Vertical Seismic Excitations Research Articles

Evaluation of Conventionally Designed Reinforced Concrete Beams Against Vertical Seismic Excitation

Evaluation of Conventionally Designed Reinforced Concrete Beams Against Vertical Seismic Excitation

Investigating the influence of an approach bridge on a pile-supported wharf at a liquefiable site under horizontal and vertical seismic excitations

The approach bridge of the pile-supported wharf is an important structure that connects the pile foundation platform and the land, and it has a significant impact on the safety of the high-pile wharf. However, the influence of an approach bridge on the seismic dynamic response of a pile-supported wharf has often been neglected in previous studies. Besides, the excess pore water pressure (Δu) generated under combined vertical and horizontal seismic components is typically greater than that induced by unidirectional excitations, which may further impact the dynamic response of pile-supported wharf. Firstly, this study developed a numerical method for simulating the approach bridge of a pile-supported wharf. Secondly, the three-dimensional finite element model of a pile-supported wharf with an approach bridge is established to investigate the dynamic response during horizontal and vertical seismic components. Additionally, the effects of seismic frequency and relative density of liquefied layer on the dynamic response of pile-supported wharf were also studied. By comparing with the experimental results, the numerical model effectively simulated the overall response of the pile-supported wharf and the liquefaction behavior of the surrounding soil. During high-frequency earthquakes, the influence of the approach bridge on the dynamic response of the pile-supported wharf is minimal, whereas it has a more significant impact during low-frequency earthquakes. Furthermore, vertical seismic components significantly amplify the effect of approach bridge on the lateral displacement and internal forces of piles. The effect of the approach bridge on the lateral displacement and internal force of the pile decreases with the increase of the relative density of the liquefaction layer.

Seismic response of tripod suction bucket foundation for offshore wind turbine considering multidirectional earthquake loads

Tripod suction buckets offer several advantages as offshore wind turbine (OWT) foundations, including cost-effective installation, high stability, and resistance to overturning. In seismically active regions, OWTs experience horizontal and vertical directions seismic excitations. This study employed an advanced three-dimensional nonlinear finite element analysis to investigate the influence of vertical seismic motions on the dynamic behavior of tripod bucket foundations installed in nonhomogeneous clay deposits. By adopting a simple kinematic hardening model to capture the foundation-soil nonlinear dynamic interaction, parametric analyses were conducted to study the effect of vertical seismic motions, considering several earthquake types and undrained shear strengths of the clay deposit. The results show that the influence of the vertical seismic motion on the dynamic response and deformation of the nacelle depends on the dominant frequency of the vertical seismic motion and the overturning resistance capacity of the OWT in different horizontal directions. The deformation mechanisms of an OWT vary with the strengths of the clay deposits. Based on these analyses, this study offers insights into the influence of vertical seismic motions on the dynamic response of tripod suction bucket foundations.

Vehicle–Bridge Interaction Dynamic Analysis of Continuous Rigid Frame Composite Box Girder Bridge with Corrugated Steel Webs under Seismic Excitation

To study the vehicle–bridge interaction (VBI) of highway bridges under seismic excitation, a vehicle–bridge couple analysis method based on Ansys is proposed. The 1/2 vehicle model and space beam element model were established to analyze the VBI response of Lanzhou Xiaoshagou bridge. The self-excited excitation of the system is represented by road surface irregularity randomness, while the external excitation is represented by an earthquake. The impact of seismic types, seismic direction, seismic intensity, vehicle speed, and road surface irregularity on the bridge vibration under the vehicle–bridge coupling during an earthquake is thoroughly analyzed. The results reveal that the type of earthquake significantly influences the dynamic response of the bridge, showing a minimum difference of 31.4%. The intensity of the earthquake is positively correlated with the dynamic response of the bridge. Longitudinal and vertical earthquakes have a more noticeable effect on the bridge’s vertical vibration compared to lateral earthquakes. The ratio of the bridge response under vertical or longitudinal seismic excitation to the response of lateral earthquakes ranges from 1.50 to 26.61. Vehicle speed, road irregularity grade, and randomness have a negligible impact on the dynamic response of vehicle–bridge interaction under an earthquake, accounting for less than 3%. These findings indicate that the analysis of earthquake-bridge vibration can simplify the VBI analysis for continuous rigid frame composite box girder bridges with corrugated steel webs under seismic conditions.

