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Pattern loads are only available in Beam mode for Live and Snow loads on multi-span beams. Sizer automatically generates all the possible patterns for such loads by selecting the active spans (where the applicable loads are applied) and inactive spans (where only Dead, Wind, half-Snow loads and any non-patterned loads are applied).
Sustained Live loads are patterned like regular Live loads.
Pattern loading is implemented using the following design code provisions: NBC 4.1.5.3, 4.1.5.5, 4.1.6.3, and 4.1.7.3; and NBC structural commentary A23.
Combinations patterned
The program continues to pattern all load combinations containing just dead and live loads, as per 4.1.5.3, or just dead and snow loads, as per 4.1.6.3. It evaluates the set of permutations of live or snow loads being on and either off (live loads) or of ½ intensity (snow loads) on each span in the beam.
Live and Snow -
Sizer doesn't patterns load combinations that contain D, L and S on the same member. According to 4.1.5.5, live and snow loads on an exterior surface should not be combined, and if the the snow loads have been transferred to an interior structural member, it would not necessarily make sense to pattern them on a span-by-span basis.
Dead load resisting failure
Sizer patterns the dead-load-resisting failure combinations (those that have a 0.9D factor) if the same combination with 1.25D is patterned.
Sustained Live load
The program patterns loads containing D, L, and sustained live loads Ls or Lf, patterning the Ls/f and L in unison. In addition, the program creates patterns for those load combinations with just D and Ls/f. This is because these combinations have a lower KD factor, 0.65, than the combinations with D + L + Ls/f ( 1.0 ) , therefore may be the critical design combination.
Note that you can turn the patterning for individual loads off if you do not wish storage or controlled fluid loads to be patterned.
Short term loads-
Patterns are not created for any combination containing wind or earthquake loads, even if they also contain live and or snow loads, because wind loads would not be patterned on a span-by-span basis to comply with NBC 4.1.7.3 (1) b. and because versions of Sizer before version 7 also did not pattern live and snow loads on combinations that also had wind loads.
Other permanent loads -
Dead loads due to soil are in the patterned combinations as dead loads. They themselves are not patterned.
Hydrostatic loads apply to columns only thus are not patterned.
Design Criteria -
Patterns are created for both strength and serviceability load combinations, so apply to all design criteria, including deflection.
The table below gives a comparison of the load combinations that are to be patterned using the previous and newest versions of Sizer using load types D, L, Ls and S. In the table, the symbol "s" refers to half snow, and _ refers to no loading. Neighbouring symbols refer to a representative two-span pattern. Patterns for Sizer 7 are created for both dead load factors (0.9 and 1.25), for Sizer 2002/5 only for 1.25D.
Loadser 7 |
Pattern |
D,L |
D + L_ |
D, Ls |
D + Ls_ |
D,S |
D + Ss |
D,L, Ls |
D + (L+Ls)_ D + Ls_ |
The table below shows all the pattern load combinations that are created with just two spans on the member.
LOAD COMBINATIONS:
===================================================================================
Load Types: D=dead W=wind S=snow H=earth,groundwater E=earthquake
L=live(use,occupancy) Ls=live(storage,equipment) Lc=concentrated live
SW=self-weight - results shown here are based on 0.104 kN/m x 1.4
SW is not included in the remaining LC results presented here.
Load Pattern: s=S/2 L=L+Ls
LC# Ultimate Limit States Serviceability Limit States Pattern
---- --------------------- --------------------------- -------
Importance factors also included:
Snow: 1.0 Snow: 0.9
0: SW SW -
1: 1.4D only 1.0D only -
2: 1.25D + 1.5L 1.0D + 1.0L -
3: 1.25D + 1.5Ls 1.0D + 1.0Ls -
4: 1.25D + 1.5S 1.0D + 1.0S -
5: 1.25D + 1.5L + 1.5Ls 1.0D + 1.0L + 1.0Ls -
6: 1.25D + 1.5L + 1.5Ls + 0.5S 1.0D + 1.0L + 1.0Ls + 0.5S -
7: 1.25D + 0.5L + 1.0Ls + 1.5S 1.0D + 0.5L + 1.0Ls + 1.0S -
8: 0.9D + 1.5Ls - -
9: 0.9D + 1.5S - -
10: 0.9D + 1.5L + 1.5Ls - -
11: 0.9D + 1.5L + 1.5Ls + 0.5S - -
12: 0.9D + 0.5L + 1.0Ls + 1.5S - -
13: 1.25D + 1.5Ls 1.0D + 1.0Ls L_
14: 1.25D + 1.5Ls 1.0D + 1.0Ls _L
15: 1.25D + 1.5L + 1.5Ls 1.0D + 1.0L + 1.0Ls L_
16: 1.25D + 1.5L + 1.5Ls 1.0D + 1.0L + 1.0Ls _L
17: 0.9D + 1.5Ls - L_
18: 0.9D + 1.5Ls - _L
19: 0.9D + 1.5L + 1.5Ls - L_
20: 0.9D + 1.5L + 1.5Ls - _L
21: 1.25D + 1.5S 1.0D + 1.0S Ss
22: 1.25D + 1.5S 1.0D + 1.0S sS
23: 0.9D + 1.5S - Ss
24: 0.9D + 1.5S - sS
Concentrated Load Check
The concentrated load combinations are generated in addition to pattern loads when the Concentrated Load Check is active. Each of these combinations represents the series of load combinations generated as the concentrated load moves along the span. The concentrated load replaces any live (occupancy) load in all load combinations except for pattern loads. It would be too computationally expensive to generate this series for each pattern load. This the program verifies all of the load combinations it ordinarily does, plus those combinations derived by replacing the live (occupancy) loads in the non-patterned combinations.
See also - Load Combinations, Concentrated Load Check