Component Of Earthquake Research Articles

An earthquake-triggered submarine mass failure mechanism for the 1994 Mindoro tsunami in the Philippines: Constraints from numerical modeling and submarine geomorphology

Tsunamis have been known to result from a wide range of phenomena, such as earthquakes, volcanic eruptions, submarine mass failures, and meteorite impacts. Of earthquake-generated tsunamis, those arising from strike-slip mechanisms are less common, with the 1994 Mindoro tsunami in the Philippines among the few known examples. The 1994 Mindoro tsunami followed a Mw 7.1 earthquake along the right-lateral Aglubang River Fault. The tsunami affected the coasts surrounding the Verde Island Passage, one of the Philippines’ insular seas located between the islands of Luzon and Mindoro, and east of the West Philippine Sea margin. A total of 78 lives were lost due to the earthquake and tsunami, with 41 being directly attributed to the tsunami alone. Despite the close spatial and temporal association between the 1994 Mindoro earthquake and tsunami, previous numerical modeling suggests the need for other contributing mechanisms for the 1994 tsunami. In this study, we conducted submarine geomorphological mapping of the South Pass within the Verde Island Passage, with particular focus on identifying possible submarine mass failures. Identification of submarine features were based on Red Relief Image Map (RIMM), Topographic Position Index (topographic position index)-based landform classification, and profile and plan curvatures derived from high-resolution bathymetry data. Among the important submarine features mapped include the San Andres submarine mass failure (SASMF). The San Andres submarine mass failure has an estimated volume of 0.0483 km3 and is located within the Malaylay Submarine Canyon System in the Verde Island Passage, ∼1 km offshore of San Andres in Baco, Oriental Mindoro. We also explored two tsunami models (EQ-only and EQ+SMF) for the 1994 Mindoro tsunami using JAGURS. The source mechanisms for both models included an earthquake component based on the Mw 7.1 earthquake, while the EQ+SMF also included an additional submarine mass failure component based on the mapped San Andres submarine mass failure. Modeled wave heights from the EQ-only model drastically underestimates the observed wave heights for the 1994 Mindoro tsunami. In contrast, the EQ+SMF model tsunami wave height estimates were closer to the observed data. As such, we propose an earthquake-triggered, submarine mass failure source mechanism for the 1994 Mindoro tsunami.

Seismic Analysis of Steel Tanks Subjected to Transitional-Rotational Components of Earthquakes

ABSTRACT In this study, the response of the steel water storage tank considering the water-structure interaction under the effects of the transitional and rotational components of the earthquake as well as the soil-structure interaction was evaluated using the Eulerian-Lagrangian method. Seismic loading consisted of rotational and transitional components of the earthquake. Rotational components of the earthquake were first obtained using the transitional components. Then, the seismic analysis of the tanks considering four different tank models with empty and 90% full reservoirs and five different foundation models with and without considering the rotational components was done. Foundation flexibility and its effect on the structure performance were addressed by changing the foundation stiffness from the rigid to the very soft one. Water-structure interaction was considered in the analysis taking into account the fluid compressibility and the energy absorption boundaries. Results showed that in most cases by applying the rotational components, the maximum displacements and shear stress decreased. Maximum displacement reduction values for tanks with height to radius ratios of 0.4, 1, 2, and 3 for empty tanks are 51.62, 32.32, 24.0, and 23.79, respectively, and tanks with 90% full are 49.42, 42.86, 28.88, 26.74, respectively. Also, principle stress decreased in most cases, and in few cases, an increase was observed. This decrease in shear stress was far higher for empty reservoirs than full reservoirs. By increasing the tank height, reducing effects of the rotational components in the seismic response of the tanks reduced, and the structural responses with and without applying the rotational components got close to each other. Results also showed that the rotational components have a significant effect on the structural response in terms of changing the location of the maximum responses in whole cases as well as increasing the maximum response in a few cases.

