Bar Forces Research Articles

Forces on bars in high-consistency mill-scale refiners: Effect of consistency

The contact mechanics that arise during bar-crossing impacts are responsible for inducing the stresses, and corresponding strains, that develop raw wood fibre into useful papermaking pulp. Enhancing our knowledge of the interactions that make up these impacts, and how they are affected by process variables, is therefore a necessary step to advancing refiner technology. Experiments by Senger and Ouellet [1] involving individual fibre bundles, or flocs, in a single-bar refiner have indicated that bar forces are dependent on floc consistency, floc grammage and bar edge sharpness. These results offered insight into previously unexplainable behavior, but investigation of these relationships in mill-scale refiners was restricted by lack of available measurement technology. This investigation is now possible with the development of a refiner force sensor (RFS) that replaces a small segment of refiner bar, and is capable of measuring normal and shear forces experienced during individual bar-crossing impacts. Bar forces from RFS tests in two mill-scale refiners under nominal operation have already been reported [2]. During the same installations, consistency within the refining zone was also varied in individual experiments. The principal goal of this work is to report on the effects of refining consistency on recorded bar forces in these two trials.

Research on Asymmetric and Negative Offset Mechanism of Large-Scale Steel Plate Rolling Shear

According to revised Cailikefu’s rolling shear force formula, motion path equation of spatial seven-bar path is built, and mechanical model, with such new structural features as asymmetric and negative offset, is thus successfully established for 2800 mm heavy shear of some Iron&Steel Company. Shear force and bar force of steel plate, before and after adoption of asymmetric and negative offset structure, are analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. The discovery is that back-wall push force could be kept large enough at rolling start-up (i.e. the time that the maximum rolling shear produces), meanwhile, back-wall push force is the most approximate to side forces with adoption of 60mm~100mm offset. Theoretical results and on-site shear quality both indicate that new structural features such as asymmetric and negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant, which provide an effective means to improve quality of steel plate.

실시간 차량 동역학 해석을 위한 안티 롤 바 힘 계산 알고리듬

Anti roll bar model for real time multibody vehicle dynamics model has been proposed using kinematic constraint. Anti roll bar have been modeled by kinematic relationship, and mass properties are neglected. Relative angle of torsion bar spring is computed by constraint about drop-link using Newton-Raphson iteration, and then the torque of torsion bar spring can be computed with the angle and torsion spring stiffness. Finally anti roll bar force acting on both knuckle can be calculated. To validate the proposed method, half car simulations of McPherson strut suspension and full car simulations are also carried out comparing with the ADAMS vehicle model with anti roll bar. CPU times are also measured to see the real-time capabilities of the proposed method.

Musculoskeletal demands of progressions for the longswing on high bar

Kinetic analyses of the chalked bar longswing on high bar and its associated progressions were used to explain musculoskeletal contributions during the performance of these skills. Data on four international male gymnasts performing three series of chalked bar longswings and eight progressions were recorded. Customized body segment inertia parameters, two-dimensional kinematics (50 Hz), and bar forces (1000 Hz) were used as input to inverse dynamic modelling. The analysis focused on the relative contributions of the knees, hips, and shoulders with root mean squared differences between the chalked bar longswing and the progressions being used to rank the progressions. Seventy per cent of the total work occurred between 200° and 240° of angular rotation in the longswing, 67% of which was contributed by the shoulders. The shoulders were also dominant in all progressions, with the largest such contribution occurring in the looped bar longswing with “no action”. The least similar progression was the looped bar pendulum swing, while the most similar was the chalked bar bent knee longswing. This study provides a useful means for ranking progressions based on their kinetic similarity to the chalked bar longswing and builds on earlier research in identifying that progressions can be classified into those similar in physical demand (kinetics) and those similar in geometry (kinematics).

Bond Durability of Glass Fiber-Reinforced Polymer Bars Embedded in Concrete Beams

An experimental and analytical investigation of bond durability of E-glass fiber-reinforced polymer reinforcement bars in concrete beams is presented. Beams were conditioned with sustained flexural loads in indoor, outdoor, 60°C alkaline solution, or freeze/thaw environments for up to 3 years , after which they were subjected to eccentric three-point flexure tests to evaluate bond. Experimental bar force and slip were used to draw direct conclusions on bond durability, and also to calibrate a proposed local bond–slip model that incorporates concrete cover splitting. Experimental bar force at the onset of free-end slip varied little after any of the conditionings, although the characteristic of bond failure was noted to be less ductile in the moister environments. The interfacial fracture energy associated with bond–slip did not change with conditioning time in any of the environments except freeze/thaw, where a monotonic reduction versus time was seen. The effective bond length of the bar under various co...

