificially created flaws under a quasi-static loading condition over the past decades, is extended to dynamic loading conditions by using the Split Hopkinson Pressure Bar (SHPB) technique. The loading tests are conducted on specimens containing a single pre-existing open flaw (60mm ร 30mm ร 20mm) in Carrara marble. Similar to those loaded quasi-statically, white patches are observed to develop in the specimens loaded dynamically at the early stage of the loading prior to the development of observable cracks. The respective failure modes are however significantly different. For quasi-static compression, normally two macro-cracks linking the two opposite corners of the specimen and the flaw tips cause the failure of the marble specimens, producing two main fragments. In contrast, under high strain rate, four fragments associated with "X" shape deformation bands are produced irrespective of the inclination angle of the flaws. The failure is attributed to the more or less simultaneous propagation of the horsetail and anti-wing cracks. In this paper, the detailed cracking processes will be compared and discussed.
ABSTRACT Design of rock structures and analysis of rock mass behavior demands a proper understanding of the influence of loading rate on the mechanical properties of rock mass. Many researchers considered the effects of dynamic loads on rock specimens through laboratory tests and numerical methods. Nevertheless, generalizing the intact rock behavior to the rock mass is the most important issue. In this paper, the rock mass behavior in dynamic loads is studied whilestrain rates ranges from 10โ5 to 1031/s. The generalized Hoek-Brown rock criterion is used to demonstrate the rock mass behavior in several loading rates and strain rates. The database was obtained from the literature,includes uniaxial and triaxial loading of rock samples. Uniaxial compressive strength and deformability modulus of the rock mass is illustrated under different strain rates and confining pressures. The variation of rock mass properties is analyzed under dynamic loading furthermore GSI, m, s and D parameters. It was concluded that uniaxial compressive strength of the rock mass increased by increasing strain rates and dynamic loads. Indynamic triaxial loading it was observed that an increase in confining pressure, increased rock mass strength. The deformability modulus is as increase as rock mass strength in uniaxial and triaxial conditions.
- Geology > Geological Subdiscipline > Geomechanics (0.92)
- Geology > Rock Type (0.80)
ABSTRACT A study was undertaken to investigate changes in the strength and failure pattern of otherwise standard rock core specimens containing regularly spaced discontinuities. The objective was to assess changes in the nature of rock failure resulting from these discontinuities. Test core specimens were prepared from sandstone having dimensions of 44 and 110 mm for diameter and height respectively. The core specimens were cut at right angles to the longitudinal axis of the core producing composite specimens having 2, 3, 4 or 5 regularly-spaced surfaces. As well as testing specimens having dry, clean fracture surfaces, the test program also considered different infill materials and hence friction values using dry and oiled-impregnated paper. The study found the strength of specimens decreased with the number of discontinuities. While the UCS strength of the intact rock specimen was 35.8 MPa, the strength of composite specimens having five segments was reduced by 50% to 17.9 MPa. This is despite the reduction in the slenderness ratio of each segment in the composite specimen that would usually result in an increase in strength. Less sensitive were changes in infill material having little discernible effect over for the limited range of friction surfaces investigated.
- Asia > Japan (0.28)
- Oceania > Australia > New South Wales (0.15)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.36)
ABSTRACT The Particle Flow Code (PFC), a simulation code based on the distinct element method (DEM), is an effective numerical tool for simulating the failure process of hard rock. By introducing contact- and parallel-bond models and clump particle model, the code has become better able to express the ratio of uniaxial compressive strength to tensile strength of hard rock. On the other hand, a problem has been pointed out, namely, that PFC simulations with the clumped particle model cannot reproduce rapid strain-softening behavior in Brazilian tensile tests. In addition, cracks propagate too widely in the specimens, differently from the cracks observed in the experimental data. Attributing the above problem to the loading configuration, some two-dimensional PFC simulations were conducted in Brazilian tests under several loading conditions in this study. Strip loading (line loading in two dimensions) and line loading (point loading in two dimensions) were taken into consideration. From the simulation results, point loading was found to be effective for expressing rapid strain-softening behavior and crack propagation in Brazilian tensile tests.
