Earthquake Action Research Articles

Study on Dynamic Response Characteristics of Stepped Reinforced Retaining Wall

In order to further explore the influence of reinforcement materials laying position on the dynamic characteristics of reinforced retaining walls, based on FLAC3D finite difference methods for solving nonlinear problems, established with the same size of the retaining wall in practical engineering, the reinforcement material’s relative position in the retaining wall for the normalized processing, under seismic load, and the panel under the conditions of different reinforcement arrangement were analyzed, and the horizontal displacement of slope, the vertical and horizontal earth pressures behind the wall, and the distribution of potential sliding surface were calculated. The relationship between the maximum horizontal displacement of the panel and the laying position of the reinforcement was fitted by MATLAB. The results show that the horizontal displacement of the panel is about 40% smaller when the upper layer of the reinforcement is arranged than that in the lower layer for step 1, and the horizontal displacement of the reinforcement in step 2 is about 30% lower than that in other conditions when the reinforcement is arranged at the top of the slope. The reinforcement arranged in the lower layer of step 1 and the upper layer of step 2 can minimize the wall top displacement. In step 1, the vertical earth pressure and horizontal earth pressure are 19% and 5% smaller than those in other conditions when the reinforcement is arranged near the middle and lower layer of the step. In step 2, the difference between vertical and horizontal earth pressure is not obvious, and the difference between the two conditions is controlled within 5%. At the same time, soil liquefaction and uplift occur under the action of earthquake. The position of sliding crack surface has no obvious regularity with the position of reinforcement, but the position of reinforcement at the step classification is obviously better than other conditions. The fitting formula can describe the relationship between the panel displacement and the position of the reinforcement well. The conclusions can provide a point of reference for practical engineering.

Study on the slope dynamic stability considering the progressive failure of the slip surface under earthquake

The strength of a rock-soil mass shows complex and obvious weakening characteristics under seismic dynamic load. The previous stability analysis methods of a seismic slope do not fully depict the attenuation law of geotechnical materials and cannot truly reflect the stable state of a slope under earthquake action. Based on the theoretical analysis of the progressive failure mechanism and the evolution law of a seismic slope, the adverse effect of progressive failure on slope stability is clarified. According to the progressive failure process of a slope under dynamic load, the strain-softening model and vibration deterioration model are introduced to represent the attenuation law of rock strength parameters, and a calculation method of seismic slope stability coupled with vibration disturbance and progressive failure is proposed. The method considers the strength parameter characteristics of a rock-soil mass in different stages and is combined with the vector sum method to obtain the time-history curve of the slope safety factor under earthquake action, which makes the evaluation result of slope stability more accurate and reliable. The numerical examples show that this method can effectively reflect the dynamic stability of seismic slopes, and solve the problem that the traditional calculation methods are difficult to characterize the strength attenuation characteristics of rock and soil mass. If these characteristics are not considered, the calculation results will be unsafe.

Experimental study on liquefaction characteristics of saturated Yellow River silt under cycles loading

The Yellow River silt can be effectively used as highway subgrade filler, which cannot only relieve the flood control pressure in the lower reaches of the Yellow River, but also meet the economic development needs of the areas along the Yellow River, with significant economic and social benefits. It cannot be ignored that the highway subgrade may be produced liquefaction under the action of earthquake and traffic loads. The problem of the dynamic characteristics of the Yellow River silt is a fundamental scientific problem that needs to be solved urgently. In this paper, a series of undrained tests were carried out on saturated Yellow River silt. Effects of relative density Dr, effective confining pressure σ3c, loading frequency f and cycles stress ratio CSR on pore pressure, axial strain development characteristics and dynamic strength characteristics of saturated Yellow River silt were studied. The test results show that: The number of cycles vibration required for liquefaction failure of the Yellow River silt was affected by relative density, loading frequency, effective confining pressure and cycles stress ratio. There are significant differences in the stress-strain development patterns of the Yellow River silt under different frequencies. Under the action of low frequency load, the Yellow River silt presents “hardening” liquefaction characteristics. Under the action of high frequency load, the Yellow River silt presents the characteristics of “softening” liquefaction. The Yellow River silt doesn't liquefy under the effect of weak earthquakes, while it is highly susceptible to liquefaction under the effect of strong earthquakes. Compared with the high-frequency load, when the low-frequency load is applied, more energy is required for the Yellow River silt to reach the initial liquefaction state. The cycles stress ratio CSR and the relative density Dr have significant effects on the pore pressure development of the Yellow River silt. Finally, a modified Seed model was proposed to characterize the pore pressure development of the Yellow River silt.

