How ILX Calcs is tested

Every calculation type is tested, on every change, against published design examples and code tables where they exist and against hand calculations from the code equations where they do not. Every difference from a published value is explained in the documentation.

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Live results

Straight from the verification results that ship with this release.

Release 0.1.0, results generated 2026-11-02. 2,055 individual values compared in 690 runs (LRFD and ASD where the code offers both); 2,055 of them match or have a documented reason.

Documented differences

• Gust-effect factor of the ASCE 7-22 commentary example. ASCE 7-22 Commentary Table C26.11-1 lists G = 0.860 for its rigid-building example, but Eq. 26.11-6 with the table's own turbulence intensity (0.201) and background response (Q² = 0.616) gives 0.818. ILX Calcs computes 0.818 and matches every other value of the table (z̄, Iz̄, Lz̄, Q²). None on designs: the program applies Eq. 26.11-6 as written; the commentary value is 5 % higher.
• Effective moment of inertia: ACI 318-14 examples vs ACI 318-19. The StructurePoint beam and slab examples are written to ACI 318-14, which computes the effective moment of inertia with Branson's expression Ie = (Mcr/Ma)³Ig + [1 − (Mcr/Ma)³]Icr. ACI 318-19 Table 24.2.3.5 replaced it with Ie = Icr / [1 − ((2/3)Mcr/Ma)²(1 − Icr/Ig)], which gives a lower stiffness when Ma is close to Mcr. ILX Calcs uses the 318-19 expression; Mcr, Icr and Ig match the examples, and Ie agrees within 1 % where Ma is well above Mcr. Deflections of lightly cracked members are larger (more conservative) than the 318-14 values: 5 to 16 % in these examples.
• Radius of gyration for the slenderness check. ACI 318-19 6.2.5.2 permits the radius of gyration as r = √(Ig/Ag) or as 0.3 times the dimension in the direction of stability (0.25D for circles). The StructurePoint example uses √(Ig/Ag) = 4.91 in. for a 17 in. square column; ILX Calcs uses 0.3h = 5.10 in., so k ℓu/r is 22.6 instead of 23.5. k ℓu/r is about 4 % lower for a square section; both values are permitted by the code and both are below the limit of 34 in the example.
• One-way shear strength of members without shear reinforcement: ACI 318-14 examples vs ACI 318-19. ACI 318-14 Eq. 22.5.5.1 gives Vc = 2λ√f'c bw d. ACI 318-19 Table 22.5.5.1 changed it for members with less than Av,min (slabs, footings, walls): Vc = 8λs λ ρw^(1/3) √f'c bw d, with the size effect factor λs = √(2/(1 + d/10)), at most 1, and the longitudinal reinforcement ratio ρw. ILX Calcs applies ACI 318-19; the 318-14 examples show the older, higher value. For lightly reinforced slabs (ρw about 0.3 %) Vc is roughly 40 % lower than the 318-14 value: the 318-19 design is more conservative.
• Size effect in two-way (punching) shear: ACI 318-14 examples vs ACI 318-19. ACI 318-19 Table 22.6.5.2 multiplies the two-way shear stress vc by the size effect factor λs = √(2/(1 + d/10)), at most 1, (22.5.5.1.3), which ACI 318-14 did not have. For the 12.75 in. effective depth at the drop panel λs = 0.938, so vc is 265 psi instead of the published 283 psi. Punching capacity of slabs deeper than 10 in. is lower (more conservative) than in the 318-14 example.
• Punching shear around a drop panel: third expression of Table 22.6.5.2. The example's preliminary check around the 10 × 10 ft drop panel uses vc = 4λ√f'c. ACI 318-19 Table 22.6.5.2 (as 318-14) takes the least of 4λ√f'c, (2 + 4/β)λ√f'c and (2 + αs d/bo)λ√f'c; with bo = 514 in. and d = 8.5 in. the third gives 2.66λ√f'c = 188 psi, which governs. ILX Calcs applies the least of the three. ILX Calcs is about one third lower (conservative); the slab in the example still passes with a large margin (the factored shear stress is about 50 psi).