Although the Titanic disaster occurred 100 years ago, explanations of the failure rely heavily on studies of the structural failure (failure of the rivets, brittle fracture of the side plate, ... for example). Very little attention has been paid to how the ice delivered the required force. Background to the disaster is reviewed and in particular the records of experiences of passengers showing that the impact involved a โslight jarโ or a โlittle vibrationโ. These indicate small global loading but not excluding the possibility of high local loading. The construction of the Titanic is described, and in particular the overlapping plates connected by rivets. Evidence based on ultrasonic scans and calculations of the flow of water into the vessel suggests that the failure was associated with a series of slits in the hull, with a total area of about 12 square feet. Recent explorations into the strength of the rivets are described. The main focus of the paper is then introduced: the formation of high pressure zones in ice compressive failure. The total load in these tests may be of the order of several MN. The high-pressure zones are characterized by a localization of damage in the ice resulting in the formation of a distinct layer of microstructurally modified material. Pressures from the ramming of ice features in ship rams are analyzed, and it is again shown that forces associated with quite small areas may be of the order of several MN. When compared to the strength of the rivets, it is clear that enough force can be generated to cause slits of the kind deduced from the evidence. The results are also consistent with the observed small motions of the ship during impact. The Titanic was not designed for interaction with ice and avoidance would have been a wise course of action. It seems inappropriate to suggest that poor rivet construction was the cause of the sinking. The main cause was the high local loads involved in ice-structure interaction.
- North America > United States (1.00)
- North America > Canada (0.69)
Development of Composite Sandwich Structures for Arctic Region
Sohel, KMA (National University of Singapore) | Liew, J. Y. Richard (National University of Singapore) | Jiabao, Yan (National University of Singapore) | Zhang, M. H. (National University of Singapore) | Marshall, P. W. (National University of Singapore)
A cone-shaped steel-concrete composite structure has been proposed for Arctic offshore structures. This type of cone structure is able to withstand the ice forces imposed thereon by impinging ice sheets and other larger masses of ice wherein the structure has an upper conical portion coaxially positioned relative to a lower cylindrical portion. This study explores the use of curved steel concrete- steel (SCS) sandwich system in the proposed arctic cone structure. SCS sandwich system, which combines the beneficial effects of steel and concrete materials, has shown promising benefits over conventional plates and stiffeners design and heavily reinforced concrete design because of their high strength to weight ratio. Shear connectors has been proposed to connect steel face plates and cementitious core material. The proposed SCS sandwich system can reduce structural complexity in particularly the number of weld joints which are prone to fatigue and corrosion, hence increase service life, cut down the cost of fabrication, and reduce the manpower cost to operate, inspect and maintain the structure in the long run. Considering local ice load, the punching shear strength of the SCS sandwich composite shell was studied experimentally. The SCS specimens were designed using the ISO ice pressure. The experimental results show that they possess far higher resistance against patch load caused by ice. Moreover, the load-deflection behavior of the curved SCS sandwich system is ductile and it can absorb a great deal of energy at failure.
- Europe (0.95)
- North America > United States (0.69)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Materials > Construction Materials (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT This paper describes a range of techniques for estimating the capacity of offshore foundations, which has always been a main issue in foundation design and remains so today. The paper, however, takes a tack that is slightly out of the mainstream - by emphasising methods of plastic limit analysis rather than more traditional approaches. It begins with a brief history of offshore geotechnical developments, describing how design methods have evolved for shallow foundations and pile foundations, and the types of loads, site conditions and foundation geometries encountered. A number of simple solutions are provided with detailed example problems. This paper proposes that plastic limit analysis methods have the potential to supplement and enhance more traditional methods. 1. Introduction I am sincerely honoured to be invited to give the inaugural McClelland Lecture. I am humbled by the task before me as I sincerely wish to produce something that Bram McClelland would have appreciated. At first I leaned toward a subject that more characterised his expertise and interest - engineering geology, site investigation and foundation design. On further reflection however I concluded that Bram delighted in developing engineers who followed their own interests, not in his image, but in their own unique ways. That is the kind of leader he was. This epiphany led me to select a topic that has long been a passion of mine - bridging the gap, sometimes chasm, between theory and practice. I believe this is what he would have wanted from me. Estimating foundation capacity has always been a central issue in foundation analysis and design. Various different methods are employed in this practice, many of which involve ad hoc assumptions and empirical models. This paper focuses on one such advancement, plastic limit analysis (PLA), a methodology that is theoretically sound, internally consistent and surprisingly simple to apply.
- Europe (0.68)
- North America > United States > Texas (0.46)