Concrete shear wall

A rectangular cast-in-place reinforced concrete wall segment to ACI 318-19 Chapter 11 (and Chapter 18 for special structural walls), by strength design with the ASCE 7-22 2.3.1 load combinations. The wall is checked in its plane (shear, combined flexure and axial force) and, optionally, out of its plane per foot of wall (simplified method of 11.5.3 or the alternative slender wall method of 11.8).

Inputs of the concrete shear wall #

• Wall: length ℓw, thickness h, the height of the entire wall hw (it sets hw/ℓw and αc, 11.5.4.3) and the unsupported height ℓc between out-of-plane supports (11.5.3, 11.8). The self-weight of the wall (unit weight prefilled at 150 pcf) is added to D: the full height hw at the base section in plane, and the half of ℓc above midheight for the out-of-plane strip.
• Reinforcement: one curtain (at the centre) or two (one at each face) of vertical and horizontal bars with their spacing, the clear cover to the vertical bars (it sets d for out-of-plane bending) and, optionally, concentrated end bars at each end with the distance of their centroid from the wall end.
• Materials: f'c, Grade 60 or 80 reinforcement, normalweight or lightweight concrete (λ by Table 19.2.4.1) and the modulus Ec (19.2.2.1).
• In-plane loads: per load type (D, L, Lr, S, R, W, E) the axial force P (compression positive), the in-plane shear V and the in-plane moment M at the section checked (usually the base). W and E act in both directions. See Loads and combinations.
• Out-of-plane: not checked, the simplified method (11.5.3: effective length factor k of Table 11.5.3.2 is an input), or the slender wall method (11.8). The loads are per foot of wall: the axial load at the top with its eccentricity from the centreline, and the lateral pressure. The service combination for the 11.8.4 deflection is D + (factor) × one of L, Lr, S, R + (factor) × W or E; the factors are inputs prefilled from commentary R11.8.4.1 (0.5 on live loads, 0.6 on W, which is conservative against the serviceability wind Wa it suggests, and 0.7 on E).
• Special structural wall: turns on Chapter 18.10. Inputs: the height above the critical section hwcs, the number of stories ns above it (ωv, Eq. 18.10.3.1.3), the overstrength factor Ωv (Table 18.10.3.1.2: the greater of Mpr/Mu and 1.5, prefilled 1.5; it is taken as 1.0 automatically when hwcs/ℓw ≤ 1.5), the boundary element method (displacement 18.10.6.2 or stress 18.10.6.3) and, for the displacement method, the top design displacement δu.
• Code options: the single-story basement / cantilever retaining wall exception to the two-layer rule (11.7.2.3).

Auto-design (editor toolbar) varies the thickness (1-in. steps) and the vertical and horizontal bars (size and spacing). Objectives: lowest cost index (concrete, formwork, reinforcement); thinnest wall, then cost; least reinforcement. Every other input is kept; see Auto-design.

Checks performed #

The drawings (on screen, in the report and on the DXF / PDF drawing sheet) show the wall elevation with the vertical and horizontal bars at their designed spacing and the end bars; plan section A at the wall end with the thickness, the curtains, the vertical bars at their designed positions, the horizontal bars, the end bars at their designed centroid and the cover; and the in-plane design interaction diagram φPn-φMn with every factored load point (not to scale). The arrangement and ties of the end bars, boundary elements, splices, openings and the foundation are not part of the calculation and are not drawn.

Limitations #

• Solid rectangular cast-in-place segments with deformed bars; no flanges, openings, precast or prestressed walls (the precast rows of Table 11.6.1 are not used), no welded wire reinforcement.
• One section (the base) in plane; in-plane slenderness, coupling beams, wall piers (18.10.8) and the strut-and-tie alternative for squat walls (11.5.4.1) are not covered.
• The horizontal shear reinforcement stress fyt is limited to 60 ksi for ordinary walls (Table 20.2.2.4(a), conservative reading) and to the bar grade for special walls.
• Out-of-plane design is per foot of a uniform strip: concentrated loads spread per 11.8.2.2 are the engineer's input as a load per foot. Only the curtain on the tension face is counted in φMn and Icr (conservative). For the service deflection Mn and Icr are taken at the service axial force.
• Special boundary elements are found where needed but not detailed (18.10.6.4 extent, width and transverse reinforcement; 18.10.6.5 where they are not required): these are advisories for the engineer.
• Ev, Ω0 and the 0.5L option of ASCE 7-22 are not modeled.
• Items to confirm against the code text (marked [verify] in the source): the radical in 18.10.6.2(b)(ii) b ≥ √(0.025cℓw) and the order of terms of Eq. 18.10.6.2b (the extracted text lost the layout); the 11.6.2(a) cap on ρℓ ("need not exceed ρt required for strength") is not taken below 0.0025 (R11.6.2); 18.10.2.1 as printed lets only ρt drop to the 11.6 values at low shear.

Verification examples #

The wall is verified against the free StructurePoint ACI 318-19 wall examples and hand calculations derived step by step in tests/test_verify_concrete_wall.py.

Hand calculations: