Section 18.10.1/Special Structural Walls (Shear Walls)
ACI 318-19 Section 18.10 covers design and detailing for special structural walls in seismic design categories D, E, and F.
Special structural walls in SDC D, E, and F must meet the detailing requirements of Section 18.10 (the section numbers shifted in ACI 318-19; the provisions are in 18.10 for walls). These include minimum wall thickness, boundary element requirements at wall ends and openings where compressive strains exceed limits, minimum distributed horizontal and vertical reinforcement ratios of 0.0025, and maximum spacing of distributed reinforcement. Boundary elements require closely spaced confining ties similar to column ties to prevent concrete crushing and rebar buckling under cyclic seismic loading.
Why this section exists
Shear walls are the primary lateral force-resisting element in many concrete buildings. During an earthquake, the wall edges experience extreme compression and tension as the building sways. Without special detailing, the compressed edge concrete crushes, the vertical bars buckle, and the wall loses its ability to resist further cycles. Boundary elements with confining ties prevent this failure by holding the concrete and rebar together through multiple earthquake cycles.
What plan reviewers look for
Plan reviewers check shear wall sections and elevations for boundary elements at wall ends and around openings. They verify the confining tie spacing and configuration within boundary elements. They check that the distributed horizontal and vertical reinforcement meets the minimum ratio (0.0025 each way). They verify that the boundary element length is based on the compressive strain analysis, not just an arbitrary dimension.
Common violations
Related ACI 318 requirements
Section 18.10 (in ACI 318-19) provides the detailed requirements for special structural walls. Section 22.5 covers the shear strength calculation for walls. ASCE 7-22 Section 12.2.1 covers the seismic design category determination that triggers special wall requirements. Section 18.10.6 covers boundary element triggers and detailing.