Mechanical Properties of New Type Negative Offset Structure During Shearing Process of Heavy Steel Plate

Abstract According to the revised Cailikefu's rolling shear force formula, motion path equation of spatial seven-bar path was built, and a mechanical model, with the new structural feature of negative offset, was thus successfully established for 2 800 mm heavy shear of some iron and steel company. Shear and bar forces of steel plate, before and after the adoption of negative offset structure, were analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. It was found that the back-wall push force keeps large even at the time that the maximum rolling shear was obtained; meanwhile, back-wall push force is the most approximate to side forces when 60 – 100 mm of offset was adopted. Both theoretical results and on-site shear quality show that the negative offset plays an important role in ensuring the stability of pure rolling shear and keeping blade clearance constant.

Bond Stresses Along Plain Steel Reinforcing Bars in Pullout Specimens

Although recent research has recognized the existence of relationships between bond stress, slip and bar force, mechanics-based analytical prediction models for bond of plain reinforcement based on pullout specimens have not yet been established. This study establishes mechanics-based relationships between bond stress, bar force, slip at the unloaded end of the bar, and slip along the length of plain steel reinforcing bars in pullout specimens. Two 200 mm (7.9 in.) diameter by 800 mm (31.5 in.) long pullout specimens reinforced with instrumented built-up hollow reinforcing bars were tested. The derived mechanics-based relationships show that bond stress is a function of relative bar slip, slip is a function of bar force, and bar force is a function of bond stress. It is shown both analytically and experimentally that bond stress magnitudes vary along the length of the bar at all applied loads. Maximum pullout resistance was observed just before slip initiated at the unloaded end of the bar, and the bond resistance subsequently reduced as slip increased. The location of the peak bond stress shifts from the loaded end toward the unloaded end of the specimen with increasing applied load. This study also demonstrates that a previously-developed theoretical two-step bond stress-slip model captures the essential features of bond behavior observed experimentally in pullout specimens once the authors accounted for the debonding adjacent to the loaded end of the specimen.

Strut-and-Tie Model for Development of Headed Bars in Exterior Beam-Column Joint

Headed bars have been proposed as an alternative to hooked bars in anchoring longitudinal reinforcement terminated within exterior or corner beam-column joints. This paper proposes a strut-and-tie model (STM) for the development of headed bars in an exterior beam-column joint that investigates realistic force transfer by headed bars within the joint. The tensile force in a headed bar is considered to be developed by head bearing together with bond along a partial embedment length. The model consists of struts with nodal zones for head bearing and fan-shaped stress fields for bond resistance along the bonded length. The model shows how to decompose the tensile force developed in headed bars into direct strut action and fan action and their effects on joint shear strength. Tests on exterior beam-column joints without transverse reinforcement, and that neglect axial forces due to self-weight and live load, are intended to focus on the effect of anchorage capacity of headed bars on joint shear strength. Findings show that the STM explains two different load transfers from the headed bar to the exterior beam-column joint. The proposed model is also capable of considering not only the head size and material strengths, but also the structural configurations of the system under consideration. Finally, it is applicable to anchorage zones of headed bars with various geometries and boundary conditions.

Lateral buckling analysis of thin-walled laminated composite beams with monosymmetric sections

Lateral buckling of thin-walled composite beams with monosymmetric sections is studied. A general geometrically nonlinear model for thin-walled laminated composites with arbitrary open cross-section and general laminate stacking sequences is given by using systematic variational formulation based on the classical lamination theory. All the stress resultants concerning bar and shell forces are defined, and nonlinear strain tensor is derived. General nonlinear governing equations are given, and the lateral buckling equations are derived by linearizing the nonlinear governing equations. Based on the analytical model, a displacement-based one-dimensional finite element model is developed to formulate the problem. Numerical examples are obtained for thin-walled composite beams with monosymmetric cross-sections and angle-ply laminates. The effects of fiber orientation, location of applied load, modulus ratio, and height-to-span ratio on the lateral buckling load are investigated. The torsion parameter and a newly-defined composite monosymmetry parameter are also investigated for various cases.

