Slip Form Research Articles

Large scale coal silo construction by slip form method in thermal power station

Large scale coal silo construction by slip form method in thermal power station

A numerical and experimental approach to optimise sheet stamping technologies: polymers thermoforming

The technology of polymers thermoforming is taken into consideration, with the aim of developing an optimisation technique for the preliminary set-up of process parameters and for the achievement of a better control of thickness distribution, material saving and cycle-time reduction. For this purpose, a FEM code is used, specifically developed to simulate sheet forming. A viscoelastic constitutive law is adopted, in order to improve the description of material performances. The troublesome characterisation of material, which is in a plastic, almost fluid state, deserves the use of non-standard experimental test methodologies (elongational and shear tests, dynamo-mechanical tests performed above glass transition, T g ), as well as analytical developments (computation of elongational and shear viscosity, evaluation of rheological parameters as a function of temperature and shear rate). Such a behavioural model is firstly implemented in the simulation code, which is then tuned and validated through the simulation of the experimental characterisation tests. Finally, the air slip forming of a low-temperature refrigerator cell is numerically simulated and experimentally manufactured with the main purpose to predict thickness distribution and point out regions of minimum value. Notwithstanding the deep shape, which leads to remarkable thickness variations, the comparison between predicted and actual values at different locations shows a satisfactory agreement: as a matter of fact the error along the cell mid-section did not exceed 0.2 mm on average, corresponding to 5% initial thickness.

Volcaniclastic debris flows in the Clanio Valley (Campania, Italy): insights for the assessment of hazard potential

The rugged and steep slopes of the Clanio Valley (Campania, Southern Italy), mantled by volcaniclastic deposits from explosive eruptions of Somma-Vesuvius and Phlegraean Fields volcanoes, have a great potential for generating volcaniclastic debris flows. During the well-known meteorological event of May 5–6, 1998, which triggered tens of debris flows causing enormous damage and casualties in the area of Sarno–Quindici–Siano–Bracigliano (SQSB), the Clanio Valley was also affected by these hazardous phenomena. Debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips, mainly on the sides of steep valleys (slope between 26° and 45°). A map of the hazard potential was created on the basis of both field and computer-assisted morphometric data. Three classes, characterised by a high, medium and low hazard potential, were distinguished. Within the higher class, a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the May 5–6, 1998 event in the nearby Sarno–Quindici–Siano–Bracigliano area. This type of morphometric analysis can be applied rapidly by using a digital elevation model (DEM), which allows a rapid investigation of large-scale areas. Such an approach can be useful in areas characterised by similar geological and geomorphological settings.

Wind tunnel model studies to predict the action of wind on the projected 558 m Jakarta Tower

A study of wind effects was carried out at the Boundary Layer Wind Tunnel Laboratory (BLWTL) for the projected 558-m high free-standing telecommunication and observation tower for Jakarta, Indonesia. The objectives were to assist the designers with various aspects of wind action, including the overall structural loads and responses of the Tower shaft and the antenna superstructure, the local wind pressures on components of the exterior envelope, and winds in pedestrian areas. The designers of the Tower are the East China Architectural Design Institute (ECADI) and PT Menara Jakarta, Indonesia. Unfortunately, the project is halted due to the financial uncertainties in Indonesia. At the time of the stoppage, pile driving had been completed and slip forming of the concrete shaft of the Tower had begun. When completed, the Tower will exceed the height of the CN-Tower in Toronto, Canada by some 5 m.

Trends in slip forming of ceramics

El procesamiento coloidal de materiales ceramicos permite mejorar las propiedades finales de los productos, reduciendo el numero y tamano de los defectos, y aumentando la reproducibilidad del proceso. Esto exige, por una parte, el adecuado conocimiento de los parametros coloidequimicos y reologicos que rigen la estabilidad de la suspension y, por otra, el control de las variables especificas de cada proceso de conformado. La tecnica de colaje se ha utilizado tradicionalmente en la industria, dada su gran versatilidad, su bajo costo y la elevada uniformidad de las piezas asi obtenidas. Sin embargo, el desarrollo industrial impone la busqueda de nuevas tecnicas de conformado capaces de aunar las ventajas del colaje (como la posibilidad de obtener piezas de forma casi final, con el fin de reducir o eliminar la etapa de mecanizacion) con las propias de otros procesos (como los de prensado), como son la reduccion del ciclo de fabricacion y la automatizacion del proceso. Esto ha impulsado el desarrollo de nuevos procesos de conformado en los que la manipulacion de las propiedades coloidales de una suspension permiten obtener piezas de forma casi neta. En este trabajo se muestran las bases de dichas tecnicas y se discuten las tendencias actuales en el conformado coloidal de materiales ceramicos.

