基于能量方法设计的RC框架结构易损性分析

基于“强柱弱梁”的屈服机制,依据能量平衡方法设计了某6层RC框架结构,采用震级-震中距条带地震动记录选取方法,选取12条随机地震动,利用Perform-3D有限元分析软件对结构进行增量动力（IDA）分析,得到了结构的地震易损性曲线、破坏状态概率曲线以及结构破坏概率矩阵。分析结果表明:该方法设计的结构能够形成预设的“强柱弱梁”屈服机制,可以保证结构中梁充分参与耗能,同时结构具有较强的抗倒塌能力,可以满足“小震不坏,中震可修,大震不倒”的性能要求。     

楼层侧向刚度比对砌体结构地震易损性的影响分析

砌体结构的震害现象表明楼层侧向刚度不均匀分布是造成其破坏的重要原因之一。本文开展楼层侧向刚度变化对结构易损性的影响分析。以3层和6层砌体结构为例,采用等效多自由度层间剪切模型,基于非线性动力时程分析,定量研究了竖向刚度不规则性对砌体结构易损性的影响。以结构最大层间位移角为地震反应参数,借助增量动力分析及回归拟合方法,建立了基于峰值加速度的结构易损性曲线。通过改变楼层的侧向刚度值来模拟薄弱层,研究了楼层刚度变化对结构不同破坏状态超越概率的影响。通过改变底层与二层的侧向刚度比,分析了底部刚度突变对结构不同破坏状态超越概率分布的影响。研究表明:与规则结构相比,当刚度突变位于结构底层时,在地震作用下结构易损性相对较高;随着底层与二层的侧向刚度比从0.5增大至1.2,结构易损性逐渐降低。当刚度比为1.5时,结构薄弱层由底层转移至二层,结构整体易损性增加;当底层与二层侧向刚度比小于1时,结构倒塌易损性要显著高于规则结构。     

Influence of spiral anchor composite foundation on seismic vulnerability of raw soil structure

A typical single-layer raw soil structure in villages and towns in China is taken as the research object. In the probabilistic seismic demand analysis, the seismic demand model is obtained by the incremental dynamic time history analysis method. The seismic vulnerability analysis is carried out for the raw soil structure of non-foundation, strip foundation, and spiral anchor composite foundation, respectively. The spiral anchor composite foundation can reduce the seismic response and failure state of raw soil structure, and the performance level of the structure is significantly improved. Structural requirements sample data with the same ground motion intensity are analyzed by linear regression statistics. Compared with the probabilistic seismic demand model under various working conditions, the seismic demand increases gradually with the increase of intensity. The seismic vulnerability curve is summarized for comparative analysis. With the gradual deepening of the limit state, the reduction effect of spiral anchor composite foundation on the exceedance probability becomes more and more obvious, which can reduce the probability of structural failure to a certain extent.     

Framework for the derivation of analytical fragility curves and life cycle cost analysis for non-seismically designed buildings

The quantification of the devastating effects of earthquakes on buildings can be achieved with the use of earthquake risk assessment. The formulation of strategies to minimise this risk is a complex task which relies on data regarding mainly the hazard, vulnerability and remaining life of the building. In this paper, the case study of Limassol municipality is presented. Initially, the building inventory and categorisation is defined followed by the selection of hazard scenarios and the development of analytical vulnerability curves. In the final part, risk assessment is performed leading to the formulation of retrofitting strategies for long term use.     

Three-dimensional limit analysis of seismic displacement of slope reinforced with piles

Three-dimensional (3D) limit analysis of seismic stability of slopes reinforced with one row of piles is presented in this paper. A 3D rotational mechanism for earth slope is adopted. The lateral forces provided by the piles are evaluated by the theory of plastic deformation. Expressions for calculating the yield acceleration coefficient are derived. A random iteration method is employed to find the critical acceleration coefficient for the 3D slopes with or without reinforcement. Based on the kinematic theory within the frame of the pseudo-static approach, a 3D model is proposed for evaluating the critical state and the subsequent displacement response. Furthermore, Newmark׳s analytical procedure is employed to estimate the cumulative displacement induced by given earthquake loads. An example is shown to illustrate the influence of the piles on the seismic displacement of the 3D slopes.     

