EXPERIMENTAL ASSESSMENT OF THE GLOBAL CYCLIC DAMAGE OF FRAMED R/C STRUCTURES

It is accepted that failure criteria for earthquake-resistant structures should be based on energy dissipation as well as on maximum ductility. Even though rational procedures to include low-cycle fatigue in the definition of the design spectra have been derived, major difficulties arise in the definition of the cyclic damageability of the structure. The work conducted so far was mainly based on cyclic tests conducted on simple structural elements, therefore, the extension to the complete structure is not an easy task. A final cyclic test was conducted at the ELSA reaction wall facility on a four-storey full-scale reinforced concrete frame designed according to Eurocode 8, at the end of a series of pseudodynamic tests. The results allow the performance during the pseudodynamic tests to be assessed and the cyclic damageability of a complete structure to be investigated. The effects of low-cycle fatigue on a high-ductility structure turned out to be more important than expected.     

Improving Low-Cycle Fatigue Performance of High-Performance Buckling-Restrained Braces by Toe-Finished Method

The purpose of this research is to improve the low-cycle fatigue life of the buckling-restrained brace (BRB) for the development of the high-performance buckling-restrained brace (HPBRB) used in bridge engineering. The HPBRB is expected to suffer three strong earthquakes without severe damage during the lifecycle of a bridge. This article employs a low-cycle fatigue experiment, including two series of BRB specimens, all of which had been tested to failure. In the second batch, the weld toes of the rib had been ground to improve the weld's low-cycle fatigue life. According to test results under constant and variable strain amplitudes, the specimens have a great low-cycle fatigue performance. The weld of the rib clearly affects the performance of the as-welded specimens tested with the relatively small strain amplitude. The toe-finished method effectively improves the BRB's low-cycle fatigue performance. Besides, the in-plane gap width of the BRB slightly affects the low-cycle fatigue life. Finally, the low-cycle fatigue curves are compared between the BRB and the materials and the low-cycle fatigue damage evaluation formulae of the as-welded and toe-finished BRBs are recommended for the strain-based evaluation of the low-cycle fatigue damage.     

Experimental Study on Low-Cycle Fatigue Performance of Weld-Free Buckling-Restrained Braces

A type of weld-free buckling-restrained brace is proposed to eliminate the influence of welding on the low-cycle fatigue performance. The core member is manufactured with no weld existing along the overall length of the member. Three welded and three weld-free specimens under different strain amplitudes were tested, and the hysteretic behavior and low-cycle fatigue performance of the specimens were analyzed. The test results indicate that the ductility and the cumulative plastic deformation of the weld-free specimens are much higher than that of the welded ones, which are much closer to the performance of the material capacity.     

FATIGUE ANALYSIS OF MOMENT RESISTING STEEL FRAMES

A procedure for the fatigue assessment of steel building structures subjected to earthquakes is presented. The procedure constitutes an extension of the present, high-cycle, fatigue assessment to cases of low-cycle fatigue. It may serve as a basis for the introduction of a fatigue limit state in the earthquake design of steel structures. It may be also used for the damage assessment of existing steel buildings subjected to past earthquakes. By means of parametric studies, the effects of various parameters on the fatigue susceptibility of several moment resisting steel frames are studied. The influence of a number of parameters such as the type of ground motion, type of structural typology, local fatigue behaviour, overall frame design and semi-rigidity of joints on the susceptibility to damage are investigated.     

DUCTILITY AND LOAD CARRYING CAPACITY PREDICTION OF STEEL BEAM-TO-COLUMN CONNECTIONS UNDER CYCLIC REVERSAL LOADING

Abstract

The economy and reliability of steel-framed buildings in seismic areas depend basically on the hysteretic behaviour of its individual components, such as members and joints. With reference to the latter, despite the recent semi-continuous frame approach (which appears generally very convenient for the design of low- and medium-rise steel buildings), the present state of knowledge does not allow for a complete understanding of the behaviour and the low-cycle fatigue life of beam-to-column connections under dynamic loads.

