城市中，以协助道路两侧行人穿过机动车道为目的设立的公共开放的步行桥称作过街天桥，它们主要因人车分流的需求而被架设在城市中人流量大、城市公共设施密集处。我国经历几十年的发展，城市建设效率方面取得重大成果，城市空间品质的提升成为人们日益关注的话题。北京是世界上过街天桥数量密度最高的城市之一，然而由于过街天桥快速、大量的建设，过街天桥往往采用构建化的方法，省略了因地制宜的设计步骤，与周边空间在形态与功能两方面上脱节。其中北京五环内天桥数量多、密度高，周边空间的形态与功能多样，具有代表性，因此被本文选做研究对象。本文首先从宏观角度统计并分析过街天桥在北京五环内的数量密度、分布特征及其与周边空间联系状况等，展现北京五环内过街天桥的基本现状（截止2017年底）。进一步，本文将北京市五环路内的过街天桥按照周边空间界面的开放程度分为四大类：完全封闭界面、基本封闭界面、基本开放界面与完全开放界面，再对每一大类按照其功能形态进行细分至各小类。随后，对每一小类空间界面周边的过街天桥中的典型案例进行线上调研与实地调研，获取第一手资料并建模记录。文章各节主要从天桥的建设背景概况、天桥的平面形态和天桥与周边空间的整合度这三个方面入手，结合各天桥建设的历史与城市建设中遇到的机遇与阻碍进行深入分析。在各节中，根据过街天桥的具体分类辅以国内外其他城市的过街天桥案例，对北京五环内的过街天桥典例进行综合评价与优化可能性的探讨。本文的特点在于：不再关注过街天桥自身的结构、造型与材料等物理特性，而是关注过街天桥与周边空间的整合度，从城市设计的视角出发，对北京五环内的过街天桥进行调研、记录及评析。
A public open pedestrian bridge built in the city to assist pedestrians crossing the driveway is called an overpass. Overpasses are built in cities due to the need to separate walking people and flowing vehicles. They are usually built in areas where pedestrian flow is relatively high and where public facilities are relatively dense.After decades of development, China has made great achievements in urban construction efficiency. However, the improvement of urban spatial quality has gradually become an issue of increasing concern. Beijing is one of the cities with highest density of overpasses in the world. However, due to the rapid and massive construction of the overpasses in the last decades, overpasses in Beijing are often constructed as single units without considerations about the surrounding areas. As a result, they appear to be separated from their contexts. The number and density of overpasses within the 5th Ring Road in Beijing is significantly high, and the texture and function of their surrounding areas are diverse. Thus, overpasses and their contexts within the 5th Ring Road in Beijing were selected as the study object of this article.? First of all, from a general point of view, this article gives a statistically analysis of the number, density and distribution of overpasses in the range of study, and their relationships with their contexts. These analyses are presented as charts and diagrams, in order to present a general picture of overpasses within Beijing’s 5th Ring Road visually and vividly. Further, all 432 overpasses are categorized into four major classes — completely closed interface, basically closed interface, basically open interface and completely open interface. Then for each class, this article subdivides into smaller classes, and present the details about one or more typical case of each class. The research begins with online researches and goes on with field investigations aiming to obtain first-hand information about each overpass and model them digitally. With consideration of the construction process and history regulations, this article also judges and analyzes the cases from the perspectives of accessibility and integration. Also, comparison between overpasses in Beijing and foreign cities are included in order to evaluate the quality of overpasses in Beijing more objectively, and to discuss the optimal possibility for overpass design.This article is special for its concentration on the integration degree of overpasses with their contexts instead of the physical characteristics of overpasses themselves. From the perspective of urban design, this article investigates, records and analyzes the overpasses within the 5th Ring Road in Beijing.
