Compares several bar configurations of a reinforced concrete slab section, 1 m wide, side by side, to SIA 262:2025: bending resistance, shear without stirrups, cracking moment and minimum reinforcement, anchorage and lap lengths, stiffness and service stresses. Every step shows its formula and the clause it comes from.

What it checks

For each configuration, in its own column of one table:

Section: d, d′, a_s, a′_s and ρ.
Bending resistance m_Rd, clause 4.3.2.1, with x from equilibrium at ε_c2d on the compressed face and f_cd over 0.85 · x (4.2.1.5, Figure 12). Also m_Rd,0 without the compression-face bars, and m′_Rd for the opposite moment.
Ductility: the tension bars yield at failure (ε_s ≥ ε_yd); x/d ≤ 0.35 · 435/f_yd for redistribution without a check (4.1.4.2.5); x/d ≤ 0.5 · 435/f_yd (4.1.4.2.6).
Shear without stirrups: v_Rd = k_d · τ_cd · d_v, 4.3.3.2.1, equation (35), with k_d from equation (36) and k_g from equation (37).
Cracking moment m_cr with f_ct,eff = k_t · f_ctm (4.4.1.3, equations (99) and (100)), the minimum reinforcement m_Rd ≥ m_cr (4.3.1.2) and the spacing s_s ≤ min(1.2 · h ; 300 mm) (5.5.3.1).
Anchorage and laps: k_cp (5.2.5.6), c_d (5.2.5.2, equation (105)), l_bd (5.2.5.6, equation (108)), l_bd,hook (5.2.5.8) and l_sd (5.2.6.6); for the compression-face bars l′_bd, l′_bd,c (5.2.5.7) and l′_sd,c (5.2.6.7).
Stiffness, uncracked and cracked: I_I, x_II and I_II.
Bar stress at cracking σ_s,r (4.4.2.3.4), against Table 17.

What you enter and what you get

You enter the configurations in a table, one line each: diameter and spacing of the tension bars and of the compression-face bars, the two covers and the thickness. Then the concrete and steel properties, ε_c2d, the resistance factors, the bond conditions (5.2.5.3), where the tension bars lie in the pour, and the stress in lapped bars (5.2.6.6). Optional: m_d, v_d, the crack requirement level and a service moment m.

You get one column per configuration, ending in a pass or fail, and a drawing of the section, strains and forces of the configuration you choose. With the Basic plan, it prints as an A4 calculation note.

Assumptions and limits

For the inner layer of a mesh, add the diameter of the outer bars to the cover.
Without m_d, ε_v = 1.5 · f_yd/E_s takes m_d equal to m_Rd (4.3.3.2.3, equation (41)), the lowest v_Rd; d_v = d. Leave D_max blank to skip shear.
Anchorage assumes σ_sd = f_yd, straight bars and a side cover equal to c. Laps assume all bars lapped in one section, touching (Figure 39a).
When x is shallower than d′, the compression-face bars are in tension and add to m_Rd. Count them only if they are anchored beyond the section.
The ductility limits are recommendations.

Worked example

Nine configurations side by side, from Ø10 to Ø30 at 150 mm on the tension face with Ø10 or Ø12 at 150 mm on the other face, in slabs 200 to 500 mm thick with covers of 30 to 78 mm, f_ck = 30 N/mm² and f_yk = 500 N/mm², without design or service actions; configuration 4, Ø16 over Ø10 at 150 mm in a 500 mm slab, is drawn. These are the module's own results for its worked example, computed when this page was built.

Inputs
Input	Value	Ref.
Configurations to compare	[[10,150,10,150,60,60,200],[12,150,12,150,30,30,300],[14,150,10,150,60,60,500],[16,150,10,150,60,60,500],[18,150,10,150,78,78,500],[20,150,10,150,74,74,250],[22,150,10,150,40,40,500],[26,150,10,150,40,40,500],[30,150,10,150,40,40,500]]
Configuration drawn in the figures	4 — Ø16@150 / Ø10@150
Characteristic compressive strength f_ck	30 N/mm²	§ 3.1.2.2.2
Ultimate compressive strain ε_c2d	3.5 ‰	§ 4.2.1.5
Mean tensile strength f_ctm	2.9 N/mm²	§ 3.1.2.2.4
Modulus of elasticity E_cm	30000 N/mm²	§ 3.1.2.3.3
Largest aggregate size D_max	32 mm	§ 4.3.3.2.1
Characteristic yield strength f_yk	500 N/mm²	§ 3.2.2.2
Modulus of elasticity E_s	205000 N/mm²	§ 3.2.2.4
Resistance factor for concrete γ_c	1.5	§ 2.4.2.6
Resistance factor for steel γ_s	1.15	§ 2.4.2.6
Duration factor η_t	1.0 — both conditions of 4.2.1.3 met	§ 4.2.1.3
Bond conditions	From the position of the bars in the pour (5.2.5.3)	§ 5.2.5.3
Tension bars in the pour	At the bottom of the pour (span, positive moment)	§ 5.2.5.3
Stress in the lapped tension bars σ_sd	1.0·f_yd — plastic strains excluded, or at most half the bars lapped	§ 5.2.6.6
Tensile strength for cracking	Mean tensile strength (4.4.1.3)	§ 4.4.1.3
Crack requirement level	Normal	§ 4.4.2.2.3

