Papers by ruben boroschek
The publisher does not give any warranty express or implied or make any representation that the c... more The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. This work presents the results of a study carried out to characterize the mechanical response of a high damping rubber to be used in designing and constructing energy dissipating devices and base isolators for controling strong vibrations in civil engineering structures. A new parametric model of the elastomer is proposed to be employed in the design procedure and structural analysis of passive controlled structures. The parameters of the model are calibrated using experimental data obtained from tests on rubber specimens under different loading paths. The main dissipating energy mechanisms of the rubber are identified. The proposed model is able to reproduce those main mechanisms as well as geometric second order effects such as tension stiffening due to the effect of axial strains in the response. The response predicted by the proposed model is compared with that obtained from experimental tests and from the Kelvin and plasticity models.
SUMMARY In this article, a new bidirectional tuned liquid column damper (BTLCD) is proposed for c... more SUMMARY In this article, a new bidirectional tuned liquid column damper (BTLCD) is proposed for controlling the seismic response of structures. The device acts as two independent and orthogonal tuned liquid column dampers (TLCDs), but due to its configuration, it requires less liquid than two equivalent independent TLCDs. The equations of motion of the system formed by the BTLCD and the primary structure to be controlled are obtained by means of Lagrangian dynamics explicitly considering the non-symetrical action of the damping forces. First, the primary structure was assumed to have two degrees of freedom (DOFs). Assuming that the system is excited by a base acceleration that can be considered to be a white noise random process, the optimum design parameters of the device were obtained to min-imise the response of the primary structure. The optimum design parameters are presented as expressions covering a wide range of possible configurations for the device in a controlled structure. The use of a BTLCD to control the seismic response of several DOF structures was also studied, showing that if the structural response occurs mainly in two perpendicular modes, then the optimum design parameters for two DOF structures can be used. Experimental analyses of the BTLCD are developed in order to verify its dynamical properties. Finally, the device is designed for controlling the seismic response of a six DOF scale model. Numerical analyses are developed in order to verify the effectiveness and accuracy of the equations and design procedures proposed herein.
A bidirectional tuned liquid column damper for reducing the seismic response of buildings
Structural Control and Health Monitoring, 2015
Slip Distribution of the 2005 Mw 7.8 Tarapaca, Chile Earthquake
On June 13, 2005, a large earthquake with a preliminary USGS moment magnitude of 7.8 struck the T... more On June 13, 2005, a large earthquake with a preliminary USGS moment magnitude of 7.8 struck the Tarapaca province in Chile. The initial USGS focal mechanism and Harvard CMT indicate that this was an approximately 115 km deep normal faulting event located over 200 km inland of the Peru-Chile trench. However, little else is known about the source mechanism of
Site characterization at Chilean strong-motion stations: Comparison of downhole and microtremor shear-wave velocity methods
Soil Dynamics and Earthquake Engineering, 2015
ABSTRACT
Modal Parameter Variation of an Earthquake Damaged Building
Conference Proceedings of the Society for Experimental Mechanics Series, 2012
Tectonophysics, 2002
The 1943 Illapel seismic gap, central Chile (30 -32BS), was partially reactivated in 1997 -1998 b... more The 1943 Illapel seismic gap, central Chile (30 -32BS), was partially reactivated in 1997 -1998 by two distinct seismic clusters. On July 1997, a swarm of offshore earthquakes occurred on the northern part of the gap, along the coupled zone between Nazca and South American plates. Most of the focal mechanisms computed for these earthquakes show thrust faulting solutions. The July 1997 swarm was followed on October 15, 1997 by the Punitaqui main event (Mw = 7.1), which destroyed the majority of adobe constructions in Punitaqui village and its environs. The main event focal mechanism indicates normal faulting with the more vertical plane considered as the active fault. This event is located inland at 68-km depth and it is assumed to be within the oceanic subducted plate, as are most of the more destructive Chilean seismic events. Aftershocks occurred mainly to the north of the Punitaqui mainshock location, in the central-eastern part of the Illapel seismic gap, but at shallower depths, with the two largest showing thrust focal mechanisms. The seismicity since 1964 has been relocated with a master event technique and a Joint Hypocenter Determination (JHD) algorithm, using teleseismic and regional data, along with aftershock data recorded by a temporary local seismic network and strong motion stations. These data show that the 1997 seismic clusters occurred at zones within the Illapel gap where low seismicity was observed during the considered time period. The analysis of P and T axis directions along the subduction zone, using the Harvard Centroid Moment Tensor solutions since 1977, shows that the oceanic slab is in a downdip extensional regime. In contrast, the Punitaqui mainshock is related to compression resulting from the flexure of the oceanic plate, which becomes subhorizontal at depths of about 100 km. Analog strong motion data of the Punitaqui main event show that the greatest accelerations are on the horizontal components. The highest amplitude spectra of the acceleration is in the frequency band 2.5 -10 Hz, in agreement with the energy band responsible for the collapsed adobe constructions. The isoseismal map derived from the distribution of observed damage show that a high percentage of destruction is due to the proximity of the mainshock, the poor quality of adobe houses and probably local site amplification effects. D
