Damages on reinforced concrete buildings due to consecutive earthquakes in Van

Consecutive earthquakes occurred on October 23rd, 2011 in Ercis and on November 9th, 2011 in Edremit that are townships located 90 km and 18 km far from Van city in Turkey, respectively. A total of 28,000 buildings were damaged or collapsed in the city center and the surrounding villages after the Ercis earthquake. This number reached 35,000 after the Edremit earthquake. In the area where the earthquakes occurred, almost all the reinforced concrete buildings were affected.This study presents field observations of damages on reinforced concrete buildings due to the consecutive earthquakes that occurred in Van, Turkey. Damages appearing in the buildings may occur due to several reasons such as site effect, poor construction quality, poor concrete strength, poor detailing in beam-column joints, detailing of stronger beam than column, soft stories, weak stories, inadequate reinforcement, short lap splices, incorrect end hook angle, and short columns. Aftershocks also caused progressive damages on the buildings within 17 days after the earthquakes. According to the results of this study, most of the damaged buildings were not designed and constructed according to the Turkish earthquake code, the so-called Specification for Buildings to be built in Seismic Zones.     

芦山7.0级强烈地震砖混民居震害调查与分析

2013年4月20日四川省芦山县发生Ms7.0级强烈地震,造成了大量民居建筑的严重破坏甚至倒塌.本文通过对芦山地震中民居建筑的震害调查,系统总结了砖混民居这一量大面广建筑结构的破坏形式和损伤机制.汶川地震后的新建民居在抗震措施方面有较大幅度的提高,比如大多具有抗震构造措施、采用240mm承重墙等,因此整体震害较轻,但是新建居民在建设房屋时,抗震构造措施的布局有很大的随意性,具体表现在平面内布置不足和竖向分布不规则,导致整体约束效果下降,进而结构发生破坏.雅安地区多处于山坡软土地带、建筑物多临近河流,同时民居建筑的基坑开挖普遍较浅,处理不当,在地震过程中出现地基不均匀沉降,基础遭到破坏,并造成上部结构破坏.相比之下,地基得到妥善处理、严格按照抗震规范设计的民居,震害十分轻微.本文建议继续增强对居民的防震减灾宣传,普及民居抗震构造知识,进行民居的实用抗震措施和地基处理方法的研究,并针对各类民居震害情况,研究有效、经济和快速的加固改造技术.     

Collapse simulation of reinforced concrete high‐rise building induced by extreme earthquakes

Collapse resistance of high‐rise buildings has become a research focus because of the frequent occurrence of strong earthquakes and terrorist attacks in recent years. Research development has demonstrated that numerical simulation is becoming one of the most powerful tools for collapse analysis in addition to the conventional laboratory model tests and post‐earthquake investigations. In this paper, a finite element method based numerical model encompassing fiber‐beam element model, multilayer shell model, and elemental deactivation technique is proposed to predict the collapse process of high‐rise buildings subjected to extreme earthquake. The potential collapse processes are simulated for a simple 10‐story RC frame and two existing RC high‐rise buildings of 18‐story and 20‐story frame–core tube systems. The influences of different failure criteria used are discussed in some detail. The analysis results indicate that the proposed numerical model is capable of simulating the collapse process of existing high‐rise buildings by identifying potentially weak components of the structure that may induce collapse. The study outcome will be beneficial to aid further development of optimal design philosophy. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic capacity of irregular unreinforced masonry walls with openings

Masonry buildings are often characterized by geometric irregularities. In many cases, such buildings meet global regularity requirements provided by seismic codes, but they are composed by irregular walls with openings. The latter are masonry walls characterized by (i) openings of different sizes, (ii) openings misaligned in the horizontal and/or vertical direction, or (iii) a variable number of openings per story. An irregular layout of openings can induce not only a nonuniform distribution of gravity loads among masonry piers but also unfavorable damage localizations resulting in a premature collapse of the wall and hence a higher seismic vulnerability. This paper is aimed at providing a simplified methodology to assess the effects of irregularities on the in‐plane seismic capacity of unreinforced masonry (URM) walls with openings. To this end, a macroelement method was developed and validated through experimental results available in the literature. The proposed methodology was based on the quantification of wall irregularities by means of geometric indices and their effects on seismic capacity of URM walls with openings through both sensitivity and regression analyses. Sensitivity analysis was based on a high number of static pushover analyses and allowed to assess variations in key seismic capacity parameters. Regression analysis let to describe each capacity parameter under varying irregularity index, providing empirical models for seismic assessment of irregular URM walls with openings. The in‐plane seismic capacity was found to be significantly affected by wall irregularities, especially in the case of openings with different heights. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of fundamental period of low‐rise and mid‐rise reinforced concrete buildings

Fundamental period of vibration appears to be one of the most critical parameter for the seismic design of buildings because this period strongly affects the magnitude of seismic forces. In this paper, an empirical formula for estimating the fundamental period of reinforced concrete structures is recommended, on the basis of the vibration analysis of 20 different real building configurations. These structures have already been constructed in Greece, and they are analyzed by using in detail 3‐D finite element models and modal eigenvalue analysis. These models take into account the presence of external and internal infill walls, which are usually ignored as nonstructural elements. This neglect leads to unreliable evaluation of period because the infill walls' contribution to the lateral stiffness and therefore to the fundamental period of vibration is also ignored. Furthermore, taking into account that the flexibility of soil elongates the fundamental period, the soil–structure interaction effect is also considered. To achieve a unique, simple, and effective empirical expression for the fundamental period of vibration, a comprehensive nonlinear regression analysis is applied for the datasets of buildings under consideration. This empirical expression is also compared with the similar expressions from the pertinent literature. Copyright © 2013 John Wiley & Sons, Ltd.     

