Evaluation of the seismic response of stone pagodas using centrifuge model tests

This study attempts to propose dynamic centrifuge model tests as a method of seismic risk assessment in order to discover how stone architectural heritages with masonry structures have endured seismic load, and whether there is any possibility of future earthquake damage. Dynamic centrifuge tests have been conducted for one fifteenth scale models of Seok-ga-tap and the five-storey stone pagoda of Jeongnimsa temple site, which are Korean representative stone pagodas. In order to make input motions of the earthquake simulator, site investigation and site-specific response analysis have been performed. The models of two stone pagodas, which have the same number of pieces with the real structures, have been produced and the dynamic centrifuge tests have been conducted for the model pagodas. Accelerometers were attached at different heights of the pagoda. The measured acceleration records and frequency responses were analysed during dynamic centrifuge test. Two real earthquake records, Hachinohe and Ofunato earthquakes and a sweeping signal with ranged frequency were utilised for input motions of dynamic centrifuge tests to evaluate the behaviour of the stone pagodas. For Seok-ga-tap models, it was observed that acceleration tends to be amplified with height. The third floor body shows at most 2.5 amplification of acceleration in comparison to the surface ground. The amplification was at a frequency of 3.83 Hz and it was considered as the natural frequency of the pagoda. For the five-storey stone pagoda, the seismic wave energy significantly reduced while it passed the first body floor, and then the peak acceleration was gradually amplified upwards. It was found that the pagodas did not collapse when the peak acceleration of ground surface was raised to 0.4 g. Given that the maximum design seismic acceleration specified in Korean seismic design guide is 0.22 g and the amplification ratio of peak acceleration in the supporting ground of the pagodas ranges from 1.45 to 1.74, it can be shown that the two pagodas are stable against 2400-year return period earthquake level, and have excellent seismic performance.     

砖石古塔抗震性能评估方法及抗震加固措施研究

为了提高砖石古塔的抗震性能,针对其地震反应特点,研究了砖石古塔的抗震薄弱部位、抗震性能评估方法、评价指标以及抗震加固措施。主要研究结论为:（1）提出了采用极限承载能力与层间位移角2个指标综合评估砖石古塔的抗震性能,并通过工程实例验证了该方法的有效性。（2）提出了对穿锚杆锁定内外钢带围箍和竖向贯穿钢筋为主,聚丙烯酸脂乳液砂浆裂缝注浆为辅的砖石古塔综合抗震加固措施。（3）砖石古塔塔底截面为承载能力抗震薄弱部位,抗拉能力不足是导致塔体破坏的主要原因。（4）地震作用下,砖石古塔随着塔体层数的增加,层间位移角增大,顶层塔体为变形能力薄弱部位。该研究结果可为砖石古塔的抗震性能评估与抗震加固提供参考。     

砖石古塔抗震性能计算

砖石古塔为典型的中国古代建筑。由于建造年代久远,大多数古塔都遭受过地震的破坏。5.12汶川大地震对四川省都江堰奎光塔造成了严重的破坏。为了对其进行有效的抗震保护,本文结合奎光塔的结构特点,讨论了中国砖石古塔的抗震机理,得到了砖石古塔的抗震性能计算方法。     

2015年尼泊尔地震三维发震构造及地震危险性研究

2015年4月25日尼泊尔M_W7.8地震发生在喜马拉雅造山带上,人们普遍认为该地震不足以释放该造山带上累积的能量,但对该地区后续地震危险性评价多基于二维或是假三维的形变反演计算结果.本研究从2015年尼泊尔地震主震与其最大余震M_W7.3地震之间的关系出发,着重分析讨论了尼泊尔地震的时间和空间的非均匀性,结合震源机制解、地壳速度结构、精定位后的余震分布及InSAR反演结果,建立了三维发震构造模型,利用非线性摩擦有限元方法,对一个地震周期内断层摩擦行为和块体变形进行了模拟,将计算结果和地表同震形变、形变反演的同震破裂、历史地震时空演化进行对比,在确认该三维模型可靠性的基础上,讨论了该地区后续地震的可能位置,认为在1934年比哈—尼泊尔M_W~8.1地震以东区域,还存在发生大地震的可能,在最大余震M_W7.3地震东南部位,还存在发生中大地震的可能.     

