基于地震易损性的框架结构的优化方法

给出了一种框架结构地震易损性优化的准则算法．根据优化准则构造了一种修改设计变量的格式,提出了设计方案可行性调整的方法并推导了计算公式,给出了优化算法的计算步骤,并通过一个算例阐述了这种算法的应用。     

The generation of spectrum compatible accelerograms for the design of nuclear power plants

Based on the main features of the computer program THGE, the paper reviews the techniques which are available for the construction of an accelerogram whose response spectrum matches a design spectrum. First, a sample accelerogram is generated as the product of the stationary random sequence by a deterministic shape function. It is assumed that the spectral properties of the stationary process have been determined in a previous step, in order to lead to the design spectrum as expected maximum responses of a set of single degree of freedom oscillators. The principal properties of the Fast Fourier Transform which is used for this first step are reviewed. The paper then describes the procedures which are available, both in the frequency domain and in the time domain, to improve the agreement between the response spectrum and the target. It also discusses some related issues, such as the response spectrum calculations, the statistical dependence between the three earthquake components, the duration of the time history, the variability of the secondary response to various samples and the generation of an accelerogram whose response spectra envelop a set of design spectra. The point of view adopted is the one of the structural engineer.     

How to construct future IDF curves,under changing climate,for sites with scarce rainfall records?

Optimal designs of stormwater systems rely very much on the rainfall Intensity–Duration–Frequency (IDF) curves. As climate has shown significant changes in rainfall characteristics in many regions, the adequacy of the existing IDF curves is called for particularly when the rainfall are much more intense. For data sparse sites/regions, developing IDF curves for the future climate is even challenging. The current practice for such regions is, for example, to ‘borrow’ or ‘interpolate’ data from regions of climatologically similar characteristics. A novel (3‐step) Downscaling‐Comparison‐Derivation (DCD) approach was presented in the earlier study to derive IDF curves for present climate using the extracted Dynamically Downscaled data an ungauged site, Darmaga Station in Java Island, Indonesia and the approach works extremely well. In this study, a well validated (3‐step) DCD approach was applied to develop present‐day IDF curves at stations with short or no rainfall record. This paper presents a new approach in which data are extracted from a high spatial resolution Regional Climate Model (RCM; 30 × 30 km over the study domain) driven by Reanalysis data. A site in Java, Indonesia, is selected to demonstrate the application of this approach. Extremes from projected rainfall (6‐hourly results; ERA40 Reanalysis) are first used to derive IDF curves for three sites (meteorological stations) where IDF curves exist; biases observed resulting from these sites are captured and serve as very useful information in the derivation of present‐day IDF curves for sites with short or no rainfall record. The final product of the present‐day climate‐derived IDF curves fall within a specific range, +38% to +45%. This range allows designers to decide on a value within the lower and upper bounds, normally subjected to engineering, economic, social and environmental concerns. Deriving future IDF curves for Stations with existing IDF curves and ungauged sites with simulation data from RCM driven by global climate model (GCM ECHAM5) (6‐hourly results; A2 emission scenario) have also been presented. The proposed approach can be extended to other emission scenarios so that a bandwidth of uncertainties can be assessed to create appropriate and effective adaptation strategies/measures to address climate change and its impacts. Copyright © 2013 John Wiley & Sons, Ltd.     

Numbers of scaled and matched accelerograms required for inelastic dynamic analyses

Selecting, scaling and matching accelerograms are critically important to engineering design and assessment, enabling structural response to be determined with greater confidence and through fewer analyses than if unscaled accelerograms are employed. This paper considers the response of an 8‐storey multiple‐degree‐of‐freedom reinforced concrete structure to accelerograms selected, linearly scaled or spectrally matched using five different techniques. The first method consists of selecting real records on the basis of seismological characteristics, while the remaining methods make an initial selection on the basis of magnitude and spectral shape before (1) scaling to the target spectral acceleration at the initial period; (2) scaling to the target spectrum over a range of periods; (3) using wavelet adjustments to match the target spectrum and (4) using wavelet adjustments to match multiple target spectra for multiple damping ratios. The analyses indicate that the number of records required to obtain a stable estimate of the response decreases drastically as one moves through these methods. The exact number varies among damage measures and is related to the predictability of the damage measure. For measures such as peak roof and inter‐storey drift, member end rotation and the Park and Ang damage index, as few as one or two records are required to estimate the response to within ±5% (for a 64% confidence level) if matching to multiple damping ratios is conducted. Bias checks are made using predictive equations of the expected response derived from the results of 1656 nonlinear time‐domain analyses of the structure under the action of unscaled accelerograms. Copyright © 2008 John Wiley & Sons, Ltd.     

