Diego Lopez-Garcia

Seismic Response of Adjacent Steel Structures Connected by Passive Device

In this study, the seismic response of adjacent steel structures linked to one another at different floor levels by passive devices is evaluated. Two types of connectors are considered: linear viscous dampers and linear springs. Various combinations of type and location of the connectors are analyzed for wide ranges of their characteristics. Influence of the structural properties (ratio of number of stories and ratio of fundamental periods) and the properties of the excitation (frequency) on the story response are also investigated. The results show that reduction of the story drift and the floor acceleration is not possible if the structures are connected to one another solely by the springs. However, it is feasible if the structures are linked to one another by either: (a) viscous dampers or (b) combinations of viscous dampers and springs. Herein, response reductions corresponding to case (b) are generally smaller than those corresponding to case (a). Also, the coupling control approach is more effective in controlling the response than the uncoupled approach.

Bidirectional pushover analysis of irregular structures

AbstractPushover analysis is one of the most-used nonlinear static procedures for the seismic assessment of structures; therefore, nowadays it is extensively used by practicing engineers for the seismic analysis of virtually every type of building. This paper proposes a bidirectional pushover analysis (BPA) method to overcome the limitations of current pushover methods to assess the seismic response of irregular (both in plan and in elevation) buildings subjected to bidirectional ground motions. The extended N2 method and the proposed BPA method were applied to estimate the nonlinear response of six highly irregular reinforced concrete frame structures designed according to the requirements of Eurocode 8. Results in terms of interstory drifts and floor rotations are compared with those given by nonlinear response history analysis (NRHA). For the latter, a suite of twenty Italian bidirectional seismic ground motions was selected. It was found that results given by the proposed BPA method match those given ...

The Influence of Accidental Torsion on the Inelastic Dynamic Response of Buildings During Earthquakes

Nonlinear dynamic analysis is becoming an accepted procedure to assess the performance of building structures during earthquakes. Several documents have emerged to provide guidance in terms of mathematical modeling, ground motion selection and scaling, and acceptability of results. While there are some significant differences in these documents, one feature in common is that explicit inclusion of accidental torsion in the nonlinear response history analysis is generally not required. One notable exception is ASCE/SEI 7-16 (2017), which requires performing nonlinear analyses, including accidental torsion when the building has a torsional irregularity. The analysis presented in this paper supports this requirement, but also shows that neglecting accidental torsion in the analysis of torsionally regular buildings can be problematic. Failure to include accidental torsion in nonlinear analysis of torsionally irregular buildings may indicate stable response instead of dynamic instability, or may significantly underpredict deformations and thereby falsely indicate that deformation-based acceptance criteria have been met. Additionally, it is shown that simultaneous application of ground shaking in orthogonal directions is essential, and that the spatial distribution of geometric nonlinearities related to global torsional response must be included directly in the analysis.

Life-cycle based design of mass dampers for the Chilean region and its application for the evaluation of the effectiveness of tuned liquid dampers with floating roof

The assessment of the effectiveness of mass dampers for the Chilean region within a multi-objective decision framework utilizing life-cycle performance criteria is considered in this paper. The implementation of this framework focuses here on the evaluation of the potential as a cost-effective protection device of a recently proposed liquid damper, called tuned liquid damper with floating roof (TLD-FR). The TLD-FR maintains the advantages of traditional tuned liquid dampers (TLDs), i.e. low cost, easy tuning, alternative use of water, while establishing a linear and generally more robust/predictable damper behavior (than TLDs) through the introduction of a floating roof. At the same time it suffers (like all other liquid dampers) from the fact that only a portion of the total mass contributes directly to the vibration suppression, reducing its potential effectiveness when compared to traditional tuned mass dampers. A life-cycle design approach is investigated here for assessing the compromise between these two features, i.e. reduced initial cost but also reduced effectiveness (and therefore higher cost from seismic losses), when evaluating the potential for TLD-FRs for the Chilean region. Leveraging the linear behavior of the TLD-FR a simple parameterization of the equations of motion is established, enabling the formulation of a design framework that beyond TLDs-FR is common for other type of linear mass dampers, something that supports a seamless comparison to them. This framework relies on a probabilistic characterization of the uncertainties impacting the seismic performance. Quantification of this performance through time-history analysis is considered and the seismic hazard is described by a stochastic ground motion model that is calibrated to offer hazard-compatibility with ground motion prediction equations available for Chile. Two different criteria related to life-cycle performance are utilized in the design optimization, in an effort to support a comprehensive comparison between the examined devices. The first one, representing overall direct benefits, is the total life-cycle cost of the system, composed of the upfront device cost and the anticipated seismic losses over the lifetime of the structure. The second criterion, incorporating risk-averse concepts into the decision making, is related to consequences (repair cost) with a specific probability of exceedance over the lifetime of the structure. A multi-objective optimization is established and stochastic simulation is used to estimate all required risk measures. As an illustrative example, the performance of different mass dampers placed on a 21-story building in the Santiago area is examined.

