Abstract Performance-Based Earthquake Engineering (PBEE) aims at designing structures that are ab... more Abstract Performance-Based Earthquake Engineering (PBEE) aims at designing structures that are able to satisfy multiple target performance levels at different ground motion intensities. The performance levels can be introduced into the overall design process through energy concepts. It is acknowledged that the design of structures protected by control systems such as base isolation or energy dissipation devices can be efficiently optimized by using an energy-based approach. The energy-based design approach incorporated within the probabilistic framework of the performance-based design is a promising design method. In its development, three important energy-based dissipation parameters are critically needed to evaluate, which are the ratio of hysteretic energy to input energy EH/EI, normalized cumulative damage η, as well as the equivalent number of cycles neq. Therefore, this study has taken a comprehensive investigation of these parameters for four hysteretic systems of structures with the vibration period of 0.05s–4s for 7 damping ratios, that is 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, and 6 ductility factors, that is 2, 3, 4, 5, 6 and 8. Empirical formulas of predicting the mean values and standard deviations of the energy-based dissipation parameters are proposed as a function of vibration period, damping ratio, and ductility factors. The proposed predictive models can be easily and conveniently used to evaluate the energy-based dissipation parameters in a deterministic and probabilistic manner in the energy-based design in the framework of PBEE.
The present work deals with monitoring of reinforced concrete (RC) structures by means of the aco... more The present work deals with monitoring of reinforced concrete (RC) structures by means of the acoustic emission method, when they are subjected to bidirectional seismic actions (X-Y) with a shaking table. The RC specimens consisted in three columns connected to a 3x3 m2 waffle slab. A proper filtering process of AE signals was conducted to avoid the influence of secondary source mechanisms like friction. After that, the accumulated energy of AE signals was compared with the plastic strain energy released by concrete cracking of the specimen. The AE location analysis shows a concentration of activity and intensity at the bottom of columns and at the waffle slab-column connections. This result is in good agreement with the damage observed by visual inspection and by means of strain gage sensors attached to the reinforcing bars.
Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2019
One of the gaps of knowledge for the application of the energy-based approach to conventional str... more One of the gaps of knowledge for the application of the energy-based approach to conventional structures concerns the evaluation of the energy dissipation capacity of structural elements and systems. Addressing this issue calls for experimental data on structural members, structures or substructures subjected to realistic seismic loadings. The best source for such information is the dynamic shake table test. It can reproduce complex effects such as cumulative damage and rate-of-loading effects, that play an important role in the response of the structure. However this type of tests are very costly and time consuming. Therefore, it is necessary to complete the test information with numerical simulations. This paper provides information on the energy dissipation capacity of columns subjected to one and to two components of the seismic action. This information comes from shake table test conducted on RC waffle flat plate structures supported on isolated columns. The energy dissipated at the base of the columns until collapse is estimated applying different approaches.
This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinf... more This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs.
A key aspect of the seismic design of structures is the distribution of the lateral strength, bec... more A key aspect of the seismic design of structures is the distribution of the lateral strength, because it governs the distribution of the cumulative plastic strain energy (i.e., the damage) among the stories. The lateral shear strength of a story i is commonly normalized by the upward weight of the building and expressed by a shear force coefficient αi. The cumulative plastic strain energy in a given story i can be normalized by the product of its lateral strength and yield displacement, and expressed by a plastic deformation ratio ηi. The distribution αi/α1 that makes ηi equal in all stories is called the optimum yield-shear force distribution. It constitutes a major aim of design; a second aim is to achieve similar ductility demand in all stories. This paper proposes a new approach for deriving the optimum yield-shear force coefficient distribution of structures without underground stories and equipped with metallic dampers. It is shown, both numerically and experimentally, that st...
Prestressed monoblock railway sleepers are concrete elements with almost no reinforcement apart f... more Prestressed monoblock railway sleepers are concrete elements with almost no reinforcement apart from the prestressing wires, which makes them very sensitive to any stress variation that can induce tensile stresses. In recent years, severe longitudinal cracking has been observed in a number of sleepers in hot regions of Spain, even before these elements were put in service. This work studies the problem while considering the thermal variation as the main factor affecting this cracking phenomenon. A non-linear static load-step analysis is applied on a non-linear finite element model to reproduce the problem and, after its experimental validation, the influence of three design parameters of the sleepers are studied: the nature of concrete aggregates, the dowel thickness, and the dowel material. The results show that all these three parameters may have significant influence on the problem, with the dowel material being the most important parameter. When the dowels are made of a material...