Effect of near-fault vertical seismic excitation on running safety of trains on high-speed railway bridges

The vertical component of near-fault earthquake motion is significant and may result in the derailment of trains that are running on bridges. In this study, a shaking table test of a train running on a high-speed railway bridge is performed based on a four-array shaking table and a 1:10 scale model of the train-track-bridge, and the corresponding numerical model is established. The reliability of the numerical model is first verified by test results. Then, with safety and comfort indexes as evaluation criteria, the test and numerical data are analyzed to reveal the near-fault vertical seismic effects on the running safety of trains on bridges. Finally, with the wheel-rail relative displacement of the test and derailment evaluation indexes of the numerical simulation, the near-fault vertical seismic effects on the derailment of trains running on bridges are analyzed to explore the derailment mechanism. The results show that near-fault vertical seismic excitation generally has a negative impact on the running safety of trains on bridges, with a maximum impact of 27% under selected seismic excitations. Furthermore, the negative impact increases with the vertical-to-horizontal peak acceleration ratio. The safety threshold of peak ground acceleration is often reduced due to vertical seismic effects, and the maximum reduction reaches 14.3% under Northridge-01 seismic excitation. In the case of a given lateral seismic excitation, vertical seismic excitation increases the maximum distance that the wheel-rail contact point moves laterally towards the wheel flange and further promotes flange climb derailment. Moreover, vertical seismic excitation reduces the minimum value of the wheel-rail vertical force and increases the possibility of jumping derailment.

Experimental Investigations of the Seismic Response of a Large Underground Structure at a Soft Loess Site

Based on an underground structure located at a soft loess site in Xi’an as the engineering background, this paper investigated a seismic response and damage model of subway stations at a soft loess site using a large-scale shaking table test, considering the different characteristics of ground motions. The quantitative analysis of the acceleration response and the seismic subsidence of the soft loess site were subjected to different earthquake excitations; based on the experimental results and the corresponding analysis, the development and distribution of seismic structural damage were studied, and the damage mechanism of underground structures in a soft loess area under a strong earthquake was explored. The results indicate that the peak accelerations of the site soil first remained unchanged then increased significantly along the soil height, and the amplification effect of the acceleration response was the most significant at the soil surface. The soft loess soil underwent significant subsidence, and the underground structure was raised compared to both sides of the cover soil; the collapsibility of the soft loess soil was sensitive to strong earthquakes with vertical components. The underground structures in soft loess suffered heavy damage, which rapidly entered the elastic–plastic stage. The composite effect of the collapsibility and vertical seismic excitation impaired the load-carrying capacity of the middle columns, and the strong horizontal seismic excitation enlarged the lateral force and accelerated structural damage development; the underground structure reached failure when plastic damage expended most of the middle columns and structural joints. These results are significant for the seismic design of underground structures in adverse soil conditions.

A vertical isolator with high horizontal resistance for layered isolation of large hub buildings

A layered isolation system is proposed for large hub buildings by installing horizontal isolators at the base of the substructure and vertical isolators at the supports of the long-span spatial structure separately. Significant horizontal static forces which can be close to the gravity loads of the spatial structure are normally generated on the vertical isolators, which will seriously affect the vertical isolation effect. In this paper, a vertical isolator with high horizontal resistance is developed for the layered isolation system of large hub buildings. The developed isolator is composed of a horizontal-force-resisting component and a vertical-isolation component. The horizontal-force-resisting component is designed to resist horizontal forces from the spatial structure and restrain the horizontal displacement of the isolator. The vertical-isolation component is designed to support vertical loads of the spatial structure and isolate vertical seismic excitations. A series of vertical sinusoidal motion tests and numerical simulations are carried out to investigate the vertical hysteretic behavior of the isolator considering horizontal forces. The maximum horizontal force is as large as the designed gravity load on the isolator. Results show that the vertical hysteretic behavior has typical friction characteristic and it is influenced by the loading conditions, the geometric parameters of the horizontal-force-resisting component and the friction coefficient of the pin connections. Additionally, a theoretical model of the vertical restoring force of the isolator is derived and validated, and the vertical isolation performance is analyzed based on the model. The vertical seismic responses of the long-span spatial structure can be reduced by up to 60%–80%. The developed isolator is proved to be an efficient solution for vertical isolation considering large horizontal forces.

