南京长江大桥桥头堡抗震加固受力性能研究

为研究南京长江大桥桥头堡填充墙加固对结构抗震性能的影响,提出考虑较高填充墙开裂的双斜撑模型,用于罕遇地震工况下桥头堡的抗震性能计算,同时提出考虑填充墙加固后刚度增强效应的建模方法。利用SAP2000建立了加固前后用于多遇地震工况、设防地震工况及罕遇地震工况的分析模型,并选取了桥头堡在1974年经历的实际地震激励时程及El-Centro地震激励时程作为激励进行了加固前后结构的抗震性能分析比较。研究发现,填充墙加固后桥头堡的抗震性能有了明显提升,其位移响应峰值约下降8%~23%,层间位移角响应峰值约下降12%~22%,而且桥头堡结构在设防地震情况下2个方向的层间位移角均满足了规范要求。另外,在罕遇地震工况下,未加固的填充墙开裂会使结构的扭转刚度下降,而填充墙加固可有效提升结构的扭转刚度,降低桥头堡在地震时发生扭转振动的概率。这2种地震荷载激励的分析结果差异约在3%~21%不等,且响应峰值出现的位置也有一些不同,故对桥头堡进行抗震时程分析时建议选取多条地震波输入综合分析。研究成果可为同类型的钢筋混凝土建筑遗产的抗震加固提供借鉴和参考。     

Comparison of Numerical and Experimental Seismic Responses of FREI-Supported Un-reinforced Brick Masonry Model Building

Comparative study of numerically and experimentally obtained seismic responses of un-reinforced masonry building supported on in-house designed un-bonded fibre reinforced elastomeric isolator (U-FREI) are presented in this article. The effectiveness of U-FREI is established very clearly in terms of controlled dynamic response of the model building. Experimental studies are carried out on a shake table with elaborate instrumentations for measurement of acceleration and displacements at different floor levels. Numerical study of the model building supported on U-FREI is carried out to compare the results with experimental investigation. Multi-linear pivot hysteretic plasticity model is used to simulate the behavior of FREI, while plate elements are used for brick-masonry walls. Experimentally obtained force-displacement curves of FREI are used for defining the properties of multi-linear model representing FREI. The dynamic responses obtained from the numerical studies are compared with those from experimental investigations. This study indicates that the seismic responses of building supported on U-FREI can be numerically evaluated with quite reasonable accuracy. A good numerical model can be judiciously used at the preliminary design stage, followed by actual testing and construction of the base isolated building.     

Experimental Study on Seismically Resilient Two-Span Bridge Models Designed for Disassembly

Shake-table studies were conducted on a ¼-scale, 2-span bridge model incorporating a newly-developed concept of replaceable plastic hinges and columns that can be easily assembled and disassembled. The plastic hinges incorporate novel materials that mitigate column damage and permanent drift, allowing the bridge to undergo intense seismic shaking and remain operational when most conventional bridges would warrant demolition. Designed to be disassembled, the column components have the potential to be reused, which is intended to help mitigate the environmental impact from material extraction and manufacture. The concept feasibility was demonstrated by assembling, testing, and disassembling the same bridge model twice.     

Effectiveness of FRCM Reinforcement Applied to Masonry Walls Subject to Axial Force and Out-Of-Plane Loads Evaluated by Experimental and Numerical Studies

ABSTRACT

An experimental campaign and a numerical analysis devoted to the investigation of the out-of-plane behavior of masonry walls reinforced with Fiber Reinforced Cementitious Matrix (FRCM) are presented here. The main goal of this study is to analyze and evaluate the effectiveness of the strengthening system, by discussing failure modes and capacity of strengthened masonry walls, in order to assess their behavior under out-of-plane horizontal actions, such as, for example, seismic actions. A purposely designed experimental set-up, able to separately and independently apply an axial force and out-of-plane horizontal actions on masonry walls, was used. Experimental results are discussed and compared with the outcomes of nonlinear analyses performed on simplified finite element models of the walls. A proper evaluation of the flexural capacity of FRCM strengthened walls is the first step of the ongoing process of drawing reliable code guidelines leading to a safe design of strengthened masonry structures.     