Calculation: Values common to every configuration
Step	Value	Ref.
Factor for the brittleness of strong concrete(40/f_ck)^(1/3) ≤ 1	η_fc = 1.000	§ 4.2.1.2 (26)
Design compressive strength of the concreteη_fc·η_t·f_ck/γ_cacting over 0.85·x (Figure 12)	f_cd = 20.0 N/mm²	§ 2.4.2.3 (2)
Design yield strength of the steelf_yk/γ_s	f_yd = 434.8 N/mm²	§ 2.4.2.5 (4)
Yield strain of the steelf_yd/E_s	ε_yd = 2.12 ‰
Limits of x/d for ductility0.35·435/f_yd (redistribution without check) ; 0.5·435/f_yd (to be avoided above)	x/d = 0.350 ; 0.500	§ 4.1.4.2.5
Design shear stress limit0.3·√f_ck/γ_c	τ_cd = 1.10 N/mm²	§ 2.4.2.4 (3)
Aggregate factor48/(16 + D_max·min(1 ; (60/f_ck)²)) ≥ 1.2	k_g = 1.200	§ 4.3.3.2.1 (37)
Tensile strength for crackingtimes k_t = 1/(1 + 0.5·t), t = h/3 in m, for each thickness (100)	f_ctm = 2.90 N/mm²	§ 4.4.1.3 (99)
Modular ratioE_s/E_cm	α_e = 6.83

