This historic adaptive reuse project is a part of the Plant Riverside District, a 670,000-square-foot complex located just feet away from the Savannah River in Georgia. Initially built in 1912 as the Savannah Electric & Power Company’s power station, the building sat vacant from 2005 until 2016.
Transforming the skeleton of the Savannah Power Plant building into a new JW Marriott Hotel from the inside out, the open space of the original boiler room was replaced with five levels of new framing. The engineers used composite steel joists topped with four inches of lightweight concrete on composite metal deck. The use of this system eliminated the need for foundation retrofit at all gravity columns while satisfying the tight floor-to-floor clearance requirements.
For the structural design firm on the project, Browder + LeGuizamon and Associates, a major structural challenge was the analysis and re-design of the building’s lateral system, triggered by replacing and adding entire floor levels as well as installing large new openings in the exterior masonry walls. Most of the original building was not designed for lateral resistance; however, thanks to the availability of archived structural drawings, the engineers pieced together a 3-D analysis model, which included details of built-up beams and columns to study the global behavior of the building pre- and post-renovation. The structural retrofit necessitated the installation of new steel braces through both new and existing beams and the complete replacement of existing braces to accommodate stairs and corridors. The engineer’s design and sequencing eliminated the need for temporary bracing while supporting two 115-ton existing steel stacks. Additionally, brace lines had to be located to work with the usage of the public areas on the lower level. The industrial feel of the power plant lent itself to the incorporation of primary structural elements into the interiors. It was a key in successfully combining structural functionality with design aesthetics.
Outside of design and constructability considerations, Browder + LeGuizamon engineers collaborated closely with the project’s architect, Campo Architects, to maintain the historical character of the renovated building. This was most apparent in the roof framing of the powerplant’s turbine hall with its existing 55-foot-long roof trusses spanning across the three-story atrium, which became the hotel’s main lobby. The original trusses had to be maintained despite the need to install two levels of a suspended walkway around three sides of the atrium to provide access to guest rooms. Suspending the walkway from the trusses required strengthening of all chords and web members, including their connections, therefore altering most of the historically authentic features of these members. Engineers solved this issue by installing new back-span beams behind the existing columns together with cantilevered outriggers on the lobby side that were moment-connected through the column. Walkway beams then spanned between the outriggers, and faux hanger rods and clevis were added to give the appearance of a suspended walkway. However, creating the moment connection posed a challenge of its own due to the joint’s inaccessibility and space constraints for welding. This had to be resolved through intensive coordination with the steel fabricator.
Beyond usage as a luxury hotel and entertainment center in Savannah, the building had also to perform an essential function of being the central link to the other buildings in the complex. This called for designing connecting tunnels through the basement level to the adjacent buildings on the west and east side. The tunnel to the West Hotel was particularly challenging due to an existing five-foot-deep grade beam supporting the entire west façade and new entrance canopy, which meant that the grade beam had to remain in place during construction. The challenge was to maneuver the position and slope of the 6-foot by 10-foot tunnel in such a way as to pass under the grade beam, a particularly difficult task due to limited space and adjacent foundation walls that had to be shored during construction. The engineers further utilized the tunnel’s concrete walls as support for the canopy column to simplify construction.
Browder + LeGuizamon developed multiple design options for each renovation component and examined these for constructability and level of impact on the existing structure before selecting optimal solutions. This complex renovation was successfully completed thanks to the well-thought-out design, quick reactions to unforeseen conditions in the field, and close collaboration with Campo Architects and AECOM Hunt, the general contractor for the project.■
Browder + LeGuizamon and Associates, Inc. was an Outstanding Award Winner for the Savannah Plant Riverside Project in the 2021 Annual NCSEA Excellence in Structural Engineering Awards Program in the Category – Forensic/Renovation/Retrofit/Rehabilitation Structures over $20M.
