East Market: Restoring Philadelphia’s “Main Street”

East Market lays between Philadelphia’s booming business, shopping and entertainment district of Center City and its eastern Old City district. Bound by Market, Chestnut, 11th, and 12th Streets, East Market is a 4.3 acre site that is playing a large role in transforming the area east of City Hall. Revitalizing the area is a crucial part of the City of Philadelphia’s plan to restore Market Street’s position as Philadelphia’s “Main Street.”

Phase one of the development, which topped off in November of 2016, is located on the corner of 11th and Market. Phase one is a 400,000-square foot steel frame development consisting of two floors of retail space, 15 floors of apartments (332 luxury units), and one level of below grade parking. Phase two of the East Market project, located at the corner of 12th and Market, began construction in January 2017 and will consist of another retail podium and residential tower.

The Harman Group, structural engineers and parking consultants for the project, had to determine how to structure the transformation of a difficult urban site to realize the vision of the developer, National Real Estate Development, and the architects, BLT Architects.

The sites of Phase one and Phase two interface with existing buildings on the south side, requiring structural modifications of the existing buildings to integrate them into the below grade infrastructure of the new project. While on the north side of the site, The Harman Group had to accommodate a Southeastern Pennsylvania Transportation Authority (SEPTA) subway tunnel. This required careful planning with various contractors as well as city and state agencies to ensure that the East Market project was being built to serve all users.

With buildings like East Market, The Harman Group’s engineers find it works best to layout out the column grid to work with a parking circulation plan and then work up, in this case to the residential and retail levels. Working with the architects, The Harman Group went through various iterations of a parking plan to evaluate the effects of different column layouts on the retail and residential spaces above. They eventually settled on a base grid of 27’-6” square, which allows for 24 foot wide drive aisles as required by Philadelphia building code, and allows for three parking spots in each bay.

The lateral system in the Phase one building posed a greater challenge than the column grid.  The apartment tower is an “L” shaped building. The Harman Group utilized a combination of concentric and eccentric braced frames in the sail direction of each leg of the “L”, while using moment frames in the perpendicular direction, again, in each leg of the “L”.

During the schematic phase of the project, all reasonable structural systems were considered for East Market. In the end steel frame won out for the combination of future flexibility in the retail areas, combined with economical floor to floor heights in the apartment tower with the use of plank on steel construction. The flexibility of a steel frame system has already come into play with modifications to accommodate the needs of retails tenants.

The Harman Group has been commissioned to complete work on Phase two of the project, a 250,000 square-foot, 21-story, residential tower constructed of steel and precast plank over a two-story retail podium. Steel erection for the Phase two podium began in January of 2017 and construction is expected to be completed by Fall of 2018.

Learn more about this project by visiting https://harmangroup.com/projects/east-market/

By Chris Gottschall