Structural integrity of precast concrete modular construction

■ Recommended updates to design guidelines and connection details to preserve structural integrity in precast concrete modular construction are presented. The American Concrete Institute’s (ACI’s) Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19) contains structural integrity provisions for precast concrete panel buildings but does not address the structural integrity of precast concrete modules. ACI 318 requires spaced steel ties in all directions to tie the precast concrete panel elements together. These criteria are impractical for precast concrete modules due to the construction methods and the overall rigidity of each module. Precast concrete modules are inherently stable, even when subjected to General Services Administration (GSA) criteria for partial removal of structural walls or corners, which require that if a portion of a wall or an entire module is removed, the remaining portions must have sufficient capacity to carry the resulting gravity loads. This paper examines the stress increases due to partial wall removal and the possibility of total module removal. It discusses strength reserves, provides recommendations for future editions of ACI 318 and the PCI Design Handbook: Precast and Prestressed Concrete, and presents conceptual connections that provide the continuity and ductility needed to maintain structural integrity following total module removal.