Earthquake Engineering & Structural Dynamics, 2018
Reinforced concrete waffle-flat plate (WFP) structures present 2 important drawbacks for use as a... more Reinforced concrete waffle-flat plate (WFP) structures present 2 important drawbacks for use as a main seismic resisting system: low lateral stiffness and limited ductility. Yet the former can serve a positive purpose when, in parallel, the flexible WFP structure is combined with a stiff system lending high-energy dissipation capacity, to form a "flexible-stiff mixed structure." This paper experimentally investigates the seismic performance of WFP structures (flexible system) equipped with hysteretic dampers (stiff system) through shake-table tests conducted on a 2/5-scale test specimen. The WFP structure was designed only for gravitational loads. The lateral strength and stiffness provided by the dampers at each story were, respectively, about 3 and 7 times greater than those of the bare WFP structure. The mixed system was subjected to a sequence of seismic simulations representing frequent to very rare ground motions. Under the seismic simulations associated with earthquakes having return periods ranging from 93 to 1894 years, the WFP structure performed in the level of "immediate occupancy," with maximum interstory drifts up to about 1%. The dampers dissipated most (75%) of the energy input by the earthquake.
Earthquake Engineering & Structural Dynamics, 2019
SummaryThe bidirectional response of a portion of a reinforced concrete (RC) waffle‐flat plate (W... more SummaryThe bidirectional response of a portion of a reinforced concrete (RC) waffle‐flat plate (WFP) structure subjected to far‐field ground motions is studied through shake table tests. The test specimen is a scaled portion of a prototype structure designed under current building codes and located in a region of moderate seismicity of the Mediterranean area. The specimen was subjected to a sequence of tests of increasing acceleration amplitude that respectively represented very frequent, frequent, design, and very rare earthquakes at the site. The test structure performed well (basically in the elastic domain) under very frequent and frequent earthquakes, approached the boundary between the performance levels of life safety and near collapse under the design earthquake, and collapsed under the very rare earthquake. Damage concentrated at column bases and at the transverse beams of the exterior plate‐to‐column connection. Columns dissipated about 10% of the total energy that contrib...
Earthquake Engineering & Structural Dynamics, 2015
SummaryShaking table tests were conducted on a scaled reinforced concrete waffle–flat plate struc... more SummaryShaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period PR. The test structure performed well for the simulations associated with PR = 95, 475 and 975 years but collapsed under the maximum considered earthquake of PR = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate‐to‐column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental bas...
: The city of Lorca (Spain) was hit on May 11th 2011 by two consecutive earthquakes with 4.6 and ... more : The city of Lorca (Spain) was hit on May 11th 2011 by two consecutive earthquakes with 4.6 and 5.2 Mw respectively, causing casualties and important damage in buildings. Lorca is located in the south-east region of Spain and settled on the trace of the Murcia-Totana-Lorca fault. Although the magnitudes of these ground motions were not severe, the damage observed was considerable over a great amount of buildings. More than 300 of them have been demolished and many others are being retrofitted. This paper reports a field study on the damage caused by these earthquakes. The observed damage is related with the structural typology. Further, prototypes of the damaged buildings are idealized with nonlinear numerical models and their seismic behavior and proneness to damage concentration is further investigated through dynamic response analyses.
Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced c... more Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced concrete frames subjected to lateral loads. These braces may develop high axial tension forces, and transferring them appropriately to the existing beam-column joints is a key challenge. This paper investigates a solution for connecting the end-plate of the steel brace with the frame, using (1) shear-key plates fixed to the concrete with anchor bolts, and (2) a low friction material inserted between the end-plates and the shear-key plates. The presence of the low friction material impedes the development of tension forces in the anchor bolts and ensures that they are basically subjected to shear forces. This prevents brittle types of failure (concrete cone failure, pull-out/pry-out failure), and results in a reduction of the number of anchors required as well as anchorage height. The efficiency and validity of the proposed brace-frame connection is investigated experimentally by means of shaking table tests conducted on a 3 Â 3 Â 3 m 3 scaled reinforced concrete frame retrofitted with brace-type hysteretic dampers.
Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería, 2012
Forjado reticular Ensayo de laboratorio Fisuración distribuida del hormigón Leyes constitutivas e... more Forjado reticular Ensayo de laboratorio Fisuración distribuida del hormigón Leyes constitutivas en tensiones-deformaciones medias Elementos tipo fibra Elementos tipo capa r e s u m e n En este artículo se analizan distintas alternativas para modelar conexiones interiores forjado reticularpilar de hormigón armado y se propone una solución que con un coste computacional razonable proporcione resultados muy próximos a los experimentales. El modelo propuesto se valida numéricamente con los resultados obtenidos previamente de un ensayo de laboratorio realizado sobre un espécimen a escala 3/5 de la misma tipología estructural, sometido a ensayo cuasi-estático hasta el colapso. Para tal fin, se aplica la teoría avanzada de mecánica no lineal de hormigón armado sobre un modelo tridimensional de elementos finitos en análisis no-lineal: elementos tipo fibra para componentes unidimensionales y tipo capa para los bidimensionales. Los resultados principales de la simulación fueron: a) la obtención de la curva de capacidad mediante un análisis de empuje incremental (push-over) con control de desplazamientos; b) las curvas histeréticas en la losa, y c) los patrones de fisuras, logrando una concordancia revelada con los resultados experimentales.
The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes... more The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes 4.6 and 5.2 M w , causing casualties and important damage in buildings. Many of the damaged structures were reinforced concrete frames with wide beams. This study quantifies the expected level of damage on this structural type in the case of the Lorca earthquake by means of a seismic index /" that compares the energy input by the earthquake with the energy absorption/dissipation capacity of the structure. The prototype frames investigated represent structures designed in two time periods (1994-2002 and 2003-2008), in which the applicable codes were different. The influence of the masonry infill walls and the proneness of the frames to concentrate damage in a given story were further investigated through nonlinear dynamic response analyses. It is found that (1) the seismic index method predicts levels of damage that range from moderate/severe to complete collapse; this prediction is consistent with the observed damage; (2) the presence of masonry infill walls makes the structure very prone to damage concentration and reduces the overall seismic capacity of the building; and (3) a proper hierarchy of strength between beams and columns that guarantees the formation of a strong column-weak beam mechanism (as prescribed by seismic codes), as well as the adoption of countermeasures to avoid the negative interaction between non-structural infill walls and the main frame, would have reduced the level of damage from I v = l (collapse) to about /" = 0.5 (moderate/severe damage).
The seismic design of conventional frame structures is meant to enhance plastic deformations at b... more The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (Wpi) normalized by the product of the story shear force (Qyi) and drift (δyi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, Wpi /ΣWpj, can be evaluated from the deviation of Qyi with respect to an “optimum value” that would make the ratio Wpi/(Qyiδyi)—i.e. the damage—equal in all s...
La tesis plantea un metodo de proyecto sismorresistente para estructuras con forjado reticular y ... more La tesis plantea un metodo de proyecto sismorresistente para estructuras con forjado reticular y disipadores de energia segun la metodologia del proyecto basado en prestaciones y la filosofia de calculo basada en el balance de energia propuesta por Housner-Akiyama. Se establecen tres niveles de peligrosidad sismica, con unos determinados niveles de prestaciones a cumplir en cada uno de ellos para estructuras de tipo residencial, tomando como referencia el documento VISION 2000 propuesto por la SEAOC (Structural Engineer Association of California) en el ano 1995, en el que se presentan los fundamentos del proyecto basado en prestaciones. Se trata de aprovechar las caracteristicas de flexibilidad frente a cargas laterales de las estructuras con forjado reticular, asi como su versatilidad y amplia tradicion constructiva en paises como Espana, en el marco de las estructuras mixtas rigido-flexibles planteadas por Akiyama H. La parte flexible, denominada estructura principal, la constituy...
