Vertical Component Of Earthquake Research Articles

Analyzing Vertical Earthquake Vibrations and Moving Vehicle Loads for Structural Health Monitoring and Vibration Suppression in Bridges

The design of bridges often overlooks the vertical component of earthquakes or considers it of secondary importance, despite compelling evidence indicating specific structural damage caused by primary earthquake waves. Conversely, during the operational phase, the combined influence of ground motion and moving loads from vehicles can significantly impact the structural health monitoring (SHM) of bridges. This study aims to evaluate the simultaneous effect of vertical earthquake vibrations and moving vehicle loads on simply supported bridges. The research employs a practical methodology based on the eigenfunction expansion method to analyze change of deflection due to the effect of these concurrent forces under seven different earthquake records. It is shown that within a realistic range of vehicle mass and velocity, the average of changing the maximum deflection at the mid-span of the main beam (denoted as M_n) reaches up to 163% under various scenarios. Subsequently, the seismic parameters influencing this phenomenon are identified through a statistical analysis of set of 100 different earthquake records with unique features. A linear regression equation is presented to predict the M_n based on the earthquake specific properties. Additionally, to control the vertical vibration of bridge systems, a novel vibration suppression system utilizing steel pipe dampers is introduced, and its reliability is examined across a broad spectrum of bridge flexural rigidity. The results indicate that the system's efficiency depends on M_n and the soil type of the bridge construction, enabling a reduction in structural sections (up to 27%) while achieving the same maximum target deflection in the initial state. This efficiency leads to a more economical design solution, emphasizing the potential benefits of the proposed system for practical application.

The Derivation of Vertical Damping Reduction Factors for the Design and Analysis of Structures Using Acceleration, Velocity, and Displacement Spectra

Damping reduction factors (DRFs) play a vital role in the seismic design of structures. DRFs have been widely studied due to their primary importance to the lateral resistance of structures subjected to earthquakes. On the other hand, devastating earthquakes have occurred all over the world, and recently, the Kahramanmaraş earthquakes in Turkey revealed the import of the vertical component of earthquakes and their impact on structures and infrastructures. Considering the importance of this parameter, this paper aims to develop new damping reduction factor (DRF) equations for the acceleration (DRFa), velocity (DRFv), and displacement spectra (DRFd) of the vertical components of earthquakes. For this purpose, 775 real ground motion records were selected from the Pacific Earthquake Engineering Research (PEER) strong motion database, and the vertical elastic response spectra of selected records were computed according to linear dynamic analysis. Taking the 5%-damped vertical response spectra as the target, the vertical spectral damping reduction factors (DRFa, DRFv, and DRFd) were computed for 1%, 3%, 10%, 15%, 20%, 30%, and 40% damping ratios. The effect of the earthquake magnitude, distance, and soil types on the DRFs was investigated. The results indicated that magnitude, distance, and soil type had no particular effect on the trend in the DRFs. Based on the evaluations, extensive statistical analyses were carried out, and new prediction equations were developed according to the nonlinear regression method. The developed equations were then compared to those found in the literature and seismic design codes. The comparisons proved that the proposed DRFa, DRFd, and DRFv models are strongly compatible with real DRFs and show strong robustness compared to existing models.

Evaluation of Steel Diagrid Structural System Under Near-Fault Earthquakes

ABSTRACTThe diagrid structural system has become popular in the construction of high-rise buildings in light of significant advantages over other structural systems. The present study explores the effects of the vertical near-fault earthquake component on the axial forces of diagonal elements in steel diagrid structures. Nonlinear time-history analysis was carried out using 11 near-fault earthquake records. A total of nine three-dimensional models of 12, 18, and 24 stories, each with diagonal angles of 45, 63.4, and 71.5 degrees, were designed and analyzed. Due to the three-dimensional modeling complexities of diagrid structures, a method was developed to transform three-dimensional models into two-dimensional ones. Finally, the scenarios with and without the vertical earthquake component were compared. It was found that the incorporation of the vertical earthquake component into the analysis of diagrid structures substantially influenced the axial forces of diagonal elements. This can affect the design load estimation of diagonal elements as the main components of a diagrid structure.

