High Earthquake Intensity Research Articles

Study on the Model Test of the Antibreaking Effect of Fiber Reinforced Concrete Lining in Tunnel

In order to study the antibreaking effect of the fiber reinforced concrete lining in the tunnel, this paper takes the a subway tunnel engineering project in F2-3 section of Jiujiawan fault as the research background and carries out the antibreaking model test of the fiber reinforced concrete lining in the active fault zone of high earthquake intensity. The results show that the antibreaking effect of the principle stress and the longitudinal strain of the fiber reinforced concrete lining are 30%∼40% and 80%∼90%, respectively, and the minimum value of the structural safety factor is increased by 4∼5 times. The antibreaking effect of hybrid fiber reinforced concrete lining is better than that of steel fiber reinforced concrete lining. The safety of steel polypropylene hybrid fiber reinforced concrete tunnel lining is the highest, and its minimum structural safety factor is 1.62. In the aspect of improving the antibreaking effect of the tunnel, the toughening effect of fiber reinforced concrete is stronger than that of reinforcing. The research results are of great significance to improve the antibreaking effect of tunnels in active fault areas with high earthquake intensity.

Ground motion duration effect on responses of hydraulic shallow-buried tunnel under SV-waves excitations

Although intensive research of the influence of ground motion duration on structural cumulative damage has been carried out, the influence of dynamic responses in underground tunnels remains a heated debate. This study attempts to highlight the importance of the ground motion duration effect on hydraulic tunnels subjected to deep-focus earthquakes. In the study, a set of 18 recorded accelerograms with a wide-range of durations were employed. A spectrally equivalent method serves to distinguish the effect of duration from other ground motion features, and then the seismic input model was simulated using SV-wave excitation based on a viscous-spring boundary, which was verified by the time-domain waves analysis method. The nonlinear analysis results demonstrate that the risk of collapse of the hydraulic tunnel is higher under long-duration ground motion than that of short-duration ground motion of the same seismic intensity. In a low intensity earthquake, the ground motion duration has little effect on the damage energy consumption of a hydraulic tunnel lining, but in a high intensity earthquake, dissipation of the damage energy and damage index of concrete shows a nonlinear growth trend accompanied by the increase of ground motion duration, which has a great influence on the deformation and stress of hydraulic tunnels, and correlation analysis shows that the correlation coefficient is greater than 0.8. Therefore, the duration of ground motion should be taken into consideration except for its intensity and frequency content in the design of hydraulic tunnel, and evaluation of seismic risk.

Seismic analysis and retrofitting countermeasure for 1315 kV capacitor with multi-column posts

A number of power substations and converter stations are inevitably built in high earthquake intensity regions. There are many types of electrical equipment with multi-column posts in power substations and converter stations. The PLC/RI capacitor with high seismic vulnerability is a typical electrical equipment with multi-column posts. A 1315 kV PLC/RI capacitor was modeled and analyzed using finite element technique. The modal analysis results show that the primary frequency of the capacitor is close to the earthquake dominant frequency. Additionally, the 2nd, 3rd and 4th order frequencies are within the range of the flat segment of the seismic response spectrum. After performing seismic analysis, the most fragile location was identified, that is the porcelain insulator at the bottom of the capacitor. The stress safety factor of the porcelain insulator is 0.71, which indicates the capacitor does not meet the seismic requirement for peak ground acceleration (PGA) = 0.3 g. To improve the seismic performance of capacitor with multi-column posts, enhancing connection stiffness of the structure is proposed. Based on this countermeasure, the thickness of the connecting plate between the upper hollow composite insulators and the porcelain insulators at the bottom of capacitor was increased from 20 mm to 50 mm. After the optimization, the 1315kV PLC/RI capacitor satisfies the seismic requirement for PGA value of 0.3 g.

