Jiaxing Cultural Axis Pedestrian Bridge
Entry numberYBFootbridge-140126
AuthorHi-Line Work
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Concept Summary Intro & Site The Jiaxing Bridge stands to be an iconic bridge for Jiaxing Ancient City, extending the city’s striking cultural axis across to Haogu Tower and connecting the historic town and South Lake. The site is steeped in history, from adjacent stone bridges, architecture along the grand canal, and the aforementioned Haogu Tower. In parallel, the district stands as a site for a contemporary development, integrating modernity and preemptively building for the future. Thus, it is of paramount importance that the proposed bridge strengthens the cultural corridor, promotes connectivity between historical districts, responds to the ancient history of the site while providing a contemporary structure, and promotes sustainable practices looking forward to a climate-conscious future. Concept Jiaxing Bridge is here proposed to directly extend the Ancient City Central Cultural Axis, launching from the north bank of the Huancheng River and landing in front of Haogu Tower, promoting a direct and uninterrupted line of sight to the tower. This crossing celebrates the cultural axis, while providing a strong, historic terminus to the corridor. This deliberate siting results in an oblique river crossing, requiring a long structural span. The adjacent brick arch ZiYang Bridge provides initial inspiration for a series of three contemporary arches, spanning the Huancheng River, Shanghai-Kunming Railway, and Yuanhu Road respectively. A single grand arch serves as the deck of the bridge, unifying the three structural arches below. This series of arches was refined to maintain desired river, rail, and road clearances while also seeking to minimize the vertical height of the bridge, as to not disrupt the existing skyline and view corridors. Further inspired by the traditional brick bridge, this proposal seeks to acknowledge ancient brick construction while proposing a minimalist structure with a low impact on its surroundings. A facade of staggered vertical elements flows along the arch of the bridge, imbuing the bridge elevation with a brick pattern outline, harkening back to the ancient city. As the bridge rises from the banks of the Huancheng River, this “brick” facade steps outward, mirroring the tiered Haogu Tower framed in the distance. While the outline of the brick is solid, the brick is infilled with a transparent screen, providing views through the bridge to the surrounding historical site and nature. Simultaneously, the perforated screen lends volume to the bridge, accentuating the bridge’s dynamic form. The inherent lightness offered by the steel construction and transparent material choice allows the bridge to float over the landscape. The Jiaxing Bridge would thus embrace both the modern and the historic within a single arch gesture. Circulation The Jiaxing Bridge proposal seeks to provide connectivity between previously separated districts, offering direct and uninterrupted routes from the Ancient City to South Lake and Haogu Tower, with additional connection to the south bank of the Huancheng River. Arriving from the northern cultural axis, visitors can ascend steps or walk their bike up to the apex of the bridge. The bridge peak sits slightly above the treeline, providing views not just to the tower, but to all of surrounding Jiaxing. From the peak of the bridge, visitors can descend directly to the South Lake district, landing at the foot of Haogu Tower. The bridge is here imagined as not just an avenue of moment, but as a destination. Strips of landscape are integrated with the bridge deck, including seating, gathering areas, and shading foliage. The bridge can serve as a nexus - a meeting point where friends and family can meet before entering the cultural district, or just to look out upon the water. Further, the bridge features a gathering stair below deck, embedded within the structural arch across Huancheng River. This occupiable stair serves two purposes. First, it provides connectivity from the south bank of the Huancheng River to the upper deck of the bridge, and subsequently to both the north bank of the river and South Lake district. Second, the gathering stair is a sheltered escape from the heat, providing a shaded area with tiered seating. Performances or small gatherings could be hosted within this space, or a visual media presentation could be projected upwards to the bottom of the bridge deck, providing an immersive experience for visitors. Structure The weight of the bridge is primarily supported by a series of double steel arches, deliberately clad to create a sculpted structural arc. The bridge deck consists of a concrete slab supported by a series of segmented steel trusses, embedded within the bridge deck. The trusses transfer their load to a colonnade of steel pipe columns, spaced evenly across the bridge, which in turn transfer gravity loads to the arches below. The arches are relatively shallow, generating significant thrust forces at their base, requiring a concrete foundation and piles at each arch base. Laterally, the combination of steel pipe columns and steel deck truss form a moment frame, with the base of the moment frame pinned to the steel arch below, such that lateral load through the system is resisted via column bending capacity. Additional bracing could be added to further transfer lateral forces to the arches below. Each arch set is connected to each other by a series of horizontal cross ties, serving to unite the two arches. Constructability & Feasibility Thought to constructability and feasibility were at the forefront of the bridge design, and decisions were made to rationalize the geometry. First and foremost, the implementation of the long-span arch here removes any requirement for structural piers in the Huancheng River itself, significantly reducing environmental impact and decreasing costs associated with river construction. Further, the structural arches are here designed as segments of a circle, a known geometry, easing the steel fabrication process. The bridge deck itself, although appearing as an arc in elevation, can be rationalized into a series of linear segments. Thus, all deck truss elements can be linear and constructed with stock steel sizes.This geometric system is repeated through every bay of the structure. The brick-inspired facade, while appearing complex, is generated via a consistent translation of the arc curve defining the bridge deck, such that typical vertical elements have the same length, simplifying fabrication. The facade could be installed in modules supported at each interval by two of the structural column elements. Thus, the facade could be prefabricated off-site and crane lifted into position. Further, structural steel is a known material familiar to regional contractors. While the proposal is novel and exciting, the materials are not unprecedented and can be rationalized into understandable components. Within the scheme, Glass Fiber Reinforced Concrete can be used to clad steel elements to provide a textured finish. Perforated panel screens can be cut using digital fabrication to again simplify construction. Efforts to value-engineer the cost of construction are as important as efforts to inspect and maintain the bridge, reducing the life cycle cost of the bridge. Bridge inspections should be completed every two years, or per governing code, to review for flaws in finishing material, critical structural members, or water damage. Further, proactive maintenance should be completed to seal deck joints, paint exposed elements, and correct water damage. Proactive inspection and maintenance are key to maximizing the lifespan of the bridge. Techno Economic index/ Sustainability The Jiaxing Bridge proposal here seeks to promote sustainable design and construction practices, considering lifecycle costs as well as the construction cost on the built environment. Towards a Techno Economic Viability Study, the design team has here enumerated a number of design decisions and measures that can be taken to demonstrate the feasibility of the bridge proposal. ● Reduce environmental impact by avoiding constructing new piers in the river. ● Use of known and local materials to reduce embodied carbon associated with extraction and transportation. ● Standardize bridge design to enable pre-fabrication and reduce material waste. ● Implement inspection and maintenance plan to reduce bridge life-cycle costs. ● Consider material qualities early in the project to provide a clear basis for consideration of embodied carbon. To that end, the below table provided an early estimate of material quantities and carbon impact for the bridge superstructure, to be refined during design development.