Evaluation of the effect of the vertical component of an earthquake on the seismic response of container cranes using the shake table test

In this study, the effect of the vertical component of earthquakes on the seismic response of a container crane was investigated by using the shake table test on a 1/20 scale container crane. The effect was investigated by comparing the seismic response of the container crane when subjected to the horizontal component of earthquakes versus the horizontal and vertical components of earthquakes. The seismic responses of the container crane were compared based on acceleration responses, displacements, and internal forces. The main findings of this study are as follows: (1) Vertical acceleration response increased when the vertical and horizontal components of earthquakes were used simultaneously. A maximum increase of 79% was observed for the vertical acceleration response at the trolley-boom girder. The horizontal acceleration response either increased or decreased. The maximum difference was 24% when the container crane was subjected to horizontal component earthquakes versus horizontal and vertical component earthquakes. (2) The horizontal displacements of the container crane increased or decreased under the simultaneous action of the horizontal and vertical components of the earthquakes. The maximum difference was 278% with regard to the derailment of the seaside legs. (3) The internal forces at the top of the lower legs were affected by adding the vertical component of the earthquakes. The maximum difference in the axial force response was 100%, while that of the bending moment was 24%. Therefore, the seismic response of container cranes should be analyzed with and without the vertical component of earthquakes to determine the most extreme case of the seismic response.

Capacity assessment of segment-to-segment joints in precast unbonded segmental bridge decks under vertical seismic mainshock and aftershocks

Precast segmental construction of concrete bridge decks has become increasingly popular due to short construction time and low cost compared with other construction methods. However, during earthquake excitation the segment-to-segment joints in post-tensioned bridge decks may constitute a weak part of the superstructure, particularly due to the lack of continuous rebar that is present in cast-in-place decks. This research investigates the effects of the vertical component of earthquakes on the joints of the superstructure of bridges in near-fault regions. Specifically, a sample non-continuous precast segmental bridge with unbonded cables and constructed with the span-by-span method, has been studied using a detailed two-dimensional non-linear Incremental Dynamic Analysis (IDA) and Nonlinear Pushover Analysis (NPO). The results indicate that the vertical component of the earthquake could significantly adversely affect the joints’ behavior, especially in the upward direction. This may cause failure in the critical joints at midspan earlier than other common collapse prevention (CP) limit states such as deck sliding on the seat. The joint failure occurs easier in the mainshock-damaged bridge than in the intact one. Hence, the collapse probability can increase by up to 47% for the considered cases.

The Effect of the Vertical Component of the Earthquake on a Regular Masonry Wall

The effect of the vertical component of earthquakes on the structural behaviour of unreinforced masonry (URM) walls is usually not considered by technical codes for ordinary buildings. Recent scientific literature, however, indicates that the earthquake vertical component may play a significant role in the crack pattern of URM walls and their collapse. This paper investigates the effect of the vertical seismic component on the capacity and damage scenario for a two-story regular URM wall, described with a detailed micro-modelling approach. Pushover and nonlinear time history analyses are carried out with and without the vertical component and under different dead loads representative of typical stress states for URM structures. The inter-story drift and roof drift ratios are introduced as Engineering Demand Parameters (EDPs), and their correlation with the Ground Motion Parameters (GMPs) of the horizontal and vertical components is discussed. The results show a very good correlation between the seismic demand and the GMPs of the vertical component, demonstrating the influence of the vertical component on the global seismic response. Moreover, the study shows that the influence of the vertical component increases with the vertical load applied to the structure, which indicates that the vertical ground motion component cannot be a priori neglected for URM walls when moderate to large vertical GMPs are expected.

Nonlinear seismic analysis of RC framed structures with horizontal and vertical base-isolation

The ratio of the vertical-to-horizontal peak ground accelerations highlights the fact that values greater than one tend to occur in the near-fault area, where the corresponding ratio of spectral accelerations may be amplified in the range of low vibration periods. The high vertical-to-horizontal stiffness of a base-isolation system (e.g. high-damping-rubber bearings, HDRBs) of a reinforced concrete (RC) framed structure causes the superstructure to behave like a fixed-base one in the vertical direction. Seismic damage induced by vertical excitation is generally located at the upper storeys, where the effects of gravity loads generally prevail over those of the horizontal loads and an amplification of the vertical motion is expected. In the present work, attention is focused on the combination of horizontal and vertical base-isolation resulting from the in-series vertical arrangement of a HDRB and a HDR layer, the latter not affecting the horizontal stiffness of the isolator but reducing its vertical stiffness. The main objective is to evaluate the isolation ratio in the vertical direction that needs to be considered for effective protection against significant vertical component of near-fault earthquakes. A five-storey RC framed structure is first designed as fixed-base in a medium-risk zone, in compliance with a former Italian seismic code. It is retrofitted by the insertion of a horizontal-vertical base-isolation system, with nominal, upper-bound, lower-bound and mixed design properties defined by current European seismic codes. Nonlinear seismic analysis of the test structures is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research Center database and scaled to match the design spectrum of acceleration. Finally, the vertical stiffness to be assigned to the isolation system to obtain a shift from the vibration periods of maximum amplification is evaluated by wavelet analysis, including the moving resonance effect induced by inelastic deformation of the superstructure.