Dynamic behaviour of reinforced soil retaining wall under horizontal seismic loading

Based on the status that the reinforced soil retaining wall (RSRW) is difficult to popularize in highway in high earthquake intensity region of China. The dynamic behavior of modular-block RSRW was investigated by large-scale shaking table tests. The standard soil was taken as the backfill. The concrete blocks were selected as panel. The geogrid was reinforcement. The failure mode of the wall was observed, and dynamic response and the displacements were measured. The results showed that, the middle of retaining wall panel was slightly bulged under the inputted earthquake motion, the mortar on the surface of wall was breaking down. When the input motion was WL2.0g (model scale: 1/2), the blocks at the top fell down, then the retaining wall was destroyed. The settlements of the soil and lateral displacement of the wall increased with the increase of the acceleration motion. The acceleration amplification factor is decreased with the increase of input acceleration. When the input acceleration was larger than 0.8g, the acceleration amplification factor of upper wall gradually is decreased less than 1. When model scale and inputting earthquake motion is different, the range of acceleration amplification factor is different. Shaking table tests results of RSRW with different panel forms and reinforced materials are summarized. The results show that seismic behaviour of RSRW is excellent. It is advise to revise some items of “Chinese Specification of Seismic Design for Highway Engineering” in order to promote the application of RSRW in highway.

Enhancing Friction Pendulum Isolation Systems Using Passive and Semi-Active Dampers

Friction pendulum systems (FPSs) are a common solution for isolating civil engineering structures under ground movements. The result is a base-isolated structure in which the base exhibits low shear stiffness in such a way that the input energy of the earthquake is concentrated and dissipated into it, leaving the superstructure free of damage. As a consequence, large displacements of the FPS may be demanded depending on the earthquake intensity and the fundamental period of the FPS. To accommodate these displacements, large-size isolators with high friction coefficients are usually required. However, the FPS will then exhibit poor re-centering capacity and the risk of future shocks will increase due to previous residual displacements, especially for low-intensity earthquakes. An alternative solution is to include a semi-active damper to the FPS, keeping the friction coefficient low and achieving both, limited base displacement under high-intensity earthquakes and good re-centering capacity under low-intensity ones. Thus, this work presents a design methodology for base isolators formed by an FPS with a damper added. The design methodology is applied to an FPS with a passive damper and to an FPS with a semi-active damper. Two ON-OFF control strategies are studied: (i) a fairly simple phase control, and (ii), a mechanical energy-predictive based algorithm. The advantages of semi-active FPSs with low friction coefficients with respect to FPS with high friction coefficients are demonstrated. The results with the designed semi-active FPS are compared with the single FPS and the FPS with a passive damper. Finally, the use of semi-active FPS allows us to enhance the FPS performance as the isolator size can be reduced while keeping the capacity to cope with low and high-intensity earthquakes without residual displacements.

An innovative quantitative analysis methodology for Natech events triggered by earthquakes in chemical tank farms

Natech events triggered by earthquakes are one of the major threats in chemical clusters. Earthquake can not only cause serious damage to equipment, but also hinder the rescue operations and exacerbate the evolution and escalation of accidents. In order to analyze the complicated domino accident scenarios under earthquake in chemical tank farms, an innovative quantitative analysis method is proposed. The algorithm based on Monte Carlo simulation for domino probabilities considers the multiple escalation vectors of the same accident unit and the synergistic effect of multiple escalation vectors from different units. Domino probabilities at different levels can be analyzed for specific primary scenario and overall scenarios. Two different rescue operation states considering and not considering the impact of earthquake are analyzed in case study. The results show that earthquake greatly increases the risk of chemical tank farm and rescue operations with longer time lead to higher domino probabilities due to higher escalation probabilities; the domino accident evolves faster and has higher probabilities in the primary scenario with multiple accident sources; the domino probabilities above third level are small for overall scenarios, especially in the case of high earthquake intensity. The methodology can also be applied to the analysis of complex specific accident scenarios and provide support for the setting of safety barriers and emergency resources.

