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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).
Roof Live loads are patterned like regular Live loads.
The actual number of patterns considered depends upon what load types are present. Sizer will generate patterns for the following combinations of load types:
Load Types Present |
Combinations that can be patterned |
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D+L |
D+S |
D+Lr |
D+L+S |
D+L+Lr |
D, L |
Yes |
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D, S |
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Yes |
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D, Lr |
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Yes |
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D, L, S |
Yes |
Yes |
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Yes |
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D, L, Lr |
Yes |
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Yes |
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Yes |
D, L, S, Lr |
Yes |
Yes |
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Yes |
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D, S, Lr |
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Yes |
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Yes |
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(D=dead L=live S=snow W=wind I=impact Lr=live roof )
Live and roof live loads are patterned together, that is, they both or neither are considered to be present on a span. Snow load are patterned by placing one-half the full snow load on a pattern span. Snow and live area patterned by placing 1/2 the full snow load on a pattern span, and the full live load and snow loads on the other spans.
If both Live and Snow loads are present and identified as "patterned" , then separate patterns will be generated for combinations of D+L, D+S and D+L+S. A six-span beam will cause 63 patterns to be generated for each combination (3x63 = 189 patterns in all). Below is an example of the combinations and patterns generated for a three-span beam:
LOAD COMBINATIONS: ASCE 7-02
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1: D only 15: D+S (pattern: ssS)
2: D+L 16: D+S (pattern: SsS)
3: D+.75(L+S) 17: D+S (pattern: sSS)
4: D+S 18: D+S (pattern: SSS)
5: D+L (pattern: L__) 19: D+.75(L+S) (pattern: Xss)
6: D+L (pattern: _L_) 20: D+.75(L+S) (pattern: sXs)
7: D+L (pattern: LL_) 21: D+.75(L+S) (pattern: XXs)
8: D+L (pattern: __L) 22: D+.75(L+S) (pattern: ssX)
9: D+L (pattern: L_L) 23: D+.75(L+S) (pattern: XsX)
10: D+L (pattern: _LL) 24: D+.75(L+S) (pattern: sXX)
11: D+L (pattern: LLL) 25: D+.75(L+S) (pattern: XXX)
12: D+S (pattern: Sss) 26: D+Lc
13: D+S (pattern: sSs) 27: D+.75(Lc+S)
14: D+S (pattern: SSs)
(D=dead L=live S=snow W=wind I=impact C=construction CLd=concentrated)
(Load Pattern: s=S/2, X=L+S or L+C, _=no pattern load in this span)
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