Experimental assessment on aseismic capacity of a perimeter diagrid concrete core structure: Shake table tests

Perimeter diagrid concrete core (PDCC) is a structural system used for high-rise building applications. Quantifying their seismic safety is of interest to owners and decision makers due to the lack of the comprehensive understanding of the seismic performance of the high-rise PDCC structure. To systematically evaluate the seismic performance, a 36-story PDCC structure has been assessed using 1/20 scaled shake table tests. In addition, a detailed nonlinear finite element model (FEM) of the PDCC structure was built for comparison and analysis with the shaking table test. The damage to the perimeter diagrid bracings, the RC structural walls, the diagonal beam, under earthquake excitations have been assessed and discussed systematically based on the experimental and numerical results. The analysis result shows that the PDCC structure has a high performance under the earthquake load that can be used as an efficient seismic force-resisting system. Under the action of horizontal earthquakes, the axial force of the diagonal braces on the same floor varies greatly, and the axial force of the diagonal brace is related to the number of other diagonal braces on its axis. In terms of seismic damage to the perimeter diagonal braces, the most severe seismic damage is concentrated in the diagonal braces with higher axial forces, while the damage to other diagonal braces with smaller axial forces is less severe. And the seismic damage of diagonal bracing has a tendency to expand to other surrounding diagonal braces.

Seismic Responses of a Tunnel-Soil-Surface Structure System under Multidimensional Near-Field and Far-Field Seismic Waves through a Shaking Table Test

In this paper, a tunnel-soil-surface structure system is taken as the research object, and shaking table tests of multidimensional near-field and far-field seismic waves are carried out to study the dynamic response law of the tunnel, the soil and the surface structure. The test results show that the response of the soil under the far-field seismic wave is relatively stronger, but due to the high-energy velocity pulse of the near-field seismic wave, the difference in acceleration response of the soil under near-field and far-field seismic waves gradually decreases as the input ground motion intensity increases. The existence of the tunnel causes the seismic response of the soil near the tunnel to be obviously different from that of the soil far away from the tunnel. After considering the vertical earthquake action, the acceleration response of the soil slightly increases. The surface structure-pile foundation has a certain influence on the seismic response of the middle section of the shallow tunnel. In addition, the input of vertical ground motion causes greater tensile strain in the tunnel. For the deformation of the surface structure, the period of acceleration response spectra of vertical ground motion close to the fundamental period of the structure in the vertical direction leads to a significant change in the vertical response, which is also the reason for the increase of the lateral deformation. The vertical seismic component has a significant influence on the dynamic response of the tunnel-soil-surface structure system, and the influence of vertical ground motion should be fully considered in seismic design.

Spatial Distribution Characteristics of Microbial Mineralization in Saturated Sand Centrifuge Shaking Table Test.

