A bridge is a functional structure that requires the selection of an appropriate structural typology, taking into account factors such as the actual topography of the bridge site and its geographical location. Let's delve into various geographical locations to discuss the variations in bridge selection methodologies.

Urban bridges primarily encompass crossing bridges, overpasses and footbridge. Given the varying functional requirements of each specific bridge type coupled with its architectural property being traversed, the aesthetic design of their beams ought to adopt distinct configurations accordingly.

Urban Bridge

(1) Crossing Bridges: Generally, these bridges extend above street thoroughfares, with heavy vehicular traffic under their arches. Given their prominent presence in the cityscape, aesthetic design should be given special consideration. Optimal choices include models with simple and lightweight lines, moderate beam heights like prestressed continuous box beam bridges or steel box beam bridges. Keeping the beam height visually understated is crucial, as larger cantilever arms would diminish the sense of verticality. Modify the impact of such structures by curving beams and sculpted trenches, among other features. Bridge piers can resemble thin-walled vases with an arc profile or a grand cantilevered T Shape pier; this not only reduces the number of bridge columns and optimizes space, but also creates a clear effect.

(2) Overpasses: These structures are primarily designed to meet the overall route's demands, and tend to have long spans, primarily using precast small box girders and precast hollow plates for the superstructure, and cylindrical and square columns for the substructure. Enhancing the aesthetics of the bridge could involve hanging baskets filled with flowers on both side barriers, creating vibrant colors that enhance its scenic appeal.

(3) Footbridge: These structures primarily consist of prestressed reinforced concrete or steel. Representative bridge types could include simple girder bridges, continuous girder bridges, arch bridges, and steel truss bridges. Attractive box section appearances could be used for the beam cross section.

Suburban Bridge

Suburban bridges are typically located along highways and roads due to their topographical constraints, and they primarily take the form of elevated structures. Conventional architectures dominate these bridges due to their substantial length, often exceeding 100 meters. The superstructure is often constructed with precast concrete, a construction technique that is often convenient and uses common precast small box girders, hollow panels. Span lengths range from 20m to 40m. These precast beams are typically fabricated at a designated site before being delivered to the bridge's position for installation and connection. The construction quality is easy to regulate and the assembly process is progressing rapidly. Circular pier and thin walled pillar are commonly used for the substructure of the bridge. Circular piers are commonly used on relatively flat terrains as it enables simple and fast construction. On steeper slopes where horizontal changes are significant, thin walled pillars, typically T-shaped, that use rectangular cross-sections, come into play. Incorporating thin walls reduces the number of pillars, minimizes the amount of excavation required in steep slopes, and reduces the risk of construction.

Bridges Across Rivers and Seas

Crossing rivers and seas requires significant bridge spans, especially in the contemporary field of bridge construction. Under increasing pressure from the navigation and water departments for their pioneering work on the hydraulic flow of rivers, the greater the navigational height, the greater the required span. In addition, the design must strive to minimize impediments to river flood discharge and to streamline the ratio of obstructions as much as possible. Consequently, the main span of bridges routinely exceeds 200 metres to meet navigational requirements while reducing the number of pier clusters across the river channel.

Common types used for such crossings include continuous box girder bridges (CBGs) and continuous rigid frame bridges, cable stayed bridges, and suspension bridges. CBG and continuous rigid frame bridges typically span less than 200 meters, beyond which inclined tower or suspension bridges are usually preferred due to their increased capacity to cross water bodies. CBGs and continuous rigid frame bridges often adopt a box-shaped section with flared edges, whereas CBGs generally use solid or hollow slab pier foundations focusing on collision resistance, ergo the thick and robust pier body design. The base type of the lower structure of continuous rigid frame bridges depends on various parameters including pier height and span, so when the pier height and span diameter of the height-span ratio is relatively small, double thin walled piers are recommended, and for higher ratios, single-limb thin-walled hollow pier.

When it comes to bridges over 200 meters in length, cable-stayed bridges are suitable options. The distinguishing feature of a cable-stayed bridge is that horizontal tension cables suspending the deck form part of the structure, thus adding multiple flexible supports within the girder, significantly reducing the internal bending moment, reducing girder dimensions, and boosting bridge span capabilities. When bridge spans reach even greater lengths, suspension bridges are the best choice. This type mainly relies on two towers at each end supporting the weight of the bridge deck through web-like cables suspended between them. Similarly, suspension bridges leverage the weights of hanging cables from the primary anchorages, thus introducing additional flexible supports within the girder and further reducing the internal bending moment, scaling down the girder volume, and thus increasing the span of the surveyed bridge.

To Wrap Up

This discussion focuses on selecting bridge forms across various geographical locations.In urban areas, aesthetic landscape design is a top priority, requiring simple and streamlined bridge models such as prestressed continuous box girder bridges or steel box beam bridges. For bridges in mountainous or suburban regions, viaduct and precast structures such as precast box girders and cylindrical bridge abutments are preferred due to their ease of construction and ability to maintain quality. When it comes to crossing rivers or oceans safely, large span structures such as suspension bridges and cable-stayed bridges can offer viable options to consider.

It is recommended that constructors make informed decisions when selecting bridging designs, taking into account specific conditions determined through detailed analysis, incorporating geographic specifics, functional necessities, and aesthetic preferences. This practice will enhance the functionality and aesthetic appeal of bridges.