Seismic analysis of liquid storage tank using oblate spheroid base isolation system based on rolling friction

The seismic isolation of ground-supported cylindrical liquid storage tank using the newly developed oblate spheroid base isolation (OSBI) system is investigated. The OSBI is an ellipsoidal-shaped isolator in both of its horizontal axes and dissipates seismic input energy in rolling friction apart from period lengthening achieved through the oblateness. The detailed mathematical formulation and governing dynamical equations of motion for a tank mounted on the non-linear OSBI are derived and analyzed using the numerical integration technique to unravel the underlying mechanics behind its dynamic behavior. An idealized mechanical model of the tank consists of three-lumped masses: convective, impulsive, and rigid. The dynamic responses are investigated for the tank subjected to uni-directional sinusoidal harmonic motion as well as to five time-varying, bi-directional horizontal components of earthquakes. The seismic response of the liquid storage tanks with the OSBI system is compared with that of the same tank either isolated using pure-friction (P-F) system or kept non-isolated. In order to understand the dynamic behavior of the tank mounted on the OSBI system, the influence of different isolator parameters such as eccentricity, coefficient of rolling friction, and aspect ratio of the tank are studied. The energy responses are also evaluated to assess the performance of the OSBI system. From the present study, it is found that the OSBI system is effective in mitigating the seismic response in the liquid storage tanks.

Vertical component effects of earthquake and soil-structure interaction on steel gabled frames

With an increase in the width of the steel gabled frame (SGF) span, in general, the structural mass considerably increases, as a result of which the vertical ground motions can exert significant inertial force on the members of a structure. Although numerous studies have confirmed the destructive effects of the vertical component of earthquake on concrete and steel structures, no research has been devoted to the impact of this component on steel gabled structures yet. Hence, the findings of this research will, at best, unveil possible new dimensions of these types of structures. Moreover, the investigation into the behavior of such structures with regard to the effects of soil-structure interaction (SSI) can help gain a more accurate understanding of their behavior. To this aim, in the present paper, an incremental dynamic analysis (IDA) was conducted for the first time on four SGFs with spans of 20 m and 60 m and heights of 6 m and 12 m with and without consideration of the vertical component of earthquake as well as SSI. Results were collected in the form of multi-record IDA curves, summarized IDA curves, fragility curves and probabilistic seismic demand analysis (PSDA) curves, indicating that the vertical component of earthquake had a determinative role on the seismic performance of wide-span SGFs. This component causes the structure to reach the nonlinear region more quickly, raises the stiffness changes in the nonlinear region, enlarges the data dispersion and demand sensitivity, intensifies the softening behavior, reduces the dynamic capacity, raises the failure probability, enhances the uncertainty, increases the mean annual frequency (MAF) and accelerates the damage in such structures. However, SSI does not have any significant role in the seismic performance of SGFs; just partially leading to more conservative results, especially when they have wide spans. Besides, the results of the PSDA analysis showed that under similar conditions, short-period SGFs are more vulnerable than long-period SGFs and should be prioritized for retrofitting.

Acceleration Amplitude of the Vertical Component of Colombian Earthquakes


 
 
 
 
 
 
 Past studies have demonstrated that the vertical earthquake component can substantially affect the seismic performance of bridges and buildings. This component is typically ignored or, when included in the design, is estimated as two-thirds of the horizontal seismic design earthquake. This paper presents the characterization of the acceleration amplitude of the vertical component of moderate and strong earthquakes in Colombia (Moment magnitude Mw > 4) that occurred between June 1993 and April 2020. A total of 42 seismic records registered at less than 50 km from the rupture plane and with horizontal acceleration peaks greater than 0.05g were selected. The peak ground acceleration (PGA) of the three components and the ratio between those PGAs were calculated. Additionally, the relationship among those parameters and the magnitude and epicentral and hypocentral distances were determined. The results showed that the V/H ratio equal to 2/3 is not always valid to represent the effects of the vertical component in structures subjected to the moderate and strong ground motions in Colombia.
 
