抗震设计规范之近断层中小地震影响

近年来发生的中小震级地震中 ,在靠近断层附近观测到的记录中具有显著加速度和速度峰值 ,对结构造成了极大的破坏 ,同时 ,现行抗震设计规范多是以大震级地震记录为基础建立起来的 ,很少考虑断层距对结构地震反应的影响。本文在充分收集近断层地震记录的基础上 ,对近断层中小震级地震动的峰值和反应谱进行了统计分析 ,并和我国的结构抗震设计规范进行了对比 ,指出了现行抗震设计规范的不足之处 ,得出了一些有益的结果 ,为今后抗震设计规范的完善和结构的抗震计算提供了参考。     

中美规范关于地震波的选择与框架-核心筒结构弹塑性时程分析

简述了中美两国抗震设计规范中有关地震波选择的相关条文,列举了工程实践中常用的选波方法,并对选出的地震波反应谱特性进行了比较。中美两国规范中建议的选波方法均要求选择能与规范的设计反应谱相一致的地震波,不同之处为中国规范是将地震波峰值加速度调幅至规范规定值,而美国规范是将某一周期范围内地震波反应谱调幅至与设计反应谱接近,调幅后的地震波峰值加速度无明显规律。按照中美两国抗震设计规范分别设计了两栋相似框架 核心筒结构,建立了两结构的弹塑性分析模型。根据中国规范建议方法选择出7组地震波,进行弹塑性时程分析。分析结果表明：在相应于中国8度罕遇地震的多组地震波作用下,中美两国规范设计方案在地震作用初期地震响应基本一致,在后期由于结构配筋形式与配筋数量等差异,结构损伤程度不同;按中国规范设计方案的最大层间位移角为按美国规范设计方案的1.03~1.17倍,连梁最大塑性变形为按美国规范设计方案的0.67~0.98倍,剪力墙应变沿层高的分布接近,美国规范设计结构纵筋的屈服应变是中国规范设计方案的1.2倍,按中国规范设计方案的剪力墙损伤程度重于按美国规范设计的剪力墙。     

Strength reduction factor demands for building structures under different seismic levels

Damage levels of building structures under a design earthquake are closely related to the assigned values of strength reduction factors. This paper is to investigate the strength reduction factor demands of building structures that were designed considering various earthquake ground intensity levels, soil ground types, and strength reduction factors. In the investigation, a huge number of rigorous nonlinear inelastic dynamic response analyses of various analytical models of five‐story and nine‐story frame structures were conducted under various generated ground motions with variations in phrase angles but identical response spectral acceleration amplitudes. Various scaled earthquake records were also considered for evidence of the investigation. The obtained results showed that when the same values of the strength reduction factors were used for determination of the design lateral seismic forces, the damage and reliability level demands of the structures designed for moderate seismic areas were much less than those for severe seismic ones. As a result, it is proposed that the strength reduction factor demands given in design codes can additionally be expressed in a linear relation of the maximum ground acceleration. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic fragility assessment of effectiveness of viscous dampers in R/C buildings under scenario earthquakes

Fragility curves are used to represent the probabilities that the structural damages, under various level of seismic excitation, exceed specified damage states by means of earthquake intensity–damage relations. In this study, the fragility curves have been developed for comparative seismic evaluation of several retrofitting measures by incorporation of fluid viscous (VS) dampers applied to a representative high-rise reinforced concrete (R/C) office building located in Istanbul. In the retrofitting strategies considered, similar type of VS dampers was used and designed to provide the structure with three different effective damping ratios of 10%, 15%, and 20%. In the fragility analysis, a set of 240 artificially generated earthquake ground motions compatible with the design spectrum selected to represent the variability in ground motion was employed to study nonlinear dynamic responses of the structures before and after retrofit. Four damage states: slight, moderate, major, and collapse were defined to express the condition of damage. The fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of peak ground acceleration (PGA), spectral acceleration (S_a), spectral displacement (S_d). Comparison of the fragility curves indicated that the VS dampers were very effective in attenuating seismic structural response under various earthquake ground motions. It was also found that a two-fold reduction in the probability of exceeding damage states might be achieved by introducing passive VS damper systems.     

