By Joe Porcaro, PE
Concrete and masonry structures that display visually severe distress warrant the intervention of an experienced specialty structural engineer to enable the owner to develop an informed and cost-effective strategy based on multiple options. Owners may not be aware of the stabilization with strengthening in-place (SSIP) option. An uninformed decision for demolition (rip-out) and replacement (ROAR) of the partial structure shall be regarded as the worst-case option. This scenario is most pertinent for historic structures. Preservation engineers can provide owners with a range of options that are sustainable and maintain the historic fabric and aesthetics.
The historic First Lutheran Church in New Britain, Conn., was completed in 1906. Because of an extended history of continual and pervasive water intrusion to the occupied space, and the resultant severe structural distress of the stone (dolomitic marble) masonry facades, the church congregation was compelled to seriously evaluate drastic options.
Both towers of the church are composite walls comprised of ashlar stone masonry veneer (rectangular units) and multiple wythe brick masonry back-up. The ashlar is random (not coursed); the dolomitic marble was quarried in Ashley Falls, Mass.
Structural distress included substantial and visually evident separation (bulging) of the stone wythe from the brick masonry back-up, dimensional distortion and instability at the corner of the South Tower, various types of joint mortar deterioration, step cracks in veneer, and separation between wood frames for stained glass windows and stone veneer. In addition, the interior plaster finishes were subjected to continual deterioration, disengagement, and costly repairs caused by water intrusion.
Abandonment of the historic church or demolition of the upper and lower sections of both towers appeared to be the only viable options. The preservation engineer obtained cost proposals from multiple contractors for demolition. Subsequently, a vote by the congregation to remain and the financially non-viable demolition cost rendered these options unacceptable. Chain-link fencing and a steel cable system were installed previously for public safety and to capture stone veneer that demonstrated incipient failure with separation to the sidewalk below.
However, implementation of integrated structural remedial methods with laboratory and field tests in conjunction with a non-conventional project delivery system resulted in preservation of the building’s historic fabric and aesthetics. Very substantial cost reduction of approximately 50 percent was realized with this system compared to the demolition option. The towers were structurally stabilized and strengthened in-place (SSIP) rather than demolished. The drastic option of demolition (rip-out) and replacement (ROAR) was avoided successfully.
Laboratory and field tests utilized by the structural engineer included petrographic examination of both the original and re-pointing joint mortar, core drilled samples of the brick masonry back-up, surface penetrating radar, and asbestos content of existing sealant in combination with detailed visual reviews for structural condition investigation. Remedial methods consisted of engineered, stainless steel grout injection anchors (approximately 400); tuckpointing; trowel-applied repair of marble veneer; removal, replacement and re-construction of localized areas of veneer and brick masonry back-up; pressure grouting between stone and brick wythes; water repellent; as well as extensive repair and partial replacement of wood frames for exterior windows.
A non-conventional project delivery system to minimize owner costs included having the owner purchase bulk materials directly from the manufacturers. Four distinct subcontractors implemented the overall project with integrated means and methods. The structural engineer’s role was construction advisor, schedule coordinator, and quality assurance. The owner functioned as the general contractor. Access for towers was primarily by means of mast climber platforms supplemented and interconnected with pipe scaffolding.
The First Lutheran Church is listed on both the National and Connecticut State Register of Historic Places.
Joe Porcaro, PE
AJP Engineering, LLC