THE CHALLENGE
Completely restore and renovate the exterior and interior of the four-story Amory Building and the eleven-story Blake Building to convert into to the iconic Godfrey Hotel.
CBI’S SOLUTION
CBI Consulting Inc. was the Engineer of Record for restoration of the façade. To meet budget constraints and retain as much of the historical fabric as possible, the original metal was retained and refurbished to start the next 100 year cycle. It originally appeared the terracotta was beyond salvage, but an additional study was funded to determine the extent of salvage of individual elements. CBI developed a “deconstruct mockup” process to view a portion of the existing wall as a representative sample, so rather than building a mockup wall section of a typical bay to study the cost of a detailed rehabilitation, the process consisted of quantifying through test cuts and excavating terracotta elements, some of which were repairable and others beyond salvage. This process revealed that on a floor by floor basis, stones were bearing one on another and at each floor level, supported on steel brackets which were a component of the structural steel sub-frame.
Replacement products that were considered included traditional terracotta, glass fiber reinforced polymer (GFRP), and precast concrete. GFRP elements, although economical, are not easily adaptable as bearing pieces which meant removing existing stones that could otherwise remain, simply to allow full floor height run of GFRP between steel brackets. Terracotta was discounted because of limited replacement quantities, and that over nine different shapes/sizes would be needed. A local pre-caster responded with a desirable turnaround time for concrete replication and provided the opportunity to use multiple templates.
The next task was to develop a method to secure terracotta pieces that were intact yet no longer secured by the original ¼” square ties that had long since deteriorated as a result of environmental corrosion. Some ties simply corroded through their cross section resulting in no damage to the stone (terracotta) so the stones could be reused. In other cases, oxidation corrosion of the steel (rust jacking) caused pressure so extensive that the stone split or spalled, requiring replacement. In order to salvage as much original terracotta as possible, an effort was set in motion to determine how to best secure the stone.
The approach that ended up working was the use of helical anchors. Test installation using blind installation conditions followed by pull tests and exposing the anchor attachment within the wall for observation were successful. Anchors could be drilled from the exterior to anchor to the masonry substrate or in another condition to secure to the wood framing of the abandoned window counterweight boxes that were part of the original construction. Timing the installation of the helix anchor to the complete demolition of the original building interior allowed observation of the anchor installation from the interior to be sure that the substructure intended to secure the anchor was adequate.
Having the benefit of the “deconstructed mockup” and with mast climbers in place to facilitate closer observation of the façade, the team was able to salvage more than 75% of the existing terracotta. The original estimate of 25% replacement on which the job was budgeted and approved, was all the more conservative and ultimately reduced to approximately 13% replacement.