This paper presents a criterion for the definition of the low-cycle fatigue strength of steel connections, and proposes two approaches for the design of steel frames in seismic zones via the assessment of the fatigue damage, which is evaluated alternatively on the basis of either the ductility or of the load carrying capacity.     

Experimental Analysis of Bolted Steel Beam-to-Column Connections: Component Identification

In this paper, the results of an experimental program dealing with the ultimate behavior of bolted beam-to-column connections under cyclic actions are presented. The design criteria adopted for tested specimens are discussed in detail, aiming to point out how the ultimate behavior can be governed by properly strengthening the components for which yielding has to be prevented. To this scope, the component approach is adopted as a design tool for component hierarchy criteria. The aim of the paper is the investigation of the actual possibility of extending the component approach to the prediction of the cyclic response of beam-to-column joints. To this scope, the attention has been focused on the possibility to evaluate the overall energy dissipation capacity starting from the energy dissipation of the single joint components, provided that they are properly identified and their cyclic behavior is properly measured.     

纸张理化指标与老化时间的统计学分析

为了探究纸张的保存寿命,本项目对竹纸、宣纸、新闻纸、字典纸和构皮纸等5种纸张进行了干热加速老化实验,并对老化前后纸张的主要理化指标(返黄值、抗张指数、撕裂指数、耐折指数、聚合度、铜价和冷抽提pH值)进行检测。最后通过Pearson等级相关系数研究了上述理化指标与老化时间的相关性,从而揭示出纸张保存寿命预测的方法。研究发现5种纸张的抗张指数、铜价和聚合度与老化时间的相关性都较好。分别各有4种纸张的返黄值、冷抽提pH值和撕裂指数与老化时间的相关系数都在0.9以上,相关性非常好。仅有一种纸张的耐折指数与老化时间的相关性较好。本研究的结果对于大多数纸张保存寿命的预测具有参考价值。     

Experimental Investigation of Exterior Unreinforced Beam-Column Joints with Plain and Deformed Bars

Experimental tests on four full-scale exterior unreinforced reinforced concrete (RC) beam-column joints, representative of the existing non-conforming RC frame buildings, are carried out. The specimens have different longitudinal reinforcements (plain or deformed) and they are designed in order to be representative of two typical design practices (for gravity loads only or according to an obsolete seismic code). Different failure modes are observed, namely joint failure with or without beam yielding. The local response of the joint panel is analyzed. The different joint deformation mechanisms and their contribution to the deformability and to the energy dissipation capacity of the sub-assemblages are evaluated.     

Cyclic Modeling of Bolted Beam-to-Column Connections: Component Approach

The work is aimed at the prediction of the cyclic response of bolted beam-to-column joints starting from the knowledge of their geometrical and mechanical properties. To this scope a mechanical model is developed within the framework of the component approach already codified by Eurocode 3 for monotonic loadings.

Accuracy of the developed mechanical model is investigated by means of the comparison between numerical and experimental results with reference to an experimental program carried out at Salerno University. The obtained results are encouraging about the possibility of extending the component approach to the prediction of the cyclic response of bolted connections.     

Predicting Ductile Crack Initiation of Steel Bridge Structures Due to Extremely Low-Cycle Fatigue Using Local and Non-Local Models

The strain-based prediction model combining the Miner's rule and Manson-Coffin's relationship provides a local parameter for evaluating the ductile crack initiation of steel structures, and some modified models based on it were proposed to evaluate extremely low-cycle fatigue (ELCF) behaviors of steel structures. Previous research has confirmed these local models to be an accurate index for ductile crack initiation in steel bridge piers, however it is found to quite depend on the mesh size of the numerical model used. In this study, a non local damage parameter is presented and successfully applied to ductile crack initiation life assessment of steel bridge piers subjected to earthquake-type cyclic loading. The non local damage parameter is based on averaging the strains over the effective plane using a weight function in the exponential form, and introduces the non local damage parameter to replace the local state variable. Finite element analysis with three different mesh sizes is employed. Comparisons of the local and non local solutions with those of experiments indicate that the non local prediction model can predict the ductile crack initiation of steel bridge piers with good accuracy regardless of the specimen geometries and loading histories, meanwhile the mesh independent nature of the non local model is also demonstrated.     