• Clear span for the minimum thickness of slabs with beams. Table 8.3.1.2, note [2], measures ℓn face to face of the beams. The example uses the clear span between the columns (22 ft − 18 in. = 246 in.) and gets 5.69 in.; with the 14 in. beams the code span is 250 in. and the minimum thickness is 5.79 in. αfm and β match the example. ILX Calcs requires 0.1 in. more; the 6 in. slab of the example satisfies both.
• One-way shear of footings: ACI 318-14 examples vs ACI 318-19. The StructurePoint footing examples (Wight Examples 15-1 and 15-2) use ACI 318-14, Vc = 2λ√f'c bw d. ACI 318-19 Table 22.5.5.1(c) gives Vc = 8λs λ ρw^(1/3) √f'c bw d for members without stirrups (λs may be taken as 1.0 for footings, 13.2.6.2). With the light flexural steel of footings (ρw about 0.25 %) this is about 45 % lower. The factored shear matches the examples; only the strength differs. Under ACI 318-19 both example footings need a few inches more thickness for one-way shear. ILX Calcs (ACI 318-19) is more conservative than the 318-14 value: a design shear strength of 165 kips instead of 308 kips (square footing) and 55 instead of 96 kips per 10 ft (wall footing).
• Effective depth for one-way shear of a two-layer footing. The example checks one-way shear with the average effective depth of the two bar layers (28 in.). ILX Calcs uses the effective depth of the bars spanning in the direction checked (28.5 in. for the bottom layer, 27.5 in. for the upper layer, each direction checked), as ACI 318-19 22.5 defines d for the section considered. The critical section moves by 0.5 in., so the factored shear is 1.6 % lower in the bottom-layer direction and 1.7 % higher in the other. Negligible; ILX Calcs checks both directions with their own d, so the governing (upper-layer) direction is covered.
• Development length: simplified table vs general equation. The example takes ℓd from the simplified expressions of ACI 318-14 Table 25.4.2.2 (54.8 in. for a #8 bar). ILX Calcs uses the general Eq. 25.4.2.4(a) of ACI 318-19 with the confinement term (cb + Ktr)/db = 2.5 (3.5 in. cover to the bar centre, 12.7 in. spacing), which the code permits for every case and which gives 32.9 in. ILX Calcs requires a shorter, code-permitted length; the 55 in. available beyond the column face satisfies both.
• Punching at an edge column close to the long edges of a combined footing. With the footing thickened to 40 in. (d = 36.5 in.), the side faces of the 24 in. exterior column are 36 in. from the long edges of the 8 ft footing, which is less than d. ILX Calcs then also checks the critical section that runs to those edges (ACI 318-19 Fig. R22.6.4.3, 'regard as free edge'), and that two-sided section governs (factored shear stress 243 psi). The example checks only the three-sided section (157 psi); the program matches that value for the 36 in. footing, where the sides are farther than d from the edges. ILX Calcs is more conservative for columns within d of a footing edge: here it asks for more thickness than the example.
• Size effect in two-way shear of pile caps: ACI 318-14 example vs ACI 318-19. ACI 318-19 Table 22.6.5.2 multiplies vc by the size effect factor λs = √(2/(1 + d/10)), 0.745 for d = 26 in. Section 13.2.6.2 lets footings and mats neglect it, but not pile caps, so ILX Calcs applies it. The ACI 318-14 example has no size effect: a design shear strength of 947 kips at the column instead of 706 kips. The factored shear of 684 kips matches. ILX Calcs (ACI 318-19) is about 25 % more conservative in two-way shear; the example's 33 in. cap still passes (684 kips of factored shear against 706 kips of strength).
