Seismic rehabilitation performance of steel side plate moment connections

Moment connections in an existing steel building located in Kaohsiung, Taiwan were rehabilitated to satisfy seismic requirements based on the 2005 AISC seismic provisions. Construction of the building was ceased in 1996 due to financial difficulties and was recommenced in 2007 with enhanced connection performance. Steel moment connections in the existing building were constructed by groove welding the beam flanges and bolting the beam web to the column. Four moment connections, two from the existing steel building, were cyclically tested. A non‐rehabilitated moment connection with bolted web‐welded flanges was tested as a benchmark. Three moment connections rehabilitated by welding full‐depth side plates between the column face and beam flange inner side were tested to validate the rehabilitation performance. Test results revealed that (1) the non‐rehabilitated existing moment connection made by in situ welding process prior to 1996 had similar deformation capacity as contemporary connection specimens made by laboratory welding process, (2) all rehabilitated moment connections exhibited excellent performance, exceeding a 4% drift without fractures of beam flange groove‐welded joints, and (3) presence of the full‐depth side plates effectively reduced beam flange tensile strain near the column face by almost half compared with the non‐rehabilitated moment connection. The connection specimens were also modeled using the non‐linear finite element computer program ABAQUS to further confirm the effectiveness of the side plate in transferring beam moments to the column and to investigate potential sources of connection failure. A design procedure was made based on experimental and analytical studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Seismic imaging of deep hydrocarbon reservoirs

This paper examines those aspects of reflection seismology which require special consideration when imaging deeper hydrocarbon reservoirs, including the constraints imposed by vertical resolution, lateral resolution, and velocity analysis. We derive quantitative expressions relating the uncertainties in stacking velocities and in interval velocities derived from stacking velocities to acquisition parameters, as well as expressions for the lateral resolution which can theoretically be achieved for migrated seismic images. This analysis shows that the most significant limitations of seismic imaging at depth involve the finite lateral resolution of the seismic method, and the proper lateral positioning of seismic images. These difficulties are overcome in large measure through the proper migration of a seismic dataset, which becomes more critical as deeper horizons are imaged. If these horizons are suspected of having significant 3-D structure, a strong argument may be made for acquiring a 3-D seismic survey over the prospect. Migration of this dataset will then generate an image of the subsurface with good lateral resolution in both the X and Y directions.     

On seismic strengthening area before strong and great shocks and its mechanism

IntroductionI.thasbeenpayingattentiontotheanomalousphenomenonbyseismologiststhattheearthquakeactivityoftenstrengthensinacertainspaceandduringacertaintimearoundthesourceareabeforeastrongearthquake.Mogi(1969)pointedoutthataringdistributiveareaofthestrengthenedearthquakeactivityoftenappearsaroundthesourcearea10to20yearsbeforegreatshock,whichcalledaringphenomenon(or"doughnut").Afterthat,otherscholarsreportedinsuccessionthatringdistributionofearthquakeactivityoccurredbeforeastrongertquakeorevenbefo…     

断层厚度的地震效应和非对称地震矩张量

本文导出了具有厚度和滑动弱化区域的断层的非对称地震矩张量表示式,指出要求地震矩张量具有对称性不是一个绝对必要的限制.在非对称地震矩张量中,位错项对应于对称地震矩张量,拉力项对应于非对称地震矩张量.由于拉力项等效于单力偶,所以在非对称地震矩张量解的两个节面上,沿滑动矢量方向的力偶强度不再相同,与较大力偶相联系的节面为断层面,与较小力偶相联系的节面为辅助面.这一性质可用以从两个正交的节面中判断哪一个节面是断层面.如果忽略拉力项,会高估与位错对应的标量地震矩.只有满足相应的约束条件的非对称地震矩张量才能表示具有厚度和滑动弱化区域的断层模型,并从中分离出与位错和拉力对应的地震矩张量.     

各向异性ATI介质剪切位错源地震矩张量

考虑震源区为各向异性ATI介质情形下,给出了剪切位错源地震矩张量解析表达式并模拟了震源区各向异性对双力偶分量(DC)、补偿线性偶极子分量(CLVD)和各向同性分量(ISO)的影响.结果表明,即使剪切位错源仍能产生非双力偶各向同性分量,其导致沿着ATI介质对称轴方向体积变化;当断层面位于ATI介质对称平面或者震源区为各向同性介质时,剪切位错源在辐射意义上才可等效为双力偶机制.     