Evaluation of deformation-based seismic performance of RECC frames based on IDA method

Engineered Cementitious Composites (ECC) is a typical High Performance Fiber Reinforced Cement-based Composite (HPFRCC), which possesses the characteristics of ultra-high tensile ductility and energy dissipation capacity. One of the potential applications of ECC is to replace conventional concrete in the seismic resistant structures. However, to date, the investigation on seismic performance of ECC at the structural level is still limited. This paper aims at evaluating the seismic performance of RECC frame on the basis of Performance-based Seismic Design (PBSD) concept and discussing the feasibility and practicability of applying ECC in structures for improving the seismic performance. The non-linear behavior of ECC material was simulated especially considering the strain hardening behavior in tension. By using the Incremental Dynamic Analysis (IDA) method, three types of frames, consisting of a normal RC frame, a RECC frame and an RECC/RC composite frame, were analyzed to evaluate the structural dynamic behavior of the frames. Comparative studies on the deformation limit states at five levels of seismic performance for these three different types of frames validated that RECC frames have superior deformation capacity comparing to traditional RC frames under high intensity earthquake. Comparison results also indicated that rationally applying ECC in key region of the structures can not only improve the seismic performance and deformation capacity of structures but also control the construction cost.

Failures of masonry dwelling triggered by East Anatolian Fault earthquakes in Turkey

Turkey is located on active fault zones such as the East Anatolian Fault (EAF), the North Anatolian Fault (NAF) and the Anatolian-Aegean Subduction Zone (AASZ). Ground seismicity activities of the NAF zone are relatively active compared with other faults. Eleven high-intensity earthquakes have been produced on this fault zone since 1939. Whereas the EAF zone was relatively quiescent in the last century, on the basis of historical records, destructive seismic activities occurred on the EAF zone in the last two decades. In this study, the rupture reason of faults, updated active fault data, and seismic maps are presented briefly. Moreover, failure reasons and failure mechanism of conventional masonry structures damaged from seismic ground motions on the EAF zone are evaluated in detail. Possible solutions are suggested on the basis of seismic codes. For this purpose, EAF-sourced earthquakes, i.e. 2003 Bingöl, 2010 Kovancılar (Elazığ), 2011 Maden (Elazığ), 2011 Tabanlı (Van) and Edremit (Van) hit in last two decades on this fault are investigated. Failures of conventional masonry buildings triggered from these earthquakes are assessed. Statistical evaluation, damage of earthquakes and failure pattern are deeply investigated and revealed. Eventually, one of the most significant reasons of severe damage or collapse to masonry structures due to this seismicity is the inability to construct the structures according to the requirements of seismic codes.

Calculation and Analysis of Fatigue Life of Gravity Dam Based on FEM

Gravity dam is a hydraulic structure subjected to high stress loads by its own weight to maintain its stability. Gravity dams mainly bear the pressure of reservoir water changes, the impact of high-intensity earthquakes, the wind and waves, the vibration of generator sets, etc. Therefore, the structural safety of dams is a major event related to engineering safety. It has very important theoretical significance and practical value for dam structural safety analysis. In this paper, the concrete gravity dam is taken as the main research object. The dam is modeled by the finite element method. According to the water level of the dam reservoir, the static and dynamic analysis of the dam under various responses, the deformation situation and strain situation of the dam is studied. Then combined with seismic wave selection and power spectrum estimation method, the seismic performance of the dam is analyzed. The specific method is to find the weak point of the dam and study the fatigue life of the dam to obtain the overall fatigue life of the dam.

Cyclic tests and analyses of extended endplate composite connections to CFDST columns

ABSTRACT Many existing investigations have focused on the performance of concrete filled double skin steel tubular (CFDST) members. However, there is a lack of research on the behavior of beam to CFDST column joints. This paper presents an experimental investigation and a numerical analysis of the CFDST column to composite beam joint with extended end plates. A series of joint specimens, that were composed of composite beams and square and circular CFDST columns connected by extended end plates and blind bolts, were tested under lateral cyclic loads. In addition, analytical models for this type of connection were established by ABAQUS software. The bolt washer and nut were idealized as circular parts to solve the convergence problem induced by the complex interactions. Nonlinear springs were employed to simulate the behavior of shear studs. The predicted results from the analytical models coincided well with the test results in terms of the failure modes and hysteretic curves. Furthermore, a total of sixteen parameters were analyzed to assess their influence on the structural behavior of typical square and circular CFDST column composite connections with extended end plates. The experimental and analytical results demonstrate that the extended end plate composite connections to square and circular CFDST columns have excellent seismic performance and are applicable in high-intensity earthquake regions.

