Time History Analysis Method Research Articles

Seismic design and performance analysis of perforated rubber buffer layer in tunnel

Tunnels may be damaged under earthquakes, which has been observed by many earthquake events, and the buffer layer is proposed and widely investigated as a damping measure. The rubber is considered as a qualified buffer layer material because of its small elastic modulus and super elasticity, but its high price makes it difficult to apply in practical engineering. Therefore, four types of rubber buffer layers are proposed in this study, including the common rubber buffer layer and three types of perforated rubber buffer layers (PRBL), which can reduce the seismic damage and cost of tunnels. A pseudo-static method for calculating the seismic response of tunnels under horizontal and vertical earthquake motions is proposed and verified. Based on proposed pseudo-static method, a seismic design method for the buffer layer is present, and the proposed seismic design process is used to study the seismic mitigation performance of buffer layers. The initial design of the buffer layer under earthquake action E1 is carried out by pseudo-static method, and then the seismic mitigation performance is verified through dynamic time history analysis method under earthquake action E2. The earthquake action E1 and earthquake action E2 are the earthquake actions with short and long return periods of the engineering site, respectively. The results show that the common rubber buffer layer has almost no seismic mitigation performance, and the three types of PRBLs have good seismic mitigation performance. The type IV buffer layer is strip-shaped PRBL and the holes are along the longitudinal direction of the tunnel, and it has optimal seismic mitigation performance. The effects of vertical earthquake motion and peak ground acceleration (PGA) on the seismic mitigation performance of the buffer layer are studied. The results show that vertical earthquake motion has little effect on the seismic mitigation performance of different types of buffer layers. For different PGAs, the type IV buffer layer is able to efficiently decrease the peak internal force of secondary lining. The results also prove the validity of design method.

Human-Induced Vibration Analysis and Reduction Design for Super Long Span Pedestrian Arch Bridges with Tuned Mass Dampers

With the increasing demands on span length, aesthetics, and urban landscapes of pedestrian bridges, the fundamental frequency of pedestrian bridges is continuing to decrease, and their vibration and walking comfort issues are becoming increasingly prominent. The pedestrian load model of the pedestrian bridge was introduced here referencing current design specifications, and a spatial finite element model was established to study the dynamic characteristics of the case of a long-span pedestrian arch bridge. The comfort of the bridge under human-induced vibration was analyzed using the time history analysis method. According to the optimal damper parameter expression, the design parameters of the damper were obtained. In addition, the vibration reduction effects of different generalized mass ratios were analyzed, and the damping effects of setting the tuned mass damper (TMD) at different positions were compared. The results indicated that setting the TMD on the bridge can enhance the damping effect, and the transverse vibration can be suppressed by setting TMDs on both the arch ribs and the bridge deck. The research content could provide recommended parameters for the vibration reduction design of long-span pedestrian arch bridges.

EVALUASI KINERJA STRUKTUR BANGUNAN GEDUNG TAHAN GEMPA DENGAN METODE ANALISIS RESPONS SPEKTRUM DAN TIME HISTORY

The city of Bandung is one of the cities that is prone to earthquakes because it is passed by the Lembang fault. Therefore, buildings in the city of Bandung should have implemented the concept of earthquake-resistant buildings in their construction. To avoid the occurrence of damage or collapse of the structure of the building against an earthquake, it is necessary to analyze the building against the earthquake. This study aims to determine how many deviations occur in the building due to the earthquake and the performance of the building structure. The method used is the response spectrum and time history analysis method and then evaluates the performance of the structure against earthquakes using the ATC-40 standard. The building that is the case study is the Directorate of Drugs and the Directorate of Intelligence and Security for the West Java Police, which consists of 5 floors. Structural modeling and analysis were performed using ETABS v20. Earthquake records used are Imperial Valley, Kobe and Trinidad earthquakes. Based on the results of the analysis of the maximum deviation with the response spectrum method 26.74 mm in the X direction and 26.46 mm in the Y direction. Meanwhile, for the time history analysis, it was obtained 33.05 mm in the X direction and 28.96 in the Y direction. The maximum value of the total deviation obtained 0.0016 m and the maximum value of inelastic deviation obtained 0.0014 m so that it shows the level of performance of this building structure based on ATC-40 is Immediate Occupancy (IO), which means the structure is in a safe condition.Keywords : ATC-40, earthquake resistant buildings, spectrum response, time history,