Seismic yield displacements of plane moment resisting and x-braced steel frames

Approximate formulae for the estimation of lateral displacements at first yielding of plane steel frames under seismic excitations are provided for use in a performance based seismic design and more particularly, in a direct displacement based seismic design of these structures. These formulae, which are functions of the geometrical and design properties of the frames, are derived on the basis of seismic response data obtained with the aid of extensive dynamic inelastic analyses involving 36 moment resisting and 36 x-braced plane steel frames with steel grade S235, S275 and S355 under 84 ordinary seismic ground motions. Comparison of the proposed formulae against other simpler existing formulae, reveals the higher accuracy of the proposed ones.     

Seismic moment tensor of Pribaikalye earthquakes from the surface-wave amplitude spectra

The method of surface-wave amplitude spectra inversion for the seismic moment tensor (SMT) is implemented and tested in the Pribaikalye region. The SMTs are calculated for 39 events with M _w = 4.4–6.3, which occurred in the region in 2000–2011. Based on the obtained data, the seismotectionic deformations of the crust are estimated in two seismically active areas-the Northern Pribaikalye and northeastern Baikal rift zone. It is found that on a level of moderate-magnitude events, the region is dominated by the regimes of subhorizontal northwestern extension and strike-slip faulting, which reflects the long-term trends in the stress field of the crust in these parts of the rift.     

Seismic ground-roll noise attenuation using deep learning

We propose to adopt a deep learning based framework using generative adversarial networks for ground-roll attenuation in land seismic data. Accounting for the non-stationary properties of seismic data and the associated ground-roll noise, we create training labels using local time–frequency transform and regularized non-stationary regression. The basic idea is to train the network using a few shot gathers such that the network can learn the weights associated with noise attenuation for the training shot gathers. We then apply the learned weights to test ground-roll attenuation on shot gathers, that are not a part of training input to obtain the desired signal. This approach gives results similar to local time–frequency transform and regularized non-stationary regression but at a significantly reduced computational cost. The proposed approach automates the ground-roll attenuation process without requiring any manual input in picking the parameters for each shot gather other than in the training data. Tests on field-data examples verify the effectiveness of the proposed approach.     

Seismic fracture evaluation of diaphragm joints in welded beam-to-box column moment connections

Steel box columns are widely used in steel building structures in Taiwan due to their dual strong axes. To transfer the beam-end moment to the column, diaphragm plates of the same thickness and elevations as the beam flanges are usually welded inside the box column. The electro-slag welding (ESW) process is widely used to connect the diaphragms to the column flanges in Taiwan because of its convenience and efficiency. However, ESW may increase the hardness of the welds and heat-affected zones (HAZs), while reducing the Charpy-V notch strength in the HAZ. This situation can cause premature fracture of the diaphragm-to-column flange welds before a large plastic rotation is developed in the beam-to-box column joints. To quantify the critical eccentricity and the effectiveness of fracture prediction, this study uses fracture prediction models and finite element model (FEM) analysis to correlate the test results. In this study, two beam-to-box column connection subassembly tests are conducted with different loading protocols and ESW chamber shapes. To implement a fracture prediction model, the material parameters are established from circumferential notched tensile tests and FEM analysis. Test results indicate that the fracture instances can be predicted on the basis of the cumulative plastic deformation in the HAZs. Analytical results indicate that fracture instances and locations are sensitive to the relative locations of the ESW joints and beam flange. Tests also confirm that the possible fracture of the diaphragm-to-column flange joints can be mitigated by enlarging the chamber of the ESW joint.     

Seismic vulnerability evaluation of RC moment frame buildings in moderate seismic zones

A multi‐level seismic vulnerability assessment of reinforced concrete moment frame buildings located in moderate seismic zones (0.25g) is performed on a set of ductile versions of low‐ to mid‐rise two‐dimensional moment frames. The study is illustrated through application to comparative trial designs of two (4‐ and 8‐story) buildings adopting both space‐ and perimeter‐framed approaches. All frames are dimensioned as per the emerging version of the seismic design code in Egypt. These new seismic provisions are in line with current European norms for seismic design of buildings. Code‐compliant designs (CCD), as well as a proposed modified code design relaxing design drift demands for the investigated buildings, are examined to test their effectiveness and reliability. Applying nonlinear inelastic incremental dynamic analyses, fragility curves (FC) for the frames are developed corresponding to various code‐specified performance levels. Code preset lower and upper bounds on design acceleration and drift, respectively, are also addressed along with their implications, if imposed, on the frames seismic performance and vulnerability. Annual spectral acceleration hazard curves for the case study frames are also generated. Estimates for mean annual frequency (MAF) of exceeding various performance levels are then computed through an integration process of the data resulting from the FC with the site hazard curves. The study demonstrates that the proposed design procedure relaxing design drift demands delivers more economic building designs relative to CCDs, yet without risking the global safety of the structure. The relaxed design technique suggested herein, even though scoring higher, as expected by intuition, MAF of exceeding various code‐limiting performance levels expressed in terms of interstory drift ratios, still guarantees a reasonably acceptable actual margin against violating code limits for such levels. Copyright © 2010 John Wiley & Sons, Ltd.     