Identification of the tensile force in high-tension bars using modal sensitivities

In certain field applications involving the repair or replacement of structural members, the knowledge of the tensile forces in tension members may be critical in the selection of the retrofit or rehabilitation process. To date, several methods have been presented to estimate in situ tensile forces using static and/or dynamic responses of the tension members. However, each and every one of these methods has its disadvantages as well as advantages in its procedures, level of accuracy, and equipment requirements. This paper presents a practical method to identify the tensile force in a high-tension bar using the changes in the modal sensitivities. The methodology can identify not only the tensile force but also other related parameters such as the magnitude of end constraint. The methodology utilizes the sensitivity relationship between the natural frequencies, the structural parameters, and the tensile force in the member. In this paper, the basic elements of the approach are summarized and the proposed method is validated using both numerical and experimental data. Also, the impact of model uncertainty to the performance of the parameter identification is investigated.

Evaluation of Slab Shape Under Controlled Environmental Conditions

During the curing of Portland cement concrete (PCC) pavements, temperature and moisture gradients in the concrete cause pavement slabs to deform from their initial as-placed shape. Daily and seasonal environmental cycling can then cause the slabs to expand and contract horizontally with changes in average temperature and moisture conditions, and curl and warp vertically as temperature and moisture gradients change through the slab depth. This article reports on a study that evaluated slab shape under controlled environmental conditions. In the study, two 3.66 m (12 ft) wide, by 13.72 m (45 ft) long, by 254 mm (10 in) thick concrete pavements were constructed in the Ohio Accelerated Pavement Loading Facility (APLF). Transverse contraction joints were placed at 4.57 m (15 ft) intervals to create three contiguous 4.57 m (15 ft) long slabs in each pavement. Dowel bars were added to the joints in one pavement, and the other pavement was left undoweled. Results demonstrated large upward vertical deformations along the slab edges early in the curing cycle, and these deformations continued to increase throughout the duration of the tests. The slightly smaller vertical movements observed in the doweled pavement were attributed to the presence of the dowel bars. The authors conclude that by restraining joint movement, dowel bars transferred load to adjacent slabs and reduced slab deformation. They note that forces in the dowel bars were smaller than expected from reports on previous investigations, particularly during the curing process. When modeling PCC pavements, loss of support from the base should be considered as dead and live load stresses are generated in cantilevered slabs.

Comparison of Bond Strength of Steel Bars in Normal- and High-Strength Concrete

A comparative analytical study of the average bond strength at failure of reinforcing bars embedded in unconfined normal-strength concrete (NSC) and high-strength concrete (HSC) is undertaken. The analysis makes use of an experimentally derived local bond stress-slip model and considers the progressive bond deterioration along the development/splice length with the increase in bar force. Results of the average bond strength (or development/splice strength) predicted by the analysis showed excellent agreement with experimental data for both NSC and HSC. The analysis predicted a highly nonuniform bond stress distribution at bond failure along the development/splice length, particularly for HSC. Below a certain limit of the development/splice length (about 15-20db), the average bond strength at failure, normalized to fc′1/2, is larger for HSC as compared to NSC. However, as the development length increases beyond this limit, the normalized bond strength of HSC becomes progressively smaller than that of NSC. ...

Effect of Confinement on Bond Strength between Steel Bars and Concrete

This work experimentally examines the local bond aspect between steel bars and concrete confined with ordinary transverse steel. The test parameters included diameter of reinforcing bar, ratio of concrete cover to bar diameter, and area of transverse reinforcement. Results were compared with those of similar specimens for concrete confined either internally using steel fiber reinforcement or externally using fiber-reinforced polymer (FRP) sheets. Based on the comparisons, a unified expression for the local bond strength of confined concrete is derived, and a general model for the local bond stress-slip response is proposed and used to conduct an analytical evaluation of the effect of confinement on development/splice strength. Results predicted by the analysis were in good agreement with experimental results. For small development/splice lengths corresponding to local bond conditions, confining the concrete only slightly increases the local bond resistance but leads to considerable improvement in the ductility of bond failure. The corresponding ductility at the local level allows, for the practical range of development/splice lengths, more bar lugs to participate in resisting the applied bar force resulting in a more uniform bond stress distribution along the development/splice length and, consequently, a sizable increase in the average bond strength at bond failure as compared with plain unconfined concrete. The bond strength due to FRP confinement increases in proportion to the modulus of elasticity of the FRP material. For the same area of transverse reinforcement per unit length along the splice, taking into account the relative modulus of elasticity of the confining materials, external confinement of concrete using FRP sheets is more effective in increasing the development/splice strength than internal confinement with ordinary transverse steel. A general design expression is proposed to estimate the development/splice length of steel bars embedded in concrete confined with ordinary transverse steel, FRP, or steel-fiber reinforcement.

