Showing papers on "Flexural rigidity published in 1996"

Flexural rigidity of microtubules measured with the use of optical tweezers

Abstract: The flexural rigidity of single microtubules is measured using optical tweezers. Two new methods are presented. In both the optical forces of the laser trap are used to directly manipulate microtubules grown off the ends of Chlamydomonas axonemes. The shapes of the microtubules are observed by video microscopy as the hydrodynamic forces of viscous flow counteract the elastic restoring forces when the microtubules are moved actively relative to the surrounding buffer medium. To determine the flexural rigidity, the bending of a microtubule is analyzed under a given velocity distribution along its length. Microtubules incubated with taxol after polymerization are measured to be more flexible than those without taxol added. On the other hand, MAPs are shown to increase microtubule stiffness.

Flexural response of concrete beams reinforced with FRP reinforcing bars

Abstract: The authors conducted an experimental and theoretical comparison between flexural behaviors of concrete beams reinforced with fiber reinforced plastic (FRP) reinforcing bars and identical conventionally reinforced ones. Comparisons were made in relation to cracking behavior, load-carrying capacities and modes of failure, load-deflection response, flexural rigidity, and strain distribution. The results revealed that perfect bond exists between FRP reinforcing bars and the surrounding concrete. Also, American Concrete Institute (ACI) Code formulas for predicting deflection response, cracking-ultimate moments, and cracked-effective moments of inertia can easily be adapted for modeling the flexural behavior of concrete beams reinforced with FRP reinforcing bars if appropriate modifications are made.

Practical Formulas for Estimation of Cable Tension by Vibration Method

Abstract: The vibration method is usually used for field measurement of cable tension during the construction of cable system bridges such as an arch bridge stiffened with inclined cables or a cable-stayed bridge. Practical formulas for the vibration method are proposed herein taking the effects of flexural rigidity and sag of a cable into account. The formulas are based on the approximate solutions of high accuracy for the equation of inclined cable with flexural rigidity. Cable tensions are easily estimated by these formulas using measured natural frequencies of low-order modes. The practical formulas presented herein are applicable to various cables, regardless of length and tension as far as the vibration of firstor second-order mode is measurable. As to a very long cable that cannot be easily excited artificially, a formula is presented by using natural frequencies of high-order modes obtained from stationary microvibrations. The accuracy is confirmed through comparison of the values obtained by practical form...

Functions of fish skin: flexural stiffness and steady swimming of longnose gar, Lepisosteus osseus

Abstract: The functions of fish skin during swimming remain enigmatic. Does skin stiffen the body and alter the propagation of the axial undulatory wave? To address this question, we measured the skin's in situ flexural stiffness and in vivo mechanical role in the longnose gar Lepisosteus osseus. To measure flexural stiffness, dead gar were gripped and bent in a device that measured applied bending moment (N m) and the resulting midline curvature (m-1). From these values, the flexural stiffness of the body (EI in N m2) was calculated before and after sequential alterations of skin structure. Cutting of the dermis between two caudal scale rows significantly reduced the flexural stiffness of the body and increased the neutral zone of curvature, a region of bending without detectable stiffness. Neither bending property was significantly altered by the removal of a caudal scale row. These alterations in skin structure were also made in live gar and the kinematics of steady swimming was measured before and after each treatment. Cutting of the dermis between two caudal scale rows, performed under anesthesia, changed the swimming kinematics of the fish: tailbeat frequency (Hz) and propulsive wave speed (body lengths per second, L s-1) decreased, while the depth (in L) of the trailing edge of the tail increased. The decreases in tailbeat frequency and wave speed are consistent with predictions of the theory of forced, harmonic vibrations; wave speed, if equated with resonance frequency, is proportional to the square root of a structure's stiffness. While it did not significantly reduce the body's flexural stiffness, surgical removal of a caudal scale row resulted in increased tailbeat amplitude and the relative total hydrodynamic power. In an attempt to understand the specific function of the scale row, we propose a model in which a scale row resists medio-lateral force applied by a single myomere, thus functioning to enhance mechanical advantage for bending. Finally, surgical removal of a precaudal scale row did not significantly alter any of the kinematic variables. This lack of effect is associated with a lower midline curvature of the precaudal region during swimming compared with that of the caudal region. Overall, these results demonstrate a causal relationship between skin, the passive flexural stiffness it imparts to the body and the influence of body stiffness on the undulatory wave speed and cycle frequency at which gar choose to swim.

