Jorge Riera - Academia.edu (original) (raw)
Papers by Jorge Riera
Fatigue & Fracture of Engineering Materials & Structures
The prediction of the response of structures subjected to projectiles impact may often be accompl... more The prediction of the response of structures subjected to projectiles impact may often be accomplished by means of empirical or semi-empirical formulas available in the technical literature, which address mainly cases of relevance in engineering practice in terms of the observed failure modes. The paper presents an evaluation of the performance of the equations most widely used in predictions of penetration, scabbing and perforation of concrete and rock structures by comparing the predicted results with experimentally observed response and with the results of detailed numerical analyses employing the truss-like Discrete Element Method (DEM). Numerical DEM predictions were shown to be close to the experimentally determined responses of concrete plates subjected to impact throughout the range of velocities examined and were also consistent with the empirical formulas. In all cases the authors attempted to quantify the uncertainty inherent both in the predictions of empirical formulas ...
Fatigue & Fracture of Engineering Materials & Structures
The prediction of the response of reinforced concrete structures subjected to projectiles impact ... more The prediction of the response of reinforced concrete structures subjected to projectiles impact still presents open questions. These include the rate dependence of material properties, the interaction between concrete and steel reinforcement and the simulation of fracture and fragmentation. Because the appearance of discontinuities in the target structure is difficult to account using a continuum approach, the application of discrete models was developed as an appealing alternative. A version of the discrete model in which nodal masses are linked by an array of uniaxial elements, herein called discrete element method, is used in this study. This method was implemented in the system Abaqus to take advantage of its numerical and post-processing capabilities. A reinforced concrete rectangular plate subjected to impact of a projectile is examined in detail. Comparisons between experimental and numerical results are shown with the aim of validating the proposed method.
Structure and Infrastructure Engineering, 2010
The use of transmission line conductors arranged in bundles is presently being considered as an a... more The use of transmission line conductors arranged in bundles is presently being considered as an attractive technology in order to reduce losses in long distance energy transportation. Although the technology leads to significant increases in power capacity per line, the dynamic behaviour of arbitrary bundle configurations under wind action has not yet been fully clarified. In this paper, a procedure
Structural Control and Health Monitoring, 2007
The practical difficulties presented by forced vibration testing of large structures, such as tal... more The practical difficulties presented by forced vibration testing of large structures, such as tall buildings, dams or bridges, led to a vast interest in structural monitoring through ambient vibrations, which usually allows the proper identification of modal properties, natural frequencies, damping and modes of vibration. Changes in these modal properties constitute an indication of structural damage, which may then be assessed on the basis of experimental evidence. The authors describe an approach to determine the socalled damage damping and stiffness matrices, which are essential to identify the location and intensity of damage. No restrictions are introduced on the damping matrix of the system. The approach requires ambient vibration data records of all relevant co-ordinates used in the structural model, which are processed employing the SSI-Cov method in conjunction with a modal analysis procedure. The identification method is illustrated with examples using experimental measurements on a reinforced concrete beam and a reduced scale multi-storey plane frame structure, also laboratory tested, as well as the theoretical simulated vibration response of a multi-storey concrete frame subjected to seismic excitation. Additional difficulties presented by field monitoring of large structures are briefly examined at the end of the paper.
Engineering Structures, 2004
Both for purposes of seismic retrofitting and in new designs of building frames, external energy ... more Both for purposes of seismic retrofitting and in new designs of building frames, external energy dissipation systems may be 19 advantageously used. In this paper, the improvement of the system reliability achieved through use of external passive metallic or 20 viscous dampers is assessed by simulation. The effect of the dissipation system is numerically evaluated using the properties of a 21 prototype lead-rings damper developed at LDEC, UFRGS in conjunction with methods for nonlinear structural dynamic analy-22 sis. To obtain robust estimators of the reliability, a database including acceleration records with markedly different characteristics 23 was used in the simulation study. On the premise that the efficiency of a dampers system can best be assessed on a reliability 24 basis, full reliability analyses of typical steel and reinforced concrete frame buildings are performed, showing that a five-fold 25 reduction in the probability of failure may be achieved by introducing external metallic or similar dampers systems. 26 28 29 30 42 and design recommendations, meeting considerable 43 success, in terms of preservation of life, i.e. of avoiding 44 failure. 45 However, the approach presents some obvious defi-46 ciencies: energy dissipation is achieved through structural 47 Ã Corresponding
Engineering Structures, 2004
The paper contains experimental and theoretical evidence on the joint influence of size and strai... more The paper contains experimental and theoretical evidence on the joint influence of size and strain rate on the mechanical properties of steel. Applying basic principles of continuum mechanics and dimensional analysis, the conditions for the existence of a characteristic dimension and a characteristic strain rate of the material are derived. The form of the relations between homologous material properties is
Engineering Structures, 2004
The mechanical properties of engineering materials are routinely determined by testing. In practi... more The mechanical properties of engineering materials are routinely determined by testing. In practice, the dimensions of structural elements are often much larger than those of the samples that, for technical or economic reasons, can be subjected to laboratory testing. Consequently, testing is usually conducted on reduced scale models or material samples. At the same time, available theories of material behavior that predict size or strain rate effects are receiving increasing attention in the technical literature. However, finite element models or similar representations, used for engineering predictions of the strength or loading capacity of large structures, rarely consider the influence of scale.
