Nature Of Ground Motion Research Articles

Shaking Table Seismic Experimental Investigation of Lightweight Rigid Bodies

This study presents the findings of an extensive shaking table experimental campaign conducted on nine free-standing wooden specimens, aiming at providing insights on the rigid body motion of free-standing objects. The specimens, which differ in slenderness and size, are characterized by impairments in their base surface and most likely in their shapes, which also lead to asymmetric responses. The imperfections of the tested objects are an additional source of uncertainty with respect to the intrinsic chaotic character of the rigid body motion, which is a crucial factor that prevents the reproducibility of the tests and induces discrepancies between specimen responses and those of their ideal models. A contactless measurement strategy is employed to assure unaltered data acquisition. The experimental campaign includes free vibration tests, pulse excitation, and natural ground motions tests; the dynamic responses of the specimens are organized and rearranged, aiming at providing a comprehensive set of data that could be employed for calibrating numerical models accounting for imperfect conditions. The damping properties of the specimens are discussed, providing a novel estimation of the coefficient of restitution based on the free vibration tests. The limits of the ideal simple rigid model are highlighted, and the roles of size factor and aspect ratio are discussed according to the obtained results.

GROUND DEFORMATION ANALYSIS USING BASIC PRODUCTS OF THE COPERNICUS GROUND MOTION SERVICE

Abstract. Monitoring ground deformation at national and regional level with millimetre-scale precision, nowadays, is possible by using Advanced Differential Interferometric SAR (A-DInSAR) techniques. This study concerns the results of the European Ground Motion Service (EGMS), part of the Copernicus Land Monitoring Service, which detects and measures land displacement at European scale. This Service provides reliable and consistent information regarding natural ground motion phenomena such as landslides and subsidence. The ground motion is derived from Synthetic Aperture Radar (SAR) time-series analysis of Sentinel-1A/B data. These data, which provide full coverage of Europe from two different observation geometries (ascending and descending) every six days, are processed at full resolution. The paper is focused on the exploitation of the basic product of EGMS for both regional and local purposes. Analysing the slope and aspect of the deformation field is the novelty of this investigation. In particular, the focus is put on the generation of wide-area differential deformation maps. Such maps indicate the gradient of the deformation field. The obtained information is not only beneficial for monitoring anthropogenic phenomena but also vital for urban management and planning. Most of the significant damages to manmade structures and infrastructures are associated with high deformation gradient values. Thus, monitoring the temporal and spatial variations of deformation gradient is essential for dynamic analysis, early-warning, and risk assessment in urban areas. Although EGMS productions are prepared for monitoring at regional level, their resolutions are high enough to investigate at local level. Therefore, this paper considers the local deformations that affect single structures or infrastructures. Local differences in such deformation can indicate damages in the corresponding structures and infrastructures. We illustrate these types of analysis to generate differential deformation maps using datasets available at CTTC.

Archaeoseismological project in Ostia: Tracking evidence on seismic damage by nonlinear numerical simulations

Within the framework of an archaeoseismological project in Ostia (Italy), this paper discusses archaeological evidence of historic seismic damage of one of the arcade pillars in a building originally used as a warehouse for goods - “Piccolo Mercato” - located in the North-West part of the archaeological site. This interdisciplinary study is aimed at providing an interpretation of the detected damage by performing some numerical simulations. One of the pillars was represented by a finite element (FE) model, considering natural ground motion records. FE model allowed to conduct complete nonlinear time-history analyses. The results cross-validate the already provided interpretation of the historic damage, and suggest a possible dateline.

Optimal design of Magnetorheological damper for seismic response reduction of Base-Isolated structures considering Soil-Structure interaction

