Tilt-up wall panel
A site-cast concrete wall panel that spans vertically from its base to the roof, designed out of plane by the alternative slender wall method of ACI 318-19 11.8 with the ASCE 7-22 2.3.1 load combinations (strength design). A solid panel is one design strip over its full width. A panel with a door or window opening is designed as two design strips (legs), one on each side of the opening, by the approach of ACI 551.2R-15 7.2 as the StructurePoint tilt-up examples apply it: each leg carries the loads of its own width plus one half of the opening.
Inputs of the tilt-up panel #
- Panel: width, the height ℓc between the base and the roof support (the simply supported span of 11.8.2.1), the parapet height above the roof support, the structural thickness h (deduct reveals and form liners yourself) and the self-weight (150 pcf prefilled). The parapet weight is included above midheight; wind on the parapet, which would reduce the midheight moment, is conservatively not counted.
- Opening: none (solid panel), a door (from the base) or a window (with a sill height), its width and height and its distance from the left panel edge. Each leg must be at least 1 ft wide and the opening head must stay at least 6 in. below the roof support. The design strip width limit (12h prefilled) is the guideline of ACI 551.2R-15 7.2 ("about 12 times the panel thickness", not an ACI 318 limit): a wider leg counts only this width for strength and stiffness, while it still carries the loads of the whole leg plus half the opening.
- Reinforcement: one layer at the center or two layers (one at each face, with the clear cover), the vertical and horizontal bars and spacings (per layer), the bars added at each jamb (left and right separately; with two layers, the total of both faces, half of which are taken on the tension face), and the header bars above the opening. The vertical steel of a strip is As = Ab b / s plus the jamb bars (the area per width, not a bar count).
- Materials: f'c, Grade 60 or 80, normalweight or lightweight concrete and Ec, as in the other concrete types.
- Loads: roof reactions at points along the top (joists or girders: load type, value, position from the left edge and eccentricity from the panel centerline), line loads along the top (ledger, deck) with their eccentricity, the strength-level wind pressure W and an optional strength-level out-of-plane seismic pressure E (for example ASCE 7-22 12.11.1). With an opening, the roof loads are shared between the legs as a simple beam across the panel top supported at the leg centerlines (statics; loads outside the centerlines are cantilevered); the lateral pressure acts on the tributary width (leg + half the opening) over the full height, which is conservative for a window.
- Code options: the row of Table 11.6.1 (a tilt-up panel is cast elsewhere than its final position and so is precast by the ACI 318 definition; the cast-in-place row is the conservative choice of the StructurePoint and ACI 551 examples and is prefilled), the precast wall exposure (spacing limit 18 in. exterior, 30 in. interior, 11.7.2.2) and the service factors on L-type loads (0.5), W (0.6) and E (0.7) for the deflection check (R11.8.4.1: D + 0.5L + Wa, D + 0.5L + 0.7E; Wa from serviceability wind speeds may be less than 0.6W).
Auto-design (editor toolbar) varies the thickness (1/4-in. steps), the vertical and horizontal bars (size and spacing) and the added jamb bars at each side of the opening. Objectives: lowest cost index (concrete, reinforcement); thinnest panel, then cost; least reinforcement. Every other input is kept; see Auto-design.
Checks of the tilt-up panel #
Every strip is checked for every ASCE 7-22 2.3.1 combination of the load types present; the step list shows the governing one.
| Check | Basis |
|---|---|
| Out-of-plane flexure with P-Δ | Pum = Pua + factored self-weight above midheight; Mua = wu ℓc²/8 + Pua e/2; Icr = n Ase (d − c)² + b c³/3 with n = Es/Ec ≥ 6 and Ase = As + Pu h/(2 fy d) (Eq. 11.8.3.1c, R11.8.3.1); Mu = Mua / (1 − Pum/(0.75 Kb)), Kb = 48 Ec Icr / (5 ℓc²) (Eq. 11.8.3.1d, the closed form of 11.8.3.1(b)); Δu = Mu / (0.75 Kb) (Eq. 11.8.3.1b); against φMn at Pum by strain compatibility (22.2), φ = 0.90 |
| Tension-controlled section | εt ≥ εty + 0.003 for every combination (11.8.1.1(b), Table 21.2.2) |
| φMn at least Mcr | Mcr = fr Ig / (h/2), fr = 7.5λ√f'c (11.8.1.1(c), 19.2.3.1) |
| Axial stress | Pum / Ag ≤ 0.06 f'c at midheight (11.8.1.1(d)) |
| Out-of-plane shear | Vu = wu ℓc / 2 against φVc of Table 22.5.5.1(c) with λs (11.5.5.1), axial compression neglected |
| Service deflection | Δs by Table 11.8.4.1 with Ma = Msa + Ps Δs iterated (Eq. 11.8.4.2), Δcr and Δn by Eqs. 11.8.4.3a and b (Mn and Icr at the service axial force), Δs ≤ ℓc/150 (11.8.1.1(e)); service combinations D + (factor) W or E with and without each L-type load |
| Minimum reinforcement | Table 11.6.1, cast-in-place or precast row (the engineer's choice) |
| Bar spacing | 3h and 18 in. (11.7.2.1, 11.7.3.1) or, for precast, 5h and 18 / 30 in. (11.7.2.2, 11.7.3.2) |
| Two layers | Walls thicker than 10 in. (11.7.2.3) |
| Bars around the opening | At least one No. 5 bar (one layer) or two (two layers) at each jamb and at the header, in addition to the minimum reinforcement (11.7.5.1) |
| Strip method | Advisory when the opening is wider than ℓc/2 (ACI 551.2R-15 7.2 guideline) |
The drawings (on screen, in the report and on the DXF / PDF drawing sheet) show the panel elevation (outline, parapet, roof support line, opening, widths and heights), the typical wall section through the (left) design strip (supports, roof reaction with its eccentricity, the lateral pressure over ℓc, the vertical bars) and a plan section at the jamb (thickness, vertical bars at their spacing from the opening edge, jamb bars, horizontal bars, cover). Bar lengths, laps, header bar anchorage, embeds, lifting inserts, braces and the footing are not part of the calculation.
