What is Ca Load Combinations used for in structural engineering?

Ca Load Combinations provides values required for steel design calculations including capacity checks, connection design, and detailing. It is referenced in structural design codes and used by practicing engineers during the design of buildings, bridges, and industrial structures.

Can I use these reference values directly in my design?

Yes, provided the values match your governing code edition and project specifications. Always cross-reference against the primary source (code document, manufacturer data, or published standard). The information on this page is for educational use — final verification by a licensed engineer is required.

How often are these reference values updated?

Reference content is maintained to align with current code editions. When a new edition of AISC 360, AS 4100, EN 1993, or CSA S16 is published, values are reviewed and updated. Check the last-modified date at the bottom of the page and verify against the current edition for your jurisdiction.

Ca Load Combinations | Steel Calculator

Where:

D = dead load
L = live load (including roof live and snow loads where applicable)
S = snow load (ground snow ÃÂÃÂ CBS ÃÂÃÂ shape factor)
W = wind load
E = earthquake load (per NBCC 2020 Clause 4.1.8)
T = temperature effects (not shown — see NBCC for temperature combinations)

ULS Combinations with Temperature

When temperature effects T are significant:

Comb	Load Combination
9	1.0 ÃÂÃÂ D + 1.0 ÃÂÃÂ T + 0.5 ÃÂÃÂ L
10	1.0 ÃÂÃÂ D + 1.0 ÃÂÃÂ T + 0.5 ÃÂÃÂ S

Importance Factors

Per NBCC 2020 Table 4.1.3.3:

Building Category	I_E (Earthquake)	I_W (Wind)	I_S (Snow)
Low (ULS) — farm buildings, storage	0.80	0.80	0.80
Normal — offices, residential, schools	1.00	1.00	1.00
High — schools, community centres	1.25	1.15	1.15
Post-Disaster — hospitals, fire stations	1.50	1.25	1.25

Importance factors multiply the corresponding loads in the combination:

Wind load in Comb 5: 1.4 ÃÂÃÂ I_W ÃÂÃÂ W
Snow load in Comb 4: 1.5 ÃÂÃÂ I_S ÃÂÃÂ S
Earthquake in Comb 7: 1.0 ÃÂÃÂ I_E ÃÂÃÂ E

Serviceability Limit States (SLS) Combinations

Per NBCC 2020 Clause 4.1.3.3 for deflection and drift:

Comb	Load Combination	Application
1	1.0 ÃÂÃÂ D + 1.0 ÃÂÃÂ L	Total deflection (floor beams)
2	1.0 ÃÂÃÂ D + 0.5 ÃÂÃÂ L + 0.5 ÃÂÃÂ S	Total deflection (roof beams with snow)
3	1.0 ÃÂÃÂ L	Live load deflection only
4	1.0 ÃÂÃÂ W	Wind drift (interstorey)
5	1.0 ÃÂÃÂ D + 0.5 ÃÂÃÂ L + 0.4 ÃÂÃÂ W	Wind-induced vibration

Deflection Limits per CSA S16

Per CSA S16:24 Clause 25.3 (Serviceability):

Element	Limit	Load Case
Roof beams — live load	L/180	1.0 ÃÂÃÂ L
Roof beams — total load	L/240	1.0 ÃÂÃÂ D + 0.5 ÃÂÃÂ L + 0.5 ÃÂÃÂ S
Floor beams — live load	L/300 to L/360	1.0 ÃÂÃÂ L
Floor beams — total load	L/300	1.0 ÃÂÃÂ D + 1.0 ÃÂÃÂ L
Cantilevers — live load	L/180	1.0 ÃÂÃÂ L
Crane girders — live load	L/600 to L/1000	1.0 ÃÂÃÂ L
Interstorey drift (wind)	H/400	1.0 ÃÂÃÂ W

Load Combination Factors Summary

Load	ULS Factor (Principal)	ULS Factor (Companion)	SLS Factor
Dead load D	1.25 (or 1.0)	1.0	1.0
Live load L	1.5	0.5	0.5-1.0
Snow S	1.5	0.4	0.5
Wind W	1.4	0.4	1.0 (drift)
Earthquake E	1.0	—	— (not checked)
Temperature T	1.0	—	1.0

Snow Load Calculation

Per NBCC 2020 Clause 4.1.6:

Ground snow load S_s — from NBCC 2020 Appendix C (location-specific)

Roof snow load: S = S_s ÃÂÃÂ C_b ÃÂÃÂ C_w ÃÂÃÂ C_s ÃÂÃÂ C_a ÃÂÃÂ S_r

Where:

C_b = basic roof snow load factor (0.8 for most roofs)
C_w = wind exposure factor (1.0 for normal, 0.75 for exposed, 1.25 for sheltered)
C_s = slope factor (1.0 for flat roofs, reduces with slope)
C_a = accumulation factor (for drifts, sliding snow)
S_r = 1.0 kPa for most of Canada (rain-on-snow surcharge)

Worked Example — Load Combinations for Steel Frame

Given: Steel building frame in Toronto. Bay width = 9.0 m, tributary width = 9.0 m. Normal importance (I_S = I_W = I_E = 1.0). Calculate factored loads for a roof beam.

