Showing papers on "Stiffness published in 1974"
TL;DR: In this paper, an inelastic dynamic analysis method was developed for reinforced concrete frame structures to account for stiffness characteristics related to cracking of the concrete, yielding and strain hardening of the reinforcement, bond slip of tensile reinforcement in a joint core, and stiffness degradation due to load reversals.
Abstract: An inelastic dynamic analysis method was developed for reinforced concrete frame structures. The analytical model was able to account for stiffness characteristics related to cracking of the concrete, yielding and strain hardening of the reinforcement, bond slip of tensile reinforcement in a joint core, and stiffness degradation due to load reversals. The location of point of contraflexure in a member was taken into consideration to account for the distribution of inelastic deformation. The analysis method was tested by comparing calculated response waveforms with observed response waveforms of a small-scale three-story one-bay reinforced concrete frame structure, which was subjected to an intense base motion on the University of Illinois Earthquake Simulator. The observed waveforms at large amplitudes were favorably simulated by the analytical model based on the material properties and geometry of the test structure.
148 citations
TL;DR: In this paper, an exact discussion of the conductivity of disordered resistor networks and spin-wave stiffness in disordered Heisenberg ferromagnets, by considering the special case of the Bethe lattice, is given.
Abstract: An exact discussion is given of the conductivity of disordered resistor networks and of the related problem of spin-wave stiffness in disordered Heisenberg ferromagnets, by considering the special case of the Bethe lattice. For arbitrary substitutional disorder an exact nonlinear integral equation is obtained for a generating function determining the conductivity and spin-wave stiffness in such branching models. An effective medium (coherent potential) approximation is shown to provide an asymptotically exact solution in the limit of high coordination number z. Its extension, to order (1/z)4, is obtained.
114 citations
01 Feb 1974
TL;DR: In this paper, the dent resistance of doubly curved rectangular panels in various steels and aluminum alloys was studied and an empirical equation was developed that relates dent resistance to the yield strength, modulus of eleasticity, metal thickness, and panel geometry of stiffness.
Abstract: The dent resistance of doubly curved rectangular panels in various steels and aluminum alloys was studied. Dent depth on the order of magnitude of the panel thickness was determined. An empirical equation was developed that relates dent resistance to the yield strengths, modulus of eleasticity, metal thickness, and panel geometry of stiffness. Dent resistance increases with an increases in yield strength, thickness and panel radii of curvature, but decreases with an increase in modulus of elasticity and stiffness.
62 citations
TL;DR: In this article, a beam bending stiffness is derived as a function of all the bending stiffness coefficients of a laminated plate, and the validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates.
Abstract: Equations applicable to a general class of symmetrically laminated beams are derived by considering a beam as a special case of a laminated plate. The beam bending stiffness thus becomes a function of all the bending stiffness coefficients of a laminated plate. The validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates. In addition, it is shown that flex strength on general composite laminates is extremely difficult to interpret, even though the stresses can be calculated from the modified beam theory. Discontinuities in the in-plane stresses at layer interfaces lead to a state of stress which is difficult to compare to standard laminate tensile coupons.
59 citations
TL;DR: Elastic and viscous stiffness of canine left ventricles was measured continuously over the entire cardiac cycle and increased proportionally with ventricular pressure, and the percentage change in elastic stiffness from diastole to systole was greater than that of viscously stiffness.