The synthesis of strong ground motion accelerograms from existing records

The paper discusses the synthesis of acceleration time histories primarily for use in structural response estimation. A proposed model for the acceleration time history is based on the summation of dispersive wave modes over the range of frequencies of typical interest to structural response. The values of the modal amplitudes and the travel times (or group velocities) are, for cases examined here, extracted from a target earthquake (or an ensemble of them). The synthetic accelerograms are constructed from these parameters with the inclusion of a probabilistic definition of those or other characteristics of the strong ground shaking and, in particular, the modal phase angle. The probability distributions of the peak acceleration and the integral of the square acceleration of the synthetic records are examined along with comparisons of the pseudo spectral velocity (PSV) response.     

Numerical simulation of ground acceleration spectra and accelerograms for engineering application

A numerical approach to the earthquake ground motion analysis is proposed for regions where no accelerograms are available. Using Haskell matrix techniques, the response spectra of a layered substratum for SV waves were calculated and then multiplied by the spectra corresponding to Brune's type pulses. The ground acceleration spectra were obtained for different angles of pulse incidence at the substratum base. The spectrum shape depends upon the substratum response and the pulse shape, while its level was related to the maximum ground acceleration corresponding to the expected maximum intensity. Transformation of the ground spectra into the time domain produced numerical accelerograms for horizontal and vertical components and for different angles of pulse incidence. Finally, a standard statistical procedure was applied to obtain the design response spectra used in engineering applications.     

Analysis of accelerograms recorded in the source zone of the 1995 Neftegorsk earthquake and computation of synthetic accelerograms

The strongest Neftegorsk earthquake, which occurred in 1995 in the northern part of the Sakhalin Island, was studied by the Epicentral Seismological Expedition, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. The performed observations yielded the unique accelerograms of strong aftershocks, which were then applied as a basis for detailed analyses. The recorded accelerations were in satisfactory compliance with the current ground motion relations. The design spectra developed on the basis of analyzed records were proposed as an example. The synthetic accelerograms were calculated using the records of the strongest aftershocks for two modal earthquakes by the empirical Green’s function technique. This technique can be recommended for practical application as the most physically substantiated method taking into account all regional features.     

Seismic design of RC structures: A critical assessment in the framework of multi‐objective optimization

The assessment of seismic design codes has been the subject of intensive research work in an effort to reveal weak points that originated from the limitations in predicting with acceptable precision the response of the structures under moderate or severe earthquakes. The objective of this work is to evaluate the European seismic design code, i.e. the Eurocode 8 (EC8), when used for the design of 3D reinforced concrete buildings, versus a performance‐based design (PBD) procedure, in the framework of a multi‐objective optimization concept. The initial construction cost and the maximum interstorey drift for the 10/50 hazard level are the two objectives considered for the formulation of the multi‐objective optimization problem. The solution of such optimization problems is represented by the Pareto front curve which is the geometric locus of all Pareto optimum solutions. Limit‐state fragility curves for selected designs, taken from the Pareto front curves of the EC8 and PBD formulations, are developed for assessing the two seismic design procedures. Through this comparison it was found that a linear analysis in conjunction with the behaviour factor q of EC8 cannot capture the nonlinear behaviour of an RC structure. Consequently the corrected EC8 Pareto front curve, using the nonlinear static procedure, differs significantly with regard to the corresponding Pareto front obtained according to EC8. Furthermore, similar designs, with respect to the initial construction cost, obtained through the EC8 and PBD formulations were found to exhibit different maximum interstorey drift and limit‐state fragility curves. Copyright © 2007 John Wiley & Sons, Ltd.     

基于强震记录估算同震位移的研究进展及方法

通过对强震加速度记录估算同震位移技术自20世纪40年代以来国内外研究成果的总结,系统地阐述了通过近断层加速度记录计算同震位移的相关理论、方法的发展历程和成就。首先简述了基于强震记录估算同震位移的意义和普遍存在的漂移现象,然后总结了从模拟记录到数字记录两个阶段计算同震位移所取得的成果,接着归纳了为解决漂移现象所采取的3种基于时程拟合的方法和2种基于小波分析的方法,最后对基于数字强震仪记录估算同震位移的未来研究进行了展望。     

强震记录仪器响应失真校正的权函数方法—时域离散序列数值分析方法与应用研究之二

简要评述了现有强震记录仪器响应失真校正方法的优点和存在的不足。在文献[1]的基础上，提出了对强震记录进行仪器响应失真校正的权函数方法，并推导建立了相应的计算公式。通过设计真实地震动为已知的算例，对加速度摆和速度摆强震仪的未校正记录，和用不同方法获得的校正记录的精度（或误差）进行了对比分析。理论和算例分析表明，本文方法简单、实用，具有很高的计算机精度且无稳定性问题。     

