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Browsing by Author "Llera Martin, Juan Carlos de la"

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A bidirectional and homogeneous tuned mass damper: A new device for passive control of vibrations
(Elsevier Sci. Ltd., 2007) Almazan, Jose L.; Llera Martin, Juan Carlos de la; Inaudi, Jose A.; Lopez Garcia, Diego; Izquierdo, Luis E.
Passive tuned-mass dampers (TMDs) are a very efficient solution for the control of vibrations in structures subjected to long-duration, narrow-band excitations. In this study, a Bidirectional and Homogeneous Tuned Mass Damper (BH-TMD) is proposed. The pendular mass is supported by cables and linked to a unidirectional friction damper with its axis perpendicular to the direction of motion. Some advantages of the proposed BH-TMD are: (1) its bidirectional nature that allows control of vibrations in both principal directions; (2) the capacity to tune the device in each principal direction independently; (3) its energy dissipation capacity that is proportional to the square of the displacement amplitude, (4) its low maintenance cost. Numerical results show that, under either unidirectional or bidirectional seismic excitations, the level of response reduction achieved by the proposed BH-TMD is similar to that obtained from an "ideal" linear viscous device. Moreover, experimental shaking table tests performed using a scaled BH-TMD model confirm that the proposed device is homogeneous, and, hence, its equivalent oscillation period and damping ratio are independent of the motion amplitude. (C) 2006 Elsevier Ltd. All rights reserved.
A comparative study of concentrated plasticity models in dynamic analysis of building structures
(Wiley, 2005) Dides, MA; Llera Martin, Juan Carlos de la
Concentrated plasticity (CP) models are frequently used in static and dynamic building analysis and have been implemented in available commercial software. This investigation deals with three different CP-models, a simplified macroelement model (SEM) for a complete building story, a frame element with elasto-plastic interaction hinges (PH), and a frame element with fiber hinges (FB). The objectives of this work are to evaluate the quality of the earthquake responses predicted by these models and to identify important aspects of their implementation and limitations for their use in dynamic analysis. The three elements are tested in a single-story asymmetric plan building and in a three-story steel building. Results show that base shear and global response values are usually computed with better accuracy than interstory deformations and local responses. Besides, the main limitation of elasto-plastic CP models is to control the displacement offsets that result from perfect elasto-plastic behavior. On the other hand, calibration of the SEM-model shows that global responses in steel structures may be computed within 20% error in the mean at a computational cost two orders of magnitude smaller than that of the other CP elements considered. However, the three element models considered lead to increasing levels of accuracy in the dynamic response and their use depends on the refinement of the analysis performed. Copyright (C) 2005 John Wiley & Sons, Ltd.
A Consistently Processed Strong-Motion Database for Chilean Earthquakes
(Seismological Society of America, 2022) Castro, Sebastián; Benavente, Roberto; Crempien de la Carrera, Jorge; Candia, Gabriel; Llera Martin, Juan Carlos de la
© Seismological Society of America.Since the 1985 M 8.0 central Chile earthquake, national strong-motion seismic networks have recorded ten megathrust earthquakes with magnitudes greater than M 7.5 at the convergent margin, defined by the contact between the Nazca and South American plates. The analysis of these earthquake records have led to improved hazard analyses and design codes for conventional and seismically protected structures. Although strong-motion baseline correction is required for a meaningful interpretation of these records, correction methods have not been applied consistently in time. The inconsistencies between correction methods have been neglected in the practical use of these records in practice. Consequently, this work aims to provide a new strong-motion database for researchers and engineers, which has been processed by traceable and consistent data processing techniques. The record database comes from three uncorrected strong motion Chilean databases. All the records are corrected using a four-step novel methodology, which detects the P-wave arrival and introduces a baseline correction based on the reversible-jump Markov chain Monte Carlo method. The resulting strong motion database has more than 2000 events from 1985 to the date, and it is available to download at the Simulation Based Earthquake Risk and Resilience of Interdependent Systems and Networks (SIBER-RISK) project website.