Calcium carbonate induced by microorganisms can quickly fill and cement sand particles, thereby effectively reducing the potential for the liquefaction of sand. This process could represent a new green approach to the liquefaction treatment of saturated sand and has good prospects for application. However, owing to the diversity of microbial activities and the heterogenous spatiotemporal distribution of bacterial nutrient seepage in sandy soil foundations, the resultant complex distribution of calcium carbonate deposition in a sandy soil foundation can lead to differences in solidification strength and improvement effect. To understand the influence of earthquake action on the liquefaction resistance of saturated sand treated by microorganisms, and to evaluate the effect of microbial technology on sand liquefaction prevention under dynamic load, this study simulated the dynamic stress conditions of saturated sand under shear waves, using the world′s first centrifuge shaking table (R500B), which realizes horizontal and vertical two-way vibration. On the basis of spatial heterogeneity of microbial mineralization after centrifuge shaking table tests, the effect of microbial strengthening on liquefied sand was analyzed, and the spatial distribution of calcium carbonate mineralization was examined. The results showed that the distribution of microorganisms in the solidified soil exhibited obvious spatial heterogeneity with a significant edge effect. Although microbial mineralization effectively improved the liquefaction resistance of saturated sand, a sudden change in the process of calcium carbonate deposition altered the cementation of the sand with depth. Moreover, the curing strength had obvious complexity and uncertainty that directly affected the shear stiffness of the soil under dynamic load, and this constitutes one of the reasons for the degradation of shear stiffness of sand during liquefaction. The derived conclusions could be used as a reference for engineering applications of microbial treatment of a liquefiable sandy soil foundation.

Reliability Analysis of Slope Reinforced by Anchors under Earthquake Action

Reliability Analysis of Slope Reinforced by Anchors under Earthquake Action

Discussion of “Effects of Pile Tip Support Condition on Pile Behavior under the Action of a Large Earthquake” by Shuji Tamura, Koyo Torii, and Naoki Iriguchi

Discussion of “Effects of Pile Tip Support Condition on Pile Behavior under the Action of a Large Earthquake” by Shuji Tamura, Koyo Torii, and Naoki Iriguchi

Closure to “Effects of Pile Tip Support Condition on Pile Behavior under the Action of a Large Earthquake” by Shuji Tamura, Koyo Torii, and Naoki Iriguchi

Closure to “Effects of Pile Tip Support Condition on Pile Behavior under the Action of a Large Earthquake” by Shuji Tamura, Koyo Torii, and Naoki Iriguchi

Response Spectrum Analysis with Regular and Irregular Structures with Diagrid Systems Using Etabs

Abstract: One of the most catastrophic natural disasters is an earthquake. that wreak havoc on buildings and the loss of life. The irregularities of a building or an asymmetrical system are often found in construction due to the need for architecture view in buildings. Today, the use of buildings and economic barriers requires that vertical and unusual structures be built in urban areas. Therefore proposing measures to reduce the damage to these buildings during an earthquake is important. Strict rules of design and analysis of unusual structures have been applied in view of their high risk of injury compared to conventional structures. There are different types of structural deficiencies depending on their location and width, but most importantly, they are divided into two groups - horizontal irregularities and vertical irregularities. In the study, both irregularities are considered. The current paper seeks to investigate the proportional distribution of lateral forces arising from earthquake action at each floor level due to changes in the strength of the frame in the irregular structure. In accordance with the provisions of the Bureau of Indian Standard (BIS) 1893: 2002 (part1), the unusual G + 14 vertical building is modeled as a model of the simplified lump mass to analyze the rigidity of the floors. To analyse parameters such as storey drift, storey displacement and story base shear under seismic force under dynamic analysis are studied

Calculation for Permanent Displacement of Single Slip Surface of Multi-Stage Loess Slope Based on Energy Method