Study of insertion task of a flexible wire into a hole by using visual tracking observed by stereo vision

Abstract: Measuring the force on a flexible wire is difficult by using force/torque sensors when the flexural rigidity of the wire is small because the wire buckles and the force on the wire is smaller than the force that can be measured by a force/torque sensor. This paper presents a method of calculating the force on a wire from its shape observed by stereo vision. We propose a method of inserting the wire into a hole in a wall by using the estimated force. Three experiments have been successfully carried out.

Flexural behaviour of reinforced concrete beams strengthened with carbon fibre sheets

Abstract: This paper presents the results of an experimental study on flexural behaviour of reinforced concrete (RC) beams strengthened with carbon fibre (CF)-reinforced plastic sheets. The CF sheets were bonded on the soffit of the beam using epoxy resin adhesive. Six medium-sized RC beams were tested in bending to evaluate reinforcing effects of the CF sheets. A large-sized RC beam which was initially crack-damaged by pre-loading and subsequently repaired by injection of epoxy resin was also tested to simulate the performance in real structures. The results indicated that the flexural rigidity and strength of the RC beams are increased by reinforcing with the CF sheets. Beneficial reinforcing effects were also observed for the crack-damaged RC beam.

Design procedure for reinforced concrete beams with large web openings

Abstract: Based on test evidence, guidelines for the placement of large web openings in reinforced concrete beams are given, following which a simple design procedure is suggested Generally, openings should be positioned so that chords have sufficient concrete area to develop the ultimate compression block in flexure and adequate depth to provide effective shear reinforcement They should not be deeper than one-half the beam depth and should be located not closer than one-half the beam depth from supports or concentrated loads For analyses for elastic bending moments and shear forces by conventional methods, the recommended procedure uses an equivalent shear stiffness incorporating an effective length for the opening and considers the applied shear to be carried in proportion to the flexural stiffness of the chords The design of chords for strength follows ACI code provisions Cracking at the opening is controlled by proper detailing, while deflections are calculated using the same analysis procedure but considering cracked moment of inertia and checking against code requirements

Electrostatic rigidity of charged membranes in systems without added salt

Abstract: The thermodynamics of surfactants in solution has largely been understood in the framework of the flexible surface model. We calculate the bending rigidity for a case where this model might be put to a strong test: ionic surfactant systems with no added salt to screen the electrostatics. In so doing, we present a perturbative solution to the Poisson-Boltzmann equation for the case of two undulating sheets with intervening counterions. The predictions to which this leads for the bending modulus are shown (for a particular choice of undulation mode) to be identical to that of the solution for the geometry of concentric cylinders. This indicates that the curvature free energy is independent of the global aggregate geometry, even in systems with counterions only.

Flexural Behavior of Reinforced Concrete Masonry Wallsunder Out-of-Plane Monotonic Loads

Abstract: This paper presents the test results of an investigation carried out to study the behavior and flexural strength of vertically spanned reinforced concrete block masonry walls under out-of-plane monotonic loading. The study presented in this paper, which is part of the U.S.-Japan Coordinated Program on Masonry Building Research, addresses the elastic and inelastic behavior of reinforced block masonry walls. Six walls were tested to determine the effects of percentage and location of vertical reinforcement, block size, and extent of grouting. The behavior included cracking patterns and cracking moments, load-deflection curves up to and beyond the peak load, and displacement ductility. Test results showed that the percentage and location of vertical steel (centrally located versus staggered) had a significant effect on wall load-deflection curves, strength, and ductility. The extent of grouting (partially versus fully grouted) affected cracking load and consequently, flexural rigidity and deflection under service loads. The extent of grouting, however, did not show an adverse effect on wall stability in the inelastic range. The specified value of the modulus of rupture in the UBC-94 code is much lower than the experimental values of maximum tensile stress at first crack obtained for fully grouted walls. The theoretical analysis for the ultimate strength based on the Whitney stress block method that is included in the UBC-94 code showed a good correlation with the experimental results. Displacement ductility ratios ranged from 1.79 for the wall with 0.44 percent vertical steel to 16 for the wall with 0.19 percent steel. As expected, the displacement ductility of the wall panels decreased as the percentage of vertical reinforcement increased.

Diamond-like-carbon coated aramid fibers having improved mechanical properties

Abstract: A process for improving the mechanical properties, particularly the flexural rigidity, of aramid fibers by directly depositing a diamond-like-carbon coating onto the surface of the fibers. Diamond-like-carbon (DLC) coated aramid fibers having increased flexural rigidity are also disclosed. DLC coated aramid fibers show an increase in flexural rigidity and suppression of low yielding behavior when compared to uncoated aramid fibers.