清式木建筑透榫节点加固方法的试验研究

我国传统木结构建筑的各构件间主要采用榫卯连接,这种节点形式在较大水平地震作用下容易出现局部拔榫、节点松脱现象,不利于结构的稳定和承载。为此针对榫卯节点的抗震性能及加固进行试验研究。依据清工部《工程做法则例》设计制作了4个足尺透榫节点试件,其中3个试件分别采用竹斜撑、角钢和碳纤维(简称CFRP)布进行加固。在改进榫卯节点拟静力试验装置的基础上完成了低周反复荷载试验,分析了对比节点和加固节点的破坏机理、承载力、延性、刚度退化、耗能和榫头拔出过程。试验结果表明,竹斜撑、角钢和CFRP布加固节点的正向峰值荷载较对比节点分别提高了92.4%、54.6%和63.0%,反向峰值荷载则分别提高了61.5%、75.7%和39.0%。对比节点和角钢加固节点初期刚度基本相同,且随转角增加出现先增大后减小的过程;竹斜撑加固和碳纤维布加固节点的初始刚度显著大于对比节点,随着转角的增加呈单调减少。此外,竹斜撑和角钢加固节点的榫头拔出长度明显小于相同转角下对比节点的榫头拔出长度,表明竹斜撑和角钢均起到了延缓榫头拔出的作用。     

Experimental Investigation on the Seismic Behavior of Beam-Column Joints Reinforced with Superelastic Shape Memory Alloys

Superelastic Shape Memory Alloys (SE SMAs) are unique alloys that have the ability to undergo large deformations and return to their undeformed shape by removal of stresses. This study aims at assessing the seismic behavior of beam-column joints reinforced with SE SMAs. Two large-scale beam-column joints were tested under reversed cyclic loading. While the first joint was reinforced with regular steel rebars, SE SMA rebars were used in the second one. Both joints were selected from a Reinforced Concrete (RC) building located in the high seismic region of western Canada and designed and detailed according to current Canadian standards. The behavior of the two specimens under reversed cyclic loading, including their drifts, rotations, and ability to dissipate energy, were compared. The results showed that the SMA-reinforced beam-column joint specimen was able to recover most of its post-yield deformation. Thus, it would require a minimum amount of repair even after a strong earthquake.     

Seismic behavior of two Portuguese adobe buildings: part II —numerical modeling and fragility assessment

Considering the likely unfavorable behavior under seismic action of adobe construction, this article aims at providing a seismic fragility characterization of two adobe Portuguese traditional buildings, using numerical models calibrated over experimental results. The study of such two case-study buildings in the region of Aveiro contributes to the understanding of the seismic fragility of adobe construction in the region in general. The buildings were numerically modeled to estimate their structural behavior under seismic loading using adobe material properties that were calibrated based on the experimental results of a cyclic in-plane test of a full-scale double-Tshaped adobe wall. The method chosen to characterize adobe masonry and model its nonlinear behavior followed a total strain crack-based macro-modeling (TSCM) approach, whereas pushover analysis was carried out to reproduce the pseudo-static experimental test in order to enable a refined calibration of adobe masonry mechanical properties. Fragility functions were then derived, based on the above-mentioned numerical models, using nonlinear static analysis, bringing further insight on the seismic fragility of traditional Portuguese adobe construction.     