At present, there are still some gaps in the theoretical calculation of the permanent displacement of the multi-stage loess slope under the action of earthquake. Therefore, this paper firstly uses the GEO-Studio finite element software to explore the influence of the comprehensive slope rate on the permanent displacement when the slope rate of each grade of multi-stage loess slope changes and the stage of multi-stage slope changes. The results show that it is feasible to use the comprehensive slope rate to calculate the permanent displacement of the sliding body of the multi-stage loess slope under the action of earthquake. On the basis of this conclusion, in order to simplify the calculation of permanent displacement of potential sliding soil, the other geometric parameters of the multi-stage loess slope are replaced by the comprehensive slope rate, combined with the Newmark slider displacement analysis method and energy conservation principle, and then the calculation method of permanent displacement of potential sliding soil of multi-stage loess slope under the action of earthquake is deduced. Through an example, the permanent displacement calculated by the proposed algorithm are compared with those calculated by the PLAXIS 3D software and GEO-Studio software. The results show that the permanent displacement calculated by this method is close to that calculated by the GEO-Studio software, and the difference is only 2%, and thus, the rationality of the proposed method for calculating the permanent displacement of the multi-stage loess slope under the action of earthquake is verified. The algorithm proposed in this paper provides a theoretical reference for the calculation of the permanent displacement of multi-stage loess slope under the action of earthquake.

Inelastic Dynamic Time-history Analysis of a Frame-wall Structrue

The teaching building of QiaoTou School is a frame-wall structure, which has 14 storeys. In this paper, the elastoplastic model of the structure is studied. On this basis, the dynamic elastoplastic analysis of the structure is carried out by using YJK software, and the nonlinear dynamic responses of the structure, including structural deformation, component damage, are investigated under the action of rare earthquake. The results show that the buckling meets the target of "no collapse under strong earthquake".

Experimental and Numerical Investigation for Seismic Performance of a Large-Scale LNG Storage Tank Structure Model

As special equipment for storing energy, the safety performance of liquified natural gas (LNG) storage tanks under earthquake action is extremely important. To study the dynamic characteristics of the large-scale LNG storage tank structure and the dynamic response under earthquake action, the shaking table test and numerical simulation analysis of the LNG storage tank structure model are carried out. The results of the shaking table test demonstrate that the natural vibration frequency of the tank model is significantly reduced after the isolation measures are taken. The acceleration response of the seismic storage tank increases approximately linearly along the direction of height, and the seismic isolation bearing has a significant seismic isolation effect on the acceleration of the storage tank. The numerical simulation results show that the seismic responses and their spectral characteristic curves of the numerical model and the shaking table test are the same, which verifies the feasibility and rationality of the numerical model. After seismic isolation measures are taken, the seismic responses of large-scale LNG storage tanks, such as base shear force, overturning bending moment and acceleration, are reduced to varying degrees, but the displacement of the storage tank increases to some extent. When carrying out the seismic isolation design of LNG storage tanks, it is necessary to focus on the displacement of the storage tank to prevent damage of the auxiliary pipeline led by excessive displacement.

Analysis of an empirical seismic fragility prediction model of wooden roof truss buildings

To explore the vulnerability of wood roof truss buildings (WRTBs) under earthquake action, the empirical damage typical characteristics of 12,343.4 × 104 m2 and 21,490 buildings of this type of building that suffered different degrees of loss in 22 typical destructive earthquakes in China from 1993 to 2013 were observed and analysed. Based on the analysis methods of the nonlinear vulnerability model, probability statistics, and prediction model, a novel fragility probability matrix, plane, surface, nonlinear regression curve, and function model of different intensity zones under the latest Chinese macrointensity standard (GB/T 17742–2020, CMS-20) assessment were established, and vulnerability curve models were employed based on the damage ratio (DR) and actual cumulative damage probability (ACDP) parameters. According to 1993–1999, 2000–2010, and after 2011, the time-varying fragility specimen data were classified and censusly analysed. The fragility prediction curve models of DR and ACDP were performed using the probabilistic demand modal analysis method. Combined with the matrix probability and confidence interval calculation model, a novel regional mean fragility index domain model for typical structural (WRTB) vulnerability assessment was developed.