Influence of local postbuckling behaviour on bending of thin-walled beams

Abstract: The influence of the local postbuckling behaviour on the bending of thinwalled beams is studied. The analysis of the postbuckling behaviour of a prismatic column-beam subject to compression and bending is employed in order to determine the overall flexural stiffness of a beam after local buckling. The asymptotic Koiter method is used in the second order approximation. The determination of post-buckling coefficients enables one to find the beam's flexural stiffness without the necessity of using hypotheses on effective widths of eccentrically compressed plates. It is shown that the post-buckling equilibrium branch in a bending moment-global curvature coordinate system for a perfectly elastic thin-walled beam is rectilinear (in the second order approximation of' the asymptotic method). Simple analytical relations are presented between the slope of the post-buckling equilibrium branch of global bending and post-buckling coefficients for local buckling mode. The results obtained are compared with data reported by other authors.

Bending instability of composite tubes

Abstract: In this paper, a set of simple formulations is derived to predict the instability critical loads of orthotropic composite tubes under pure bending. The formulations are based on the assumption that the instability of an orthotropic composite tube under pure bending is due to the ovalization of its cross section. For the static instability case, the ovalization increases steadily as the curvature increases, which results in a reduction in the bending rigidity of the tube. The interaction of longitudinal bending and cross-section ovalization causes the tube to have a limit load instability. For the dynamic instability case, the instability of the tube is due to the interaction of two vibrations, one is the longitudinal bending of the tube as a beam, the other is the circumfer­ ential bending of the tube as a thin-walled shell.

The Wrinkling of Thin, Flat, Rectangular Webs

Abstract: A web is termed wrinkled when one of the in-plane principal stresses is tensile and the other is sufficiently compressive. A criterion is derived that predicts wrinkling of isotropic, compressible rectangular webs under uniform in-plane principal stresses. The compressive stress at impending wrinkling depends on the flexural stiffness, and it equals zero in the case of a membrane. A criterion of wrinkling is also derived using isotropic, incompressible membrane theory. This criterion predicts an infinite number of wrinkle waves in a wrinkled region. With small flexural stiffness, the number of wrinkle waves becomes finite at wrinkling and it is predictable along with the shape and the size of the wrinkled region. The number of the wrinkle waves increases as the aspect ratio of the rectangular web increases, as the in-plane principal tension increases, and as the flexural stiffness decreases. Analyses of wrinkling of a rectangular web under simple shear and under uniform longitudinal stretching illustrate the above predictions.

Flexural strengthening of reinforced concrete beams using bonded polymer composite plates.

Abstract: The in situ rehabilitation or upgrading of reinforced concrete (RC) members using bonded steel plates has been proven in the field to be an effective, convenient and economic method of improving structural performance. However, disadvantages inherent in the use of steel have stimulated research into the possibility of using fibre- reinforced polymer (FRP) materials in its place, providing a non-corrosive, more versatile strengthening system. The aim of this investigation was to provide a detailed study of the flexural strengthening of RC beams using FRP plates. Experimental testing of 1.0 m length specimens was used to illustrate the feasibility and general characteristics of external FRP strengthening. A parametric study was also carried out to evaluate the influence of basic geometric and material parameters on overall performance. Larger-scale 2.3 m length beams were used to confirm the general behaviour observed in the 1.0 m tests. The structural effects of pre-tensioning the FRP plate prior to bonding to the beam were also examined. Although moderate increases in flexural rigidity and strength over a non-prestressed member were attained by the use of this technique, the greatest influence observed was restraint on the initiation and development of cracking. The performance of the component materials and overall strengthened system under sustained load application and adverse environmental conditions was considered experimentally. The results, although somewhat limited, suggest that environmental deterioration of the mechanical properties of bulk adhesive specimens does not necessarily imply a degradation of the bond performance in situ or a reduction in the long-term structural behaviour of the strengthened member. Similarly, the viscoelastic nature exhibited by the epoxy adhesive when tested in isolation did not appear to affect the time-dependent behaviour of the strengthened member; the addition of the externally bonded FRP plate appeared to have only beneficial influences on long-term behaviour. The effectiveness of theoretical methods of predicting FRP strengthened beam response to load application was finally assessed. A simple, iterative analytical technique was generally found to provide good correlation with the global behaviour determined experimentally. Theories proposed to account for the occurrence of premature failure of steel plated beams were evaluated; these appear to be unsuitable for FRP strengthened members. Use of the finite element (FE) method for predicting flexural response was also investigated. In this case, agreement with behaviour observed in testing was found to be poor. This was attributed to the representation of material response incorporated in the FE package.