The base isolation technique is a well-known strategy used for the seismic protection of structures. It introduces a highly deformable device between the structure and the foundation to isolate the main structure from the ground motions. Despite the continuous enhancement of base isolation techniques, the limitations of this strategy are well known to researchers and engineers. Base isolation systems undergo large displacement under strong earthquake motions, which usually results in structural damage and users’ discomfort. In this study, a magnetorheological (MR) damper is used to improve the performance of a benchmark base-isolated building by placing the MR damper between the base of the structure and the foundation. The soil-structure interaction (SSI) effect is included in the study by considering three types of soil, denoted dense, medium, and soft. The soil is introduced through two degrees of freedom, namely, sway and rocking, based on the cone simplified linear model. The MR damper parameters are optimized using a particle swarm optimization (PSO) algorithm under a set of benchmark earthquake records. The optimal local parameters related to each benchmark earthquake and soil type are averaged to obtain general optimum parameters. The acquired general optimum parameters are then used to study the dynamical response of the benchmark base-isolated building controlled by the MR damper, considering an array of 100 natural earthquake ground motions. The obtained results show an enhancement of the dynamic response under all soils conditions compared to non-optimized and base isolation only scenarios. Several engineering demand parameters (EDP) and response indicators were investigated in this study, including top floor and base displacements, inter-storey drift, storey drift, top floor acceleration, and base shear. The results obtained show the effectiveness of the optimization in improving the response of base-isolated structures. It also demonstrates the dependence of damper parameters on soil typologies.

Optimum design of tuned mass damper with pinched hysteresis under nonstationary stochastic seismic ground motion

The optimum design of a recent tuned mass damper with pinched hysteresis (TMD-PH) for seismic protection of structures is here investigated. The considered device consists of mixed NiTiNOL-steel wire ropes undergoing combined tension-flexure cycles. Previous studies demonstrated that concurrent interwire friction and phase transformation of the shape memory material exhibited by these composite wire ropes generate a peculiar pinched hysteretic behavior, which can be well described by means of a modified Bouc–Wen model. A stochastic-based optimum design methodology is here proposed for such TMD-PH, which is tailored to determine the best design parameters for the seismic protection of general structural systems. The seismic ground motion is modeled as a filtered nonstationary random process whereas the inherent pinched hysteresis of the device is dealt with via the stochastic linearization technique. The expressions of the linearization coefficients are obtained ad hoc and the optimum design of the TMD-PH is formulated as box-constrained single-objective optimization problem. Three objective function formulations are considered to reflect alternative design philosophies, namely, displacement-, acceleration- and energy-based design strategies. Unlike most literature studies addressing the optimum design of vibration absorbers via finite difference-based numerical schemes or non-gradient-based metaheuristic methods, the search for the optimal parameters of the TMD-PH is here performed by means of an iterative semi-analytical gradient-based numerical technique in which the derivatives for the covariance matrix of the system response are calculated analytically. A comprehensive numerical campaign is finally presented. First, a parametric study is carried out to evaluate the effects of the protected system characteristics and those of the seismic ground motion duration on the optimal parameters and performance of the device under consideration. The performance of the TMD-PH optimized according to the proposed methodology is also assessed in the context of a practical case study which makes use of synthetic and natural seismic ground motion records.

Analysis of bilinear hysteretic structures with nonlinear fluid viscous dampers using modified stochastic linearization technique

Viscous dampers are increasingly used to design seismic resistant structures in modern construction due to their ability to reduce structural and non-structural damage by absorbing a large portion of the earthquake input energy. To facilitate the design of such complex nonlinear systems, this study aims to propose new non-Gaussian probability density functions (PDFs) to improve the accuracy in the determination of the seismic response of bilinear hysteretic structures equipped with linearized nonlinear viscous dampers. The employed linearization method is based on a stochastic linearization technique using stationary response velocity PDFs, while the difference between the governing nonlinear differential equation and the equivalent linear equation is minimized. To generate suitable functions, a Genetic Algorithm (GA) optimization method is adopted for both hard and soft soil-based structures equipped with nonlinear viscous dampers using three different power coefficients. The computational error of the employed modified stochastic linearization technique is then evaluated for single-degree-of-freedom (SDOF) systems under a set of five thousand randomly generated earthquake excitations with peak ground accelerations (PGAs) of 0.2 g to 0.6 g. The results indicate that the proposed method can significantly reduce (up to 80%) the computational errors. Subsequently, the lateral roof displacements of 5-story structures equipped with nonlinear viscous dampers are obtained under a set of natural ground motions using different linearization methods. It is shown that the proposed functions lead to the least error for both hard and soft soil-based structures compared to the accurate results.

Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow (<30 m) across the island, bedrock shear wave velocities have a significant influence on the impedance contrast and amplifications. Bedrock shear wave velocity is usually very variable due to the differences in rock formations, level of weathering and fracturing. The level of this uncertainty is shown to be greatly decreased when rock quality designation (RQD) data, common information when bore hole data are logged, is available since it is highly correlated with both shear and compression wave velocities. The results are used to derive region-specific site amplification factors as a function of both Vs30 and site fundamental frequency and compared to those of the National Building Code of Canada (2015). The results of the study indicate that there are large uncertainties associated with these parameters due to variability in soil profiles, soil properties and input seismic ground motions. Average and confidence intervals for the mean and for predictions of amplification factors are calculated for each site class to quantify this uncertainty. Amplifications normalized relative to class C are obtained by accounting for the correlation between site class amplifications for given ground motions. Non-linearity in the analysis of equivalent linear 1-D site response is taken into account by introducing the non-linear G/Gmax and damping ratios curves. In this method, it is assumed that the shear strain compatible shear modulus and damping ratio values remains constant throughout the duration of the seismic excitation. This assumption is not fully applicable to a case when loose saturated soil profile undergo heavy shaking (PGA > 0.3 g). In this study, all simulations with input motion PGA >0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.

Reconciling Eurocode 8 Part 1 and Part 2 Two-component Record Selection

ABSTRACT Eurocode 8 (EC8) allows the use of dynamic analysis for the design and assessment of structures and provides some constraints for the selection of acceleration time-histories as seismic input. However, when it comes to the selection of two-horizontal-component natural ground motion records, parts 1 and 2 of EC8, stipulate apparently different criteria. The first aim of this paper is to build up on previous studies and investigate whether this difference in provisions translates into the selection of systematically different sets of records. A series of record selection case-studies presented in this study, corroborate the preliminary findings of previous work, and show that this is not the case, that is, record sets chosen according to one group of criteria tend to satisfy the other by default. A second aim is to investigate the different options for selecting multi-component ground motion records in part 1, which turn out to be equivalent. Finally, a third issue tackled is the effect that different definitions of spectral acceleration, that the design spectrum refers to, can have on spectrum-compatible record selection, when two horizontal components are involved. The results indicate that, for some of these alternative definitions, such as maximum or random component spectral acceleration, sets obtained via direct spectrum compatibility may not always agree with a simple application of Eurocode 8 provisions. On the other hand, when spectral acceleration is defined as the geometric mean of the two components, consolidated record selection algorithms appear to guarantee spectrum compatibility.

Improved damping reduction factor models for different response spectra

The rationality and reliability of the damping reduction factor are of great significance to the seismic design of building structures. However, the values of damping reduction factor predicted by the existing models have great dispersions, which are mainly related to the regression model and the considered influencing factors. Based on the linear time history analysis of a single-degree-of-freedom system under 4716 ground motions, the influence degrees of the damping ratio, the natural vibration period, the ratio between the ground predominant period and the natural vibration period, the earthquake magnitude, the rupture distance, the site type (the average shear wave velocity in the top 30 m of soil), the significant duration, and the peak ground velocity to acceleration ratio (PGV/PGA) on the damping reduction factor are evaluated by the Spearman rank correlation coefficient. After that, improved damping reduction factor models are respectively proposed for different response spectra, in which only the damping ratio and the natural vibration period are considered as variables. Through the comparison with the existing damping reduction factor models and the robustness test under different natural ground motions, the improved damping reduction factor models are proved to have a reasonable expression form and strong robustness, which can accurately predict the damping reduction factors for different response spectra.

Nonlinear soil effects on observed and simulated response spectra

AbstractSoil effects are collectively referred to the influences that local geology and morphology of soil deposits have on ground motions coming from bedrock. The quantification of soil effects in building codes has a great impact in the design of structures because soil factors amplify the reference seismic input, which is typically defined for rock‐type soil class from probabilistic seismic hazards analysis. This topic, within earthquake engineering, represents one of the typical interfaces between structural engineering, geotechnical engineering and engineering seismology. In fact, this issue is generally addressed with different approaches depending on the background of the researchers. This article investigates soil effects combining the viewpoints of structural and geotechnical engineers and seismologists. It is shown that the averaging technique adopted for the definition of ground motion predictive models for spectral ordinates does not play a significant role in defining the results of rock‐like soil classes. However, for other soil classes characterized by soil effects, different methods of averaging the spectral ordinates produce significant differences. The main result of this study is the proposal of a new analytical formulation for the quantification of soil amplification factors for both acceleration and displacement response spectra. The proposed formulation is based on a database of real ground motions and simulated accelerograms. The latter have been obtained through stochastic ground response analyses, with the propagation of natural ground motions on rock‐like soil class through randomly generated soil deposits representative of different soil classes of Eurocode 8 and the Italian Building Code. The comparison between real and simulated data revealed the crucial role of soil nonlinearity in the definition of soil effects, which is also in relation with the variation of magnitude, fault distance and the intensity measures expected on outcropping rock.

