Non-linear static analysis of masonry buildings based on a strut-and-tie modeling

This paper presents an analytical method for evaluating the capacity curve of masonry buildings according to non-linear static analysis. This method splits the building into stories, and the vertical structures of each story into masonry panels, which are analyzed individually by a new push-over analysis. The behavior of each panel is reproduced with an evolutive strut-and-tie model, which simulates the uncracked and cracked behavior of the panel subjected to a vertical constant force and a lateral force that increases up to the complete development of the failure mechanism. The strut-and-tie model provides the capacity curve of the panel. The composition of the capacity curves of all the panels of a story provides the capacity curve of this story. The capacity curves of all the stories of the building can be used to obtain either the maximum drift that the building can withstand or the behavior factor of the structure. Either outcome allows the specific dissipation capacity and overstrength of the masonry building to be considered in the seismic analyses, which provides ultimate limit state verifications with more reliability.The proposed method is applied to a school building. The comparison between seismic safety assessed with this method and with a linear dynamic analysis, all other parameters being equal, shows that the latter approach is overly-conservative and misleading. In fact, the specific inelastic capacity, which only the former approach can consider, influences greatly the seismic behavior of the case study.     

Comparison of nonlinear static methods for the assessment of asymmetric buildings

Traditional nonlinear static methods, e.g. the original version of the N2 method implemented in Eurocode 8, are not always effective in the assessment of asymmetric structures because of the errors committed in the evaluation of the torsional response. To overcome this shortcoming, two methods have recently been suggested by Kreslin and Fajfar (Bull Earthquake Eng 10(2):695–715, 2012) and Bosco et al. (Earthq Eng Struct Dyn 41:1751–1773, 2012). In particular, the method proposed by Kreslin and Fajfar adjusts the results of the nonlinear static analysis by means of those of a standard modal response spectrum analysis. In the method proposed by Bosco et al., the researchers suggested the use of two nonlinear static analyses characterized by lateral forces applied to different points of the deck. In this paper, the two improved nonlinear static methods and the original N2 method are applied to predict the maximum dynamic response of single- and multi-storey systems subjected to artificial and recorded accelerograms. The results highlight that the improved nonlinear static methods provide estimates which are more accurate than those of the original N2 method. Further, the comparison of the results identifies the range of the structural properties within which the original N2 method is still reliable and the range within which one of the two improved methods should be preferred.     

Envelope‐based pushover analysis procedure for the approximate seismic response analysis of buildings

An envelope‐based pushover analysis procedure is presented that assumes that the seismic demand for each response parameter is controlled by a predominant system failure mode that may vary according to the ground motion. To be able to simulate the most important system failure modes, several pushover analyses need to be performed, as in a modal pushover analysis procedure, whereas the total seismic demand is determined by enveloping the results associated with each pushover analysis. The demand for the most common system failure mode resulting from the ‘first‐mode’ pushover analysis is obtained by response history analysis for the equivalent ‘modal‐based’ SDOF model, whereas demand for other failure modes is based on the ‘failure‐based’ SDOF models. This makes the envelope‐based pushover analysis procedure equivalent to the N2 method provided that it involves only ‘first‐mode’ pushover analysis and response history analysis of the corresponding ‘modal‐based’ SDOF model. It is shown that the accuracy of the approximate 16th, 50th and 84th percentile response expressed in terms of IDA curves does not decrease with the height of the building or with the intensity of ground motion. This is because the estimates of the roof displacement and the maximum storey drift due to individual ground motions were predicted with a sufficient degree of accuracy for almost all the ground motions from the analysed sets. Copyright © 2013 John Wiley & Sons, Ltd.     

高层钢结构抗震pushover分析的侧向力分布模式及其影响

本文针对高层钢结构抗震Pushover分析的适用性和侧向力分布模式的选取等问题,首先,介绍和分析了Pushover分析常用的五种侧向力分布模式及其本质特征;然后,给出了判断侧向力分布模式合理性的准则;最后,通过对比一座15层的平面钢框架结构在Ⅳ类场地的典型地震动下的非线性时程分析和五种侧向力分布下的Pushover分析中的破坏形式和弹塑性反应,研究了高层钢结构抗震Pushover分析的适用性和各侧向力分布模式的合理性;在此基础上,本文给出了高层钢结构Pushover分析时侧向力分布模式的选取建议。     

Multimode pushover analysis for asymmetric buildings under biaxial seismic excitation based on a new concept of the equivalent single degree of freedom system