Limitations #
- One opening at most; a panel with two or more openings, a multi-story (continuous) panel or a panel with a thickened pilaster is not covered.
- In-plane shear and overturning of the panel (a shear wall), the header above the opening as an in-plane deep member, and the connections (ledger, embeds, roof and base anchorage) are not designed; 11.8.2.2 (spreading of concentrated loads) is replaced by the strip tributary widths.
- Lifting, stripping and bracing are not checked. The methods for handling stresses (insert patterns, impact factors, the stress limit against the modulus of rupture) are in ACI 551.2R-15 Chapter 8 and the Tilt-Up Concrete Association manuals, which are not freely available; no free worked example could be obtained (a free MIT thesis on lifting stresses could not be downloaded). See research/DOCUMENTS_NEEDED.md.
- Only the bars at the tension face count in φMn and Icr (the compression layer of a two-layer panel is neglected, conservative); the compression and tension directions of W and E are taken as the same magnitude.
- The lateral load acts over ℓc only; wind on the parapet and the base fixity are neglected. Ev and the Ω0 load combinations of ASCE 7-22 are not modeled.
Verification examples #
Verification status: 66 values compared in 5 examples (3 published, 2 hand calculations from the cited equations): 66 within tolerance, 0 recorded deviations. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.
The panel is verified against the two free StructurePoint ACI 318-19 tilt-up examples (ACI 551.2R-15 Examples B.1 and B.2) and hand calculations derived step by step in tests/test_verify_tilt_up_panel.py (66 values).
| Example | Source | What it checks | Published | ILX Calcs |
|---|---|---|---|---|
| SP-TU | StructurePoint, Tilt-Up Wall Panel (ACI 318-19 – ACI 551), pp. 8–12, 36 | Solid 15 ft × 6.25 in. panel, 16 #6, ℓc = 29.5 ft, 1.2D + 1.6Lr + 0.5W | Self-weight above midheight 19.04 kips, Pum = 43.49 kips, Mua = 24.77, Mu = 61.00, Mn = 106.55, Mcr = 46.32 kip-ft, Icr = 353.56 in⁴, Kb = 97.64 kips; service Ps = 26.24 kips, Msa = 20.32, Ma = 20.84 kip-ft, Δcr = 0.550, Δs = 0.247 in. | equal within 0.1 % |
| SP-TUO-L | StructurePoint, Tilt-Up Wall Panel with Opening (ACI 318-19 – ACI 551), pp. 8–13, 27 | Left leg, 4 ft + 5 ft tributary, 7 #6 | Joist loads 4.48 / 4.67 kips, Pum = 31.87 kips, Mua = 14.92, Mu = 31.68, φMn = 60.13, Mcr = 24.21 kip-ft, Icr = 290.85 in⁴, Kb = 80.32 kips, Δu = 6.311 in., Pum/Ag = 75.89 psi, Ma = 12.55 kip-ft, Δs = 0.203 in. | equal within 0.5 %; φMn 60.31 (+0.3 %) |
| SP-TUO-R | Same, p. 14 | Right leg, 6 ft + 5 ft tributary, 7 #6 | Joist loads 5.12 / 5.33 kips, Pum = 37.97 kips, Mua = 18.11, Mu = 37.38, φMn = 65.35, Mcr = 36.32 kip-ft, Icr = 355.58, Ig = 4,019.53 in⁴, Kb = 98.20 kips, Δu = 6.091 in., Δs = 0.164 in. | equal within 0.5 %; φMn 65.50 (+0.2 %) |
The examples compute φMn with Ase from Pum and the stress block from Pum/φ; ILX Calcs uses strain compatibility at Pum, which for a single centered layer is Mn = (As fy + Pu)(d − a/2) and matches the solid-panel example exactly.
Hand calculations:
| Example | What it checks |
|---|---|
| TU-1 | Solid 12 ft × 7.25 in. panel, #5 @ 12 in., ℓc = 24 ft, W = 30 psf, 0.9D + 1.0W: Pu, Mua, Icr, Mu, φMn, Δu, Mcr in closed form |
| TU-2 | Design strips: a roof load shared between the legs by statics, the self-weight above midheight of a leg with the panel above a door head, the tributary wind |
No free worked example of lifting stresses or of a panel with a window (sill) was found; the window case uses the same strip equations with the self-weight area checked in tests/test_tilt_up_panel.py.