Showing papers on "Flexural rigidity published in 1994"

Flexural rigidity of the Basin and Range-Colorado Plateau-Rocky Mountain transition from coherence analysis of gravity and topography

Abstract: Stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography. However, the spatial resolution of coherence analysis has been limited by use of two-dimensional periodogram spectra from very large (greater than 10(exp 5)sq km) windows that generally include multiple tectonic features. Using a two-dimensional spectral estimator based on the maximum entropy method, the spatial resolution of flexural proerties can be enhanced by a factor of 4 or more, enabling more detailed analysis at the scale of individual tectonic features. This new approach is used to map the spatial variation of flexural rigidity along the Basin and Range transition to the Colorado Plateau and Middle Rocky Mountains physiographic provinces. Large variations in flexural isostatic responses are found, with rigidities ranging from as low as 8.7 x 10(exp 20) N m (elastic thickness (T(sub e) = 4.6 km) in the Basin and Range to as high as 4.1 x 10(exp 24) N m T(sub e) = 77 km) in the Middle Rocky Mountains. These results compare favorably woith independent determinations of flexural rigidity in the region. Areas of low flexural rigidity correlate strongly with areas of high surface heat flow, as is expected from the contingence of flexural rigidity on a temperature-dependent flow law. Also, late Cenozoic normal faults with large displacements are found primarily in area of low flexural rigidity region. The highest flexural rigidity is found within the Archean Wyoming craton, where evidence suggests that deeply rooted cratonic lithosphere may play a role in determining the distribution of tectonism at the surface.

Seismic Performance of Steel‐Encased Composite Columns

Abstract: An experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions. Eight two‐thirds‐scale specimens were tested, each consisting of a structural steel shape encased in reinforced concrete. The parameters studied in the test program included the degree of concrete confinement required to achieve adequate ductility under cyclic loading, effectiveness of flange shear studs for enhancing flexural stiffness and strength, concrete compressive strength, and the shear resistance mechanism of the composite column. The results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited. The encased steel shape was found to provide the primary resistance to transverse shear during overloading, with the shear studs not effective in enhancing the flexural resistance to lateral loading. The specimen flexural capacity under combined axia...

The Pin-Force Model Revisited

Abstract: The pin-force model is one of the earliest models developed for beams actuated in bending. In this model, the actuators and substrates are considered as separate elastic bodies and the forces from the actuators are transferred to the substrates by "pins" at the edges of the actuators. Although this model of force transfer is consistent with the assumed perfect bonding scenario, where the shear stress is concentrated in a small area close to the edge of the actuator, it fails to provide the correct structural response for the case where the actuator is relatively thick. In this paper, while retaining the basic features of this model (i.e., treating the actuator and beam as separate bodies), the corrections necessary to upgrade this model to the level of the more accurate Bernoulli-Euler model are presented. The basic difference lies in the appropriate inclusion of the actuator flexural stiffness in the structural moment-curvature equations. Two configurations are considered: one in which the actuators are ...

Performance of Pultruded FRP Connections under Static and Dynamic Loads

Abstract: The objective of this paper is to introduce a new design concept for con necting structural pultruded shapes. In this study, evaluation of the performance of a new class of pultruded fiber reinforced plastic (PFRP) beam-to-column connections under both static and dynamic loading conditions is presented. The connecting elements are com posed of newly developed FRP universal connectors (UC), PFRP threaded rods and nuts with and without high-strength epoxy adhesives. Experimental and analytical studies on the rotational stiffness and the ultimate flexural strength are presented. A simple linearized expression for each connection is given along with the corresponding flexural ultimate capacity. Average flexural stiffness coefficients, for design purpose, are also provided. Discussion on the different ultimate modes of failure is also provided. For the dynamic part of this study, results of experimental dynamic tests of PFRP structural shapes and connections is presented. The thin-walled elements used in this ...

Element Identification of Member Properties of Framed Structures

Abstract: Structural‐parameter identification of member properties of framed structures is conducted at the element level. By substructuring, a frame element is isolated from the complete structure, and the state equation used for parameter estimation is derived from the equation of motion of the frame element. Using the extended Kalman filter with weighted global iteration, the physical characteristics such as the axial rigidity, flexural rigidity, and damping parameters of a frame element are identified. Numerical simulation studies are done for two‐story plane frames, and the member properties of the frame elements are estimated. The convergence behavior of the parameters is observed and the possible cause of divergence is explored. The results show that the convergence behavior of the identified parameters is affected by a number of factors such as initial guess of the parameters, number of observed responses, and the choice of observed response.