不同设防标准RC框架结构基于易损性分析的抗震性能评估

借助非线性动力时程分析,对严格按照规范Ⅶ、Ⅷ、Ⅸ度设计的5个三跨6层钢筋混凝土框架结构开展易损性分析,建立了基于峰值加速度的易损性曲线。从易损性的角度对不同设防标准RC框架结构的抗震性能做了定量评价,并探讨了设防标准对RC框架结构易损性的影响。分析表明,对应于设防小震、中震及大震水平的峰值加速度,结构“小震不坏”、“中震可修”和“大震不倒”的失效概率均在18%以内,可认为结构满足三水准的性态控制目标。随着结构设防标准的提高,其易损性随之降低,相同峰值加速度对应的各个破坏状态的超越概率均有所降低。此外,将框架结构的设防烈度提高1度,其“大震不倒”的失效概率会明显减小。而将框架结构的设防烈度降低1度,其“大震不倒”的失效概率会显著增加,最高可达4倍。     

Seismic performance sensitivity and uncertainty analysis of gravity dams

Uncertainties in structural engineering are often arising from the modeling assumptions and errors, or from variability in input loadings. A practical approach for dealing with them is to perform sensitivity and uncertainty analysis in the framework of stochastic and probabilistic methods. These analyses can be statically and dynamically performed through nonlinear static pushover and IDA techniques, respectively. Of the existing structures, concrete gravity dams are infrastructures which may encounter many uncertainties. In this research, probabilistic analysis of the seismic performance of gravity dams is presented. The main characteristics of the nonlinear tensile behavior of mass concrete, along with the intensity of earthquake excitations are considered as random variables in the probabilistic analysis. Using the tallest non‐overflow monolith of the Pine Flat gravity dam as a case study, its response under static and dynamic situations is reliably examined utilizing different combinations of parameters in the material and the seismic loading. The sensitivity analysis reveals the relative importance of each parameter independently. It will be shown that the undamaged modulus of elasticity and tensile strength of mass concrete have more significant roles on the seismic resistance of the dam than the ultimate inelastic tensile strain. In order to propagate the parametric uncertainty to the actual seismic performance of the dam, probabilistic simulation methods such as Monte Carlo simulation with Latin hypercube sampling, and approximate moment estimation techniques will be used. The final results illustrate the possibility of using a mean‐parameter dam model to estimate the mean seismic performance of the dam. Copyright © 2014 John Wiley & Sons, Ltd.     

不同轴压比钢筋混凝土圆柱桥墩地震易损性分析

以墩顶漂移率为指标运用ABAQUS有限元软件对钢筋混凝土桥墩进行地震易损性分析。对钢筋混凝土桥墩模型进行精细网格划分,运用循环往复Pushover方法模拟钢筋混凝土桥墩破坏界限值,以此界限值为标准对轴压比为0.20、0.22、0.24、0.26和0.30钢筋混凝土桥墩进行增量动力分析（IDA）。研究结果表明:结构的破坏超越概率,随着轴压比的增大而增大;考虑钢筋混凝土桥墩延性抗震性能,设计轴压比不宜超过0.30;轴压比为0.24~0.26时,钢筋混凝土桥墩破坏概率增加不大,宜为合理的轴压比。     

Static vulnerability of an existing r.c. structure and seismic retrofitting by CFRP and base-isolation: A case study

The assessment of the static vulnerability under gravity loads of existing reinforced concrete (r.c.) framed buildings is a serious problem that requires the use of reliable methodologies to evaluate ductile and brittle mechanisms. The present work compares alternative formulations of member chord rotation and section and joint shear strength, proposed by Italian and European seismic codes and guidelines and other expressions available in the scientific literature. To this end, a r.c. framed building built sixty years ago with bi-directional (perimeter) and mono-directional (interior) plane frames, originally designed for five storeys then elevated to six during construction, is studied. A full characterization of the structure and its materials is carried out by means of destructive and non-destructive methods. Then, retrofitting based on the use of both innovative material, such as carbon fibre reinforced polymers (CFRP), and technology, such as base-isolation, are adopted to improve the static and seismic performances of the original structure. Finally, nonlinear analyses are carried out on a three-dimensional fibre model of the original and retrofitted structures, where an elastic linear law idealizes the behaviour of the CFRP up to tension failure and viscoelastic linear and bilinear models are used to idealize the behaviour of the elastomeric and sliding bearings, respectively.     

三峡澎溪河水-气界面温室气体模型估算及其敏感性分析

模型估算法是水-气界面温室气体通量监测的主要方法,所得成果也不胜枚举.然而监测过程中诸多环境因素会对最终结果产生不确定的影响.结合三峡库区澎溪河背景条件,利用模型估算法进行水-气界面温室气体通量(以CO_2为例)估算,并且采用修正Morris筛选法尝试分析模型估算法中各个参数对温室气体扩散通量(以CO_2为例)的局部敏感性.研究结果表明:利用模型估算法计算三峡澎溪河流域水-气界面温室气体通量具有较高的可行性和可靠性;风速、水温以及pH值会对监测结果产生影响,且风速越强、水温越高、pH值越小,CO_2扩散通量就越大;pH值是高灵敏参数,风速和水温是灵敏参数.在三峡库区澎溪河监测过程中更应注意pH值的精确性,每次采样前需校正仪器.     