 
 
 
 
 

A New Model for Vertical-to-Horizontal Response Spectral Ratios for Central and Eastern North America

ABSTRACT It is a well-known fact that critical structures are required to be designed for the vertical effects of earthquake ground motions as well as the horizontal effects. We developed a new model for the spectral ratio of vertical-to-horizontal components of earthquakes (V/H ratio) for central and eastern North America (CENA). The proposed V/H ratio model has the advantage of considering the earthquake magnitude, source-to-site distance, and the shear-wave velocity of soil deposits in the upper 30 m of the site for peak ground acceleration and a wide range of spectral periods (0.01–10.0 s). The model evaluation is based on a comprehensive set of regression analysis of the compiled Next Generation Attenuation-East database of the available CENA recordings with M ≥ 3.4 and Rrup<1000 km. The median value of the geometric mean of the orthogonal horizontal motions rotated through all possible nonredundant rotation angles, known as the RotD50, is used along with the vertical component to perform regression using the nonlinear mixed-effect regression. We excluded the earthquakes and recording stations in the Gulf Coast region due to their different ground motion attenuation (Dreiling et al., 2014). To compute V/H ratios for the Gulf Coast region, we refer the readers to the study of Haji-Soltani et al. (2017). Moreover, we excluded the National Earthquake Hazard Reduction Program site class E sites from consideration because of their complex site response characteristics and their potential for nonlinear site effects. The predicted V/H ratios from the proposed model are compared with recently published V/H ratio models. We suggest our model to be used for developing the vertical response spectra for CENA sites.

Effect of vertical-to-horizontal acceleration ratio of earthquake components on the utilization of buckling-restrained braces in steel frames

This paper presents an approach to design the buckling-restrained braces (BRB) system based on the resisting work of the steel braced structures to mitigate the structural seismic collapse. This approach covers the influence of different structural brace variables, the vertical-to-horizontal acceleration ratio (V/H ratio), and the percentage of brace utilization on structural resistance to seismic collapse considering column loss. The determination of this column loss relies on the probabilistic calculation of the critical demand-capacity ratio of the column element that poses the highest threat to fail under large lateral displacements. The investigation uses thirty-six archetypes of steel braced structures with regard to the V/H ratios and various structural parameters related to the bracing systems. The results of the proposed BRB design expand the role of the bracing systems from the protection of the structure against the lateral loading to the prevention of the vertical structural collapse.

Effects of Earthquake Components on Seismic Progressive Collapse Potential of Steel Frames

Effects of Earthquake Components on Seismic Progressive Collapse Potential of Steel Frames

Effects of Vertical Component of Earthquakes on Cable-Stayed Bridges

The vertical component of ground motions is known to cause severe damages to certain structures. Long span cable-stayed bridges are among those vulnerable structures due to their high mass and cables that take no compression. In this paper, the vertical earthquake effects on several cable-stayed bridges have been investigated using 3-D nonlinear time history finite element analyses. Different main span lengths, pylon shapes and pylon/deck connection types are considered. The results indicates that the vertical ground motion component should be considered in the analysis of such bridges and affects many key elements of the bridge.

Behavior of Reinforced Concrete Frames on Flexible Foundations Subjected to Both Horizontal and Vertical Ground Motions

This paper investigates the behaviour of combined horizontal and vertical accelerations on the seismic response of reinforced concrete resting on shallow foundations. Five and nine-storey buildings are considered to represent low- and medium- rise buildings. The building was assumed to be founded on shallow foundation with soil class corresponding to soft soil deposits, the soil of foundation was modelled by an equivalent massless spring coupled with a gap. The accelergrams used in this investigation in the nonlinear range are the horizontal and vertical components of the New Hall earthquake. Although most building codes postulate that SSI generally decreases the force demand of buildings, and increases the deformation demand, it was found that the inclusion of the vertical ground motion with SSI, the horizontal displacement are decreased compared to the case with only the horizontal component.

