Earthquake Engineering Analysis Research Articles

Effect of hemp bio composite strengthening on masonry barrel vaults damage

Masonry vaults are common structural elements of the Italian architectural heritage, significantly vulnerable to seismic loads. For this reason strengthening is often required. In the last decade, the use of traditional reinforcement techniques has been progressively replaced by Fiber Reinforced Polymers (FRP) bonded at the vault extrados/intrados. However, this approach has shown drawbacks mainly associated to the polymeric nature of matrix and physical compatibility between the matrix and the masonry support. Consequently, FRP strengthening evolved to innovative composite materials obtained by cement based matrix, i.e. Fiber Reinforced Cementitious Matrix (FRCM). Moreover, within the growing environmental sustainability issues, the scientific research is focusing on the development of biodegradable composite materials, based on vegetal fibers and natural matrices. This paper presents the results of experimental tests on two full-scale masonry vaults with the same geometry and mechanical properties: one is unreinforced and one is reinforced at the extrados by continuous bidirectional hemp ropes bonded in a layer of cocciopesto matrix (i.e. a mix of ground clay bricks and organic binder). The two models were built and tested in the 3D shaking table system of the Laboratory of Earthquake Engineering and Dynamic Analysis (LEDA) at Enna Kore University. Each vault was subjected to seismic loads and dynamic identification tests: the seismic load was given with increasing amplitude at the base of the two models while the dynamic identification tests were carried out after each seismic sequence in order to evaluate the variation of the dynamic properties, testifying structural damage. The strengthening effectiveness was assessed by comparing the damages detected on the unreinforced and reinforced masonry vaults. Results showed that the proposed bio composite strengthening material is effective for improving the seismic performance of masonry vaults.

Design of a Biaxial Laminar Shear Box for 1g Shaking Table Tests

In this paper, the design of a new laminar shear box at the Laboratory of Earthquake Engineering and Dynamic Analysis (L.E.D.A.) of the University of Enna “Kore” (Sicily, Italy), is presented. The laminar box has been developed to investigate the liquefaction phenomenon and to validate advanced numerical models and/or the numerical approaches assessed to simulate and prevent related effects. The first part of the paper describes in detail the types of soil containers that have been used in the last three decades around the world. Particular attention is paid to laminar shear box and liquefaction studies. Moreover, the most important factors that affect the performance of a laminar shear box are reported. The last part of the paper describes components, properties, and design advantages of the new laminar shear box for 1g shaking table tests at L.E.D.A. The new laminar box has a rectangular cross section and consists of 16 layers. Each layer is composed of two frames: an inner frame and an outer frame. The inner frame has an internal dimension of 2570 mm by 2310 mm, while the outer frame has an internal dimension of 2700 mm by 2770 mm. Between the layers, there is a 20 mm gap, making the total height 1600 mm.

Quantifying seismic response uncertainty of electrical substation structures using endurance time method

A new procedure is proposed to quantify uncertainties involved in the seismic response of structures including ground motion and modeling variability. The advent of performance-based earthquake engineering (PBEE) and probabilistic seismic risk analysis necessitates consideration of uncertainties in predicting seismic responses. However, the high computational cost of conventional methods restricts their application to only simple numerical models. The present study employs the endurance time (ET) method concept to predict the response distribution which requires much less computational efforts than conventional methods. The proposed procedure for the quantification of record-to-record variability uses adaptation of the ET excitation function’s response spectrum with those of ground motions in a range of structural natural period. The proposed procedure for the quantification of modeling variability is a sampling-based approach in which ET analysis is carried out on randomly generated structural models. The application of the methods is investigated in predicting the response distribution of two electrical substation structures. The results are compared with the benchmark methods such as incremental dynamic analysis (IDA) in order to evaluate the accuracy level of the method. It is found that the proposed method can predict the distribution of responses with less than 15% discrepancy relative to the benchmark method at the majority of intensity levels, while the computational effort reduces more than 15 times compared to the benchmark method. Thus, the proposed method provides a strong tool extending the application of the performance-based design in structures with a reasonable computational cost.

Structural topology optimization of tall buildings for dynamic seismic excitation using modal decomposition

Structural topology optimization has been successfully investigated to improve the designs of a variety of civil, mechanical and aerospace applications. While topology optimization for static loading is fairly well developed, methods for dynamic seismic loading remain a challenge. In this paper, dynamic topology optimization methods are reviewed and contrasted, focusing on frequency domain techniques. Inspired by earthquake engineering analysis methods, a dynamic topology optimization formulation called the sum of modal compliances (SMC) is proposed. By considering multiple eigenmodes, the structural vibration is minimized for a seismic excitation, described by a response spectrum. The formulation handles design-dependent loading, due to inertial effects, by performing a series of design-independent topology optimization problems, between which, the seismic modal load vector is updated. Applications for the lateral bracing of high-rise buildings on 2D and 3D examples demonstrate the capabilities of the procedure and conceptual understanding of optimization for seismic loading. Results demonstrate that the optimized topology is influenced by the earthquake frequency content, which is dependent on the soil and seismological effects beneath the structure.

