Showing papers on "Bending moment published in 1996"

The Importance of Body Stiffness in Undulatory Propulsion

Abstract: During steady swimming in fish, the dynamic form taken by the axial undulatory wave may depend on the bending stiffness of the body. Previous studies have suggested the hypothesis that fish use their muscles to modulate body stiffness. In order to expand the theoretical and experimental tools available for testing this hypothesis, we explored the relationship between body stiffness, muscle activity, and undulatory waveform in the mechanical context of dynamically bending beams. We propose that fish minimize the mechanical cost of bending by increasing their body stiffness, which would allow them to tune their body's natural frequency to match the tailbeat frequency at a given swimming speed. A review of the literature reveals that the form of the undulatory wave, as measured by propulsive wavelength, is highly variable within species, a result which calls into question the use of propulsive wavelength as a species-specific indicator of swimming mode. At the same time, the smallest wavelength within a species is inversely proportional to the number of vertebrae across taxa ( r 2 = 0.21). In order to determine if intact fish bodies are capable of increasing bending stiffness, we introduce a method for stimulating muscle in the body of a dead fish while it is being cyclically bent at physiological frequencies. The bending moment (N m) and angular displacement (radians) are measured during dynamic bending with and without muscle stimulation. Initial results from these whole body work loops demonstrate that largemouth bass possess the capability to increase body stiffness by using their muscles to generate negative mechanical work.

Method and apparatus for breaking brittle materials

Abstract: A system for breaking large sheets of brittle material, such as glass, into smaller sheets, in which one laser (16) is moved across a glass sheet (10) having two major surfaces (11) to form two vent cracks (19, 19a) in the glass sheet (10); a first vent crack (19) in a first path on one side of the glass sheet (10), and a second vent crack (19a) in a second path on the other side of sheeet (10). The glass sheet (10) is broken into smaller sheets by applying a bending moment under the vent cracks (19, 19a).

Analysis of Piled Raft Systems in Layered Soil

Abstract: This paper presents a method of analysis for piled raft systems constructed in layered soils. The method presented takes account of the interactions of the raft, piles and soil without the cost of a full three-dimensional rigorous analysis. This is done by the use of finite layer methods for the analysis of the soil and finite element methods for the raft. Examples are provided in the paper for piled rafts constructed on layered soils, and results are presented for bending moments in the raft and loads in the piles.

Linear and nonlinear hydroelastic analysis of high-speed vessels

Abstract: A linear formulation of ship hydroelasticity is presented. Appropriate body boundary conditions of flexible modes are obtained and the hydroelastic version of high-speed strip theory is established. A nonlinear time-domain simulation method is also presented. The total response is decomposed into linear and nonlinear parts. The linear part is evaluated using appropriate linear potential-flow theory and the nonlinear part comes from the convolution of the impulse response functions of linear ship-fluid system and the nonlinear hydrodynamic forces. Four high-speed vessels with different ship lengths but with similar body plan and internal structural arrangement are used as examples. The calculations of midship bending moments are carried out at different forward speeds and head sea states. The results show that the hydroelastic effect in linear extreme response is insignificant and that the hydrodynamic damping plays a leading role in the flexible modes when the dynamic amplification of ship hull becomes important. The results also indicate that strong nonlinearity is the most prominent feature of high- speed vessels even in the moderate sea state and must be taken into account. The nonlinear influences are more remarkable in ships at large Froude numbers than in those at small ones. and more important in sagging moment than in hogging moment.

On the Hydoroelastic Response of Box-Shaped Floating Structure with Shallow Draft

Abstract: A pontoon type structure was recently highlighted since The Floating Structures Association of Japan proposed the new concept as the most beneficial one in 1994. The structure is supposed to be mat-like structure with length of 4 to 5 kilometers and depth (draft) of 5 (1) meters. The concept was further developed by The Technological Research Association of Mega-Float which was established in 1995. They constructed 300 meter long prototype structure to carry out at-sea test. The authors carried out tank tests to investigate hydroelastic response of the prototype structure using its scale model. The research was undertaken partly as joint work with T. R. A. of Mega-Float. The scale ratio of the model was decided as 1/30, with length of 9.75 meters, breadth of 1.95 meters and draft of 1.66 centimeters. The model was designed on the basis of the law of similitude and has elastically similar bending rigidity with 300 meter long prototype structure. A series of tank tests had been conducted focusing on the elastic response of the model in regular waves. The vertical motions have been detected through potentiometers and the bending moment through strain gages both distributed on the upper surface of the model. The analysis method based on 2-D structure and 2-D fluid modeling has been established in which the structure is approximated as a rectangular plate and the hydrodynamic characteristics is evaluated using the pressure distribution method based on the zero-draft Green function. The equation of motion, in which the interaction between structure and fluid is taken into account, is solved by the direct procedure instead of by modal analysis. The calculated results show quite satisfactory agreement with the experiment and the study has highlighted some remarkable characteristics concerning hydroelastic behavior.