A design procedure for buildings equipped with energy dissipation devices using nonclassical damping and iso-performance curves
(2019) Llera Martin, Juan Carlos de la; Munoz, Juan P.; Besa Vial, Juan José
A Functional Loss Assessment of a Hospital System in the Bio-Bio Province
(EARTHQUAKE ENGINEERING RESEARCH INST, 2012) Mitrani Reiser, Judith; Llera Martin, Juan Carlos de la; Mahoney, Michael; Holmes, William T.; Bissell, Rick; Kirsch, Thomas
The objectives of this study were to introduce a damage and loss-of-function survey tool that can be used to standardize future assessment of hospital performance, to assess the impact of the 2010 Chilean earthquake on the functions of the public hospital system in the Bio-Bio Province, and to translate these results as lessons that can be applied to U.S. hospitals. This study focused on damage to structural and nonstructural components, utility services, and equipment, as well as loss of supplies and personnel. Structural engineers completed a visual inspection of facilities, and hospital administrators were surveyed to assess the overall impact on operations. All hospitals lost communications, electrical power, and water for several days. All hospitals reported some physical damage although only one suffered significant structural damage. The lessons learned from Chile are applied to U.S. practice of hospital seismic mitigation. [DOI: 10.1193/1.4000044]
A general design method for buildings with energy dissipation devices
(National Information Centre of Earthquake Engineering, 2017) Llera Martin, Juan Carlos de la; Besa Vergara, Juan José
A general design procedure for elastic buildings equipped with linear and non-linear energy dissipating devices is presented herein. The procedure begins with an estimation of the total amount of equivalent damping and stiffness required to achieve a predefined building performance. The method defines the modal significance of some key design performance indicators, and then focuses on the control of the modal properties by solving a singular two-parameter eigenvalue problem. Although simple, the definition of a new measure of modal significance in the classical and non-classical damping case, is also critical for faster convergence of the method. The incorporation of non-classical damping in the design algorithm appears to be critical, and expands its applicability significantly. The design output provides a target frequency shift and damping ratio for the complete structure, obtained from the so called iso-performance design curves (IPCs), which cover the whole design space spanned by these two design variables representing the supplemental stiffness and damping of the devices. Once the linear equivalent properties of the dampers are obtained, the equivalent stiffness and damping of the devices are transformed into parameters that characterize the inelastic force-deformation constitutive models of the physical dampers. The design procedure does not require any a-priori definition of a specific damper type. The design procedure was validated using 8 conventional buildings that were severely damaged during the February 27, 2010 Chile earthquake, and a rather complex free-plan building with two towers of a rhomboid-shape plan. Estimation errors between response reduction factors using linear versus inelastic modeling of the EDDs were usually less than 10% for the 9 buildings considered. The design procedure proposed is better described as a conceptual and practical framework for the design of buildings with passive EDDs. Its step-by-step nature can take advantage of future research in any of the current research topics described herein and could be easily adapted to new knowledge in the field.
A long-stroke semi-active MR damper for building control using tuned masses
(National Information Centre of Earthquake Engineering, 2017) Zemp, René; Llera Martin, Juan Carlos de la; Almazán Campillay, José Luis; Weber, F.