In this paper a new multimode pushover procedure is presented in order to achieve an approximate estimation of structural performance of asymmetric buildings under biaxial seismic excitation. The steps of the proposed methodology are quite similar to those of the well-known Modal Pushover Analysis. However, the establishment of the equivalent single-degree-of-freedom (E-SDOF) systems is based on a new concept, in order to take into account multidirectional seismic effects. The proposed methodology does not require independent analysis in each direction and the application of simplified superposition formulas for the combination of the horizontal seismic components is avoided. In addition, a reduction of the computational cost in relevance to other multimode procedures is achieved. After a brief outline of the theoretical background, a representative numerical example is given. Finally, the accuracy of the proposed methodology is evaluated by an extensive parametric study, which shows that, in general, it provides a useful design tool.     

Evaluation of the seismic response of masonry buildings based on energy functions

This work is based on energies evaluated from the responses of 12 stone and brick masonry systems subjected to 58 shaking table tests. The evolution of input energy during a damaging base excitation is correlated to the change of the damage patterns of the considered buildings. The comparison among energies dissipated and absorbed by the buildings during the various shocks gives some hints on strengthening strategies. It is found that damage to spandrel beams produces a more significant energy absorption than other types of damage. Copyright © 2001 John Wiley & Sons, Ltd.     

基于自由振动响应的基础隔震建筑减震能力评估方法研究

目前国内外已修建完成了大量隔震建筑,但仅有少量经受了地震检验,绝大部分隔震结构减震能力能否达到设计目标尚存疑问.本文针对基础隔震建筑,提出了一种基于自由振动响应的减震能力评估方法.首先,对隔震建筑进行多级幅值初位移自由振动原位试验,获取结构的抗震能力曲线;其次,根据地震反应谱建立地震需求曲面,进而确定隔震结构性能点;最...     

Extension of N2 method to plan irregular buildings considering accidental eccentricity

The paper deals with the topic of analyses performed according to modern code provisions, in particular Eurocode 8 (EC8) rules. Non linear static and non linear dynamic analyses of a plan irregular multi-storey r/c frame building designed according to Eurocode 2 (EC2) and EC8 provisions are carried out.The extension of the N2 method to torsionally flexible structures, as applied in previous papers, does not consider the accidental eccentricity, which is prescribed by EC8 also in the case of non linear static analysis. In this paper, three methods combining the accidental eccentricity prescribed by EC8 to the procedure which extends the N2 method to torsionally flexible structures are proposed and discussed. Each of them provides four modal response spectrum analyses (one for each model, corresponding to each position of centre of mass) and eight non linear static analyses (two signs for four models). NLSA(meth. n.2) seems to be the more reliable method of the three proposed, because it better fits absolute displacements obtained by non linear dynamic analysis.In the paper it is also observed that the value of the behaviour factor assigned by EC8 to torsionally flexible systems seems too conservative.     

Full-scale dynamic testing of response-controlled buildings and their components: concepts,methods, and findings

A series of shake-table tests was conducted by inserting and replacing 4 different types of dampers, or by removing them in a full-scale 5-story steel frame building. The objective is to validate response-control technologies that are increasingly adopted for major Japanese buildings without being attested to-date by a major earthquake. Test results are briefly described, and good performance of the dampers and frame demonstrated. The concepts of the full-scale building tests and various contributions are discussed. The difficulty associated with full-scale dynamic testing is explained.     

Full-scale dynamic testing of response-controlled buildings and their components:concepts,methods,and findings

A series of shake-table tests was conducted by inserting and replacing 4 different types of dampers,or by removing them in a full-scale 5-story steel frame building. The objective is to validate response-control technologies that are increasingly adopted for major Japanese buildings without being attested to-date by a major earthquake. Test results are briefly described,and good performance of the dampers and frame demonstrated. The concepts of the full-scale building tests and various contributions are discussed. The difficulty associated with full-scale dynamic testing is explained.     