A new modified stochastic linearization technique to analyze structures with nonlinear fluid viscous dampers

Nonlinear viscous dampers can efficiently improve the seismic performance of structures by dissipating large amounts of earthquake-induced energy. In common practice, the spectral analysis of structures with nonlinear viscous dampers is generally conducted based on an estimated equivalent damping ratio. To this end, the stochastic linearization technique can be used as an effective probabilistic approach to take into account the evolutionary characteristics of the input earthquake excitation. This study aims to present optimal non-Gaussian probability density functions to improve the accuracy of the stochastic linearization technique for nonlinear viscous dampers in both firm and soft soil-based structures. It is shown that by using the optimum probability density functions, the computational error of the stochastic linearization technique for a single-degree-of-freedom structure under simulated ground motions, with a range of peak ground accelerations between 0.1 and 0.6 g, is reduced by up to 70%. The efficiency of the proposed probability density functions is then demonstrated for multi-degree-of-freedom structures, by estimating the roof displacements of a six-story steel frame with nonlinear viscous dampers under a set of natural ground motions using different linearization methods. The comparison of the stochastic linearization technique estimated responses with the exact values confirms that using the proposed probability density functions leads to considerably lower errors in both firm and soft soil-based structures compared with the other linearization techniques.

Comparison of Novel Seismic Protection Devices to Attenuate the Earthquake Induced Energy

This study addresses an alternative use of viscous dampers (VDs) associated with buckling restrained braces (BRBs) as innovative seismic protection devices. For this purpose, 4-, 8- and 12-story steel bare frames were designed with 6.5 m equal span length and 4 m story height. Thereafter, they were seismically improved by mounting the VDs and BRBs in three patterns, namely outer bays, inner bays, and all bays over the frame heights. The structures were modeled using SAP 2000 software and evaluated by the nonlinear time history analyses subjected to the six natural ground motions. The seismic responses of the structures were investigated for the lateral displacement, interstory drift, absolute acceleration, maximum base shear, and time history of roof displacement. The results clearly indicated that the VDs and BRBs reduced seismic demands significantly compared to the bare frame. Moreover, the all-bay pattern performed better than the others.

Seismic rocking effects on a mine tower under induced and natural earthquakes

Recent research in engineering seismology demonstrated that in addition to three translational seismic excitations along x, y and z axes, one should also consider rotational components about these axes when calculating design seismic loads for structures. The objective of this paper is to present the results of a seismic response numerical analysis of a mine tower (also called in the literature a headframe or a pit frame). These structures are used in deep mining on the ground surface to hoist output (e.g. copper ore or coal). The mine towers belong to the tall, slender structures, for which rocking excitations may be important. In the numerical example, a typical steel headframe 64 m high is analysed under two records of simultaneous rocking and horizontal seismic action of an induced mine shock and a natural earthquake. As a result, a complicated interaction of rocking seismic effects with horizontal excitations is observed. The contribution of the rocking component may sometimes reduce the overall seismic response, but in most cases, it substantially increases the seismic response of the analysed headframe. It is concluded that in the analysed case of the 64 m mining tower, the seismic response, including the rocking ground motion effects, may increase up to 31% (for natural earthquake ground motion) or even up to 135% (for mining-induced, rockburst seismic effects). This means that not only in the case of the design of very tall buildings or industrial chimneys but also for specific yet very common structures like mine towers, including the rotational seismic effects may play an important role.