Stiffness of asphalt-aggregate mixes

Abstract: This report presents an evaluation of several test systems for stiffness determination of asphalt-aggregate mixes, including 1) axial resilient stiffness, 2) diametral resilient stiffness, 3) resilient and dynamic flexural stiffness, and 4) dynamic shear stiffness. All of the stiffness test systems were found to be sensitive to mix and test variables, especially to asphalt source, asphalt content, aggregate type, and air-void content. Temperature had the greatest effect on stiffness for axial, diametral, and flexural stiffnesses. On the basis of the data presented it is recommended that the use of diametral stiffness measurements be limited to temperatures equal to or less than 20 deg C. Models are presented to permit estimation of flexural stiffness (and loss-stiffness) from shear stiffness (and loss-stiffness in shear) at 20 deg C and 10 Hz frequency.

Straightening of Crimped and Hooked Fibers in Converging Transport Ducts: Computational Modeling:

Abstract: A two-dimensional dynamics model for the motion of fibers in an accelerating laminar air flow is presented. Nonlinear model equations for each fiber include effects of inertia, air drag, and flexural rigidity. This rigidity, or stiffness, acts in such a way that a curled or hooked fiber resists being straightened. Randomly distributed fiber crimps at the inlet can be preferentially straightened as the fibers are transported in two converging ducts. Statistical measures of straightening are provided.

Lateral Postbuckling Analysis of Beam Columns

Abstract: This is a study of the elastic lateral post buckling response of a simply supported beam under uniform bending acting on the plane of major bending rigidity, in which the effect of an axial compreisson is also included. The study established the stability or instability of the critical state; the initial (nonlinearly elastic) postbuckling equilibrium path in an analytic form, using a nonlinear bending-moment-curvature relationship and linear kinematic relations; the margin of postbuckling strength or the degree of sensitivity to imperfections; and the elastic limit state design load.

Instability of Tapered Thin‐Walled Beams of Generic Section

Abstract: Buckling loads and natural frequencies and the corresponding modal shapes and forms for thin‐walled tapered beams of open sections are examined using the finite‐element method. A tapered thin‐walled bar finite element with seven degrees of freedom at each node is adopted. In the virtual work formulation, the updated Lagrangian approach is adopted in which the effect of geometric nonlinearity is considered. A rigorous expression for strains based on membrane theory of shells is considered. The flexural stiffness matrix, geometric stiffness matrix, and consistent mass matrices are derived in a companion paper. The convergence and accuracy of the method is tested based on other numerical results. Using the present theory, one is able to investigate various torsional and flexural static and dynamic instability problems. Examples are presented and comparisons are made with the existing solutions.

Scaling modulus as a degree of freedom in the design of locust legs

Abstract: Previous work has shown that the scaling of mechanical behaviour in bending of the metathoracic tibiae of the African desert locust (Schistocerca gregaria) is not predicted by the scaling of external dimensions. The flexural stiffness of the tibia scales to (body mass)1.53, which is similar to the predictions of the elastic similarity model of scaling. The external dimensions, however, scale in a manner that produces relatively more elongate limb segments ­ an observation that differs from the predictions of any existing scaling model. In this paper, we examined two alternative hypotheses to explain this uncoupling of morphology and mechanics: (1) that the load-bearing cuticular material is distributed in the legs in a manner that is not indicated by changes in external dimensions, or (2) that the stiffness of the cuticular material is altered to produce the observed scaling of flexural stiffness. The second moment of area (I) scaled to (body mass)1.19, which was similar to scaling I to (tibial radius)4. This indicates that the relationship between the external dimensions of the tibiae and the specific distribution of load-bearing material is conserved independently of scale. Therefore, the locust achieves the observed scaling of flexural stiffness by altering the modulus of the load-bearing cuticular material. In fact, the time-dependent modulus (E') scales to (body mass)0.311. In essence, the scaled material stiffness provides a degree of freedom in design in addition to external morphological dimensions in accommodating the changing demands placed on a skeletal structure with increases in body size.

Changes in Fabric Mechanical Properties After Pressure Decatizing as Measured by FAST

Abstract: We have investigated the effects of decatizing temperature, prior rotary pressing, and fabric initial regain on the mechanical properties of decatized fabrics of various constructions and dyeing stages Undyed and plain weave fabrics were the most sensitive to decatizing treatment Higher decatizing temperature consistently increased exten sibility and bias extension and decreased bending rigidity Rotary pressing had a marked influence on the mechanical properties of fabrics subsequently set by pressure deca tizing ; the resulting decrease in tensile properties and increase in bending rigidity are explained by simple mechanisms The magnitude of changes in the warp and weft extensions, bias extension, and bending rigidity with setting temperature and rotary pressing is analyzed and discussed in relation to various fabric types

Effect of joint rigidity on buckling strength of single layer lattice domes.