Seismic risk assessment for the mega-city of Istanbul: Ductility, strength and maximum interstory drift demands

This study investigates the seismic demands due to the catastrophic 1999 M_w=7.4 Kocaeli and the M_w=7.1 Duzce earthquakes. The inelastic response spectra for the Kocaeli and Duzce earthquakes are investigated for systems with known strength and ductility. An analytical fiber element model is developed for a typical reinforced concrete building in Turkey. The interstory drifts are calculated from nonlinear dynamic analysis using 26 recorded strong-motion data from the 1999 Kocaeli and the Duzce earthquakes. In the dynamic analysis, the structural members are modeled by employing distributed plasticity fiber elements and both geometrical as well as material nonlinearities are taken into account. This study shows that the ductility and interstory drift demands due to the Kocaeli and the Duzce earthquakes were very severe (well above the code prescribed values) even for moderately inelastic structures. It is apparent from the results that the forward directivity effect is the most influential factor on the interstory drift demand. Both the distance to the fault rupture and the site conditions affect seismic demands, but the site conditions and the local topography are more influential than the distance from the fault rupture. This study shows that substantial damage should be expected in a future earthquake at all districts of Istanbul, but especially at Avcilar, Cekmece, Fatih, Bakirkoy and the Zeytinburnu districts. It is also shown that base isolation may substantially improve the performance of a structure in the inelastic domain and base isolated structures may be designed for lower minimum lateral strengths and higher strength reduction factors.     

Assessment of buckling-restrained braced frame reliability using an experimental limit-state model and stochastic dynamic analysis

Buckling-restrained braces(BRBs)have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems.A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression.Although design guidelines for BRB applications have been developed,systematic procedures for assessing performance and quantifying reliability are still needed.This paper presents an analytical framework for assessing buckling-restrained braced f...     

考虑非均匀地幔的重力-地震联合建模

本文提出在综合地球物理研究中,为了使重力数据处理和反演更加符合实际的地质情况,重力-地震联合建模分析时应当考虑非均匀地幔物质的重力效应.本文针对含油气盆地结构、断裂构造、大陆边缘演化和洋陆转换带等热点地质问题,广泛调研了全球范围内多个地区的综合地球物理研究成果,及其对应的地幔深部结构,发现地幔的横向不均一性是普遍存在的.在以往许多基于重力、地震数据的综合研究实践中,重力异常分离和建模分析通常都是在地壳内部（莫霍面以上）进行的.这种处理方式实际上是以均匀地幔为假设前提,虽然简化了重力异常分离和建模分析的难度,但忽略了地球深部的不均匀性所带来的重力异常,所获得的剩余重力异常和在此基础上进行的密度结构反演、地质解释会存在偏差.本文通过对模型界面的2D正演,定量探讨了非均匀地幔对布格重力异常的影响.在对四川盆地的实例研究中,剥离了非均匀地幔的重力效应,2.5D重震联合模拟的结果明显优于均匀地幔假设条件下的结果.

     

Direct estimation of the seismic demand and capacity of oscillators with multi‐linear static pushovers through IDA

SPO2IDA is introduced, a software tool that is capable of recreating the seismic behaviour of oscillators with complex quadrilinear backbones. It provides a direct connection between the static pushover (SPO) curve and the results of incremental dynamic analysis (IDA), a computer‐intensive procedure that offers thorough demand and capacity prediction capability by using a series of nonlinear dynamic analyses under a suitably scaled suite of ground motion records. To achieve this, the seismic behaviour of numerous single‐degree‐of‐freedom (SDOF) systems is investigated through IDA. The oscillators have a wide range of periods and feature pinching hysteresis with backbones ranging from simple bilinear to complex quadrilinear with an elastic, a hardening and a negative‐stiffness segment plus a final residual plateau that terminates with a drop to zero strength. An efficient method is introduced to treat the backbone shape by summarizing the analysis results into the 16, 50 and 84% fractile IDA curves, reducing them to a few shape parameters and finding simpler backbones that reproduce the IDA curves of complex ones. Thus, vast economies are realized while important intuition is gained on the role of the backbone shape to the seismic performance. The final product is SPO2IDA, an accurate, spreadsheet‐level tool for performance‐based earthquake engineering that can rapidly estimate demands and limit‐state capacities, strength reduction R‐factors and inelastic displacement ratios for any SDOF system with such a quadrilinear SPO curve. Copyright © 2006 John Wiley & Sons, Ltd.     