Full-Scale Experimental Verification of Soft-Story-Only Retrofits of Wood-Frame Buildings using Hybrid Testing

The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame buildings based on existing data, and the method had not been verified through full-scale experimental testing. This article presents two different retrofit designs based directly on the FEMA P-807 Guidelines that were examined at several different seismic intensity levels. The effects of the retrofits on damage to the upper stories were investigated. The results from the hybrid testing verify that designs following the FEMA P-807 Guidelines meet specified performance levels and appear to successfully prevent collapse at significantly higher seismic intensity levels well beyond for which they were designed. Based on the test results presented in this article, it is recommended that the soft-story-only retrofit procedure can be followed when financial or other constraints limit the retrofit from bringing the soft-story building up to current code or applying performance-based procedures.     

Full-Scale Shaking Table Tests on a Substandard RC Building Repaired and Strengthened with Post-Tensioned Metal Straps

The effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) technique at enhancing the seismic behavior of a substandard RC building was investigated through full-scale, shake-table tests during the EU-funded project BANDIT. The building had inadequate reinforcement detailing in columns and joints to replicate old construction practices. After the bare building was initially damaged significantly, it was repaired and strengthened with PTMS to perform additional seismic tests. The PTMS technique improved considerably the seismic performance of the tested building. While the bare building experienced critical damage at an earthquake of PGA = 0.15 g, the PTMS-strengthened building sustained a PGA = 0.35 g earthquake without compromising stability.     

Seismic Fragility Assessment of Lightly Reinforced Concrete Structural Walls

Development of fragility functions is a pertinent stage in seismic performance assessment of structures. A database of lightly Reinforced Concrete (RC) walls under simulated seismic loading is compiled from the literature to establish the drift-based seismic fragility functions. To classify the damage states experienced by RC walls, the Park-Ang Damage model is amended in this research. Then, the modified Bouc-Wen-Baber-Noori hysteresis model is implemented in ABAQUS to predict the hysteresis behavior of RC walls. Thereafter, the proposed hysteresis model is employed to develop the seismic fragility curves of low to mid-rise RC walls in Singapore using incremental dynamic analysis approach.     

Application of an Extended Bouc-Wen Model in Seismic Response Prediction of Unbonded Fiber-Reinforced Isolators

The focus of this article is on seismic-response prediction of Stable Unbonded-Fiber Reinforced Elastomeric Isolators (SU-FREIs). The lateral load-displacement of a SU-FREI can be characterized with a gradual softening that is followed by stiffening. An extended Bouc-Wen Model is developed to simulate the response behavior of SU-FREIs under seismic events. To examine the accuracy of model, the response of a base isolated structure to different input earthquakes were simulated and compared with the results of a previous shake table study. Results of this study indicate that the proposed Bouc-Wen Model is robust and reasonably accurate in seismic analysis of SU-FREIs.     

水平地震作用下大式带斗栱木结构古建筑的抗倒塌性能分析

基于根据宋代《营造法式》制作的某单层单开间殿堂式木结构振动台模型,建立了考虑柱础滑移隔震、榫卯半刚性连接及斗栱减震性能的空间杆系有限元模型。通过模型的数值计算值与振动台实测数据之间的对比分析,验证了建模方法的正确性。提出了柱脚滑移倒塌的相对位移判定准则及柱架层间倒塌的最大层间位移角判定准则,并采用增量动力分析(IDA)方法对这两种倒塌机制进行研究。结果表明:木结构古建筑在普通地震波作用下不易出现柱脚滑移倒塌;层间倒塌为长周期地震波作用下最易出现的倒塌机制;相对于普通地震波而言,木结构古建筑受长周期地震波作用的影响更大。     

TUNING OF SEISMIC HAZARD ESTIMATES BY MEANS OF OBSERVED SITE INTENSITIES

Probabilistic seismic hazard is usually assessed by means of computer codes using seis-mogenic sources, parametric catalogues, seismicity rates and attenuation relationships. All these ingredients are conditioned by expert judgement that influences the final results. Even the attenuation relationships, though strictly based on experimental data, are considered a weak point due to the difficulty of modelling the interaction between seismic energy radiation and site response, and because earthquakes do not usually repeat themselves according to one theoretical model. Recently, methods making wide use of site intensity data have been developed in regions such as Italy, where the observed seismic history at selected sites is quite exhaustive. We analyzed these observations to assess seismic hazard at about 600 sites. We used a probabilistic counting technique, integrating the observations (when necessary), with computed shakings obtained from a logistic-type attenuation model. The results were then compared with the estimates provided by the recent seismic hazard map of Italy, compiled according to the traditional probabilistic seismic hazard approach. The match shows significant differences for some sites. A tentative explanation which seems to point to three alternatives is provided: (1) The mismatch between the two methodologies might appear because the stationary assumption has a poor fit with reality (at least in certain areas); (2) Some sites show a response that is systematically different from the average values predicted using attenuation relationships; (3) The definition of seismogenic zones leads to a bias in the seismicity rate estimate.     

