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Identification of force from response data of a nonlinear system
26A
ANALYSIS TECHNIQUES:DESIGN METHODS
This paper presents the results of an experimental investigation into the shear behaviour of rock-conerete joints with roughness in the idealised forms of regular and irregular triangles. The tests were carried out in a large direct shear machine under conditions of constant normal load and constant normal stiffness using rock specimens which were typical of a soft mudstone. For both the regular and irregular joints, failure was accompanied by shearing and crushing of the rock asperities. However, the principal difference between the responses of the two types of joint was that the irregular joints, particularly under conditions of constant normal stiffness, showed a much greater relative ductility than the regular joints. (Authors)
951185 Comparison of calculational approaches for structural deformation in jointed rock P. E. Senseny & D. A. Simons, International Journal for Numerical & Analytical Methods in Geomechanics, 18(5), 1994, pp 327-344. Results from five different computer models for structural deformation in jointed rock are compared for a problem involving stress-wave loading of a lined circular tunnel in a jointed medium. The computer models include two discrete element codes and three finite element codes. All codes had some difficulties with a sequence of preliminary problems solved to 'shake down' the computer codes. However, most of the shortcomings of each code were readily overcome. Results showed that three codes could obtain similar answers for tunnel closure, stress around the tunnel and slip on the joints. (from Authors)
951186 Construction of a three-dimensional block structure on the basis of jointed rock parameters estimating the stability of underground workings G. G. Kocharyan & A. M. Kulyukin, Soil Mechanics & Foundation Engineering, 31(2), 1994, pp 62-66; translated from: Osnovaniya, Fundamenty i Mekhanika Gruntov. A method is proposed for constructing a three-dimensional block structure on the basis of jointed rock parameters. The possibility of estimating the stability of underground structures on the basis of a geometric analysis of the block structure and isolating the most dangerous sections is shown. A method of determining the optimal location of an underground structure from the parameters of the joint system is given. (Journal summary)
Stress analysis 951187 Micrnstructural analysis of strain Iocalisation in clay P. Y. Hicher, H. Wahyudi & D. Tessier, Computers & Geotechnics, 16(3), 1994, pp 205-222. The conditions of strain localisation in clay have been studied in order to provide a better understanding of physical mechanisms. The influence of testing factors such as boundary conditions, sample dimensions, overconsolidation ratio has been examined. The density inside the shear hands has been determined by means of local water content measurements and X-ray scanning. With the use of Scanning and Transmission Electron Microscopes observations were made at the particle level which show a strong reorientation of the particles along the failure surfaces, as well as a significant breaking of the aggregates and of the particles themselves. These results indicate that large displacements with rotation took place in the localised zones. (Authors)
951188 Effects of rigidity layering, gravity and stress relaxation on 3-D subsurface fault displacement fields X. Q. Ma & N. J. Kusznir, Geophysical Journal International, 118(1), 1994, pp 201-220. Elastic dislocation theory has been modified to determine 3-D subsurface displacements for faults in a three-layer elasticgravitational medium. A new set of kernel functions for Fourier-Bessel integrals describing subsurface displacements have been derived, using the Thomson-Haskell propagator matrix technique, and has been used to investigate the effect of layering and gravity on subsurface displacement fields. The elastic-gravitational dislocation model has been used to examine co-seismic and post-seismic components of surface and subsurface displacement during extension of continental lithosphere. The model has also been used to investigate the development of Moho topography during continental extension. (from Authors)
Design methods 951189 Analytical and numerical solutions for wave propagation in water-saturated porous layered half-space J. T. Yazdi, S. Valliappan & Chongbin Zhao, Soil Dynamics & Earthquake Engineering, 13(4), 1994, pp 249-257. A fluid-saturated one-layer continuum underlain by a rigid half-space is considered. An exact solution is developed in frequency domain for analyzing disturbance induced by a strip footing located at the surface with vertical harmonic excitation. Since the analytical solution can be used only for very simple conditions, a finite element model has been developed also and compared with the exact solution. It is shown that finite element results are in close agreement with the results which have been obtained by a transformation technique. The proposed finite element scheme can take into account the complex geometry and inhomogeneity for practical problems. The analytical results exhibit the overall characteristic of wave propagation in porous media and provide a representative test problem which can be used for a quantitative evaluation of the accuracy of various numerical solution methods. (Authors)
951190 Identification of force from response data of a nonlinear system Ming L. Wang & T. J. Kreitinger, Soil Dynamics & Earthquake Engineering, 13(4), 1994, pp 267-280. Force identification is a type of system identification procedure which determines applied force from system responses. To identify the force, one can consider that the system model and its parameters are known, and then use the measured response of the system to determine the unknown forces. In contrast, postulating the system model and its parameter values is a difficult task, especially when considering a nonlinear system where the model poses many unknowns or inherent mathematical problems. In this research, a more direct way to identify the unknown force without knowing the model of the system is proposed. The approach, called the sum of weighted acceleration technique (SWAT), is a method that can predict input forces with measured linear and nonlinear structural responses. SWAT employs measured accelerations multiplied by effective or optimal weights to estimate the input force. Results using this method show that the force calculated using SWAT accurately predicts the force which excites a nonlinear structure response. The technique could be applied to both constrained and unconstrained structures. (Authors)
