Westchester County Department of Public Works
Savin Engineers provided structural evaluation and design services for the removal and replacement of the aging steel dome roofs on three anaerobic sludge digesters. This project was completed on a 'fast-track' basis with extremely short turn-around times. It involved close coordination with plant personnel and the removal contractor during the first phase. The existing roofs consisted of structural steel framing with a steel deck plate overlain by insulation and a roofing membrane. Two of the digesters are 70-feet in diameter; the third is 56-feet in diameter. All three domes are unsupported by interior columns for their entire spans.
Design for the removal of the existing roofs included the installation of shoring towers and support trusses to secure the roof during removal and the placement of a 330 ton crane for removal of the entire dome assembly as one unit. Design of the new roofs included an evaluation of materials to resist the corrosive atmosphere of the digester interior. Materials investigated included carbon steel, stainless steel, aluminum, fiberglass and prestressed concrete. Design also included the installation of additional instrumentation for remote monitoring of tank liquid levels and gas pressures. Gas pressure relief valves were integrated with existing odor control facilities to reduce odors in the event of pressure blowoffs.