These recommendations are for the determination of connection proportions and details that are intended to provide for adequate performance of the connection of cast-in-place reinforced concrete slab-column connections. The recommendations are written to satisfy serviceability, strength, and ductility requirements related to the intended functions of the connection.
Design of the connection between a slab and its supporting member requires consideration of both the joint (the volume common to the slab and the supporting element) and the portion of the slab or slab and beams immediately adjacent to the joint. No reported cases of joint distress have been identified by the Committee. However, several connection failures associated with inadequate performance of the slab adjacent to the joint have been reported. Many of these have occurred during construction when young concrete received loads from more than one floor as a consequence of shoring and reshoring. The disastrous consequences of some failures, including total collapse of the structure, emphasize the importance of the design of the connection. It is the objective of these recommendations to alert the designer to those aspects of behavior that should be considered in design of the connection and to suggest design procedures that will lead to adequate connection performance.
Previous reports and codes (ACI 318) have summarized available information and presented some design recommendations. The present recommendations are based on data presented in those earlier reports and more recent data.
The recommendations are intended to serve as a guide to practice.
These recommendations apply only to slab-column connections in monolithic concrete structures, with or without drop panels or column capitals, without slab shear reinforcement, without prestressed reinforcement, and using normal weight or lightweight concrete having design compression strength assumed not to exceed 6000 psi. Construction that combines slab-column and beam-column framing in orthogonal directions at individual connections is included, but these recommendations are limited to problems related to the transfer of loads in the direction perpendicular to the beam axis. The provisions are limited to connections for which severe inelastic load reversals are not anticipated. The recommendations do not apply to multistory slab-column construction in regions of high seismic risk in which the slab connection is a part of the primary lateral load resisting system. Slab-column framing is inappropriate for such applications.
These recommendations are limited to slab-column connections of cast-in-place reinforced concrete floor construction, including ribbed floor slab construction and slab-column connections with transverse beams. Recommendations are made elsewhere (ACI 352R) for connections in which framing is predominantly by action between beams and columns.
The recommendations do not consider connections with slab shear reinforcement, slab-wall connections, precast or prestressed connections, or slabs on grade. The Committee is continuing study of these aspects of connection design. Relevant information on these subjects can be found in the literature. (See References 5, 11, and 13 through 18 for slab shear reinforcement, References 19 and 20 for slab-wall connections, and ACI 423.3R, and References 21 through 26 for prestressed prestressed connections.) Although structures having concrete compressive strength exceeding 6000 psi are within the realm of this document, the recommendations limit the assumed maximum value of compressive strength to 6000 psi.
Slab-column framing is generally inadequate as the primary lateral load resisting system of multistory buildings located in regions of high seismic risk (such as Zones 3 and 4 as defined in ANSI A.58.1 and UBC) because of problems associated with excessive lateral drift and inadequate shear and moment transfer capacity at the connection. In regions of high seismic risk, if designed according to provisions of these recommendations, slab-column framing may be acceptable in lowrise construction and multistory construction in which lateral loads are carried by a stiffer lateral load resisting system. In regions of low and moderate seismic risk (such as Zones I and 2 as defined in ANSI A.58.1 and UBC), slab-column frames may be adequate as the primary lateral load resisting system, provided the connection design recommendations in this document are followed.