Empirical Low‐Frequency Earthquakes Synthesized From Tectonic Tremor Records

AbstractTectonic tremor and low‐frequency earthquakes (LFEs) are two different representations of the high‐frequency (>1 Hz) components of broadband slow earthquakes, which have been discovered in various tectonic regions. Although LFEs are considered building blocks of tremor, it is difficult to find constituent LFEs for some long‐duration tremor sequences. Here we introduce a new scheme to synthesize an impulsive response from a tremor source, or empirical LFE (eLFE), from complex tremor sequences. The eLFE is constructed by maximizing the absolute amplitude (L∞ norm) of the normalized and stacked waveforms of many tremor sequences at many stations. This problem includes a highly multimodal objective function, which is maximized via a combined optimization method that incorporates a genetic algorithm and iterative improvements. We first apply this method to several validation tests using synthetic tremor waveforms and real LFEs, and then tremor activities where few nearby LFEs have been detected. One example is the Okayama tremor, which has been known to be extraordinarily sensitive to tidal stress. The eLFE is helpful in determining the accurate hypocentral location and recovering the long‐term comprehensive tremor activity via a matched‐filter analysis. The well‐constrained depth of the Okayama tremor sources is less than 30 km, which suggests that the subducting Philippine Sea Plate is very shallow at this distant location from the trench axis. This eLFE scheme highlights the fact that tremor sequences may be composed of random fluctuations that are not necessarily impulsive and emphasizes the importance of characterizing such randomness to better understand slow earthquake behavior.

A novel insight into vertical ground motion modelling in earthquake engineering

AbstractRecent observations of failure and damage of buildings and structures under seismic action has led to an increasing interest for an in‐depth analysis of the vertical component of site ground motion. In particular, when dealing with saturated soils, the current engineering practice does not usually go beyond the simplified – formulation of the Biot's equations describing the coupled hydro‐mechanical behaviour, thus neglecting some terms of fluid inertial forces, despite the presence of more refined formulations, for example, the – formulation. Therefore, a theoretical and numerical validation of the – formulation as compared with the – formulation is proposed in this work, where the numerical simulations are compared with the analytical solution for the – formulation, which is also derived and illustrated in this text. The comparison between the two formulations and the analytical solution is provided for different levels of permeability and dynamic actions, which are representative of a wide scenario of site ground properties and seismic hazard in the vertical direction. In particular, the soil response is analysed in terms of acceleration and pore pressure time history, frequency content, acceleration response spectrum, and amplification ratio of acceleration. This study extends the discussion of the limits of applicability of the – formulation with respect to the rigorous solution of Biot's equations (obtained here with – formulation) to the context of a complex dynamic regime provided by the vertical components of real earthquake records, and paves the way for further investigations.

The collapse margin ratio of steel frames considering the vertical component of earthquake ground motions

The FEMA P695 methodology does not consider the application of the vertical component of ground motions in nonlinear response history dynamic analyses for obtaining collapse margin ratios. The vertical component of earthquake affects the demand on the steel moment frame and flexural capacity of the columns in interaction with the fluctuating axial load. This paper investigates the effect of the vertical component of far- and near-field ground motions on the seismic collapse capacity of low-, mid-, and high-rise buildings. Various span lengths, story heights, and seismic mass ratios have been taken into account to cover the significant parameters in amplifying vertical earthquake damages. More than 50,000 nonlinear response history dynamic analyses are performed to obtain seismic collapse margin ratios considering (1) the horizontal components of ground motion, (2) the horizontal plus vertical components of the earthquake, (3) the horizontal components of ground motion along with dead load factors suggested by ASCE7–16 to represent the vertical earthquake loading. Results are compared numerically, and the robustness of the procedure suggested by ASCE7–16 is assessed. It is shown that the adverse effect of the vertical component of the earthquake on the collapse capacity of the considered archetype buildings increases with the increase in the fundamental vertical period of buildings. Finally, adjusting equations using dimensionless parameters are developed for estimating the seismic collapse margin ratio of structures considering the vertical component of the ground motion. The proposed equations adjust the corresponding collapse margin ratio obtained using the horizontal components of ground motion.

