- Email: [email protected]
14. Analysis and design of frames
84
ABSTRAC FS
14.
O'Callaghan, J. J. Ryan and T. P. Divane. Analysis and design of frames, J. agric. Engng Res. 12 (3), 222-228 (1967). A survey of theories applicable to the analysis of braced and unbraced frames is given. Calculated values obtained by elasticity theory, strain energy theory and torsional resistance theory are compared with experimental results, for four different frame configurations. Existing theoretical methods are shown to be inadequate. A new theory, which gives good agreement with experimental results, is presented. (Author's Summary)
15.
J. A. Overton and C. R. Ennos. Some uses of electro-hydraulic vibrators in the development of road vehicles. Environ. Engng, 28, 21-25 (1967). The electro-hydraulic vibrator is considered the most suitable form of generator for investigating the behaviour of the vehicle system when excited by vertical inputs through the pneumatic tyre, since it has excellent low-frequency characteristics and will accept high pre-loads. It consists of a piston-type actuator into which are introduced controlled impulses of fluid, metered by a servo-valve. Theoretical and experimental performance limits are shown. No significant difference is found between response curves for a vibrator with and without a mounted vehicle, indicating that the vehicle system is effectively decoupled from the vibrator. The servo system must be checked for amplitude linearity and limits of threshhold performance. The latter, which is directly related to servo-system friction, is extremely important, particularly with lightly-damped structures such as vehicle bodies, when force levers of perhaps 5-10 Ib are required. Harmonic distortion of the displacement output should be less than 5 % over the full frequency range. Deteriorationoftheservovalvecancausewave-formdistortion. The harmonic distortion present for excitation force and response acceleration during a pneumatic-typre test at various frequencies, and distortion in vibration tests at 17 c/s input on a complete vehicle are shown. Methods of avoiding distortion are explained. Results of initial studies on vehicles and suspensions are presented. The rigid-body response of a medium-sized vehicle on its suspension, when the front vibrators operated 180 deg. out of phase with the rear, is shown. The modes of vibration of mathematical tyre models represented by cylindrical shells are illustrated. The first mode is effectively the rigid-body mode with the air acting as the main spring medium. The higher modes are due mainly to deformation of the shell structure. Tests in radial-and cross-ply tyres, showing the first two modes, appear to confirm these findings. (M.I.R.A.)
16.
D. R. Phatak. A new method to compute the stress at any point in a soil mass due to a uniformly distributed load on the footing, Soil Mech. Fndn Eng. 5 (3), 347 350 (1966). Methods are available to compute the stress at a point in a soil mass due to a distributed load on a finite surface area, provided the point considered is vertically below the corner of the loaded area. However, no rational method exists to compute vertical stress at a chosen point in a soil mass due to a simple footing of small width and great length, when the point is not at the corner. Such footings are commonly employed for foundation purposes in residential buildings. An expression has been evolved to compute the stress at any point in a soil mass due to uniformly distributed load on the footing on the basis of theory of elasticity. (From author's summary)
17.
E. N. Thrower. An apparatus for measuring the dynamic stiffness of roads and soils. J. sci. lnstrum. 44, 537-540 (1967). The article describes a small and portable apparatus designed to measure the dynamic stiffness of roads and soils under sinusoidal loading, at frequencies between 5 and 1000 Hz. An electromagnetic vibrator applies forces of up to :514 lb (about its dead weight of 45 lb)to the road surface, the force itself and the resulting displacement of the road surface being measured by means of electrical transducers feeding a phase-sensitive voltmeter. Values of the elastic stiffness of the construction and values of the damping are obtained. Check tests of the behaviour of the apparatus are described, and some typical results on various types of road pavement are given. (Author's Summary)
18.
A. C. Tory and R. W. Sparrow. The influence of diaphragm flexibility on the performance of an earth pressure cell, J. sci. Instrum. 44, 781-785 (1967). A theoretical analysis of the effect of a flexible diaphragm on the calibration of a pressure cell subjected to one dimensional compression is presented together with the results predicted for range of cell thickness to diameter ratios, in soils of different moduli. The likely over or under registration of a cell in a given soil can be readily obtained and, more important, the probable
ABSTRAC FS
14.
