Effects of adding illegal storeys to structural systems

Earthquakes in Turkey are frequently occurring disasters, causing much loss of life and property. It is tragic indeed that earthquakes should share the agenda with amnesty laws for illegal buildings. Illegal buildings are those constructed without authorization, legal bureaucratic sanction and, in most cases, without normal engineering control and checks. Buildings may become illegal for a variety of reasons. The very prospect of a waiver bill for illegal buildings spurs further illegal construction. The status of illegal buildings may legally change in time. What is an illegal building today may well be legal tomorrow under these circumstances. The present study deals with two different kinds of building: one is the framed building and the other has shear-wall frame. The capacity ratios, storey drifts and natural periods for the legally approved buildings and the effects of illegal or legal additional floors on these values are compared. It is determined that these buildings with illegal storeys should be strengthened and retrofitted by providing cast in-situ reinforced concrete shear walls.     

Seismic damage and performance of Palazzo Centi after L’Aquila earthquake: A paradigmatic case study of effectiveness of mechanical steel ties

This paper concerns the seismic response of Palazzo Centi after the 2009 L’Aquila earthquake. Built in the second half of XVIII century, Palazzo Centi is a three-storied building characterized by a rectangular plan with a central court. The vertical structural system is made of masonry walls arranged in plan to form a regular mesh.After the 2009 L’Aquila earthquake the building showed a widespread damage occurred in the vertical masonry structures with more intensity at upper storeys; there were also damages to non-structural parts: light masonry and fake vaults. The building case study is a paradigmatic example because during the 2009 earthquake, differently from other historical masonry buildings, it responded “reasonably” well in the main structural parts. The seismic behaviour was analyzed thoroughly in order to investigate the effectiveness of the, initially unknown, recent retrofit interventions carried out in 2003. These mechanical interventions proved to be the reason of the good seismic behaviour of the building and that “saved” it from more serious damages.On the basis of the data acquired by the authors during the post-earthquake reconnaissance activities and from the structural analyzes results, in conclusion, the case study of Palazzo Centi demonstrated to represent a clear example of the effectiveness of the traditional techniques in designing and retrofitting of masonry buildings.     

Failure analysis of newly constructed RC buildings designed according to 2007 Turkish Seismic Code during the October 23, 2011 Van earthquake

In the Van Earthquake of magnitude Mw = 7.2 on October 23, 2011, 48,666 buildings were severely damaged or collapsed, 604 people lost their lives and 1301 people were injured. During this earthquake, not only the buildings designed in accordance with the old earthquake codes but also the ones designed in accordance with the current Turkish Earthquake Code (TEC) were severely damaged. The purpose of this study is to reveal the reasons why the RC buildings designed in accordance with the current TEC as a result of static and dynamic calculations were severely damaged in the recent earthquakes. In this study, first, the buildings that were designed in accordance with the last two earthquake codes and damaged during the Van Earthquake on 23 October 2011 have been examined. Then, another severely damaged building that was designed in accordance with the TEC 2007 has been chosen as a possible model for similar situations. In order to explore the reasons behind the damage, detailed examination has been made both in the damaged structure and in its design calculations. Both situations in the project and implementation of the design have been analyzed by using IdeCAD and Sta4CAD modeling, as well as Sap2000 through which weak structural members have been determined. The findings have been evaluated in terms of design and implementation flaws, in compliance with the TEC 2007, modeling and acceptance error. When analyzed by modeling of its project, the building has not revealed any insufficient columns; however, in its implementation analysis, the damaged members have appeared to be insufficient. It has been determined that the damage was due to improper implementation of the project, incompatible production according to the TEC 2007 and lack of inspection. To mitigate possible fatalities and damages in the future earthquakes, implementations should be fully represented in the model of the projects, structural members in the projects should be built identically to their design, attention should be paid to the anticipated limitations in TEC 2007 during implementation, and stages of project and implementation should be inspected sufficiently.     