Seismic fragility functions for slope stability analysis with multiple vulnerability states

The seismic performance and stability analysis of slopes are important in predicating damage and mitigating potential losses in landslide-prone areas. Fragility functions can give results of slope performance assessment that are more comprehensive and richer. This study presents a procedure of constructing seismic fragility functions for slope stability analysis with various vulnerability states based on incremental dynamic analysis (IDA). IDA is a performance-based earthquake engineering analysis based on a series of dynamic time history analyses conducted for suitable multiple-scaled seismic records. IDA not only estimates the seismic demand and capacity of systems but also provides basic data for the estimation of fragility functions. Firstly, an ensemble of seismic records meeting the requirements of specific site conditions of a slope is selected to consider the randomness of ground motion. A series of seismic stability analyses of the slope are performed to obtain the dynamic safety factor time history of the slope. Each minimum safety factor and corresponding seismic intensity measure is then extracted to develop a set of IDA curves. On the basis of IDA results, analytical seismic fragility functions of a slope are developed considering the prescribed various vulnerability states of the slope in terms of the safety factor. The failure probabilities of exceeding different specific vulnerability states for a given intensity measure of the earthquake are finally obtained.

Updated evaluation metrics for optimal intensity measure selection in probabilistic seismic demand models

This study proposes an update on the criteria that are typically used to select the optimal intensity measures (IMs) for development of probabilistic seismic demand models (PSDMs), which relate the input seismic hazard and structural responses. Employing an optimal IM contributes to decreasing the uncertainty in the PSDMs, which, in turn, increases the reliability of the PSDMs used in performance-based earthquake engineering analyses. In the literature, the optimality of the IMs is generally evaluated by the following metrics: efficiency; practicality; proficiency, which is the composite of efficiency and practicality; sufficiency; and hazard computability. The present study shows that the current criteria for evaluating the practicality and proficiency features may mislead the selection of the optimal IM when IMs with different ranges and magnitudes are investigated. Moreover, the efficiency metric can provide biased results when comparing IMs for predicting demands of different structural components or types of systems. As a result, alternative solutions are proposed to investigate the efficiency, practicality, and proficiency features of the IMs. The suggested metrics are employed in a case study to evaluate the IMs used to develop PSDMs for multi-span continuous steel girder bridges in Texas subjected to human-induced seismic hazard.

OpenSees Three-Dimensional Computational Modeling of Ground-Structure Systems and Liquefaction Scenarios

The OpenSees computational platform has allowed unprecedented opportunities for conducting seismic nonlinear soil-structure interaction simulations. On the geotechnical side, capabilities such as coupled solid-fluid formulations and nonlinear incremental-plasticity approaches allow for representation of the involved dynamic/seismic responses. This paper presents recent research that facilitated such endeavors in terms of response of ground-foundation-structure systems using advanced material modeling techniques and high-performance computing resources. Representative numerical results are shown for large-scale soil-structure systems, and ground modification liquefaction countermeasures. In addition, graphical user interface enabling tools for routine usage of such 3D simulation environments are presented, as an important element in support of wider adoption and practical applications. In this context, Performance-Based Earthquake Engineering (PBEE) analysis of bridge-ground systems is highlighted as an important topical application

Fiber-hinge modeling of engineered cementitious composite flexural members under large deformations

Engineered cementitious composites (ECC) and other ductile cement-based materials have emerged as alternative materials to traditional concrete to improve the damage resistance, deformation capacity, and energy absorption capacity of structures in seismic applications. Developing computationally efficient numerical models and simulation techniques to predict the nonlinear response of ductile concrete materials can improve the engineering community’s understanding of the performance of structures using these emerging materials. In this study, a numerical modeling strategy was developed, calibrated, and evaluated that can capture the cyclic response of reinforced ECC components under lateral load reversals at high deformations including component failure due to reinforcement fracture. A fiber-based lumped-plasticity model was adopted to simulate the non-linear response of reinforced ECC components. A simple expression for plastic-hinge length was developed to predict the force-deformation response and deformation associated with reinforcement fracture. Inaccuracies in the initial stiffness and cyclic response were mitigated by calibrating the rotational stiffness of an elastic spring and cyclic degradation parameters of a steel material model. The proposed modeling strategy was evaluated on 18 specimens using different cyclic deformation histories and reinforcement ratios. The modeling approach was compared to experimentally determined lateral strength, energy dissipation, deformation capacity, and longitudinal reinforcement strains to assess the accuracy of the strategy. This research provides a method to simulate the performance of ductile cement-based materials under large deformations, including collapse, and will improve the performance-based earthquake engineering analysis techniques for structures using ductile cementitious materials.