Abstract Performance-Based Earthquake Engineering (PBEE) aims at designing structures that are ab... more Abstract Performance-Based Earthquake Engineering (PBEE) aims at designing structures that are able to satisfy multiple target performance levels at different ground motion intensities. The performance levels can be introduced into the overall design process through energy concepts. It is acknowledged that the design of structures protected by control systems such as base isolation or energy dissipation devices can be efficiently optimized by using an energy-based approach. The energy-based design approach incorporated within the probabilistic framework of the performance-based design is a promising design method. In its development, three important energy-based dissipation parameters are critically needed to evaluate, which are the ratio of hysteretic energy to input energy EH/EI, normalized cumulative damage η, as well as the equivalent number of cycles neq. Therefore, this study has taken a comprehensive investigation of these parameters for four hysteretic systems of structures with the vibration period of 0.05s–4s for 7 damping ratios, that is 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, and 6 ductility factors, that is 2, 3, 4, 5, 6 and 8. Empirical formulas of predicting the mean values and standard deviations of the energy-based dissipation parameters are proposed as a function of vibration period, damping ratio, and ductility factors. The proposed predictive models can be easily and conveniently used to evaluate the energy-based dissipation parameters in a deterministic and probabilistic manner in the energy-based design in the framework of PBEE.
The present work deals with monitoring of reinforced concrete (RC) structures by means of the aco... more The present work deals with monitoring of reinforced concrete (RC) structures by means of the acoustic emission method, when they are subjected to bidirectional seismic actions (X-Y) with a shaking table. The RC specimens consisted in three columns connected to a 3x3 m2 waffle slab. A proper filtering process of AE signals was conducted to avoid the influence of secondary source mechanisms like friction. After that, the accumulated energy of AE signals was compared with the plastic strain energy released by concrete cracking of the specimen. The AE location analysis shows a concentration of activity and intensity at the bottom of columns and at the waffle slab-column connections. This result is in good agreement with the damage observed by visual inspection and by means of strain gage sensors attached to the reinforcing bars.
Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2019
One of the gaps of knowledge for the application of the energy-based approach to conventional str... more One of the gaps of knowledge for the application of the energy-based approach to conventional structures concerns the evaluation of the energy dissipation capacity of structural elements and systems. Addressing this issue calls for experimental data on structural members, structures or substructures subjected to realistic seismic loadings. The best source for such information is the dynamic shake table test. It can reproduce complex effects such as cumulative damage and rate-of-loading effects, that play an important role in the response of the structure. However this type of tests are very costly and time consuming. Therefore, it is necessary to complete the test information with numerical simulations. This paper provides information on the energy dissipation capacity of columns subjected to one and to two components of the seismic action. This information comes from shake table test conducted on RC waffle flat plate structures supported on isolated columns. The energy dissipated at the base of the columns until collapse is estimated applying different approaches.
This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinf... more This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs.
A key aspect of the seismic design of structures is the distribution of the lateral strength, bec... more A key aspect of the seismic design of structures is the distribution of the lateral strength, because it governs the distribution of the cumulative plastic strain energy (i.e., the damage) among the stories. The lateral shear strength of a story i is commonly normalized by the upward weight of the building and expressed by a shear force coefficient αi. The cumulative plastic strain energy in a given story i can be normalized by the product of its lateral strength and yield displacement, and expressed by a plastic deformation ratio ηi. The distribution αi/α1 that makes ηi equal in all stories is called the optimum yield-shear force distribution. It constitutes a major aim of design; a second aim is to achieve similar ductility demand in all stories. This paper proposes a new approach for deriving the optimum yield-shear force coefficient distribution of structures without underground stories and equipped with metallic dampers. It is shown, both numerically and experimentally, that st...
Prestressed monoblock railway sleepers are concrete elements with almost no reinforcement apart f... more Prestressed monoblock railway sleepers are concrete elements with almost no reinforcement apart from the prestressing wires, which makes them very sensitive to any stress variation that can induce tensile stresses. In recent years, severe longitudinal cracking has been observed in a number of sleepers in hot regions of Spain, even before these elements were put in service. This work studies the problem while considering the thermal variation as the main factor affecting this cracking phenomenon. A non-linear static load-step analysis is applied on a non-linear finite element model to reproduce the problem and, after its experimental validation, the influence of three design parameters of the sleepers are studied: the nature of concrete aggregates, the dowel thickness, and the dowel material. The results show that all these three parameters may have significant influence on the problem, with the dowel material being the most important parameter. When the dowels are made of a material...