某周期比超限偏心结构地震反应控制分析

本文以周期比超限的某偏心结构工程为研究背景,基于SAP2000建立三维有限元模型,采用黏滞阻尼器、黏弹性阻尼器、软钢阻尼器、复合铅黏弹性阻尼器和钢支撑五种减震方案对其进行扭转控制,针对不同扭转控制方案分别进行了模态分析、反应谱分析和动力时程分析,对比研究了多遇地震作用下各控制方案的周期比、层间位移、支撑内力及阻尼器的耗能能力。研究表明:五种控制方案均具有有效抑制结构扭转振动响应的能力,降低结构的最大层间位移角,并使之满足规范要求;后四种控制方案能明显减小结构的周期比,将结构第一扭转反应控制在第三振型;对于此类偏心结构体系的扭转振动控制,本文建议阻尼器设置应尽量远离刚度中心,以达到最佳扭转控制效果。     

大型火力发电厂框排架混合结构主厂房动力特性试验与分析

选取1 000MW大型火力发电厂新型混合结构主厂房体系的三跨三榀进行缩尺比为1/7的空间模型试验研究.采用锤击法测试模型结构的动力特性,得到其自振频率和振型,并根据相似关系换算到原型结构.使用SAP2000软件建立混合结构主厂房模型和原型结构的有限元模型,进行模态分析,得到模型和原型结构的频率和振型,并与试验结果进行对比分析.可为大型火力发电厂新型混合结构主厂房体系的抗震性能研究提供依据.     

Dimensional analysis of structures with translating and rocking foundations under near-fault ground motions

This paper evaluates the inertial soil–structure interaction (SSI) effects on linear and bilinear structures supported on foundation that is able to translate and rock when subject to near-fault ground motions. Through rigorous dimensional analysis, the peak structural responses (e.g. structural drift and total acceleration) of the soil–foundation–structure interacting (SFSI) systems are characterized by a set of dimensionless Π-parameters, which can decisively describe the interactive behavior of SFSI systems. By comparing the normalized structural responses of various structure–foundation systems with their fixed-base counterparts, the study reveals that SSI effects highly depend on the structure-to-pulse frequency ratio, Π_ω, the foundation-to-structure stiffness ratio, Π_k, damping coefficient of foundation impedance, Π_c, the foundation rocking, and the development of nonlinearity in structures. For linear structures, the SSI effects are insignificant when the structure-to-pulse frequency ratio (Π_ω) is smaller than 1.5 and can amplify the structural responses when Π_ω is higher than 1.5. Foundation rocking can shift and enlarge the response amplification zone of SSI. For nonlinear structures, SSI tends to reduce the structural responses for Π_ω<3 while can increase the ductility demands for Π_ω≥3. The bilinear structures may experience more significant SSI effects than linear structures in certain frequency ranges. The numerical simulations on ten real building cases exhibiting significant rocking and a detailed case study on a nine-story frame structure demonstrate the applicability of dimensional analysis results to predict the SSI effects on realistic building structures. The study demonstrates that the dimensional analysis provides a concise and systematic way of evaluating SSI effects.     

Simulating water temperatures and stratification of a pre‐alpine lake with a hydrodynamic model: calibration and sensitivity analysis of climatic input parameters

We report on the calibration of the one‐dimensional hydrodynamic lake model Dynamic Reservoir Simulation Model to simulate the water temperature conditions of the pre‐alpine Lake Ammersee (southeast Germany) that is a representative of deep and large lakes in this region. Special focus is given to the calibration in order to reproduce the correct thermal distribution and stratification including the time of onset and duration of summer stratification. To ensure the application of the model to investigate the impact of climate change on lakes, an analysis of the model sensitivity under stepwise modification of meteorological input parameters (air temperature, wind speed, precipitation, global radiation, cloud cover, vapour pressure and tributary water temperature) was conducted. The total mean error of the calibration results is ?0.23 °C, the root mean square error amounts to 1.012 °C. All characteristics of the annual stratification cycle were reproduced accurately by the model. Additionally, the simulated deviations for all applied modifications of the input parameters for the sensitivity analysis can be differentiated in the high temporal resolution of monthly values for each specific depth. The smallest applied alteration to each modified input parameter caused a maximum deviation in the simulation results of at least 0.26 °C. The most sensitive reactions of the model can be observed through modifications of the input parameters air temperature and wind speed. Hence, the results show that further investigations at Lake Ammersee, such as coupling the hydrodynamic model with chemo‐dynamic models to assess the impact of changing climate on biochemical conditions within lakes, can be carried out using Dynamic Reservoir Simulation Model. Copyright © 2012 John Wiley & Sons, Ltd.