Abstract: The present paper discusses the effect of the joint rigidity on the buckling strength of single layer lattice domes, with regular three way grids, under vertical loading. The effect of bending rigidity of joints on the overall strength of domes is investigated from three viewpoints; (1) how the joint rigidity contributes to the reduction of buckling loads, (2) how the reduction can be interrelated to compressive strength curves in terms of the generalized slenderness for the member most relevant to the overall buckling of domes, and (3) whether the strength curves will resemble those for beam-columns in tall buildings and for continuum shells, or will not. For present semi-rigid cases, by reflecting the reduction of buckling loads for perfect rigid cases on a specific modification of the generalized slenderness, the member strength curve is available in a similar way for the rigid-jointed lattice domes.

Shear-lag effect in CFRP I-beams under three-point bending

Abstract: Shear-lag effect in CFRP (carbon-fiberreinforced plastic) I-beams is investigated by applying Reissner's method concerning box beams to CFRP I-beams. This modified beam theory (MBT) assumes that the flanges are orthotropic and includes the effect of the shearing rigidity of the web and the deformation of the flanges themselves. The anisotropy of the flanges causes the decrease of the flexural rigidity of I-beams. The decrease, however, is restrained by a preventive action on the shear-lag effect in the flanges with a decrease of the anisotropy ratio due to the selection of fiber orientation. In order to verify this MBT, I-beam structures were fabricated from carbon fiber and epoxy resin using three different lay-up schemes: unidirectional, quasi-isotropic, and a ±45-deg angle-ply. The stiffness and shear-lag effect of these I-beams were measured and compared with results from the composite beam theory and MBT. The theoretical load-deflection curves and the strain distributions agreed well with the corresponding experimental results.

Indoor unit of air-conditioner

Abstract: PURPOSE:To reduce the weight and noises of an indoor unit of an airconditioner embedded in ceiling. CONSTITUTION:Rising portions 14 for increasing the flexural rigidity of a top plate 2 and side plates 3 are provided in top plate 2 and side plates 3 constituting a housing 1 of an indoor unit. By providing these rising portions 14, the rigidity of the housing is heightened and the weight of the same is lightened. As a result, the weight of the indoor unit can be lightened. Further, by lightening the weight of the indoor unit, the installation efficiency of the same is enhanced and the safety of workers is also enhanced. Furthermore, the vibration of the housing can be minimized by heightening the rigidity of the housing, and the noises of the indoor unit can also be reduced.

The Theory of the Resistance to Bending of Set Plain-woven Fabrics

Abstract: A theoretical analysis of the resistance to bending of set plain-woven fabrics is presented. It is shown that no forces will be generated at the crossover points between the warp and weft threads when a fabric is bent by an external couple. The analysis yields convenient formulae for calculating the bending parameters of fabrics, the bending rigidity Band coercive couple M 0. The formulae show reasonable agreement with experimental results and good consistency with the conclusion which was drawn from data computation by Grosberg.

A packaging material and a method for its manufacture

Abstract: Packaging material for self-supporting packaging container walls can be given the desired flexural rigidity by being laminated to an inherently rigid material such as cardboard. Rigidity can also be achieved if two material layers are fixed at a given spacing from one another. According to the invention, this can be attained in that two material layers (1, 2) define an interjacent chamber (4) which is filled with gas under pressure. The material is produced by the material layers (1, 2) being sealed to one another over a portion of their surface such that a chamber (4) is formed which is filled with, for example, air under pressure.

Integration of the finite element and beam propagation methods to determine performance of microbend sensors

Abstract: Many parameters contribute to the performance of microbend sensors. These include fiber core radius, cladding radius, jacket radius, core and cladding refractive indices, core refracti"e index profile, fiber flexural rigidity, light source wavelength, light source power, spatial bend wavelength, number of bends and bend amplitude. Electromagnetic wave theory predicts that power lost from the core in a microbend is optimum when the fiber's spatial bend frequency equals the difference in propagation constants between the propagating and radiated modes.

Special Issue on Structural Materials. Strength and Deformation Characteristics of Reinforced Concrete Beam Strengthened with Carbon Fiber-Reinforced Plastics Plate under Static and Fatigue Loading.