A Technique for Separating the Gravitational Torques of Bars and Spirals in Disk Galaxies

We describe a Fourier-based method of separating bars from spirals in near-infrared images. The method takes advantage of the fact that a bar is typically a feature with a relatively fixed position angle and uses the simple assumption that the relative Fourier amplitudes due to the bar decline with radius past a maximum in the same or a similar manner as they rose to that maximum. With such an assumption, the bar can be extrapolated into the spiral region and removed from an image, leaving just the spiral and the axisymmetric background disk light. We refer to such a bar-subtracted image as the "spiral plus disk" image. The axisymmetric background (Fourier index m = 0 image) can then be added back to the bar image to give the "bar plus disk" image. The procedure allows us to estimate the maximum gravitational torque per unit mass per unit square of the circular speed for the bar and spiral forcing separately, parameters that quantitatively define the bar strength Qb and the spiral strength Qs following the recent study of Buta & Block. For the first time, we are able to measure the torques generated by spiral arms alone, and we can now define spiral torque classes, in the same manner as bar torque classes are delineated. We outline the complete procedure here using a 2.1 μm image of NGC 6951, a prototypical SAB(rs)bc spiral having an absolute blue magnitude of -21 and a maximum rotation velocity of 230 km s-1. Comparison between a rotation curve predicted from the m = 0 near-infrared light distribution and an observed rotation curve suggests that NGC 6951 is maximum disk in its bar and main spiral region, implying that our assumption of a constant mass-to-light ratio in our analysis is probably reliable. We justify our assumption on how to make the bar extrapolation using an analysis of NGC 4394, a barred spiral with only weak near-infrared spiral structure, and we justify the number of needed Fourier terms using NGC 1530, one of the most strongly barred galaxies (bar class 7) known. We also evaluate the main uncertainties in the technique. Allowing for uncertainties in vertical scale height, bar extrapolation, sky subtraction, orientation parameters, and the asymmetry in the spiral arms themselves, we estimate Qb = 0.28 ± 0.04 and Qs = 0.21 ± 0.06 for NGC 6951.

Fundamental solution and integral equations for Timoshenko beams

It is well known that Timoshenko’s theory is a refined beam theory which takes shear deformation and rotatory inertia into account. Here, for the first time, an integral equation description for all relevant states, the deflection, the rotation, the bending moment, and the shear forces is derived. Adding the well known integral equations for axial displacements and forces in bars under tension, arbitrary plane frame structures can be modelled by adequate combinations of these equations. Examples show the exactness of the results and demonstrate the applicability of this boundary integral formulation which can be considered as a first step to dynamic analyses of Timoshenko beam systems.

On continuity of the design-to-state mappings for trusses with variable topology

In this paper, we investigate the continuity of the mappings which, for a given set of cross-sectional areas of a truss, gives the bar forces and nodal displacements present in equilibrium. We allow the areas to approach and attain zero values, and hence analyse continuity of the state mappings even as the topology is altered. The main results are then applied to optimal design, primarily the stress-constrained minimum weight problem, to illustrate how they can be used to establish existence of solutions and validity of “ ε-perturbations” that are common in computational topology optimization.