新疆于田县流水墓地26号墓出土人骨的古病理学和人类学初步研究

前言古病理学作为一个新的研究领域,主要是对考古发掘出土的人骨进行自然科学范畴的医学检查,因此这一科学领域涉及到医学、人类学和考古学。古病理学研究的对象通常为出土的古代人骨,也有很少量的干尸,甚至还有在沼泽中保存的尸体。因为考     

The use of magnetometry and pole-dipole resistivity for locating Nabataean Hawar archeological site in the SW-Jordan

This paper is focused on the joint use of magnetometry and pole-dipole electrical resistivity geophysical methods for assessing their capability in the detection of a prehistoric site in the southwestern Jordan. The survey area, Auara, was built in the first century BC during the Nabataean time and is located in a very arid environment framed on the east and north by white sandstone hills. In order to test this site, a number of magnetic stations and two pole-dipole resistivity traverses were carried out in the investigated area. Magnetic data were taken with one sensor at height of 0.8 m along survey lines spaced 1 m apart. Resistivity measurements were carried out utilizing the pole-dipole array along two profiles. A total of 32 geoelectrical stations spaced 2 m were made along the two profiles. Magnetic method found structure with contrasting physical properties to those of the surrounding material. The archeological interpretation of such structure is in terms of rectangular cistern (pool) with dimensions 26 × 16 m. A probable location of two buried walls spaced 16 m are indicated by low resistivity values.     

Some Issues in Seismic Analysis and Design of Blockwork Wharves

During past decades, a number of ports worldwide have suffered extensive earthquake-related damage. As seaports play a key role in the world's economy, their seismic performance should be enhanced, clearly stated and reliably pursued by designers. This work focuses on seismic vulnerability of wharves in Italy. According to a recently carried out statistical study, most of the existing wharves are gravity-type, made of superimposed, dry-connected blocks, particularly in older facilities. Such technology is widely in use worldwide but it has not attracted much research interest so far. In the present study, the validity of current, simplified design approaches has been investigated by comparison with the results of inelastic dynamic time-history analyses. Permanent displacements of the wall blocks have been calculated. Available performance criteria have been reviewed. A real wharf structure in the Port of Ancona (Italy) has been studied in depth, as a methodological example. For such structure, a parametric study has been conducted with the aim of investigating the role played by different design parameters and to assess the validity of the widely in use pseudo-static method.     

中国明代木质古建西安鼓楼彩绘的分析研究

鉴于有关中国木质古建彩绘材料及技术的研究报道较少,本工作通过光学显微镜、扫描电镜能谱(SEMEDX)、X射线衍射及气相色谱质谱(GC/MS)分析方法,对建于公元1380年的中国西安明代鼓楼木建表面彩绘样品进行了科学检测研究,分析了其中的无机材料组成及彩绘所用粘合剂,并收集了所涉及到的相关历史资料。分析结果表明,木建表面彩绘的材料组成和制作技术与历史调查获得的信息完全吻合。地仗层主要由粘土、石灰、干性油(桐油)及纤维织物组成,且地仗层保持最初的原材料。颜料分析结果显示,尽管修复时所使用的粘合剂与最初建造时的粘合剂完全相同,但目前彩绘的颜料即有原来使用的材料,也有十八世纪修复时所使用的材料。     

公路汽车振动对晋祠圣母殿宋代彩塑影响研究

为了研究公路的交通振动对彩塑损伤状况,对山西省晋祠圣母殿内彩塑进行了脉动和汽车振动测试。脉动测试与分析得到了彩塑基频自振周期、阻尼比及传递函数;单车公路汽车振动测试及利用传递函数进行的多车振动数值计算分析,得到了彩塑在单车行走下的最大位移为3.40×10-2μm,五车纵列行走振动最大位移为1.32×10-1μm,及在不同汽车流下的振动位移。根据彩塑残损情况和振动最大位移角2.24×10-7rad,提出了瞬时振动对晋祠泥质彩塑影响的判定等级和准则;根据疲劳损伤理论和振动测试结果,提出了持久振动对晋祠泥质彩塑损伤的判定准则;根据晋祠泥质彩塑的现状损伤和其在振动时的瞬时位移极限角,提出了不同等级公路应有的避让距离分别为3200m、2400m、1800m、1200m、800m,并对晋祠周围的公路状况进行了判定。