超高鉄筋コンクリート煙突の設計と施工

A tall reinforced concrete stack in height of 200m, is reported on the structural design scheme and construction method. The stack has a trapezoidal plan with cut backs at four corners. Structural performance under strong winds was monitored in the wind tunnel tests. New construction system is adopted including development of bond preventive slip form. Wall foundation concrete pile contributes to producing a stable continuous structure system.

Characteristics of magnetic fabrics of Jiangshan-Shaoxing collision belt and its tectonic implications

The study of anisotropy of magnetic susceptibility (AMS) of rocks from the northern part of Jiangshan-Shaoxing collisional belt demonstrates that the minimum principal AMS axes are the most concentrated one in various types of rocks. The planar projection of the minimum axis shows that the main compressive stress lies on northwest 30°–60°, which trends dominantly in northwest-southeast of Chencai area and arc-like disperse towards both north and south of Chencai. The inclination of the minimum axis illustrates that the Huaxia block is moving northwesterly. Although the maximum axes show slightly dispersal, they are within the confidential circle. The maximum axis intersects with the lineation with a small angle, suggesting that the Jiangshan-Shaoxing collision belt be of a sinistral shear slip. By comparison with magnetic fabrics of various rocks, intensive collision of the Jiangshan-Shaoxing belt was in Late Triassic and sustained to the late Yanshanian period in the form of sinistral shear slip.

FLOW SOFTENING DURING HOT COMPRESSION OF Cu-3.45 wt.% Ti ALLOY

Hot compression tests were performed on supersaturated Cu-3.46 wt.% Ti alloy at the temperatures of 873 K and 973 K. Constant true strain rates of 1.4 × 10 −4 s −1 and 6.9 × 10 −3 s −1 were used. The flow curves were characterized by a single peak followed by continuous flow softening until the sample fracture. The strain to the flow stress peak was found to depend on both the deformation temperature and the applied strain rate. The flow softening (flow stress decrease) was more pronounced during deformation at 873 K for the used strain rates. Strain hardening and precipitation process were together responsible for the initial hardening of the material until the flow stress maximum has been reached. Moreover, the strain localization in a form of coarse slip and shear bands was intensified with increased strain value. It resulted in additional sites for discontinuous precipitation beside the high angle grain boundaries and might be responsible for the flow stress decrease at larger strains. The microstructure of hot deformed samples did not reveal any evidence for dynamic recrystallization during hot deformation in the presence of precipitates. However, dynamic particles coarsening within shear bands was observed and has been assumed to be responsible for further strain softening of the hot deformed sample. It was also suggested that the flow stress was partly reduced due to dynamic recovery which intensified in the course of discontinuous growth and particles coarsening within shear bands. As expected, the flow stress value was affected by the discontinuous precipitation process more effectively in those samples which were deformed at higher temperatures and low strain rates. Flow localization was significantly reduced during hot deformation of the material containing the structure transformed by discontinuous precipitation. © Acta Metallurgica Inc.

Superlocalization of plastic deformation in crystals at high temperatures

Plastic strain distribution and dislocation structure in alkali halide (LiF, LiF:Mg, NaCl, KCl) and ferroelectric (NaNO 2) crystals under constant tensile or compressive stress at high temperatures ( T > 0.6 T m) have been studied. It was found that plastic deformation instabilities at instantaneous deformation occur, namely deformed samples exhibit microbands with very high local shear strain of about 10 3%. The local strain rate in microbands is much more than 5 s −1. These narrow microbands (between 2 and 10 urn in different crystals) are oriented in accordance with the slip systems in crystals. The average distance between microbands is usually from 20 to 100 μm. The surface steps corresponding to local high shear strains are observed in the form of wavy slip. Sometimes, a change in the relief (a depression or a bump) of the surface parallel to the Burgers vector is also observed inside the microbands. The increase of local strain during deformation occurs mainly due to the creation of new microbands rather than by shear in already existing ones. Possible mechanisms of plastic instability in highly strained microbands are discussed.