基于IDA方法的小雁塔结构抗震性能评估

以小雁塔结构为原型,通过试验研究建立其材料本构模型;应用IDA分析方法,建立IDA分析曲线并对小雁塔结构进行增量动力弹塑性分析,判断小雁塔结构的最不利位置,定义IDA分析的极限状态;将IDA曲线的斜率下降幅值与小雁塔结构性能水准相对应,划分小雁塔结构的性能水准指标;通过对小雁塔结构在增量地震动强度作用下地震响应分析和不同性能状态下各层的楼层位移和层间位移角的变化规律,对小雁塔结构进行了抗震性能评估;研究表明:基于IDA分析方法的小雁塔抗震性能评估可以考虑结构抗震能力的随机因素,精确地描述小雁塔结构在地震过程中的行为。该方法为类似砖石古塔结构的抗震性能评估提供了新途径。     

Seismic test of a full‐scale model of a five‐storey stone pagoda

A moderate size earthquake of magnitude 5 occurred at Whagae‐Myun, Hadong‐Gun, Kyongsangnam‐Do, Korea on 4 July 1936. It caused severe damage to the buildings and other structures in Sang‐Gye‐Sa, a famous and beautiful Buddhist temple. A five‐storey stone pagoda was standing in front of Keumdang, the main building. The top component of the pagoda was tipped over and fell down to the ground during the earthquake. In order to have a quantitative estimate of the intensity of the earthquake, a full‐scale model was constructed through a rigorous verification process. The completed model was mounted on a shaking table and subjected to two kinds of dynamic test: exploratory test and fragility test. The exploratory test was performed with low intensity shaking. In the fragility test, the failure modes of the model were investigated while increasing the shaking intensity. The construction details of the model are described and test procedures are reported. Important relations between failure modes and characteristics of ground motion were obtained from the tests. The intensity of the 1936 earthquake was estimated from the examination of test results. Copyright © 2003 John Wiley & Sons, Ltd.     

中国及邻域强震震后变形监测及岩石流变性质研究

大地测量技术观测的震后变形是地壳和地幔岩石对同震应力扰动的变形响应,震后变形的强度及时空演化特征主要受断层面的摩擦性质、下地壳及上地幔岩石的流变参数等控制。震后大地测量被广泛用于研究断层及深部岩石的流变性质及其动力学过程,是对岩石力学实验、冰后回弹等手段探测结果的检验和补充。本文回顾性地总结了中国及邻域中强地震震后变形监测成效,这些震例主要集中在青藏高原内部和边界带。通过对包括昆仑山口西地震、汶川地震和尼泊尔地震在内的发生在青藏高原及周缘的强震震后变形机制、岩石圈流变参数约束等方面的研究,大大提升了对青藏高原不同区域深部岩石流变结构和性质的认识,为研究地震周期变形、地震危险性、青藏高原的形变模式、高原演化动力学提供了观测依据和定量参数。同时,指出进一步约束青藏高原深部岩石流变参数,一方面需要进一步提高西部地区连续GNSS监测能力,另一方面需要与地球物理成像技术进行融合。     

The Gorkha earthquake of April 25, 2015 in Nepal: Tectonic position,aftershock process,and possibilities of forecasting the evolution of seismic situation

The characteristics of the foci for the main shock and strongest aftershocks of the Gorkha earthquake of April 25, 2015 in Nepal are described. The macroseismic data and examples of seismic dislocations are discussed. The progression of the release of seismic energy by the aftershock process is analyzed. The data for the geophysical and seismological precursors of the main shock and the strongest aftershock of May 12, 2015 are presented. These data allowed us to formulate the short-term forecast of this event.     