• Pile-cap one-way shear: weight of the cap and rounding of the pile share. For piles 1 in. inside the critical section, ACI 318-19 13.4.6.5 counts a linear share of the reaction, 5/12 of 114 kips = 47.5 kips; the example rounds it to 48 kips and takes a factored shear of 96 kips, ignoring the cap weight. ILX Calcs includes the cap weight in the pile reactions and subtracts the factored weight of the cap beyond the section: 93.7 kips. 2.4 % lower shear than the rounded published value, 1.4 % lower than the unrounded one; both follow from statics with the cap weight.
• Axial load term in the one-way shear of a retaining-wall stem. ACI 318-19 Table 22.5.5.1(c) adds Nu/(6Ag) to the shear stress for axial compression. The example counts the stem's own weight above the base (Nu = 3.08 kips per foot, +2.7 psi) and gets a design shear strength of 10.98 kips per foot. ILX Calcs neglects Nu (permitted, conservative) and gets 10.67 kips per foot with the same λs = 0.92 and ρw. ILX Calcs is 3 % more conservative in stem shear.
• Bearing length of DG1 Example 4.7-12 from rounded intermediate values. AISC Design Guide 1 Example 4.7-12 solves Eq. 4-65 as Y = 17.5 in. − 17.2 in. = 0.300 in., subtracting two numbers rounded to 0.1 in.; the unrounded terms (f + N/2 = 17.5 in., square root 17.226 in. for LRFD and 17.253 in. for ASD) give Y = 0.274 in. (LRFD) and 0.247 in. (ASD). With Eq. 4-63 the rod tension is then 111.5 kips (LRFD) and 66.9 kips (ASD) instead of the published 113 and 68.4 kips. ILX Calcs uses the unrounded values; qmax (42.0 and 27.9 kips/in.) matches the Example. Rod tension 1.3 % (LRFD) and 2.2 % (ASD) lower than the rounded published values; the bearing length is a fraction of an inch either way and does not change the plate design.
• Partially grouted wall as an equivalent thickness in the TMS shear wall webinar. In Examples SD-2 and SD-3 of the TMS webinar handout (TMS 402-16), the interaction diagram and the maximum reinforcement check treat the partially grouted wall as a solid wall of equivalent (averaged) thickness, 3.39 in. for grout at 48 in. ILX Calcs takes the compression zone as the face shells plus the grouted cells, as the TMS 402 Commentary to the maximum reinforcement provision describes. The published 0.9 Pn at the maximum reinforcement strain is 323 / 364 kips (ILX 354 / 393 kips) and the wall of SD-2 is stressed to 94 % of its flexural design strength (ILX 89 %). The net shear area, the shear strengths and the neutral axis depth agree. ILX gives a larger compression block in the partially grouted wall: 8 to 10 % more axial capacity at the maximum reinforcement strain and 6 % more flexural strength in these examples. The FEMA P-1051 example (face shells plus grouted cells, as ILX) agrees within 0.2 %.
• Cold work of forming in the SSMA allowable moments. The SSMA Product Technical Guide includes the strength increase from the cold work of forming (AISI S100 Section A7.2) in the allowable moments marked with its footnote 2, such as 30.33 kip-in. for the 600S162-54 at 50 ksi. ILX Calcs uses the specified yield stress without that increase. ILX is lower (conservative): 27.80 kip-in. for the 600S162-54 at 50 ksi. Sections without the footnote agree within 0.3 %.
• Effective section modulus of the 600S162-54 at 50 ksi in the SSMA guide. The SSMA guide lists Sxe = 0.916 in.³ for the 600S162-54 at 50 ksi. The AISI S100 effective width procedure (flange with its edge stiffener, lip reduced by RI, web under stress gradient) gives 0.928 in.³, both in ILX Calcs and in the independent hand calculation of example CS-4. The SSMA program details are not published; the other sections compared (600S162-33, 800S162-43, 800S162-54, 1000S162-54) agree within 0.3 %. The narrow 362S162 sections differ more (362S162-54 at 50 ksi: 0.444 in.³ listed, 0.468 in.³ by S100) and are not used as examples. ILX is 1.4 % higher than the guide for this section.
