SIMULATION OF THE CYCLIC BEHAVIOUR OF R/C RECTANGULAR HOLLOW SECTION BRIDGE PIERS VIA A DETAILED NUMERICAL MODEL

In the search for robust constitutive models suitable for reproducing the performance of bridge piers during a seismic event, this paper details the simulation of the cyclic responses of four rectangular hollow section R/C bridge piers. These four R/C bridge piers were built at scale 1/2.5 and tested experimentally. Both tall and short piers are considered, covering situations where bending or shear are of relevance. Furthermore, the four piers were reinforced according to rather different design strategies: (I) the first is a 30-year-old bridge designed without allowance to the seismic action, and (ii) the second is a bridge fulfilling the EC8 provisions. The detailed constitutive model that provides the numerical predictions includes two submodels: one with two scalar damage variables, reproducing the tensile and compressive degradations of concrete, and the other is based on the Giuffre-Menegotto-Pinto formulation, simulating the cyclic behaviour of the re-inforcement. The Damage Mechanics submodel is implemented at the Gauss points of the finite elements that discretize the concrete, whereas the steel submodel is implemented on the 2-noded truss elements adopted for the rebars. A comparison between the numerical and the experimental results is discussed in detail in this paper.     

CONCEPTUAL DESIGN OF ISOLATION SYSTEMS FOR BRIDGE STRUCTURES

Abstract

In the first part of this paper the objectives of an isolation system for a bridge structure are discussed, in relation to modelling options and modification of the traditional capacity design principles. A displacement-based design approach is then presented, using a linear equivalent single degree-of-freedom model. The preliminary design of an isolation system for existing bridges is based on the definition of a “structure regularity” which allows the estimation of whether the response of the real structure will be similar to that predicted in the preliminary design phase. The efficiency of the approach is shown in designing the isolation system for a highly irregular bridge.     

Prehistory of Native Americans on the Central American Land Bridge: Colonization,Dispersal, and Divergence

The Central American land bridge has served as a passageway for animals and humans moving between North and South America. Nevertheless, after the first waves of human immigration at the end of the Pleistocene, contact between the native peoples who remained on this isthmus and other peoples living in continental areas where civilization ultimately developed, is characterized, according to the field record, by the transfer of crops, technologies, and goods, until ca.1400 BP when speakers of Mesoamerican languages occupied the northwestern edge (Gran Nicoya). The ancestors of modern-day speakers of Chibchan and Chocoan languages underwent social and cultural diversification mostly within the confines of the land bridge. Some Precolumbian residents altered vegetation immediately after first arrival at least 11,000 years ago, and began to add domesticated crops to their subsistence inventory between 9000 and 7000 BP. Maize and manioc (or cassava), domesticated outside the land bridge, were introduced in Preceramic times, early in the period between 7000 and 4500 BP, and gradually dominated regional agriculture as they became more productive, and as human populations increased and spread into virgin areas. Diversity in material culture is visible ca. 6000 BP, and becomes more apparent after the introduction of pottery ca. 4500 BP. By 2000 BP culture areas with distinctive artifact inventories are discernible. Between 2500 and 1300 BP hierarchies among regions, sites, social groups, and individuals point to the establishment of chiefdoms whose elite members came to demand large numbers of costume and sumptuary goods. A few special centers with stone sculptures and low-scale architecture served a social universe larger than the chiefdom, such as clusters of recently fissioned social groups with memories of a common heritage. Social interactions on the land bridge, endowed with productive bottomlands, highland valleys, and coastal habitats, appear always to have been strongest among neighboring groups.     

南宋宫廷绘画中的“谍画”之谜

本文根据宋代的文献材料,从大量的宋人册页中甄别出一些在军事上具有特殊功用的绘画。据考,在南宋出使金国的使团人员中,潜藏有擅长山水画、人马画的画院画家,他们奉命描绘金国的山川地形和女真人的军事活动,笔者称此类带有间谍用途的南宋宫廷绘画为“谍画”。本文阐述了“谍画”的发展历史,特别是南宋出现”谍画“的政治、军事等方面的历史原因,对此类“谍画“进行了详细的剖析,发现宇文虚中、萧照和陈居中等是可知的南宋”谍画“的作者。此种从军事角度认识某些宫廷绘画,尚属尝试。     

