A 1970’s-era office complex located in the Midwest consisted of one three-story building and one five-story building with a courtyard. Exterior cladding for these buildings was comprised of precast reinforced concrete panels. In the Fall of 2015, a roof-level cladding panel fell to the ground without warning. As a result, CTLGroup was called to investigate the causes of the incident.
The fallen panel and its connections to the building frame were investigated. This investigation revealed that the connection plates on the building frame had failed either by cracking of embedment concrete or fracturing of welds. Based on these findings, the connections of a significant number of additional panels were investigated. Findings of the broader investigation revealed widespread cracking of building frame concrete at connection locations, failed welds, and undocumented revisions to panel connection details. Structural analyses indicated the presence of large forces in connections due to restraint of panel volume changes. These large forces were determined to be the cause of the connection failures.
Cladding connection repairs were designed and included the installation of new, supplemental steel connections between the panels and building frame. Repair work was performed during off-hours to minimize disruption to office tenants. The work was completed in 2016.