脉冲荷载作用下土中浅埋钢筋混凝土框架直剪破坏分析(Ⅱ.应用)

本文应用文献[5]所提出的计算方法，分析了集团装药爆炸条件下土中浅埋框架迎爆面构件的动力响应及破坏模式，并分析了影响结构直剪破坏的因素。最后通过大量计算，给出了集团装药爆炸条件下土中浅埋钢筋混凝土框架发生直剪破坏的条件。     

脉冲荷载作用下土中浅埋钢筋混凝土框架直剪破坏分析(I.理论)

本文以常规武器爆炸荷载作用下土中浅埋钢筋混凝土框架为研究对象，将迎爆面构件简化为梁．基于一维情况下土与结构相互作用和Timoshenko梁理论，并引入梁的弯曲和直剪破坏准则，通过采用有限差分方法，建立了常规武器爆炸荷载作用下土中浅埋梁的动力响应和破坏模式分析方法。     

A non-linear masonry infill macro-model to represent the global behaviour of buildings under cyclic loading

The presence of masonry infill walls in RC buildings is very common. However, and even today, in the design of new buildings and in the assessment of existing ones, these infill walls are usually considered as non-structural elements and their influence in the structural response is generally ignored. For horizontal loading, infill panels can drastically modify the response, attracting forces to parts of the structure that have not been designed to resist them. This paper presents an improved non-linear numerical simulation model for the influence of the masonry infill walls in the seismic behavior of structure. The model is implemented in the PORANL program. After the implementation and calibration of the proposed masonry model, a series of non-linear dynamic analyses of a building representative of Modern Architecture in Europe were carried out. The main objective was to investigate the behavior of this type of building, and any weakness under seismic loading. The building geometry and the dimensions of the RC elements and infill walls were set in the original project, and confirmed in the technical visits. The building under study has nine storeys and the structure is mainly composed of 12 plane frames oriented in the transversal direction. The building was analyzed with a simplified plane model, for each direction, and the existing infill panels were looked at in accordance with their dimensions and location. The earthquake action adopted in this study was simulated through three series of artificially generated earthquakes, for a medium/high seismic risk scenario in Europe.     

Burglary resistance of thermal insulating clay unit masonry (RC 3)

In 2017 the Austrian Clay Masonry Industry carried out a test of burglary resistance according to ÖNORM EN 1627 for the first time. A window was fixed in a highly insulated clay masonry wall (with declared compressive strength of the clay units 7.5 N/mm²). Resistance class RC 3 was verified for the window, the fixing to the wall and the wall itself.     

网架结构在地震下的失效模式及其数值表述

通过对地震作用下不同形式的网架结构进行大规模数值计算,以最大节点位移超过结构跨度的1/50为失效准则,分析了其动力失效模式及特征,将决定网架结构动力失效模式的因素提炼为四个方面：结构8P杆件比例、全时程的最大位移、平均单杆塑性应变能以及临失效前平均位移与最大位移的比值。由于网架结构各失效模式之间存在模糊性,利用模糊C-均值方法分析以上四个因素,进而将网架动力失效模式归为三类：失稳型局部失效、强度型整体失效和强度型局部失效。结果表明,模糊C-均值方法可以有效地划分网架结构的失效模式,并将自然语言描述的失效模式转变为数字语言的表述,得到各失效模式的典型数字特征,可用于识别其他网架结构,为结构的性能化设计打下基础。     

Failure study of a bridge subjected to pounding and sliding under severe ground motions

Under strong ground excitations, highway bridge structures may experience severe nonlinear behaviors including the yielding and plastic deformation of pier members, and sometimes the pounding between adjacent decks induced by the local failure of hinge bearings necessary for restraining the girders. A kind of hinge bearing requires the use of steel dowels and is typical in many existing bridges. The objective of this study is to investigate why such hinge bearing did not function and how it contributed to the deck-falling failure of one particular highway bridge stricken by the 1999 Chi–Chi earthquake (magnitude 7.3) in Taiwan. To achieve this, incremental time history analyses for discrete dynamic systems are conducted on a group of models that incorporate sliding and impacting elements, to address nonlinear behaviors as a result of the failed bearing. Causes for discrepancy in bridge responses to seismic motions between the designed and the observed are disclosed by means of comparative study of models based on different scenarios. The study demonstrates that details of the bearing can significantly change overall behaviors of a bridge. In order to ensure the expected performance of a bridge during severe earthquakes, both designer and constructor should exercise caution.     