The structure based design of metal forming operations

The work summarizes the recent experimental studies and theoretical considerations on the nature of plastic deformation in metallic materials. Specifically, it concentrates upon the rules which the heterogeneous deformation obeys and which differ radically from those of the homogeneous deformation. Formulation of such rules is based upon the experiments which provide the very fundamental information about the criterion of slip in crystalline materials, choice and sequence of operation of slip systems and conditions under which “crystallographically determined” slip may be replaced by transgranular shear. The correlation of this form of slip with metal structure and global mechanical properties is given. The results of the studies allow to predict the onset of heterogeneous mode of deformation and what is even more important, they show the means due to which the mode of deformation may have taken under control. The very practical aspect of the work consists itself in the concept “of the structure based design” of metal forming operation. It is shown, that the scheme and sequence of straining in a particular forming operation appears extremely important from the point of view of the energy consumption of the process and the final structure of the metal. The examples of “energy saving” metal forming operations, designed according to the concept, are presented.

SLIP FORMING ACROSS THE DESERT - THE CONSTRUCTION OF THE AZRAQ TO JAFR HIGHWAY PROJECT IN JORDAN.

Hot desert environments with low humidity and strong winds provide some of the most difficult conditions in which to build good concrete roads. This paper describes the materials, plant and methods that were used to construct successfully the Azraq to Jafr highway in Jordan where these conditions prevailed. Of particular importance to the outcome of the project were the use of good quality materials and the most suitable concrete mixing and paving plant available, together with the adoption of very effective curing procedures. Contraction joint dowel bars were mechanically inserted by th slip form paver, which resulted in the very good results that are given in this paper

Kinking of shallow dip‐slip zones

A two‐dimensional crack model is used to investigate the effect of the free surface on the propagation of kink cracks that develop at the tip of dip‐slip shear zones. The slip zones undergo frictional sliding under tectonic loading with the presence of the gravitational force. Because the numerical scheme incorporates the exact asymptotic form of slip near the end of the shear zone, results for the stress intensity factors are accurate. The calculations show that crack opening occurs along a portion of the planar slip zone near the kink as well as at the kink itself. For a typical shallow reverse dip‐slip zone, the mode I stress intensity factor at the tip of the kink can be 60% greater than that for a full space. The effect of free surface is negligible if the ratio of the depth of the shallow end to the length of the slip zone is greater than two. The influence of the free surface makes it possible for the kink crack to grow to much greater length. Under compressive tectonic loading, the kink that develops at the shallow end of a shear zone does not move toward the free surface; instead, the kink curves away from the free surface, extends stably parallel to the free surface, and is then arrested at a finite length. The calculations suggest that rupture termination of a reverse dip‐slip earthquake may be due to extensive tensile cracking near the free surface and that the growth of long extensional fractures parallel to the free surface dissipate sufficient energy to stop the fault rupture. In addition, the present calculations demonstrate that the orientation and the length of observed vein sets are consistent with the extensional fractures developed near the tip of the dip‐slip zone.

Curved slip zones in an elastic half-plane

Abstract Slip on a curved fault loaded by far-field compressive stress induces changes in normal stress along the fault surface. A two-dimensional crack model is developed to quantify these stresses for curved fault geometries. Under plane strain (or plane stress), the curved slipping region is replaced by continuously distributed dislocations, and the corresponding singular integral equation for the dislocation density is derived and solved numerically. Because our solution scheme incorporates the exact asymptotic form of slip near the end of the slipping region, results for the stress intensity factors are accurate. To determine the effects of fault curvature on faulting, the changes in fault-normal stress accompanying dip-slip are calculated for typical faulting events. The changes in normal stress accompanying normal faulting increase the frictional resistance to slip advance near the free surface, and those accompanying reverse faulting reduce the frictional resistance to slip advance near the free surface. Under compressional tectonic loading, slip is retarded on the planar slip zones of higher dips, but enhanced if the dip decreases with depth. On the other hand, under extensional tectonic loading, slip is retarded on the planar slip zones of smaller dips, but enhanced if the dip increases with depth. Curvature of a concave-downward slip zone enhances compressive normal stress at the shallow end of the slip zone under compressional tectonic loading, tending to prevent propagation of the slip zones to the free surface. On the other hand, the curvature of a concave-upward slip zone reduces the compressive normal stress at the shallow end under the uniform extensional tectonic loading, thus assisting propagation of slip zones to the free surface. By contrast, for deep slip zones, the changes in normal stress are practically not affected by the fault curvature. To illustrate the local stress field near a sharp bend, we examine a sharply curved slip zone subjected to frictional sliding. Slip on such a fault induces significant compressional fault-normal stress near the bend. These changes add compression across the slip zone, thus increasing the frictional resistance to slip over the curved bend. Our results show that the magnitude of induced normal stresses is sharply localized near the bend.