• Beam stability factor of the AWC TR 14 ridge beam example. AWC Technical Report 14 Example 3.1 (2-1/2 × 21 24F-V4 glulam braced by joists at 4 ft) takes CL from the report's own buckling-moment method (Mcr = 1.3 Cb Ce E'y05 Iy / lu), giving CL = 0.88 and M' = 37,250 ft-lb. ILX Calcs applies NDS 2024 3.3.3: effective length le = 2.06 lu from Table 3.3.3, RB = 18.2 and CL = 0.857 (M' = 36,200 ft-lb). The NDS values the report also uses (Fbx* = 2,760 psi, CV = 0.9871, M = 36,750 ft-lb) agree. The program is 2.8 % lower (conservative) than the TR 14 method for this beam; NDS 3.3.3 is the method of the code.
• Lower bound of Cs in the FEMA P-2192 coupled-wall example. FEMA P-2192-V1 Section 4.5.1.7 writes the lower bound 0.044 SDS Ie but evaluates it with 0.65 g (the SD1 of the example) instead of SDS = 1.10 g, giving 0.029. ASCE 7-22 Eq. 12.8-6 with SDS = 1.10 g gives 0.0484, which ILX Calcs computes. None on the result: the governing Cs (0.048, the long-period limit) and the base shear (2,090 kips) agree with the example.
• Base shear of the FEMA P-2192 composite plate shear wall example. FEMA P-2192-V1 Section 5.5.3.6 multiplies Cs rounded to 0.048 by W = 25,844 kips (its Table 5-4 sums to 25,855 kips). ILX Calcs keeps the unrounded Cs = 0.044 SDS = 0.04844 (Eq. 12.8-6 governs) and W = 25,855 kips, so V, the story forces and the overturning moment are 1.2 % higher; the period, k and the distribution factors Cvx agree. The program is 1.2 % higher (conservative) than the example.
• Torsional constant J of rolled W-shapes. The AISC Shapes Database computes J of rolled shapes including the web-to-flange fillets (El Darwish and Johnston). ILX Calcs uses the open thin-walled formula Σ b t³/3 on the plate centre lines and ignores the fillets, as the step text says, so J of a W24X68 is 1.75 in.⁴ against the tabulated 1.87 in.⁴ (6.5 % lower). Every other property of the shape (A, I, S, Z) matches within 0.5 %. J is a little low (conservative for torsional buckling); use the database value for rolled shapes.
• Weak-axis properties of a channel with sloped flanges. American Standard channels (C shapes) have flanges that taper; the database tf is the average thickness. ILX Calcs models parallel flanges of that average thickness without fillets, which moves area toward the flange tips: for C10X20 Iy is 3.51 in.⁴ against 2.80 in.⁴. The strong-axis values (A, Ix, Sx, Zx) match within 0.5 %. Use the database (or the built-up option with the real taper) for weak-axis properties of rolled channels.
• Minor principal moment of inertia of a rolled angle. Rolled angles have rounded leg toes; ILX Calcs models square toes with the heel fillet r = kdes − t. For L4X4X1/2 A, Ix and the centroid match within 1 %, but the minor principal Iz is 2.32 in.⁴ against 2.25 in.⁴ (3 % higher), because the square toes put a little more area far from the minor axis. Iz of a rolled angle is about 3 % high; use the database value for single-angle design.
• Moment distribution stopped after two cycles. Example 12.3 of Udoeyo's Structural Analysis distributes the moments for only two cycles with distribution factors rounded to 0.01, so the column moments are not converged: the printed column moments MBD = 14.94 and MDB = 7.47 kip-ft against the exact stiffness solution 15.09 and 7.55 kip-ft (1.0 % apart). The beam moments of the same example match within 0.4 %. None: the program gives the exact elastic solution.