Evaluation and generalization of temperature‐based methods for calculating evaporation

Seven temperature‐based equations, each representing a typical form, were evaluated and compared for determining evaporation at two climatological stations (Rawson Lake and Atikokan) in north‐western Ontario, Canada. The comparison was first made using the original constant values involved in each equation, and then using the recalibrated constant values. The results show that when the original constant values were used, larger biases existed for most of the equations for both stations. When recalibrated constant values were substituted for the original constant values, six of the seven equations improved for both stations. Using locally calibrated parameter values, all seven equations worked well for determining mean seasonal evaporation values. For monthly evaporation values, the modified Blaney–Criddle method produced least error for all months for both stations, followed by the Hargreaves and Thornthwaite methods. The Linacre, Kharrufa and Hamon methods showed a significant bias in September for both stations. With properly determined constant values, the modified Blaney–Criddle, the Hargreaves and Thornthwaite methods can be recommended for estimating evaporation in the study region, as far as temperature‐based methods are concerned. Copyright © 2001 John Wiley & Sons, Ltd.     

Evaluation and generalization of radiation‐based methods for calculating evaporation

Eight radiation‐based equations for determining evaporation were evaluated and expressed in five generalized forms. Five evaporation equations (Abtew, Hargreaves, Makkink, Priestley and Taylor and Turc), where each represents one generalized form, were then compared with pan evaporation measured at Changins station in Switzerland. The comparison was first made using the original constant values involved in each equation, and then using the recalibrated constant values. Evaluation of the Priestley and Taylor equation requires net radiation data as input, in this study, net radiation was estimated using Equation (16) owing to the lack of observation data. The results showed that when the original constant values were used, large errors resulted for most of the equations. When recalibrated constant values were substituted for the original constant values, four of the five equations improved greatly, and all five equations performed well for determining mean annual evaporation. For seasonal and monthly evaporation, the Hargreaves and Turc equations showed a significant bias, especially for cold months. With properly determined constant values, the Makkink and modified Priestley and Taylor equations resulted in monthly evaporation values that agreed most closely with pan evaporation in the study region. The simple Abtew equation can also be used when other meteorological data except radiation are not available. Copyright © 2000 John Wiley & Sons, Ltd.     

建筑物地震损失风险与保险费用的确定方法

本文结合我国地震危险性和建筑物抗震设防标准提出了地震损失风险评估概率模型,并给出了建筑物地震保险金额和保险费率的计算方法。用该方法可以计算各类建筑物的保险费用,计算结果与国际地震保险业的经验数据较一致。同时,本文还利用GIS技术展示了与保险金额和保险费率的空间分布状态相关的属性数据,为保险当事人提供了实施地震保险的科学依据。     

基于模型正演的折射静校正方法研究与应用

随着地震勘探区域地质条件复杂化,静校正在资料处理中的作用日显重要.本文模拟研究了折射渡在不同地质条件中的特性,完成了正演模型下的折射波静校正量计算,并将静校正后记录与理论模型记录对比,分析该方法的准确性,总结折射波静校正方法的技术难点,提出一种更准确优越的解决方法.最后,运用该方法选取最合理的参数,并配合先进的处理软件...     

基于费用效益分析的建筑物加固决策体系研究

突发地震灾害往往带来巨大的生命财产损失,对建筑物进行科学合理的震前加固及震后功能快速修复;对降低地震灾害损失具有重要意义。通过定义社会贴现率和残值率等加固效益分析评价参数,基于加固费用模型和地震直接经济损失模型进行了加固费用现值与效益现值计算;采用费用效益比（Cost-Benefit Ratio,CBR）作为评价指标对建筑物进行加固决策分析,并最终建立了相应的加固决策体系。最后将提出的理论、模型及方法集成于课题组研发的"中国地震灾害损失评估系统（CEDLAS）"补充建立加固决策分析模块,进而通过陕西省灞桥区的综合应用示范,验证所建立的加固决策体系的合理性。研究可为政府制定在役建筑物的加固决策提供科学依据。     

Seasonal variability in mesopause region temperatures over Fort Collins, CO (41°N, 105°W) based on lidar observations, 1990 through 2007

Nearly 900 nocturnal temperature profiles (85–105 km) from the Colorado State University Na lidar at Fort Collins, CO (40.59N, 105.14W) from 1990 to 2007. After the removal of an episodic warming attributable to Mt. Pinatubo eruption, the time series is analyzed as the sum of the climatological mean, annual and semiannual oscillation, solar cycle effect and trends along with possible annual/semiannual modulation of the latter two. The direct seasonal variation is consistent with the concept of the two-level mesopause. The trends in summer and winter are comparable 90–96 km at −0.15±0.1 K/year. The summer trend turns positive above 96 km. The winter trend is negative with minimum of −0.3 K/year at 100 km but positive at 104 km. The negative trend values are a factor of five smaller than an earlier analysis of the early part of this data due to removal of an episodic event.