Seismic vulnerability analysis of steel buildings in Bogotá, Colombia

A number of mid-height steel buildings have been erected recently in Bogotá. Their seismic risk might be high, given the new microzonation of Bogotá and the lack of previous studies; remarkably, the response reduction factors were commonly obtained from general recommendations. The objective of this work is to investigate the seismic performance of these buildings. This study is carried out on eighteen representative buildings. All these edifices have plan symmetry and are uniform along their height. Span-length: 6 ¿ 8 m; number of floors: 5, 10, 15. Earthquake-resistant systems: moment-resistant frames, concentrically-braced frames and eccentricallybraced frames (using chevron braces). For each building, eight seismic zones have been considered. The vulnerability has been evaluated by “push-over” analyses. In the moment-resistant frames and in the eccentrically-braced frames the nonlinearities are concentrated in the plastic hinges near the connections; in the concentrically-braced frames the nonlinearities are allocated in the braces.Postprint (published version

Would RC wide-beam buildings in Spain have survived Lorca earthquake (11-05-2011)?

Lorca earthquake (11-05-2011) is most destructive event recorded in Spain, causing nine fatalities and other severe consequences. Its important intensity was rather unexpected, and serious concern arose regarding risk of building stock in Spain. This paper analyzes performance, under Lorca earthquake, of RC buildings with one-way slabs with wide beams. This construction type is chosen for its high vulnerability and for being vastly widespread in Spain. This study is conducted on 3 and 6-story prototype representative buildings. These buildings are designed for three major seismic zones in Spain: low seismicity, moderate seismicity (as Lorca) and medium seismicity (as Granada). Seismic performance under Lorca earthquake is numerically investigated through nonlinear time-history analyses. Results show that buildings designed without any seismic provision (i.e. those in low seismicity zones) do not survive Lorca record, even with cooperation of masonry infill walls. Buildings with seismic design (i.e. those in Lorca and Granada zones) can survive Lorca earthquake only with collaboration of infill walls. To raise reliability of these conclusions, a sensitivity analysis to most influencing parameters is conducted.Postprint (author's final draft

New formulation for estimating the damping parameter of the Kelvin-Voigt model for seismic pounding simulation

Seismic pounding between adjoining buildings frequently causes serious damage; although collision can be avoided with proper separation, can still occur due to code non-fulfillment, loose requirements of old codes, and seismicity underestimation. Inside this context, this work deals with collision between two buildings with aligned slabs. The simulation of this phenomenon is not obvious, involving stress traveling waves, high-frequency behavior, and local effects. Complex distributed continuum mechanics-based models can be used, but are time-consuming; conversely, the concentrated Kelvin-Voigt model can be utilized instead, being simple and inexpensive, yet accurate. Its behavior is characterized by damping and stiffness parameters; the damping influence is particularly important and a number of estimation criteria have been proposed. Among them, the Anagnostopoulos formulation is simple, and provides satisfactory results in most situations. That formulation consists in estimating the damping parameter after a given target value of the coefficient of restitution; the influence, during impact, of the colliding building structures and the seismic excitation is neglected. This paper proposes an alternative approach that releases one of the aforementioned assumptions: the influence of the building structures and their initial separation is taken into consideration. A simplified parametric study oriented to investigate the performance of the proposed strategy is performed; it is found that the accuracy of the Anagnostopoulos formulation is improved in a number of situations. Noticeably, this gain is obtained at a low computational cost. The proposed formulation is satisfactorily utilized to analyze pounding between two multi-story multi-bay RC buildings and to simulate a shaking table pounding experiment.Peer ReviewedPostprint (author's final draft

State-of-the-art of research on seismic pounding between buildings with aligned slabs

Collision between adjoining buildings with aligned slabs is relevant, since the huge impact forces significantly modify the buildings dynamic behavior. The separation required by the regulations avoids pounding; however, even in recent buildings, impact can occur due to not fulfillment of codes and seismicity underestimation. Given the importance of this issue, a significant research effort has been undertaken worldwide, and a considerable number of papers are available. The complexity of this field and this abundance of information might require a review task. This paper presents a summary of the theoretical developments, discusses the most common simulation software, provides an overview of the previous research, offers recommendations to researchers, and identifies research needs.Postprint (published version

New methodology for calculating damage variables evolution in Plastic Damage Model for RC structures

