Silman assisted in the modernization of the Internal Revenue Service Building – the first of the large federal office buildings to be constructed in Federal Triangle in 1928. The building houses seven floors of office and support space, and is divided into four quadrants (completed in 1928) and an annex (completed in 1936). Modernization of this project included reconstruction of the entire basement slab structure, support for new mechanical systems, and evaluation and investigation of the building’s historic façade.
The IRS Building is steel framed, supported on a pile foundation with a basement slab-on-grade. The basement level showed evidence of soil subsidence up to 3 feet, which compromised the structural integrity of the floor slabs. Silman designed the new basement level structure to replace the damaged slabs. Through detailed non-destructive investigations and geotechnical investigations, the cause and potential alternate solutions to wholesale replacement of slabs were developed. Additional studies were performed to evaluate the capacity of existing foundation systems for the additional weight of new framed levels.
In an effort to improve the security of the building, Silman upgraded the windows to resist blast loads and checked walls for a balanced design against blast pressure. This involved analyzing the existing structure and working with blast consultants to compare analysis. Coordinated field testing was then performed to determine material properties and strengths, and to check the results provided by blast consultants of full blast testing.
Façade investigation included masonry limestone and marble systems. Various environmental elements had stained and damaged the façade and structural issues included keystone settlement and cracking distress at courtyard and railing anchorages. Cleaning and repair recommendations were made with consideration to the historic sensitivity of the building materials and knowledge of the Secretary of the Interior’s standards.