Failure analysis of seven masonry churches severely damaged during the 2012 Emilia-Romagna (Italy) earthquake: Non-linear dynamic analyses vs conventional static approaches

This study presents a detailed failure analysis of seven masonry churches, which were severely damaged during the 2012 Emilia-Romagna (Italy) seismic sequence, by means of 3D FE non-linear dynamic simulations. The main aims of the numerical investigations are: (1) to carry out a sufficiently wide sensitivity study on different specific case studies to have an insight into the role played by the geometry – which is always unique for churches – and by the irregularities; (2) to validate or address the limits of applicability of the most widespread conventional static approaches recommended by Italian Code, i.e. kinematic limit and pushover analyses. Non-linear dynamic analyses are carried out assuming that masonry behaves as a non-linear material exhibiting softening and damage, frictional behavior and different strength in tension and compression. The set of case studies investigated in this work shows how conventional static approaches are still capable of roughly identifying the most critical macro-elements that usually activate a failure mechanism, but that the results (e.g. collapse acceleration, behavior factor) are affected by a level of approximation that may considerably depend on in-plan irregularity and hypotheses done on the interlocking between contiguous walls. From the comparative analyses carried out, it is authors’ opinion that it is always beneficial to perform different types of analysis in order to have a comprehensive insight into the portions of the structure that can suffer a partial collapse with high probability. Once the active mechanism is identified, non-linear dynamic analyses, with more sophisticated material models and with refined FE discretizations of the critical regions, may be useful to deepen the knowledge of the behavior of such complex structures under seismic actions.     

热冲击作用下的陶瓷材料破裂过程数值分析

运用热传导和热2力耦合的相关理论 , 借助统计分布来考虑陶瓷中存在的微孔洞和微裂隙 ; 建立了一种可以模拟陶瓷遭受热冲击作用下的裂纹萌生、 扩展过程的数值模拟方法 , 并通过材料破坏过程分析系统 (RF2PA , Realistic Failure Process Analysis) 加以实施。该数值方法基于细观非均匀性假设 , 突破了以往连续介质力学视陶瓷为均匀介质的假设 , 并从细观损伤角度考虑陶瓷热冲击破坏演化的过程。运用该方法对三面绝热、 一面受热冲击的平板状陶瓷材料的破裂过程进行了数值试验。结果表明 : 起始裂纹发端于受热冲击表面 , 且在初始的裂纹萌生阶段 , 在受热冲击表面产生一系列无序的裂纹 ; 但随着时间的延续 , 裂纹逐渐演变成多条近乎平行的、沿受冲击表面内法向方向扩展的主裂纹 , 其中一些裂纹的发展受到了屏蔽 , 这一结果与试验结果吻合较好。本数值方法为相关研究提供了新的思路。      

Failure of Heat-Exchanger Tubes due to Localized Scaling and Microstructural Transformation

Failure of tubes in a bayonet-type high-pressure heat exchanger was caused by water interruption. The failures were accompanied by excessive plastic deformation, and cracks were found in the thick inner scale on the failed tubes. In the fractured regions, the tube inner surfaces and microstructures showed excessively thick scales and carbide networks, while the locations opposite fractures were scale free. These observations suggest the occurrence of localized heating that subsequently caused bulging and failures. Further inspection of the tube bundles also showed augmented scale thickness in sound tubes. It was recommended that the entire tube bundle be replaced.     

十六栋高楼爆破简介及118号楼未倒原因分析

深圳市一次爆破拆除16栋高楼,总建筑面积达51 000 m2,刷新了国内拆除爆破的记录,其复杂的起爆网路布设及高楼原地坍塌爆破的试验成功,是当前拆除爆破先进技术的体现.但是,其中118号楼未能按设计要求定向倾倒.简要介绍了该次拆除爆破的技术措施,重点分析了118号楼爆破未倒的原因和体会,供爆破界参考.     

