"Our aspiration was to be scarless. We wanted the memory of the weld to be very discreet."
Part transportation center, part event space, and part community gathering place, Dilworth Park is a lively, multipurpose hub immediately adjacent to Philadelphia's iconic City Hall. When designing a café for the renovated park, we wanted to honor the structure's one-of-a-kind backdrop in a way that complimented City Hall's intricate masonry. One of the reasons City Hall is so striking is the singularity of its material–the building's stone exterior is both structure, finish, and envelope. We envisioned a new building that would likewise reflect its singularity with architecturally exposed structural steel (AESS) acting as both structure and finish.
AESS already has a higher tolerance, finish, quality, and appearance than traditional structural steel. However, like City Hall's elaborate masonry, the café's steel needed to push the boundaries of what AESS can look like. We wanted to exceed AESS's regional and national standards, increasing its tolerance, durability, graffiti resistance, and ease of maintenance. But most importantly, we wanted to preserve the mystery of how the steel is assembled by making its welds as seamless as possible.
The joints between welded steel are usually grinded down to minimize their appearance, but most welds still leave a scar. For Dilworth Park's café, we wanted to avoid that scar and create the illusion that the café had been crafted from a single piece of cast steel. After developing a method to achieve these unscarred welds, we recruited a local fabricator and asked him to test our design in a simulation that recreated on-site conditions.
The end result was a mockup that tested overhead welds and joined three different structural components. The process proved that this type of weld was possible and helped us identify potential challenges and obstacles. Additionally, we were able to use this mockup as part of our pre-bid process to ensure that the contractor had proof of our specifications to compare with the on-site construction. Thanks to this effort, the finished building includes a thin roof edge joined with an invisible weld that enhances its contemporary, timeless design.