Tensile fracture of rock at high confining pressure: Implications for dike propagation

Field observations indicate that zones of inelastic deformation produced at the tips of propagating dikes can be much larger than those produced at the tips of tensile cracks in laboratory experiments. This is in direct conflict with the concept that fracture toughness and fracture energy are rock properties, independent of crack size and loading configuration. A Barenblatt model that treats fracture resistance as an internal cohesive stress acting at the crack tip is used to investigate the effect of confining pressure on rock tensile failure. When the confining pressure exceeds the cohesive strength of the rock, as it does at depths greater than several hundred meters, Linear Elastic Fracture Mechanics is inapplicable and the near‐tip stress field of a propagating crack is determined by the crack size and loading configuration as well as by rock properties. As inelastic deformation depends upon the near‐tip stress field, it follows that fracture energy may also depend upon crack size and loading configuration. For a propagating dike, the near‐tip stress field is dominated by the large suction acting within a small (∼several meter) cavity at the tip generated by viscous flow of magma within the dike. Perturbations to the ambient stress are on the order of the cavity suction and act over regions on the order of the cavity length. The tip cavity pressure may be maintained by exsolution of magmatic volatiles or by influx of host rock pore fluids; inelastic deformation is enhanced by the latter. For a tip cavity pressure maintained by influx of pore fluids, the pore pressure exceeds the least compressive stress off the dike plane, even while it equals the least compressive stress at the dike tip. This can lead to tensile failure off the dike plane and the formation of observed dike‐parallel joints. Shear stresses scale with the cavity suction and may produce shear failure off the dike plane; such deformation is generally enhanced if the dike is intruded perpendicular to the least compressive stress. For sills intruded parallel to bedding, shear failure in the form of bedding plane slip can lead to the observed blunting and fingering of the intrusion front. Because the tip cavity grows with dike size, the energy consumed by rock fracture also increases with dike size and is potentially as significant for large dikes as for small dikes, a view not adopted by existing fluid mechanical models of dike propagation.

Concrete Structures for Development of Offshore Fields

Summary Concrete structures represent competitive solutions for developing many offshore fields. They are of particular interest when storage is required and as floating support structures. Furthermore, concrete reusable platforms may represent cost-saving solutions for many applications. To design optimum structures, designers must be realistic with respect to the structural capacity of concrete for offshore use. Introduction Experience in the North Sea has shown that concrete support structures are competitive with steel jacket structures in terms of initial investments and maintenance costs. This experience is considered relevant for other areas, particularly for countries that must import steel, for icy areas, for offshore areas without infrastructure, for places where oil storage facilities are required, and for areas where large crane vessels are not available to lift heavy steel structures or large topside modules. Furthermore, concrete floaters [tension-leg platforms (TLP's) and catenary anchored structures] are attractive as minimum-cost solutions for deepwater applications. This paper discusses the requirements and infrastructure needed to design and fabricate concrete structures. Particular attention is given to availability of cement, aggregate, reinforcement steel, and prestressing cables. This paper also discusses design competence and required computer facilities, as well as the availability of barges, a shipyard dock, or a special-purpose construction dock. We describe the fabrication, installation, and removal processes. Removal is becoming increasingly important in a world gradually becoming more aware of environmental stability. We give examples of efficient designs suitable for optimum development of small fields and fields requiring storage. These examples include traditional concrete structures constructed with form work or slip forming. Furthermore, novel concrete truss structures fabricated by joining precast tubes and nodes by prestressing cables and grout are discussed. We provide charts that give concrete volumes for a range of applications to enable operators to perform their own economic analyses.