Abstract: TEMPLETON, GORDON H., AND Louxs R. NARDTZZI. Elastic and viscous stifness of the canine left ventricle. J. Ap pl. Ph ysiol. 36 ( I ) : 123-I 27. 1974.-Elastic and viscous stiffness of canine left ventricles was measured continuously over the entire cardiac cycle. These mechanical properties were determined from the sinusoidally varying portion of the left ventricular pressure induced by an externally applied sinusoidal volume change with a constant peak amplitude of 0.5 ml and a frequency of 22 Hz. The sinusoidal pressure perturbations varied during the cardiac cycle both in peak amplitude and in the time of occurrence of the peak amplitude with respect to the volume changes that produced them. Determinations were made of ventricular stiffness, or elastance, which is defined as the ratio of the peak change in the pressure perturbations to the peak change in volume. Stiffness and the time difference between the occurrence of the peak volumetric perturbation and the corresponding peak of the pressure perturbation were used to calculate the elastic and viscous components of ventricular stiffness. These elastic and viscous components of stiffness increased proportionally with ventricular pressure, and the percentage change in elastic stiffness from diastole to systole was greater than that of viscous stiffness.
55 citations
Patent•
19 Sep 1974
TL;DR: In this paper, the authors propose a stiffness meter for tightening a fastener by including an additional circuit responsive to the comparator output for sequentially storing information representative of the maximum stiffness developed up to any given point during the tightening operation and for producing a stop signal when the instantaneous stiffness has dropped to a predetermined ratio of the maximal stiffness.
Abstract: A meter for determining stiffness or torque gradient including, in one embodiment, a deflectable coupling connected between an output shaft and a power input shaft, sensing means for developing two separate series of signals representative of the displacement of the input and output shafts respectively, a comparator for determining from the two series of signals a function of the stiffness or torque gradient and, in another embodiment, including a single shaft having an input end and an output end, transducer means associated with the shaft for developing a signal representative of the torque being applied through the shaft, sensing means for developing a signal representative of the displacement of the shaft, and comparator means for determining from the two signals a function of the stiffness or torque gradient. Either embodiment of the stiffness meter may be used for tightening a fastener by including an additional circuit responsive to the comparator output for sequentially storing information representative of the maximum stiffness developed up to any given point during the tightening operation and for producing a stop signal when the instantaneous stiffness has dropped to a predetermined ratio of the maximum stiffness.
55 citations
TL;DR: In this article, the mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported and a number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density.
Abstract: The mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported. Both organic and inorganic fiber reinforcements were used in fiber volume fractions of 0.10 to 0.50. A number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density. The dependence of composite properties on the properties of the constituent materials is discussed. Fiber efficiency factors for strength and modulus are presented and models for predicting composite mechanical behavior are reviewed.
54 citations
52 citations
TL;DR: In this paper, a finite element procedure for determining the critical buckling load for three-dimensional structures idealized by planar two-dimensional elements is presented, which is applicable to structures whose instabilities involve small displacements and elastic behavior, i.e., linear elastic buckling.
Abstract: A finite element procedure for determining the critical buckling load for three-dimensional structures idealized by planar two-dimensional elements is presented. This procedure is applicable to structures whose instabilities involve small displacements and elastic behavior, i.e., linear elastic buckling. Local and overall structural instabilities may be treated together with complex loading and support conditions. The smallest eigenvalue corresponding to the smallest buckling load is determined by an inverse iteration procedure. The accuracy of this finite element procedure is evaluated by comparison with a number of problems for which classical solutions are available. A simply supported wide-flange beam with a stiffener, lateral restraints, and various rotational restraints is presented to illustrate the versatility of the procedure as well as the effect of the restraints on the buckling load. In addition, a comparison between the subject procedure and recent experimental results on a continuous wide-flange beam is presented.
47 citations
TL;DR: In this paper, the relative performances of braced and tied-back wall systems are compared and key factors in the different performances of the two systems are isolated and the degree of their influence demonstrated.
Abstract: Parametric finite element studies are described that illustrate the relative performances of braced and tied-back wall systems. Key factors in the different performances of the two systems are isolated and the degree of their influence demonstrated. Circumstances are shown where tied-back wall systems perform better than braced wall systems and vice versa. Additionally, the influence of prestress load, wall stiffness, tie-back stiffness, excavation depth, and tie-back spacing on tied-back wall performance are investigated. By judicious choice of these parameters it is shown that the designer can significantly reduce wall movements and soil settlements.
