Bridge type selection and modeling belong to the category of conceptual design. They are interrelated and influence each other, which is the most creative stage in structural design and an important link in bridge mechanics and aesthetics. A reasonable bridge type will make the structure itself not only meet the use function, but also present a sense of contribution and beauty without doing or less decoration, giving people spiritual enjoyment. On the other hand, once the bridge selection is unreasonable and the shape is improper, although the bridge can meet the use function after completion, it will be wasted due to excessive investment, or it will be criticized for its chaotic, dull and out of tune with the environment. Therefore, if designers want to design a bridge that can meet the use function and give people a sense of beauty, they must take the bridge selection and modeling seriously.
1 Main factors affecting bridge type selection and modeling
Bridge type selection and modeling requires selecting a bridge structure form that is not only beautiful, safe and durable, but also economical, reasonable, convenient to construct and advanced in technology based on comprehensive consideration of the objective conditions at the bridge site (including topography, features, geology, hydrology, navigation, etc.), the mechanical characteristics of the structural system and the aesthetics and landscape of the bridge. The main factors affecting the selection and modeling of bridge structures can be summarized into two aspects: functional requirements and constraints. The functional requirements are mainly reflected in the requirements of safety, applicability, economy, beauty and maintenance. The constraints of bridge selection and modeling mainly include natural conditions, economic conditions, time conditions and technical conditions.
2 bridge type selection
bridge type selection depends on functional requirements and constraints, which is the same as the traditional bridge type scheme determination process. In addition to natural conditions, technical conditions and other factors, different bridge structural systems also have some factors that affect the bridge type selection. For example, the system factors of arch bridge include deck position, main arch type, number of arch ribs, etc., while the system factors of cable-stayed bridge include the number of cable towers, the number and arrangement of cable planes, the connection relationship between tower piers and beams, etc.
in the bridge type selection, we can use the idea of "exhaustive method" to determine the system factors and material factors that affect the bridge type selection, and then combine the factors, and then screen them, and select some reasonable bridge types that meet the constraints. Take arch bridge and cable-stayed bridge as examples to briefly explain them respectively.
2.1 arch bridge selection
As one of the oldest bridge types, the arch bridge is deeply loved by designers for its structural beauty of combining rigidity with flexibility. With the progress of science and technology and the application of new materials and new technologies, the structural forms of arch bridges have made great progress in the world.
The system factors that affect the type selection of arch bridges mainly include:
1. Structural system. Including thrust arch (such as Henrik Bridge), non-thrust arch (such as Feynman Bridge) and composite arch (such as Caiyuanba Bridge).
2. Bridge deck position. Including through type (such as Wanxian Yangtze River Bridge), through type (such as Lupu Bridge) and through type (such as Fehmann Bridge).
3. Form of arch axis. Including arc arch bridge (such as Zhao Zhouqiao), parabolic arch bridge (such as Sydney Harbour Bridge), catenary arch bridge (such as Yagusha Bridge) and so on.
4. number of arch ribs. Including single rib, double rib (such as Lupu Bridge) and triple rib (such as Dashengguan Bridge).
2.2 cable-stayed bridge selection
Cable-stayed bridge is favored by people because of its excellent spanning ability and simple and powerful structural form, and it has become the most widely used structural form of modern bridges, especially bridges and landmark bridges.
The system factors that affect the type selection of cable-stayed bridges mainly include:
1. Layout of pylon. Monolithic (such as Stonecutters Bridge), inverted V-shaped (such as Milu Bridge), inverted Y-shaped (such as Sutong Bridge), herringbone (such as Nanjing Yangtze River Third Bridge), diamond-shaped (such as Hangzhou Bay Bridge) and so on.
2. Layout of stay cables. Cable is divided into single cable plane (such as Donghai Bridge), double cable plane (such as Taiqiao Bridge on the Yangtze River in eastern Hubei), three cable planes (such as Tianxingzhou Bridge) and four cable planes (such as Tingjiu Bridge in Hong Kong).
According to the layout shape of cable plane, it can be divided into radial shape (such as French Saint-Nazaire Bridge), fan shape (such as Nanjing Yangtze River Third Bridge) and parallel shape (such as Alamiro Bridge), and the application of empty cable plane (including curved cable plane) and combined cable plane is also increasing.
3. span arrangement of holes. Twin towers and three spans (such as Duoduoluo Bridge), single tower and two spans (such as Minpu Second Bridge), single tower and one span (such as Alamiro Bridge) and multi-tower and multi-span (such as Milu Bridge).