Fragility-based methodology for evaluating the time-dependent seismic performance of post-tensioned timber frames

Since 2010, the construction of post-tensioned wooden buildings (Pres-Lam) has been growing rapidly worldwide. Pres-Lam technology combines unbonded post-tensioning tendons and supplemental damping devices to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. In low seismic areas, designers may choose not to provide additional damping, relying only on the post-tensioning contribution. However, post-tensioning decreases over time due to creep phenomena arising in compressed timber members. As a consequence, there is a reduction of the clamping forces between the elements. This reduction affects the seismic response of Pres-Lam buildings in the case of low- and high-intensity earthquakes. Therefore, understanding and accounting for the post-tensioning losses and their uncertainty are paramount for a robust assessment of the safety of Pres-Lam constructions. So far, however, there have been no comprehensive studies which tackle the overall seismic performance of such systems in the presence of time-varying post-tension losses and the associated uncertainty. This study tackles this research gap by introducing a comprehensive seismic evaluation of Pres-Lam systems based on time-dependent fragility curves. The proposed fragility analysis is specifically designed to account systematically for time-varying post-tension losses and the related uncertainty. The method is applied to two case studies, designed, respectively, with and without supplemental damping devices. In terms of structural performance, results show that the use of additional dissipaters mitigates the effect of post-tensioning loss for earthquakes of high intensity. Conversely, performance under low-intensity earthquakes is strongly dependent on the post-tensioning value, as the reduction of stiffness due to the anticipated rocking motion activation would lead to damage to non-structural elements.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Seismic multi-level optimization of dissipative re-centering systems

Seismic resilience is a key feature for buildings that play a strategic role within the community. In this framework, not only the structural and non-structural elements damage but also the protracted structural dysfunction can contribute significantly to overall seismic damage and post-seismic crisis situations. Reduction of the residual and peak displacements and energy dissipation by replaceable elements are some effective aspects to pursue in order to enhance the resilience. Control systems able to adapt their response based on the nature of events, such as active or semi-active, can achieve the best results, but also require higher costs and their complexity jeopardizes their reliability; on the other hand, a passive control system is not able to adapt but its functioning is more reliable and characterized by lower costs. In this study it is proposed a strategy for the optimization of the dissipative capacity of a seismic resistant system obtained placing in parallel two different groups dissipative Re-Centering Devices, specifically designed to enhance the energy dissipation, one for the low and the other for the high intensity earthquakes. In this way the efficiency of the system in dissipating the seismic energy is kept less sensitive to the seismic intensity compared to the case of only one group of dissipative devices.

Model Tests on the Antibreaking Countermeasures for Tunnel Lining Across Stick‐Slip Faults

In order to improve the structural safety and stability of the tunnels crossing stick‐slip fault, an indoor model test on the effect of tunnel antibreaking measures under the influence of fault stick‐slip movements was conducted. Using contact pressure, longitudinal strain, and safety factor, the antibreaking effect of tunnels was compared and analyzed under 5 kinds of operating conditions, mainly including no measures, structural strengthening, structural strengthening and reducing dislocation layer, structural strengthening and reducing dislocation joint, structural strengthening and reducing dislocation layer, and reducing dislocation joint. The results showed that the longitudinal strain and contact pressure of the tunnel changed markedly (from severe change to more uniform change) when the reducing dislocation measures were adopted in the test, reducing dislocation layer/joint or reducing dislocation layer and reducing dislocation joint. The effect of reducing the fault stick‐slip dislocation on the tunnel structure is very limited by only taking structure strengthening measures. The effect of reducing the fault stick‐slip dislocation on the tunnel structure is obvious by using the reducing dislocation method, and the minimum safety factor is increased by more than 8 times. The effect of resisting and reducing the fault stick‐slip dislocation on the tunnel structure is remarkable by adopting the measures of the structural strengthening and reducing dislocation layer and reducing dislocation joint, and the minimum safety factor is increased by more than 25.45 times. The results can provide reference for the design of antibreaking for the stick‐slip fault tunnel in high earthquake intensity and dangerous mountainous areas.