Earthquake Engineering & Structural Dynamics, 2018
Reinforced concrete waffle-flat plate (WFP) structures present 2 important drawbacks for use as a... more Reinforced concrete waffle-flat plate (WFP) structures present 2 important drawbacks for use as a main seismic resisting system: low lateral stiffness and limited ductility. Yet the former can serve a positive purpose when, in parallel, the flexible WFP structure is combined with a stiff system lending high-energy dissipation capacity, to form a "flexible-stiff mixed structure." This paper experimentally investigates the seismic performance of WFP structures (flexible system) equipped with hysteretic dampers (stiff system) through shake-table tests conducted on a 2/5-scale test specimen. The WFP structure was designed only for gravitational loads. The lateral strength and stiffness provided by the dampers at each story were, respectively, about 3 and 7 times greater than those of the bare WFP structure. The mixed system was subjected to a sequence of seismic simulations representing frequent to very rare ground motions. Under the seismic simulations associated with earthquakes having return periods ranging from 93 to 1894 years, the WFP structure performed in the level of "immediate occupancy," with maximum interstory drifts up to about 1%. The dampers dissipated most (75%) of the energy input by the earthquake.
Earthquake Engineering & Structural Dynamics, 2019
SummaryThe bidirectional response of a portion of a reinforced concrete (RC) waffle‐flat plate (W... more SummaryThe bidirectional response of a portion of a reinforced concrete (RC) waffle‐flat plate (WFP) structure subjected to far‐field ground motions is studied through shake table tests. The test specimen is a scaled portion of a prototype structure designed under current building codes and located in a region of moderate seismicity of the Mediterranean area. The specimen was subjected to a sequence of tests of increasing acceleration amplitude that respectively represented very frequent, frequent, design, and very rare earthquakes at the site. The test structure performed well (basically in the elastic domain) under very frequent and frequent earthquakes, approached the boundary between the performance levels of life safety and near collapse under the design earthquake, and collapsed under the very rare earthquake. Damage concentrated at column bases and at the transverse beams of the exterior plate‐to‐column connection. Columns dissipated about 10% of the total energy that contrib...
Earthquake Engineering & Structural Dynamics, 2015
SummaryShaking table tests were conducted on a scaled reinforced concrete waffle–flat plate struc... more SummaryShaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period PR. The test structure performed well for the simulations associated with PR = 95, 475 and 975 years but collapsed under the maximum considered earthquake of PR = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate‐to‐column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental bas...
: The city of Lorca (Spain) was hit on May 11th 2011 by two consecutive earthquakes with 4.6 and ... more : The city of Lorca (Spain) was hit on May 11th 2011 by two consecutive earthquakes with 4.6 and 5.2 Mw respectively, causing casualties and important damage in buildings. Lorca is located in the south-east region of Spain and settled on the trace of the Murcia-Totana-Lorca fault. Although the magnitudes of these ground motions were not severe, the damage observed was considerable over a great amount of buildings. More than 300 of them have been demolished and many others are being retrofitted. This paper reports a field study on the damage caused by these earthquakes. The observed damage is related with the structural typology. Further, prototypes of the damaged buildings are idealized with nonlinear numerical models and their seismic behavior and proneness to damage concentration is further investigated through dynamic response analyses.
Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced c... more Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced concrete frames subjected to lateral loads. These braces may develop high axial tension forces, and transferring them appropriately to the existing beam-column joints is a key challenge. This paper investigates a solution for connecting the end-plate of the steel brace with the frame, using (1) shear-key plates fixed to the concrete with anchor bolts, and (2) a low friction material inserted between the end-plates and the shear-key plates. The presence of the low friction material impedes the development of tension forces in the anchor bolts and ensures that they are basically subjected to shear forces. This prevents brittle types of failure (concrete cone failure, pull-out/pry-out failure), and results in a reduction of the number of anchors required as well as anchorage height. The efficiency and validity of the proposed brace-frame connection is investigated experimentally by means of shaking table tests conducted on a 3 Â 3 Â 3 m 3 scaled reinforced concrete frame retrofitted with brace-type hysteretic dampers.
Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería, 2012
Forjado reticular Ensayo de laboratorio Fisuración distribuida del hormigón Leyes constitutivas e... more Forjado reticular Ensayo de laboratorio Fisuración distribuida del hormigón Leyes constitutivas en tensiones-deformaciones medias Elementos tipo fibra Elementos tipo capa r e s u m e n En este artículo se analizan distintas alternativas para modelar conexiones interiores forjado reticularpilar de hormigón armado y se propone una solución que con un coste computacional razonable proporcione resultados muy próximos a los experimentales. El modelo propuesto se valida numéricamente con los resultados obtenidos previamente de un ensayo de laboratorio realizado sobre un espécimen a escala 3/5 de la misma tipología estructural, sometido a ensayo cuasi-estático hasta el colapso. Para tal fin, se aplica la teoría avanzada de mecánica no lineal de hormigón armado sobre un modelo tridimensional de elementos finitos en análisis no-lineal: elementos tipo fibra para componentes unidimensionales y tipo capa para los bidimensionales. Los resultados principales de la simulación fueron: a) la obtención de la curva de capacidad mediante un análisis de empuje incremental (push-over) con control de desplazamientos; b) las curvas histeréticas en la losa, y c) los patrones de fisuras, logrando una concordancia revelada con los resultados experimentales.
The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes... more The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes 4.6 and 5.2 M w , causing casualties and important damage in buildings. Many of the damaged structures were reinforced concrete frames with wide beams. This study quantifies the expected level of damage on this structural type in the case of the Lorca earthquake by means of a seismic index /" that compares the energy input by the earthquake with the energy absorption/dissipation capacity of the structure. The prototype frames investigated represent structures designed in two time periods (1994-2002 and 2003-2008), in which the applicable codes were different. The influence of the masonry infill walls and the proneness of the frames to concentrate damage in a given story were further investigated through nonlinear dynamic response analyses. It is found that (1) the seismic index method predicts levels of damage that range from moderate/severe to complete collapse; this prediction is consistent with the observed damage; (2) the presence of masonry infill walls makes the structure very prone to damage concentration and reduces the overall seismic capacity of the building; and (3) a proper hierarchy of strength between beams and columns that guarantees the formation of a strong column-weak beam mechanism (as prescribed by seismic codes), as well as the adoption of countermeasures to avoid the negative interaction between non-structural infill walls and the main frame, would have reduced the level of damage from I v = l (collapse) to about /" = 0.5 (moderate/severe damage).
The seismic design of conventional frame structures is meant to enhance plastic deformations at b... more The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (Wpi) normalized by the product of the story shear force (Qyi) and drift (δyi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, Wpi /ΣWpj, can be evaluated from the deviation of Qyi with respect to an “optimum value” that would make the ratio Wpi/(Qyiδyi)—i.e. the damage—equal in all s...
La tesis plantea un metodo de proyecto sismorresistente para estructuras con forjado reticular y ... more La tesis plantea un metodo de proyecto sismorresistente para estructuras con forjado reticular y disipadores de energia segun la metodologia del proyecto basado en prestaciones y la filosofia de calculo basada en el balance de energia propuesta por Housner-Akiyama. Se establecen tres niveles de peligrosidad sismica, con unos determinados niveles de prestaciones a cumplir en cada uno de ellos para estructuras de tipo residencial, tomando como referencia el documento VISION 2000 propuesto por la SEAOC (Structural Engineer Association of California) en el ano 1995, en el que se presentan los fundamentos del proyecto basado en prestaciones. Se trata de aprovechar las caracteristicas de flexibilidad frente a cargas laterales de las estructuras con forjado reticular, asi como su versatilidad y amplia tradicion constructiva en paises como Espana, en el marco de las estructuras mixtas rigido-flexibles planteadas por Akiyama H. La parte flexible, denominada estructura principal, la constituy...
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