ANALYSIS TECHNIQUES:DESIGN METHODS
This paper presents the results of an experimental investigation into the shear behaviour of rock-conerete joints with roughness in the idealised forms of regular and irregular triangles. The tests were carried out in a large direct shear machine under conditions of constant normal load and constant normal stiffness using rock specimens which were typical of a soft mudstone. For both the regular and irregular joints, failure was accompanied by shearing and crushing of the rock asperities. However, the principal difference between the responses of the two types of joint was that the irregular joints, particularly under conditions of constant normal stiffness, showed a much greater relative ductility than the regular joints. (Authors)
951185 Comparison of calculational approaches for structural deformation in jointed rock P. E. Senseny & D. A. Simons, International Journal for Numerical & Analytical Methods in Geomechanics, 18(5), 1994, pp 327-344. Results from five different computer models for structural deformation in jointed rock are compared for a problem involving stress-wave loading of a lined circular tunnel in a jointed medium. The computer models include two discrete element codes and three finite element codes. All codes had some difficulties with a sequence of preliminary problems solved to 'shake down' the computer codes. However, most of the shortcomings of each code were readily overcome. Results showed that three codes could obtain similar answers for tunnel closure, stress around the tunnel and slip on the joints. (from Authors)
951186 Construction of a three-dimensional block structure on the basis of jointed rock parameters estimating the stability of underground workings G. G. Kocharyan & A. M. Kulyukin, Soil Mechanics & Foundation Engineering, 31(2), 1994, pp 62-66; translated from: Osnovaniya, Fundamenty i Mekhanika Gruntov. A method is proposed for constructing a three-dimensional block structure on the basis of jointed rock parameters. The possibility of estimating the stability of underground structures on the basis of a geometric analysis of the block structure and isolating the most dangerous sections is shown. A method of determining the optimal location of an underground structure from the parameters of the joint system is given. (Journal summary)
Stress analysis 951187 Micrnstructural analysis of strain Iocalisation in clay P. Y. Hicher, H. Wahyudi & D. Tessier, Computers & Geotechnics, 16(3), 1994, pp 205-222. The conditions of strain localisation in clay have been studied in order to provide a better understanding of physical mechanisms. The influence of testing factors such as boundary conditions, sample dimensions, overconsolidation ratio has been examined. The density inside the shear hands has been determined by means of local water content measurements and X-ray scanning. With the use of Scanning and Transmission Electron Microscopes observations were made at the particle level which show a strong reorientation of the particles along the failure surfaces, as well as a significant breaking of the aggregates and of the particles themselves. These results indicate that large displacements with rotation took place in the localised zones. (Authors)
951188 Effects of rigidity layering, gravity and stress relaxation on 3-D subsurface fault displacement fields X. Q. Ma & N. J. Kusznir, Geophysical Journal International, 118(1), 1994, pp 201-220. Elastic dislocation theory has been modified to determine 3-D subsurface displacements for faults in a three-layer elasticgravitational medium. A new set of kernel functions for Fourier-Bessel integrals describing subsurface displacements have been derived, using the Thomson-Haskell propagator matrix technique, and has been used to investigate the effect of layering and gravity on subsurface displacement fields. The elastic-gravitational dislocation model has been used to examine co-seismic and post-seismic components of surface and subsurface displacement during extension of continental lithosphere. The model has also been used to investigate the development of Moho topography during continental extension. (from Authors)
Design methods 951189 Analytical and numerical solutions for wave propagation in water-saturated porous layered half-space J. T. Yazdi, S. Valliappan & Chongbin Zhao, Soil Dynamics & Earthquake Engineering, 13(4), 1994, pp 249-257. A fluid-saturated one-layer continuum underlain by a rigid half-space is considered. An exact solution is developed in frequency domain for analyzing disturbance induced by a strip footing located at the surface with vertical harmonic excitation. Since the analytical solution can be used only for very simple conditions, a finite element model has been developed also and compared with the exact solution. It is shown that finite element results are in close agreement with the results which have been obtained by a transformation technique. The proposed finite element scheme can take into account the complex geometry and inhomogeneity for practical problems. The analytical results exhibit the overall characteristic of wave propagation in porous media and provide a representative test problem which can be used for a quantitative evaluation of the accuracy of various numerical solution methods. (Authors)
951190 Identification of force from response data of a nonlinear system Ming L. Wang & T. J. Kreitinger, Soil Dynamics & Earthquake Engineering, 13(4), 1994, pp 267-280. Force identification is a type of system identification procedure which determines applied force from system responses. To identify the force, one can consider that the system model and its parameters are known, and then use the measured response of the system to determine the unknown forces. In contrast, postulating the system model and its parameter values is a difficult task, especially when considering a nonlinear system where the model poses many unknowns or inherent mathematical problems. In this research, a more direct way to identify the unknown force without knowing the model of the system is proposed. The approach, called the sum of weighted acceleration technique (SWAT), is a method that can predict input forces with measured linear and nonlinear structural responses. SWAT employs measured accelerations multiplied by effective or optimal weights to estimate the input force. Results using this method show that the force calculated using SWAT accurately predicts the force which excites a nonlinear structure response. The technique could be applied to both constrained and unconstrained structures. (Authors)