Modeling for Moment-Rotation Characteristics for End-Plate Connections

Abstract: An analytical procedure is proposed to establish the nonlinear moment-rotation (\iM-Φ) characteristics for the bolted end-plate connections in flexibly jointed steel frames. The connection characteristics are assumed to depend on the component behavior of the tension zone, the compression zone, and the shear zone. The column flange and end plate with each bolt row in the tension zone are considered as a series of T-stub assembly with the effective length recommended by the Eurocode 3. Based on the beam and yield-line theory, the elastoplastic force-deformation relationship for each T-stub assembly is derived. With the consideration of the deformation of column web in compression and shear zone, the connection rotation Φ under bending moment \iM is evaluated accordingly. The proposed analytical model is compared with some experimental results of extended and flush end-plate connections, and the feasibility and validation of the proposed model are demonstrated.

Pile response due to unsupported excavation-induced lateral soil movement

Abstract: In this paper, a two-stage analysis involving the finite element method and the boundary element method is used to study pile response due to excavtion-induced lateral soil movements, focusing on u...

A three-dimensional study of loads across the fracture for different fracture sites of the mandible

Abstract: The loads across the fracture depend on variables such as position of the fracture and the bite point. Up to now, no study has described systematically the influence of these two variables on these loads. The aim of this study was to describe and compare value and direction of the loads across the fracture for different positions of fractures in the mandible. In a three-dimensional model, bending and torsion moments and shear forces were compared for five mandibular fractures. The fractures were located in, respectively, the angle, posterior body, anterior body, canine and symphysis region. Positive bending moments were defined to give compression at the border, negative bending moments to give compression at the alveolar side of the mandible. The angle and posterior body fracture have high positive bending moments, small torsion moments and high shear forces. The anterior body, canine and symphysis fracture have high negative bending moments and high torsion moments with similar maximum values. The number of bite points with negative bending moments were different for all fractures. These bite points were always located on the fractured side. It is concluded that mandibular fractures can be divided roughly into two groups with similar load patterns across the fracture. One group consists of angle and posterior body fractures, the other group consists of anterior body, canine and symphysis fractures.

Forces in pile foundations under seismic loading

Abstract: The purpose of this paper is to study the relative significance of kinematic and inertial interaction on the magnitude of forces induced in pile foundations by a seismic disturbance. The structure is modeled as a single-degree-of-freedom (SDOF) oscillator and the foundation is a typical pile group embedded in a homogeneous half-space. A three-dimensional Green’s function-based formulation, which rigorously models the pile-soil-pile interaction, is used to calculate the forces in the piles during the seismic kinematic- and inertial-interaction phases. Different structures, represented by their aspect ratios and natural frequencies, and different pile foundations, characterized by their pile rigidities and spacings, are considered in this study. The results show that the seismic shear force and bending moment in a pile are strongly contributed by the kinematic seismic interaction, except in a band approaching the natural frequency of the pile-soil-structure system. In this frequency band, the inertial interaction dominates the pile forces. The extent of contribution from the inertial interaction is governed by the damping of the foundation.

Bending mechanism and stereoscope using same

Abstract: A bending mechanism comprising a tubular body or linear body having a bending part, a movable part which can move in the lengthwise direction of said tubular body or linear body, two actuators formed to antagonize via said movable part, and a pull wire which extends in the lengthwise direction along the bending part, one end of the wire being fixed to one end side of the bending part and the other end of the wire being fixed to the movable part set at the other end side of the bending part, wherein at least one of the two actuators is a shape memory element, and a stereoscope. The bending mechanism of the present invention is free of displacement of movable part when bending action is not needed, since two actuators are used which antagonize each other via movable part, whereby buckling of the bending part can be prevented. The simple structure of activator unit of the present invention facilitates reduction of the size of the structure. The stereoscope of the present invention is free of buckling of image guide and the like, and angle of convergence can be adjusted easily and a desired three-dimensional view can be obtained easily.