Laboratory Tire Wear Simulation Derived from Computer Modeling of Suspension Dynamics

Abstract A method for determining the effect of suspension dynamics on tire wear has been developed. Typical city cycle maneuvers are defined by instrumented vehicle testing and data in the form of forward velocities and steer angles are used as an input to an ADAMS computer model of the vehicle. A simulation of the maneuvers generates a tire's operating environment in the form of normal load, slip, and camber variations, which contain all the subtle effects of the vehicle's suspension, steering, and handling characteristics. A cyclic repetition of the tire's operating environment is constructed and used to control an MTS Flat-Trac machine. In this way, accelerated tire wear can be generated in the laboratory which is directly related to the design features of the vehicle's suspension and steering systems.

Through a Glass Darkly: Ultrasound and Prenatal Bonding

Prenatal ultrasound scans are believed to enable mothers to form an early affectionate bond to their child, to provide a reassuring image of the fetus, and to promote improvements in mothers' health behaviors on the behalf of the fetus. Observational studies suggest that scans done early may slightly improve maternal-fetal bonding but that those done after quickening are not associated with attachment. Short-term effects on maternal health behaviors, including less smoking, less drinking of alcohol, and more visits to dentists, were detected in a randomized trial when detailed information was given during the scan. This trial also suggested that women's anxiety was actually increased during scans, and then allayed by positive feedback from the operator. Not all women considered scans reassuring in one interview study, and other authors found that mothers' interpretations of scans depended on their personal and social circumstances. As used in everyday practice, ultrasound scans are not always accompanied by feedback, and when feedback occurs it is sometimes in the form of slips of the tongue, incorrect diagnoses, identification of structures that cannot be deciphered, and language that is unfamiliar and alarming to mothers. This "diagnostic toxicity" of ultrasound scans of the fetus has not been studied.

On the apparent relation between adhesive failure and melt fracture

The theory of adhesive failure between elastomers and a nonpolymeric surface provides a framework for the analysis of melt fracture in polymer melts. Peeling experiments on LLDPE below the melt processing temperature are shown to predict the onset of melt extrudate surface distortion and the functional form and magnitude of subsequent wall slip in capillary flow experiments using the same polymer. The equation for the slip velocity is based only on peeling experiments and knowledge of the temperature‐ and pressure‐dependence of the viscoelastic shift factor.

The vane‐in‐cup as a novel rheometer geometry for shear thinning and thixotropic materials

We have addressed the question of the suitability of the vane‐in‐cup as a rheometer geometry. A numerical simulation of this geometry was conducted for a power‐law fluid and the results compared with a similar study for a conventional bob‐in‐cup geometry. The comparison indicates that for a sufficiently shear‐thinning fluid (of shear‐thinning index less than 0.5) the fluid within the periphery of the vane blades is essentially trapped there and turns with the vane as a solid body. Calculation of the shear stress at the cup wall indicates that this quantity is equal in both geometries for a given rotational rate of the spindle. Thus the torque required to turn the spindle would be the same and identical flow curves would be predicted. This prediction was tested on two fluids thought to possess a yield stress: a 5.5% sodium carboxymethylcellulose (CMC) solution and a 4.2% Veegum PRO clay suspension. Equivalent flow curves were obtained at very low stresses/shear rates but a sudden, catastrophic viscosity loss was found for both fluids with the bob at shear rates which were still quite low. Such a loss was observed with the vane as well, but at much higher shear rates. It is suggested that this phenomenon is a form of apparent slip due to the formation of a thixotropic layer at the bob/vane surface. The much flatter stress profile obtained in the vane geometry is reasoned to postpone the formation of this layer. Rheological data obtained with the vane appear to be a faithful representation of these materials and show the absence of a true yield stress.

Lakehead terminal elevators: aspects of their engineering history

Massive grain elevators have been a dominant feature of the waterfront at Thunder Bay since 1883 when the first terminal was under construction. The earliest terminal elevators built by the Canadian Pacific Railway were constructed in the wooden crib technique on a pile foundation. By the turn of the century, the inadequacies of the crib terminals forced engineers to experiment with new materials and new design concepts for terminal elevators. Steel, tile, and reinforced concrete all came into use for terminal elevator construction between 1898 and 1903. By 1910, the plan of the elevator had evolved from a single building into four separate structures. The appearance of the typical Lakehead terminal elevator today is the result of these engineering experiments which occurred at the end of the nineteenth century and in the early years of the twentieth. Key words: grain elevators, concrete construction, slip forms, formwork, bins, silos, timber construction, crib walls, cribs, steel construction.