Deborah Slaton and David S. Patterson, AIA
On a building constructed in 1929 with exterior loadbearing masonry walls, modifications were made to loadbearing masonry demising walls during past renovation efforts. A recent investigation has revealed these modifications present a serious structural stability problem for the building.
The building consists of two adjacent rectangular sections of equal width; one approximately 14 m (45 ft) in height, and the other approximately 18 m (60 ft) tall, creating a tower relative to the lower section. A three-wythe loadbearing masonry wall separates the two sections of the building and serves as the exterior wall of the tower where it extends above the roof of the lower portion of the building. Both building sections are steel framed; however, the spandrel beams of the tower rely on the masonry demising wall for bearing (without benefit of steel columns). The roof framing for the tower and lower portion of the building also rely on the masonry demising wall for support.
During the investigation it was discovered several openings had been made in the loadbearing masonry demising wall directly adjacent a common exterior wall where the demising wall terminated, apparently to accommodate the passage of mechanical ductwork (which has long since been abandoned and removed). One such opening, approximately 1.5 m (5 ft) wide and 1 m (3 ft) in height, occurred directly adjacent the common exterior wall of the building; creation of this opening undermined the end support for a spandrel beam. Recognizing the masonry above the opening needed to be supported, the contractor who created the opening fashioned a lintel utilizing two 2x12s laid flat (in the weak direction) supported at each end by two 2×4 jack studs. The jack studs at the edge of the opening adjacent the exterior wall rested on the top of the undermined steel bearing plate for the spandrel beam; however, no supplemental support was provided for the bearing plate itself. Support of the masonry above other openings made in the demising wall was also discovered to be insufficient or non-existent.
The undermining of the wall’s integrity, and insufficient support of the masonry, are evidenced by significant cracking that has occurred in the masonry above the opening, as well as outward movement of the exterior wall adjacent the demising wall. These conditions raise the question: what were they thinking when these modifications to the demising wall were made?
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.
Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at email@example.com.
David S. Patterson, AIA, is an architect and senior principal with WJE’s office
in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. He can be reached at firstname.lastname@example.org.