Seismic demand evaluation of medium ductility RC moment frames using nonlinear procedures

Performance-based earthquake engineering is a recent focus of research that has resulted in widely developed design methodologies due to its ability to realistically simulate structural response characteristics.Precise prediction of seismic demands is a key component of performance-based design methodologies.This paper presents a seismic demand evaluation of reinforced concrete moment frames with medium ductility.The accuracy of utilizing simplified nonlinear static analysis is assessed by comparison against the results of time history analysis on a number of frames.Displacement profiles,drift demand and maximum plastic rotation were computed to assess seismic demands.Estimated seismic demands were compared to acceptance criteria in FEMA 356.The results indicate that these frames have sufficient capacity to resist interstory drifts that are greater than the limit value.     

深水崎岖海底地震数据成像方法与应用

本文针对深水崎岖海底地震数据深部成像困难的问题,讨论了波动方程叠前深度域保幅偏移的基本理论,利用数值模型验证了波动方程叠前深度域保幅偏移算法的保持振幅特性,给出了该方法与非保幅偏移方法对于复杂构造成像精度的对比,证明了保幅偏移方法可以提高复杂构造的成像精度.本文还将波动方程叠前深度域保幅偏移算法应用到实际资料的处理中,处理结果表明该方法能够有效消除崎岖海底对深部地层的影响.     

深层-超深层碳酸盐岩多类型储集体地震预测

塔里木盆地、四川盆地以及鄂尔多斯盆地深层-超深层碳酸盐岩油气藏是中国油气勘探的重要领域.由于中国海相深层碳酸盐岩储层发育的主控因素差异很大, 碳酸盐岩储集体类型多, 非均质性极强.随着深度增加, 海相地层地震资料信噪比低、分辨率变差, 增加了碳酸盐岩储层地震预测的难度.本文提出了以“相、面、断”三种端元为基础的深层碳酸盐岩储集体分类的新方法, 针对相控型、面控型和断控型三种类型储集体, 形成了相应的储集体预测方法、流程, 包括: (1)川西雷口坡组气田潮坪相白云岩薄储层“三型两构”组合预测技术; (2)川北茅口组气藏礁滩相白云岩薄储层地震沉积学分析约束的高分辨率反演技术; (3)顺北油气田奥陶系断控储集体基于振幅响应正演模拟的定性-定量描述; (4)大牛地奥陶系不整合面岩溶储集体地质规律指导下的波形分类与古地貌刻画技术.这些方法围绕特定类型储集体的特征, 充分运用地质分析所建立的储集体模式, 较好地预测了储集体的厚度、物性、含油气性及分布范围, 实现了单纯依据地震数据无法达到的预测目标, 取得了良好的应用效果, 有力支撑了深层-超深层油气勘探突破与高效开发.

     

Seismic response of self-centering prestressed concrete moment resisting frames with web friction devices

This paper examines the seismic response of self-centering prestressed concrete moment resisting frames (SCPC-MRFs) with web friction devices. Nonlinear dynamic analyses under ground motion ensembles corresponding to two seismic hazard levels are performed. The results of SCPC-MRFs are compared with those of monolithic reinforced concrete (RC) MRFs in terms of global and local responses. Seismic analyses results show that SCPC-MRFs generally experience similar peak story drifts, less beam end rotations, and much smaller residual deformations as compared with those of RC-MRFs. However, it is also found that SCPC-MRFs sustained larger column plastic rotations than RC-MRFs and are more sensitive to the formation of a soft story. In general, the 8-story SCPC-MRFs show better seismic performances than the 4-story ones. Mainshock–aftershock analyses show that the incremental effect of aftershock on damage extent is much smaller for the SCPC-MRFs than for the RC-MRFs.     