Estimation of Tail Distribution of the Annual Maximum Earthquake Magnitude Using Extreme Value Theory

The goal of many earthquake engineering analyses is to ensure that a structure can withstand a given level of ground shaking while maintaining a desired level of performance. But there is a great deal of uncertainty about the numerous factors that impact the level of ground shaking. probabilistic seismic hazard analyses (PSHA) aim to quantify these uncertainties and combine them to produce an explicit description of the distribution of future shaking that may occur at a site. Among others, the distribution of the magnitudes is required by PSHA. This paper presents a new approach to estimate both the tail distribution of earthquake magnitudes and the tail distribution of the maximum earthquake magnitude over a year. This approach uses extreme value models based on Poisson process. The main innovations consist of combining the use of the generalized Pareto distribution (GPD) to model the tail distribution of earthquake magnitudes and the exact relation leading to the tail distribution of the annual maximum earthquake magnitude. We also propose a statistical inference that takes into account the growing incompleteness of the data in earlier times, which enables us to use as much available data as we can. This paper also provides a sensitivity analysis, which quantifies the robustness of the results with respect to two types of uncertainty: the statistical uncertainty due to the limited number of data used for the statistical inference and the uncertainty related to the determination of the complete observation periods of time by the seismologists. We detail validation tests to check the main assumptions underlying the probabilistic model: the Poisson occurrences of earthquakes and the GPD behavior of the tail distribution. The methodology is applied to an area located in the south of France, which provides estimates of some extreme quantiles of the annual maximum earthquake magnitude.

Unification of Seismic Performance Estimation and Real Estate Investment Analysis to Model Post-Earthquake Building Repair Decisions

Post earthquake decisions on whether to repair or to demolish and rebuild a damaged commercial building can be influenced by factors other than repair costs. These factors include the property's ability to generate income and the conditions of the real estate market—factors not currently considered in seismic performance estimation models. This paper introduces a framework that unifies performance-based earthquake engineering and real estate investment analysis to model cases in which repair of damaged buildings is feasible, but redevelopment or leaving the building unrepaired and vacant might offer greater economic value. A three-stage approach for quantifying the likelihood of repair, redevelopment, or leaving the property vacant is proposed. First, building seismic performance analysis is conducted using FEMA P-58 and Resilience-based Earthquake Design Initiative (REDi) methodologies; then, given repair and redevelopment costs and times, the net present value decision rule is used to evaluate alternative outcomes; and finally, the results from the two stages are integrated to quantify the probability of different decisions. An illustrative case study of four reinforced concrete buildings highlights the insights provided by the proposed framework.

Liquefaction analysis and damage evaluation of embankment-type structures

The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction of embankment-type structures. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g., excessive settlements, lateral spreading and slope instability. The present work discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation’s soil liquefaction. A levee-foundation system is simulated, and the influence of characteristics of input ground motion, as well as of the position of liquefied layer on the liquefaction-induced failure, is evaluated. For the current levee model, its induced damage level (i.e., induced crest settlements) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. The respective role of input ground motion characteristics is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. A circular collapse surface is generated inside the liquefied region and extends toward the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no significant effect on the levee response is found. This research work provides a reference case study for seismic assessment of embankment-type structures subjected to earthquake and proposes a high-performance computational framework accessible to engineers.

An approach to quantify the influence of ground motion uncertainty on elastoplastic system acceleration in incremental dynamic analysis

Inclusion of ground motion–induced uncertainty in structural response evaluation is an essential component for performance-based earthquake engineering. In current practice, ground motion uncertainty is often represented in performance-based earthquake engineering analysis empirically through the use of one or more ground motion suites. How to quantitatively characterize ground motion–induced structural response uncertainty propagation at different seismic hazard levels has not been thoroughly studied to date. In this study, a procedure to quantify the influence of ground motion uncertainty on elastoplastic single-degree-of-freedom acceleration responses in an incremental dynamic analysis is proposed. By modeling the shape of the incremental dynamic analysis curves, the formula to calculate uncertainty in maximum acceleration responses of linear systems and elastoplastic single-degree-of-freedom systems is constructed. This closed-form calculation provided a quantitative way to establish statistical equivalency for different ground motion suites with regard to acceleration response in these simple systems. This equivalence was validated through a numerical experiment, in which an equivalent ground motion suite for an existing ground motion suite was constructed and shown to yield statistically similar acceleration responses to that of the existing ground motion suite at all intensity levels.