In this research the comprehensive development of a long-stroke MR-damper designed to control the earthquake performance of an existing 21-story reinforced concrete building in Santiago (Chile) by reacting on one of its tuned masses is presented. The ±1 m stroke MR-damper design is quite unique and considered the nominal response of the building equipped with two pendular masses of weight 160 tons each, and tuned to the fundamental mode of the structure. The realscale long-stroke MR-damper was designed by our research team and manufactured in Chile. The MR-damper was tested using a special testing rig designed to study devices with long stroke at large deformation velocities. The rig was implemented in the dynamics and vibration control laboratory at Universidad Catolica de Chile. Both, the long-stroke MRdamper and the control algorithm were experimentally validated using a suite of periodic and seismic signals. For the building numerical simulations, the nominal MR-damper force-displacement constitutive relationship was replaced by the measured force-displacement response of the damper in order to validate the theoretical MR-damper model used. Such model was used in simulations to predict the performance of the TM-MR damper assembly in the design phase of the damper. Furthermore, a new real-time structural displacement sensor was developed with this application since conventional technology and methods to measure building displacement are inaccurate for a real-time displacement control as proposed with this application. The real-time building displacement sensor was validated using a scaled-down building prototype subjected to shaking table tests before an actual size sensor was implemented within a test building. All electronic components of the tuned-mass MR-damper assembly were tested with a shaking table and subjected to strong motion accelerations while the MR-damper was working in its active mode. It is concluded that the proposed tuned-mass MRdamper solution is technically feasible and may be advantageous in some real-life situations. The stage of development of the technology reached a point that enables commercial implementation in a real structure.
A macro-element model for inelastic building analysis
(2000) Llera Martin, Juan Carlos de la; Vásquez P., Jorge; Chopra, Anil K.; Almazán Campillay, José Luis
A three-dimensional model for approximate inelastic analysis of buildings is presented herein. The model is based on a single macro-element per building storey. The inelastic properties of the model are characterized by the so-called ultimate storey shear and torque (USST) surfaces. Different algorithms for the construction of these surfaces, as well as their applications in building modelling, are presented and discussed. Two alternative procedures are developed to integrate the force-deformation constitutive relationship of the macroelements. The first one follows the exact trajectory of the load path of the structure on the USST, and the second uses linear programming without ever forming the USST surface. The accuracy of the model and integration procedure is evaluated by means of the earthquake response of single-storey systems. The model and integration procedure developed is finally used to compute the inelastic response of a seven-storey R/C building. The results of this investigation show that the model proposed, although approximate, can be effective in estimating the inelastic deformation demand of a building. It also enables the engineer to capture and interpret important features of the three-dimensional inelastic response of a structure even before performing any inelastic dynamic analysis. Copyright (C) 2000 John Wiley & Sons, Ltd.
A macroeconomic disaster risk analysis: the case study of Chile
(ELSEVIER, 2022) Marulanda, M. C.; Llera Martin, Juan Carlos de la; Cardona, Omar Darío
From a macroeconomic perspective, the occurrence of disasters, especially high-impact events, can lead to financial stress in a country due to the sudden high demand for resources to restore affected exposed assets. Disaster risk is a sovereign risk and implies a non-explicit contingent liability that, in many cases, has a major impact on fiscal sustainability. Two risk composite indicators have been used to measure the impact that potential disasters can mean for a country: (i) The Disaster Deficit Index (DDI), which measures a country's financial capacity to cover the economic losses generated after the occurrence of high-impact events; and (ii) A complementary index (DDI'), which indicates the fraction that the expected annual loss would represent to the annual surplus of a country. This paper describes the overall macroeconomic impact of disasters and presents DDI results for Chile, which allows national-level decision-makers to understand the economic implications of disasters for the country and the need to consider this kind of information in the long-term policies. Results of the DDI for Chile illustrate that extreme disasters would imply the need for a significant amount of budgetary resources from the government. Estimated losses would be double the available budget resources and the financing of the recovery could mean restrictions to invest in other ongoing social and development needs of the country. This macroeconomic risk in Chile may be hedged by strategically setting up a risk financial structure based on adequate loss estimation criteria, using different available alternatives such as public and private assets insurance, disasters' reserves, contingency credits contracts, and investing in prevention and mitigation to reduce potential economic losses.
