钢筋混凝土烟囱在竖向地震作用下的反应

众所周知,钢筋混凝土烟囱在地震作用下,一般可有四种反应:水平反应,竖向反应,扭转反应和摇摆反应。钢筋混凝土烟囱在地震作用下的水平反应问题,国内外学者已进行了广泛的研究,本文只就钢筋混凝土烟囱在地震作用下的竖向反应作些讨论,其它有关扭转和摇摆问题以及地震时的竖向共振问题留待以后再论述。一、关于竖向振动的计算模型问题大量震害调查和地震记录都说明,钢筋混凝土烟囱在地震作用下有竖向振动,而且这一观点已为广大科学工作者和工程设计人     

竖向地震作用的重要性

通过对国内外大量地震记录的比较分析,提出竖向地震作用对结构具有不可忽视的影响。简要叙述了计算竖向地震作用的方法以及竖向地震作用的研究进展。从国内外一些震害现象阐述了结构抗震分析中考虑竖向地震作用的重要性,并归纳了地震分析中的一种新观点。     

烟囱竖向地震作用的计算方法综述

近些年来,国内外学者对烟囱结构的竖向地震作用展开了深入的研究,取得了丰硕的成果。本文简要介绍了国内外关于烟囱结构竖向地震作用的计算方法,包括竖向地震作用系数法、振型分解法、纵波应力法、行波分析法、半有限元一半解析法、简化计算法、冲量法等,并对存在的问题以及今后的研究方向提出了自己的看法。     

考虑场地土影响的高耸结构竖向地震作用分析

高耸结构的震害资料表明,竖向地震作用对结构的破坏起很大的作用。根据冲击原理,考虑场地土的影响,对高耸结构的竖向地震作用进行了计算分析。结果表明,场地土类别对竖向地震作用的影响较大,场地土类别越高,竖向地震力越大。Ⅱ类场地土上的烟囱在9度区才会产生竖向拉力;Ⅳ类场地土上的烟囱在7度区就会产生竖向拉力,在9度区则会产生非常大的竖向拉力和竖向压力。因此在高耸结构的竖向地震作用计算中,场地土的影响因素应引起足够的重视。     

烟囱竖向地震响应的试验与研究

本文通过对烟囱竖向地震响应的试验与理论研究 ,讨论分析了竖向地震力分布规律 ,理论分析结果与试验结论及实际震害规律三者吻合较好。     

板式楼梯的抗震性能设计

通过板式楼梯的典型震害分析,揭示结构破坏机理.通过对多遇地震、设防烈度地震,预估的罕遇地震作用下的竖向地震作用组合抗震计算,总结板式楼梯抗震验算的基本规律,并给出了切实可行的抗震构造措施.     

竖向地震作用计算方法简评

大量的地震资料和震害记录表明,竖向地震作用对建筑结构的影响不容忽视.对竖向地震作用的研究有待完善.本文对竖向地震作用计算方法和需要考虑的竖向地震作用的结构形式进行了归纳总结,并指出了今后需要研究解决的问题.     

高耸烟囱结构竖向地震响应的模型试验研究及分析

为了研究高耸烟囱在竖向地震作用下的动力响应特性,对180m钢筋混凝土烟囱和45m砖烟囱分别进行了1:40和 1:15比尺的振动台模拟试验研究,并采用波动理论对试验模型进行了动力比较分析。试验和理论分析结果表明:竖向地 震作用下,高耸烟囱的地震响应以一阶竖向振动为主,最大应变随地震烈度的增加逐渐从顶部附近向下移动到1／3-1／2 高度附近;水平地震作用下高耸烟囱以二阶以上振型振动为主,最大应变部位在2／3高度附近。针对烟囱结构薄弱部位随 地震烈度的变化情况,进一步阐明了计算高柔结构和特定条件下某些结构的竖向地震作用的必要性。     

日本神户市建筑结构震害特征分析

本文采用冲量原理计算竖向地震作用，并考虑与水平地震共同作用，对日本神户市建筑结构震害特征进行了分析，供抗震设计时参考。     

竖向地震作用计算的规范规定和依据

<正> 1 引言震后所进行的震害调查表明,诸如砖烟囱、出屋顶小烟囱、煤矿井塔等结构的震害现象是与竖向地震作用有关的。1976年唐山大地震时,唐山市区某些建筑不是倾斜倒塌,而是在原位置“叠合”倒塌,更证实了这一点。为此,有关地震时建筑的破坏是否与竖向地震运动有关的研究日益引起了关注。     

钢筋混凝土烟囱减震有限元分析

为降低大震下钢筋混凝土结构的刚度,以减轻结构物的地震灾害,采用在筒壁上开竖缝的方法,研究其对抗震性能的影响。对不同竖缝宽度、长度及不同数量的钢筋混凝土烟囱,用有限元法进行了对比分析,得出了些结论供工程参考。     

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reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century.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.     