RC框架基于典型相关分析的地震动多元破坏势评估

为了更加全面地评估地震动对结构的潜在破坏势,考虑多个地震动强度参数和多个结构损伤参数对地震动破坏势的影响,提出一种基于典型相关分析的地震动多元破坏势评估方法。为说明所提方法,以具有不同高度和不同抗震设防水平的16个钢筋混凝土框架结构为研究对象,采用100条真实地震动记录作为地震输入。将与地震动加速度、速度和位移相关的8个地震动强度参数进行对数线性组合,构造成地震动多元强度参数的典型变量。将结构最大层间位移角、整体损伤指数、最大楼层加速度进行对数线性组合,构造成结构多元损伤参数的典型变量。通过使地震动强度参数的典型变量和结构损伤参数的典型变量的相关系数达到最大,获得可以较好评估地震动破坏势的复合地震动参数。研究结果表明：相比于单一地震动参数,复合地震动参数可以更好地评估地震动的破坏势,其与结构损伤的相关性也更强。     

Probabilistic seismic response and uncertainty analysis of continuous bridges under near-fault ground motions

Performance-based seismic design can generate predictable structure damage result with given seismic hazard. However, there are multiple sources of uncertainties in the seismic design process that can affect desired performance predictability. This paper mainly focuses on the effects of near-fault pulse-like ground motions and the uncertainties in bridge modeling on the seismic demands of regular continuous highway bridges. By modeling a regular continuous bridge with OpenSees software, a series of nonlinear dynamic time-history analysis of the bridge at three different site conditions under near-fault pulse-like ground motions are carried out. The relationships between different Intensity Measure (IM) parameters and the Engineering Demand Parameter (EDP) are discussed. After selecting the peak ground acceleration as the most correlated IM parameter and the drift ratio of the bridge column as the EDP parameter, a probabilistic seismic demand model is developed for near-fault earthquake ground motions for 3 different site conditions. On this basis, the uncertainty analysis is conducted with the key sources of uncertainty during the finite element modeling. All the results are quantified by the “swing” base on the specific distribution range of each uncertainty parameter both in near-fault and far-fault cases. All the ground motions are selected from PEER database, while the bridge case study is a typical regular highway bridge designed in accordance with the Chinese Guidelines for Seismic Design of Highway Bridges. The results show that PGA is a proper IM parameter for setting up a linear probabilistic seismic demand model; damping ratio, pier diameter and concrete strength are the main uncertainty parameters during bridge modeling, which should be considered both in near-fault and far-fault ground motion cases.     

Response of nonlinear single-degree-of-freedom structures to random acceleration sequences

Current seismic codes specify design earthquake loads as single events. The structure, however, may experience multiple ground accelerations in a short period of time. The evidence from recent earthquakes confirms this scenario. For instance, the 2004 Niigata earthquake consisted of two acceleration sequences. An earthquake of repeated sequences can cause more damage to the structure than a single ordinary event, due to the accumulation of inelastic deformations. However, information on repeated acceleration sequences is currently limited. This paper proposes a simple stochastic model for representing repeated acceleration sequences. Subsequently, the model is used in investigating the response of nonlinear single-degree-of-freedom (SDOF) structures to random earthquakes of repeated sequences. The ground acceleration is represented as a stationary Gaussian random process modulated by an envelope function of repeated character. The structural response is quantified in terms of the input and hysteretic energies, ductility demand, damage indices and failure probability. Numerical demonstrations of the response of nonlinear SDOF systems to acceleration sequences are provided.     