Investigation on artificial boundary problem in the combined finite-discrete element method (FDEM)

The combined finite-discrete element method (FDEM) is an advanced finite and discrete element coupling method, which can commendably simulate the large deformation and fracture process of materials. The explicit solution method in FDEM is naturally suitable for solving dynamic problems, and the key to dynamic analysis is to establish artificial boundary conditions that can be prepared to simulate infinite domain motion. At present, there is only the viscous boundary condition in the original FDEM, but this is only applicable for solving the internal source wave problems (e.g., blasting, mechanical vibration), and there are no artificial boundary conditions for solving the external source wave problems (e.g., earthquake). Therefore, three artificial boundary conditions have been developed in the present study to enhance the ability of FDEM to conduct dynamic response analysis. Firstly, the basic principle of FDEM and the existing viscous boundary condition are briefly introduced. Then, three newly added boundary conditions are introduced in sequence: (1) viscous-spring boundary condition, which can absorb stress wave energy at the boundary and restore the residual displacement to meet the actual engineering; (2) free-field boundary condition, which is coupled with free-field motion to absorb scattered waves at the lateral boundaries of the model, and the algorithms of mesh matching retrieval and coupling calculation are also introduced; (3) static-dynamic unified boundary condition, which can accurately transform the fixed boundary under the quasi-static analysis into the non-reflective boundary condition under the dynamic analysis. Finally, several classic models are built to verify the feasibility of the newly added boundary conditions. The comparison with the shaking table test also shows that the improved FDEM can be used for seismic response analysis under actual earthquakes.

Effect of uncertainty on the seismic behaviour of fixed pile-founded offshore platforms

ABSTRACT Fixed pile-founded offshore platforms require careful consideration during their analysis, design, and assessment because uncertainty in design variables can decrease the reliability of the structures. The present study investigated the sensitivity of seismic engineering demand parameters to stochastic and epistemic modelling variables for a fixed pile-founded jacket platform. Tornado diagram analysis and the first-order second-moment techniques were employed to examine the effects of 11 variables on engineering demand parameters under real earthquake loads and the importance of each variable was determined. As the nonlinear response of the pile foundation is a crucial source of nonlinearity in offshore platform response, a robust model considering soil–pile–structure–fluid interaction was employed. This study varied from previous research as it employed a three-dimensional model, fluid environment modelling, and earthquake actions in perpendicular directions. These differences resulted in more realistic approximations of the seismic behaviour of the platforms. It was found that the effects of different variables, especially water depth, should be considered in order to produce better performance evaluations of a structure for a more efficient and cost-effective design.

Evaluación de la vulnerabilidad sísmica del puente de carretera "Moche" ubicado en la carretera nacional pe1n usando el método de espectro de capacidad

In active seismic zones, such as the Peruvian coast, tools for predicting the potential negative impacts of earthquakes are essential for planning mitigation, emergency, and recovery of transportation facilities. For instance, the capacity of a road bridge network after a seismic event to carry traffic flow depends on the degree of expected damage and the related repair costs and downtime. This paper determines the degree of vulnerability of highway bridges to the action of probable earthquakes during the structure's lifetime by applying the capacity spectrum assessment method known as FRACAS (FRAgility through CApacity Spectrum assessment). This approach allows fragility curves to be obtained from analyzing a structure subjected to a series of seismic records of different characteristics. In this way, the method can explain the effect of variability in seismic demand and structural characteristics on the damage statistics simulated for the type of structure and evaluate the associated uncertainty in predicting fragility. As a case study, it is applied the methodology described in the evaluation of the Moche bridge, located in the region of La Libertad (Peruvian coast), which is in an Operational damage state according to an in situ inspection. From the seismic vulnerability assessment, it is obtained that until earthquakes with accelerations of 1.7g, the Moche bridge has a 60% probability of incursion into a Life Safety damage state, being the probability of incursion into a Collapse damage state less than 10%. This methodology is recommended to determine the reliability of bridges, considering the cumulative damage due to probable seismic events during the bridges' lifetime.