Journal of Seismology, 2011
Earthquake hazard along the Peru-Chile subduction zone is amongst the highest in the world. The d... more Earthquake hazard along the Peru-Chile subduction zone is amongst the highest in the world. The development of a database of subduction-zone strong-motion recordings is therefore of great importance for ground-motion prediction in this region. Accelerograms recorded by the different networks operators in Peru and Chile have been compiled and processed in a uniform manner and information on the source parameters of the causative earthquakes, fault-plane geometries and local site conditions at the recording stations has been collected and reviewed to obtain high-quality metadata. The compiled database consists of 98 triaxial ground-motion recordings from 15 subduction-type events with moment magnitudes ranging from 6.3 to 8.4, recorded at 55 different sites in Peru and Chile, between 1966 and. While the database presented in this study is not sufficient for the derivation of a new predictive equation for ground motions from subduction events in the Peru-Chile region, it significantly expands the global database of strong-motion data and associated metadata that can be used in the derivation of predictive equations for subduction environments. Additionally, the compiled database will allow the assessment of the existing predictive models for subduction-type events in terms of their suitability for the Peru-Chile region, which directly influences seismic hazard assessment in this region.
Journal of Seismology, 2006
The Departments of Civil Engineering and Geophysics of the University of Chile, together with int... more The Departments of Civil Engineering and Geophysics of the University of Chile, together with international institutions, deployed strong-motion stations in the northern Chile seismic gap. These instruments recorded the June 23, 2001 M w = 8.4 earthquake that occurred in Southern Peru. This earthquake exhibited at stiff deep soil sites in northern Chile, relatively large maximum accelerations although the recording stations are located more than 400 km away from the epicentral region and 200 km from the southern edge of the rupture. Typical accelerations at these distances are in the order of 0.30 g, considerably larger than those expected from recently presented attenuation formulae. Frequency and Wavelet Decomposition of the signals are presented from which the evolution of the amplitude, as a function of selected frequency bands, is analyzed. Typical Central Frequency varies from 3 to 4.8 Hz for horizontal records and 4.5 to 9.5 Hz for vertical records. Ninety five percent of the record energy is concentrated below 11 Hz.
Journal of Geophysical Research, 2007
Structural Health Monitoring Performance During the 2010 Gigantic Chile Earthquake
Effect of SMA Braces in a Steel Frame Building
Journal of Earthquake Engineering, 2007
Journal of Constructional Steel Research, 2008
This study presents the details of an experimental investigation on a prototype partially restrai... more This study presents the details of an experimental investigation on a prototype partially restrained connection using copper-based shape memory alloy (SMA) bars. The proposed configuration consists of an end-plate connection between a rectangular hollow structural steel beam and a wide flange steel column, where four CuAlBe (φ = 3 mm) bars, in austenitic phase, are used to prestress the end-plate to the column flange. A physical model of the connection was tested by applying a controlled cyclic displacement history at the tip of the beam with two different characteristic frequencies of 0.25 and 1 Hz. Potentiometers and load cells were used to measure strains and stresses in the bars and the displacement and load applied at the beam tip. Similar bars, with the same thermal treatment, had been previously tested in cyclic tension at several nominal strains and frequencies, showing superelastic behavior for deformations up to 2.3% strain. In static tensile tests, the fracture strain was approximately 8%, with a transgranular fracture mechanism. The equivalent damping ratio for the single bar test increases for larger strains, being 6% for a 2.3% strain. The beam-column connection also exhibited superelastic behavior, a moderate level of energy dissipation, and no strength degradation after being subjected to several cycles up to 3% drift. Finally, a set of numerical simulations are conducted to compare the performance of a rigid steel frame and a partially restrained frame with SMA connections using a three-story benchmark structure. c
Dynamic Characteristics of Chilean Bridges with Seismic Protection
