Precast Concrete Diaphragms - Special Inspections

Chapter 17, Table 1705.3, of the 2021 edition of the International Building Code (IBC) code book added special inspection requirements for precast concrete diaphragms. The reason for the additional code compliance criteria in Table 1705.3 is that IBC 2021 adopted ACI 318-19, “Building Code Requirements for Structural Concrete.” ACI 318-19, Section 26.13.1.3, requires inspecting concrete panel placement and reinforcement in precast diaphragms assigned to Seismic Design Categories (SDC) C, D, E, and F using moderate or high-deformability connections.

A special inspector must observe the installation of embedded parts and check for the completion of reinforcement continuity across joints and the completion of field connections when structures are assigned to SDC C, D, E, and F categories. The special inspection is continuous, focusing on the reinforcement continuity across the joint, embedded parts installation, and onsite connections completion. Special inspection type #12 in Table 1705.3 mirrors the ACI 318 requirement to check diaphragm connections against the installation tolerance requirement criteria ACI 550.5, “Code Requirements for the Design of Precast Concrete Diaphragms for Earthquake Motions.” This installation tolerance is usually ± ? inch according to ACI 550.5.

So what, exactly, is a diaphragm? A diaphragm is a structural element that transmits lateral loads to the vertical existing elements of a structure (such as shear walls or frames).

To summarize, two new items have been added to Table 1705.3 in the IBC 2021 version of the IBC code: special inspection types #11 and #12, discussed herein.

?IBC 2021, Table 1705.3, Special Inspection Type #11 For precast concrete diaphragm connections or reinforcement at joints classified as moderate or high deformability elements (MDE or HDE) in structures assigned to Seismic Design Category C, D, E or F, inspect such connections and reinforcement in the field for:

a. Installation of the embedded parts.

b. Completion of the continuity of reinforcement across joints.

c. Completion of connections in the field.

For more information or further enthusiastic discourse on topics of CODE, please contact Alan Tuck at: [email protected] or 540.344.7939.