Feasibility study of a passive rate-independent damping device for the seismic protection of low-frequency structures

The first two decades of the 21st century witnessed adverse effects induced by low-frequency components of severe earthquakes in low-frequency structures. In the 2011 Great East Japan Earthquake, it was reported that many high-rise buildings suffered long-duration vibration with excessive displacements, resulting in damaged interior and exterior walls. Thus, the development of displacement control technologies for the seismic protection of low-frequency structures has been identified as a growing challenge in the field of earthquake engineering. Previous related studies suggest that rate-independent linear damping (RILD) can be a viable option for reducing excessive displacements in low-frequency structures. Because most of the studies on RILD mainly focused on theoretical aspects, practical applications of RILD have not been investigated. This study mainly aims to examine the feasibility of the physical implementation of RILD. The effectiveness of a passive causal RILD device comprising a Maxwell-type damper and a negative stiffness for the protection of low-frequency structures is examined based on the approaches of real-time hybrid simulation and frequency-domain analysis. The results of this study confirmed that the passive causal RILD device could achieve a control effect in its displacement response and floor response acceleration in low-frequency structures similar to that of ideal RILD for the majority of selected earthquake records.

Effects of the vertical component of ground motion on the seismic performance of Bhakra Gravity Dam

In this paper, the earthquake component effects on the seismic performance of Bhakra Gravity Dam in India are investigated. For the purpose, Bhakra Dam is modeled two-dimensionally considering dam-reservoir-foundation interaction. In the finite element modeling, dam and foundation are represented by PLANE182 elements in ANSYS with different material properties, and fluid is considered with FLUID29 elements. This type of element provides translation and pressure degrees of freedom. Linear time history analyses on the dam are performed by considering components of the 1991 Uttarkashi and 1999 Chamoli (NW Himalaya) Earthquakes in India. During the analyses firstly the horizontal component of earthquakes are applied to system and results are obtained, and then both of horizontal and vertical components are applied to the systems together. In the analyses, element matrices are computed using the Gauss numerical integration technique. The Newmark method is used in the solution of the equation of motions. Also, Rayleigh damping is considered. The seismic performance of Bhakra Dam is examined and presented by dynamic characteristics, displacements, principal stresses, and demand-capacity ratios. The results showed that the vertical components of the earthquake significantly affect the response of the dam. The results show that the vertical component with the horizontal component cause biggest tensile stresses compared to only the horizontal component for both earthquakes. However, displacement response is changed depending on the ground motion. As a conclusion of this study it can be said that the vertical component changes the structural response of the dam on both of the good and bad behaviors.

Evaluation of Hydrodynamic Pressure Distribution in Reservoir of Concrete Gravity Dam under Vertical Vibration Using an Analytical Solution

Fluid-structure interaction causes a hydrodynamic force, which can be exerted to the dam and affects its response. The effect of vertical excitation of ground motion on dynamic behavior of concrete gravity dam is the most important because of the interaction between foundation and reservoir. So, the foundation-reservoir interaction should be taken into account in designing concrete dams. In most studies, the effects of the vertical component of vibration have been ignored. While in vertical vibration, due to the interaction of the reservoir and the foundation, a significant hydrodynamic pressure is produced in the tank, which increases the dam response. In this study, the hydrodynamic pressure wave propagation in the reservoir of a concrete gravity dam caused by interaction with the foundation under vertical vibration is investigated using an analytical method. To achieve an analytical solution, the reservoir is assumed to be rectangular, and a harmonic load is vertically applied on the system from the foundation. Considering the acoustic nature of the reservoir fluid under harmonic vibration, a new method using the separation of variables method has been used for solution of hydrodynamic wave equation. The results show a significant effect of the vertical component of earthquake on the amount of induced pressure distributed in the reservoir, which has been omitted in most previous studies. Obtained results of the proposed model can be extended to more complicated models in terms of different loading and geometrical conditions.

On the Influence of the Vertical Earthquake Component on Structural Responses of High-Rise Buildings Isolated with Double Friction Pendulum Bearings

The double friction pendulum (DFP) bearing is adapted from the well-known single friction pendulum (SFP) bearing. This type of bearings has been widely used for structural vibration controls. The main advantage of the DFP is its capacity to accommodate larger displacements as compared with the SFP one. This paper aims to assess the effect of the vertical earthquake component on the seismic behaviour of a base-isolated high-rise building. In this respect, the mathematical model of the building subjected to earthquake excitations with an implementation of a DFP bearing system is established. The model presented herein considers earthquake excitations in horizontal (X and Y) and vertical (Z) directions. A series model of two friction elements is presented for the bearing, where the friction load of the bearing surface is governed by a modified Bouc-Wen model, which is dependent on the sliding velocity and the contact pressure. The numerical results of an example of a base-isolated 9-story steel building subjected to near-source and far-field earthquakes show the high effectiveness of the bearing system in reduction of the seismic response of the building, especially in the near-source region, as well as exhibit considerable effectiveness of the vertical earthquake component on the bearing and structural behaviour.