TL;DR: In this article, an analytical unit of large size and idealization of highly nonlinear behaviors are developed in order to overcome the difficulties of applying finite element methods directly to the analysis of a ship structure.
Abstract: There are many deep girders in a ship structure as the main strength members. Under increasing loads, local failures, such as buckling, yielding etc., occur in these members. These phenomena decrease the stiffness of the members and these changes of relative stiffness in the structure induce redistribution of internal forces and the structure finally shows its ultimate strength.A ship structure is composed of so many such members and its behavior to the ultimate strength is highly nonlinear. There are powerful tools to analyze nonlinear behavior, such as the finite element method, finite strip method, etc. However, the analysis by these methods requires enormous computing time for calculation and in the present circumstances it is impossible to apply these methods directly.To overcome these difficulties, an analytical unit of large size and idealization of the highly nonlinear behaviors are developed in this paper. A “Girder Element” is proposed, of which stiffness matrices are derived for indivisual kinematic condition, such as after buckling, at the ultimate strength or plastic strength under compression, bending, and/or shear. Based on these idealized behaviors, a method of ultimate strength analysis is proposed. The result of analysis by this method represents well the detail behavior of example structures, of which simple one well coincides experimental behavior conducted in this study. The computing time is remarkably very short.These nature of the new method promises the validity and possibility of the method to the ultimate strength analysis of structure of large size.
TL;DR: In this paper, a method of analysis of the global behavior of long curved or straight single-cell girders with or without initial stress is presented, based on thin-wall beam elements that include the modes of longitudinal warping and of transverse distortion of cross section.
Abstract: A method of analysis of the global behavior of long curved or straight single-cell girders with or without initial stress is presented. It is based on thin-wall beam elements that include the modes of longitudinal warping and of transverse distortion of cross section. Deformations due to shear forces and transverse bimoment are included, and it is found that the well-known spurious shear stiffness in very slender beams is eliminated by virtue of the fact that the interpolation polynomials for transverse displacements and for longitudinal displacements (due to rotations and warping) are linear and quadratic, respectively, and an interior mode is used. The element is treated as a mapped image of one parent unit element and the stiffness matrix is in integration in three dimensions, which is numerical in general, but could be carried out explicitly in special cases. Numerical examples of deformation of horizontally curved bridge girders, and of lateral buckling of box arches, as well as straight girders, validate the formulation and indicate good agreement with solutions by other methods.
01 Jan 1974
TL;DR: In this paper, the theory of complex mode shapes for damped oscillatory mechanical systems is explained, using the matrix of transfer functions in the Laplace domain, defined to be the solutions to the homogeneous system equation.
Abstract: The theory of complex mode shapes for damped oscillatory mechanical systems is explained, using the matrix of transfer functions in the Laplace domain. These mode shapes are defined to be the solutions to the homogeneous system equation. It is shown that a complete transfer matrix can be constructed once one row or column of it has been measured, and hence that mass, stiffness, and damping matrices corresponding to a lumped equivalent model of the tested structure can also be obtained from the measured data.
TL;DR: In this paper, the results of an analytical study of the behavior of braced and unbraced frames and subassemblages are presented. And the analysis shows that the PΔ effects significantly reduce the load carrying capacity of both types of structures, especially when these units are required to provide lateral support to more flexible frame units.
Abstract: In the paper the results of an analytical study of the behavior of braced and unbraced frames and subassemblages is presented. The analysis assumes elastic perfectly plastic member response and includes the effects of axial loads on frame deformations, axial loads on member stiffness, axial shortening of columns, finite column width, and hinge reversal. The results of the analysis show that the lateral stiffness of braced and unbraced frames designed under similar conditions were approximately the same. The analysis shows that the PΔ effects significantly reduce the load carrying capacity of both types of structures, especially when these units are required to provide lateral support to more flexible frame units.
TL;DR: In this paper, it was shown that the stiffness matrices of the three finite elements presented by Turner, Pian and Wilson are identical and that the three resulting stiffness matrix matrices are identical.
