The Keystone Bridge, proposed for the Jiaxing Ancient City, is a collaboration with Honglin Li and Chenyu Huang.
The Keystone Bridge crosses the Huancheng River, extending the existing cultural axis to the existing Haogu Tower, promoting a direct line of sight to the tower and providing a strong terminus to the Jiaxing Ancient City district.
The deliberate oblique siting requires a long structural span to avoid introducing piers in the Huancheng River or existing right-of-ways. The bridge elevation thus borrows inspiration from adjacent arch bridges, proposing three structural arches crossing the Huancheng River, Shanghai-Kunming Railway, and Yuanhu Road. These three small arches work in tandem with one super arch, extending the cultural axis and providing pedestrian connections across the river and to Haogu Tower.
The interplay between the two sets of arches, upper and lower, creates an opportunity for architectural expression. Chinese masonry of adjacent bridges inspires the running bond pattern of the façade screen. The screen is inlaid with perforated panels, which serve to accentuate the form of the bridge while still allowing for the passage of light.
This faux brick screen is supported by a series of structural columns. The columns transfer loads from the upper deck to the pinned compression arches below.
A truss embedded within the bridge deck transfers vertical loads to the columns, and subsequently to the compression arches below.
Lateral loads are similarly distributed to the columns, which act in bending to transfer lateral loads to the laterally braced compression arch below. Combined with the rigid deck, the lateral system can be considered as a series of moment frames.
The structural proposal results in a bridge interior that requires no cross-bracing, meaning that the interior of the bridge can be inhabited.
Named for the keystone brick in a compression arch, the Keystone Bridge is inspired by historical Chinese masonry bridges, but introduces steel and long span structural systems to propose a modern bridge situated within an ancient and deeply cultural context.