Developing a multi-variable vulnerability function for a class of multi-span continuous concrete box-girder highway bridges with emphasis on near-field earthquakes

The most common tools in seismic performance assessment of highway bridges are single-variable fragility curves. However, fragility curves are not confidently reliable due to utilizing only a single intensity measure (IM). Alternatively, single- and multi-variable vulnerability functions, of which the latter is scarce and rather complex, have been proposed for that purpose, yet without considering the effects of the strong vertical component of near-field earthquakes. This study aimed to develop a multi-variable vulnerability function for multi-span continuous concrete box-girder bridges, accentuating near-field earthquakes. Ten bridge models corresponding to the 1971-1990 design era were considered and analyzed, subjected to three-component records of 164 earthquakes using OpenSees framework. First, 28 IMs related to horizontal and vertical ground motions, and 12 engineering demand parameters were utilized, and a set of potentially optimal IMs were determined through optimality investigation. Then, to ensure that identified IMs are authentically optimal candidates, Lasso regression was employed, introducing 12 IMs as optimal. Finally, Step-wise regressions were conducted to reduce the complexity of the proposed equation. Results revealed peak ground acceleration, peak ground velocity, and velocity spectrum intensity of the horizontal component of ground motion, and acceleration spectrum intensities of both horizontal and vertical components as optimal ones.

Assessment of the inelastic structural response of building models that consider the combination of orthogonal seismic effects

For design purposes, the orthogonal seismic effects are combined using a percentage combination rule. The most common rules estimate the total structural response as the sum of 100% of the effects caused by one earthquake component acting along one direction of the structure plus a percentage α of the response caused by the orthogonal earthquake component acting along the perpendicular direction of the structure. Usually, values of α = 30% or 40% are specified. There is no clear consensus regarding the use of a specific value of α. In this paper, a comprehensive parametric study is presented to analyze the effects of using a particular value of α on both the ductility demands and the total cost of buildings. The aim of the study is to obtain optimal values of α to minimize the total cost of buildings considering the following variables: structure dynamic properties, earthquake angle of incidence (0–360°), reduction factor of design elastic forces (design ductility demand) (Q = 2 or 4) and type of soil (firm or soft). Values of α = 10%, 30%, 50%, 70% and 100% are analyzed. The studied models are idealized building structural models with several combinations of vibration periods along both model orthogonal directions. Combining all values of the studied variables, a total of 66,600 different cases were designed and analyzed. Based on both the designs and the analysis nonlinear results, the total costs of the studied cases were computed. The total cost for each case was evaluated considering the following building costs: initial cost, repair cost, content loss, income loss, and losses due to both injured and deceased people. The main results of the investigation indicate that the optimal average values of α that minimize the building total cost are: For firm soil: α¯OPT = 0.85 for Q = 2 and α¯OPT = 0.94 for Q = 4. For soft soil: α¯OPT = 0.22 for both values of Q.

Maximum mean square response and critical orientation under bi-directional seismic excitation

Power Spectrum Analysis (PSA) consists one of the seismic analysis methods proposed by modern code provisions. In the context of PSA, the computation of seismic behavior is achieved by a stochastic analysis that yields mean square values. A method that can be used for the determination of maximum or mean square response is the response history analysis. In the present study, analytical formulas are developed for the determination of the maximum mean square value and the corresponding critical incident angle of any scalar response quantity under two horizontal seismic components for any time interval of ground motion within the context of linear response history analysis. An R/C building is analyzed in order to demonstrate the variation of the maximum mean square response with the incident angle. The maximum mean square response values over all incident angles are calculated using the developed formulas. The results show that the application of the earthquake components along the structural axes can underestimate the mean square response.