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.     

Some Discussions on Data-Driven Testing of Ground-Motion Prediction Equations under the Turkish Ground-Motion Database

Data-driven testing of ground-motion prediction equations (GMPEs) can help researchers in the ranking and selection of GMPEs for seismic hazard assessment. This paper presents and discusses the details of the major features of well-known testing methods which employ likelihood and Euclidean distance concepts. A set of local, regional, and global GMPEs are assessed under a ground-motion database. The data-driven testing of GMPEs is supported by thorough residual analyses under the database, providing valuable insights into the testing of GMPEs. The researchers are advised to evaluate all options together instead of focusing on a specific tool to build well-structured ground-motion logic trees.     

Site Classification Assessment for Estimating Empirical Attenuation Relationships for Central-Northern Italy Earthquakes

The aim of this article is to investigate the ground motion attenuation of the most industrialized and populated regions of Italy, evaluating the capability of different approaches to estimate site dependent models. The 5.2 local magnitude earthquake on November 24, 2004 shocked the areas of Northern Italy producing damage of about 215 million euros. The data set, including 243 earthquakes of local magnitude up to 5.2, has been collected in the period December 2002–October 2005 by 30 three-component seismic stations managed by Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Milano (INGV-MI). Empirical attenuation relationships have been estimated for horizontal peak ground velocity (PGHV), acceleration (PGHA), displacement (PGHD), and for response spectral acceleration (SA) for periods between 0.1 and 1.5 s. To estimate suitable attenuation models, in particular for sites characterized by thick sedimentary geological formations, a soil discrimination based on EU8 code can lead to wrong evaluations. On the contrary, a classification based on H/V spectral ratios of seismic ambient noise (NHV) allows the models to fit better real and predicted data and to reduce the uncertainties of the process. For each receiver, NHV have been strengthened by additional H/V spectral ratio of earthquake data (EHV), calculated considering different portions of the analysed signals. In order to validate the PGHA attenuation relationship for greater magnitudes, accelerometric records, relative to Central-Northern Italy strong motions occurring in the last 30 years, have been collected and superimposed to our attenuation curves.     

Classical Temples and Industrial Stores: Survey Analysis of Historic Unreinforced Masonry (URM) Precincts to Inform Urban Seismic Risk Mitigation

ABSTRACT

Oamaru, Winton, and Invercargill feature some of New Zealand’s most intact heritage precincts that are confronted by ongoing threats of seismic activity. The 2010/2011 Canterbury earthquake sequence and Canterbury Earthquakes Royal Commission of 2012, identified a nationwide trend through the proportion of deaths that occurred in public places as a result of the prevalent historic unreinforced masonry (URM) building stock. The reported study was undertaken to address urban safety and seismic risk mitigation through the lens of heritage conservation. The range of classically designed public buildings and industrial warehouses in the South Island of New Zealand were often produced by singular architectural practices, using locally sourced materials and construction techniques. It is vital to incorporate an examination of unique architectural qualities within urban seismic risk assessment and mitigation. Historic urban layout, architectural deployment of masonry, and extent of retrofits were recorded through onsite visual surveys via Geographical Information Systems and three-dimensional representation technologies. Extending the scope of information collected for engineering seismic risk assessment by focusing on the historical architectural context informs the selection of future mitigation measures. Oamaru, Winton, and Invercargill present intriguing case studies for multidisciplinary analysis, prior to testing urban-scale survey approaches within comparable historic centers across New Zealand.     

HINTS ABOUT SITE AMPLIFICATION EFFECTS COMPARING MACROSEISMIC HAZARD ESTIMATE WITH MICROTREMOR MEASUREMENTS: THE AGRI VALLEY (ITALY) EXAMPLE

We approach from a new standpoint the problem of estimating seismic hazard for some towns and villages located in Val d'Agri area (Southern Italy) that in the past have been affected by several seismic events. The estimates are carried out using a method that is based on the analysis of site seismic history extracted from macroseismic catalogues. To study the influence of site effects two different procedures have been performed: in the first, seismic hazard estimates have been deduced from epicentral data only, in the second, intensity data actually observed at the site are also considered. The difference between the two estimates can be correlated with local variations of seismic response due to local geological features which are responsible for possible cases of amplification. In order to validate the presence of such correlation, seismic hazard estimates have been compared to site amplification measurements obtained by using the HVSR (Horizontal to Vertical Spectral Ratio) technique. Our findings reveal a good correlation between seismic hazard enhancements and the presence of site amplification effects. The application of this kind of analysis to the Val d'Agri area has pointed out that the joint estimates of site seismic hazard enhancement and HVSR measurements could be a helpful tool to identify problems related to seismic microzonation.     