Identification of critical ground motions for seismic performance assessment of structures

A method is established to identify critical earthquake ground motions that are to be used in physical testing or subsequent advanced computational studies to enable seismic performance to be assessed. The ground motion identification procedure consists of: choosing a suitable suite of ground motions and an appropriate intensity measure; selecting a computational tool and modelling the structure accordingly; performing Incremental Dynamic Analysis on a non‐linear model of the structure; interpreting these results into 50th (median) and 90th percentile performance bounds; and identifying the critical ground motions that are close to these defining probabilistic curves at ground motion intensities corresponding to the design basis earthquake and the maximum considered earthquake. An illustrative example of the procedure is given for a reinforced concrete highway bridge pier designed to New Zealand specifications. Pseudodynamic tests and finite element based time history analyses are performed on the pier using three earthquake ground motions identified as: (i) a Design Basis Earthquake (10% probability in 50 years) with 90 percent confidence of non‐exceedance; (ii) a Maximum Considered Event (2% probability in 50 years) representing a median response; and (iii) a Maximum Considered Event representing 90 percent confidence of non‐exceedance. Copyright © 2006 John Wiley & Sons, Ltd.     

An energy-based envelope function for the stochastic simulation of earthquake accelerograms

An energy-based envelope function is developed for use in the stochastic simulation of earthquake ground motion. The envelope function is directly related to the Arias intensity of the ground motion as well to the manner in which this Arias intensity is built-up over time. It is shown that this build-up, represented by a Husid plot, can be very well modelled using a simple lognormal distribution. The proposed envelope makes use of parameters that are commonly available in seismic design situations, either following a deterministic scenario-type analysis or following a more comprehensive probabilistic seismic hazard analysis (PSHA), either in terms of Arias intensity or the more common spectral acceleration. The shape parameters of the envelope function are estimated following the calculation of the analytic envelopes for a large number of records from PEER Next Generation of Attenuation (NGA) database. The envelope may also be used to predict the distribution of peak ground acceleration values corresponding to an earthquake scenario. The distribution thus obtained is remarkably consistent with those of the recent NGA models.     

Selection of spectrum- and seismo-compatible accelerograms for the Tuscany region in Central Italy

This article illustrates the results of a study aimed at developing a methodology for the automatic identification of the seismic input at outcropping rock sites and flat topographic conditions necessary to carry out non-linear dynamic analysis of structures and geotechnical systems. The seismic input is provided in terms of a set of 7 natural accelerograms recorded on outcropping rock and satisfying the average spectral compatibility requirements prescribed by the Italian seismic code (NTC08).The study focuses on the territory encompassing Tuscany region in Central Italy and it has been carried out for six return periods, which are 50, 75, 101, 475, 712 and 949 years. The procedure involved four main steps: (1) grouping of the response spectra with similar features; (2) definition of the reference response spectrum for each group; (3) selection of spectrum-compatible accelerograms using the reference response spectrum of each group; and (4) linear scaling of the accelerograms to satisfy the compatibility requirement with respect to other response spectra of the group. The last step is implemented through an interactive, user-friendly program named SCALCONA 2.0, which provides the seismic input in agreement with the site location and return period specified by the user. The program is freely available at the following web site: http://www.rete.toscana.it/sett/pta/sismica/01informazione/banchedati/input_sismici/progettazione/index.htm.     

Inelastic displacement ratios for evaluation of structures built on soft soil sites

This paper summarizes the results of a comprehensive statistical study aimed at evaluating peak lateral inelastic displacement demands of structures with known lateral strength and stiffness built on soft soil site conditions. For that purpose, empirical information on inelastic displacement ratios which are defined as the ratio of peak lateral inelastic displacement demands to peak elastic displacement demands are investigated. Inelastic displacement ratios were computed from the response of single‐degree‐of‐freedom systems having 6 levels of relative lateral strength when subjected to 118 earthquake ground motions recorded on bay‐mud sites of the San Francisco Bay Area and on soft soil sites located in the former lake‐bed zone of Mexico City. Mean inelastic displacement ratios and their corresponding scatter are presented for both ground motion ensembles. The influence of period of vibration normalized by the predominant period of the ground motion, the level of lateral strength, earthquake magnitude, and distance to the source are evaluated and discussed. In addition, the effects of post‐yield stiffness and of stiffness and strength degradation on inelastic displacement ratios are also investigated. It is concluded that magnitude and distance to the source have negligible effects on constant‐strength inelastic displacement ratios. Results also indicate that weak and stiffness‐degrading structures in the short spectral region could experience inelastic displacement demands larger than those corresponding to non‐degrading structures. Finally, a simplified equation obtained using regression analyses aimed at estimating mean inelastic displacement ratios is proposed for assisting structural engineers in performance‐based assessment of structures built on soft soil sites. Copyright © 2006 John Wiley & Sons, Ltd.     