The behavior of reinforced concrete (RC) structures under severe demands, as strong ground motions, is highly complex; this is mainly due to joint operation of concrete and steel, with several coupled failure modes. Furthermore, given the increasing awareness and concern for the important seismic worldwide risk, new developments have arisen in earthquake engineering. Nonetheless, simplified numerical models are widely used (given their moderate computational cost), and many developments rely mainly on them. The authors have started a long-term research whose final objective is to provide, by using advanced numerical models, solid basis for these developments. Those models are based on continuum mechanics, and consider Plastic Damage Model to simulate concrete behavior. Within this context, this paper presents a new methodology to calculate damage variables evolution; the proposed approach is based in the Lubliner/Lee/Fenves formulation and provides closed-form expressions of the compressive and tensile damage variables in terms of the corresponding strains. This methodology does not require calibration with experimental results and incorporates a strategy to avoid mesh-sensitivity. A particular algorithm, suitable for implementation in Abaqus, is described. Mesh-insensitivity is validated in a simple tension example. Accuracy and reliability are verified by simulating a cyclic experiment on a plain concrete specimen. Two laboratory experiments consisting in pushing until failure two 2-D RC frames are simulated with the proposed approach to investigate its ability to reproduce actual monotonic behavior of RC structures; the obtained results are also compared with the aforementioned simplified models that are commonly employed in earthquake engineering.Postprint (published version

Sistemas de control de estructuras de edificación por cables activos

En este artículo se propone un sistema de control activo de estructuras de edificación sometidas a excitaciones dinámicas (sísinicas o del viento) en el que los mecanismos actuadores son cables activos. La originalidad de la propuesta radica en la forma de instalar los cables activos en la estructura de los edificios objeto de control. La efectividad del sistema de control para reducir las oscilaciones horizontales de edificios con un coste razonable de energía es analizada mediante ensayos numéricos sobre dos edificios de 23 plantas cuyas estructuras son representativas de las tipologías estructurales más comúnmente utilizadas en edificios de esa altura. Se analiza exhaustivamente la robustez del sistema de control simulando numéricamente experiencias de control en situaciones límite. El análisis de los resultados obtenidos permite concluir que los cables activos son útiles para constituir sistemas de coiitrol de edificios de altura inedia, especialmente si su comportamiento dinámico horizontal es más similar al de una viga que al de un pórtico por existir pantallas verticales de rigidización.In tliis paper a control systein by active tendons is proposed and its effectiveness to reduce tlie dynaiiiic response of building structures with a reasonable cost of &ergy is tested by means of numerical experiments considering two 23-story buildings (called Bl and B2) subjected to seisinic and wind excitations. Bl is a franie building while Ba is a shear wall building. The dynamic behaviours of buildings Bl and Bg are representative of those of the different types of structures inost coimmonly used in buildings of about this nuinber of floors. The results of the numerical experiments allow to conclude that active cables are useful to constitute a feasible. reliable and iobust control system of mediun-high buildings and that tbey are more effectivé in buildiiigs with a dynainic beliaviour similar to tlie one of building B2.Peer Reviewe

Sistemas de control de estructuras de edificación por cables activos

En este artículo se propone un sistema de control activo de estructuras de edificación sometidas a excitaciones dinámicas (sísinicas o del viento) en el que los mecanismos actuadores son cables activos. La originalidad de la propuesta radica en la forma de instalar los cables activos en la estructura de los edificios objeto de control. La efectividad del sistema de control para reducir las oscilaciones horizontales de edificios con un coste razonable de energía es analizada mediante ensayos numéricos sobre dos edificios de 23 plantas cuyas estructuras son representativas de las tipologías estructurales más comúnmente utilizadas en edificios de esa altura. Se analiza exhaustivamente la robustez del sistema de control simulando numéricamente experiencias de control en situaciones límite. El análisis de los resultados obtenidos permite concluir que los cables activos son útiles para constituir sistemas de coiitrol de edificios de altura inedia, especialmente si su comportamiento dinámico horizontal es más similar al de una viga que al de un pórtico por existir pantallas verticales de rigidización.In tliis paper a control systein by active tendons is proposed and its effectiveness to reduce tlie dynaiiiic response of building structures with a reasonable cost of &ergy is tested by means of numerical experiments considering two 23-story buildings (called Bl and B2) subjected to seisinic and wind excitations. Bl is a franie building while Ba is a shear wall building. The dynamic behaviours of buildings Bl and Bg are representative of those of the different types of structures inost coimmonly used in buildings of about this nuinber of floors. The results of the numerical experiments allow to conclude that active cables are useful to constitute a feasible. reliable and iobust control system of mediun-high buildings and that tbey are more effectivé in buildiiigs with a dynainic beliaviour similar to tlie one of building B2.Peer Reviewe