Abstract: One of the first finite elements presented was that by Turner et al.1 Pian2 presented a hybrid plane stress element and Wilson et al.3 presented a non-conforming displacement element. It is shown that the three resulting stiffness matrices are identical.
TL;DR: In this article, a matrix stiffness analysis of the general space frame is developed for linear elastic connections related to every possible displacement at the end of each member, and correction matrices are also derived for modifying the usual rigid joint analysis.
Abstract: Rectilinear plane and space frame with elastic connections occur in building frames; and with diagonal bracings, they also occur in scaffolding. The matrix stiffness analysis of the general space frame is developed for linear elastic connections related to every possible displacement at the end of each member. Correction matrices are also derived for modifying the usual rigid joint analysis. Examples are given of the elastic analysis of a plane framework and a simple space portal allowing for various elastic connections at the ends of some or all of the members.
TL;DR: In this paper, a polynomial expansion of the displacement model is proposed to improve the stiffness of the model, e.g. by direct approximation of the strain field as opposed to its derivation from the displacement field.
TL;DR: In this paper, Likins et al. extended their work on finite element appendage equations for hybrid coordinate dynamic analysis and on the dynamic analysis of a system of hinge-connected rigid bodies with nonrigid appendages to the simulation of non-rigid spacecraft.
01 Jan 1974
TL;DR: In this paper, it is shown that the normal and shear stiffness of machine surfaces can be calculated from the parameters that define the normal stiffness of the machine surfaces, which can then be used to calculate the shear stiffness.
Abstract: This paper presents in the first place some remarks on the normal and shear stiffness of machine surfaces. It is shown that the shear stiffness can be calculated from the parameters that define the normal stiffness of the machine surfaces.
TL;DR: In this article, an approach to study the flexural and torsional deformation of multistory shear wall buildings for lateral loading has been presented, where the out-of-plane stiffness of the floor side is taken into account by means of connecting beams.
Abstract: An approach to study the flexural and torsional deformation of multistory shear wall buildings for lateral loading has been presented. The out-of-plane stiffness of the floor side is taken into account by means of connecting beams. The problem is described in terms of three generalized displacement functions of the structure. No restriction is placed on the complexity of the floor plan layout. An example is worked out to show the importance of floor slab stiffness and comparisons are made with the results based on the finite element approach.
TL;DR: A mathematical model is presented describing the time- and length-dependent behavior of cardiac muscle, which successfully predicts force development during both isometric and isotonic contractions, observed deactivation of the contractile element during isotonic shortening, and the apparent dependence of series elastic stiffness on time after stimulation during quick-release and quick-stretch experiments.
Abstract: A mathematical model is presented describing the time- and length-dependent behavior of cardiac muscle. The model describes a wider variety of experimental data than do previously published models. It incorporates a modification of the Hill equation describing the force-velocity relation. Based on the sliding filament theory, the revised equation includes the effects of finite cross-bridge compliance proposed by A. F. Huxley. The essential simplicity of the Hill equation is retained; however, the model successfully predicts force development during both isometric and isotonic contractions, observed deactivation of the contractile element during isotonic shortening, and the apparent dependence of series elastic stiffness on time after stimulation during quick-release and quick-stretch experiments.
TL;DR: In this paper, an analytical solution is presented to predict the performance of an externally pressurized porous gas thrust bearing, where the wall thickness of the pad is small compared to its radius, and expressions for the bearing characteristics can be given in a closed form.