Processing of strong-motion accelerograms: needs, options and consequences

Recordings from strong-motion accelerographs are of fundamental importance in earthquake engineering, forming the basis for all characterizations of ground shaking employed for seismic design. The recordings, particularly those from analog instruments, invariably contain noise that can mask and distort the ground-motion signal at both high and low frequencies. For any application of recorded accelerograms in engineering seismology or earthquake engineering, it is important to identify the presence of this noise in the digitized time-history and its influence on the parameters that are to be derived from the records. If the parameters of interest are affected by noise then appropriate processing needs to be applied to the records, although it must be accepted from the outset that it is generally not possible to recover the actual ground motion over a wide range of frequencies. There are many schemes available for processing strong-motion data and it is important to be aware of the merits and pitfalls associated with each option. Equally important is to appreciate the effects of the procedures on the records in order to avoid errors in the interpretation and use of the results. Options for processing strong-motion accelerograms are presented, discussed and evaluated from the perspective of engineering application.     

基于单台加速度记录的混合全局优化HVSR反演场地浅层速度结构

利用水平与竖向谱比（HVSR）方法反演场地速度结构是国际上迅速发展的研究领域.HVSR反演计算实质是一个土层场地模型空间搜索的全局优化问题,当模型搜索空间的复杂程度增大时,目前常用的搜索算法收敛速度慢,计算效率较低.本文实现了一种结合遗传和模拟退火方法优点的混合全局优化HVSR反演算法,通过理论模型和竖向台阵实测数据的检验,表明该算法能获得很好的反演效果,较好地解决了蒙特卡罗方法收敛速度慢,遗传算法收敛早熟和模拟退火算法搜索效率低的问题.本文在此基础上讨论了单台加速度S波记录用于场地速度结构HVSR反演的适用性,为基于单个地震台的地震观测记录反演浅层速度结构提供了一种高效且较为准确的反演方法.

     

How to construct recursive digital filters for baseflow separation

Recursive digital filtering of hydrographs is a baseflow separation method that can easily be automated and has been recommended for providing reproducible results. In the past, different formulations of the most simple filter type, the so‐called one‐parameter filter, have been proposed. In this paper, a theoretical framework is developed for filter algorithms that were constructed under the assumption that the outflow from an aquifer is linearly proportional to its storage. It is shown that these one‐parameter filters describing an exponential baseflow recession are all special cases of a two‐parameter filter whose equation is specified. Its parameters are the recession constant—which can be objectively determined by a recession analysis—and BFI_max, the maximum value of the baseflow index that can be modelled by the algorithm. This introduces a subjective element into the baseflow calculation, since BFI_max is not measurable. A preliminary analysis based on the results of conventional separation techniques shows that it might be possible to find typical BFI_max values for classes of catchments that can be unequivocally distinguished by their hydrological and hydrogeological characteristics. Copyright © 2004 John Wiley & Sons, Ltd.     

强震近场加速度峰值比和反应谱统计分析

本文对国内外数十次强地震的近场加速度记录进行了统计分析，给出了近场加速度峰值比及反应谱的统计结果，并将统计反应谱与设计反应谱进行了比较。     

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.     

Multi-objective optimization of a dissipative connection for seismic protection of wall-frame structures

This paper deals with the optimum design of a passive seismic control strategy which adopts a linear dissipative connection in a wall-frame system. The two sub-structures, the wall and the frame, respectively, are modeled as single degree of freedom systems, and are excited by a ground motion represented by a filtered non stationary stochastic process. The passive control strategy is based on a "global protection", which aims to protect both sub-structures. For this purpose, a multi-objective optimum design is formulated where two conflicting objective functions coexist: these are the displacement of the frame and the shear in the wall. In order to obtain the optimum solution in terms of Pareto set, a genetic algorithm approach—the NSGA-II—is adopted. The novelty of the proposed method is the use of a multi-dimensional criterion for the design of the dissipative connection and to consider a global seismic protection criterion. This is a very important issue in modern Technical Codes, where several performance requirements are fixed and often conflicting.