Numerical Modeling of Seismic Responses and Seismic Measures of Tunnel Crossing a Fault Zone: A Case Study

The investigation shows that Longxi Tunnel, across a fault zone, was severely damaged during the 2008 Wenchuan earthquake, China. In this paper, the dynamic time history analysis method is used to study the seismic response characteristics of Longxi Tunnel and the aseismic effect of seismic measures. The interfaces of the fault are simulated by bonded interfaces. The results show that high earthquake intensity, high in situ stress, and fault zone are the main reasons for damage of Longxi Tunnel. The inconsistent motion response between the normal surrounding rocks and surrounding rocks within the fault zone resulted in the damage of Longxi Tunnel, and the maximum displacement difference reaches 50 cm. With the seismic measure by setting shake absorb layer and seismic joints, the tunnel has better performance: the maximum peak internal force of the tunnel structure is reduced by about 26% and the acceleration is reduced by 30%. Seismic measures should not only be considered within fault zones but also extend to adjacent surrounding rocks. In this study, the fault seismic measures of Longxi Tunnel should be no less than 4.0 times the tunnel diameter.

Seismic Response Analysis and Connection Performance Evaluation of a Hybrid Coupled PEC Wall System

This paper proposes a hybrid coupled partially encased composite (PEC) wall system, obtained through the connection of two PEC walls by means of the shear critical steel coupling beams with an innovative welded connection. This structural solution is designed to take advantage of both the stiffness of the PEC walls (required to limit building damage under frequent earthquakes) and the ductility of the steel coupling beams (necessary to dissipate energy under medium‐intensity and high‐intensity earthquakes). The connection performance of an innovative rigid joint with different configurations in this system is studied through pseudostatic analysis, and the seismic performance of the proposed hybrid coupled PEC wall system is evaluated through multirecord nonlinear dynamic analysis of a set of case studies. Adopted finite element models are developed and validated against the available experimental results. A summary of the results is presented and discussed to highlight the potential of the proposed hybrid coupled PEC wall systems. The key feature of this system is development of a reasonable two‐level yielding mechanism (the first level is the yielding of the coupling beams, and the second level is the yielding of the PEC wall) without damage to the welded joints.

Vibration Tests and Structural Identification of the Bell Tower of Palermo Cathedral

Background: The recent seismic events in Italy have underlined once more the need for seismic prevention for historic constructions of architectural interest and in general, the building heritage. During the above-mentioned earthquakes, different masonry monumental buildings have been lost due to the intrinsic vulnerability and ageing that reduced the structural member strength. This has made the community understand more that prevention is a necessary choice for the protection of monuments. Objective: The paper aims at demonstrating a strategy of investigation providing the possibility of health judgment, identifying a computational model for the assessment of structural capacity under service and exceptional loading like/due to high-intensity earthquakes. Considering its cost, the proposed approach is applicable only for monumental buildings. In detail, activity regarding the Bell Tower of the Palermo Cathedral is described. This investigation is framed in a huge campaign aimed at assessing the health of monuments in Palermo and their capacity to resist expected seismic actions. Methods: The process of the dynamic identification of the Bell Tower of Palermo Cathedral is discussed starting from the measurement of the response by high sensitivity seismometers and the analysis of the response signals. Then, the formulation of a Finite Element (FE) model of the tower is proposed after the identification of the main modal shapes. Once the Finite Element (FE) model was assessed, it was possible to evaluate the Bell Tower safety level in service and faced with exceptional loads. Results: The structural signals recorded along the height of the tower were analyzed to recognize the variation of the frequency content varying the external environmental loads. The signals were processed to obtain the experimental modal shapes. An FE model was defined whose mechanical parameters were successfully calibrated to give the experimental modal shapes. Conclusion: The analysis of the response signals made it possible to identify the actual behavior of the structure and its compatibility with the service loads. Further, an effective structural model of the Bell Tower of Palermo Cathedral was possible for assessing its capacity level.