高层建筑物施工高程基准的竖向传递方法比较

为了保证高层建筑物施工测量的高程精度,文中采用全站仪天顶距法和悬挂钢尺法两种方法进行施工高程基准的竖向传递.文中介绍两种方法的具体操作流程以及影响精度的因素,并以某高层建筑物为例,利用测量数据对两种方法进行对比及精度分析,证明两种方法均具有较高的精度,各有优势,均能广泛应用于高层建筑物施工测量中.     

Experimental study on retrofit of school buildings by adding sandwich columns to partition brick walls

Thousands of buildings were damaged by the devastating Chi‐Chi earthquake on September 21, 1999. Of all the public buildings, school buildings are the most vulnerable to earthquake damage, and the retrofitting of existing school buildings becomes a stringent issue. In addition to cost effectiveness, the impact of retrofitting methods on the functions of the school buildings needs to be considered. This paper therefore proposes the retrofitting of school buildings by adding sandwich columns onto partition brick walls. The sandwich column is divided into two parts and is added to the two sides of the partition brick wall held with pairs of U‐shaped bars. The retrofit does not require the removal of windows or doors in the longitudinal direction making the proposed method cost effective and minimizes the impact on the function of the school buildings. Five full‐scale specimens without and with retrofitting were designed and fabricated for testing based on the partition brick wall frames of the existing school buildings. The specimens were subjected to cyclic loading in the out‐of‐plane direction through a loading frame so that the columns deformed with double curvatures. The experimental results verified the feasibility of the proposed retrofit method. The data showed that the lateral strength of the retrofitted specimen doubled that which was not and that the residual strength of the retrofitted specimen was just as high as the ultimate strength of the specimen without retrofitting. The analytical results in lateral strength yielded conservative figures compared with experimental measurements. Copyright © 2011 John Wiley & Sons, Ltd.     

The applicability of the N2 method to the estimation of torsional effects in asymmetric base‐isolated buildings

The paper deals with the applicability of the extended N2 method to base‐isolated plan‐asymmetric building structures. The results obtained by the usual pushover analysis of a 3D structural model are further combined with the aid of linear dynamic (spectral) analysis to account for the dynamic effects caused by structural asymmetry. In the paper, the method has been applied to the seismic analysis of a mass‐eccentric four‐storeyed RC frame building isolated with lead rubber bearings. Three different positions of the center of isolation system (CI) with respect to the center of mass (CM) and the center of stiffness of the superstructure (CS) were considered. The response was analyzed for three different eccentricities, three different torsional to lateral frequency ratios of the superstructure, and two ground motion intensities. The stiffness of the isolators was selected for three different protection levels, which resulted in elastic as well as moderately to excessively damaged superstructure performance levels. The results are presented in terms of the top, base and relative displacements, as well as the stiff/flexible side amplification factors. A more detailed insight into the nonlinear behavior of the superstructure is given in a form of ductility factors for the flexible and stiff side frames. The results of the extended N2 method for selected lateral load distributions are compared with the average results of nonlinear dynamic analyses. It was concluded that the extended N2 method could, with certain limitations, provide a reasonable prediction of the torsional influences in minor to moderately asymmetric base‐isolated structures. Copyright © 2010 John Wiley & Sons, Ltd.     

相邻建筑考虑桩-土-结构相互作用(PSSI)碰撞分析

采用Penzien模型及Hertzdamp碰撞单元,建立了相邻结构考虑PSSI的碰撞模型,推导了其碰撞动力方程,并对相邻结构进行了碰撞模拟和参数分析.研究表明:虽然PSSI对结构本身的地震响应影响并不大,但对相邻结构的碰撞响应影响明显.同时,在一定范围内,防震缝宽度、碰撞刚度、结构周期比、桩的截面惯性矩以及土的剪切波速...     

Seismic design analysis of the country masonry school buildings in the meizoseismal area

Several reinforcing schemes are illustrated that are based on the loading characteristics of typical country masonry school buildings with sparsely spaced transversal walls and large depth. From the seismic damage observed following the Wenchuan Earthquake, the effects of reinforcing schemes, tie-columns and tie-beams on the seismic resistance of masonry buildings are analyzed. The concept of improving the ductility of these types of buildings is presented. Finally, some suggestions are proposed for the design of masonry buildings with sparsely spaced transversal walls and large depth.