Calculation: Resistance table — one column per configuration
Step	1Ø10@150Ø10@150h = 200 mm	2Ø12@150Ø12@150h = 300 mm	3Ø14@150Ø10@150h = 500 mm	4Ø16@150Ø10@150h = 500 mm	5Ø18@150Ø10@150h = 500 mm	6Ø20@150Ø10@150h = 250 mm	7Ø22@150Ø10@150h = 500 mm	8Ø26@150Ø10@150h = 500 mm	9Ø30@150Ø10@150h = 500 mm	Ref.
Reinforcement and section
Tension bars, diameter Ø_s mm	10	12	14	16	18	20	22	26	30
Tension bars, spacing s_s mm	150	150	150	150	150	150	150	150	150
Compression-face bars, diameter Ø′_s mm	10	12	10	10	10	10	10	10	10
Compression-face bars, spacing s′_s mm	150	150	150	150	150	150	150	150	150
Cover, tension face c mm	60	30	60	60	78	74	40	40	40
Cover, compression face c′ mm	60	30	60	60	78	74	40	40	40
Thickness of the slab h mm	200	300	500	500	500	250	500	500	500
Effective depth d mmh − c − Ø_s/2	135	264	433	432	413	166	449	447	445
Depth of the compression-face bars d′ mmc′ + Ø′_s/2	65	36	65	65	83	79	45	45	45
Bars per metre n 1/m1000/s_s	6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67
Steel area, tension bars a_s mm²/mπ·Ø_s²/4 · 1000/s_s	524	754	1,026	1,340	1,696	2,094	2,534	3,540	4,712
Steel area, compression-face bars a′_s mm²/mπ·Ø′_s²/4 · 1000/s′_s	524	754	524	524	524	524	524	524	524
Reinforcement ratio, tension bars ρ %a_s/(b·d), b = 1000 mm	0.388	0.286	0.237	0.310	0.411	1.262	0.564	0.792	1.059
Reinforcement ratio, compression-face bars ρ′ %a′_s/(b·d)	0.388	0.286	0.121	0.121	0.127	0.315	0.117	0.117	0.118
Bending resistance — ultimate limit state
Depth of the compression zone x mmequilibrium: f_cd·b·0.85·x + a′_s·σ′_sd = a_s·σ_sd, with ε_c2d at the compressed face	26.8	28.2	39.6	44.5	54.8	60.4	59.9	81.3	108.2	§ 4.2.1.5
Relative depth of the compression zone x/d	0.198	0.107	0.092	0.103	0.133	0.364	0.133	0.182	0.243
Strain of the tension bars ε_s ‰ε_c2d·(d − x)/x	14.14	29.32	34.73	30.49	22.89	6.12	22.72	15.75	10.89
Stress of the tension bars σ_sd N/mm²E_s·ε_s ≤ f_yd	435	435	435	435	435	435	435	435	435
Strain of the compression-face bars ε′_s ‰ε_c2d·(x − d′)/x; negative: the bars are in tension	-4.99	-0.98	-2.24	-1.61	-1.80	-1.08	0.87	1.56	2.04
Stress of the compression-face bars σ′_sd N/mm²E_s·ε′_s, \|σ′_sd\| ≤ f_yd; compression positive	-435	-200	-435	-331	-370	-221	179	320	419
Lever arm of the internal forces z mmm_Rd/(a_s·σ_sd)	177	263	441	427	405	147	422	411	399
Bending resistance m_Rd kNm/mf_cd·b·0.85·x·(d − 0.85·x/2) + a′_s·σ′_sd·(d − d′)	40.3	86.2	196.6	248.7	299.0	134.0	465.0	633.1	817.7	§ 4.3.2.1
Bending resistance, tension bars alone m_Rd,0 kNm/mthe compression-face bars left out	29.4	83.9	188.2	243.3	291.0	130.4	464.4	628.7	806.8
Resistance to the opposite moment m′_Rd kNm/mthe compression-face bars in tension, the tension bars on the compressed side	40.3	86.2	117.6	120.5	134.6	77.4	115.3	117.2	119.1
Tension bars yield at failure ε_yd/ε_sε_s ≥ ε_yd: a ductile failure, the steel yields before the concrete crushes	0.15Pass	0.07Pass	0.06Pass	0.07Pass	0.09Pass	0.35Pass	0.09Pass	0.13Pass	0.19Pass
Ductility for redistribution without a check (x/d)/limx/d ≤ 0.35·435/f_yd; above, redistribute only with a check of the rotation capacity	0.57met	0.30met	0.26met	0.29met	0.38met	1.04exceeded	0.38met	0.52met	0.69met	§ 4.1.4.2.5
Ductility of the compression zone (x/d)/limx/d ≤ 0.5·435/f_yd, to be avoided above as far as possible	0.40met	0.21met	0.18met	0.21met	0.27met	0.73met	0.27met	0.36met	0.49met	§ 4.1.4.2.6
Shear without stirrups — ultimate limit state
Strain for the shear resistance ε_v ‰1.5·f_yd/E_s: m_d taken equal to m_Rd (41), the lowest v_Rd	3.181	3.181	3.181	3.181	3.181	3.181	3.181	3.181	3.181	§ 4.3.3.2.3 (41)
Coefficient k_d1/(1 + ε_v·d·k_g)	0.660	0.498	0.377	0.377	0.388	0.612	0.368	0.369	0.371	§ 4.3.3.2.1 (36)
Shear resistance per metre v_Rd kN/mk_d·τ_cd·d_v, d_v = d	97.6	144.0	178.8	178.6	175.6	111.3	181.2	180.9	180.6	§ 4.3.3.2.1 (35)
Cracking moment and detailing
Size factor k_t1/(1 + 0.5·h/3), h in m	0.968	0.952	0.923	0.923	0.923	0.960	0.923	0.923	0.923	§ 4.4.1.3 (100)
Effective tensile strength f_ct,eff N/mm²k_t·f_ctm	2.81	2.76	2.68	2.68	2.68	2.78	2.68	2.68	2.68	§ 4.4.1.3 (99)
Cracking moment m_cr kNm/mf_ct,eff·b·h²/6	18.7	41.4	111.5	111.5	111.5	29.0	111.5	111.5	111.5	§ 4.3.1.2