Nonlinear seismic analysis of irregular base isolated structures using a new modified lateral load pattern

Nowadays, seismic isolation systems are increasingly used by engineers for retrofitting existing structures and designing new ones. Nevertheless, limited studies have been conducted on the performance evaluation of the nonlinear static analysis methods for estimating the seismic demands of the base isolated structures. The current study proposes a new modified lateral load pattern for seismic analysis of base isolated structures using modified capacity spectrum method (MCSM). Moreover, this study investigates the applicability of the modal pushover analysis (MPA) and modified capacity spectrum methods for assessing the base isolated structures with setback irregularity. To this end, two types of steel moment resisting structures including 3-story (low-rise) and 9-story (medium-rise) with different irregularities in elevation are considered. All the structures are isolated by three types of lead rubber bearing (LRB) isolators with various stiffnesses. In order to consider the effect of ground motion, two types of near-fault and far-fault ground motions are selected. To evaluate the performance of the MCSM and MPA methods, the structural seismic demands estimated by these methods are compared with their benchmark values obtained by the nonlinear time history analysis method. The obtained results show the superiority of the modified capacity spectrum method and the effectiveness of the new modified lateral load pattern presented for this method.

The Seismic Response of Ultra-High Voltage Gas-Insulated Transmission Lines

As an important part of the substation, the seismic capacity of ultra-high voltage (UHV) electrical equipment is related to the safe and stable operation of the substation and the whole power grid. The UHV gas-insulated transmission lines (GIL) have many structural characteristics, such as long pipeline distance, the large span between supports and the obvious amplification effect of supports. Its natural frequency is close to the predominant frequency of the seismic wave, resulting in its susceptibility to resonance or resonance-like and high seismic susceptibility. In order to analyze the seismic performance of UHV GIL better, the vibration mode decomposition response spectrum method and the dynamic time-history analysis method are used to analyze the seismic response of UHV GIL in this paper. The search for seismic weak positions of GIL is a reference for effectively improving the seismic performance of UHV GIL.

A Review Paper on Linear and Nonlinear Analysis of G+15 Story Building with and without Shear Wall by using Time History Analysis Method

Abstract: An earthquake is the result of the rapid release of deformation energy stored in the earth's crust, which generates seismic waves. The structures are sensitive to earthquakes and structural damage. In order to take preventive measures against damage to structures due to ground motion, it is important to know the characteristics of ground motion. The most important dynamic characteristics of an earthquake are peak ground acceleration, frequency content, and duration. These characteristics play the main rule in the study of the behavior of structures during earthquake ground motion. Earthquake analysis of a multistory structure is performed using linear and non-linear methods. The response spectrum analysis method is linear dynamic analysis. The time history method is used for nonlinear dynamic analysis. In this paper, the response spectrum method is used for linear analysis. The time history method is used for nonlinear analysis. For the time history method Both analyzes are performed using ETABs software. Linear Time History analysis of RCC building considering 4 different time histories is carried out. The time history data of Bhuj earthquake, Chamba earthquake, Chamoli earthquake and NE (Myanmar) earthquake has been considered. Here, a building has been modelled using Etabs software for seismic analysis and time history analysis. This paper highlights the effects of different time histories of different region on the same structure. The effects under considerations are story shear, building deflection and story drif

EVALUASI KINERJA PILAR JEMBATAN LEMAH IRENG II BERDASARKAN PERFORMANCE BASED SEISMIC DESIGN

Lemah Ireng II Bridge is a type of box girder balance cantilever bridge located in Semarang Regency, Central Java, which was completed in 2014. The renewal of bridge loading regulations in 2016 consisted of SNI 1725:2016 for standard load and SNI 2833:2016 for earthquake load. Changes in earthquake loading regulations resulted in an increase in the ground surface spectra value in the short period (Sds, T=0,2 second) in the longitudinal direction by 38.47% and in the transverse direction by 45.39% as a result of updating the earthquake map and the earthquake response modification factor. To determine the level of bridge performance against the applicable earthquake regulations based on the pier structure parameters, the Non-Linear Time History Analysis (NLTHA) method is used. The NLTHA method uses seven deaggregated ground motion records which aim to represent the ground motions that occur at the bridge site. Parameter limits at the pier to determined performance level of bridge based on NCHRP Synthesis 440 and NCHRP Research Report 949. According to the results of performance-based analysis, the bridge pier structure meets the Fully Operational performance level based on the parameters of drift, compressive strain of concrete and tensile strain of steel reinforcement. At this level of performance, after an earthquake the structure suffers very little damage so no repairs are needed and the bridge can function immediately after the earthquake.