Rocking effect on seismic response of a multi-story traditional timber pagoda model

Characterized by discontinuous vertical elements and high aspect ratios, multi-story traditional timber pagodas in Southeast Asia have been of interest to many researchers. Combined with shake table tests on a one-fifth scaled seven-story traditional timber pagoda, this paper investigates the effect of rocking on the seismic behavior of multi-story traditional timber pagodas. Firstly, to describe the rocking behavior of timber columns, a modified empirical formula is proposed and verified by experiments. Secondly, considering discontinuous columns in multi-story traditional timber pagodas as rocking elements, mechanical properties of such columns under lateral loading are determined by use of the proposed formula. Thirdly, a simplified numerical model is developed in OpenSees, with which time history analyses are conducted to simulate the dynamic responses of the scaled timber pagoda subjected to earthquake excitations of various intensities (0.2 g, 0.44 g and 0.8 g). Finally, the numerical and shake-table experimental results are compared and discussed. It is found that the numerical simulation captures efficiently and with high accuracy most of the dynamic response characteristics along the structural height under each excitation intensity, including acceleration responses, displacement peaks and major natural frequencies. Major conclusion of this study is that the rocking-based numerical simulation can effectively predict the dynamic responses of the pagoda model under high intensity earthquakes. The proposed simulation method can be conveniently utilized to provide reasonable references for design or strengthening similar structures.

Map of Earthquake Prone Areas Using Geographic Information Systems(Peta Daerah Rawan Gempa Menggunakan Sistem Informasi Geografis)

This study aims to map the earthquake prone areas, and identify the nearest alternative route for evacuation of earthquake victims in Singkarak District, Solok Regency, West Sumatra. This research method was conducted with descriptive methods that analyzed by GIS (Geographic Information System) based on intensity scale (MMI). The results of this study stated that 90% of villages in Singkarak District had a high earthquake intensity, with an acceleration of the land surface of more than 0.34 g. For evacuation areas can be directed away from areas with steep cliffs and areas close to high buildings and should be directed in the direction close to Lake Singkarak, because the area around this has a low earthquake risk with earthquake acceleration of only 0.1 g.

Verification of stochastic seismic analysis method and seismic performance evaluation based on multi-indices for high CFRDs

Many high concrete-faced rockfill dams (CFRDs) are located in areas with high earthquake intensity where the ground motions are characterized by randomness; consequently, it is significant to study the seismic responses and evaluate the seismic performance using dynamic time-history analysis by a stochastic vibration method based on failure probability theory. In this paper, a recently developed generalized probability density evolution method (GPDEM) coupled with a spectral representation-random function method is verified to be suitable for strongly nonlinear structures in high CFRDs during earthquakes by comparing the accuracy and efficiency of the GPDEM with those of the Monte Carlo method (MCM). The GPDEM combined with the currently deterministic dam finite element time-history response analysis using a series of simple and common methods, is adopted to analyze the stochastic seismic responses, dynamic probability evaluation and failure probability of high CFRDs subjected to stochastic earthquake excitation. The statistical and probabilistic information of the typical physical quantities are compared between the GPDEM and MCM after a series of deterministic dynamic calculations, and the dynamic nonlinear behavior of rockfills and the random characteristics of ground motions are presented. The strong correspondence between the results obtained using the traditional stochastic probability MCM analysis and the GPDEM analysis demonstrates the accuracy and effectiveness of the newly proposed method despite its significantly lower computational burden. Finally, the failure probabilities of a high CFRD with different failure grades based on three universal evaluation indices are determined by constructing a virtual GPDEM process. The results demonstrate that the GPDEM shows promise as an approach that can reliably analyze strongly nonlinear structures, such as earth-rockfill dams and other geotechnical engineering structures.