基于ECC的小雁塔抗震加固性能分析

高延性纤维增强水泥基复合材料(ECC)是一种高强度、高延性的新型建筑材料,在加固工程中具有广泛的应用前景。本文利用ECC的高延性和抗剪性,提出一种采用ECC面层加固小雁塔的保护方案,以提高古塔抗震性能;通过有限元软件ANSYS进行模拟分析,比较了小雁塔加固前后的地震响应。分析结果表明:采用ECC面层加固可显著增强塔身整体的延性和承载力,有效地提高塔体损伤容限,为ECC在古塔抗震加固的实际应用中提供借鉴,可作为古塔抗震保护的新途径。     

The catastrophic earthquake of April 25, 2015, in Nepal: Analysis of seismological data

The paper analyzes available seismic data of the Geophysical Survey of the Russian Academy of Sciences on the catastrophic earthquake with Ms = 7.9 occurred in Nepal on April 25, 2015. It is shown that this earthquake (also called Gorkha) in its coseismic stage reflected the dynamic situation in the collision zone between the Indian and Eurasian plates, and occurred in the area of the Main Frontal Thrust in the Himalayas. In the last 15 years, the seismicity of this area has demonstrated the features of strong earthquake preparation. The study results are presented for the early postseismic stage (in the first month after the mainshock). It is found that the pattern of a decrease in aftershock activity is similar to that obtained by Tatevossian and Aptekman (2008) for the world’s earthquakes with M > 8. It is regular in the first 11–16 days and can be described by the Omori law, whereas on 17th day after the mainshock, the exponent characterizing the rate of change in the flow of events becomes to irregular. The spatial and temporal distribution of aftershocks of the 2015 Gorkha earthquake qualitatively and quantitatively indicates the heterogeneity of a seismogenic interface of the Himalayan arc collision zone between the Indian and Eurasian plates.     

银川海宝塔动力特性测试及抗震性能分析

为了给银川市海宝塔的修缮保护工作提供参考依据,对其动力特性及结构损伤状况开展测试和数值模拟分析。首先对海宝塔的材料强度进行测试和计算,得出塔砌体的抗压强度及弹性模量;然后对该塔进行环境激励作用下的振动响应测试,得到塔东西和南北方向的1阶频率;最后建立数值模型并分析其模态与抗震性能,得到海宝塔的动力特性与地震作用下塔体各层的层间位移角,并基于砖石古塔破坏状态位移准则以及损伤指标开展损伤分析。结果表明：海宝塔东西方向和南北方向的1阶频率较为接近,但不同楼层的振动频谱曲线差异较大,尤其是峰值点数量;楼层越高,最大位移和层间位移角越大,受损也越严重;结构总体刚度退化较为严重,存在较大安全隐患,需进一步开展深入分析并采取保护措施。     

Observational fragility functions for residential stone masonry buildings in Nepal

This paper outlines the seismic vulnerability of rural stone masonry buildings affected by the 2015 Gorkha earthquake sequence. Summary of field observation is presented first and empirical fragility curves are developed from the detailed damage assessment data from 603 villages in central, eastern and western Nepal. Fragility curves are developed on the basis of 665,515 building damage cases collected during the post-earthquake detailed damage assessment campaign conducted by Government of Nepal. Two sets of fragility functions are derived using peak ground acceleration and spectral acceleration at 0.3 s as the intensity measures. The sum of the results highlights that stone masonry buildings in Nepal are highly vulnerable even in the case of low to moderate ground shaking. The results further indicate that in the case of strong to major earthquakes, most of the stone masonry buildings in Nepal would sustain severe damage or collapse.     

Dynamic characteristics and seismic behavior of prefabricated steel stairs in a full‐scale five‐story building shake table test program

This paper investigates the dynamic characteristics and seismic behavior of prefabricated steel stairs in a full‐scale five‐story building shake table test program. The test building was subjected to a suite of earthquake input motions and low‐amplitude white noise base excitations first, while the building was isolated at its base, and subsequently while it was fixed to the shake table platen. This paper presents the modal characteristics of the stairs identified using the data recorded from white noise base excitation tests as well as the physical and measured responses of the stairs from the earthquake tests. The observed damage to the stairs is categorized into three distinct damage states and is correlated with the interstory drift demands of the building. These shake table tests highlight the seismic vulnerability of modern designed stair systems and in particular identifies as a key research need the importance of improving the deformability of flight‐to‐building connections. Copyright © 2015 John Wiley & Sons, Ltd.     