Elastogravity Waves and Dynamic Ground Motions in the Korean Peninsula Generated by the March 11, 2011MW9.0 Tohoku‐Oki Megathrust Earthquake

AbstractThe mass dislocations caused by large coseismic slips in megathrust earthquakes are large enough to produce elastogravity waves. Despite, successful identification of elastogravity‐wave development during megathrust earthquakes, the nature of ground motions and hazard potentials in regional and teleseismic distances remains unknown. The dynamic ground motions from the March 11, 2011MW9.0 Tohoku‐Oki megathrust earthquake are retrieved from broadband seismic records throughout the Korean Peninsula. The dynamic ground motions of the megathrust earthquake are dominated by low‐frequency (<0.1 Hz) energy that is a mixture of elastogravity waves and seismic waves. The peak dynamic ground displacements in the Korean Peninsula reached ∼20 cm with horizontal permanent displacements of ∼2 cm or more. Radially‐polarized elastogravity waves developed instantly at the event origin time. Very‐long‐period (<0.004 Hz) energy is a mixture of seismic waves and coseismic permanent displacements, presenting radially polarized retrograde particle motions for ∼600 s. The peak ground displacements (PGDs) and velocities for the Tohoku‐Oki earthquake are larger than those for a localMW5.4 earthquake. The peak ground motions vary azimuthally following the source radiation pattern. The tangential PGD increases with distance along continental ray paths due to the development of crustally guided waves. Large and slow dynamic ground motions cause dynamic stress changes of ∼1.8 MPa in the lithosphere of the Korean Peninsula, while the properties of the mantle are scarcely affected by slow dynamic motions. The large long‐period displacements induced by megathrust earthquakes may cause considerable long‐duration distortion on large buildings at regional and teleseismic distances. The characteristic elastogravity‐wave features may be used for detection of mass‐dislocation events.

Effects of mainshock-aftershock sequences on fragility analysis of RC buildings with ageing

This paper presents the seismic vulnerability assessment of existing RC buildings designed according to previous non-seismic codes that are exposed to various levels of corrosion and mainshock-aftershock sequences. A refined finite element model of an existing four-storey reinforced concrete building is adopted. Twenty as-recorded natural ground motions are collected from international databases to perform incremental dynamic analyses for the inelastic response of the testbed building. The effects of corrosion are applied on external beams and columns to simulate a realistic exposure. The robust fragility assessment is conducted for a range of seismic intensity measures. Moreover, a new intensity measure, based on the modified acceleration spectrum intensity, is proposed. Such seismic parameter accounts for the elongation period experienced by structures during earthquake events and appears to be more reliable and accurate for corroded RC structures than the most adopted peak ground acceleration and spectral acceleration at the first natural period. The results of the comprehensive numerical simulations contribute to providing relevant indications on the non-linear response of existing corroded buildings under multiple excitations and, highlight that current seismic codes are no longer conservative for such detrimental phenomena.

Analytical investigation of the seismic response of elastic oscillators placed on the top of rocking storey

In the present study the seismic response of elastic single degree of freedom oscillators placed on the top of a rocking storey is examined. A storey comprised of columns that may uplift under ground motion excitations can be regarded as an innovative and cost effective base isolation technique. Regarding the podium structural systems, apart from studying the rocking response in order to avoid the rocking overturn, it is important to examine the seismic demand on the superstructure so as to assess the rocking storey as base isolation system. From this point of view, structural as well as ground motion parameters that affect the seismic demands of the superstructure are examined. For this purpose, the superstructure’s response spectra, of various structural configurations, under free rocking response, analytical pulses and natural ground motions are presented and discussed. Finally, the effect of different assumptions regarding energy dissipation during impact on the response of the superstructure is investigated. The study of the podium structures results in useful remarks concerning the performance of the rocking storey as a base isolation system.

Seismic performance of dual systems coupling moment‐resisting and buckling‐restrained braced frames

SummaryBuckling‐restrained braces (BRBs) have proven to be very effective in improving the seismic performance of existing and new structures. They provide strength, stiffness and add energy dissipation to the structure. However, being BRBs characterized by a low post‐elastic stiffness, their use may lead to residual deformations hindering the building's reparability and to excessive cumulative ductility demand possibly compromising the residual capacity of BRBs. To overcome these drawbacks, BRB frames (BRBFs) can be coupled with moment‐resisting frames (MRFs) to form dual systems. If properly designed, MRFs acting as back‐up frames allow the control of the residual drifts and the optimization of the performance of the BRBs. The contribution of this study is to provide insights into the performance and residual capacity of BRBFs‐MRFs dual systems and to shed light on the influence of the main BRB's design parameters. To this end, a nondimensional formulation of the equation of motion is introduced for a single degree of freedom system, and an extensive parametric study is performed for a set of natural ground motion records with different characteristics and scaled to various intensity levels. This allows the investigation of a wide range of configurations, considering different levels of the relative strength and ductility demand of BRBFs and MRFs, and obtains useful information for their design. Finally, two case study frames, modeled as two‐dimensional nonlinear multi‐degree of freedom systems, are analyzed, and the results were compared to those obtained from the nondimensional formulation to show the capabilities and the limitations of the adopted methodology and of the SDOF approximation.