Minimum reinforcement: no brittle failure at cracking m_cr/m_Rdm_Rd ≥ m_cr	0.46Pass	0.48Pass	0.57Pass	0.45Pass	0.37Pass	0.22Pass	0.24Pass	0.18Pass	0.14Pass	§ 4.3.1.2
Largest bar spacing s_max mmmin(1.2·h ; 300 mm)	240	300	300	300	300	300	300	300	300	§ 5.5.3.1
Spacing of the main bars in the most stressed zones s_s/s_maxs_s ≤ min(1.2·h ; 300 mm)	0.63Pass	0.50Pass	0.50Pass	0.50Pass	0.50Pass	0.50Pass	0.50Pass	0.50Pass	0.50Pass	§ 5.5.3.1
Anchorage and laps
Bond, tension bars k_cp1.0 good, 1.2 moderate (Figure 36b), 1.4 under bentonite	1.0good	1.0good	1.0good	1.0good	1.0good	1.0good	1.0good	1.0good	1.0good	§ 5.2.5.6
Cover value for the anchorage, tension bars c_d mmmin(0.5·(s_s − Ø_s) ; c ; 3.75·Ø_s), side cover taken as c	38	30	53	60	66	65	40	40	40	§ 5.2.5.2 (105)
Anchorage length, tension bars l_bd mm50·k_cp·Ø · (σ_sd/435)^1.5 · (25/f_ck)^0.5 · (Ø/20)^(1/3) · (1.5·Ø/c_d)^0.5 ≥ 10·Ø, with σ_sd = f_yd	229	358	359	428	507	620	941	1,278	1,661	§ 5.2.5.6 (108)
Anchorage length in diameters l_bd/Ø_s	22.9	29.8	25.6	26.8	28.2	31.0	42.8	49.2	55.4
With an end hook or transverse compression l_bd,hook mml_bd − 15·Ø_s ≥ 10·Ø_s	100	178	149	188	237	320	611	888	1,211	§ 5.2.5.8
Lap length, tension bars l_sd mm1.2·l_bd(f_yd) ≥ 15·Ø_s, c_s = s_s − 2·Ø_s for touching bars (Figure 39a)	275	429	430	518	655	808	1,129	1,534	1,994	§ 5.2.6.6
Bond, compression-face bars k′_cp	1.0good	1.0good	1.2moderate	1.2moderate	1.2moderate	1.0good	1.2moderate	1.2moderate	1.2moderate	§ 5.2.5.6
Anchorage length, compression-face bars in tension l′_bd mmeq. (108) with Ø′_s, s′_s, c′; for the opposite moment	229	358	275	275	275	229	275	275	275	§ 5.2.5.6 (108)
Anchorage length, compression-face bars in compression l′_bd,c mml′_bd − 15·Ø′_s ≥ 10·Ø′_s, cover beyond the bar end > 5·Ø′_s	100	178	125	125	125	100	125	125	125	§ 5.2.5.7
Lap length, compression-face bars in compression l′_sd,c mm1.2·l′_bd(f_yd) ≥ 15·Ø′_s	275	429	330	330	330	275	330	330	330	§ 5.2.6.7
Stiffness — serviceability
Centroid of the uncracked section y_I mmfrom the compressed face, bars counted with α_e	100.0	150.0	251.0	251.7	252.2	126.4	254.5	256.6	258.9
Second moment, uncracked I_I 10⁶ mm⁴/m	674	2,364	10,721	10,779	10,762	1,329	11,120	11,324	11,548
Neutral axis, cracked x_II mmb·x²/2 + (α_e − 1)·a′_s·(x − d′) = α_e·a_s·(d − x)	31.3	46.4	71.0	79.8	86.8	57.2	107.1	123.2	138.5
Second moment, cracked I_II 10⁶ mm⁴/mb·x³/3 + α_e·a_s·(d − x)² + (α_e − 1)·a′_s·(x − d′)²	53	278	1,038	1,306	1,452	233	2,446	3,178	3,937
Flexural stiffness, uncracked E_cm·I_I kNm²/m	20,224	70,930	321,634	323,363	322,872	39,858	333,603	339,711	346,441
Flexural stiffness, cracked E_cm·I_II kNm²/m	1,583	8,332	31,152	39,187	43,546	7,005	73,367	95,337	118,120
Cracked over uncracked stiffness I_II/I_I	0.078	0.117	0.097	0.121	0.135	0.176	0.220	0.281	0.341
Steel stress — crack limitation and yielding (Table 17)
Bar stress at cracking σ_s,r N/mm²m_cr on the cracked section: α_e·m_cr·(d − x_II)/I_II — imposed or restrained deformations, f_ct,eff reached	251	222	266	206	171	92	107	78	59	§ 4.4.2.3.4
Crack limitation at cracking (minimum reinforcement) σ_s,r/f_ykσ_s,r ≤ f_yk (normal requirements)	0.50Pass	0.44Pass	0.53Pass	0.41Pass	0.34Pass	0.18Pass	0.21Pass	0.16Pass	0.12Pass	Table 17
Summary
Every check of this columnthe verifications above; the ductility limits are recommendations	Pass	Pass	Pass	Pass	Pass	Pass	Pass	Pass	Pass

How this module is verified

Verified clause by clause against SIA 262:2025 and against independent calculations used on real projects, before release.

Questions

What changes with the crack requirement level?

It selects the admissible bar stresses of Table 17. Normal: σ_s ≤ f_yk. Increased and high: σ_s ≤ σ_s,adm of equation (102), and σ_s ≤ f_yd − 80 N/mm² against yielding in service.

When is the lap stress taken as 1.2 · f_yd?

Where plastic strains cannot be excluded, unless at most half of the bars are lapped in one section, the lap is confined, or a plane stress state prevents cracking.

Can I print the calculation?

The full calculation is shown on screen, free and without an account. A print-ready A4 calculation note is part of the Basic plan.

Norm: SIA 262:2025 · Page updated: 24 October 2026

Slab section resistance table to SIA 262

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