Track 1: Decline vs. Revival: Tempering the Impulse to Tear Down and Start Over
4 - Minimally-disruptive seismic strengthening and adaptive re-use of the Hibernia Bank building
Monday, September 24
2:45 PM - 4:15 PM
Location: BNCC- 101AH
The Albert Pissis-designed Hibernia Bank Building, an 1892/1904 Neo-classical Revival building in San Francisco, was lauded as an architectural masterpiece when originally constructed. Abandoned for nearly 20 years after its large central banking hall ceased to provide functionality for modern day banking operations, this unreinforced masonry building in the now-reviving Mid-Market district was the subject of a recently completed rehabilitation project. Despite its long term abandonment, the extraordinary historic interiors that extend throughout the main floor, and its monumental granite block masonry exterior elevations constructed from locally-quarried granite, remained essentially intact since their initial restoration following the 1906 earthquake-caused conflagration.
The project was initiated as a seismic-strengthening and adaptive re-use project, but economics dictated that the building also be modified to accommodate assembly occupancy. From the outset, the engineering team was committed to minimizing seismic and structural interventions that might needlessly destroy historic materials, locating supplemental structure deemed to be necessary in out-of-the-way parts of the building, and using new structural elements to leverage, rather than supplant, the existing structure. The extant rocking capacity of the masonry piers and walls that allowed the bank to survive the 1906 earthquake shaking was calculated to provide approximately 50 percent of the total lateral resistance needed to comply with present-day requirements. Selective supplemental retrofits that could be added surgically to improve integrity, stability, and continuity of vulnerable structural elements --- such as center cores with specially formulated polymer grout to boost the integrity of the masonry walls --- were designed to provide the balance of the required lateral resistance. The resulting project left the interiors, including the ornamental plaster, tilework and skylights in the banking hall, historic office spaces and entrances, and the exterior granite, virtually undisturbed. Interior hollow clay tile was stabilized rather than removed.
Avoiding disruption to the historic fabric required the development of several engineering “firsts”, including cold-formed steel shear walls using steel decking, which eliminated the risks of casting concrete in historically significant spaces, and permitted the geometry of the existing space, and all decorative trim features and floor tile to be remain unchanged. These walls were also more compatible with the stiffness of rocking masonry piers than concrete shear walls. Integration of the seven existing sub-diaphragms on the roof into a coherent whole was accomplished with carbon fiber and a system of reinforced concrete collectors, bond beams and “shear tabs” that interconnect the existing roof decks by means of pre-tensioned shear friction connections that preclude slippage and preloading of the carbon fiber. The use of pre-tensioned shear friction connections to prevent preloading of carbon fiber reinforcement was necessary to salvage the existing roof diaphragm and is also believed to be a first of its kind.
- appreciate that with appropriate attention to it, preservation goals can be prioritized and driven by engineers such that they are completely compatible with seismic safety goals.
- see how outside-the-box engineering can be utilized far more effectively than traditional brute force methods to minimize disruption to historic fabric without compromising seismic safety
- recognize that although adaptive re-use projects may entail substantial structural/seismic interventions with the potential to introduce risk to historic fabric, setting preservation as a project priority for all project team members at the outset of the project will enhance the feasibility of the project by reducing the risk
- see how non-traditional materials and methods of construction can be selected and incorporated into the structural design of interventions to reduce the risk of damage, thereby enhancing the success of an adaptive re-use project, even if substantial structural intervention is necessary