高端旅游的基准与标准探讨

本文对我国正在兴起的高端旅游的基本概念,高端旅游诞生的时代背景,高端旅游的基本内涵,高端旅游的基准与标准制定进行了初步的探讨。     

浙闽木拱廊桥的人居文化特殊意义

依然流传在我国浙南、闽北山区的一种特殊的木构拱桥,以其精巧的结构和优美的造型形成独特的山地人景观。作为具有强烈的原生性(indigenous)的山地建筑化遗产,它所具有的研究价值是多方面的。本通过对木拱桥的地理环境介绍以及历史、民俗的研究,试图将木拱桥作为一种特殊的山地人居化遗产,进行相关的探讨。     

强风作用下木拱廊桥的风振响应分析——以文兴桥为例

中国传统木拱廊桥采用较短的木材构件,形成了较大的桥梁跨度,其整体造型优美,结构巧妙,构造特殊,具有重要的历史价值、艺术价值和科学价值。我国现存的传统木拱廊桥仅有百余座,集中分布于我国浙南和闽北地区,大多建于明清至民国时期,是我国木构桥梁建造技术和古代人民智慧的体现,而近些年来由于台风洪水等自然灾害导致的传统木拱廊桥破坏甚至损毁的事件时有发生。现有的对于传统木拱廊桥的研究大多着眼于其历史艺术价值和建造技术工艺等方面,鲜有对于其结构性能的研究,尤其缺乏强风作用下木拱廊桥的风振响应性能的深入研究。本工作为研究中国传统木拱廊桥在强风作用下的风振响应性能,以典型传统木拱廊桥——浙江泰顺的文兴桥为例,基于几何尺寸的精确测绘,采用SAP2000建立有限元模型进行了木拱廊桥的动力特性分析。研究内容包括以下几方面:首先,采用线性滤波法,基于自回归(AR)法模拟风场,利用MATLAB软件编写脉动风速时程。此后,由于我国现行的规范没有给出适用于木拱廊桥这一结构类型的风压体型系数,本工作通过CFD软件FLUENT风洞数值模拟得到适用于文兴桥的风压体型系数。最后,将模拟编译得到的时程风压作用于文兴桥的有限元模型得到其风振响应。计算结果表明:结构主振型为第一阶横向水平振动;风荷载对三节苗和五节苗两边最外侧的斜苗影响较大,对五节苗平苗的影响较大;下部剪刀撑的最大拉、压应力超过抗拉、抗压强度;剪刀撑脱榫将使下部斜撑的轴压力突增从而导致整体结构抗侧能力大幅降低;强风作用下传统木拱廊桥的时程计算风振系数为1.43～1.75,由此可见木拱廊桥风动力效应不容忽视。本研究成果反映了我国传统木拱廊桥在风荷载作用下结构构件的受力规律和整体结构的动力特性,并为我国传统木拱廊桥的风振性能评估和抗风保护提供理论依据,更科学地保护这一宝贵的建筑遗产类型。     

Bearing capacity assessment of a 14th century arch bridge in Lecco (Italy)

The article presents the results of an experimental and numerical investigation on Azzone Visconti bridge, a 14th century arch bridge in Lecco (northern Italy). Starting from the historical data and from an extensive mechanical characterization of both the soil constituting the riverbed and of the masonry constituting the piers, the aim of the study is to investigate the bearing capacity of the bridge. A testing loading scheme defined according to the current Italian Code is adopted to check the structural behavior. A simplified finite element structural model was conceived and calibrated as a control tool to safely perform the experimental tests. Post-test nonlinear finite element analyses have allowed the prediction of the bridge bearing capacity and the definition of the bridge class according to the Italian regulations.     

徐连与鲁南两经济带带情和发展的比较研究

首先通过对徐连与鲁南两经济带在自然资源、位置交通、人口城镇及经济基础等条件的客观评析,指出它们的同异与优劣之处;其次对两经济带的地缘历史嬗变进行简明回溯,认为无论是目前还是将来,都当以"淮海经济区"为共建目标;最后就两带合理分工协作、共同发展振兴等议题提出一些初步看法。     

汉画像石中桥梁图像探析

本文主要通过汉代画像石中的桥梁图像,并结合画像砖、壁画等,探讨了汉代的桥梁建造状况。