Load Data:

Dead load: D = 3.0 kPa (roofing + steel + mechanical)
Roof live load: L_r = 1.0 kPa (NBCC minimum for access)
Snow load: S_s = 1.8 kPa (Toronto ground snow), C_b = 0.8, C_w = 1.0, C_s = 1.0 S = 1.8 ÃÂÃÂ 0.8 ÃÂÃÂ 1.0 ÃÂÃÂ 1.0 = 1.44 kPa
Wind load: W = 0.6 kPa (from NBCC 2020 static wind procedure, q_30 ÃÂÃÂ C_p ÃÂÃÂ C_e)

Factored Load per Metre of Beam (9.0 m tributary):

Comb	Load Combination	w_f (kN/m)
1	1.4 ÃÂÃÂ D = 1.4 ÃÂÃÂ 27.0 =	37.8
2	1.25 ÃÂÃÂ D + 1.5 ÃÂÃÂ L_r = 1.25 ÃÂÃÂ 27.0 + 1.5 ÃÂÃÂ 9.0 =	47.3
3	1.25 ÃÂÃÂ D + 1.5 ÃÂÃÂ L_r + 0.4 ÃÂÃÂ S = 33.75 + 13.5 + 0.4 ÃÂÃÂ 13.0 =	52.4
4	1.25 ÃÂÃÂ D + 1.5 ÃÂÃÂ S + 0.5 ÃÂÃÂ L_r = 33.75 + 19.5 + 4.5 =	57.8
5	1.25 ÃÂÃÂ D + 1.4 ÃÂÃÂ W + 0.5 ÃÂÃÂ L_r = 33.75 + 7.56 + 4.5 =	45.8
6	1.25 ÃÂÃÂ D + 1.4 ÃÂÃÂ W + 0.5 ÃÂÃÂ S = 33.75 + 7.56 + 6.5 =	47.8

Governing ULS combination: Comb 4 (snow principal) = 57.8 kN/m

SLS deflection check: Live load only: w = 1.0 ÃÂÃÂ L_r = 9.0 kN/m Delta = 5 ÃÂÃÂ 9.0 ÃÂÃÂ 9000^4 / (384 ÃÂÃÂ 200,000 ÃÂÃÂ I_x) For W410ÃÂÃÂ60 (I_x = 216 ÃÂÃÂ 10^6 mm^4): Delta = 39.3 mm L/360 = 9000/360 = 25 mm. 39.3 > 25 mm. NOT OK.

Increase to W530ÃÂÃÂ82 (I_x = 485 ÃÂÃÂ 10^6 mm^4): Delta = 39.3 ÃÂÃÂ (216/485) = 17.5 mm. 17.5 < 25 mm. OK.

Result: W530ÃÂÃÂ82, 350W. Governed by SLS deflection, not strength.

Design Resources

Frequently Asked Questions

What is the difference between ULS and SLS load combinations per NBCC 2020? ULS (Ultimate Limit States) combinations apply load factors > 1.0 to account for the probability of exceedance and are used for strength design of members and connections. SLS (Serviceability Limit States) combinations use specified (unfactored or partially factored) loads for deflection, drift, and vibration checks. For a typical steel beam: ULS combination 2 (1.25D + 1.5L) governs strength, while SLS (1.0L) governs deflection.

How do NBCC 2020 load combinations differ from ASCE 7? NBCC 2020 uses a principal load / companion load framework where only one load at a time is considered the principal load with its full factor. Companion loads receive reduced factors (0.5 for L, 0.4 for S/W). ASCE 7 applies full factors to all loads simultaneously. The dead load factor is 1.25 in NBCC vs 1.2 in ASCE 7. Live load is 1.5 vs 1.6. Wind is 1.4 vs 1.0 (ASD) or 1.0 (LRFD with wind directionality). These differences matter for cross-border projects.

What is the importance factor I_E and when does it apply? I_E is the earthquake importance factor that multiplies the seismic base shear per NBCC 2020 Clause 4.1.8. It ranges from 0.80 (low importance) to 1.50 (post-disaster). I_W (wind importance) and I_S (snow importance) are separate factors applied in combinations 5-6 and 4 respectively. A normal importance building uses I_E = I_W = I_S = 1.0. A post-disaster hospital uses I_E = 1.50, I_W = I_S = 1.25.

When does SLS govern over ULS for steel beam design? SLS (deflection) often governs for steel floor beams with longer spans (L > 8 m), especially where L/360 live load limits apply. A beam that satisfies strength with Cf/Cr = 0.5-0.7 may still deflect L/250 > L/360, requiring a deeper section. For roof beams in heavy snow regions (S_s > 2.5 kPa), SLS also frequently governs. Always run both ULS and SLS checks — do not assume strength governs.

Educational reference only. Load combinations per NBCC 2020 Division B Clause 4.1.3.2. Verify importance factors, load data, and companion action factors with the project structural engineer. See also CISC Handbook of Steel Construction (Part 2 — Loads and Design Criteria) for commentary on load combination application in Canadian steel design practice. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.