江苏省县域经济集聚和收敛的空间计量分析

通过探索性空间数据分析和空间计量分析方法,以实际人均GDP为测度指标,对江苏省65个县市的经济空间集聚、增长收敛性以及收敛机制进行讨论。研究发现1993-2009年实际人均GDP显示出越来越高的全局正相关,局部空间相关性也有增强的趋势。空间计量分析结果表明江苏省县域经济存在着β收敛,分时段研究为不同研究时段选择恰当的空间收敛模型后,收敛速度加快。技术扩散收敛机制和资本收敛机制分别在研究区间的前期和后期占主导作用,收敛机制的转变与江苏省在20世纪90年代末开始实行的区域协调发展政策密切相关。     

Characterization of timber masonry walls with dynamic tests

Timber-framed wall buildings are seen all over Europe, especially in seismic regions, given its adequacy to resist earthquakes. The “Pombalino” buildings, developed after the great 1755 earthquake that destroyed Lisbon, constitute one of the best examples of historic seismic-resistant structures based on timber-framed masonry walls. The research presented in this article aimed at experimentally evaluating the seismic behavior of the “Pombalino” buildings. The experimental program was based on extensive dynamic testing on sub-structures of typical “Frontal” walls (the timber masonry walls), carried out at the LNEC (the Portuguese National Laboratory of Civil Engineering) shaking table. The tests comprised (a) seismic tests, in which the seismic action was applied with increasing amplitude in one direction; and (b) dynamic identification tests, aiming at evaluating the dynamic properties of the sub-structures and their evolution with damage accumulation.     

Seismic Fragility Evaluation of Lightly Reinforced Concrete Beam-Column Joints

Fragility functions play an essential role in evaluating the seismic vulnerability of structures. To establish the seismic fragility functions of lightly Reinforced Concrete (RC) beam-column joints, the Park-Ang Damage model has been amended to quantify the damage states and the modified Bouc-Wen-Baber-Noori model has been employed and implemented in ABAQUS to predict the structural hysteresis behavior. Following successful calibration of the numerical results of a RC test frame from literature, the proposed model has been utilized to assess the seismic fragility curves of low to mid-rise RC frames in Singapore for 30 scaled ground motions using incremental dynamic analysis approach.     

Seismic Vulnerability Assessment of the Urban Building Environment in Nablus,Palestine

ABSTRACT

This article describes a specifically developed framework to produce a seismic physical vulnerability model of residential buildings in Nablus (Palestine) within the European project SASPARM2.0. Based on the structural taxonomy of the territory, two different forms were defined to collect geometrical and structural data of buildings by different stakeholders (citizens and practitioners). This data was then employed to produce fragility curves using the mechanics-based procedure SP-BELA. To estimate seismic risk, the developed fragility model was combined with a hazard curve for the corresponding location. The described procedure is implemented in a WebGIS platform that allows to georeference and assess the surveyed buildings and define retrofitting strategies. Finally, the article carries out a comparison between the fragility curves of buildings in Nablus and the ones calculated for similar building typologies within a UNDP Jordan project aiming at the integrated risk assessment in Wadi Musa and surroundings.     

SYSTEM IDENTIFICATION OF FEI-TSUI ARCH DAM FROM FORCED VIBRATION AND SEISMIC RESPONSE DATA

This paper presents the experimental investigation of the Fei-Tsui arch dam using the forced vibration test and its seismic response data. A forced vibration test was conducted on Fei-Tsui dam, this study presents the identified dynamic properties of the dam from these test data. For the identification of dam properties from seismic response data, in order to consider the nonuniform excitation of the seismic input and to describe the global behavior of the dam, the multiple input/multiple output discrete-time ARX model with least square estimation is applied to identify the dynamic characteristics of the dam. The system modal frequency, damping ratio and frequency response function are identified from both the forced vibration and seismic response data. To verify the accuracy of the identification result, comparison between discrete-time ARX model and a frequency domain conditioned spectral analysis was made. Finally, the spatial variation of ground motion across the free-field canyon surface is also studied.