Control activo de estructuras con aislamiento de base

En este artículo se propone un sistema de control activo como protección antisismica suplementaria para edificios con aislamiento de base y se analiza su viabilidad de forma numérica. Se considera una única fuerza de control actuando al nivel de la planta inferior. El algoritmo de control se basa en la estrategia de control predictivo, formulada para tener en cuenta el problema del tiempo de retardo en los actuadores. Los resultados obtenidos muestran que es posible lograr una reducción de las aceleraciones absolutas notablemente superior a la que se alcanza con el efecto pasivo del sistema de aislamiento de base. Ello puede ser útil en edificios que alberguen equipos especialmente sensibles.Peer Reviewe

Generating damping modification factors after artificial inputs in scenarios of local records scarcity

The damping modification factors are utilized to alter the design spectral ordinates for constructions whose damping differs significantly from 5%, this being the level that is routinely considered by most codes. Such factors are habitually evaluated after suites of historical inputs representing the local seismicity. However, such records may not be readily available, due either to moderate seismicity or to limited seismological network; in such cases, representative artificial accelerograms might be used instead. This paper proposes a methodology for establishing damping modification factors after artificial inputs generated to match the 5% design spectra; this approach can be used for countries, regions or cities. The proposed methodology is based on performing dynamic analyses on underdamped and overdamped SDOF linear systems by using the aforementioned selected accelerograms. Although previous studies have highlighted the differences among factors generated after natural and artificial inputs, it has been observed that such discrepancies are mainly due to the longest significant (Trifunac) duration of the artificial accelerograms. Therefore, the artificial inputs are generated as their duration fits those of the available local strong motion records. An application to Colombia is presented; the results are compared with those for some available Colombian records. The sensitivity of the calculated factors to the soil type, period and seismic zone is investigated; matching expressions are provided. Such expressions are compared with the prescriptions of major design codes and with other studies. The suitability of the proposed formulation is further verified in an example on an isolated hospital building.Peer ReviewedPostprint (author's final draft

Numerical solution of the equations of motion of multi-story buildings with severe nonlinearities

Este artículo presenta un algoritmo para resolver las ecuaciones del movimiento de edificios de varias plantas que incorporan disipadores de energía friccionales como protección sismorresistente. El comportamiento de los disipadores se representa mediante modelos de Coulomb de rozamiento seco; estos introducen no linealidades severas en el comportamiento dinámico de la estructura cada vez que cambian las condiciones de contacto (bloqueo o deslizamiento) en los disipadores. Estas no linealidades complican la resolución de las ecuaciones del movimiento, ya que habitualmente este se describe mediante modelos planos de masas concentradas cuyos grados de libertad son los desplazamientos de las plantas y, al variar las condiciones de bloqueo o de deslizamiento, los grados de libertad deben ser modificados: para condiciones de bloqueo estos son solamente los desplazamientos de las plantas, mientras que para condiciones de deslizamiento han de considerarse, además, los desplazamientos de los disipadores. En artículos previos se ha verificado la exactitud del algoritmo comparándolo satisfactoriamente con resultados experimentales; asimismo, se ha constatado la eficacia computacional del algoritmo comparando ventajosamente los recursos requeridos (en términos de tiempo de cálculo o de asignación de memoria) con los de otros algoritmos. Los objetivos de este artículo son, por un lado, describir en detalle la resolución numérica de las ecuaciones del movimiento y, por otro, presentar ejemplos representativos que confirmen la capacidad del algoritmo para reproducir el comportamiento dinámico de edificios con disipadores y que ilustren de forma preliminar la utilidad de dichos dispositivos para reducir las oscilaciones de la estructura que proteger.This paper presents a new algorithm for solving the equations of motion of multi-storey buildings that incorporate frictional energy dissipators as seismic protection. The behavior of the dissipators is represented by Coulomb dry friction models; they introduce severe nonlinearities in the dynamic behavior of the structure every time that the contact conditions (stick or slip) change in the dissipators. These nonlinearities complicate the resolution of the equations of motion as it usually is described by lumped masses models whose degrees of freedom are the displacements of the floors and, as the stick or slip conditions change, the degrees of freedom must be modified: for blocking conditions they are only the displacements of the storeys while under sliding conditions the displacements of the dissipators have to be also considered. In previous articles the accuracy of the proposed algorithm has been verified by comparison with experimental results; as well, the computational efficiency of the algorithm has been confirmed by comparing the required resources (in terms of computation time and of memory allocation) with those of other algorithms. The objectives of this paper are to describe in detail the numerical solution of the equations of motion and present representative examples confirming the ability of the algorithm to reproduce the dynamic behavior of buildings with friction dissipators and reporting preliminarily about the usefulness of such devices to reduce the oscillations of the structure to be protected.Peer Reviewe