On the Influence of Unexpected Earthquake Severity and Dampers Placement on Isolated Structures Subjected to Pounding Using the Modified Endurance Time Method

The aim of this study is to investigate the performance of isolated structures by considering the possibility of impact under severe earthquakes. In the design of isolated structures, the required displacement capacity is determined based on the considered earthquake hazard level. However, there is a possibility of an impact caused by moat walls or adjacent structures under severe earthquakes. Dampers are used in this study to improve the performance of structural and nonstructural components. In this regard, three isolated structures (6, 9, and 12 stories) equipped with Triple Friction Pendulum Isolator (TFPI) are designed under earthquake hazard levels of BSE-1 with return periods of 475 years. Based on the different positions of these three structures relative to each other, four scenarios are defined to investigate the effect of impact. Modified endurance time (MET) method, as a cost-efficient nonlinear time history analysis method, is employed for structural evaluation under variable earthquake hazard levels. The placement of dampers is also taken into account in evaluating the effect of dampers. Therefore, the structures have been retrofitted once by adding damping and stiffness devices (ADAS) on the stories and once by adding fluid viscous dampers (FVD) at the isolated level. Results indicate that structures might collapse under earthquake hazard levels of BSE-2 with return periods of 2475 years. This matter is influenced by the adjacency of two isolated structures next to each other, and the severity of this fact depends on the height of the structures and the displacement capacity of the isolators so that the tall, isolated structures have decreased the performance of the adjacent shorter isolated structure. Moreover, the placement of dampers has a significant influence on the performance of structural and nonstructural components, depending on the reason for the impact.

Comparative study of sinus earthquake forces and ground motion on structure behavioral response using linear time history analysis method

This study aimed to calculate the design earthquake with a harmonic sine wave approach at a frequency of 1.5 Hz; 2.5 Hz; 3.5 Hz; 4;5 Hz, as well as Loma Prieta, Northridge, and Kobe ground motion. In addition, a structural response review was also carried out based on a comparison of the effects of the ground motion and sine wave earthquake forces. This study used an experimental method of modelling an apartment building with a scale of 1: 50. The case study was located in Mantrijeron, Yogyakarta, which has a seismic category in the medium-size class. The analysis phase began with material definition, element dimension estimation, modelling by analysis software, loading estimation, structural analysis, and comparison of structural responses based on the deviation. The results indicate that the building model could withstand dynamic loads from harmonic waves up to a frequency of 5.5 Hz for one minute of vibration. The most significant deviation is shown at a frequency of 4.5 Hz with an x-axis direction of 0.110 and a y-direction of 0.160. The structural response resulting from ground motion loading shows that the highest deviation occurred due to the influence of the Kobe earthquake, with a deviation of 0.063 in the x-axis direction and 0.054 in the y-axis direction. Based on these results, the effect of harmonic sine waves is greater than the ground motion loading on the response of the building structure, so it is used as an experimental loading through a vibrating table with the actual residual deviation results showing a value of 0.9 mm in the y-axis direction. The difference in structural response results could be caused by the supports and connections modelling in planning through analysis software which could not precisely represent the actual implementation of the building model.

Case Study of Seismic Assessment of a Short Irregular Historic Reinforced Concrete Structure: Time-History Vs. Pushover Nonlinear Methods

ABSTRACT The selection of appropriate analysis method for the seismic assessment of existing structures and the reliability of its results are of utmost importance, as they determine the magnitude of potential damage in a future seismic event, as well as the demands for strengthening and ductility during retrofitting. This paper examines a historical concrete building in Nicosia, Cyprus, that exhibits strong irregularities, both in plan and elevation. The aim is to compare the results of the static pushover to the nonlinear time-history analysis method, to better understand the applicability limits of the pushover analysis when applied on irregular, historic concrete structures.