3 Bridge modeling
3.1 Basic factors affecting bridge modeling
Excellent bridge design should have the following characteristics: in application, it should fully meet the functional requirements; In terms of safety, it should meet the needs of bearing and durability: in terms of technology, it should reflect the new development of science and technology and engineering; in terms of modeling, it should be integrated with architectural art; In construction, it is necessary to use reasonable materials and combine them with construction practice. Bridge designers should consider the local social, historical and natural environment and make full use of architectural aesthetic principles on the basic premise of ensuring reasonable structure.
3.2 Bridge Aesthetics and Modeling Design
Looking back at the bridge projects in the history at home and abroad, it is not difficult to find that the predecessors attached great importance to the aesthetic characteristics of bridges as buildings. However, in recent decades, due to the rapid infrastructure construction in China, on the one hand, the aesthetic treatment of most small and medium-span bridges has not been paid enough attention; on the other hand, due to overemphasis on the importance of bridge modeling or misinterpretation and misuse of modeling principles, some bridges with huge investment and unsatisfactory aesthetic effects have been built.
As a bridge designer, you should not only have extensive scientific and technical knowledge and engineering design ability, but also have certain aesthetic and artistic accomplishment and creative conception ability, so as to better realize the combination of technology and art according to the needs of modern society. Create a design that can meet the requirements of the times from function to form.
① contents of bridge modeling design
mechanical properties and form composition are the two basic starting points of bridge modeling design. Bridge modeling design is more practical and operable. From the overall layout to the detailed structure, bridge modeling design strives to achieve the integration of form and function, and the unity of expression and beauty at different levels. Bridge modeling should adapt to the geographical characteristics, landscape characteristics and regional customs and culture of the bridge site, and conform to the basic principles of technical aesthetics such as proportional balance, rhythm and rhythm in structural form. The content of modeling design includes modeling concept design, overall modeling design, component modeling design, color design, lighting design, greening and decoration, etc. The content and depth of modeling design should be different according to the scale of bridge construction, the characteristics of bridge area and the purpose of bridge construction.
② Basic methods of bridge modeling design
The establishment and enrichment of design concepts must be based on the accurate grasp of environmental conditions and structural performance, and at the same time, it should be integrated into the creative work of designers. In the design process of bridge modeling, the main configuration should be determined according to the design concept, the characteristics of the environment and the design conditions of the bridge, and other configurations should be coordinated based on it to achieve outstanding focus. After forming the modeling unit through necessary integration, it can be further changed and expanded in the whole bridge range in combination with structural performance. The basic modeling design methods include unit modeling, integral modeling, linear design, proportional design, topology optimization and so on. The bionic modeling design of bridge is a common means to realize the modeling innovation of bridge architecture.
3.3 bionic design of bridge
When the development of human creativity is limited, don't forget to return to the original source of inspiration, that is, nature. After billions of years of cruel elimination, only those species that can adapt to the harsh external environment can be preserved and evolved. It is not difficult to find that there are not only many kinds of creatures in nature, but also many species have the characteristics of refinement and high efficiency in their structure and function, and the creatures in nature provide a natural treasure house for human innovation. Colorful natural landscapes have always been the driving force for human beings to create beauty. Design the process of learning from nature and getting inspiration.
bionics is a new frontier discipline which imitates biological system and has the characteristics of biological system or similar characteristics. As a branch of applied biology, bionics is the inspiration of biological evolution to human research and practice in the field of bionic concepts. Bionics studies the structure and properties of biological systems, provides new design ideas and working principles for engineering technology, and is widely used in industrial design, architectural design and other fields.
(1) the bridge beam design imitating natural phenomena. Such as waves, rainbows and other natural phenomena showing curves are not unfamiliar to everyone. These natural states are not only beautiful in shape, but also quite reasonable in structural stress, and are the source of inspiration for bridge shape design.
(2) The design of bionic bridge. The design of bionic form emphasizes the feeling and flexible application of the aesthetic feeling of biological external form. Appropriate imitation of biological external morphology in bridge design can make the shape more novel and lively, and also increase the bridge functions (such as sightseeing, leisure, etc.).
(3) Bridge design with bionic structure. The existence of all structures in human society is directly or indirectly derived from nature, and only a rational understanding of biological structures can reasonably apply them to bridge modeling design. If living things want to survive, they must be supported by structures with certain strength, rigidity and stability. A grass, a beehive, a spider web and a shell look very weak, but they can resist powerful external forces. This is the role that a scientific and reasonable structure plays in organisms. In the existing bionic design of structures, designers mainly study plant structures and animal structures.
Conclusion
The selection and modeling of bridge is the most creative stage in structural design, and it is an important link to embody bridge mechanics and aesthetics. With people's higher and higher demands on the cultural and psychological needs of buildings, the design of highway bridges must also adapt to this demand. Highway bridge design engineers improve their aesthetic accomplishment and shoulder the dual responsibilities of architects and structural engineers.
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