Seismic response of adjacent buildings connected by nonlinear viscous dampers

In this study, the seismic response of a pair of linear multistory building structures linked to one another at floor levels by nonlinear passive devices is comprehensively evaluated. Three possible height-wise distributions of the connectors were analyzed for wide ranges of values of their characteristic constants. Two response quantities were considered: interstory drift and absolute floor acceleration. Results indicate that, while it is possible to reduce both response quantities in both buildings, the level of response reduction generally decreases with decreasing values of damper exponent α. Results also indicate that the response of the systems is not sensitive to the height-wise distribution of the connecting dampers. Finally, it was also found that the optimal value of the damper exponent α depends on the value of the sum of the damper coefficients of the linking devices (c1+c2= C): while the optimal value of α is 0.80 when the value of C is relatively low, the optimal value of α is 1.00 (i.e., a linear viscous damper) when the value of C is relatively high

Multihazard-Resistant Highway Bridge Bent

There are some similarities between seismic and blast effects on bridge structures: both major earthquakes and terrorist attacks/accidental explosions are rare events that can induce large inelastic deformations in the key structural components of bridges. Since many bridges are (or will be) located in areas of moderate or high seismic activity, and because many bridges are potential terrorist targets, there is a need to develop structural systems capable of performing equally well under both events. This paper presents the findings of research to establish a multi-hazard bridge pier concept capable of providing an adequate level of protection against collapse under both seismic and blast loading, and whose members’ dimensions are not very different from those currently found in typical highway bridges. A series of experiments on 1/4 scale multi-hazard bridge piers was performed. Piers were concrete-filled steel tube columns (CFST columns) with different diameters (D = 4”, 5” and 6”), connected to a steel beams embedded in the cap-beam and a foundation beam. Fiber reinforced concrete was used for the cap-beam and the foundation beam to control cracking, which was deemed desirable against spalling of the concrete. The CFST column exhibited a ductile behavior under blast load, and no significant damage was suffered by the fiber reinforced concrete cap-beam as a result of the blast pressures.

Numerical assessment of accumulated seismic damage in a historic masonry building. A case study

ABSTRACT The current state of damage of a two-story unreinforced masonry historic building in Santiago de Chile is mainly due to the occurrence of the earthquakes of March 3, 1985 (Mw 8.0) and February 27, 2010 (Mw 8.8). Among the modern strategies available for a structural assessment of this type of constructions, nonlinear time-history analysis offers interesting possibilities but its use remains little explored because of their high computational demand. In this context, this article investigates the capabilities of a numerical strategy, based on macro-modelling, to simulate the accumulated seismic damage of a historic masonry building subjected to large seismic events. For this purpose, longitudinal and transverse components of accelerograms of the two large earthquakes that were recorded near the building are considered. Nonlinear time-history analyses were carried out in sequence using a global finite element (FE) model of the structure. The results show that the current crack pattern observed in the building can be simulated satisfactorily by the numerical approach adopted.

Soil-Structure Interaction for Integrated Design of Weakened and Damped Structures

Previous research has shown the effectiveness of the integrated design of weakening and damping techniques (WeD) for the seismic retrofitting of structures. Indeed, WeD techniques are able to reduce inter-story drifts and total accelerations, the two major performance measures to evaluate the seismic behavior of structures. Past research has been applied to fixed-based structures considering relatively stiff soil conditions. It has been suspected, though, that using such techniques in soft soil sites while considering soil structure interaction, may diminish some of the advantages observed in past research. This paper examines the effect of site conditions and soil-structure interaction on the seismic performance of Weakening and Damping techniques. An established rheological soil-shallow foundation-structure model with equivalent linear soil behavior and nonlinear behavior of the superstructure has been used. A large number of models incorporating wide range of soil, foundation and structural parameters ...

Design of flow isolation systems through multi-objective criteria for the seismic-risk performance

This paper discusses a probabilistic framework for performance assessment and optimal design of floor isolation systems for the protection of acceleration sensitive contents. A multi-objective formulation is considered for the optimization problem with the two competing objectives corresponding to (i) maximization of the level of protection offered to the sensitive content (acceleration reduction) and (ii) minimization of the demand for appropriate clearance to avoid collision to surrounding objects (floor displacement reduction). Uncertainties are addressed by characterizing these objectives in terms of the associated seismic risk, whereas a surrogate modeling approach is developed to evaluate this risk and support the design optimization. As an illustrative example, the design of a polynomial friction pendulum isolator system is presented. The formulation is demonstrated to efficiently provide design solutions with different performance levels across the considered competing objectives, offering a range of options for selecting the final protection system.

Seismic optimization of a novel tuned sloshing damper for the Chilean region based on life-cycle cost criteria

The design of a new liquid damper device is considered in this paper based on life-cycle criteria. This new device, called Tuned Liquid Damper with Floating Roof (TLD-FR) maintains the advantages of traditional Tuned Liquid Dampers (low cost, easy tuning, alternative use of water) while establishing a linear and generally more robust/predictable damper behaviour through the introduction of a floating roof. This behaviour can be characterized by four dimensional parameters that represent the design variables for the system and are all related to the tank geometry. A probabilistic framework is established to perform the design optimization considering seismic risk criteria specific to the Chilean region. Quantification of this risk through time-history analysis is considered and the seismic hazard is described by a stochastic ground motion model that is calibrated to offer hazard-compatibility with ground motion prediction equations available for Chile. Two different criteria related to life-cycle performance are utilized in the design optimization. The first one, representing overall direct benefits, is the life-cycle cost of the system, composed of the upfront TLD-FR cost and the anticipated seismic losses over the lifetime of the structure. The second criterion, focusing on the performance of building contents, is the peak acceleration with a specific probability of exceedance over the lifetime of the structure. A multi-objective optimization is therefore established and stochastic simulation is used to estimate all required risk measures, whereas a Kriging metamodel is developed to support an efficient optimization process.