A new method for assessing compatibility of consolodation procedures with conservation principles: Intervention Qualitiy Index
Llera Martin, Juan Carlos de la; Palazzi, Nuria Chiara; Misseri, Giulia; Sandoval, Cristián; Tonietti, Ugo; Rovero, Luisa
In current times, built heritage is being lost at an alarming rate due to natural and human hazards. Policies for its protection and rehabilitation involve, among other things, challenges related to the refinement of suitable structural strengthening approaches. The arduous balance between gaining acceptable safety levels for occupants without deploying intrusive devices, inconsistent with conservation principles such as those of the ICOMOS charters, is not a simple task. The interest and efforts of the scientific community in this regard have been increasing for decades, but still, it is the structural professional´s responsibility and experience which must define this arduous balance on a case-to-case basis. This study addresses the question: How can the quality of structural rehabilitation interventions be assessed in light of conservation principles such as those given by ICOMOS? Here, a preliminary method - called “Intervention Quality Index” (IQI) method is proposed. It assesses the restoration intervention quality in relation to: (i) the level of compliance given by the conservation´s principle score (conservation´s factor, CF); and (ii) the current state of conservation of the monument (safety factor of building considering the seismic intensity, Δs). The IQI method considers the compliance level of the designed reinforcement with conservation principle, formalized through the fulfillment of a category, i.e. respected, partially respected, and not respected. Then, these judgments are translated into scores and statistically evaluated. Scores are attributed in relation to the relevance of the fulfillment of a certain conservation principle (authenticity, minimal intervention and intrusiveness, compatibility, recognizability and reversibility) for the seismic structural safety point of view. Preliminary results show that an effective employment of traditional earthquake-resistant practices together with a wise use of modern retrofit strategies allow for the preservation and reinforcement of built heritage without harming its identity
A nonlinear model for multilayered rubber isolators based on a co-rotational formulation
(2017) Maureira, N.; Llera Martin, Juan Carlos de la; Oyarzo, C.; Miranda Camus, Sebastián
This article proposes a geometrically nonlinear co-rotational model aimed to characterize the mechanical behavior of elastomeric seismic isolators. The model is able to capture the axial and lateral coupling in both axial directions, i.e. compression and tension of the isolator. Also reproduces the instability the loads in tension as well as in compression, and provides theoretical evidence of the non-symmetric behavior of the isolator in these two directions. To validate model results, a quasistatic analysis was performed on a typical isolator with many different shape factors. From the parametric analysis performed, it is observed that buckling loads are higher in tension than in compression. However, as the shape factor of the isolator increases, the behavior in compression and tension becomes symmetric. It becomes apparent that significant differences in normal stresses and strains under tensile and compressives loads are observed for axial loads smaller than 10% of the nominal buckling load. The example presented shows that lateral displacements of about ±25% of isolator radius and tension forces up to 10% of the buckling load are possible without inducing cavitation in the rubber. Accuracy of the model was also tested against finite element model results and experimental data showing satisfactory results. Furthermore, a response-history analysis of an isolated structure is presented and compared for two isolator models: the two-spring model and the model proposed herein. Finally, material nonlinearity was introduced in the dynamic analysis using a Bouc-Wen type element in parallel with the isolator. The responses are similar between models; however, significant differences occur locally in the isolator for high axial loads and/or large lateral displacements.
A physical model for dynamic analysis of wine barrel stacks
(2010) Candia,Gabriel; Llera Martin, Juan Carlos de la; Almazán Campillay, José Luis
A probabilistic seismic hazard assessment of southern Peru and Northern Chile
(2020) Das, Ranjit; Gonzalez, G.; Llera Martin, Juan Carlos de la; Sáez Robert, Esteban; Salazar, P.; Gonzalez, J.; Meneses, C.