Journal of Bridge Engineering, 2005
International Journal for Numerical Methods in Engineering, 2009
The poor performance of some reinforced concrete (RC) structures during strong earthquakes has al... more The poor performance of some reinforced concrete (RC) structures during strong earthquakes has alerted about the need of improving their seismic behavior, especially when they are designed according to obsolete codes and show low structural damping, important second-order effects and low ductility, among other defects. These characteristics allow proposing the use of energy-dissipating devices for improving their seismic behavior. In this work, the non-linear dynamic response of RC buildings with energy dissipators is studied using advanced computational techniques. A fully geometric and constitutive non-linear model for the description of the dynamic behavior of framed structures is developed. The model is based on the geometrically exact formulation for beams in finite deformation. Points on the cross section are composed of several simple materials. The mixing theory is used to treat the resulting composite. A specific type of element is proposed for modeling the dissipators including the corresponding constitutive relations. Special attention is paid to the development of local and global damage indices for describing the performance of the buildings. Finally, numerical tests are presented for validating the ability of the model for reproducing the non-linear seismic response of buildings with dissipators. ‡ The symbol SO(3) is used to denote the finite rotation manifold . § The indices i and range over {1, 2, 3} and {2, 3}, respectively, and summation convention hold. The symbol (·) ,x is used to denote partial differentiation of (·) with respect to x. ¶ Supposing that K is parameterized in terms of the spatial rotation vector and following the results of References it is possible to show that K = hK with ˆ = axial[ h] ∈R 3 an admissible infinitesimal rotation.
Engineering Structures, 1998
An experimental four-story building, supported on high damping rubber isolators, was constructed ... more An experimental four-story building, supported on high damping rubber isolators, was constructed in Santiago, Chile in 1992. The building and a conventional twin, standing nearby, are instrumented with a local network of digital accelerometers. At least 24 earthquakes of different intensities have been registered in the past three years by the recording system. Data was also obtained at the isolated building for pull-back testing in an effort to evaluate the constitutive characteristics of the bearings. This paper describes the bearing verification testing program as well as the experiments carried out at the isolated building. It also contains the analysis of the records obtained for actual earthquakes, for both the isolated and the conventional building, using parametric and non-parametric identification techniques. For the earthquake records obtained, the reduction in the maximum acceleration at the roof level for the isolated building, as compared to the conventional one, varies from 1 to 3.5 times, depending on the level of the maximum ground acceleration and the characteristics of the earthquake motions.
Engineering Structures, 2003
The central zone of Chile is located in a high seismic risk area with occurrence of magnitude 7 e... more The central zone of Chile is located in a high seismic risk area with occurrence of magnitude 7 earthquakes every 10 years and magnitude 8 events every 90 years. This paper deals with the mechanical and dynamic characteristics of a 383 m long seismic isolated bridge located in that area. The tests carried out on rubber components, isolators and the bridge structure are presented. Some simple structural models that show good correlation with measured response are also addressed. A strong motion permanent network installed on the bridge allowed the recording of ambient-traffic vibrations as well as seismic motions. Seismic records show the beneficial effect of the isolation in the horizontal direction, but important amplification occurs in the vertical direction for relatively high frequency components.
Experimental verification of basic analytical assumptions used in the analysis of structural wall buildings
Engineering Structures, 2000
... Records were processed with standard software and an Ormsby bandpass filter withramps 0.150.... more ... Records were processed with standard software and an Ormsby bandpass filter withramps 0.150.25 and 2325 Hz. Acceleration and displacement response records for the events are presented in Fig. 5, Fig. 6, Fig. 7 and Fig. 8. ...
Experimental evaluation of the dynamic properties of a wharf structure
Engineering Structures, 2011
This paper presents the results from a series of experimental tests carried out to determine the ... more This paper presents the results from a series of experimental tests carried out to determine the damping characteristics of a section of a 375 m long pile-supported wharf structure under forced excitation. The test program was designed with two primary objectives: (1) to identify the fundamental damping of the structure by using structural microvibration signals produced by tides, wind and microtremors,
Strong Ground Motion Attributes of the 2010 M w 8.8 Maule, Chile, Earthquake
Earthquake Spectra, 2012
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Papers by ruben boroschek