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.
 
 
 
 
 
 

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.

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.

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.

Influence of the Vertical Earthquake Component on the Shear Vibration of Buildings on Sliding Foundations

The paper studied the vibrations of the buildings on the sliding foundation with dry friction under the action of real earthquakes at the intensity of 8 and 9 on the MSK-64 scale. It was developed a unique algorithm for calculating the displacements, velocities, accelerations, and shear forces resulting from the simultaneous action of the horizontal and vertical components of the seismogram record. It was studied four-story and nine-story buildings under the set of the three earthquake records. It was shown that the use of a sliding foundation does not always lead to a significant reduction in the shear force on the building floors and that the vertical component of the seismic effect has a significant influence on the shear vibration of the building.

Parametric study for long-span roof truss subjected to vertical ground motion

Generally in the seismic resistant design of structures, effects of horizontal ground motions are mainly considered and effects of vertical ground motions (VGMs) are ignored. However, considering the field evidences of damage of structures due to vertical component of ground motion for near-fault earthquakes, the importance of inclusion of effect of vertical component of earthquake in seismic design has been recognized. Therefore in this paper, a parametric study has been carried out on 25 m long-span industrial steel roof truss with the help of 12 near-fault ground motions without pulse. The parameters related to roof truss as well as an earthquake data are studied to get the response of long-span roof truss under vertical ground motion (VGM) with nonlinear time history analysis using SAP2000V19.2.1 software. From the parametric study, it has been realized that for a chosen long-span industrial roof truss, the parameters such as vertical to horizontal peak ground acceleration ratio, axial force, vertical displacement and base bending moment are identified as critical. From the time history analysis results, it is also found that response of truss under vertical ground motion is critical for ground motions having V/H ratio more than 1 and therefore the long-span structure in near-fault zone should be considered separately in design rather than taken as 2/3 of horizontal acceleration as per given in IS1893:2016 (Part-1).

The effects of mainshock-aftershock in successive earthquakes on the response of RC moment-resisting frames considering the influence of the vertical seismic component

The sequential earthquakes and the vertical component of earthquakes can cause extensive damages to structures. In this study, by applying the incremental dynamic collapse analysis, considering the stability, final curvature and interstory drift, as performance criteria for the intact and damaged structures under the mainshock, the fragility curves are studied. The analyses have been performed for two reinforced concrete moment-resisting frames (RC-MRFs) of 6- and 10-story buildings by considering two scenarios of the horizontal component and the simultaneous effects of the horizontal and vertical components of the earthquakes for two structural conditions with and without damage. The provided fragility curves indicate the probability of the collapse of the structures due to the intensities of the earthquakes and the response of the structures, as well as the exceedance probability of the maximum interstory drifts of the damaged structures under the impact of aftershocks from first damage state (DS1) and second damage state (DS2) in terms of earthquakes intensities. In the DS1, the structure under the mainshock reaches a maximum interstory drift of 0.5%, and in the DS2; it reaches a maximum interstory drift of 0.8%. The results obtained using the incremental dynamic analysis (IDA) method indicate that the damages caused by the previous events and considering the vertical component of the earthquake have significant influences on the interstory drift related to the collapse of the structure. Considering the vertical and horizontal components of the earthquake, as well as the seismic sequence reduces the maximum interstory drift corresponding to the collapse of the structure. By applying the regression analysis some practical equations were submitted to be employed in similar cases as a guideline.

Effect of near-field earthquake on isolated bridge considering soil–structure interaction

In the 1995 Kobe earthquake, different bearing fractures were observed in isolated bridges. Piers and bearings were the first and second vulnerable structural elements. The estimation load due to far-field earthquakes can be calculated using BS EN 1998-1:2004, but research on this issue for near-field earthquakes is limited. The aim of this study was to verify the effect of the vertical component of near-field earthquakes on structural responses and compare the results with values suggested using BS EN 1998-1:2004. An isolated bridge was designed based on Eurocode standards and modelled in OpenSees. Moreover, since soil–structure interaction (SSI) has an inherent effect on bridge structures, the induced vertical accelerations were compared with and without SSI effects. It was found that vertical acceleration decreased in the model including SSI effects. The shear strain of the elastomers was found to be within the range allowed by BS EN 1998-2:2005.