Physics-based seismic input for engineering applications: a case study in the Aterno river valley, Central Italy

In this paper, we present 3D physics-based numerical simulations, in the near-source region at the regional scale, of the 2009, April 6, L’Aquila earthquake (central Italy), based on improved models of the Aterno river basin geology and source kinematics. The simulations were carried out by an open-source code, SPEED, based on a discontinuous Galerkin spectral element method. The numerical mesh of the Aterno basin was built on a detailed subsurface geological model and on the evaluation of the dynamic properties of the soils. The source model was selected among the kinematic solutions available in the literature as the one that fits best the near-source observations. Broadband ground motions were then generated through a hybrid method, combining 3D low frequency waveforms with high-frequency stochastic synthetics. To provide an example of application as seismic input to earthquake engineering analyses in the time domain, results of this approach were used for 2D site response analyses at Castelnuovo, a village severely damaged by the earthquake, and in the neighborhood of which no seismic record was available. SPEED simulation satisfactorily reproduces the recorded accelerograms in the frequency range 0.1–0.7 Hz. The site response analysis at the local scale shows that the amplification of the hill is more significant at its natural frequency, due to topographic and stratigraphic factors, than at the peak of the seismic input simulated by SPEED, that is at about 3 s along the fault-normal component. The presented application supports the conclusion that 3D physics-based numerical simulations do have the potential to become an alternative for determination of input ground motion for earthquake engineering analyses, especially for those scenarios for which real records are not available.

О связи уравнений относительного и абсолютного движения при дифференцированном сейсмическом воздействии

When a structure is subjected to a differentiated seismic impact, each of its support points is characterized by different functions of displacements, velocities and accelerations as it moves with the ground. The main purpose of this article is to show how a multidimensional kinematic impact can be converted to a form suitable for carrying out standard earthquake engineering analysis, i.e., how it is expressed in terms of translation seismic forces and seismic intensity. A description of differentiated impact in the form of a field of kinematic parameters is presented. A definition of seismic impact intensity in terms of intensity at one of the support points (anchor point) and acceleration field alteration functions (according to Y.P. Nazarov's formulation) is given. A definition of translational motion is given, and the equations of motion in absolute and relative coordinates are obtained. In the equations of motion written in absolute generalized coordinates, seismic load is expressed in the form of forces defined as the product of the support elements system stiffness matrix by the vector of support displacements. It is shown that in the equations of motion written in relative coordinates, inertial seismic forces depend, as in case of using the traditional integral description of a seismic impact, on the seismic intensity at the anchor point. The theoretical formulas are illustrated using the example of a two-dimensional frame, for each support point of which individual functions of vertical, horizontal and angular displacements are specified.

Seismic fragility analysis of concrete dams: A state-of-the-art review

Given the recent impetus for probabilistic based analyses of dams, and the limited previous attempts to address this timely question, there is a need for a comprehensive assessment of the disparate previous work. Hence, this paper provides a comprehensive and comparative review of major (over twenty) publications addressing seismic fragility analyses of concrete dams.First, fundamental concepts are reviewed and clarified to facilitate comprehension of the later part. Then, papers are individually scrutinized, key figures redrawn to provide a uniform basis for comparison. When deemed necessary, additional clarifications and cross referencing with equations in the first part are provided.Next, tables summarizing the various methods are presented, on the basis of which the authors provide a set of minimum requirements for seismic fragility curve/surface development. It is noted that the vast majority of the papers still relied on linear analyses with simplified limit states. On the other hands few papers pursued a nonlinear approach and addressed the collapse mechanism and/or hybrid limit state definitions.Finally, the contextual framework within which fragility curves are used is presented within the scope of a performance based earthquake engineering analysis of a concrete dam.

Response to Professor John Hall's discussion of Hardyniec and Charney's paper, ‘An investigation into the effects of damping and nonlinear geometry models in earthquake engineering analysis’

SummaryThe discussion presents questions regarding the recommended damping scheme from the discussed paper and provides an alternative recommendation. The discussion also requests further explanation on behavioral differences between models incorporating the P‐delta and corotational approaches that are presented in the paper. Responses to these questions are presented. Copyright © 2016 John Wiley & Sons, Ltd.