Fatigue & Fracture of Engineering Materials & Structures
The prediction of the response of structures subjected to projectiles impact may often be accompl... more The prediction of the response of structures subjected to projectiles impact may often be accomplished by means of empirical or semi-empirical formulas available in the technical literature, which address mainly cases of relevance in engineering practice in terms of the observed failure modes. The paper presents an evaluation of the performance of the equations most widely used in predictions of penetration, scabbing and perforation of concrete and rock structures by comparing the predicted results with experimentally observed response and with the results of detailed numerical analyses employing the truss-like Discrete Element Method (DEM). Numerical DEM predictions were shown to be close to the experimentally determined responses of concrete plates subjected to impact throughout the range of velocities examined and were also consistent with the empirical formulas. In all cases the authors attempted to quantify the uncertainty inherent both in the predictions of empirical formulas ...
Fatigue & Fracture of Engineering Materials & Structures
The prediction of the response of reinforced concrete structures subjected to projectiles impact ... more The prediction of the response of reinforced concrete structures subjected to projectiles impact still presents open questions. These include the rate dependence of material properties, the interaction between concrete and steel reinforcement and the simulation of fracture and fragmentation. Because the appearance of discontinuities in the target structure is difficult to account using a continuum approach, the application of discrete models was developed as an appealing alternative. A version of the discrete model in which nodal masses are linked by an array of uniaxial elements, herein called discrete element method, is used in this study. This method was implemented in the system Abaqus to take advantage of its numerical and post-processing capabilities. A reinforced concrete rectangular plate subjected to impact of a projectile is examined in detail. Comparisons between experimental and numerical results are shown with the aim of validating the proposed method.
Structure and Infrastructure Engineering, 2010
The use of transmission line conductors arranged in bundles is presently being considered as an a... more The use of transmission line conductors arranged in bundles is presently being considered as an attractive technology in order to reduce losses in long distance energy transportation. Although the technology leads to significant increases in power capacity per line, the dynamic behaviour of arbitrary bundle configurations under wind action has not yet been fully clarified. In this paper, a procedure
Structural Control and Health Monitoring, 2007
The practical difficulties presented by forced vibration testing of large structures, such as tal... more The practical difficulties presented by forced vibration testing of large structures, such as tall buildings, dams or bridges, led to a vast interest in structural monitoring through ambient vibrations, which usually allows the proper identification of modal properties, natural frequencies, damping and modes of vibration. Changes in these modal properties constitute an indication of structural damage, which may then be assessed on the basis of experimental evidence. The authors describe an approach to determine the socalled damage damping and stiffness matrices, which are essential to identify the location and intensity of damage. No restrictions are introduced on the damping matrix of the system. The approach requires ambient vibration data records of all relevant co-ordinates used in the structural model, which are processed employing the SSI-Cov method in conjunction with a modal analysis procedure. The identification method is illustrated with examples using experimental measurements on a reinforced concrete beam and a reduced scale multi-storey plane frame structure, also laboratory tested, as well as the theoretical simulated vibration response of a multi-storey concrete frame subjected to seismic excitation. Additional difficulties presented by field monitoring of large structures are briefly examined at the end of the paper.
Engineering Structures, 2004
Both for purposes of seismic retrofitting and in new designs of building frames, external energy ... more Both for purposes of seismic retrofitting and in new designs of building frames, external energy dissipation systems may be 19 advantageously used. In this paper, the improvement of the system reliability achieved through use of external passive metallic or 20 viscous dampers is assessed by simulation. The effect of the dissipation system is numerically evaluated using the properties of a 21 prototype lead-rings damper developed at LDEC, UFRGS in conjunction with methods for nonlinear structural dynamic analy-22 sis. To obtain robust estimators of the reliability, a database including acceleration records with markedly different characteristics 23 was used in the simulation study. On the premise that the efficiency of a dampers system can best be assessed on a reliability 24 basis, full reliability analyses of typical steel and reinforced concrete frame buildings are performed, showing that a five-fold 25 reduction in the probability of failure may be achieved by introducing external metallic or similar dampers systems. 26 28 29 30 42 and design recommendations, meeting considerable 43 success, in terms of preservation of life, i.e. of avoiding 44 failure. 45 However, the approach presents some obvious defi-46 ciencies: energy dissipation is achieved through structural 47 Ã Corresponding
Engineering Structures, 2004
The paper contains experimental and theoretical evidence on the joint influence of size and strai... more The paper contains experimental and theoretical evidence on the joint influence of size and strain rate on the mechanical properties of steel. Applying basic principles of continuum mechanics and dimensional analysis, the conditions for the existence of a characteristic dimension and a characteristic strain rate of the material are derived. The form of the relations between homologous material properties is
Engineering Structures, 2004
The mechanical properties of engineering materials are routinely determined by testing. In practi... more The mechanical properties of engineering materials are routinely determined by testing. In practice, the dimensions of structural elements are often much larger than those of the samples that, for technical or economic reasons, can be subjected to laboratory testing. Consequently, testing is usually conducted on reduced scale models or material samples. At the same time, available theories of material behavior that predict size or strain rate effects are receiving increasing attention in the technical literature. However, finite element models or similar representations, used for engineering predictions of the strength or loading capacity of large structures, rarely consider the influence of scale.