Experimental studies on the flexural reinforcing effect of carbon fiber sheet bonded to reinforced concrete beam

Abstract: Lately, bonding carbon fiber (hereafter called CF) sheets to a concrete structure has been developed as a new reinforcing method in Japan. In this study, a series of flexural tests were conducted in order to confirm the reinforcing effect and verify and suggest a new design method. Two kinds of CF sheets were used: high elastic modulus (hereafter called HM) CF and standard (hereafter called I.M.) CF. Based on the results of experiments, the following conclusions were drawn: 1) Reinforcing with CF sheets can increase initial cracking load, flexural strength and rigidity, and decrease strain of rebar. 2) In particular, HMCF exhibits excellent reinforcing effects. For example, in comparison with the control specimen, 2 layer HMCF sheets doubled flexural rigidity. 3) It is confirmed that a combination of conventional elastic theory can be applied to the design of RC beam reinforced with CF sheets.

Low Stress Mechanical Behavior of Cotton / Polyester Yarns and Fabrics in Relation to Fiber Distribution Within the Yarn

Abstract: Low stress mechanical properties of cotton /polyester yams representing random fiber disposition and core-sheath construction are compared to determine the influence of fiber distribution on yam properties. The yams are converted into plain weave fabrics under identical conditions, and fabric properties are compared to understand how yam properties translate into fabric properties. The core-sheath yarn (polyester core/cotton-covered yam) shows lower values for bending rigidity, bending hysteresis, compressive resilience, and tensile elongation. The same yarn also shows higher values for compressive softness and tensile modulus. The lower tensile elongation and higher tensile modulus of the core-sheath yam is reflected in the lower elongation and higher modulus of the corresponding fabric. However, bending and compression properties of the core-sheath yarn are inversely related to bending and compression properties of the corresponding fabric. Results show that yarn bulk and compression properties exert a ...

Reduced Persistence Length and Fluctuation-Induced Interactions of Directed Semiflexible Polymers on Fluctuating surfaces

Abstract: We consider directed semiflexible polymers embedded in a fluctuating surface which is governed by either surface tension or bending rigidity. The attractive interactions induced by the fluctuations of the surface reduce the rigidity of the polymers. In particular, it is shown that for arbitrarily stiff parallel polymers, there is a characteristic separation below which they prefer to bend rather than stay linear. The out-of plane fluctuations of the polymer, screen out the long-range fluctuation-induced forces, resulting in only a short-ranged effective attraction.

Buckling stiffening structure of i girder

Abstract: PURPOSE: To increase the lateral-buckling strength of an I girder by forming end-section stiffening materials as beltlike vertical members extended along the axis of the I girder at the right and left end sections of the compression-side flange of the I girder respectively CONSTITUTION: Vertical beltlike end-section stiffening materials 1 extended along the axis of an I girder 02, in which upper ends are welded, are formed at the right and left ends of a compression-side flange 2 as the upper flange of the I girder 02 respectively Ideal lateral buckling moment Mcr =(π/ Io ) (EIYGJd )(I+EJw Io G Jd )} (Where IY represents lateral flexural rigidity, JW warping rigidity, Jd pure torsional rigidity, E Young's modulus, and G shear modulus of rigidity) Since lateral flexural rigidity IY and warping rigidity JW in above-mentioned formula are increased remarkably by a small end-section stiffening material 1, ideal lateral buckling moment Mcr is augmented, thus largely improving lateral buckling strength

Design considerations for mirror materials

Abstract: The key requirements for an optical mirror material include low density, high Young's modulus, low coefficient of thermal expansion, high thermal conductivity, and high diffusivity. Not included among these are fracture toughness and stress corrosion constant, which control slow crack growth and long-term reliability under static or dynamic loads during manufacturing and in-service. The reliability requirement becomes crucial as the mirror size increases and/or its mission takes on strategic importance. This paper compares the critical properties of three ultralow expansion materials, namely ULETM, Zerodur and AstrositallTM. It demonstrates how these properties affect the bending rigidity and safe allowable stress for the mirror subjected to different types of loading, namely: (i) its own weight and (ii) external load. An analysis of bending rigidity, bending stress, and safe allowable stress shows that mirror blanks of two different materials can be designed to be equivalent in terms of their rigidity without any weight penalty. The lower modulus and lightweight material like ULE glass requires about 10 percent higher thickness which reduces the bending stresses 20 percent compared to those in Zerodur or Astrositall mirrors of identical size. The lower stress, according to Power law fatigue model, is highly beneficial in that it improves the mechanical reliability of ULE mirror during manufacturing, transportation, installation and in-service by two orders of magnitude over that of Zerodur and Astrositall mirrors. The fatigue and fracture data for the three materials are used to estimate the safe allowable stress for facilitating mirror design from mechanical reliability point of view.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reduced persistence length and fluctuation-induced interactions of directed semiflexible polymers on fluctuating surfaces