Abstract: The carbon fiber-reinforced plastic (CFRP) plate bonding is a method in which CFRP plates are bonded by mean of epoxy resin to the surface of existing reinforced concrete (RC) structures. This method permits the insufficient amount of steel bars in the section of the structural member to be compensated externally. Therefore, it is considered that this method will become widely used under a corrosive environment since the CFRP plate is rust-proof.In this study, the strength and deformation characteristics of the RC beam strengthened with a CFRP plate under static and fatigue loading were dealt with. The experiments revealed the mode of failure for the beam bonded with a CFRP plate and subjected to static incremental loading to be flexural failure, and both the flexural rigidity and ultimate strength to increase. The fatigue failure for the beam bonded with a CFRP plate under the repetitive loading was not produced by the fatigue fracture of CFRP plate but by that of steel bars. The fatigue strength at 2×106 cycles of load repetition for the RC beam bonded with a CFRP plate was 57 percent of the static strength of the same beam.

The Bending Properties of Multi‐ply Worsted Yarns

Abstract: Presents a mathematical treatment of the large‐scale bending behaviour of multi‐ply yarn. Based on the assumptions that: each individual fibre in the yarn has the form of a doubly‐wound helix; each fibre is an inextensible slender rod; and interaction between fibres is ignored. The yarn‐bending rigidity is calculated as an average rigidity of an assembly of coaxial helices. There is good agreement between the predicted and measured values of yarn bending rigidity for a wool worsted knitting yarn. Also predicts the position, curvature and twist components as well as the strain energy of the deformed fibre.

Hard rod and frustum model of two-dimensional vesicles

Abstract: A two-dimensional vesicle of hard rods subject to a shadowing interaction is analy2ed by Monte Carlo simulations. From the mode analysis of the shape fluctuation of the vesicle, the bending rigidity is estimated microscopically and the relation between the rod length and the bending rigidity is studied. A scaling relation of a mean square radius of gyration is investigated and compared with that proposed by Leibler, Singh and Fisher. Increasing osmotic pressure a vesicle performs a shape transition from a circular to bi-lobocyte shape. A vesicle with a spontaneous curvature is also studied by using molecules of a frustum shape.

Soft and Repulsive:. Relationship Between Lipid Membrane In-Plane Fluctuations, Bending Rigidity, and Repulsive Undulation Forces

Abstract: Lipid membranes are soft and flexible bilayer surfaces that exhibit a substantial degree of in-plane fluctuations which become very strong near lipid phase transitions and in phase separation regions. The fluctuations couple to the out-of-plane motions as well as the large-scale mechanical modulii of the membrane leading to a thermal renormalization of, e.g., the bending rigidity. For multilamellar arrays of membranes, changes in the bending rigidity in turn lead to changes in the entropic repulsive undulation forces that act between the lamellae and which determine their swelling behavior. We briefly review recent results obtained from theoretical and experimental studies of phospholipid bilayers that clarify the relationship between lipid bilayer in-plane fluctuations (in density and composition), bending rigidity, and repulsive undulation forces. The results discussed derive from computer simulation calculations, field theory, as well as small angle neutron scattering.

Thermosensitive stencil printing sheet

Abstract: PURPOSE: To obtain a stencil printing sheet which produces a sharply printed image and demonstrates superb running and anti-crease properties by specifying tensile strength and bending rigidity, ie the strength and resiliency of the sheet CONSTITUTION: This thermosensitive stencil printing sheet is composed of thermoplastic resin film and a porous support consisting mainly of synthetic fiber laminated together In addition, the tensile strength of the sheet in a vertical direction is, at least, 03kgf/cm and the bending rigidity B value in a vertical or a horizontal direction is, at least, 002gfcm /cm

Method of measuring bending rigidity of golf club shaft and device thereof

Abstract: PURPOSE: To improve the reliability of measurement, by making it possible to easily measure the bending rigidity in the whole directions around the axial center of a golf shaft. CONSTITUTION: A measuring device is provided with end support means 20, 30 holding the outer peripheral face of both ends 1a, 1c of a golf shaft 1, an intermediate support means 40 holding and bending the outer peripheral face at the almost central part of the shaft toward the opposite direction against the support ends 20, 30 at both ends, and a load detector 50 of the bending loads on the golf club shaft 1. The golf club shaft 1 is supported by the end support means 20, 30 and the intermediate support means 40 and a bending displacement in the right angled direction arises in the axial center of the intermediate part lb. And then the bending rigidity of the shaft is measured. COPYRIGHT: (C)1995,JPO