Generated Load Combinations

Load combinations for allowable stress design used in Sizer are automatically generated from:

ASCE 7-10	Section 2.4.1 Allowable Stress Design - Basic Combinations
ICC IBC 2012	Section 1605.3 Basic Load Combinations. These are the same load combinations as for ASCE 7.

The following table lists the load combinations with combination factors:

A factor followed by the load type letter e.g .6D factors that load type, otherwise the factors are 1
The combination factor applies to all loads except dead loads, and only applies when there are more than one of these loads. The combination factors also apply to patterned loads
Load combinations shown in the table are constructed from those in ASCE 7 Section 2.4.1 and by creating load combinations from the ASCE 7 combinations with any of the load types removed, even if the load type is on the member. By removing a load type the combination can become critical due to load duration factor or counteracting forces.
A combination is only considered when all of its component load types are present on them member.
Impact loads are not included in ASCE 7 2.4.1, but load combinations are generated with impact loads considered as a separate load type because these combinations have a different load duration factor and a shear reduction factor for glulam members.

		LOAD TYPES
Sizer	ASCE 7 2.4.1	D	L	Lr	S	W	I	E	Combination Factors
1	1	D							1
2	2	D	L						1
3	4	D	L	Lr					.75
4	4	D	L	Lr			I		.75
5	6a	D	L	Lr		.6W			.75
6	6a	D	L	Lr		.6W	I		.75
7	4	D	L		S				.75
8	4	D	L		S		I		.75
9	6a	D	L		S	.6W			.75
10	6a	D	L		S	.6W	I		.75
11	6a	D	L			.6W			.75
12	6a	D	L			.6W	I		.75
13	2	D	L				I		1
14	3	D		Lr					1
15	6a	D		Lr		.6W			.75
16	6a	D		Lr		.6W	I		.75
17	4	D		Lr			I		.75
18	3	D			S				1
19	6a	D			S	.6W			.75
20	6a	D			S	.6W	I		.75
21	4	D			S		I		.75
22	7	.6D				.6W			1
23	5	D				.6W			1
24	6a	D				.6W	I		.75
25	2	D					I		1
26	6b	D	L		S			.7E	.75
27	6b	D	L		S		I	.7E	.75
28	6b	D	L					.7E	.75
29	6b	D	L				I	.7E	.75
30	6b	D			S			.7E	.75
31	6b	D			S		I	.7E	.75
32	5	D						.7E	1
33	8	.6D						.7E	1
34	6b	D					I	.7E	.75

D = dead, L = floor live, Lr = Live roof, S = snow, W = wind, E = Earthquake

I = impact ( = live load with load duration factor for impact loads)

For example, the following basic combinations are listed in the analysis output when dead, live, snow and wind loads are applied to a beam for the ASCE 7 design standard.

 LOAD COMBINATIONS: ASCE 7-10

===================================================================================

 1: D only                               7: D+.75(S+W)

 2: D+L                                  8: .6D+W

 3: D+.75(L+S)                           9: D+W

 4: D+.75(L+S+W)

 5: D+.75(L+W)

 6: D+S

(D=dead  L=live  S=snow  W=wind  I=impact  C=construction  Lc=concentrated)

Combinations for Concentrated Load Check

The previous example would generate the following load combinations for a Concentrated Load check:

LOAD COMBINATIONS: ASCE 7-10

===================================================================================

 1: D only                               8: .6D+W

 2: D+L                                  9: D+W

 3: D+.75(L+S)                          10: D+Lc

 4: D+.75(L+S+W)                        11: D+.75(Lc+S)

 5: D+.75(L+W)                          12: D+.75(Lc+S+W)

 6: D+S                                 13: D+.75(Lc+W)

 7: D+.75(S+W)

(D=dead  L=live  S=snow  W=wind  I=impact  C=construction  Lc=concentrated)