基于IDA方法的交河故城金刚宝座式塔土建筑遗址地震易损性分析

增量动力分析（IDA）作为动力形式的静力推覆法,被广泛应用于建筑结构的抗震能力分析和性能评估中,但其在土建筑遗址地震易损性分析中的应用甚少。基于IDA方法尝试对交河故城塔林区金刚宝座式塔土建筑遗址进行在地震作用下的易损性和抗震能力分析,以谱加速度S_a（T₁,5%）作为地震动强度指标,最大层间位移角θ_max作为结构损伤指标进行IDA分析,得到土建筑遗址在一系列调幅地震动作用下的IDA曲线、地震需求概率模型和易损性曲线,计算出模型的倒塌率和CMR值。通过以上分析得出金刚宝座式塔的易损性和抗震能力,为今后土建筑遗址抗震保护提供理论基础和分析思路。     

Site amplification in the Kathmandu Valley during the 2015 <Emphasis Type="Bold">M</Emphasis>7.6 Gorkha,Nepal earthquake

The 25th April 2015 M7.6 Gorkha earthquake caused significant damage to buildings and infrastructure in both Kathmandu and surrounding areas as well as triggering numerous, large landslides. This resulted in the loss of approximately 8600 lives. In order to learn how the impact of such events can be reduced on communities both in Nepal and elsewhere, the Earthquake Engineering Field Investigation Team (EEFIT) reconnaissance mission was undertaken, aiming to look at damage patterns within the country. Passive, microtremor recordings in severely damaged areas of the Kathmandu Valley, as well as at the main seismic recording station in Kathmandu (USGS station KATNP) are used to determined preliminary shear wave velocity (V_s) profiles for each site. These profiles are converted into spectral acceleration using the input motion of the Gorkha earthquake. The results are limited, but show clear site amplification within the Siddhitol Region. The resulting ground motions exceed the design levels from the Nepalese Building Codes, indicating the need for site-specific hazard analysis and for revision of the building code to address the effect of site amplification.     

Accuracy of nonlinear static procedures for the seismic assessment of shear critical structures

The nonlinear behavior of reinforced concrete (RC) members represents a key issue in the seismic performance assessment of structures. Many structures constructed in the 1980s or earlier were designed based on force limits; thus they often exhibit brittle failure modes, strength and stiffness degradation, and severe pinching effects. Field surveys and experimental evidence have demonstrated that such inelastic responses affect the global behavior of RC structural systems. Efforts have been made to consider the degrading stiffness and strength in the simplified nonlinear static procedures commonly adopted by practitioners. This paper investigates the accuracy of such procedures for the seismic performance assessment of RC structural systems. Refined finite element models of a shear critical bridge bent and a flexure‐critical bridge pier are used as reference models. The numerical models are validated against experimental results and used to evaluate the inelastic dynamic response of the structures subjected to earthquake ground motions with increasing amplitude. The maximum response from the refined numerical models is compared against the results from the simplified static procedures, namely modified capacity spectrum method and coefficient method in FEMA‐440. The accuracy of the static procedures in estimating the displacement demand of a flexure‐critical system and shear‐critical system is discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

论发震构造特性在潜在震源区参数确定中的应用

发震构造特性是潜在震源区划分及其地震年发生率确定的重要依据。潜在震源区除了反映“未来具有发生破坏性地震的地区”的内涵外,还应反映高震级档地震具有相似复发特征的涵义。由于在地震活动性参数统计单元内,有一些具有不同本底地震的活动构造块体,为更好地反映地震活动的空间不均匀性,考虑潜在震源区的三级划分是有必要的。通过分析潜在震源区内高震级档地震的复发特征,计算预测时段内潜在震源区的高震级档地震的发震概率,采用预测时段内概率等效转换获得地震年平均发生率的方法,有助于在中国地震危险性分析框架内考虑潜在震源区的强震复发特性。另外,文中还对潜在震源区内特征地震次级震级档频度不足的特性和发震构造上强震非均匀性在地震危险性分析中的应用问题进行了探讨     