Southern Peru and northern Chile (17–30°S, 67–74°W) make up a seismically active region due to the convergence of the Nazca Plate and the South American Plate. The region has experienced a number of destructive earthquakes and tsunamis over the past few centuries, which have caused loss of human life and significant damage to infrastructure, highlighting the importance of seismic hazard assessment in the region. In fact, a reliable seismic hazard assessment is critical for developing policies for seismic hazard mitigation and risk reduction. In this study, we performed a probabilistic seismic hazard assessment (PSHA) of the study area based on an earthquake catalog that was very carefully analyzed. In earlier studies, we demonstrated that inappropriate treatment of the earthquake catalog can result in a serious bias in evaluations of seismicity parameters (e.g., a bias of up to 42% in the “b” parameter of the Gutenberg–Richter law). To address this issue, we compiled a homogenous earthquake catalog consisting of 39,977 events during the 1513–2016 period and accounted for site-specific local effects by developing site-specific scaling relationships between different measures of magnitude (e.g., mb, Ms, MD) and moment magnitude (Mw). The study area was subdivided into 15 seismogenic zones, accounting for site-specific seismicity patterns. The parameters “a” and “b” of the Gutenberg–Richter law were estimated for each zone based on independent earthquake events. The PSHA was performed using a standard logic tree approach, which allowed us to systematically take into account the model-based uncertainty and its influence on the estimated ground motion parameters. Uniform hazard spectra for return periods of 475 and 2475 years were estimated for peak ground accelerations and spectral accelerations at 0.2 s and 1.0 s to meet the definitions of seismic hazards provided by the International Building Code (IBC, International Code Council [ICC], 2009). This study is expected to provide a basis for design maps for building codes and emergency planning.
A regularized fiber element model for reinforced concrete shear walls
(2016) Vásquez P., Jorge; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés
Reinforced concrete shear walls are used because they provide high lateral stiffness and resistance to extreme seismic loads. However, with the increase in building height, these walls have become slenderer and hence responsible of carrying larger axial and shear loads. Because 2D/3D finite element inelastic models for walls are still complex and computationally demanding, simplified but accurate and efficient fiber element models are necessary to quickly assess the expected seismic performance of these buildings. A classic fiber element model is modified herein to produce objective results under particular loading conditions of the walls, that is, high axial loads, low axial loads, and nearly constant bending moment. To make it more widely applicable, a shear model based on the modified compression field theory was added to this fiber element. Consequently, this paper shows the formulation of the proposed element and its validation with different experimental results of cyclic tests reported in the literature. It was found that in order to get objective responses in the element, the regularization techniques based on fracture energy had to be modified, and nonlinearities because of buckling and fracture of steel bars, concrete crushing, and strain penetration effects were needed to replicate the experimental cyclic behavior. Thus, even under the assumption of plane sections, which makes the element simple and computationally efficient, the proposed element was able to reproduce the experimental data, and therefore, it can be used to estimate the seismic performance of walls in reinforced concrete buildings
A simplified and versatile element model for elastomeric seismic isolation bearings
(SAGE PUBLICATIONS INC, 2021) Miranda Camus, Sebastián; Miranda, Eduardo; Llera Martin, Juan Carlos de la
A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters' identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.
A simplified model for analysis and design of asymmetric-plan buildings
(1995) Llera Martin, Juan Carlos de la; Chopra, Anil K.
A new simplified model for analysis and design of multistorey buildings is developed. The model is based on a single super-element per building storey capable of representing the elastic and inelastic properties of the storey. This is done by matching the stiffness matrices and ultimate yield surface of the storey with that of the element; this surface relates storey shear and storey torque. For practical convenience, these surfaces are parametrized in terms of seven important physical parameters controlling the seismic response of asymmetric structures. Several numerical studies showed that the accuracy of the super-element model is satisfactory for most design purposes; the errors in peak responses are expected to be less than 20 per cent for most practical structures. Among the important advantages of this simplified model is that the time required in formulating, analysing and interpreting the structural model and its response is at least an order of magnitude smaller than for any conventional 3-D inelastic model. This enables the engineer to try different structural configurations and, thus, produce designs that have the desired seismic behaviour and are cost-effective. Furthermore, it has been shown through a multistorey building example that the super-element model is a powerful tool for conceptual design of a building. In spite of its simplicity, the model uses an accurate representation of the storey-shear and torque surfaces, which enables it to capture the fundamental features controlling the inelastic behaviour of the building.
