Skyscape is the design proposal by RZAPS for Courtland Street/Ralph McGill Boulevard Bridge in Downtown, Atlanta.
The city of Atlanta has long been considered a horizontal landscape of autonomous neighborhoods distributed over a large metropolitan area. The central core of the city is experienced by many via Interstate 75/85 (Atlanta Connector). With the ongoing transformation that has brought in an influx of new residents and businesses, increasingly the freeways are not just for circulating within the greater metropolitan area but also to access the streets and neighborhoods of Downtown Atlanta.
The bridge enhancement program can effectively communicate to a very broad audience the arrival of Downtown as a diverse and vital urban distinct. With the 20th Anniversary of the American Institute of Architects’ Legacy Project, an improvement of the bridge will continue the tradition of providing an architectural addition of lasting value affirming the city’s aspirations to improve its core for the 21st century and make it a better place to live and work.
RZAPS has been selected and awarded as a finalist of the Atlanta Bridgescape Competition with the design proposal SKYSCAPE.
The idea of Skyscape sprang from an awareness that of primary importance was the need to redefine the existing relation of the large irregular geometries of the bridge to its surrounding context.
Skyscape “smoothes out” the uneven edges creating a three-dimensional “facade” on the bridge for both those on the bridge and those below on the freeway.
Skyscape is a complex geometry designed using a computer-assisted parametric process. The development of geometrically complex structures is iterative, from analysis to modeling, computation and modifications, seamless between design and construction. Technical feasibility and costs are the most important influencing constraints that can be studied via the parametric process. The derivation of forms is the result of surface triangulation (based on a 3D Delaunay algorithm) that optimizes the quantity of material used and minimizes structure. The same geometrical model is brought into another computational process in order to define costs and prepare for the fabrication. All supporting structure and surfaces, including cladding and joints, are derived this way.
Typically the main goals of “rationalization” through the parametric process focus on minimizing gaps between adjacent elements and improving the properties of geometric offsets. Being open-air without the need to be watertight allows us significant latitude in this respect. An additional benefit is that the open site allows for on-site prefabrication.
Skyscape is a “kit of parts” comprised of metallic triangular panels that are held by a frame. Inspired by the safety fencing used on overpass bridges, the material is common and relatively low-cost; consisting of three self-framing structures comprised of a steel-tube supporting frame with roll-formed panels and steel attachments. Using the triangle, the most stable form in nature, allows the elements to be oriented along three directions creating a structure reminiscent of a cloud.
The structure is derived from 3D-Delaunay triangulation, a mathematics and computational geometry, where the smallest angles are maximized to provide a frame of great stability and highly stress resistant joints. The geometry generated by the algorithm for computing the triangulation was derived using a Finite Elements Software whereby performance is analyzed against main case loads to define its shape. The optimal configuration that reduces the skin displacement in critical points and the size of the framing was defined through an iterative process of form finding. By adding connections to the ground loads the structure was greatly reduced with almost all moment frames eliminated. The resulting canopy structure is comprised of a double frame HSS 4 x 0.250 pipe section with a single frame HSS 6 x .0.335 pipe section along the edge of the geometry.
Computer generated techniques allow for the surface perforations to be finely calibrated in terms of gradient; that through a parametric algorithm manages their distribution in terms of the opening (hole) size (IN) and the percentage of open area (OA). The surface perforations respond to three circumstances: providing rain/sun protection while underneath, viewing the freeway below and the city beyond, and for the motorist looking up from below. The process allows for the design of a configuration of surface perforations that precisely responds to the different circumstances of the site while providing output data for fabrication.
An important part of the design process consists of the optimization of the input data for the complex surface. To design the panel layout and the parametric details of the steel members the geometry generated by the algorithm is brought into a different computational process. The main triangular geometry is subdivided optimizing the panel area for laser-cutting with maximum efficiency in terms of material and cost. By providing real time output data, the algorithm allows management of the characteristics of the geometry: surface area, perimeter, weight, barycenter (center of mass), and laser-cut boundary of each element. The design and manufacturing constraints are updated dynamically based on available resources.
At street level, the project area includes three zones of Folk Art Park: Homage to St. EON’S Pasaquan, Rolling Hills of Georgia, and Windmills. The park originally was intended to enliven these highly visible, unused public spaces by displaying some of the state’s folkloric art and currently is in need of improvements. Folk art expresses cultural identity by conveying shared community values and aesthetics. The art form encompasses a range of utilitarian and decorative media often using whatever materials the artist is able to acquire.
The artwork, experienced in the context of a cloud, will be doubly felt as a culmination of imagination. A writer recently described American folk art as providing all the “benefits of a grandmother: it weaves beautiful tapestries, tells elaborate legends which creep into your dreams and are equally precious to your heart from childhood to adulthood.” The Cloud provides the context within which generations can build memories of their city and dreams for its future. The Cloud may also become a metaphor of infinite associations: everything from the literary history of the South, with its unique use of language to convey landscape, to cloud computing – an association to Atlanta’s fast-growing tech business sector.