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

Aeroelastic optimization of a helicopter rotor to reduce vibration and dynamic stresses

Abstract: Optimization studies are carried out for a four-bladed, soft in-plane hingeless rotor consisting of a twocell composite box-beam spar. The design variables are the ply angles of the box-beam walls. The objective functions are the vibratory hub loads and the vibratory blade bending moments; constraints are imposed on blade rotating frequencies and aeroelastic stability. The objective functions are first minimized individually, and then a combined optimization is performed to minimize both the objectives simultaneously. As compared to the starting design, the optimum solution results in a 15-60% reduction of the 4/rev hub loads as well as a reduction in the peak-to-peak flap and lag bending moments of 11 and 14%, respectively. Starting from an initially infeasible starting design with a 3% requirement on lag mode damping, the optimum solution with composite chordwise bending-torsion coupling results in an increase in lag mode damping of over 200% compared to the starting design.

An experimental verification of the generalized beam theory applied to interactive buckling problems

Abstract: Previous papers (Refs 1–4) have presented a method of analysis for any open unbranched thin walled section considering both rigid body movement and cross section distortion (including local buckling). Reference 1 described how the Generalized Beam Theory (GBT) can be used to calculate generalized section properties for all modes, including each of the four rigid body modes and the distortional modes. The additional section properties evolved from GBT were then used in Ref. 2 to consider second order elastic critical buckling problems. This paper compares the critical buckling predictions of GBT with the results obtained in two series of tests carried out on lipped and unlipped channels subject to a major axis bending moment. These predictions are then combined with the yield criteria of EC3 to allow a comparison with the analysis of these tests carried out by Lindner and Aschinger (Ref. 5). The paper concludes that the Generalized Theory is a powerful and effective analysis tool for the solution of interactive buckling problems where both local and overall buckling can occur.

Identification of material parameters in constitutive model for sheet metals from cyclic bending tests

Abstract: This paper deals with the identification of material parameters in a constitutive model for sheet metals using the bending moment versus curvature diagrams obtained by cyclic bending tests. The model can describe the cyclic strain hardening by the isotropic hardening and the Bauschinger effect by the kinematic hardening. An optimization technique based on the iterative multipoint approximation concept was used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification problem, and the verification of this approach.

Dynamic response of cantilever retaining walls

Abstract: A critical evaluation is made of the response to horizontal ground shaking of flexible cantilever retaining walls that are elastically constrained against rotation at their base. The retained medium is idealized as a uniform, linear, viscoelastic stratum of constant thickness and semi-infinite extent in the horizontal direction. The parameters varied include the flexibilities of the wall and its base, the properties of the retained medium, and the characteristics of the ground motion. In addition to long-period, effectively static excitations, both harmonic base motions and an actual earthquake record are considered. The response quantities examined include the displacements of the wall relative to the moving base, the wall pressures, and the associated shears and bending moments. The method of analysis employed is described only briefly, emphasis being placed on the presentation and interpretation of the comprehensive numerical solutions. It is shown that, for realistic wall flexibilities, the maximum wall forces are significantly lower than those obtained for fixed-based rigid walls and potentially of the same order of magnitude as those computed by the Mononobe-Okabe method.

Estimation of Ultimate Longitudinal Bending Moment of Ships and Box Girders

Abstract: The paper describes a methodology of computing the ultimate value of the longitudinal bending moment at any cross section of a ship or box girder. The cross section has been discretized into stiffened panels (one stiffener with its associated effective plating). The limit states for these panels, both tensile and compressive, are modelled in an appropriate manner. Since the ultimate strength of the girder section is largely governed by the behaviour of the panels under compression, the authors have paid special attention in modelling the collapse as well as the post-collapse behaviour of these panels. A new stress-strain relationship is also introduced. The complete procedure has been coded into a FORTRAN program and tested against a number of box girder models and an actual ship for which the true behaviour was known. The results obtained from the proposed program appear to be quite satisfactory. Good correlation was also found when comapred with the resxults obtained by more complex and rigourous analytical methods.