Seismic reliability of steel moment resisting framed buildings retrofitted with buckling restrained braces

The present paper investigates the seismic reliability of the application of buckling restrained braces (BRBs) for seismic retrofitting of steel moment resisting framed buildings through fragility analysis. Samples of regular three‐storey and eight‐storey steel moment resisting frames were designed with lateral stiffness insufficient to comply with the code drift limitations imposed for steel moment resisting frame systems in earthquake‐prone regions. The frames were then retrofitted with concentrically chevron conventional braces and BRBs. To obtain robust estimators of the seismic reliability, a database including a wide range of natural earthquake ground motion records with markedly different characteristics was used in the fragility analysis. Nonlinear time history analyses were utilized to analyze the structures subjected to these earthquake records. The improvement of seismic reliability achieved through the use of conventional braces and BRBs was evaluated by comparing the fragility curves of the three‐storey and eight‐storey model frames before and after retrofits, considering the probabilities of four distinct damage states. Moreover, the feasibility of mitigating the seismic response of moment resisting steel structures by using conventional braces and BRBs was determined through seismic risk analysis. The results obtained indicate that both conventional braces and especially BRBs improve significantly the seismic behavior of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedance of each damage state. Copyright © 2011 John Wiley & Sons, Ltd.     

Seismic phase picking in China Seismic Array using a deep convolutional neuron network*

Seismic phase picking is the preliminary work of earthquake location and body-wave travel time tomography. Manual picking is considered as the most accurate way to access the arrival times but time consuming. Many automatic picking methods were proposed in the past decades, but their precisions are not as high as human experts especially for events with low ratio of signal to noise and later arrivals. As the increasing deployment of large seismic array, the existing methods can not meet the requirements of quick and accurate phase picking. In this study, we applied a phase picking algorithm developed on the base of deep convolutional neuron network (PickNet) to pick seismic phase arrivals in ChinArray-Phase III. The comparison of picking error of PickNet and the traditional method shows that PickNet is capable of picking more precise phases and can be applied in a large dense array. The raw picked travel-time data shows a large variation deviated from the traveltime curves. The absolute location residual is a key criteria for travel-time data selection. Besides, we proposed a flowchart to determine the accurate location of the single-station earthquake via dense seismic array and phase arrival picked by PickNet. This research expands the phase arrival dataset and improves the location accuracy of single-station earthquake.     

Seismic activity and deep conductivity structure of the Eastern Carpathians

We present results of a study of the seismicity and the geoelectric structure of the Eastern Carpathians. After the evaluation of the seismicity, new methods of processing and analyzing seismic data are developed, which allow constructing an averaged horizontal-layered velocity model of the crust in the Carpathian region of Ukraine, tracing the seismic active faults and localizing the seismic events both in horizontal and in vertical direction with a better precision. For the study of the conductivity structure beneath the Eastern Carpathians, the collected magnetovariation and magnetotelluric data are used. The depth of electrical conductivity anomalies are estimated and the resulting quasi-3D model of the conductivity structure beneath the Carpathians is compared with the seismicity in the depth range of 10 ± 2.5 km. The comparison suggests possible geological mechanisms: the seismic events occur mainly in resistive solid rock domains which surround aseismic high-conductivity zones, consisting of at least partially melted material. Aqueous fluids, or a joint effect of several mechanisms, may also play an active role in this distribution.     

The relative amplitude moment tensor method applied to the IASPEI deep earthquakes

The relative amplitude moment tensor method is used to determine the source types and source orientations of the four deep earthquakes from those selected for discussion at the 1985 General Assembly of IASPEI. Source types show no direct evidence of deviation from a double couple, and the well-constrained orientations of this source type can be derived since solutions are tightly constrained by a few important relative amplitudes, mostly involving nodal observations. These solutions are compared with the results of other methods and agree favourably with the USGS first motion solutions. The Harvard CMT solutions, however, often predict P, pP and sP relative amplitudes inconsistent with those observed, and therefore tend to be at variance with the solutions obtained here.     

Seismic design factors for RC special moment resisting frames in Dubai, UAE

This study investigates the seismic design factors for three reinforced concrete (RC) framed buildings with 4, 16 and 32-stories in Dubai, UAE utilizing nonlinear analysis. The buildings are designed according to the response spectrum procedure defined in the 2009 International Building Code (IBC’09). Two ensembles of ground motion records with 10% and 2% probability of exceedance in 50 years (10/50 and 2/50, respectively) are used. The nonlinear dynamic responses to the earthquake records are computed using IDARC-2D. Key seismic design parameters are evaluated; namely, response modification factor (R), deflection amplification factor (Cd), system overstrength factor (Ωo), and response modification factor for ductility (Rd) in addition to inelastic interstory drift. The evaluated seismic design factors are found to significantly depend on the considered ground motion (10/50 versus 2/50). Consequently, resolution to the controversy of Dubai seismicity is urged. The seismic design factors for the 2/50 records show an increase over their counterparts for the 10/50 records in the range of 200%-400%, except for the Ωo factor, which shows a mere 30% increase. Based on the observed trends, period-dependent R and Cd factors are recommended if consistent collapse probability (or collapse prevention performance) in moment frames with varying heights is to be expected.