Shaking table test of a new special-shaped arch bridge

In this work, a shaking table test was conducted on a new special-shaped arch bridge consisting of an inclined arch and a curved beam called BIACB. In order to meet a landscape requirement, the design of BIACB is unique and complex. Therefore, different from conventional bridges, it exhibits a prominent space effect and unpredictable complex seismic responses. To check the seismic performance of the BIACB, a 1:40 scaled test model was designed and fabricated to achieve a shaking table test by using simulated earthquake. The seismic responses of the tested BIACB model under three typical seismic excitations (El-Centro wave, Taft wave and Artificial wave) were explored. It is found that: (1) The scaled test bridge model can well reflect the seismic response characteristics of the prototype bridge verified by the corresponding finite element analysis. (2) Obvious dynamic amplification phenomena in the transverse and vertical directions of the bridge were observed, showing that the vertical response of the curved beam is greater than the transverse one, while the transverse response of the leaning arch is much more apparent than the vertical one. Generally, the seismic responses of BIACB under transverse seismic excitation are more obvious than those under longitudinal seismic excitation. (3) Higher-order vibration mode of the BIACB has a substantial participation under the longitudinal seismic excitation. (4) The inclined arch significantly amplifies the impact of vertical seismic excitation on the BIACB. (5) The relative variation amplitudes of suspender force of short suspenders on the BIACB are greater than that of long suspenders under longitudinal seismic excitation. The research findings are of great potential to critically guide the seismic design of relevant bridges.

Investigation on Rupture Initiation and Propagation of Traffic Tunnel under Seismic Excitation Based on Acoustic Emission Technology.

Traffic tunnels are important engineering structures in transportation, and their stability is critical to traffic safety. In particular, when these tunnels are in an earthquake-prone area, the rupture process under seismic excitation needs to be studied in depth for safer tunnel design. In this paper, based on a construction project on the Nairobi-Malaba railway in East Africa, a laboratory shaking table test with 24 working cases of seismic excitation on a mountain tunnel is designed, and the acoustic emission (AE) technique is employed to investigate the tunnel rupture process. The results show that the high frequency components between 20 and 30 kHz of AE signals are the tunnel rupturing signals under the seismic excitation under such conditions. The tunnel vault and the arch foot are prone to rupture during the seismic excitation, and the initial rupture in the arch foot and vault of the tunnel occur under the horizontal and vertical Kobe wave seismic excitation, respectively, with a maximum acceleration of 0.4 g. After the rupture initiation, the tunnel arch foot continues to rupture in the subsequent working cases regardless of whether the excitation direction is horizontal or vertical, while the tunnel vault does not rupture continuously with the implementation of the subsequent excitations. Moreover, the Kobe seismic wave has a higher degree of damage potential to underground structures than the El seismic wave.

Seismic Performance Assessment of a Single-Layer Spherical Lattice Shell Structure with Multifunctional Friction Pendulum Bearings

The dynamic responses of spatial lattice shell structures with friction pendulum bearings (FPBs) under multidimensional seismic excitations are complex. In addition, FPBs may experience uplift and separation of the bearing components owing to excessive displacements. In this study, a novel multifunctional FPB (MFPB) with a multi-defense system was developed, and its effectiveness in reducing and controlling the seismic responses of spherical lattice shell structures was evaluated. The proposed MFPB comprises an FPB, superelastic shape-memory alloy cables, and sleeve restrainers. A mechanical model of the MFPB was established, and its isolation and control behaviors were investigated through numerical simulations. Furthermore, the main characteristics and advantages of the isolation system were analyzed. Subsequently, the MFPB system was applied to a single-layer spherical lattice shell structure with surrounding columns. A computational model of the controlled structure was developed using the OpenSees software. Finally, nonlinear time history analyzes were conducted to analyze the seismic performance of controlled and uncontrolled lattice shells. The results demonstrate that the MFPB isolation system can effectively control the structural responses of isolated spatial lattice shell structures under horizontal and vertical seismic excitations and improve their seismic resilience.

Theoretical Investigation on Multiple Separation of Bridge under Near-Fault Vertical Ground Motion

In order to consider the effect of near-field vertical earthquake, a model of a two-span continuous beam bridge is established. On the basis of superposition of longitudinal and vertical seismic actions, the possible separation of vertical earthquake is considered, and the influence of separation on structural failure is calculated. The transient wave characteristic function method and the indirect mode superposition method are used to solve the response theory of the bridge structure during the earthquake. When the vertical seismic excitation period is close to the vertical natural vibration period of the bridge, structure may separate. For the high-pier-type bridge, the separation enlarges the deformation of the pier and even causes the pier failure. The external conditions such as the time difference of arrival of seismic wave and the stiffness of support will affect the deformation of bridge piers. In addition, the number of separations will also change the seismic response of the pier.