O'Callaghan, J. J. Ryan and T. P. Divane. Analysis and design of frames, J. agric. Engng Res. 12 (3), 222-228 (1967). A survey of theories applicable to the analysis of braced and unbraced frames is given. Calculated values obtained by elasticity theory, strain energy theory and torsional resistance theory are compared with experimental results, for four different frame configurations. Existing theoretical methods are shown to be inadequate. A new theory, which gives good agreement with experimental results, is presented. (Author's Summary)
15.
J. A. Overton and C. R. Ennos. Some uses of electro-hydraulic vibrators in the development of road vehicles. Environ. Engng, 28, 21-25 (1967). The electro-hydraulic vibrator is considered the most suitable form of generator for investigating the behaviour of the vehicle system when excited by vertical inputs through the pneumatic tyre, since it has excellent low-frequency characteristics and will accept high pre-loads. It consists of a piston-type actuator into which are introduced controlled impulses of fluid, metered by a servo-valve. Theoretical and experimental performance limits are shown. No significant difference is found between response curves for a vibrator with and without a mounted vehicle, indicating that the vehicle system is effectively decoupled from the vibrator. The servo system must be checked for amplitude linearity and limits of threshhold performance. The latter, which is directly related to servo-system friction, is extremely important, particularly with lightly-damped structures such as vehicle bodies, when force levers of perhaps 5-10 Ib are required. Harmonic distortion of the displacement output should be less than 5 % over the full frequency range. Deteriorationoftheservovalvecancausewave-formdistortion. The harmonic distortion present for excitation force and response acceleration during a pneumatic-typre test at various frequencies, and distortion in vibration tests at 17 c/s input on a complete vehicle are shown. Methods of avoiding distortion are explained. Results of initial studies on vehicles and suspensions are presented. The rigid-body response of a medium-sized vehicle on its suspension, when the front vibrators operated 180 deg. out of phase with the rear, is shown. The modes of vibration of mathematical tyre models represented by cylindrical shells are illustrated. The first mode is effectively the rigid-body mode with the air acting as the main spring medium. The higher modes are due mainly to deformation of the shell structure. Tests in radial-and cross-ply tyres, showing the first two modes, appear to confirm these findings. (M.I.R.A.)
16.
D. R. Phatak. A new method to compute the stress at any point in a soil mass due to a uniformly distributed load on the footing, Soil Mech. Fndn Eng. 5 (3), 347 350 (1966). Methods are available to compute the stress at a point in a soil mass due to a distributed load on a finite surface area, provided the point considered is vertically below the corner of the loaded area. However, no rational method exists to compute vertical stress at a chosen point in a soil mass due to a simple footing of small width and great length, when the point is not at the corner. Such footings are commonly employed for foundation purposes in residential buildings. An expression has been evolved to compute the stress at any point in a soil mass due to uniformly distributed load on the footing on the basis of theory of elasticity. (From author's summary)
17.
E. N. Thrower. An apparatus for measuring the dynamic stiffness of roads and soils. J. sci. lnstrum. 44, 537-540 (1967). The article describes a small and portable apparatus designed to measure the dynamic stiffness of roads and soils under sinusoidal loading, at frequencies between 5 and 1000 Hz. An electromagnetic vibrator applies forces of up to :514 lb (about its dead weight of 45 lb)to the road surface, the force itself and the resulting displacement of the road surface being measured by means of electrical transducers feeding a phase-sensitive voltmeter. Values of the elastic stiffness of the construction and values of the damping are obtained. Check tests of the behaviour of the apparatus are described, and some typical results on various types of road pavement are given. (Author's Summary)
18.
A. C. Tory and R. W. Sparrow. The influence of diaphragm flexibility on the performance of an earth pressure cell, J. sci. Instrum. 44, 781-785 (1967). A theoretical analysis of the effect of a flexible diaphragm on the calibration of a pressure cell subjected to one dimensional compression is presented together with the results predicted for range of cell thickness to diameter ratios, in soils of different moduli. The likely over or under registration of a cell in a given soil can be readily obtained and, more important, the probable