Abstract: We consider directed semiflexible polymers embedded in a fluctuating surface which is governed by either surface tension or bending rigidity. The attractive interactions induced by the fluctuations of the surface reduce the rigidity of the polymers. In particular, it is shown that for arbitrarily stiff parallel polymers, there is a characteristic separation below which they prefer to bend rather than stay linear. The out-of-plane fluctuations of the polymer screen out the long-range fluctuation-induced forces, resulting in only a short-ranged effective attraction.

Elastic and initial flexural failure analysis of unsymmetrically laminated cross-ply strips

Abstract: A finite difference version of the Dynamic Relaxation (DR) method is used to generate elastic solutions of the small and the large deflection Mindlin plate equations for unsymmetrically laminated cross-ply strips subjected to uniform lateral pressure. The Maximum Stress (Independent) and Tsai-Hill failure criteria are combined with these solutions to produce initial failure analyses. It is shown that coupling between bending and stretching due to the B11 stiffness term can cause a considerable increase or decrease in the flexural stiffness of simply supported in-plane fixed strips relative to the equivalent orthotropic strips but not necessarily in the corresponding failure pressures. It is also found that the predictions of the two failure criteria are in close agreement.

Filament yarn for air bag

Abstract: PURPOSE: To obtain polyester filament yarn having mechanical properties such as tensile strength and elongation necessary for air bag base fabric when woven or knitted and capable of giving fabrics with flexibility as well as such mechanical properties. CONSTITUTION: This filament yarn consists of polyethylene terephthalate >=0-8 in intrinsic viscosity, having the following characteristics: single fiber fineness: 1-2.5 denier; total fineness: 200-500 denier; tenacity: >=8g/d: elongation at beak: >=15%; the birefringence distribution on single fiber cross section and flexural rigidity satisfy the relationships 1 and 2, respectively. Relationship 1:▵nc-▵ns>=0.015, ▵nc>=0.170 (▵nc is the average blrefringence for the portion ranging from the center of single fiber to 70% of its radius in the radial direction; ▵ns is the average birefringence for the portion ranging from the surface of the single fiber to 30% of its radius in the radial direction); relationship 2: B ×TD (B is flexural rigidity, g.cm /FY; TD is total fineness, denier).

Monte Carlo study of a self-avoiding polymerized membrane with negative bending rigidity

Abstract: We study the possibility of a cancellation between the entropic bending rigidity due to self-avoiding interaction and negative bending rigidity. Results of Monte Carlo simulation show that a self-avoiding polymerized membrane with negative bending rigidity exhibits a phase transition from the usual floppy flat phase to a rigid folded flat (thin plate) phase. Even for flexible membranes, the complete cancellation does not occur. Based on these results, we discuss the problems in theoretical approaches to the phase transitions of polymerized membranes.

Technique for prodn. of pre-bending non-adhesion prestressed concrete beam

Abstract: A technological method for manufacturing pre-bent non-bond prestressed concrete beam includes prefabricating non-bond reinforced concrete beam, pre-applying longitudinal load to the beam, filling preserved notch, and discharging the pre-applied load The prefabricated prestressed concrete beam has very high cracking strength and bending rigidity and wider span Compared with post-tensioned one, its construction period is shortened by 20-50%

Spacer for cable

Abstract: PURPOSE: To improve the flexibility of a spacer and to improve the workability of a laying work as well by disposing a material layer having a low coefft. of elasticity between the outermost layer and a central tension member and integrating these layers. CONSTITUTION: A high-elastic modulus thermoplastic material layer 2 having grooves forming the outermost layer of a spacer is formed in order to suppress the deformation by the side pressure acting on a cable at the time of laying the cable and to protect the inside of transmission medium housing grooves 4. The material layer 3 which is arranged between the high-elastic modulus thermoplastic material layer 2 and the central tension member 1 and has a low coefft. of elasticity exhibits the effect of suppressing the bending rigidity of the spacer to a lower level. The materials for the central tension member 1 are not particularly limited, insofar as these material has have high rigidity, for which, for example, FRP, such as aramid fiber reinforced plastic, having rigidity, steel wires, etc., are exemplified. The high-elastic modulus thermoplastic material layer 2 includes, for example, a high-density polyethylene, etc., and the low-elastic modulus material layer 3 includes, for example, a foamed polyethylene, etc.