An investigation into the effects of damping and nonlinear geometry models in earthquake engineering analysis

SummaryThe growing emphasis of considering the behavior of structures at extreme performance states, such as collapse, has necessitated the characterization of the effects of varying attributes of the structural model. One source of variability that has not previously been considered is variability in the mathematical model. This study investigated the effects of changing the geometric nonlinearity approach and damping model on a four‐story buckling restrained braced frame, a four‐story steel moment resisting frame, and an eight‐story steel moment resisting frame. The variations in behavior are quantified using the maximum interstory drift ratio as the performance metric and qualified by comparing the relative displaced shapes and component response histories at the collapse performance state. Copyright © 2015 John Wiley & Sons, Ltd.

Development of empirical and analytical fragility functions using kernel smoothing methods

SummaryFragility functions that define the probabilistic relationship between structural damage and ground motion intensity are an integral part of performance‐based earthquake engineering or seismic risk analysis. This paper introduces three approaches based on kernel smoothing methods for developing analytical and empirical fragility functions. A kernel assigns a weight to each data that is inversely related to the distance between the data value and the input of the fragility function of interest. The kernel smoothing methods are, therefore, non‐parametric forms of data interpolation. These methods enable the implicit treatment of uncertainty in either or both of ground motion intensity and structural damage without making any assumption about the shape of the resulting fragility functions. They are particularly beneficial for sparse, noisy, or non‐homogeneous data sets. For illustration purposes, two types of data are considered. The first is a set of numerically simulated responses for a four‐story steel moment‐resisting frame, and the second is a set of field observations collected after the 2010 Haiti earthquake. The results demonstrate that these methods can develop continuous representations of fragility functions without specifying their functional forms and treat sparse data sets more efficiently than conventional data binning and parametric curve fitting methods. Moreover, various uncertainty analyses are conducted to address the issues of over‐fitting, bias, and confidence intervals. Copyright © 2014 John Wiley & Sons, Ltd.

New Evidence and Perspective to the Poisson Process and Earthquake Temporal Distribution from 55,000 Events around Taiwan since 1900

Earthquake prediction is by all means controversial and challenging, given the fact that some recent catastrophic earthquakes went unpredicted. Not surprisingly, statistical approaches have been utilized to model earthquake randomness in time or space. One of the suggestions is that the earthquake’s temporal probability distribution should follow the Poisson model, which is suitable for rare events by definition. As a result, the customarily used hypothesis should be largely associated with the prior judgment that earthquakes are rare, but not as a result of abundant quantitative evidence or theoretical derivation. Therefore, this study aims to offer new empirical evidence to the hypothesis based on 110-year-long earthquake data around Taiwan. From the series of statistical tests, the first statistical inference is indeed in line with the model’s proposition: the level of fitting between observation and theory is better for earthquakes with a lower mean rate. To be more specific, it shows that the Poissonian hypothesis applied to local magnitude (ML)≥3.0 earthquakes around Taiwan with a mean annual rate as high as 1,600 is clearly rejected, but as far as ML≥7.0 earthquakes with a mean rate of 0.35 per year are concerned, the same hypothesis is statistically accepted for modeling their temporal randomness. Also, according to the tests on a variety of conditions, the annual rate of approximately 0.1 per year (or 10-year return period) was suggested as a reasonable empirical estimate for Poissonian rareness. Accordingly, from a practical point of view, it should be a robust analytical presumption to use the Poisson model in daily earthquake engineering analyses because the return period of design earthquakes is longer than 10 years, if not much longer.

Effects of Seismicity Models and New Ground-Motion Prediction Equations on Seismic Hazard Assessment for Four Canadian Cities

Seismicityratesandground-motionpredictionequations(GMPEs)arethe key uncertainties in probabilistic seismic hazard analysis (PSHA). We explore the impact of new findings and knowledge from seismological and ground-motion studies on seismic hazard assessment for eastern and western Canada. Updated information includes the reevaluation of seismicity rates and their interpretation in terms of seismic source zones and the use of new GMPEs. We refer to our model as an interim updated seismic hazard model, as it does not treat all uncertainties comprehensively; rather, we address the impact of key uncertainties. Based on our updated interim seismic hazard model, uniform hazard spectra (UHS) at four major cities across Canada are obtained and compared with UHS in the current seismic hazard maps of Canada (2005/2010), whicharebasedona1995seismichazardmodeldevelopedbytheGeologicalSurveyof Canada. Sensitivity analysis highlights the significant impact of seismicity smoothing in low-to-moderate seismic regions (eastern Canada), while GMPEs are important for all regions. Moreover, our interim updated seismic hazard model can readily produce seismic hazard curves as well as seismic hazard deaggregation results for various site conditionsandformultipleprobabilitylevels;thiscapabilityisessentialforcarryingout advanced earthquake engineering analyses.