Abstract: An analytical solution is presented to predict the performance of an externally pressurized porous gas thrust bearing. When the wall thickness of the pad is small compared to its radius, the expressions for the bearing characteristics can be given in a closed form. The bearing number Λ—a dimensionless design variable—can adequately describe the performance of the bearing. The load capacity and mass flow rate progressively increase with the bearing number; the static stiffness increases with the bearing number up to Λ ∼ 4.0 and then gradually decreases. The decisive influence of permeability of the pad material in controlling the performance of the bearing is discussed and the interesting behaviour of the static stiffness as the film thickness is reduced is pointed out. It is found that there is near perfect agreement between the predicted performance of the bearing and the one experimentally evaluated. The characteristics are plotted over a wide range for the bearing number (.01 ≤ Λ ≤ 2500) in such a way that the information is of direct use to designers and applications engineers. Also, the results are given in tabular form to facilitate interpolation of the values as required.
TL;DR: In this article, an analysis of a raft foundation is developed which takes into account the interaction of the three elements of the system, i.e., the structure, the raft, and the supporting soil.
Abstract: An analysis of a raft foundation is developed which takes into account the interaction of the three elements of the system, i.e., the structure, the raft, and the supporting soil. The stiffness of the structure is incorporated into the stiffness matrix of the raft which is treated as a thin elastic plate supported on a soil mass modeled either by the Wrinkler (spring) or by the linear elastic model. A three-bay by three-bay multistory space frame supported on a square raft is analyzed and the effects of structural stiffness, relative raft-soil stiffness, and soil stiffness are considered in detail for both the Winkler and linear elastic soil models. It is shown that use of the linear elastic model leads to the conclusion that the settlement profile of a flexible raft is concave, thus there is a transfer of load to the outer columns compared with a rigid raft. In contrast, the Winkler analysis predicts a convex settlement profile. Special methods of analysis are developed for rigid structures and for highly flexible rafts.
01 May 1974
TL;DR: In this paper, an approach for the flexural analysis of reinforced concrete slabs using a piecewise linear tangent stiffness finite element incremental method applied to a layered plate element is described.
Abstract: The goal of this project is the development of an analysis technique to predict the response of a beam-slab type highway bridge superstructure subjected to the passage of an overload vehicle This report describes an approach for the flexural analysis of reinforced concrete slabs using a piecewise linear tangent stiffness finite element incremental method applied to a layered plate element Each layer of each element is assumed to be in-plane state of stress Each layer has its own biaxial stress-strain characteristics type stress-strain curve and may have inelastic, cracking, crushing and yielding nonlinearities Comparisons with laboratory tests of six reinforced concrete slabs and one beam are presented The agreement between analytic and laboratory load deflection curves is quite good Comparisons with experimentally observed crack patterns, steel strains, and concrete strains are also presented if these data were available
01 Feb 1974
TL;DR: In this paper, the effects of the state of wear, structure, load, and inflation pressure on the cornering stiffness and aligning torque stiffness of typical passenger tires are analyzed.
Abstract: The paper presents data showing the effects of the state of wear, structure, load, and inflation pressure on the cornering stiffness and aligning torque stiffness of typical passenger tires. A method is introduced and applied for assessing contributions of local elements of the tread interface to the cornering force, the cornering stiffness, the aligning torque, and the aligning stiffness. There is also a further identification of the contributions to the aligning torque from fore and aft interfacial stress distributions and from lateral stress distributions. Pneumatic trail is redefined in the light of the interfacial measurements, and values are established for various operating conditions, states of wear, and tire types.
01 Jan 1974
TL;DR: In this article, the problem of designing large-panel buildings for stability against wind loads presents complications when the shear walls are themselves of panel construction, since the joints have strength and stiffness characteristics different from those of the panels, and the problem has been examined in tests carried out in many countries which are now evaluated in this considered report by members of CIB Working Commission W23A.
Abstract: Designing large-panel buildings for stability against wind loads presents complications when the shear walls are themselves of panel construction, since the joints have strength and stiffness characteristics different from those of the panels The problem has been examined in tests carried out in many countries which are now evaluated in this considered report by members of CIB Working Commission W23A
TL;DR: In this article, the modal damping and resonant frequencies of a stiffened plate structure, with a multiple layer constrained damping treatment attached to the surface, can be predicted from a knowledge of the equivalent complex modulus properties of the treatment.