Nonlinear dynamic analysis of the deep-water bridge piers under combined earthquakes and wave actions

When the Stokes fifth-order wave is utilized to study the wave force of large-diameter bridge piers, the iterative method is usually utilized to solve the transcendental equations and then solve the wave parameter wavelength, coefficient and wave number. The solving process is particularly complicated, and the ratio of water depth and wavelength is generally assumed to be 0.1–0.15, which is suitable for shallow water depths and has not been investigated for deep water depths. In this study, the wave force and action point of the large-diameter rectangular section bridge pier under Stokes fifth-order wave action are derived, and the range of Stokes wave number is derived when the deep water level is constant. Combined with the functional analysis of transcendental equations, a program for calculating the Stokes fifth-order wave parameters is derived, and the approximate solution of the coefficient and wavelength of the Stokes wave is accurately and quickly solved. The dynamic nonlinear analysis of super deep-water large-diameter bridge pier under combined multi-dimensional earthquake and nonlinear wave action is investigated. It is found that nonlinear waves can significantly increase the dynamic response of deep-water bridge pier structure, but under combined wave and earthquake loadings on the deep-water bridge pier structure, and earthquakes play a dominant role. The influence of resonant waves and common linear waves on the dynamic response of large-diameter bridge piers in deep water depth is quite different. Resonant waves have a significant influence on the displacement response and stress response of deep-water bridge piers. When under two-dimensional earthquake and resonant wave independent loadings, the influence on the dynamic response of deep-water bridge pier structures is insignificant. When under combined earthquakes and waves loadings on the deep-water bridge pier structure, earthquakes play a significant role.

Performance Evaluation of Reinforced Concrete Columns under Simultaneously Combined Fire and Cyclic Loads

Reinforced concrete (RC) structures could suffer from the combined action of fires, earthquakes, and other loads during their life cycle; more importantly, coupled disasters lead to further deterioration and damage to structural performance. This paper investigated the multiple performances and distinguished the safe working conditions of the RC column subjected to simultaneously combined fire and cyclic loads. The numerical model considered the degradation of the mechanical properties of steel and concrete and the bond-slip performance between steel and concrete at high temperatures. The results show that the performance of RC columns with different section sizes, longitudinal reinforcement ratios, cover thicknesses, axial load ratios, and cyclic loads differs greatly under simultaneously combined fire-cyclic loads. In specific, when the cyclic load application time is less than 2 h, the cyclic load has little effect on the response of the RC column. According to the different characteristics of RC columns when subjected to combined fire-cyclic loads, the firing process of RC columns is divided into four stages. To avoid the excessive performance degradation of RC columns, the minimum designed fire resistance time of RC columns is recommended to be 2.5 times the fire resistance time of the RC column under static loads.

Seismic Analysis of Slender Monumental Structures: Current Strategies and Challenges

The preservation and seismic risk mitigation of built cultural heritage is considered today as a major priority in the international political agenda. Among the great variety of heritage structures spread worldwide, masonry towers belong to one of the most vulnerable categories against earthquake actions due to their morphological and material singularity. The proper understanding of the structural behavior of these artefacts at the micro, meso and macro scales, combined with a thorough knowledge of the best analysis practices deriving from the shared experience of the scientific community working in this field, is a fundamental prerequisite to appropriately address their seismic assessment. In this context, the present work offers an extensive discussion on the major challenges that slender monumental towers pose in terms of characterization of their actual behavior under seismic actions. A critical appraisal of the principal analysis methods applicable to the study of these structures is also presented along with a brief review of the existing modelling strategies for their numerical representation. Relevant examples are discussed in support of each argument. In spite of being a relatively young discipline, earthquake engineering has made remarkable progress in the last years and appropriate modi operandi have been consolidating to tackle the seismic assessment of unconventional systems, such as slender heritage structures. The work is conceived in a format of interest for both practitioners and researchers approaching the seismic assessment of this type of structures, and for those in need of an overall practical review of the topic.