抗震结构最不利设计地震动研究

在结构的抗震研究和设计中,如何选择实际的地震动记录作为输入一直是地震工程中至关重要的问题之一。首先给出最不利设计地震动的概念、确定原则及方法,然后利用估计地震动潜在破坏势的综合评价法,对四种场地类型分别给出长周期、短周期和中周期结构的国外、我国台湾地区及大陆地区的最不利设计地震动,给出的最不利设计地震动适用于特别重要的结构或地震危险性较高地区结构的抗震分析和研究。另外,根据地震动的潜在破坏势,还给出适用于一般重要性结构或地震危险性较低地区抗震验算的输入地震动。最后,通过工程结构的地震反应分析,初步验证文中所确定的最不利设计地震动的可靠性和正确性。     

Seismic fragility assessment of a tall reinforced concrete chimney

In China, a considerable proportion of reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century. However, few research works have been reported till date on a realistic overall assessment of the seismic performance of these existing aging RC chimney structures. Therefore, in this study, fragilities of existing RC chimney were studied. For this purpose, an existing 240 m tall RC chimney was selected and structurally modeled with a lumped mass beam (stick) model by means of the OpenSees analysis program. In order to capture the uncertainties in ground motion realizations, a series of 21 ground motions are selected from the Next Generation Attenuation database as the input motions. To develop the analytical fragility curves, nonlinear incremental dynamic analysis of the studied RC chimney was then carried out using the selected input motions, which were normalized to different excitation levels. The section curvature ductility ratio was considered as the damage index. Based on material strain and sectional analysis, four limit states (LSs) were defined for five damage state. The seismic responses of the all sections were utilized to evaluate the likelihood of exceeding the LSs. Then the peak ground acceleration (PGA)‐based seismic fragility curves of the structure were constructed assuming a lognormal distribution. Finally, under the light of these fragility curves, the damage risks in existing RC chimney were discussed. The analytical results indicated that for design level earthquake of PGA = 0.1 g (g is the gravitational acceleration) and the maximum considered earthquake of PGA = 0.22 g, the probabilities of exceeding the light damage state were around 1.5% and 44%, respectively, while the exceedance probabilities corresponding to moderate, extensive and complete damage states were approximately zero in both cases. On the other hand, fragility analysis revealed that the RC chimney structure had considerable ductility capacity and was capable to withstand a strong earthquake with some structural damages. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic performance of R/C plane frames irregular in elevation

The paper addresses multistorey reinforced concrete (R/C) frame buildings, irregular in elevation. Two ten-storey two-dimensional plane frames with two and four large setbacks in the upper floors respectively, as well as a third one, regular in elevation, have been designed to the provisions of the 2004 Eurocode 8 (EC8) for the high (DCH) and medium (DCM) ductility classes, and the same peak ground acceleration (PGA) and material characteristics. All frames have been subjected to both inelastic static pushover analysis and inelastic dynamic time-history analysis for selected input motions. The assessment of the seismic performance is based on both global and local criteria. It is concluded that the effect of the ductility class on the cost of buildings is negligible, while the seismic performance of all irregular frames appears to be equally satisfactory, not inferior to (and in some cases superior than) that of the regular ones, even for motions twice as strong as the design earthquake. As expected, DCM frames are found to be stronger and less ductile than the corresponding DCH ones. The overstrength of the irregular frames is found to be similar to that of the regular ones, while DCH frames are found to dispose higher overstrength than DCM ones. Pushover analysis seems to underestimate the response quantities in the upper floors of the irregular frames.     

7度半、8度半烈度区钢筋混凝土抗震框架的非线性动力反应研究

通过对按新规范设计的典型7度半、8度半烈度区框架结构进行多波输入下的非线性地震反应分析，并考察其在非线性动力反应下的抗震性能，在一定程度上对新规范中的有关抗震措施进行了校核。     

我国抗震设计规范设计反应谱及谱阻尼折减系数研究

在标准加速度反应谱基础上,研究并建立符合强震反应谱统计特征的谱阻尼折减系数是建立长周期、大阻尼比反应谱的一种实用方法。首先研究总结强震反应谱的统计特征,据此对我国建筑物、构筑物、核电厂、公路桥梁、工业企业电气设备等结构的抗震设计规范反应谱及谱阻尼折减系数的合理性进行定性研究,对已有改进抗震规范谱方案的合理性进行分析。结果表明：周期10 s内的相对位移反应谱值和相对速度反应谱值随阻尼比增大而减小,而绝对加速度反应谱值随阻尼比增大既可能增大也可能减小;我国各类结构抗震设计规范谱阻尼折减系数计算方案不甚合理;对规范谱及由有关学者提出的改进方案谱进行转换仅能得到适用范围有限的拟相对位移反应谱。     