Super Bar Theory and BP System in Super Span Flat Space Frames

In this paper, possible solutions to the constraints of flat space frames in large spans are summarized, including the application of multilayer forms, the introduction of novel simplexes, and the improvement in structural components. Then the base-reinforced pyramid (BP) system, which is formed by reinforcing the base of a rectangular pyramid by crossing bars, is introduced as a successful attempt to reduce maximum bar forces in double-layer space frames without densifying grids. Properties of the BP system are reviewed. Super bar theory is introduced to cope with the buckling and large internal forces of long bars. Therefore, large grids can be realized in super span flat space frames with lightweight and large clear space. Under this concept, either a reciprocal prism or, generally, its derivatives, which are composed of much shorter bars, replace long bars. Factors affecting the efficiency of super bars are analyzed in detail, and their joint design is also recommended. Details of designing super bars are clarified. The efficiency of a 200-m-span flat double-layer BP grid employing super bars as long components is proven by case studies. Finally, a new concept with reduced cross-section is developed for a super bar system to achieve a further reduction in weights.

Pushing and pulling with the upper extremities while standing: the effects of mild Alzheimer dementia and Parkinson's disease.

Eleven patients with mild dementia of Alzheimer type, 12 patients with mild to moderate Parkinson disease, and 27 control subjects of comparable age, education, and gender pushed or pulled on a rigid horizontal bar while maintaining stable erect stance. A target window (target force +/-10% maximum force) and a bar force cursor were displayed on a video screen, and subjects were asked to place the bar force cursor within the target window as quickly and as accurately as possible holding the target window for at least 1 sec. The target forces were 50% and 75% maximum force for each person, and three 4.0-sec push trials and three 4.0-sec pull trials were performed for each target force. Moments of force (torque), body motion, and extremity electromyography were measured with a computerized motion analysis system. The patients with Alzheimer's disease had only slightly lower Mini Mental State Examination (MMSE) scores (mean +/- standard deviation [SD] = 25.0 +/- 2.3) than the patients with Parkinson's disease (28.8 +/- 1.5) and control subjects (28.7 +/- 1.3). The patients with Alzheimer's disease had upper limb reaction times (0.827 +/- 0.399 sec) that were greater than those of the patients with Parkinson's disease (0.672 +/- 0.315 sec) and control subjects (0.606 +/- 0.263 sec). Furthermore, the patients with Alzheimer's disease achieved the designated target in only 46.2% of trials, which was comparable to the performance of the patients with Parkinson's disease (55.6%) but inferior to the control subjects (80.6%). Movement times did not differ significantly. The patients and control subjects initiated movement with comparable anticipatory postural activity in the lower limbs. The poor success rates of the patients with Alzheimer's disease and the patients with Parkinson's disease were attributable to inadequate visually guided adjustments in force after the initial movement began. This difficulty in making quick motor adjustments may be relevant to the tendency of patients with Alzheimer's disease to fall.

Field Performance of Stress-Laminated Timber Bridges

Stress-laminated timber bridges were introduced into the United States in the late 1980s. Since then this concept has been used for more than 500 bridges constructed on roadways throughout the United States. To evaluate the performance of these bridges, the Forest Products Laboratory of the U.S. Department of Agriculture Forest Service and FHWA initiated a nationwide bridge-monitoring program. A field evaluation and the results obtained through that monitoring program for stress-laminated bridges that have been continuously monitored for 2 or more years after installation are presented. Included are discussions related to bridge design and construction, moisture content, stressing bar force, vertical creep, load test behavior, and condition evaluation. On the basis of the monitoring program results, the performance of stress-laminated timber bridges is generally satisfactory, although there are areas in which performance can be improved.

Mechanism of shear transfer in a reinforced concrete beam

This paper presents an analysis of the results of five tests conducted on four reinforced concrete beams. The tests were performed principally to investigate the mechanics of internal shear transfer in a transversely loaded concrete beam with no shear reinforcement. Test specimens consisted of simply supported wide beams with steel flexural reinforcement. The reinforcement for two of the beams was epoxy coated. The shear span to depth ratios were 2.93, 3.32, and 3.81. Measured strains on the reinforcement were used to divide the total shear into its beam and arching action components. In all tests, beam and arching action shear transfer mechanisms were found to coexist. Apart from that with the longest span, all tests ended with rupture of the concrete along a diagonal failure surface. It is concluded that shear failure may be caused by a shift in the internal mechanics of shear transfer from beam action to arching action. Because this shift may be initiated by the yielding of reinforcement, it can be associated with the formation of a plastic hinge. There was no observed effect on the mechanics of shear transfer that could be attributed to epoxy coating of the reinforcement.Key words: arching action, beam action, one-way shear, shear transfer, reinforced concrete beam, bond forces, bar force gradient.