Research on seismic analysis methods of large and complex underground pipe structures in hard rock sites

In order to study the seismic design methods of large and complex underground pipe structures (LCUP) in hard rock sites, firstly, the structural characteristics of LCUP and the calculation principles of four typical seismic analysis methods were carefully sorted out. Secondly, based on different seismic analysis methods, the deformation and internal force response of three representative pipes were studied in detail, and the calculation accuracy and error causes of each seismic analysis method were analyzed. Finally, the advantages, disadvantages and applicability of the seismic analysis methods on typical pipes were systematically explained, and the technical route for seismic design of LCUP was proposed. The results showed that both the reaction displacement method and the reaction acceleration method can effectively analyze the seismic performance of standard section structures. The three-dimensional time-history analysis method was comprehensive and highly accurate for seismic analysis of complex spatial cross-node structures. The rigid connections of different pipes leaded to serious discontinuities in stiffness at the intersection, and the deformation and bending moment distributions were highly concentrated at the height away from the intersection. The influence range of the intersection was about three times the width of the intersection, and LCUP was classified according to this influence range. For standard section structures, seismic analysis should be carried out using the reaction acceleration method or reaction displacement method, while for spatial cross-node structures, three-dimensional time-history analysis should be used for seismic analysis. This scientific seismic design method achieved multiple optimal balances of seismic safety, analysis accuracy, efficiency and economy in the seismic analysis of large and complex underground structures. A theoretical basis and useful reference for the scientific design, accurate prediction and seismic safety evaluation of seismic response of LCUP were provided in this paper.

Research on seismic absorption of high-speed railway segmental assembled round-end hollow pier with low yield point steel connection buckle

The research aims to enhance the seismic safety of the segmental assembled round end hollow pier (SAREHP) of high-speed railway in high intensity seismic regions and ensure the repairability of the pier after earthquake. A low yield point steel connection buckle (LYPSCB), which is easy to be installed and to be replaced after earthquake damage, was proposed as a new seismic absorption measure for the pier, and the seismic absorption effect of the LYPSCB was deeply studied. Firstly, the nonlinear numerical model of the SAREHP with energy dissipation bar (SAREHP-EDB) was established according to the pseudo-static test results of the pier completed. Based on the numerical model of the SAREHP-EDB, the SAREHP with the LYPSCB (SAREHP-LYPSCB) was established and corrected. Subsequently, the influence of the LYPSCB on the hysteretic behavior of the SAREHP was studied, and the hysteretic behavior of the SAREHP-LYPSCB was comprehensively compared with a reference to the SAREHP-EDB. Furthermore, considering the far-field seismic wave and the near-field seismic wave with or without pulse, the seismic absorption effect of the LYPSCB was revealed through dynamic time history analysis method. The research results indicated that, by increasing the section contribution rate of the LYPSCB, the horizontal resistance, loading and unloading stiffness as well as energy dissipation capacity of the SAREHP-LYPSCB are significantly improved. However, the residual displacement of the pier is also indirectly increased. Therefore, it is suggested that the section contribution rate of the LYPSCB is controlled and designed in combination with the seismic target displacement and self-centering capacity demand of pier. The hysteretic behavior of the SAREHP-LYPSCB is better than that of the SAREHP-EDB, which indicated that the LYPSCB possesses better seismic absorption effect. Note that the seismic absorption effect of the LYPSCB is more obvious in resisting strong earthquake, in which the seismic absorption rate can reach 80 %. The near-field pulse seismic wave has the greatest impact on the seismic response of the SAREHP-LYPSCB compared with other types of seismic wave, which should be paid special attention.

Nonlinear Time History Analysis for Seismic Effects on Reinforced Concrete Building

A typical Reinforced Concrete (RC) building frame comprising of RC columns and connecting beams that participates in resisting the earthquake forces. Due to earthquake, reversal tension generates at both faces of a beam and column; and hence damage occur in the frame for the disability of tension carrying capacity of concrete. Therefore, the structural performance of RC building for seismic load has been analyzed by nonlinear time history analysis method for this study. A residential building located in Dhaka, Bangladesh subjected to various types of gravity load and seismic load was considered to analyze using ETABS software as per the guideline of BNBC (2020). According to the guideline of ATC 40 (1996), the seismic performances like maximum displacement and story drift for RC building were evaluated both at structural and element levels by applying El Centro (1940) ground motion at the base of the structure. Formation of plastic hinges is used as the basis to evaluate the local performance and story drift is used to evaluate the global performance. At first, the considered building was designed only for gravity load, and then for both gravity and seismic load according to BNBC (2020). Further studies have been performed on that building considering double height column at a story level. It was observed that the maximum displacement and story drift exceeds the allowable limit for all the considered cases if seismic load is applied on the structure.