Quantification study for roof truss subjected to near-fault ground motions

The effects of vertical seismic excitations have a considerable destructive potential for long-span structures, particularly for near-field earthquakes. A quantification analysis is carried out in this paper to describe the response of a 25-m long trapezoidal truss frame with a height of 9 m under Vertical Ground Motion (VGM) with the help of eight near-field seismic excitations. Linear analysis of earthquake load combinations, including VGMs, has been conducted. The VGMs are leading the design of the long-span roof truss rather than the wind load. The time history analysis is therefore performed for horizontal ground acceleration and horizontal plus vertical acceleration using SAP 2000. For this analysis, eight near-field earthquake ground motion records consisting of four with pulse and four without pulse from the PEER NGA database, consistent with the ATC-63 requirements, are selected. The response of the structure is observed in different parameters such as the axial force of the column, the vertical displacement of the ends of the roof truss and the edge of the truss, the axial load of the bottom truss, and the base moment. This work quantifies the effect of vertical seismic excitations on a long-span industrial trapezoidal truss and demonstrates the need for a time history study of the VGM component.

Near-Fault Seismic Response Analysis of Bridges Considering Girder Impact and Pier Size

Given the influence of near-fault vertical seismic action, we established a girder-spring-damping-rod model of a double-span continuous girder bridge and used the transient wave function expansion method and indirect modal function method to calculate the seismic response of the bridge. We deduced the theoretical solution for the vertical and longitudinal contact force and displacement response of the bridge structure under the action of the near-fault vertical seismic excitation, and we analyzed the influence of the vertical separation of the bridge on the bending failure of the pier. Our results show that under the action of a near-fault vertical earthquake, pier-girder separation will significantly alter the bridge’s longitudinal displacement response, and that neglecting this separation may lead to the underestimation of the pier’s bending damage. Calculations of the bending moment at the bottom of the pier under different pier heights and cross-sectional diameters showed that the separation of the pier and the girder increases the bending moment at the pier’s base. Therefore, the reasonable design of the pier size and tensile support bearing in near-fault areas may help to reduce longitudinal damage to bridges.

Frequency response analysis of concrete seawall including soil-structure-seawater interaction

In this study, a frequency-domain finite element model is proposed to evaluate the seismic response of water-structure-sediment-foundation-backfill coupling system. It includes the seawater as a compressible fluid, seawall as viscoelastic solid, backfilled soil, sediment, and foundation as two-phase poroelastic domains with dynamic behavior described by u-p formulation of Biot’s equations. The dynamic interactions among various domains are fully considered and the PML is adopted as an absorbing boundary condition to truncate the computational domain, absorbing all out-going seismic waves. The dynamic responses in the structure, water and soil are assumed to be generated by the vertical propagating shear or compressional waves from the bedrock substrate under the foundation soil. Both the actions of horizontal and vertical seismic excitations at the bottom of foundation are respectively considered. After verifying the accuracy of PML and coupled model of soil-structure-water system, a series of parametric studies are conducted to investigate the effects of sediment thickness, water depth, foundation stiffness, foundation thickness, inclination of seawall, and properties of backfilled soil including soil permeability, shear modulus, and saturation degree, on the frequency response at the top of seawall.

Seismic assessment of a cable-stayed arch bridge under three-component orthotropic earthquake excitation

The occurred damages during the past significant earthquakes have proved that vertical seismic excitation has tremendous effect on bridges. Three-component earthquake excitations are preferred to resemble the earthquakes. In this article, a cable-stayed arch bridge, a new type of bridge with the hybrid system of half-through arch and stay-cables, was analyzed under a set of different earthquake excitations (more than 21 ground motion records). Both vertical and horizontal components of the ground motions were considered to act simultaneously at the bridge supports. By using different three-component earthquake excitations, the dynamic responses of the bridge, including the displacements and accelerations of the main parts of the bridge, were obtained. The effects of various parameters such as soil type, epicentral distance, spatial variation of the ground motions, and dimensional variation of the structure were investigated. The results of the numerical study indicate that the cable-stayed arch bridge subjected to both horizontal and vertical components of earthquakes are more vulnerable than those subjected to horizontal ground motion only.

Numerical studies on full-scale steel columns under complex seismic loading

Numerical analyses using the finite element software Opensees are conducted to examine the ultimate seismic behavior of Wide-Flange steel columns used in multi-story steel frames. An OpenSees fatigue model was adopted to consider the effect of local buckling and cyclic strength degradation. The numerical model is validated with the experimental results from seven full-scale column specimens tested by the authors in an earlier study utilizing the Multiple Usage Structural Testing System (MUST). The comparisons of results include hysteretic behavior which is obtained through three cyclic tests on steel columns with two different axial load levels, and time history behaviors of four additional columns tested by pseudo-dynamic hybrid simulation with both horizontal and vertical seismic excitations. A series of parametric studies on axial load, height or width to thickness ratio of web and flange, aspect ratio of cross section, and section forms are also carried out.