上海软土场地的地震反应特征分析

近年来的宏观震害资料和强震观测记录已经证明：场地条件不仅对地震动的峰值加速度和频谱形状具有重要的影响,而且与不同类型工程结构的地震反应和震害机理也具有相当密切的关系.上海地区的第四纪沉积土层呈水平层状分布,基岩埋深可达300m左右,且浅部普遍发育有滨海沼泽相软土.因此,上海地区上覆深厚、软弱的沉积土层,对场地的地震反应特性无疑具有重要的影响.文章基于一维场地地震反应的等效线性化频域分析方法,建立了上海软土场地的动力分析模型,以El Centro地震波为例,重点分析了上海地区场地土的地震反应加速度反应和频谱特征.研究表明,在7度抗震设防即场地地面峰值加速度（PGA）等于0.1 g的情况下,上海软土场地的地表峰值加速度具有放大特性,地表加速度的频谱组成具有低频放大,高频过滤的特征,地面运动加速度反应谱的卓越周期也具有向长周期方向移动的趋势.     

Floor response spectra for light components mounted on regular moment-resisting frame structures

The peak acceleration demands for acceleration-sensitive nonstructural components supported on elastic and inelastic regular moment-resisting frame structures are statistically analyzed. The responses of a variety of stiff and flexible frame structures (with 3, 6, 9, and 18 stories) subjected to a set of 40 ground motions are evaluated. The nonstructural components under consideration are those that can be represented by single-degree-of-freedom systems with masses that are small compared to the total mass of the supporting structure. This study evaluates and quantifies the dependence of peak component accelerations on the location of the nonstructural component in the structure, the damping ratio of the component, and the properties of the supporting structure such as its modal periods, height, stiffness distribution, and strength. The results show that current seismic code provisions will not always provide an adequate characterization of peak component accelerations. Recommendations are provided to estimate peak acceleration demands for the design of nonstructural components mounted on inelastic frame structures.     

钢筋混凝土巨型框架结构及附单向TMD装置的减震结构振动台试验研究

为了研究钢筋混凝土巨型框架结构体系的抗震性能及其地震作用损伤机理,设计制作1/25的缩尺模型,并设计加工了一套调谐质量阻尼器（TMD）装置安装在模型结构顶部,进行振动台试验,得到结构的动力特性和位移响应,并对比分析了TMD的减震效果。结果表明：当在峰值加速度为0.140g的地震波作用后（相当于原型7度多遇地震）,模型结构处在弹性工作状态,在峰值加速度为0.400g的地震波作用后（相当于原型7度基本烈度）,模型结构出现轻微破坏,在峰值加速度为0.880g的地震波作用后（相当于原型7度罕遇地震）,模型结构出现中等破坏,该原型结构可以满足抗震设计的要求;TMD装置具有较好的减震效果。     

装配式方钢管混凝土柱框架-条板复合墙结构足尺振动台试验研究

为研究装配式方钢管混凝土（CFSST）柱框架-条板复合墙结构的抗震性能,对一个两层房屋足尺模型实施了振动台试验,分析了模型在不同工况下的损伤累积过程,研究了模型动力特性和地震响应的变化规律。结果表明：随着地震波峰值加速度的增大,模型自振频率逐渐降低;在地震波峰值加速度为0.7g前阻尼比逐渐增大,之后略降;楼层加速度放大系数介于1.2～1.8之间,且呈降低趋势。模型在8度基本、8度罕遇地震动作用下的最大层间位移角满足规范限值要求,且残余位移较小。模型内力变化具有阶段性特征：在墙板裂缝贯通前,条板复合墙是主要的抗侧力构件,而CFSST柱框架内力较小;裂缝贯通后,条板复合墙通过内部的摩擦错动一定程度上耗散了台面振动能量,是主要的耗能构件;最终条板复合墙裂解为多个单一条板,但仍具有较强的抗倒塌能力。总体上,条板复合墙和CFSST柱框架变形协调,共同工作性能良好,且墙体拉结措施可靠,符合规范要求。     