Solar chimney—A passive strategy for natural ventilation

Passive ventilation systems are being increasingly proposed as an alternate to mechanical ventilation systems because of their potential benefits in terms of operational cost, energy requirement and carbon dioxide emission. Solar chimney is an excellent passive ventilation system which relies on natural driving force, that is, the energy from the sun. A significant amount of research work has been done on solar chimney since the 1990s. This article presents an overview of solar chimney research that has taken place in the last two decades. The review focuses on two main areas of research - the effects of geometry and inclination angle on the ventilation performance of a solar chimney. The experimental investigations of solar chimney have dominated the existing literature. However, numerical modelling of solar chimney using computational fluid dynamics (CFD) technique has attracted increasing attention. Moreover, this review found that solar chimney as a passive ventilation strategy has not been fully understood.     

Reliability-based vector nonstationary random critical earthquake excitations for parametrically excited systems

The study considers the earthquake response of stack-like structures subjected to simultaneous action of random horizontal and vertical earthquake acceleration components. The governing equation of motion in this case is approximated by a set of coupled randomly time varying ordinary differential equations. The components of earthquake accelerations are modelled as nonstationary Gaussian random processes that are obtained by multiplying deterministic modulating functions with partially specified stationary random processes. Specifically, it is assumed that the matrix of power spectral density (psd) functions of the stationary components is not known, while, the variance, average rate of zero crossings, entropy rate and frequency range of interest are taken to be known. The unknown input psd matrix is determined such that the reliability index associated with a specified structure performance function is minimized. The solution procedure employed, combines the theory of Hasofer–Lind reliability indices, response surface modelling and constrained nonlinear optimization tools. The critical input psd matrix so obtained leads to the definition of excitation models that produce the least favorable response, which, at the same time, possess a few of the well known properties of earthquake loads. A numerical example that illustrates the concepts developed with reference to a chimney structure is provided.     

钢竹组合墙体的抗震性能试验研究

对压型钢板和竹板组成的组合墙体,进行了5块试件的抗震试验研究。对由两种不同型号和厚度的压型钢板以及不同厚度竹板的两类墙体试件进行了无竖向力水平低周反复加载和有竖向力水平低周反复加载试验,得到了各类墙体的承载力指标和位移延性系数μ、耗能系数E等抗震性能指标。试验结果表明:竹板的厚度改变对墙体的水平抗剪强度、刚度影响不大,而压型钢板的厚度和波高的变化对墙体的承载力指标和位移延性系数μ、耗能系数E等抗震性能指标影响显著。     

套筒式烟囱钢内筒腐蚀受损的分析及处理

针对某电厂套筒式烟囱建成使用仅4年,钢内筒就严重腐蚀受损的工程案例,利用有限元分析方法对该烟囱进行分析计算(包括腐蚀受损前后两种工况),研究结构动力特性。经对比分析腐蚀前后两种结构在竖向和横向荷载作用下的应力水平和稳定性,对腐蚀受损进行评估,并提出相应的处理方案。     

房屋建筑竖向减震分析

对在输入不同场地、不同频谱的地震波作用下房屋建筑的竖向减震体系进行时程分析，得到在合理控制减震装置的竖向刚度下可以有效减小竖向地震作用的结论，以达到理想的减震效果。     

Bridge support elastic reactions under vertical earthquake ground motion

In North America, bridges are not typically designed for vertical earthquake ground motion. Design codes, AASHTO in the USA and S6-06 in Canada, do not explicitly consider the effect of vertical earthquake ground motion in the design of highway bridges. However, analytical and field evidences have often drawn engineers’ attention to the damage potential of vertical earthquake ground motion to engineered bridges. This paper proposes a simplified method to calculate elastic support reactions under vertical earthquake ground motion. Support reactions are first calculated by exact dynamic method. By applying a few assumptions, a simplified method has been developed. The developed method can be readily used in the design of typical bridges with regular span distribution. This simplified method has been demonstrated with several examples.     

基于性能的烟囱抗震设计

基于性能的抗震设计已成为当前抗震研究的热点问题。作为火力发电厂重要构筑物的烟囱,必须满足我国现行《建筑抗震设计规范》的总体抗震设防目标。但是,对于普通单筒钢筋混凝土烟囱主要非结构构件的内衬以及套筒式分段支撑砖内筒烟囱,烟囱规范对其抗震几乎没有要求。通过分析,提出了烟囱内衬和砖内筒的地震作用计算方法以及构造措施。