Two-way bending experimental response of URM walls subjected to combined horizontal and vertical seismic excitation

This paper presents the results of incremental dynamic tests on full-scale unreinforced masonry (URM) walls constructed with an intentionally weakened mortar under two-way bending excitation in the out-of-plane (OOP) direction. A specimen was also subjected to simultaneous vertical and horizontal excitation. Walls were also tested in boundary conditions that have not been previously reported in the literature. Emphasis was placed on the development and interpretation of a characterisation test to estimate the torsional shear strength of bed-joints, a parameter of prime importance in the OOP two-way bending behaviour of URM walls. Analytical formulation to estimate the initial stiffness of walls based on the theory of plates is then proposed and validated. Being the first experimental campaign to address the dynamic OOP two-way bending response of full-scale URM wall panels provided the opportunity to propose simple yet mechanically rational methodologies with which both the peak force resistance as well as the displacement at which such resistance is attained can be easily estimated.

Dataset from shake-table testing of four full-scale URM walls in a two-way bending configuration subjected to combined out-of-plane horizontal and vertical excitation.

This data article provides experimental data obtained from the incremental dynamic shake-table testing of four single leaf unreinforced masonry (URM) walls constructed in Calcium Silicate (CS) bricks reported in “Two-way bending experimental response of URM walls subjected to combined horizontal and vertical seismic excitation” [1]. These walls were tested in the second phase of a larger experimental campaign addressing the out-of-plane (OOP) response of full-scale URM panels in two-way bending configurations at EUCENTRE, Pavia, Italy. Data corresponding to the first phase of testing for four single leaf and one cavity wall has already been made available through Tomassetti et al.[2] and the information necessary to interpret these results can be found in Graziotti et al.[3]. The walls of the tests reported in this data article were constructed in an intentionally weakened mortar but using the same Calcium Silicate (CS) bricks as Graziotti et al.[3]. The walls were also tested in boundary conditions that were not addressed in [3] and a specimen was also subjected to simultaneous horizontal OOP and vertical seismic excitation in one of the tests. Videos documenting the failure of specimens tested in both phases of the experimental campaign can be viewed online on YouTube [4].

Numerical study on seismic response of a rock slope with discontinuities based on the time-frequency joint analysis method

To clarify the seismic response of rock slopes, a time-frequency joint analysis method with the combined use of time, frequency and time-frequency domain analysis is proposed. The dynamic response of a rock slope with discontinuous structural planes was investigated using the finite element method (FEM). A two-dimensional model incorporating finite element meshes with infinite element boundaries for the slope was used in the FEM dynamic analyses. The numerical results show that the elevation, structural plane and direction of wave propagation have an impact on the slope amplification effect. The peak ground acceleration (PGA) under horizontal seismic excitation is approximately 1.2–1.3 times that under vertical seismic excitation. In addition, the first three natural frequencies of the slope can be obtained from the Fourier spectrum and modal analysis. The low-frequency components (<20 Hz) and high-frequency components (>20 Hz) mainly induce the overall and local deformation of the surface slope, respectively. Moreover, the dynamic response of the slope was further investigated by analysing the seismic Hilbert energy. The seismic Hilbert energy in the Hilbert energy spectrum and marginal spectrum is mainly distributed in the low-frequency and high-frequency regions, respectively. The applicability of the Hilbert energy spectrum and marginal spectrum to analyse the dynamic deformation characteristics of the slope is identified. Moreover, the relationship between the local dynamic deformation response of the slope and the occurrence of a landslide was discussed. The dynamic failure mechanism of the slope was clarified according to the frequency-domain and time-frequency domain analysis.

Multi-Directional Base Isolation System for Coupled Horizontal and Vertical Seismic Excitations

ABSTRACT The concept of a new Multi-Directional Seismic Isolation (MDSI) system is developed to enhance the seismic performance of structures under coupled horizontal-vertical excitations. The MDSI system consists of a typical isolation unit and a Super-High-Damping-Rubber (SHDR) device to tune vertical stiffness without affecting horizontal movements. The efficiency of the proposed system is demonstrated for 3-, 5-, 8- and 12-story steel frames under 10 different combined vertical-horizontal earthquake excitations. Compared to conventional base isolation systems, MDSI can reduce the maximum vertical and horizontal accelerations by up to 55% and 25%, respectively, resulting in a significant reduction of non-structural damage due to acceleration.