General:Project background and information

Instead of an individual structure, this footbridge is one critically important part of a gallery building(OCT gallery), which belongs to a large residential construction development project in Nanchang City, Jiangxi Province, China. As a symbolic structure, the design of the footbridge is supposed to reflect the local historic culture of the city, which locates at the bank of a large lake.

The foot bridge has a horse-shoe curved body of 80 meters long, providing the access from the gate to the first floor of the OCT Gallery building. Additional to the function of a ramp, this bridge is also expected to represent a special sign connecting the modern city and the natural elements including land and water.

The footbridge is spanning around an artificial lake, on the filled ground from an old lake. The Client and architect desire a unique structure of a curved geometry and no columns blocking the view. This is a main challenge on the structural design.

Figure 1: OCT Nanchang Gallery span over an artificial lake

Excellence

Figure 2：The profile of the whole footbridge

Figure 3: The architectural space created by the building and the footbridge

This footbridge has a box section made of double bridge beams with interval bracings and steel plates on both top and bottom. The strong stiffness of the bridge in torsion and shear enables the whole bridge work as an integrated curved beam, which are supported at the external bridge sides in the middle span, where the twist of the bridge can be transferred into end supports through the integrated bridge structure. Instead of cantilevered from the wall frames, the wall frame only provides the vertical pin supports to the bridge with no rotational stiffness.

Figure 4: The main body of the footbridge supported by the wall frames hidden behind the wall

Creativity and innovation

The main innovation point of this design is the integration of the bridge and wall structures, which enables the “hiding” of bridge columns from the view and introduces a visual impact of a elegant footpath floating over a lake. The curved bridge need vertical supports, and the wall frame need lateral bracing. Therefore the wall frames only provide the vertical stability and the lateral stability is mainly achieved by the curved geometry of the bridge while all the wall frame columns are fixed supported to obtain additional structural stability.

Figure 5: Bridge handrail and decking details

Elegance and good detailing

Figure 6: The elegance of the Gallery building joining to the footbridge

Figure 7: The construction details of the bridge steel structure

Figure 8: The bridge landing supports at the 1^st floor as cantilever truss protruded.

A spatial curved footbridge is carried by limited number of supports protruded from the hidden wall frames. To reduce the bridge span, the last three supports at the first floor are provided by the cantilever of the wall frames. All the steel frames will be enclosed by steel plates to form an elegant profile.

Sustainability

The ground under the bridge was top soil backfilled into an old lake The direct supports under the bridge would require a substantial and complicated foundation system, which is avoided by relocating the foundations through the innovative design. The pinned connection between the wall frame and bridge also reduce the cost of the maintenance in long term and deconstruction work after design life.

Value

As the most attractive element of the commercial residential project, the OCT Gallery of elegant profile presenting through the footbridge, improve the quality level of the whole project for the client and tenants of the properties. Combined with surrounding building of modern and classic styles, the bridge together with water fully inherits the local traditional Chinese culture.

Figure 9: The structural element arrangement of OCT gallery.

Summary

From the view points of both architecture and structural engineering, the footbridge is much more than an access path. It is a symbolic structure that bridge body of box sections supported by the supports almost invisible, produce a high impressive view to the public. It’s an important bracing structural element to the main building and the cladding wall frame. The innovative design enables the footbridge perfectly integrated into the OCT gallery building.