A simplified model for the analysis of free plan buildings using a wide-column model
(ELSEVIER SCI LTD, 2013) Encina Muñoz, Javier Andrés; Llera Martin, Juan Carlos de la
In early stages of the design of a free-plan building different structural layouts should be evaluated to achieve a satisfactory level of seismic performance. However, the urgency of initial stage decisions needed by architects and developers makes the use of complex 3D structural models impractical. For this reason, a tool that can evaluate with acceptable accuracy the expected seismic performance of these configurations is necessary. This paper introduces a simplified building model that includes the flexural contribution of the slabs, and models the shear wall cores using a wide column analogy that includes warping effects. The model introduces kinematic constraints to account for the interaction between walls and slabs. Comparison of modal and response-histories with those given by a 3D finite element model shows that the proposed model has good accuracy, leading to errors usually less than 15%. Finally, the model has been devised to include other shear-wall structural configurations, energy dissipation systems, and the inelastic behavior of walls. (C) 2013 Elsevier Ltd.. All rights reserved.
A statistical analysis of reinforced concrete wall buildings damaged during the 2010, Chile earthquake
(2015) Junemann, Rosita; Llera Martin, Juan Carlos de la; Hube Ginestar, Matías Andrés; Cifuentes Lira, Luis Abdón; Kausel, Edgar E.; Pontificia Universidad Católica de Chile. National Research Center for Integrated Natural Disaster Management; Pontificia Universidad Católica de Chile. Department of Industrial and Systems Engineering
Accidental torsion due to overturning in nominally symmetric structures isolated with the FPS
(JOHN WILEY & SONS LTD, 2003) Almazán Campillay, José Luis; Llera Martin, Juan Carlos de la
Overturning of a structure causes variations in the normal loads of the isolators supporting that structure. For frictional isolators, such variation leads to changes in the frictional forces developed and, hence, in the strength distribution in plan. For frictional pendulum system (FPS) isolators, it also causes changes in the pendular action, i.e. in the stiffness distribution of the isolation interface. Therefore, although the structure is nominally symmetric it develops lateral-torsional coupling when it is subjected to two horizontal components of ground motion. This coupling is denoted herein as accidental torsion due to overturning, and its effect in the earthquake response of nominally symmetric structures is evaluated. Several parameters are identified to control this coupling, but the most important are the slenderness of the structure and the aspect ratio of the building plan. Results are presented in terms of the torsional amplification of the deformations of the isolation base and the interstorey deformations of the superstructure. The FPS system is modelled accurately by including true large deformations and the potential uplift and impact of the isolators. Impulsive as well as subduction-type ground motions are considered in the analysis, but results show small differences between them. An upper bound for the mean-plus-one standard deviation values of the torsional amplifications for the base due to this accidental torsion is 5%. This implies that for design purposes of the isolation system such increase in deformations could probably be neglected. However, the same amplification for the interstorey deformations may be as large as 50%, depending on the torsional stiffness and slenderness of the superstructure, and should be considered in design. In general, such amplification of deformations decreases for torsionally stiffer structures and smaller height-to-base aspect ratios. Copyright (C) 2003 John Wiley Sons, Ltd.
Accidental torsion in buildings due to stiffness uncertainty
(1994) Llera Martin, Juan Carlos de la; Chopra, Anil K.
Discrepancies between the computed and actual values of the structural element stiffness imply that a building with nominally symmetric plan is actually asymmetric to some unknown degree and will undergo torsional vibration when subjected to purely translational ground motion. Such accidental torsion leads to increase in structural element deformations which is shown to be essentially insensitive to the uncoupled lateral vibration period of the system but is affected strongly by the ratio of uncoupled lateral and torsional vibration periods. The structural deformations increase, in the mean, by at most 10 and 5 per cent for R/C and steel buildings, respectively, and by much smaller amounts for a wide range of system parameters. The increase in structural deformations due to stiffness uncertainty is shown to be much smaller than implied by the accidental torsional provisions in the Uniform Building Code and most other building codes.

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