The role of talc particles in a structural adhesive submitted to fatigue loadings

The ability of structural adhesive to withstand combination of cyclic loading and service environment makes them suitable for a wide range of applications. It is nevertheless true that their mechanical and micromechanical behaviour is still little understood. The purpose of the work reported here is to study the fracture process and the role of talc fillers of an epoxy adhesive subjected to oligocyclic fatigue. Tests were conducted by using a set-up based on the Arcan fixture and experimental results have been reported for both tensile and shear cyclic loadings. The cohesive failure of the adhesive seems to set off at a specific amplitude level, whatever the loading value. By an incursion at the microstructural scale using scanning electron microscopy, we suggest an explanation of these phenomena. The foliated form of talc fillers are of major importance and seem to provide a deterministic evolution of damage.     

双层高架桥的抗震性能

为研究碳纤维布(Carbon Fiber Reinforced Polymer,CFRP)及外包型钢(Externally Wrapped Steel Section,EWSS)复合加固震损双层高架桥框架式桥墩的恢复力模型,对1榀原型对比试件、1榀无预损加固试件和2榀遭受不同地震损伤加固试件进行了低周往复加载破坏试验,获取了滞回曲线并提取骨架曲线,分析其滞回特性,提出一种弹性段和强化段为双折线、下降段为指数函数且考虑初始损伤的骨架曲线模型;采用试验数据回归拟合方法,定量描述了试件滞回曲线卸载刚度的退化规律,考虑了同级加载承载力退化和定点指向特征,建立了恢复力模型。研究结果表明：复合加固试件滞回曲线捏缩现象明显,呈倒S型,各滞回环分别相交于骨架曲线上正向、负向荷载为屈服荷载0.25倍的点,峰值荷载后EWSS产生包辛格效应;所提出的骨架曲线模型对中度震损和重度震损加固试件下降段指数函数的参数k建议取值分别为3.6和3.4;所建立的骨架曲线模型和恢复力模型计算结果与试验实测结果吻合较好,可为该类结构弹塑性地震反应分析提供依据。

     

用新型箍筋(S-clip)的钢筋混凝土桥墩抗震性能试验研究

钢筋混凝土桥柱中,复合箍筋配筋方式非常复杂,施工难度大,用钢量多,且不易保证施工质量。本文针对该配筋方式存在的问题,提出了一种新型的配筋方式,S-Clip筋。为了验证这种新型配筋方式的有效性,按照纵筋配筋率的不同,制作了两组大型桥墩柱的模型。通过两组模型的低周反复荷载试验,研究了分别采用普通复合箍筋和新型S-Clip筋的桥墩柱的抗震性能。试验结果表明,新型配筋方式能够充分发挥材料的力学性能,与原配筋方式具有相同的承载能力,而且在延性方面略有提高。在工程应用中,采用S-Clip筋提高了工程质量,加快了施工速度,节约钢材,具有广泛的应用前景。该应用技术的研究,对工程结构理论和应用技术的发展有着重要的作用。     

Assessment of structural steel from the World Trade Center towers, part III: Physical damage caused by impact of aircraft

This paper describes damage characteristics and failure modes of the recovered structural steel components from the World Trade Center (WTC) towers WTC 1 and WTC 2. Knowledge of damage to the steel elements played an important role in the investigation by ascertaining the response of the structural steel of the towers to the impact of the planes and by providing information on exterior column damage for correlations with impact damage modeled in the baseline structural performance and aircraft impact damage analysis. Results focus on the five exterior panel sections in the impact region of WTC 1 and the four core columns from near the impact regions of WTC 1 and WTC 2.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

相位角加载条件下2A12铝合金多轴疲劳失效行为

采用SDN100/1000电液伺服拉扭复合疲劳试验机对2A12铝合金进行不同相位角加载条件下多轴疲劳试验研究,通过加载循环曲线和微观断口形貌分析失效机理,对不同损伤累积模型的预测效果进行评价,修正Manson损伤曲线模型以期达到更好的预测效果。结果表明:单级加载条件下,随相位角正弦值的增加疲劳寿命线性递减,当相位角为0°时,轴向硬化、软化交替出现,切向出现循环硬化,90°加载下轴向和切向单独作用效果明显;两级累积路径下,随一级加载周次的增加多轴疲劳寿命延长,0°加载阶段轴向和切向都出现循环硬化现象,两种路径下断口都呈现出多裂纹源特征,在裂纹源区附近观察到台阶状形貌,扩展区存在大量划痕和鳞片状花样;修正后的Manson损伤曲线模型预测误差均在15%以内。