Study on the shock-absorbing effect of a new staggered story isolated structure under the long-period earthquake motion

The finite element model of a new staggered story isolated structure is established. Using the time-history analysis method, the dynamic response state of the structure at each time step is calculated by integrating the acceleration time-history data step-by-step. Three different types of seismic waves (ordinary seismic wave, near-fault impulse seismic wave, far-field quasi harmonic and long-period seismic wave) are input respectively for dynamic time history analysis. The result indicates that the new staggered story isolated structure has a good shock absorption effect under the action of three different types of seismic waves. There are certain differences in the shock absorption effect under the three kinds of ground motions. The seismic response under ordinary ground motions is minimal, but the seismic response of the structure increases in response to far-field quasi harmonic and long-period ground motions and the near-field fault pulse ground motions. Meanwhile, the inter-story shear force, inter story acceleration, inter-story displacement, damage, and the energy input are all increasing, However, compared with the aseismic structure, the inter-story shear force is reduced by 48%, the inter-story acceleration is reduced by 23%, the inter-story displacement is reduced by 48%, and the energy dissipation rate of the isolated layer is 65%. In addition, the isolated bearing is in good condition during occasional earthquakes under normal ground motion. However, the bearing exceeds the permissible range during near-fault impulse ground motion and far-field harmonic and long-period earthquakes. Therefore, special consideration should be given to the area where the far-field harmonic and long-period ground motion are involved.

Analysis of building structure performance due to earthquake load with time history analysis method using ETABS (Extended Three-Dimensional Analysis of Building Systems) software (case study: the faculty of medicine building at IGM University)

The inability of a building to withstand deviations due to earthquake strength exceeding the required safe limit is one of the factors causing the collapse of the building. Mitigation efforts that can be made to overcome the impact of earthquakes include evaluating the performance of building structures. In this study, the Faculty of Medicine building at Indo Global Mandiri University was evaluated using the time history analysis method using ETABS V.18. The results of the analysis showed that for the El Centro (1940), Mentawai-West Sumatra (2007), and Chihuahua (2010) earthquakes, based on the value of inter-level drift and maximum inter-level drift on the effect of planned earthquake loads, the service limit performance was fewer than 0.017 meters and the ultimate limit performance was fewer than 0.080 meters, so it has met permit requirements according to the Indonesian standard (SNI 1726-2019) and is included in the safe category. Based on the performance of ATC-40 obtained for the El Centro (1940) and the Mentawai-West Sumatra (2007), it produced the performance level of the structure "Immediate Occupancy", while when subjected to the load of the Chihuahua (2010), it produced the performance level of the structure "Damage Control".

Simulation analysis of structural nonlinear seismic response

Faced with the difficulty of analyzing structural nonlinear seismic response, this study focuses on the reinforced concrete frame structure and designs a frame that meets the specifications. Artificial synthetic seismic records and natural seismic records were selected, and the acceleration response of the first story of the structure was used as the output sample for the study. On the basis of a nonlinear autoregressive moving average model with external inputs, a neural network model was constructed and nonlinear seismic response simulation analysis was conducted. These results confirm that the research method has good predictive performance and can effectively predict structural nonlinear seismic response. Under the action of artificial earthquake records, there is a small difference between them and the acceleration time history curve and acceleration response peak obtained from time history analysis. Under the action of artificial seismic record ACC12, when the time is 25 s, the calculation results of time history analysis and research methods are 1.715 m/s2 and 1.403 m/s2, respectively, with the former being 0.312 m/s2 smaller than the latter. In natural earthquake records, with a characteristic period of 0.30 s, under the action of natural earthquake record USA00668, the relative energy of time history analysis is 4.997 m2/s when the time is 30 s, which is 0.938 m2/s higher than the research method. The research method can accurately analyze the nonlinear seismic response of the results.