考虑结构-土-结构相互作用的区域建筑群震害评估

建筑群震害评估计算对城市区域地震损失评估和震后快速援助救灾有着重要意义。考虑到地震中建筑物相互作用对震害的影响,进行考虑结构间相互作用的区域建筑群震害评估计算。在已有的基于结构—土—结构动力相互作用(SSSI)分析的简化离散模型基础上,扣除基础转动对输出响应的影响,引入基础上部建筑结构非线性多自由度模型,得到考虑SSSI的简化的非线性多自由度离散模型,建立考虑SSSI的区域建筑群震害评估方法。以四川大学望江校区的建筑群在汶川地震中的震害评估为例,采用该方法对该校区建筑群在汶川地震中的震害进行评估计算。同时,也对未考虑SSSI情况下的该校区建筑群震害进行计算。运用HAZUS对建筑群在汶川地震中的震害进行计算。通过对比分析实际震害调查数据、HAZUS震害计算结果和本文建筑群震害计算结果可知,相比HAZUS震害计算结果,本文建筑群震害计算结果更接近实际震害调查数据;与未考虑SSSI的建筑群震害计算结果相比,考虑SSSI的建筑群震害计算结果精确度更高,更能反映建筑群的实际震害情况。     

Numerical homogenization-based seismic assessment of an English-bond masonry prototype: Structural level application

A multiscale strategy is evaluated at a structural level for the analysis of unreinforced masonry structures. The mechanical characterization of the masonry is deduced from homogenization-based micro-scale finite element (FE) models. The derived data are here employed at a structural level via a discrete FE model. The discrete FE model is composed of quadrilateral rigid plates interconnected through vertical and horizontal interfaces. On the interfaces, between adjoining discrete elements, a model that accounts for the in- and out-of-plane behavior of masonry, with damage and plasticity, is adopted. Such interfaces represent the material pre- and post-peak regimes, its orthotropy, and, depending on the micro-model assumed, account by three-dimensional shear effects that are especially important for multi-leaf walls and complex regular textures. The discrete model has been implemented in an advanced structural analysis software where powerful built-in features as the arc-length method, line-search algorithm, and implicit or explicit solver schemes are available. The multi-scale model is applied for the dynamic study of a small English-bond masonry house prototype subjected to a series of consecutive earthquake records. Detailed comparisons between the experimental and numerical data are presented, including the results obtained through a continuous total strain rotating crack model. Quasi-static and dynamic analyses are conducted. Results demonstrate that when enough experimental information is available on the masonry components under tension, shear, and compression regimes, the approach predicts well the seismic structural response in terms of time-history displacements, seismic capacity, and damage patterns. The required computational cost (CPU time) is very attractive.     

中国地震大地测量——半个世纪的历程与科学贡献

自1966年邢台地震以来,中国尝试用大地测量手段监测地震变形,至1976年唐山地震,变形监测到达高潮,但受地面技术局限,20余年可以用于分析震源的震例寥寥。自20世纪90年代初全面进入空间观测时代以来,境内或边邻6级以上强震大多数有相应的近场变形观测和破裂模型研究,这其中又以2001年昆仑山口西、2008年汶川和2015年廓尔喀3次特大地震的变形资料相对完整、破裂特征清晰、理论成果丰富,成为近期大陆内部最引人注目的大震事件。近30年来,对包括中国台湾在内的60余次强震变形的系统研究丰富了人们对区域地震活动性及危险性的认识,也为青藏高原构造演化研究提供了观测依据与理论参考。半个世纪积累的经验、夯实的基础以及未解的难题更为未来的地震大地测量提供了历史借鉴、前进动力和发展方向。