Influence of the breakaway friction on the seismic response of buildings isolated with curved surface sliders: Parametric study and design recommendations

The breakaway friction coefficient of curved surface sliders (CSSs) governs the transition between the sticking and the sliding behavior of the isolators, and hence affects the response of an isolated building during an earthquake. When the inertia forces induced by low-to-moderate intensity excitations are not able to overcome the breakaway frictional resistance of the CSS isolation system, the structure behaves as a fixed-base building, thus experiencing higher accelerations, interstorey drifts and internal forces than the isolated building. The majority of structural analysis programs disregard the static coefficient of friction, and implement the dynamic friction coefficient only throughout the response history analysis, which may imply an increased prediction of displacement demand for the isolation system but may lead to an unsafe design for the superstructure. In this paper, the frictional resistance to sliding before the breakaway is simulated through a bidirectional plasticity domain, which has been coded in a finite element of the isolator formulated in OpenSees to incorporate the transition between the breakaway friction in the sticking phase and the velocity-dependent friction model in the subsequent sliding phase. Based on this formulation, the influence of the breakaway friction on the response of buildings isolated with CSSs is investigated numerically through an extensive parametric study comprising more than 9000 bidirectional nonlinear time history analyses (NLTHAs). The parameters cover a range of friction coefficients, superstructure properties and a large group of natural spectrum-compatible bidirectional ground motions having different intensity levels and frequency contents. The results from NLTHAs are processed statistically to elaborate regression formulae and design recommendations that can be useful to predict the trigger acceleration at which sliding motion starts, as well as to suggest how to achieve more accurate estimates of the seismic response when the breakaway friction is ignored in the structural analysis model.

Effectiveness of the displacement-based seismic performance assessment for continuous RC bridges and proposed extensions

Seismic performance assessment of existing bridges, especially those designed without seismic criteria, is paramount in earthquake-prone countries. To perform this task, the Displacement-Based Assessment (DBA) represents a satisfactory trade-off between simplicity and accuracy. After describing the modal analysis-based DBA procedure, a static-based alternative is proposed in this paper, considering its strengths and limitations. Moreover, an extension of the procedure is proposed to derive the force-displacement curve of the bridge (pseudo-pushover capacity curve). The effectiveness of the DBA methodology, implemented via simplified mechanical models, is discussed through parametric analyses to address its practical applications. The DBA approach, both modal and static, is herein adopted for the transverse analysis of a set of 36 reinforced concrete continuous-deck bridges up to six spans, with pier height in the range 8–20 m and two different values of the deck transverse stiffness. Additional sensitivity analyses (24 case studies) are conducted to investigate the accuracy of the two approaches considering: 1) the length of the bridge, 2) the amount of longitudinal reinforcement in the piers; 3) different pier typologies. The results are compared to numerical pushover and time-history analyses using three suites of 10 scaled, natural ground motions respectively consistent with low-, medium- and high-seismicity sites. For the majority of the case studies, the resulting performance assessments fall within one standard deviation of the results of the time-history analyses. For this reason, the displacement-based modal or static approaches can represent a valid alternative to numerical non-linear static analyses for continuous bridges with six spans or less.

Prof. Comparing H2 and H∞ Algorithms for Optimum Design of Tuned Mass Dampers under Near-Fault and Far-Fault Earthquake Motions

In this study, the robust optimum design of Tuned Mass Damper (TMD) is established. The H2 and H∞ norm of roof displacement transfer function are implemented and compared as the objective functions under Near-Fault (NF) and Far-Fault (FF) earthquake motions. Additionally, the consequences of different characteristics of NF ground motions such as forward-directivity and fling-step are investigated on the behavior of a benchmark 10-story controlled structure. The Colliding Bodies Optimization (CBO) is employed as an optimization technique to calculate the optimum parameters of the TMDs. The resulting statistical assessment shows that the H∞ objective function is rather superior to H2 objective function for optimum design of TMDs under NF and FF earthquake excitations. Finally, the robustness of the designed TMDs is evaluated under a large set of natural ground motions.