框架式地铁车站结构大地震近场地震反应特性的三维精细化非线性分析

基于 ABAQUS 软件的 32CPU 显式有限元并行计算集群平台,建立了深软地基土–框架式地铁地下车站结构体系三维精细化非线性地震反应分析的有限元模型,数值模拟了汶川大地震清平波、卧龙波和 100 a 超越概率 3% 的南京人工地震波作用下深软地基上三层三跨框架式地铁地下车站结构地震反应特性的差异。结果表明：大地震近场强地震动将对深软地基上地下车站结构造成严重损伤,甚至发生塑性破坏或坍塌,柱、楼板、侧墙的结合部位是抗震的不利位置,中柱为抗震最薄弱构件,输入近场地震动的峰值加速度和频谱特性对地下车站结构的地震反应均有很大影响;地下车站结构的地震反应具有明显的空间效应,且在大地震近场强地震动作用下地下结构会产生单向累积的永久位移;清平波、卧龙波作用下地下车站结构的地震反应远大于 100 a 超越概率 3% 的南京人工地震波作用下的地震反应;结构浅埋部分的地震损伤比深埋部分更大。     

碧口心墙堆石坝抗震复核分析

 经历“5•12”汶川大地震后,碧口心墙堆石坝出现不同程度的震损现象。根据汶川地震自由场峰值加速度随断层距的衰减关系,利用距坝址较近的文县地震台站(062WIX)实测记录,推求碧口水电站坝址岩基输入加速度时程。通过类比相关工程室内大型动三轴试验资料,结合筑坝材料的工程特性,确定大坝填料的动力模型参数。基于三维动力有限元分析TSDA程序,计算得到的大坝震后永久变形、心墙动孔隙水压力与实测资料较为接近;大坝的绝对加速度反应不大,最大放大倍数仅为2.36倍,坝基防渗墙的动力反应也较小。由于坝址区位于汶川地震发震断层的上盘,虽然地震持续时间较长,但地震波的高频分量发育,大坝的动力反应小于依据《水工建筑物抗震设计规范》设计反应谱合成规范波的对应值。研究结果表明,采用现代重型振动碾压技术填筑的碧口心墙堆石坝具有良好的抗震性能,现阶段土石坝抗震计算理论与方法基本合理。     

Seismic response of plane steel MRF with setbacks: Estimation of inelastic deformation demands

An extensive parametric study on the inelastic seismic response of plane steel moment resisting frames (MRF) with setbacks is presented. A family of 120 such frames, designed according to the European seismic and structural codes, are subjected to an ensemble of 30 ordinary (i.e. without near-fault effects) earthquake ground motions scaled to different intensities in order to drive the structures to different limit states. The statistical analysis of the created response databank indicates that the number of stories, beam-to-column strength ratio, geometrical irregularity and limit state under consideration strongly influence the heightwise distribution and amplitude of inelastic deformation demands. Nonlinear regression analysis is employed in order to derive simple formulae which reflect the aforementioned influences and offer, for a given strength reduction (or behaviour) factor, three important response quantities, i.e. the maximum roof displacement, the maximum interstorey drift ratio and the maximum rotation ductility along the height of the structure. A comparison of the proposed method with the procedures adopted in current seismic design codes reveals the accuracy and efficiency of the former.     

地裂缝场地地铁车站动力响应振动台试验研究

地震和地裂缝耦合作用严重威胁着地铁工程的安全.通过开展地裂缝场地(穿越地裂缝)地铁车站结构模型的振动台试验,分析了地震作用下地裂缝场地土的加速度反应、裂缝发展和车站的加速度、应变等动力反应规律.试验结果表明:模型土在临近地裂缝的一定范围内地震响应较大,且距地裂缝相同距离处,上盘的加速度响应整体上大于下盘;地裂缝场地地铁...