Soil-Structure Interaction Effects on Seismic Response of Multi-storey Buildings

The effect of soil-structure interaction (SSI) on the seismic responses of multi-storey buildings is investigated. The execution of SSI effects is conducted in two ways viz. Winkler approach and soil continuum approach. Time-history analysis methods are used for the seismic evaluation of parameters like time period, modal mass participation, base shear, lateral displacement, storey drift and inter-storey drift ratio. The present study consists of two parts; one is fixed base analysis i.e. without SSI, and the other is flexible base analysis i.e. with SSI. The buildings are modelled using finite element-based software SAP2000, where the equilibrium equations are solved by Hilber-Hughes-Taylor (HHT) method. A parametric study is performed with existing ground motion and varying numbers of stories to inherit the above parameters' responses. The results obtained from flexible base conditions are compared to those corresponding to fixed base conditions. The study shows that the behaviour of the structure changes under the SSI conditions and it may become vital in some cases; however, ambiguity also subsists with SSI.

Evaluation of Seismic Response of Irregular Buildings Subjected to Near-Field Earthquakes

This study deals with the evaluation of the seismic performance of irregular buildings by comparing various seismic responses of six types of building, namely regular building, setback building, stepped building, mass irregular building, stiffness irregular building, and building with floating columns which are constructed of Reinforced Cement Concrete (RCC) subjected to extreme earthquake loads. The nonlinear time history analysis (NTHA) method is carried out to obtain different seismic response parameters for all considered irregular and regular buildings. The structural response results are compared by applying real earthquake records of different near-field and Far-field earthquakes and were compared for four different seismic response parameters which include top storey displacement, inter-storey drift, top base shear, and pattern of plastic hinges formation. This research concludes that the storey displacement, storey drift, and top base shear is significantly less for stepped and setback buildings, and significantly high for mass irregular, stiffness irregular, and floating columns buildings as compared to a regular building. Stepped buildings yield less responses and high responses are yielded in the building with floating columns.

PERFORMANCE EVALUATION OF 34 FLOORS BUILDING STRUCTURE IN SURABAYA BASED ON SNI 1726:2012 AND SNI 1726:2019

Indonesia has undergone several earthquake regulations updates, starting from Peraturan Muatan Indonesia 1970 to SNI 1726:2019. This update requires earthquake loads with a larger return period. This has an impact on the existing buildings that were planned to use the old regulations. It is feared that the building does not meet the requirements required by the new regulations, so a review of the performance of the building is needed. This research will use a case study of a Cornell apartment building with 34 floors in the city of Surabaya, which is planned based on SNI 1726:2012 with concrete regulations SNI 2847:2013 and will be evaluated with SNI 1726:2019. The analysis uses Performance Based Design with the Nonlinear Time History Analysis method which was carried out in the 2016 ETABS program. The background to the use of the Performance Based Design method is its use which is quite easy to apply and can also be used to measure the efficiency of the structure being reviewed. The use of Nonlinear Time History Analysis is based on the fact that the use of this method has been regulated in SNI 1726:2019 and the use of this method is considered closest to the actual conditions in the field. Nonlinear Time History analysis in this study uses time history data from the Chichi earthquake in Taiwan in 1999. The evaluation of building performance is based on the performance level refer to FEMA 356. The results of the case study on the comparison of the two regulations show that there is an increase in the basic earthquake force by 1.02%. Meanwhile, in relation to drift ratio analysis, an increase of 1% on the X axis and 5.5% on the Y axis is obtained.

Dynamic Analysis of Historical Masonry Arch Bridges under Different Earthquakes: The Case of Murat Bey Bridge

Historical structures, which constitute an important part of our cultural heritage, should be well protected and carried into the future. Masonry arch bridges are significant part of these structures. In this study, the single-span Murat Bey Bridge in the province of Kütahya, built in 1460, was studied as a numerical application. Firstly, three dimensional finite element model of the bridge was constituted with SAP2000 finite element program. Static analysis of the bridge under its own weight was carried out. The modal analysis method was used to obtain the dynamic characteristics of the bridge. Then, time-history analysis method was applied for seismic evaluation of the bridge. For this purpose, the acceleration records of the 1998 Adana, 2003 Bingöl, 2011 Van and 2020 Elazığ earthquakes were taken into consideration. As a result of the dynamic analyses carried out, the displacement and stress graphs occurring on the bridge were examined. The highest displacement and stress values on the historical bridge were obtained from the acceleration records of the 2011 Van earthquake.